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Radiology

Christine Allen, CVT, Robin Delbove, RVT, LVT, and Nanette Walker Smith, RVT, CVT

Definitions
Anode The positively charged side of the x-ray tube, which holds the tungsten plate which is the target of the electron cloud. When the electron cloud collides with the target, the x-rays are formed.
Cathode The negatively charged side of the x-ray tube that contains the filament. The filament creates an electron cloud when heated.
Collimator A device that restricts the beam to a set area in order to minimize exposure.
Dosimetry Badge An indicator badge worn by those taking radiographs that measures the RADs a person receives. Should be checked/updated quarterly and is part of OSHA, hospital safety.
FFD (Focal Film Distance) The distance between the x-ray tube and the film. Increasing or decreasing this distance will have an effect on radiographic density.
Focal spot The particular area that the electron beam is aimed at on the tungsten target.
Focusing cup Holder that the filament is set into which directs the electron cloud to the anode.
Grid A series of thin lead strips designed to absorb scatter radiation, typically mounted above where the cassette lies in the bucky.
Heel effect The result of putting the thicker portion of the patient to be radiographed at the cathode end of the tube as the number of beams at the cathode end of the tube are higher - thus a higher density radiograph is produced.
Intensifying screens Thin layers of crystals inside the lining of the film cassette that glow when struck by radiation, therefore reducing the amount of radiation required to produce the image.
KVp
(kilovolt Peak)
Usually ranges between 40 - 125. The measure of the degree of contrast (or shades of gray) on a radiograph, which is controlled by the intensity at which the electrons are shot. High kVp produces a long scale of contrast, which is necessary for soft tissue radiographs where subtle changes need to be seen. Low kVp produces short scales of contrast that are necessary for bone visualization.
mA
(milliampere)
Usually ranges from 50 - 400 depending on the type of machine you have. The number of electrons produced by the filament.
MAs
(milliampere per second)
The number of the electrons (mA) multiplied by the time (in seconds) during which x-rays are shot, which determines the density (or darkness) of a radiograph. Example: 300 mA at 1/60 seconds = 5 mAs
MPD Maximum Permissible Dose of radiation allowed by the National Council on Radiation Protection and Measurements. This amount should not exceed 5 REM per year for a person in an occupation utilizing x-rays.
RAD Radiation Absorbed Dose - for the purpose of use in veterinary medicine it is the same as REM
REM Roentgen Equivalent Man - dose equivalent to man that results from exposure to ionizing radiation.
Scatter Radiation Radiation that has interacted with the patient's tissues and is scattered multi-directionally.

Details about Developing: (same process for both hand tank and automatic processors)
Developer SolutionChanges the silver halide crystals to metallic silver. The length of time the film should be in the developer depends on the temperature of the solution. The manufacturer of the developer solution will recommend the proper temperature and time for that solution.
DryingThe films are either air dried or dried in a special film dryer.
Final WashThe excess silver complexes and solution are rinsed off in this step.
FixerRemoves the remaining unchanged silver halide crystals from the film, leaving the shades of metallic silver.
Rinse BathWater bath that the film is immersed and agitated in for 30 seconds to remove the developer.

Technical Errors:
ErrorPossible Causes:
Too DarkkVp/mAs too high, FFD too short, film overdeveloped, developer too hot.
Too LightkVp/mAs too low, FFD too long, old developer, film underdeveloped, cold developer.
FogLight leak, old film, film left in room when another film was shot
Black MarksStatic electricity, thumbnail marks (after developing), light leak in cassette, dirty rollers (automatic processor)
White MarksDebris on film or in cassette, spots of fixer on film
Blurred ImageMotion
Lines across filmGridlines due to incorrect positioning of beam to grid
Clear edgeBucky tray not aligned with beam, bucky tray not pushed in all the way

Building a Technique Chart

  1. Choose a base mAs that is a multiple of 2 (so it may be easily divided for thoracic shots) and is divisible by 5 (so that it is easily converted to tabletop for extremities.)
  2. Measure the animal. Abdominal shots are preferred for building a technique chart.
  3. Select kVp: Measurement x 2 + (35-40) = kVp
  4. Use that kVp to take three test radiographs at the previously selected base mAs, at base mAs, and 2X base mAs. Evaluate the radiographs and choose the best, most detailed one. Look for a long scale of contrast and clear visualization of the abdominal tissues.
  5. Use the mAs of the best radiograph and add or subtract a factor of 2 kV for each centimeter change up to 80 cm. Add or subtract 3 up to 100 cm, and 4 above 100.
  6. Depending on the max. mAs/KVp on your machine, you may increase the KVp by 20% which will allow you to lower the mAs by 50%. When you exceed the maximum or diagnostic range of kVp on your machine, you may decrease kVp by 16% and double your mAs for a particularly thick animal.
  7. These values are for abdominal radiographs. To alter your chart for other body regions:
    1. Skull, spine, and pelvis - 2X abd. mAs
    2. Thorax - abd. mAs (depending on condition of animal - may need to increase in cases where fluid is present, or masses are suspected)
    3. Juvenile animals - abd. mAs or tabletop, depending on measurement.
    4. Extremities - Convert mAs to table top (divide by 5)

Radiation Safety:

  • No one under the age of 18 should be actively working within a radiation-producing area.
  • Always wear 0.5 mm equivalent lead gloves, apron, and protective eyewear to guard against scatter radiation. Lead or lead equivalent material is meant as protection from scatter radiation and should not be evident on the radiograph.
  • Wear a dosimetry badge on the collar on the outside of the apron to monitor the amounts of radiation you are being exposed to.
  • Always collimate down to include only the area of primary interest.
  • Use positioning devices (troughs, sandbags, tie-downs, etc.) and chemical restraint whenever possible to avoid using staff members to restrain patients
  • Pregnant women should not be in the same room as the machine when radiographs are taken.
  • Follow your state rules that govern the use of the x-ray machine and radiation safety.

Positioning Tips
Area Technique Adj. Center Measure Field of View Special Techniques / Tips
Abdomen - Lateral/VD ---- Umbilicus 12th rib Dome of diaphragm to coxofemoral joints Take at peak expiration. Make sure the spine and sternum are parallel. Gently pull hind limbs back to allow clear visualization of caudal organs.
Extremities Convert to tabletop Midway on the bone Across the thickest point Joint above to the joint below. These views usually turn out better if the animal is sedated. Watch for rotation - it is very easy on extremities.
Pelvis 2X abd. mAs (same on both lateral and VD views) Pelvis Across hips Entire pelvis and femurs Feel the wings of the ileum - they should be superimposed. Separate legs so the heads of the femurs may be visualized. For VD view must pull legs down while rotating the stifles medially so that the patellae are "on top." Sedation/anesthesia is preferred - necessary in OFA shots.
Skull - Lateral/VD 2X mAs Entire skull At the ears Tip of nose to the atlas ANIMAL SHOULD BE ANESTHETIZED.
Skull - Open Mouth 2X mAs Pharynx At the commisure Dorsal muzzle to tympanic bullae Use radiolucent mouth gag, be sure muzzle is perpendicular to cassette
Spine Cervical 2X mAs C3 Over shoulders All 7 cervical vertebrae ANIMAL SHOULD BE ANESTHETIZED.
Use positioners to keep the mid-cervical region from 'dipping'
Spine Lumbar 2X mAs L3-4 T13 All 7 lumbar vertebrae ANIMAL SHOULD BE ANESTHETIZED.
Spine Thoracic 2X mAs T7 T13 All 13 thoracic vertebrae ANIMAL SHOULD BE ANESTHETIZED.
Spine Thoracolumbar 2X mAs TL junction T13 5 thoracic - 5 lumbar vertebrae ANIMAL SHOULD BE ANESTHETIZED.
Thorax - Lateral Abd. mAs 1" caudal to the caudal aspect of scapula 12th rib Thoracic inlet to costophrenic angles (angle between the ribs and diaphragm) Take on peak inspiration: be sure to gently pull forelegs forward so the cranial aspect of the lungs may be visualized. Make sure the spine and the sternum are parallel.
Thorax - Ventrodorsal Abd. mAs Heart 12th rib Same Same. Place your hand across the caudal/ventral portion of the ribs to feel if one side is higher than the other to check for rotation.

References: Decker, Carlene. "Radiology" Parkland College. 1998, Christine Allen, CVT, Robin Delbove, RVT, LVT, and Nanette Walker Smith, RVT, CVT 03/2002

The Nerd Book
The VSPN Nerdbook was created by veterinary technicians and veterinary support staff for their colleagues. The Nerdbook provides information that veterinary technicians and support staff need in practice, but is not meant to contain everything. Procedures and policies vary among practices, so feel free to modify your Nerdbook fit your facility.
Volume One
Contributors
Introduction
Clinical Pathology
Critical Care - Triage
Emergency-Receptionist tips
Medical Calculations
Medical Records
Medical Terminology
Pharmacology
Physical Exam
Preventative Health
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