◊ Radiology ◊
Electromagnetic spectrum: -
X-ray is a part of the electromagnetic spectrum. It consists of photons, has short wavelength, high frequency, and high energy. It travels in straight line, and when it interacts with matter it is either absorbed or scattered.
Short wave length
Long wave length
X-rays have the ability to make certain substances, like calcium tungstate or the so-called rare-earth phosphors, to fluoresce. This means that these substances emit characteristic radiation within the visible spectrum after absorbing electromagnetic radiation of short wave length and high energy.
2-Photographic Effect: -
X-rays can produce latent image on a photographic film that can be visualized by processing the film. That whey they used X-rays as a diagnostic tool.
X-rays have the ability to penetrate substances or tissues (that are opaque to the visible light), and absorbed the further they pass through the object or the tissue. Amount of absorption depends upon;
*Atomic number of the object it passes through.
* The energy of the X-rays.
*The density of the tissue or the substance
4-Excitation and Ionization: -
X-rays have the ability to produce excitation and ionization of the atoms and molecule of substances (even gases) through which they are passed.
*Excitation means that an electron passes from inner shell to outer a shell of higher energy level, but it stills within the atom, energy is needed for transition of the electron and when the electron returns to its normal shell, energy is released in the form of heat.
*Ionization means that the electron leaves the atom and the atom becomes positively charged. This process requires higher amount of energy than excitation, and when an electron returns to fill the space in the shell, energy is released in the form of heat.
5-Biological Effects: -
X-rays produce biological changes in the living tissue either;
*Directly by excitation and ionization of importance cellular molecules.
*Indirectly via the chemical changes that occur near the cell, so the affected cell may be damaged.
*Genetic effects as a result of damage of chromosomes or gene mutation of the reproductive cells that affect the future generations.
*Somatic effects which are evident during an individual’s life as radiation burns or leukemia (cancer).
PRODUCTION OF X-RAYS: -
X-rays can be produced when a high-speed charged particle, usually electron, is slowed down or stopped. This can be achieved by slowing down or stopping electron by the positively charged nucleus, or when the moving electron collides an electron from the inner shell of an atom. For production of X-rays we use what is called X-ray tube, and there are three basic requirements for X-rays production in the X-ray tube. These requirements are; source of electrons (cathode), target to stop the electrons (anode), and a method for accelerating the electrons from the cathode to the anode. The X-ray tube is an evacuated glass tube into which two electrodes are sealed, and the tube is evacuated (no gas to avoid ionization and production of electrons). The head of the tube is lined with lead to prevent radiation scattering.
1-Source Of Electrons (Cathode): -
It is the negative electrode of the high voltage placed across the tube for production of electrons. Electrons are produced by heating a spiral filament of tungsten wire, by passing an electric current through it (thermionic emission). Tungsten is used because of its ability to be heated to high temperatures for thermionic emission. When a metal is heated, the movements of the outer free electrons increase even to the limit that electrons may leave the metal and form cloud of electrons around the metal, and the number of electrons in the cloud is directly proportional to the degree of heat. The number of electrons pass from the cathode to the anode represents the tube current and it is measured by (mA), and by regulating the current that heat the filament, radiographer can control the tube current. Electrons tend to repel each other and to spread as they pass the tube, so the filament is positioned in a focusing cup of nickel or molybdenum that maintained at the same negative potential as the heat filament, by this cup the electrons are confined to a narrow stream directed towards a relatively small area of the target.
2-Target To Stop The Electrons (Anode): -
It is the positively charged portion of the X-ray tube, responsible for stopping the electrons and production of X-rays, and consists of target materials (embedded in cylinder or disc, fixed or rotating anode), which are usually tungsten or tungsten-rhenum alloy that have;
*Adequate thermal conductivity.
*High melting point up to 3380°C.
*High atomic number
Only 1% of the electrons energy is converted to X-rays and the 99% of the energy is converted to heat.
3-A Method For Accelerating The Electrons From The Cathode To The Anode: -
During exposure, the anode is maintained at a high positive potential relative to the cathode, so electrons, which are emitted from the cathode, are accelerated toward the anode and strike the target. The potential difference between the cathode and the anode is measured in (kV), the higher the kV, the faster the electrons are accelerated, the higher the kinetic energy of he electrons, and the greater the energy of the X-rays produced.
RECORDING X-RAYS IMAGE: -
1-Intensifying Screen: -
It consists of plastic base, covered with white reflecting surface, uniformly coated with phosphor, and finally thin waterproof protective layer (super coat). Two screens are used to sandwich the film and the phosphor layer face the film. The role of these screens is to absorb X-rays and change it to light, and reflect the light on the film to produce the latent image on it.
There are three types of screens;
*The standard (normal, regular, or par-speed).
*The high definition (fine grain).
*The fast (high speed).
Screen phosphors: -
*They should have high absorption coefficient and be able to absorb X-rays to a considerable degree, so they must have relatively high atomic number.
*They should emit a large amount of light of a suitable energy and color.
*There should be no significant afterglow (continuous emission of light after stopping of radiation).
Calcium tungstate and zinc sulphide have been used in the manufacture of intensifying screens because they emit light in the ultraviolet-blue end of the spectrum to which the film is sensitive.
2-Film Cassette: -
It is a light-tight container, and designed to hold the film and the two intensifying screens in uniform close contact. The smooth or front face is made of materials, which are opaque to the visible light, but it is radiolucent to X-rays (aluminum, carbon fibers, or plastic). The back face of the cassette is made of heavier materials and has the catches that keep the cassette tightly shut.
3-X-Ray Film: -
It is a plastic base covered on both sides with emulsion, and the undeveloped one appears apple-green color in the daylight. The emulsion consists of gelatin containing finely dispersed minute grains of silver bromide
*Slow Films (High Detail): -
This type of films has a very fine-grained emulsion coated thinly to permit visualization of fine details. This film requires longer exposure time, and it has lower level of basic fogging.
*Medium speed Films (Standard or Par-Speed): -
It is the most available type of films and represents the compromise between fine-grain and speed.
*Fast Films (Ultra-speed): -
It needs low exposure time but it has higher level of basic fogging.
*Direct Exposure or Non Screen Film: -
It is a special film of thicker emulsion layer, supplied in light tight envelope for radiographing without the aid of intensifying screen.
PROCESSING X-RAY FILM: -
Processing of x-ray film, or changing the latent image into visible image, should be performed in dark room to avoid the un-needed effect of visible light on the film (fog). Only red lamp can be used in this room, as the wavelength of the red light has minimal effect on film.
It is a solution used to complete the reduction of silver bromide and change the silver ions into metallic silver grains. The film shouldn’t be kept for long period in this solution, otherwise, the solution can attack the unexposed silver halide too.
After immersing the film in the developer, it should be washed with water to remove the excess developer, and then the film is immersed in the fixer, which is a solution used for;
*Dissolving the unexposed silver halide and keeps its place white to gray.
*Harden the gelatin and renders it less susceptible to scratching.
Finally the film is washed with running water for 30 minutes and dried and then it can be visualized.
It is the numerical difference between two adjacent densities.
*High contrast means that the bone is very white while the surrounding tissue is black.
*Flat film or low contrast means that all the tissues are gray and merely distinguished.
Neither of these films is desirable, as the good contrast film should have long range of well-differentiated densities so that the eye can easily see the details. Causes of this poor contrast are;
1-Exposure Factors: -
*kV affects both the contrast and the density. Low kV produces high contrast (soot or whitewash film); on the other hand, the high kV causes low contrast.
*mA affects film density, and reduces the contrast when it is incorrect. Low mA causes too low amount of X-rays to reach the film, so the film seems pale, examination of the film will reveal that the X-rays penetrated the hard tissues but with few amount so that insufficient image is created leading to low contrast, on the other hand, high mA creates high amount of X-rays that make both the hard and the soft tissues so dark, and in turn it causes low contrast too.
*Distance alters contrast when it is not adjusted with the mA.
Bad processing affects contrast, and this may be due to;
*Development at too low temperature.
*Development for too short time.
*Exhaustion of the developer.
Over development can increase the contrast but it is not recommended.
Veiling of the image by fog causes low contrast as the highlights are degraded. Despite all emulsions has certain amount of fogging (basic fog), the fog level can be raised by many factors;
*Premature exposure to white light, X-rays, or bad safe lighting.
*Bad storage conditions.
*Excessive development by time or temperature (Processing fog).
Artifacts of a film can be caused by dust in the cassette, screen marks, or faulty processing. These artifacts can cause misdiagnosis. When a mark appears consistently on a film, the cassette and the screen should be examined and cleaned. Areas of poor definition represent improper contact between the screen and the film. Artifacts due to faulty manufacture of the film can be detected by reflecting the processed film in the light.
Too dark film
a-High kV. b-High mA.
a-Too long time development. b-Too high temperature.
Too pale film
a-Low kV. b-Low mA.
a-Too short time development. b-Too low temperature.
c-Exhausted developer. d-Too diluted developer.
1-High (soot or whitewash)
1-Insufficient dense tissues penetration (low kV).
2-Low (flat film)
Poor detail (un-sharpness)
1-Too long object-film distance.
2-Uneven screen contact in cassette.
3-Movement during exposure.
Fixer splash (white spots)
Local reduction of the emulsion before development
Stained films, yellow stain, Color fog (dichroic)
Insufficient rinsing or use of exhausted fixer
It is an additional density, unconnected with the primary image, and reduces contrast and details
2-Chemical fog due to over-development
a-Pre-exposure to ionizing radiation. b-Excessive secondary radiation.
a-Bad safe lighting. b-Prolonged inspection during development.
2-Localized fogging at edges
Light penetrates through the film box or the cassette
2-Airbells (clear white spots surrounded by rings)
Air bubbles on the film surface
Due to sliding across the floor
1-Clear white specks
Dust between screens
2-Small areas of light density
Dried developer splash marks on the screens
3-Fingerprints (dark or light)
Handling of the film with dirty greasy hands
RADIATION PROTECTION: -
Radiation has harmful effect on the living tissue, and this harmful effect is dependant upon;
*The dose and rate of exposure.
*The nature of exposed tissues.
Aside from burns (somatic effect), cancer (carcinogenic effect) and genetic effect are the most important harmful effects of X-rays.
Sources Of X-Ray Exposure: -
1-X-Ray Tube Head: -
As X-rays are produced at the anode during exposure, the tube is considered as a very important source of radiation, so recently it is shielded with lead except the aperture where the beam get out of the tube. At this aperture, the soft X-rays (long wave-bad quality) are filtrated then pass through the diaphragm. The head of the tube should be checked regularly by film to be sure that there is no leaking of the lead shield has occurred.
2-The Primary Beam: -
The primary beam has the ability to penetrate through;
*The protective clothing.
*The operating table.
That why it is forbidden to stand in its way, even when you wear protective clothing of lead.
3-Secondary Radiation (scatter): -
This radiation occurs when the primary beam traverse the body of patient or the table. It is less harmful than the primary beam radiation, because it is absorbed by the protective clothing. Because it travels in unexpected directions, it is harmful to unprotected persons in the room or to the unprotected areas of the body.
PRECAUTIONARY MEASURES: -
*The operating rooms should have special construction preventing people from gain access to the room during working.
*Entry to the room should be restricted by notices, displaying the international radiation symbol, and by warning lights.
*When using horizontal beams, the beam should be directed towards thick walls.
Recent x-ray machine has safety precautions, but old one should be checked regularly.
3-Protective Clothing: -
Aprons of lead should be used to protect the body from scattered radiation, and should be examined regularly for the presence of any crakes or fissures.
They contain lead materials to protect hands, and also should be examined for the presence of fissures routinely.
C-Lead Screens: -
Mobile lead screens with lead glass window can be used to;
*Monitor the animal during exposure.
*To protect the workers.
They are monitoring devices used to determine the extent to which the radiographer is exposed, and accordingly the radiographer should be prevented from gaining access to the radiology unite for a considerable
A-Radiation Protection Supervisor: -
He is the person responsible for;
*Checking the apparatus and protective clothing for safety.
*Drawing up written instruction specifying the way in which the apparatus is to be used.
*Selecting member of stuff actually participate in radiography and ensuring that they adequately instructed.
*Receiving radiation monitoring reports and taking the necessary action.
The safety of the worker and assistants is the responsibility of the radiation protection supervisor who should ensure that;
*They aware of the instructions. *They are healthy and responsible. *They are over 18 year-old.
*There is no pregnant woman worker involved in the stuff.
He is the person;
*Authorized for conducting radiography.
*Responsible for removal of all unnecessary persons from the room.
*Ensures that the assistants stand in proper position with proper protective clothing, before conducting a film.
D-General public: -
Owners may help in restraining of their animals during radiography, so the radiographer should ensure that;
*They aware with the instruction.
*Have proper protection.
*No pregnant women are present.
ESTABLISHING AN X-RAY UNITE: -
A-X-Ray Room: -
It should be roomy enough to facilitate storing and bringing of the apparatus with the minimal effort a movement.
In case of large animals, general anesthesia and restraining facilities should be present in the room. The light of the room should be under control.
The room must be supplied with all safety measures.
B-Dark Room: -
A dark room for processing of the film must be supplied to the x-ray room.
It should has equipments of processing of the film.
2-Apparatus (X-Ray Machine): -
A good X-ray machine must be present and checked regularly.
3-Accessory Apparatus (Positioning Equipments): -
A-The Table: -
It must be;
*Supplied with suitable fittings for compression bands.
*Lined with lead under the surface.
B-Cassette Stands: -
These stands are used to avoid holding of the cassette by the gloved hands.
They are objects used for positioning the animal as during dorsal view radiography.
D-Sand Bags And Soft Bads: -
They are objects used to support and restrain the portions of the animal that will not be radiographed.
4-Protection Equipments: -
All the mentioned protection equipments should be available.
5-Staff And Assistants: -
Well-trained staff and assistants should be present.
TYPES OF RADIOGRAPHS: -
Radiographs should be taken in both dorsoventral and lateral views. This is because, many legions appear normal in one view, but the lesion can be visualized when the other view is taken.
1-Plain or Survey Radiographs: -
They are the radiographs that are taken without the aid of contrast materials to visualize hard tissues like bone but they are unable to visualize soft tissue or organs.
2-Radiographs With Contrast Media: -
This type of radiographs is used to visualize soft tissue or organ that is impossibly visualized by plain radiographs due to lake of contrast with the surrounding tissues. By this technique, the structure, location, shape, and size of the organ can be effectively evaluated. Contrast technique is useful too in gaining valuable information about the mucosal lining of viscous or its content.
Contrast media should have high atomic number (barium or iodine), and they called radiopaque agents or positive contrast media, while air that is of low specific gravity, is called negative contrast media. Contrast media either introduced into the organ directly (ingestion or retrograde infusion into the bladder or uterus), or injected into the blood either to visualize blood supply or to be excreted by the kidney or the liver.
1-Barium Sulphate: -
It is used mainly for the GIT. It is completely insoluble so they neither acted on by the alimentary secretions nor absorbed via intestine. Unfortunately, if it passed through a perforation of the GIT into the chest or the abdomen, it can never be absorbed or eliminated leading to granulomatos reaction.
2-Water Soluble Iodine Preparations: -
The main criteria of this group are;
c-Very soluble in water so they can be used in high concentration.
d-Chemically stable so the iodine not released in the body.
e-Rapidly excreted by the kidney.
f-Of low viscosity and so it can be injected by small catheters.
g-Of low toxicity and irritancy.
They are injected into the blood either for direct visualization of the blood vessels or to be excreted by the kidney.
3-Agents Excreted Via The Biliary system (Cholecystopaques): -
They are organic iodine preparations absorbed form the GIT or injected intravenously and excreted by the liver and outline the bile duct and the gall bladder.
4-Viscus And Oily Agents: -
They are iodine preparations used for bronchographic or hysterosalpinographic investigations.
5-Negative Contrast Agents: -
Air, oxygen, and carbon dioxide are the most frequently used agents and the organ seems black in color.