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Introduction and historical background of veterinary radiology:

The art and science of radiology became an integral part of veterinary medicine and surgery shortly after the exposure of the first radiographic film. The veterinarians are still not able to understand the real importance of radiology in their profession. When they properly apply it they will understand the importance of their profession. Among the special radiographic procedures, survey radiography remains the standard for the majority of ante-mortem anatomic diagnosis.

     General terminologies:   

1. Radiology: It is the branch of medical science which deals with diagnostic and therapeutic  application of radiant-energy. Radiant energy are: X-rays, beta and Gamma radiations. It is also known as Roentgenology.

2. Veterinary Radiology: Branch of veterinary medical science which uses radiant energy principally for diagnostic as well as therapeutic purpose in domestic, companion, zoo and lab animals.

3. Radiologist: Any person qualified in medical/veterinary sciences and radiological physics to use radiant energy in the diagnostic, therapeutic and research field of medicine.

4. Radiograph: A visible photographic record in the film produced by X-rays passing through an object.

5. Radiographer: A technically trained/skilled person having the capacity to obtain quality radiographs for applied use by the radiologist.

6. X-rays: A special form of electromagnetic radiation, having high energy, extremely short wavelength, no mass or charge and travel at the speed of light.

 

Discovery of X-rays:

The discovery of X-rays was an accidental product of the work on the Crooke’s-type tube by Wilhelm Conrad Roentgen on 8^th Nov- 1895. A professor of physics was working in laboratory at the Physical Institute of the Uni of Wurzburg, Germany, experimenting with a type of discharge or gas tube called Crooke’s-tube. He shielded the tube with heavy black cardboard. On shielding, he found that the greenish fluorescent light could be seen on a fluorescent screen kept 9 feet away. Roentgen concluded that a new type of ray was emitted from the tube that could pass through the black covering and that rays having the capacity to pass through most of substances but left the bones and most metal visible. After further investigation, Roentgen presented a written report to the society of physics and medical sciences at the University of Wurzburg on Nov-28 1895. With his findings, he also submitted a radiograph of his wife, Bertha’s hand with a ring, which he had produced with his own X-ray tube. By as early as April 1896, changes in skin color caused by exposure to X-rays, similar to sunburn, were reported. This discovery of skin color changes resulted in the use of X-rays for radiation therapy. In the recognition of roentgen’s discovery he was awarded the Nobel Prize in 1901 Dec-10. This was  the first Nobel prize awarded in the field of Physics.                                                                                                                     

i. Name invisible rays as X-rays or unknown rays.

ii. discovered on Nov-8, 1895.

iii. Got Nobel prize on Dec 10 1901AD.

Historical background of Veterinary Radiology:

1. Nov. 8, 1895:  W.C. Roentgen discovered X-rays (1843-1923 AD)
2. 1896:  Linden Hal made first contrast picture of hand.

First oil emersed X-rays tube developed by Trowbridge.

Roentgen and colleagues made the first metal target X-rays tube.

First photographic paper developed for recording of X-rays image by Wright.

First radiograph made by Konig and Morten.

First veterinary radiograph of an equine foot published by Patan and Duncan in the March issue of veterinary journal.

Papers describing the use of X-rays in veterinary practice published by R. Eberlein and C. Troester of Germany , FTG Hobday, VE Johnson and J.A.W. Dollar of England and V. Lemoine of France.

3.  1897:  AH Becquerel discovered radioactivity of Uranium.

                  J.J. Thomsan discovered electron.

4.  1898:  Cannon used X-rays in the form of contrast studies (Wing bismuth meals) to investigate physiology of GIT.

5. 1901:  Dec.10, 1901, W.C. Roentgen awarded 1^st Nobel prize of Physics.

6. G. holtz Knecht developed first dosimeter for radiation therapy.

7. 1905: Kienbock was strips of silver bromide photographic paper to estimate dosage in radiation therapy.

8. 1913:  Gustav Bucky invented grid to remove scatter radiation.

9.  1914: W.H. Bragg and W.L. Bragg discovered that X-rays would be reflected.

10.  1917:  self rectifying generators developed for use in X-rays machine.

11. Early 1920’s: 

• Double coated film replaced old grass plate for recording X-rays image.
• Moving grid invented by Dr. Hollis Potter.
• Iodine compounds introduced for use as contrast agents.
• Total reflection, refraction and diffraction of X-rays  by ruled grading was shown by Compton and Doan.

       12. 1928: International recommendations on radiation safety precautions were published.

       13. 1930: Super voltage single section X-rays tube developed by C.C. Lauristan.

       14. 1937: Xerox radiography invented by a physicist Chester F. Carlson.

       15. 1945:  Gray Schnelle wrote 1^st American book on Veterinary Radiology.

       16.  1950: 

• Cadmium sulphide crystals were used to detect X-rays by self amplification.
• SF6 gas replaced by oil etc. as in insulating medium in transformer of portable X-rays machine.

17. 1957: The organization of Educators in Veterinary radiology (EVRS) formed in USA .

18. 1972:

• Rare earth intensifying screens invented.
• Computerized Axial Tomography (CT-Scan) developed by B.N. Hounsfield in England.
• In context of Nepal , veterinary radiology is still in toddler stage.

Possible uses of radiography in veterinary practice:

• As a diagnostic aid.
• Provide excellent anatomic information.
• To select methods or techniques of treatment eg. for fracture repair.
• To detect previous unrecognized lesions.
• To monitor efficacy of treatment schedule.
• To screen normal animals for morphological evaluation in an attempt to eradicate inherited diseases by selective breeding.
• To determine age of animals.
• To examine PM material.
• For non-destructive examination of archeological  specimen of animal origin.
• As teaching aid in subject of anatomy.
• For research purposes e.g. osteomedullography to evaluate bone healing.

Production and properties of X-rays:

1. General information:

                   X-rays are electromagnetic radiations of high energy and short wavelength and are capable of penetrating the matter. Electromagnetic radiation is a method of transporting energy through space and is distinguished by it’s wavelength, frequency and energy. It behave as a particle as well as wave.

A. Wave characteristics:

• All radiant energy travels in a wave form along a straight path and is measured by it’s wavelength.
• In series of waves, the distance between two consecutive corresponding points on a wave is called the wavelength.
• Electromagnetic radiation that has a short wavelength has high frequency and vice-versa.
• Frequency is measured by the number of cycles of the wave that pass a stationary point per second (cycles/second).
• The higher the frequency the more penetrating power the energy has through space and matter.
• All forms of electromagnetic radiation are grouped according to wavelength and frequency is called electromagnetic spectrum.

 

Measured in Angstrom units		Measured in meters
Wavelength (A◦)	Uses	Wavelength (m)	Uses
Less than 1/10	Industrial radiology	Close to 1/1000 m	Microwave – RADAR
1/10 to 1/2	Medical radiology	Close to 1 m	Television
25 to 4000	UV-rays	Close to 100 to 1000 m	Communications
4000 to 7700	Visible rays (VIGBYOR)	Close to 10000000 m	60 cycles AC
7700 to 10000000	Infrared rays

* Shorter the wavelength greater the penetrating power.

 

B. Electromagnetic radiation as a particle:

* Atoms consists of small particles called as protons, neutrons and electrons.

• An atom gas a nucleus with surrounding cloud of electrons.
• The nucleus of each atom contains protons (positively charged) and neutrons (chargeless).
• Electrons which are negatively charge travel around the nucleus in specific orbits, called shell.
• X-rays are produced when charged particles (electron) are down or stopped by the atoms of a target area.
• This process occurs inside the X-rays tube to create an X-rays beam.
• X-rays beam is composed of bundles of energy that travels in a wave.
• These bundles of energy are called photons. The photons have no mass or electrical charge.

 

2. Production of X-rays:

The following elements are necessary for X-rays production:

• Source of electrons
• A method of accelerating the electrons
• An obstacle-free path for passage of high speed electrons
• A target in which the electrons are interact, releasing energy in the form of X-rays
• An envelope (tube) to provide vacuum environment, eliminating the air molecule obstacles for the electron stream and preventing rapid oxidation of elements

Processes involved:

• X-rays tube consists of a cathode side (-ve charge) and an anode side (+ve charge) encased in a glass envelope, which is evacuated to form vacuum.
• The cathode and anode are kept apart by a short distance. When current is made to flow, a stream of fast moving electrons are produced at the cathode and directed to the anode.
• The process of formation of electrons from the cathode is known as thermo-ionic emission.
• As the electron collide and interact with the atoms of the target on the anode a great amount of energy is produced.
• The energy thus released is mostly converted into heat (99%) and only 1% of this energy in the form of X-rays.
• Thin Al-coated with window area, located on the dependent portion of the tube acts as a doorway for the exit of the X-rays.
• X-rays can only pass through the aluminium hence come outside while the ordinary rays are retained.
• The quantity of x-rays coming out can be regulated by an adjustable lead diaphragm.
• The entire tube is encased in a metal housing (by Pb) to prevent the escape of stray radiation and to protect the glass envelope from physical damage.
• All side is housed except at window.

Cathode :

The negative side of the X-rays tube is called cathode. The purpose of the cathode is to provide a source of electrons and direct these electrons towards the anode. The cathode, assembly consists of filament and focusing cup.

i. Filament: the cathode consists of a coiled wire filament that emits electrons when heated. The filament in most X-ray tubes measures approximately 0.2 cm in diameter and 1 cm in length. It is mounted on rigid wires that support it and carry the electrical current used to heat the filament. The filament of the light bulb. Filament is made from the Tungsten having high melting point (3370◦C) and high atomic number. Small portable X-rays machine have a single filament. Most modern tubes have two filaments side by side: one being smaller than other with different capacity for heat and electron emission.

ii. Focusing cup: The filament is located in a concave cup called focusing cup. This cup is made from Molybdenum because it has high melting point and is poorer conductor of heat.

Anode:  

Anode is the positive side of the x-rays tube. The target (anode) is composed of Tungsten which can withstand and dissipate high temperatures. The base of the target is made from copper. Copper acts as a conductor of heat and draws the heat away from the Tungsten target. Temperature  in excess of 1000◦C is needed for X-rays production . Hence, the anode serves 2 main functions in the X-rays tube:

1. Provide mechanical support to the target

2. Acts as good thermal conductor of heat dissipation.

The anode in X-rays tube may be of two types:

1. Stationary anode: Used in dental, portable X-rays units, where high tube current and powers are not required.

2. Rotating anode: Used in X-rays units of larger capacity to produce high intensity X-rays beam in a short-time. The rotating anodes have better heat dissipation.

3. Properties of X-rays:

1. These are electromagnetic radiations.
2. Wavelength is extremely short:  Due to this property, x-rays are able to penetrate materials that absorb or reflect visible light. The amount of absorption depends on the atomic number, density of the object and energy of the x-rays. The wavelength ranges from 0.1 to 0.5 A◦.                                                                                                                                                 
3. These are high energy radiations with high frequency. Their energy is inversely related to the wavelength.
4. This high energy help the X-rays to penetrate materials which readily absorb and reflect visible light.
5. X-rays always travel in straight line with the velocity  of light (3×10^10 cm/sec). Direction can be altered but the new path is also in straight line.

Working Principles of X-rays Machine and Radiographic Accessories:

(Filters, Restrictors, Collimators, Grid)

1. Portable X-rays Machines:  Most commonly used in veterinary practices because of their convenient transportation. Such machines can be suspended from a rack or a strap or can be positioned on a wooded block. Portable machines are equipped with small sized low weight transformer located within the tube head. Small control panel is attached to the tube stand or supported on a separate stand. These machines have stationary anode with both single and double focal spot. The maximum output varies from 70-110 kV and 15-35 mA.

Advantages:

• Cheap
• Require little maintenance
• Light in weight, so easy to transport.

       Disadvantages:

• Due to low electrical output, have limited value for radiography above the carpus and tarsus of large animals.
• Low mA necessitates longer exposure time.

      2. Mobile X-rays Machines:

       Have higher output than portable machines by virtue of their larger transformers. Some models can be also useful for radiography of the digits           in a standing animal. Usually, these machines have rotating anode with output of 90-125kV and 40-300 mA.

3. Fixed X-rays Machines:

Installed in a room especially constructed for the purposes. Large transformers are installed to have greater output. Output of these machines varies from 120-200kV and 300-1000 mA.

Advantages:

• Suitable for almost all types of radiographic examination of the large animals.
• A ceiling mounted telescoping tube support facilitates movement of the tube across the room and almost to the level of ground, apart from both vertical and horizontal X-rays beam.
• Because of high kV and mA output, exposure time is less.

Disadvantages:

• More scattering of radiation because of higher kV output.
• Expensive to purchase.
• Three phase electricity supply is required for instillation of machine.

Technical Components:

5. Every X-ray apparatus consists of more than X-ray tube.
5. The X-ray machine comprises many complex mechanisms that allow radiographer to produce quality radiograph consistently and accurately.
5. Majorly comprises:
   • Electrical components
   • Control panel

 

A.Electrical components:

• As we know the electricity is needed to heat the filament of the cathode.
• Once the electron is heated and electron cloud is available, there must be source of power to push the cloud towards the anode target area.
• These two events not only to have occur, they also be controlled properly.
• In order to control power, time and amount of release from X-ray beam following things are necessary:

i. Transformer

ii. Timers

iii. Generators

B. Control panel:

• It is separate unit connected electrically to the X-ray machine.
• The control panel consists of many knobs and switches necessary for the operation of the X-ray machine.
• It is, essential that the face of the panel and understands that not all panels are alike.

Consists of:

1. On/Off switch
2. Voltage compensator
3. Kilo-voltage selector
4. Miliamperage selector
5. Timer
6. Exposure button
7. Warning light

1. On/ Off switch:

It is a main switch to turn the unit on. The switch permits flow of the current to the tube at ‘’On’’ position and prevents the same at the ‘’Off’’ position. For safety of the X-ray tube and also to avoid accidental exposure the switch remain in ‘off’ when machine isn’t being used.

2. Voltage compensator:

The voltmeter provides manual adjustment of the transformer to allow for inconsistent electrical output from the main electrical line. The line voltage should be checked whenever the machine is turned on. Most X-ray machines are designed to operate on a 220 voltage power source. In most machines these days such a system is automatic.

3. Kilo-voltage selector:

 It allows precise selections of desired kV. Most modern X-ray machine are calibrated so that the desired value kV can be selected. However, in a number of smaller x-rays units the kilovoltage control is automatically linked with certain miliamperage.

4. Miliamperage selector:

 The component let the radiographer select the desired current to cathode filament. This method of selection varies among X-rays machines.

5. Timer:

 This mechanism allows the radiographer to pre-select the time of each exposure. The timer varies with models of x-ray machines. Example of timer include:

• Clock work timer
• A synchronous timer
• An electronic timer

The advantage of the timer is the ability to use a short exposure time with accuracy.

6. Exposure button:

               The exposure button is on the face of the control panel or attached to it by a length of cable. In either case the button should be in apposition to allow the person making the exposure to be at least two meters from the tube housing. Many X-ray machines operate on a two stage button. Two stages are necessary for the cathode filament to be activated and heated, to produce the electrons necessary for the exposure. Depression of first half of the button activates the filament and rotating anode, if present, and after few seconds, the button is fully depressed to complete the circuit for exposure.

7. Warning light:

Most control panel have light that illuminate when an exposure is made and x-rays are being emitted.

Radiographic accessories:

1. Filter

2. Restrictors

3. Collimators

4. Grid

5. X-ray film

1. Filter :

 Composed of aluminium or Aluminium-copper, combinations absorbs low energy X-rays. The filtered x-ray beam decreases the exposure dose of the patient and scatter radiation. Primary purpose of placing a filter between the patient and x-ray tube is to remove less energetic (soft) x-rays from the primary beam.

2. Restrictors/ Cone:

Restrict field size. A small field size decreases the amount of the scatter radiation.

3. Collimators:

A restricting device used to control the size of the primary x-ray beam. The beam emerges from the x-ray tube in a diverging manner. If uncontrolled, the beam could extend to considerable width.

It serves to:

1. Present unnecessary irradiation of the patient or persons involved in restraining the patient.
2. Reduce scatter radiation as well.

Several types of collimators are available which are placed in the path of x-ray beam as close the tube as housing permits. Following types of collimators are most commonly used:

1. Aperture diaphragm
2. Cones and cylinders
3. Variable aperture collimator

Inherent filtration:

 The absorption of x-rays by the x-ray tube and it’s housing is called inherent filtration.

In diagnostic x-ray tubes the glass is equal to about 0.5 mm Aluminium.

Added filtration:

Results from the absorbers(filters) placed in the path of x-ray beam.

Outside the x-ray tube and housing:

• Silver on collimator mirror
• Al/ Cu between the collimator and protective housing.

Thickness 1-1.5 mm aluminium equivalent. Can be customize (filter, thickness, type of metal).

Total filtration:

Total filtration = Inherent filtration + Added filtration

Recommended by NCRP:

Operating (kVp)	Total filtration
Below 50 kVp	0.5 mm Al
50-70 kVp	1.5 mm Al
Above 70 kVp	2.5 mm Al

 

4. Grid:

• A device placed between the patient and the radiographic film and is designed to absorb non-image forming x-rays (scatter radiation).
• Composed of alternating strips of leads (radio-dense) and spacer (radiolucent) materials.
• The lead strips are approximately 0.5mm in thickness and number between 500 and 1500 on edge.
• The spacer material usually consists of fiber, aluminium or plastic because these materials have low x-ray absorption ability.
• The strips are encased in a protective cover (usually Al) to provide strength and durability.
• The lead strips are aligned with the primary x-ray beam in a manner that allows the desirable x-rays to reach the film.
• The lead absorbs considerable amounts of the x-rays not travelling in the direction of the primary beam.
• The spacer materials permits most of the primary x-rays (desirable) to pass through the film.

Position:

1. Placed directly on the top of the cassette.
2. Built into cassette.
3. Placed directly under the x-ray tube between the patient and the cassette.

        Pattern:

• Grid pattern refers to the orientation of the lead strips in their longitudinal axis.
• The pattern of the grid can be seen from the top view.
• Two basic patterns are:

1. Linear grid:

• Lead strips are placed parallel to each other in their longitudinal axis.
• Allow primary x-ray to reach the film but absorb x-rays not travelling in perpendicular path to the film.
• Table type x-ray machine equipped with linear grid.

        2. Crossed grid/ crisscross:

• Consists of two superimposed linear grids placed at right angles to each other.
• A cross grid is more efficient in absorbing scatter radiation.

5. X-ray film:

• The purpose of x-rays film is to provide a permanent record containing essential diagnostic information.
• It consists of a polyester base coated on both sides with a light sensitive  emulsion containing silver halide crystals.
• When visible light or x-rays interacts with silver halide crystals, an invisible (latent) image is formed.
• After processing, visible image can be observed.
• Halide ions may consist any one from bromide, chloride or iodide. Silver bromide crystals are common in x-ray film.
• The color of x-ray film is apple green.

How to take radiograph?

Dark room and radiographic processing

Principle steps of taking of radiograph:

1. Case number and date.
2. Radiographic registration.
3. Owner’s name and address
4. Name of doctor/ clinician/ physician who referred for radiography
5. Recording of the patient-name if any, Species, Breed, Age, Sex, Color and body weight
6. Physical and clinical examination of patient
7. The part ascertain for radiography
8. Size of the x-ray film as per requirement or as per direction
9. Selection of cassette as per size of the x-ray film
10. Lead or rubber number and letter for film identification
11. Loading of the x-ray film in the dry bench of dark room
12. Preparation of the patient e.g. for radiography of soft tissue and organ contrast medium should be selected
13. Control of the animal by attendant or owner e.g. for vicious, furious and small animal general anesthesia is recommended
14. Radiographic positioning of the patients e.g. anterior, posterior, latero-medial, medio-lateral, dorso-ventral, ventro-dorsal
15. Selection of the exposure factor
16. Connection of the machine to the main incoming line
17. Switch on and reading of the voltage of the main line supply
18. Adjustment of the volt with the voltage stabilizer
19. Radiograph is to be taken in proper radiographic position
20. Protective measures should be taken by wearing x-ray protecting goggles, gloves and lead apron by the attendant and radiographer
21. Pressing the button of the timer
22. The exposed x-ray cassette if taken into the dry bench of the dark room and opened
23. Give identification mark on the top left corner
24. Fixing of the x-ray film in the film hanger of appropriate size
25. Proper processing of the x-ray film in the processing tank. Time of processing depends on the temperature of the processing solution which is measured by immersion thermometer
26. Drying of the x-ray film
27. Viewing the film in the lighted room or using x-ray viewing box/illuminator

 

A. Dark Room:

• The size of dark room depends on the work load and number of people working there.
• The dark room should be with a floor area of 100 sq. ft.
• The height of the ceiling must be 10-11 ft.
• The dark room should be clean, light proof and should not be damped.

A-1 Light Proofing:

• Must be completely light proof.
• The door and windows must closely fitted into their frames and strips of belt be provided in the frame.
• The door should be fixed interiorly with bolt.
• The entry into the dark room should be made through two doors in ‘Z’ manner.
• The relative humidity and temperature should be 40-60% and 10-20◦C.

A-2 Floor

• The floor shouldn’t be pours, should be resistant to chemicals, doesn’t become slippery when wet and can be easily washable.
• The suitable material for floor is earthenware tiles in acid proof cement, composition tiles or heavy duty linoleum.

A-3 Painting and safe light:

Painting: Must be painted either with good quality paint of green or white.

Safe light: The maximum sensitivity of the x-ray film is in blue region of the spectrum, so the safe light should be amber green or red filter. Amber filter provides the maximum visibility with minimum fogging tendency.

Radiation protection:

• The personnel working and x-rays accessories require protection from ionizing radiation in the dark room.
• The x-ray machine should be installed in such a way that the primary beam never be directed towards the wall of the processing room.
• It is desirable that the room should have a lead coating of 2 mm in thickness.

Dark Room setting:

There needs two distinct work point in the dark room.

1. Dry bench- where the film is loaded or unloaded
2. Wet bench- where the processing of the film is done.

These two benches should be separated or kept apart by four feet. Preferably both sides are set on the opposite wall of the dark room. The workload is orderly sequenced. The equipment should be neatly placed in adequate space. When more than one person is working the movement of each person should have specific tract.

Dry bench:

• The top of the dry bench should be made up of wood or linoleum, but not of plastic laminates because it hold static charge of the electricity and can leave mark in the film.
• On one side of the dry bench, there should be a 20’’×17’’ deep cupboard with a vertical division for storage of the film boxes in the upright standing position.
• On the other side, the light tight drawers are provided for the storage of the x-ray films.
• The processing hanger should hang over above the dry bench. A bin of waste paper is kept under dry bench.

Wet bench:

• Wet bench in the dark room is the place where the processing of the exposed x-rays film is done. The wet bench is provided with a set of four tanks with different capacity viz. 9 or 13 or 22.5 liters or above and are made up of stainless steel, vulcanite, porcelain or hard rubber.
• These tanks contain the chemical solutions for processing of the x-ray film in the sequence of : Developer, Rinser, Fixer-hardner and Washer or water for washing.
• These tanks should be either stand in low sink or deep water jacket to keep the solution at 20◦C

 

Processing of X-ray film:

• Correct processing of the exposed film is the key factor to obtain a quality radiograph and routine processing of the film is a simple procedure.
• First of all, the exposed film is unloaded from the cassette in a safety lighted dark room.
• After putting a proper identification mark, it is placed in a stainless steel processing frame.
• Consistent processing can be achieved only when the standardized solutions are employed.
• Solutions should be purchased from the reputed manufacturers and their instructions should be strictly followed.

Manual processing of the x-ray film:

It consists of five steps:

1. Developing
2. Rinsing
3. Fixing
4. Washing
5. Drying

The developing of x-ray film:

• An exposed film bears an invisible or latent image of exposed silver ions, which in developing solution converted into minute grains of metallic silver.
• The initial stirring of processing solution should be made after immersion of film.
• After specified period of time should be taken out and then go for rinsing.
• Then frequent agitation of the film should be made.

Table: Time temperature variations:

Temperature (◦F)	60	62	64	66	68	70	72	74	76
Time (Min)	9	7.5	6.5	5.5	5	4*1/4	3*3/4	3×1/4	3

 

Composition of developer solutions:

1. Metol                                                                                        8.3 gm
2. Hydroquinone                                                                         33 gm
3. Sodium sulphate (dessicate)                                                 272 gm
4. Potassium bromide                                                                 15 gm
5. Sodium carbonate                                                                    212 gm                       
6. Distilled water                                                                           to make one galloon

* The pH of the solution is basic in nature.

• Metol is a developer in a developing solution. Hydroquinone has a low reduction potential and is very sensitive to temperature. When these two are used together, there is super-additivity. Phenidone is a newer replacer of Metol and is used with Hydroquinone.
• Sodium sulfate is preservative and anti-oxidant agent to minimize aerial oxidation of the reducers. Sodium bromide/iodide is a restrainer to suppress the chemical fog. Sodium carbonate is a mild alkali that accelerates developing process. Replishment of the developer serves dual purpose of replacing the lost volume and maintaining as far as possible an even activity. After each 3- months the made up solution should be discarded.

Rinsing of the radiograph:

After a specified period in developer it should be taken out and then rinsed in water. The specified rinsing period is 30 seconds.

The composition of rinsing solution:

1.  Glacial acetic acid                                50 ml
2. Water                                                      up to 1 galloon

Fixing of the X-rays film:

The x-rays film should be placed in fixing solution and agitation of 15 seconds helps in prevention of streaking and staining of the finished solution. The removal of unexposed silver halide crystals is removed from the emulsion. For maximum hardening, the fixer takes 10 minutes. The time and temperature range is similar to that of developer i.e. optimum of 68◦F and ranged between 60-75◦F.

Comments:

• Sodium thiosulfate (hypo) is the cleaning agent in powdered fixers which dissolves and removes underdeveloped silver halide from emulsion.
• Sodium bisulfate is a preservative.
• Sodium acetate is an acidifier.
• Alum are hardners and prevents the gelatin from swelling and softening in wash water.

Final washing of the x-rays film:

Adequate washing prevents dislocation and should be performed either in running water(30 minutes) or in stagnant water (2 hours). Frequent changing of the position of the film is rewardable.

Drying of the x-rays film:

After washing the film should be properly dried in open air or in automatically heated circulated air dryer.

Automatic processing of the X-rays film:

• The automatic processor is the essential piece of equipment in every x-rays department.
• All the procedure is regulated systematically by the automatic processor.
• In this there is use of conveyor system to move the film through the developing solution, the fixing solution and the washing.
• The automatic processor will reduce film processing time when compared to manual development.

Factors affecting the production of radiographs:

1. Make and type of x-ray machine
2. Incoming line voltage
3. Miliaperage and exposure time
4. Kilovoltage
5. Distance

• Focus film distance (FFD)
• Part film distance (PFD)

6. Grid type
7. Type of film and intensifying screen
8. Thickness and nature of the part being exposed
9. Temperature and time of developing

#  Make and type of x-ray machine:

A combination of kilovoltage, miliamperage and time setting that produces a satisfactory radiograph with one machine may not necessarily produce same quality of radiograph with another machine. The maximum output from different types of x-ray machine has been summarized as follows:

Type of x-ray machine	kV	mA	mA×time (seconds) = 10 mAS
Portable	70-110	15-35
Mobile	90-125	40-300
Fixed	120-200	300-1000

Time should be always in the fraction of seconds.

#         Incoming line voltage:

A fluctuation in the line voltage will allow consistent output. To be a consistent output the incoming line voltage should be fixed.

#    Miliamperage and exposure time :

• Electrons are produced by heating the cathode filament. When a calibrated electrical current is passed through the low tension circuit of the x-ray machine, the metal of the filament is heated and electrons are released.  The process of ‘Boiling-off' the electrons from their atomic orbit is known as thermionic emission. The free electrons from a cloud around the filament. The number of electrons in the cloud is directly proportional to temperature of the filament.  The electrical current that heats the filament is measured in mA (1/1000^th of an ampere). As the mA is increased, the number of electrons available is increased and hence better definition (sharpness I.e. well defined demarcation between various structures that are recorded in film) is obtained in radiograph. The total quantity of x-rays produced during a given exposure is also dependent on the length of exposure. The period during which the x-rays are permitted to leave the x-ray tube is termed the exposure time, and is always measured in fraction of a second. There is a direct relationship between mA and exposure time (s). The quantity of x-rays required for a given exposure is best expressed as the product of mA and the time in milliamperage-second (mAS).

                 mAS                       mA×Time (s)

                    10                          20×1/2

                     10                           100×1/10

                     10                           200×1/20

                      10                            300×1/30

 

 

Advantages of maS:

1. With a shorter time setting, the possibility of motion occurring on a radiograph is decreased.
2. A shorter exposure time also decreases the exposure of the restraining personnel.
3. At higher mA setting, the greater amount of x-ray is produced.

#   Kilovoltage:

kV determines the penetrability of the x-ray beam and thus affects the radiographic density (i.e. degree of blackness or whiteness on a radiograph). The potential difference between anode and cathode is measured in kilovoltage (1000 volt or kV). The kinetic energy of the electrons when they reach the target is proportional to the potential difference between cathode and anode. Hence, during an exposure time, the anode is maintained at high positive electrical potential relative to the cathode. Due to this difference in electrical charge, the electron cloud at filament is formed into narrow beam and accelerates the anode at very high speed. The kV determines the quality of the x-ray beam and it’s ability to penetrate.

• Higher the kVp setting produce more penetrating beams with a higher percentage of the radiation reaching the film.

There is an inverse relationship exists between kVP and mAS.

• Higher the kVP settings allow for lower mAS setting which strictly demand for shorter exposure time.

The kVP can be estimated by an equation known as Sante's rule, which states:

kVP= (2× thickness) +40

Where, the thickness of anatomical part in cm is measured by caliper and 40 represents focal-film distance in inch.

Eg.

Dr. ABC has requested an abdominal radiograph on a German shepherd dog. The measurement of lateral abdomen was 15 cm.

kVP = (2×thickness) + 40

      = (2×15)+40 = 70 kVP has been to set.

#  Distance:

1. Focal-film distance(FFD):

FFD is the distance between focal spot in the target of the x-ray tube and the x-ray film. It is desirable to set optimum FFD for every radiographic exam. The most common FFD in veterinary practice ranges from 35 to 40 inches (90-100 cm). When different FFD is used, the adjustment of mAS can be calculated as:

New mAS = Old mAS × (new FFD/old FFD)²

Eg. = 10 mAS × (100/90)²

       = 12.34 mAS

2. Part-time distance (PFD):

The distance between part to be exposed and x-ray film should be kept minimum as far as possible. To get good definition and avoid magnification, the PFD should be made Zero .

 

# Grid type:

A grid prevents radiation from falling on the film and thereby impress radiographic contrast (difference in densities  in various part of the radiograph). It has been supposed that the use of grid requires increase in exposure factors. The increment depends on the ratio of grid.

Grid                   Increase exposure (mAS) by a factor of

5:1                              2

8:1(used in vet)       3

12:1                           4

#  Type of film and intensifying screen used:

The intensified screen film requires 5 times less exposure as compared to non-intensified screen film.

• To produce same quality of radiograph.

#   Thickness and nature of part to be exposed:

1. When the thickness of the tissue increases, the kVP should be increased to obtain rays having more penetrating power.
2. In addition to part thickness, the nature of the part and presence or absence of pathological lesions within the part also influences the exposure.
3. The density of part should also be considered.

#   Temperature and time of developing:

1. Temperature as well as time for developing film should be kept constant.
2. There is inverse relationship between temperature and time of developing  at higher temperature,  short duration of developing and vice versa.
3. Low temperature and or too short developing time produce under exposed radiograph.
4. Too high temperature or developing time (longer) produce a dark film that appears to be over exposed.

Temperature (◦F)	60	62	64	66	68	70	72	74	76
Time (Min)	9	7.5	6.5	5.5	5	4*1/4	3*3/4	3×1/4	3

 

Intensifying screen and it’s uses:

Intensifying screens interact with x-ray beam that has penetrated the patient and reached to the cassette. When the phosphor crystals in the screen are struck by the c-radiation: the crystal fluoresce whereby x-rays are converted into visible light. Remarkably, more than 95% of the exposure recorded in the film is due to light emitted from the intensifying screens. Only the remaining 5% of the exposure of the film results from ionization of the x-rays.

Efficiency of the screens material:

1. They must have level of x-rays absorption.
2. They must have a high x-ray to light conversion with suitable energy and color.
3. There must be little or no after glow once radiation has ceased.

Construction of intensifying screens:

An intensifying screen has four integral layers with a total thickness of about 0.4 mm

1. A base or support
2. A reflective layer
3. A phosphor crystal layer
4. A protective coat

1. A base or support:

The base serves as a flexible support to attach phosphor layer to the cassette. It is made either high grade cardboard or polyester. The base must have a tough moisture resistant surface and not become brittle with extended use.

2.   A reflective layer:

This layer is closely attached to the base and is made of a white substance such as titanium dioxide. The purpose of the reflective layer is to reflect the light emitted by phosphor layer back towards the x-ray film.

3.      A phosphor crystal layer:

This layer consists of uniformly distributed phosphor crystals held in the place with a binder material. The main function of it is to convert x-rays energy to visible layer. The materials to be used as phosphor crystals include:

• Calcium tungstate: most commonly used because of high absorption coefficient i.e. 25%
• Barium lead sulphate
• Zinc cadmium sulphate

4.   a protective layer:

It is a transparent/clear layer placed on the outer surface of the screen.

Uses of intensifying:

• To reduce the amount of radiation exposure required to produce a diagnostic radiograph.
• To utilize the less milliamperage-second (mAS), thus decreasing the dose of the radiation to the patient as well as chance of motion on radiograph.

Care of intensifying screens:

Rough handling leads to creation of the radioactive artifacts on the processed film. Routine inspection and cleaning of the screen should be done at least once in month. Following considerations should be remembered during care of the screens:

1. Keep free from marks, dust and stains
2. Never allow abrasive liquid to come in contact with screens.
3. Never allow processing solutions to splash over the screen.
4. Never touch the protective surface except at the time of the cleaning.
5. Use specific cleaner otherwise chances of the fogging.
6. Always maintain good screen-film contact.

Uses of fluoroscopy:

It is used for a number of purposes:

• To assist in surgical procedure e.g. foreign bodies removal, cardiac catheterization.
• To evaluate ventilation mechanisms e.g. trachea, lungs and diaphragm.
• In the GI tract.
• To evaluate cardiac function.

 Fluoroscopy (Adv. And Disadv.)

Fluoroscopy is essentially the visualization of a ‘’live’’ or ‘’real-time’’ radiographic image. It is a non-invasive procedure which uses x-rays to help capture and monitor video images of specific parts of the body while they are in motion.

Principles of fluoroscopy:

• X-rays cannot be seen directly and they cause certain chemicals like- Calcium tungstate, barium lead sulfate, zinc cadmium sulphide, zinc sulphide and barium platinocyanide to fluoresce or emit visible rays.
• To have visualization of image a fluorescent screens should be used which usually consists of a board smeared over with calcium tungstate.
• The x-rays coming through the patient falls on the screen and the image becomes visible.

Advantages:

• Actual movement of an internal organ or part can be observed.
• Very helpful to diagnose the hip dislocations.
• Peristalsis movement can be observed.
• Birth posture of the animal can be ascertained.
• Pulmonary emphysema and pericardial effusions can be diagnosed.

Dis-advantages

• Permanent image cannot be recorded.
• It’s use provokes additional risk of irradiation to the patients and the observer too because of increased duration of exposure to the x-rays.

Contrast radiography:

Introduction:

Contrast is defined as the visible differences between two adjacent radiographic densities.

Divided into two separate categories:   A. Radiographic contrast              B. Subject contrast

A.  Radiographic contrast:

• It is the density difference between two adjacent areas on a radiograph. When the density difference is great, the radiograph is said to have high contrast or a short scale of contrast. That is a radiograph with  the high contrast exhibits many black and white tones. E.g. a radiograph with white bone and a black background has high contrast. A radiograph that exhibits many grays and a small density differences between two adjacent areas has low contrast or a long scale of contrast. An increased number of gray tones between the white and the black tones on a radiograph constitute a long scale of contrast. Of course, there must be extremes in contrast. It is not desirable to have radiograph with too high or too low contrast.
• A good radiograph should have a suitable range of differentiated radiographic densities (black, whites and grays) so that the eye can easily see the detail.
• Radiographic contrast is influenced by:

i. Subject contrast                             ii. kVP level                    iii. Scatter radiation

iv. film type and                                 v. Film fog

Basic radiographic opacities:

Radiographic image: it is produced when x-ray goes through the body part: Penetration and absorption.

Basic radiographic opacities:

If; Air= Black

     Fat/ water= dark grey

     Bone= Gray

     Metal/ + contrast= Light gray

                                       White

B.   Subject contrast:

It is defined as the difference in density and mass between two adjacent anatomic structures, subject contrast is dependent on the thickness and density of the anatomical part. The body of the animal has many different types of tissues with variable densities. Some of the x-rays falling on a tissue get reflected, some others get absorbed, and only the remaining  ones pass through the tissue. The more radiations penetrate through the muscle as compared to the bone, this is due to difference in density of beam caused by object is subject contrast. Bone absorbs most of the x-rays falling on it, soft tissue very little and air containing organs like lungs, bowel practically nil. Bone will absorb many more x-rays than muscle or fat, assuming both have equal thickness. With appropriate exposure factors, anatomy that has high tissue density can increase the amount of whites and blacks on the radiograph; therefore high subject contrast increases the radiographic contrast.

Contrast radiography?

Under normal circumstances, soft tissue structures or organs are difficult or impossible to identify on a plain films awing to lack of contrast. When the radio-density of the tissue itself or it’s surrounding structure is deliberately altered to obtain a radiograph with enhanced visualization and demarcation, it is called contrast radiography.

Advantages of contrast radiography:

• Structures or organs can be evaluated more effectively for their size, shape and position.
• Valuable information can be gained regarding serosal or mucosal surfaces of the hollow organs or their contents which are not generally apparent in the plain radiography.
• The function of the organs can be known in rare instances.

Contrast medium:

A substance that is either radiolucent or radio-opaque that can be administered to an animal to increase radiographic contrast within an organ or syatem.

                                                           Types     

                                                

                          Positive                                             Negative

(BaSO4, Iodine-Ionic and water soluble)     (CO2,  Air, N2, NO2, O2)

1. Positive contrast media:

Materials which increase radio-density of the structure or tissue in relation to surrounding tissue are called positive contrast media. Barium or iodine preparation , contain element of high atomic number. Absorb more x-rays than do the soft tissues or bones. Radio-opaque to x-rays and appear white on a radiograph. Used to fill or outline a hollow organ (e.g. Urinary bladder, GIT) or injected into the blood vessels (sterile water based compounds only) for immediate visualization of vascular supply or for subsequent excretion evaluation.

2. Negative contrast media:

Materials having the property to increase the radio-density of the structure as compared to surrounding tissue are known as Negative contrast media. The substances having low specific gravity like room air, oxygen and carbon-dioxide are commonly used negative contrast media. Others are nitrogen and nitrous oxide. An ideal negative contrast media should be inert, quickly dissolved in fluid and quickly eliminated from the body. Substances with low specific gravity are more radiolucent to x-rays than soft tissues and have a black appearance on a radiograph.

Contrast agents:

1. Positive contrast agents:

I. Barium-sulfate preparations: medium of choice for radiographic studies if the GIT.

 Because it is:

• Completely insoluble
• Not diluted by alimentary secretions
• Not absorbed through the intestines

Forms:  Liquid, paste and powder for reconstitution with water.

Indications:

Oesophagography, Gastrography, Reticulography, Barium enema, Barium meal for GIT

Contra-indications:

• If perforation, enters into pleural and peritoneal cavity and results into granulomatous reaction.
• If entered, it should be flushed within 6-8 hrs.
• Barium inadvertently aspirated into the trachea, usually is cleared by cough.

II. Iodine preparations: The iodine compounds are divided into two sub-categories:  Water soluble agents and Viscous/ oily agent.

A. Water soluble agents: Make up the largest group of contrast agents. Most water soluble preparations are:

1. Opaque to x-rays
2. Pharmacologically inert
3. Low in viscosity for rapid injection
4. Low in toxicity
5. Rapidly excreted by kidneys and
6. Chemically stable so that no iodine is retained in the body.

Administration of positive contrast agents:

These agents are injected into a vascular system for immediate visualization of the system or subsequent demonstration of the excretory system. In addition, water soluble agents can be infused into the urinary bladder via urinary catheter to visualize the urinary mucosa, bladder shape and size. In market, these water soluble agents are available in ionic or non-ionic form.

i. Ionic preparations:

1. Meglumine iothalamate (conray-280)
2. Sodium iothalamate ( conray-420)
3. Meglumine diatrizoate (Hypaque 65%)
4. Sodium diatrizoate (Hypaque 85%)

Indications

• Phlebography, osteomedullography, Sialography, cystography, urethrography, IV pyelography.

Contra-indications:

• Due to it’s irritant effect, not indicated for angiography, myelography and arthrography.

Non-ionic forms: Metrizamide (Amipaque-30n) – for myelography, angiography and IV pyelography (renal pelvis)

2) Oily/ viscous agent:

Have limited application in veterinary radiography, only limited to lymphography. These can be used for myelography if non-ionic form isn’t available.

Negative contrast agents: E.g. Air, O2, CO2, N2, N2O

CO2 has an advantage over room air because CO2 is better absorbed into body into hollow organ, room air can cause air emboli. It is used for radiography of hollow organ (pneumocystography) and soft tissue.

3. Double contrast:

A radiographic contrast technique that uses a combination of the both positive and negative contrast media simultaneously. For example : to diagnose the foreign bodies in stomach- we have to administer both Barium meal as well as air. Urinary bladder to look for the presence of uroliths.

 

Principles of viewing and interpretation of x-ray film:

Viewing of Radiographs:

In order to evaluate a film completely, a radiograph should be viewed on and evenly lit view box in a semi-darkened room. The viewing box screen should be clean and light bulbs in working order. For obvious practical reasons, films are usually examined white it is still wet. However, wet film is swollen and as it dries it will contract and improve definition. Therefore, the radiograph for evaluating the lesions of fine detail, final examination should be postponed until radiographs dries properly. The standard radiographic viewing box has a screen measuring 17×14 inches, which is adequate for all normal radiographs. There is considerable advantage in having two viewing boxes or one with double size. So that at least two film showing suspected pathology with a normal of the same area or build up the three dimensional concepts of lesion from films taken in two different planes. In certain viewing boxes, the intensity of illumination can be varied, which facilitate the examination of films which vary in density. For areas of such density, some form of spot light may be necessary to show the details of such local areas. The light should not be too bright or strongly illuminated because it makes radiologist’s eyes to radiograph difficult. It can also be helpful to have magnifying glass when making a close inspection of films showing particularly fine detail. The position of film on the view screen is also important. Veterinary radiographers generally follow the medical protocol for viewing. Ventrodorsal or dorsoventral anatomy, such as abdomen or thorax, should be placed on the view screen so that animal is at top and patient’s right is on the viewer’s left. A laterally positioned anatomy should face the viewer’s left with spine at the top.    

Interpretation of x-rays:

Radiographic diagnosis doesn’t depend on gross radiological appearances. Radiological appearances must be able to make a specific diagnosis of a particular condition. Good interpretation is an art and requires a careful pain staking approach to each film.

Basic concepts of interpretation of radiograph:

The radiographic image is a two-dimensional representation of a three-dimensional body part. Characteristic radiographic appearance depended upon it’s thickness form and atomic number.

Relative radio-densities:

  Air, fat                                                                    soft tissue                                            bone, surgical pin

                Radiolucent                                                                                      Radio-opaque

Tissue/ object	Effective atomic number	Physical density (sp. gravity)
Gas	1-2	0.001
Fat	6-7	0.9
Soft tissue/ fluid	7-8	1
Bone	14	1.8
Metal (lead)	82	11.3

 

Relative radio-densities:

The image is a summation of anatomic shadows. Interpretation of radiographs requires imagination and logical analysis. Radiographic interpretation is based on the visualization and analysis of opacities on a radiograph.

 

Radiologic interpretation:

• Viewing the radiograph
• Three-dimensional concept
• Routine assessment of radiographs
• Every shadows visible must be evaluated.

 

Description of radiologic abnormalities (Roentgen signs):

• Changes in size of an organ or structure
• Variation in contour or shape
• Variation in number of organs
• Change in position of an organ or structure
• Alteration in opacity of an organ or structure
• Alteration in the architectural pattern of an organ or structure.

Touquet’s ten commandments of emergency radiology:

Command : 

1. Treat the patient not the radiograph
2. Take a history and examine the patient before requesting a radiograph
3. Request a radiograph only when necessary
4. Never look at the radiograph without seeing the patient and newer see the patient without re-viewing the radiograph
5. Look at the radiograph, the whole radiograph and the radiograph as a whole in appropriate settings.
6. Re-examine the patient when incongruity exists between the radiograph and the expected findings.
7. Remember the rules of two
8. Take radiographs before and after procedures
9. If a radiograph doesn’t look quite right, ask and listen (seventh rule of rules two)
10. Ensure you are protected by failsafe mechanism.

Rules of Two for interpretation:

1. Two views: One view is one view too few.
2. Two joints: Image the joint above and below a long bone.
3. Two sides: Compare the other side (difficult case only).
4. Two abnormalities: Look for a second abnormality.
5. Two occasions: Compare current films (especially for chest radiographs).
6. Two visits: Repeat the film after a procedure or after an interval.
7. Two opinions: Ask colleague for opinion or use red hot system.
8. Two records: Write down clinical and radiographic findings.
9. Two specialists: Also get a formal radiological report.
10. Two examinations: Don’t forget other tests.  Such as ultrasonography, computed tomography, computed tomography, magnetic resonance imaging, and isotope bone scanning.

Interpretation of x-ray films:

Each films should be examined noting every structure or tissue that can be :

• Identified and checking for evidence of normality and
• Abnormality

Significant variation from the normal will be indicated by one or more of the following features:

• Displacement of the structure.
• Variation in density of tissue.
• Break or variation in contour.

 

Displacement of the structure:

This may show the pathology of an adjacent organ (upward displacement of trachea can be indicative of- Enlargement of a mediastinal lymphatic gland) or the structure itself (e.g. a displaced hip)

Variation of density of tissue:

 The density may be:

• Increased (lung’s parenchyma in pneumonia) or
• Decreased (osteolysis in association with sclerosis)

 

Break or variation in contour: A break or variation in contour of the part (fracture, neoplastic enlargement of an organ). Variation in the detailed structure of the part or tissue (juvenile osteoporosis).

• To have an accurate interpretation, the radiographs should be taken in two or more planes.
•  In some instances, it will be necessary to study a series of radiographs taken over a period of time, before commenting as to whether the pathological procedures observed are progressing or regressing.
• The information gained from the radiological examination must be correlated with that obtained from clinical or laboratory examination.
• The significance of radiological findings re-assessed in the light of this further information.
• Similarly, comparison should be made with normal radiographic structures.
• A person attempting for interpretation of a radiograph must be familiar with normal radiographic anatomy of various part taken from different views.

Classification of the radiographic lesions:

After examination of the dry diagnostic radiograph, the lesions can be classified as :

1. Systemic lesions
2. Pathological lesions

Radiographic lesions can be seen as abnormal size, shape, location, magnification, density or absence of an organ or tissue.

Systemic lesions:

The entire radiograph should be examined systemically. Systemic methods include examination of each system (musculoskeletal , pulmonary, cardiac, gastro-intestinal etc.).

Pathological lesions:

Radiographic lesions can be seen as normal size, shape, location, magnification, density or absence of an organ or tissues.   

It can be further categorized as: i. Degenerative ii. Infectious iii. Anomalous iv.Neoplastic                     v. Iatrogenic

Key points:

• Request the correct radiographic examination.
• Knowledge of anatomy is essential for evaluation of a radiograph.
• Fundamental principles help reduce errors.
• Remember the rules of two and ten commandments.
• Use a systemic approach to evaluate radiographs (ABCs).

 

Radiotherapy:

Introduction:

Treatment of the diseases by means of Roentgen rays or other forms of the radioactivity. These therapies are mostly indicated to treat rapidly dividing malignant and non-malignant tumors. Radiation therapy for the treatment of neoplasms of the domestic animals has been used since discovery of x-rays. Dr. R. Eberlin of Berlin Vet. School was the first to report (1906-1912) on the use of radiotherapy in vet practice. It’s use in veterinary medicine in treating neoplasm has yet to be introduced in Nepal. Radiation therapy has been stalled due to expenses involved and alternatively, the chemotherapy is widely used.

Indications of radiotherapy:

• Localized solid neoplasms that cannot be excised but not used if neoplasm has the potential of high incidence of metastasis.
• When surgery is expected to fail or already failed.
• When regional or distant metastasis hasnot occurred.
• When radical surgery is unable to remove whole of the neoplasm.
• When bulk of the neoplasm needs reduction in size to have easy removal during surgical procedures.

Sources of the radiation exposure:

A. Natural radiation exposure

         1. Cosmic rays

         2. Environmental

               i. Terrestrial

               ii. Atmospheric

       3. Internal radiation

B. Artificial radiation exposure

 

1. Cosmic rays:

Originate in outer space and pass through atmosphere. At normal living altitudes, exposure 35 mrad/year. At altitudes above 20KM cosmic radiation becomes important.

2. Environmental:

i. Terrestrial radiation: Radioactive element such as thorium, uranium, radium and isotopes of potassium (K40).   Exposure: 50 mrad/year.

ii. Atmospheric radiation: from radioactive gas as Radon, Thoron.   Exposure: 2 mrad/year

3. Internal radiation:

i. Include minute quantities of uranium, thorium and related substances.

ii. Isotopes of K40, Strontium (Sr99) and C14.

     Exposure: 25 mrad/year

Non-occupational radiation sources:

1. Radon = 56%         2. Manmade = 17%

3. Terrestrial = 8%      4. Cosmic = 8%

5. Internal = 11%

 

B. Artificial Radiation Exposure:

1. Medical and dental: X-rays and radio-isotopes
2. Occupational exposure
3. Nuclear:

• Radioactive fall out- Important sources = C14, Cesium (Cs137), and Strontium (Sr90)
• Cs137 and Sr90 are considered most important because they are liberated in large amounts and remained radioactive for many years.

    4. Miscellaneous: Television set, Radioactive dials, Watches, Isotopes, Tagged products, Luminous markers.

Types of radiation:

1. Electromagnetic radiation:

       Radio waves, micro-waves, infrared, visible light, ultraviolet, x-rays, Gamma rays. These all are the same form of energy-the only differ in the amount of energy packets (photons) that they contain.

Characteristics:

• All have the same velocity.
• Higher frequency and very short wavelength.
• Greater power of penetration.
• It has higher energy.

2. Corpuscular radiation: It has low penetration power. E.g. µ-rays, b-particles( electrons) and photons.

Types of radiation			Approximate penetrating ability
			Air	Tissues	Lead
µ-particles			4 cm	0.05 mm	0
b-particles			6-300 cm	0.06-4.0 mm	0.005-0.3 mm
g-rays			400 cm	50 cm	0.3 mm
x-rays			120-240 cm	15-30 cm	0.3 mm
	Cosmic rays	Some components very high

 

 Alpha particles:

Physical characteristics:

• Large mass (2 photons, 2 neutrons)

Range: 1-2 inches in air

Shielding: Dead layer of skin

Biological hazards:  Internal , it can deposit large amount of energy in a small amount of body tissue.

Alpha-particles are highly energetic Helium nucleus.

Beta- Particles:

Physical characteristics:

• Small mass, electron size

Range: Short distance( one inch to 20 feet)

Shielding: Plastic

Biological hazards: Internal hazards. Externally, may be hazardous to skin and eyes.

Gamma-rays/ X-rays:

Physical characteristics:

• No mass and charge
• Electromagnetic wave or photon

Range: Very far.

• It will easily go several hundred feet.
• Very high penetrating power.

 

Shielding: Concrete, water, lead

Biological hazards:

• Whole body exposure
• The hazard may be external and/or internal.
• This depends on whether the source is inside or outside the body.

Mechanism of action of radiation:

The mechanism by which cells are killed by ionization isn’t fully understood. Two theories are postulated in this regards-

          1. Direct or target theory

          2. Indirect theory

Direct or target theory:

The radiant energy acts by direct hit on the target molecules within the cells. To ionize the molecules, either single or multiple hits are required.

During this process, energy gets deposited within the molecules which is greater than the binding energy of the electrons. 

   This results in ejection of the orbital electrons, a change in chemical configuration of the molecule and thus damage to the cells.

DNA molecules in the primary target for radiation induced cell death (especially linkages and bonds within the DNA molecules)

Ionizing radiation generates free radicals and receives oxygen intermediates that damage local cellular constituents especially DNA.

 

DNA double strands breaks are critical lesions that result in cell death.

 

Depending upon the radio-sensitivity of the tissues, dose, and duration of the radiation, there are three principal effects on the DNA molecules.

Principal effects on the DNA molecules:

1. 1. Genetic damage: Occurs in the germ cells, response is observed in the next generation.
   2. Production of the cancer:  If proper dose isn’t used upto a particular period there will be derangement of the DNA resulting in abnormal metabolic activity causing production of malignant tissues.
   3. Cell death: DNA plays an important role in cell division and for maintaining life of the cells. When radiation damages DNA, cell division is interfered. This explains the death of the cancerous cells by ionizing radiation.

 

 

Indirect theory:

This theory proposes that the energy exerts it’s effects by producing free ‘hot’ radicals, such as peroxides within the cell that damage the specific target.

 

Water molecules the major constituents of the cell and get ionized into H+ , OH- and other unstable particles such as HO2 and H2O2.

 Since these radicals are highly unstable, they react rapidly among themselves and others solutes within the solution producing a crucial biological change in the cell which leads to cell death.

#Radiation effects on biological tissues:

1. Linear energy transfer (LET): It is a measure of the rate at which energy is transferred from ionizing radiation to the exposed tissue. The biological damage increases as LET increases.
2. Oxygen effect: O2 concentration is important in determining radiation sensitivity. Hypoxic tissues are relatively resistant to the effects of radiation. Due to excessive proliferation of tumor mass, tissue amount is unable to receive required circulation and become hypoxic. Radiation therapy is more effective in oxygenated cells. During radiation therapy sensitive cells die and hypoxic cells receive more oxygen and become radiosensitive.
3. Metabolic effects: Radio-sensitivity is directly proportional to the mitotic activity of the cell and indirectly proportional to their level of specialization. Permanent cells e.g. neurons, skeletal muscles and cardiac muscles are relatively radio-resistant. Liable or dividing cells, e.g. germ cells. Marrow cells, interstitial epithelial cells and respiratory cells are more radio-sensitive. Due to this reason, fetus is considered more sensitive than child or an adult.
    

Methods of radiotherapy:   

Radiotherapy shortens the cell division and hence increases the number of cells. This is achieved by 4 R’s radiotherapy:

1. Re-oxygenation
2. Repopulation
3. Redistribution and
4. Repair

Radiotherapy is never done by a single dose; rather multiple treatments are given over a period of time, termed fractional therapy. In animals, it is usually done in 10-12 fractions of radiation dose of 4-5 Gy each time, usually three times per week.

 During fractioned therapy:

• Oxygenated cells are killed earlier.
• More oxygen becomes available to hypoxic radio-resistant cells to make them radio-sensitive.

Methods:

A.  Tele-therapy:

The radiation is kept at a distance from a lesion. It is of four types:

1. Superficial x-ray therapy: Given through x-ray machine with energy range of 60-100 kV.
2. Deep x-ray/ over-voltage therapy: Deep therapy is used to describe treatment with x-ray of energy range 200-300 kV.
3. Super-voltage therapy: X-rays therapy range of 500-1000 kV.
4. Particulate beam therapy: Electron, neutron or photon beam.

B. Brachy-therapy:

In this radio-sensitive materials are placed in direct contact with tissue being treated. Sources are usually in the form of surface applicators- needle, seeds or grains etc.

1. Permanently implanted isotopes are- Au (198), Rn (222) and K (125).
2. Removable isotopes include : Ir (192), Co (60) and Cs (137).

Particularly useful in treating the cancer of:

1. Uterus, cervix, vagina and breast.
2. Brain, head and neck cancer.
3. Thyroid, esophagus, soft tissues
4. Lung, bladder, prostrate
5. Intraocular
6. Skin
7. Bone

Specific method of brachy-therapy:

a) Interstitial brachytherapy:

E.g. Au(198), Co (60) etc. are placed within the interstitium of the neoplasm.

Advantages:

• Continues low dose of irradiation of the neoplasm and high total dose obtained.
• The dose of the surrounding normal tissues falls off because of inverse square law.
• Implantation requires single anaesthetic procedure and hospitalization.

Dis-advantages:

• Implantation is invasive.
• Difficult procedure.
• Specific training and facilities are required.

b) Plieso-therapy (surface) :  e.g. use of Sr(90) for superficial lesions.

c) Systemic brachytherapy: I (131) and P (32) can be administered systemically.

 

What is radio-isotopes?

The isotopes are those nuclides which

• Have the same atomic number but different mass number.
• i.e. isotopes of a given atom have a same number of protons but different number of neutrons.

Isotopes of elements may be:

1. Stable e.g. Carbon and Iron (i.e. N:P is 1)
2. Unstable e.g. Cobalt and Cesium.

Unstable nuclides undergo the process of decay to form stable nuclides by the process of radioactive decay.

• During the process of radioactive decay.
• There is emission of radiation energy from the isotopes.
• Such isotopes are called radio-isotopes or radio-nuclides

 

Ultrasonography (USG):

Principle:

Electricity

            Transducer

                      Ultrasound waves

                                 Tissue

                                      Image   

Introduction:

USG is a unique imaging modality for the soft tissue structures of the body. It has been routinely used in human medicine as well as in veterinary practice abroad. It is an important imaging modality in vet medicine since 1980 AD. USG, when used will be the new addition of diagnostic modality. In Nepak, it is not used popularly due to lack of technical know- how and facilities.

Ultrasound is defined as sound waves of frequencies greater than audible to the human ear i.e. greater than 20,000 Hz. Frequencies between 2 and 10 MHz are mainly used for diagnostic ultrasound.

Selection of frequencies is inversely proportional to the depth of the tissue from the scan surface. A sound wave travels in pulse and when it is reflected back it becomes an echo and this pulse-echo principle is used for ultrasound imaging. Intensity of the returning echoes is expressed as brightness in the display is known as ultrasonography. Ultrasound can provide information about the organ architecture independent of organ function. It is especially helpful in debilitated or very young patients, in which:

• contrast agents used in special procedures or exploratory surgery may be contra-indicated.

Ultrasonographic findings are not necessarily as specific as histological diagnosis. However, the ability to distinguish solid masses from those contained fluid.

• To determine the distribution of lesions in organs allows the sonographer to focus differential diagnosis.
• To formulate the management plan.

Principle:

The ultrasound has been used to produce an image or photograph of an organ or tissues and echoes are recorded as they strike tissues of different densities. USG is a diagnostic procedure using sound-waves. The ultrasonographic machines produce sound having velocity 1540 m/s. Sound waves like light rays are governed the laws of reflection and refraction. The amount of reflection and refraction while passing through the structures depends on:

1. Frequency of waves
2. Angle of striking the structure
3. Thickness and type of structures

Interaction of ultrasound with tissues:

1. Reflection: Occurs at a boundary between 2 adjacent tissues or media. Acoustic impedance (z). the ultrasound image is formed from reflected echoes.

2. Transmission: Not all the sound wave is reflected, some continues deeper into the body. These waves will reflect from deeper tissue structures.

3. Scattering: Redirection of sound in several directions, caused by interaction with small reflected or rough surface. Only portion of sound wave returns to transducer.

4. Attenuation: The deeper the wave travels in the body, the weaker it becomes. The amplitude of the wave decreases with increasing depth.

 * The miss-match between the different structures in a given part of the body provides their differentiation in imaging.

*Maximum information is provided when the beam hits the imaging structures at 90◦ angle.

                                       Ultrasound production:

Transducer contains:

• Piezoelectric elements/ crystals
• One form of energy to another
• Produces ultrasound pulses
• These elements convert electrical energy into a mechanical ultrasound wave.
• Reflected echoes return to the scan head: convert ultrasound wave into electrical signal.
• The electrical signals is then processed by the ultrasound system.

Procedures of ultrasound:

• Place a probe on skin over the part of body to be examined.
• Lubricating jelly is put on skin for better contact with body.
• Probe is connected to the wire to the ultrasound machine, which is linked to monitor.
• Pulses are sent from the probe through the skin into body.
• Ultrasound waves are back as echoes from various structures in the body.
• Echoes are detected by probe and sent to ultrasound machine through wire.
• They are displayed as a picture on monitor.
• Operator moves probe around over surface of the skin to obtain views of different angles.
• It can be use used to measure the different size. 

 

Parts of USG machine:

1. Transducer

2. CPU

3. Key board

4. Display

5. Storage device

6. Printer

 

#  How is an image is formed on the monitor?

• The amplitude of each reflected wave is represented by a dot.
• The position of the dot represent the depth from which the echo is received.
  • The brightness of the dot represents the strength of the returning echo.
  • These dots are combined to form a complete image.
• Storage reflections = white dots (Pericardium, calcified structures, diaphragm)
• Weaker reflections= grey dots (myocardium, valve tissue, vessel walls, liver)
• No reflections= black dots (Intra-cardiac cavities, gall bladder)

Advantages:

• Better delineation of the soft tissues.
• Absolutely safe, even in early stage of pregnancy.
• Not very expensive, non-invasive.
• Free from radiation hazards.
• Provides quick and dynamic visualization.
• Determines shape, size and internal consistency of an organ.
• Allows precise location of biopsy needle or instrument for collection of materials.
• Provides documentation and preservation of primary data on portable cassette and findings can be integrated with other diagnostic modalities.

Disadvantages:

• Operator dependence
• Deleterious effect on small organism on USG by acoustic cavitations.

Indications:

1. For detecting abnormalities of: Hearts, pancreas, uterus, kidneys, urinary bladder, liver, stomach, ovary, gall bladder, prostrate, spleen, cysts, intra-abdominal testicles, blood vessels.
2. For detection of developmental stages and abnormalities of the fetus if any.
3. However, it cannot be used for study of the lungs because wave cannot penetrate the air inside the lungs.
4. Bones except cartilaginous structures in the fetus cannot be studied.

 

 

Principle of Physical Therapy, it’s Classification, Scope and Limitations

Physical therapy is a technique to increase the mobility and function of joints and

muscles in animals. This technique can reduce the pain and enhance the recovery from

injury, disease, degenerative disease, age related disease and obesity. The main goal of

therapy is to increase the quality of life and decrease the pain. Each technique used in

animal physical therapy has different benefits and not all techniques are useful for all

conditions.

Classification: There are different types of physical therapy. Some of them are followings:                         

1. Massage

2. Hydrotherapy

3. Cryotherapy

4. Heat therapy

5. Passive range of motion

6. Balance therapy

7. Walking therapy

8. Cavalleti rails

9. Land treadmill

 

1) Massage: It is used in animals to relieve tension in muscles and stimulate muscle development. It speed up recovery from injury and surgery by increasing the blood flow to the area and relieving muscle spasm. It is generally used in canine physical therapy and used to improve the comfort in animals in all conditions.

2) Hydrotherapy: This technique uses water as a tool to improve the muscles and joint functions in animal. Underwater treadmill is commonly used in animal physical therapy. It provides benefits of land exercises decreasing the weight placed on the animal`s limb allowing them to ambulate and perform specific exercise due to buoyancy of water. It is very useful in dogs recovering from surgery such as anterior cruciate ligament and cranial cruciate ligament repairs and break repairs.

Benefits :                                                                         Indications:

• Increased range of motion                                            *Muscle atrophy
• Improved muscle mass and strength                            *Orthopedic disorders
• Increased endurance, weight loss and reduce pain      *Neurologic disorders
• Decreased edema and fluid pooling                        * Decreased joint function

3) Cryotherapy: Cryotherapy (or cold therapy) is the application of a cold agent to an affected area of the body, such as a surgical site, to provide therapeutic effects by reducing tissue temperature. Cryotherapy is found to be effective in the first 72 hours after acute injury or surgery.

Benefits:

• Analgesia                                                                       
•  Vasoconstriction
• Decreased blood flow to the affected area       
• Reduced cellular metabolism
• Reduction in edema, muscle spasms, and initial immune response to injury or surgery

 

Indications:

It is used in any injury or procedure that causes inflammation, pain, or decreased range of motion and neurologic disorders, such as spasticity. Specific surgical procedures where cryotherapy is indicated postoperatively for pain and swelling include:

• Femoral head and neck osteoctomy                           Other conditions:
• Tibial pleatau leveling ostectomy                            * Osteoarthritis
• Tibial tuberosity advancement                                 * Tendon and ligament  injury

 

4) Heat therapy: Heat therapyexert effects opposite to that of cryotherapy. however, both modalities are used to provide analgesia and decrease muscle spasms but the timing of application are different. Since cold therapy should be performed for the first 72 hours, heat therapy should only be initiated after 72 hours and continued for a period based on the individual patient, typically 5 to 7 days. Beginning heat therapy too early can lead to worsening edema, swelling, and potential seroma formation.

Benefits:

• Analgesia
• Decreased muscle spasms
• Increased impulse conduction and fibrous tissue elasticity
• Vasodilation
• Decreasing blood pressure if heat is applied for long periods of time

Indications:

• Chronic inflammation
• Decreased range of motion
• Pain
• Muscle tension

 

5) Passive range of motion: Passive range of motion (PROM) refers to exercises that move joints through their available range of motion without weight bearing muscle contraction.

Benefits:

• Prevention of joint and muscle contracture
• Analgesia
• Increased blood flow and lymphatic flow
• Increased synovial fluid production to decrease articular cartilage degradation
• Prevention of joint degeneration and muscle contracture during the acute rehabilitation phase of patients undergoing hemilaminectomy to treat IVDD.

 

6)Balance therapy: It can be used to improve balance once the patient has regained the ability to stand on its own or with the assistance of a sling or therapy ball. This therapy is focused on helping the animal to understand that the affected limb is no longer painful.

Benefits:

• Increase muscle mass
• Improve proprioception
• Allow early return to function11
• Rebuild core muscle strength.

Indications:

• Loss of proprioception and balance
• Muscle atrophy
• Pathologic weight shifting.
• Neurologic disorders that affect limb function
• Loss of weight bearing due to fractures or wounds
• Immobilization of a limb after ligament repair

 

7) Walking therapy: It is beneficial and applicable to any rehabilitation program.

 

Benefits:

• Increased range of motion
• Improved gait, muscle mass, and strength
• Improved circulation in blood and lymphatic vessels
• Increased endurance
• Prevention of joint degeneration

Indications: Indicated in early rehabilitation of animals refusing to use their affected limb due to muscle weakness, decreased range of motion, circulation disorders, neurologic deficits, and proprioceptive deficits.

 

Walking exercises may improve:

• Stabilized fractures
• Surgically repaired joint disorders
• Femoral head and neck ostectomy
• Stifle joint disorders, such as CCL
• Soft tissue injuries, such as superficial or deep digital flexor tendon rupture

 

8) Cavalleti rails: Cavalletti rails are rails that are raised above the ground a certain

distance for patients to walk over.

Benefits include increasing stride length, range of motion, proprioception, balance, and limb use.

Indications:

• Fractures and ligament ruptures
• Loss of proprioception in neurologic patients
• Joint and muscle pain
• Decreased range of motion
• Gait abnormalities
• Non–weight-bearing limb

 

9)Land treadmills: Treadmill walking are used in reducing pain, making the patient bear weight on the affected limb to strengthen muscles, increasing proprioception and range of motion, producing a normal gait, and providing cardiovascular and endurance benefits.

Indications:

• Orthopedic injuries
• Decreased range of motion
• Muscle atrophy
• Abnormal gait
• Decreased proprioception.

Scope of physical therapy:

 

1. Examining (history, system review and tests and measures) individuals in order to determine diagnosis, prognosis, and intervention.

2. Alleviating impairment and functional limitation by designing, implementing, and modifying therapeutic interventions.

3. Preventing injury, impairment, functional limitation, and disability, including the promotion and maintenance of fitness, health, and quality of life in all species of animals.

Limitations:

1. Takes longer time period

2. More costly

3. Continuous effort is required

4. May cause accidental hazards.

 

Computed Tomography (CT) scan

CT scan utilizes rotating X-rays around the part to be examined to make cross-sectional. Both 2 and 3- Dimensional images are reconstructed from the acquired CT data around a single axis of rotation.

Advantages:

• Important tool in medical imaging to supplement X-rays and medical USG. CT completely eliminates the superimposition of images of structures outside the area of interest.
• It constructs 3-D image
• Soft tissue, blood vessels, lungs, brain, abdomen and bones are well visualized.
• Very small changes in the tissue type can be detected
• It is the gold standard in the diagnosis of a large number of different disease entities.

Disadvantages:

• More expensive
• Time consuming
• Need injection of contrast media
• Poor image quality for bone and implant
• Require temperature monitoring

 

 

Magnetic Resonance Imaging (MRI)

It is a medical imaging technique to visualize internal structures of the body by using the property of nuclear magnetic resonance to image nuclei of atoms inside the body.

 

Advantages:

• Provides good contrast between the different soft tissue of body which makes it especially useful in imaging: Brain, muscle, heart, cancer etc.
• MRI system donot use ionizing radiation

Disadvantages

• Pets with pacemakers can not be MRIs
• Machine make noise during a scan
• Longer time (time consuming) 20-90 minutes
• Even very slight movement of the part being scanned cause motion unsharpness like images which means the scanning will need to be repeated.
• Metallic orthopaedic implants like plates, screws, wires, prosthetic joints in the area of a scan can cause distortions of the image.
• Most expensive

Diathermy:

Mechanism of action:

Diathermy uses very high frequencies (0.5-3 MHz) of electrical current. This allows diathermy to avoid the frequencies used by body systems generating electrical current, such as skeletal muscle and cardiac muscle, allowing body physiology to be broadly unaffected during it’s use.

The radiofrequencies generated by the diathermy heat the tissue to allow for cutting and coagulation by creating intracellular oscillation of molecules within the cells. Depending on the temperature reached different results occur:

At 60 – cell death , 60-99 – dehydration and tissue coagulate and at 100 – tissue vapourises (Temp is in degree celsius).

Indications:

• Promotes disintegration of inflammatory exudates and assists in their resort from by decreasing the swelling, relief of pain and restoration of the function clinically.
• In painful and exuberant callus formation and fibrous ankylosis, joint injuries.
• In post-operative adhesions in extremities.
• In traumatic and inflammatory conditions of bursas, bones and joints after the acute stage.

Contraindications:

• In acute inflammatory process accompanied by fever and myalgia.
• In tendency to hemorrhage recent hemoptysis.
• In malignant tumors.

 

Scintigraphy (Nuclear Medicine)

Radio-isotopes are used to detect functional status of the body systems.

Principle based on: Use of a pharmaceutical labeled with an isotope that after entry into the blood stream gets localized in a particular tissue or organ.

The localization of the isotopes can be then detected by using a detector or gamma camera due to emission of gamma rays from the area of interest.

Sodium iodide crystal is used which absorb gamma rays emitted by radio-isotope from the organ and converts it into light flushes.

A computer system is usually attached to the camera for gathering data and it’s display and quantification.

Most commonly used isotope is Technitium-99

Pharmaceuticals for organ imaging (e.g. pyrophosphate or methylene diphosphate for bone, macro-aggregated albumen for lung perfusion)

A scan appears as an image formed of dot. The interpretation is based on the appearance of increased (hot spots) , decreased (cold spots) radioactivity regions.

 

Advantages:

• Used to detect functional status of kidney, liver. GIT, lung, bone, brain etc.
• Scanning of bone is most commonly used by this modality.

Disadvantages:

• High cost, safety measures, etiological non-specificity and difficulty in interpretation especially in skeletal system.