Anechoic
Structure in an ultrasound image that does not produce echoes and appears black.
A-mode
Amplitude-mode image display in ultrasound imaging. The energy of the returning echo is shown as an amplitude spike at each tissue interface.
Anode
Positively charged side of the x-ray tube that receives oncoming electrons from the cathode. Both heat and x-rays are produced as a result of interactions between electrons and the metal anode.
B-mode
Brightness-mode ultrasound image display. It forms the basis of two-dimensional ultrasound images so that anatomic structures can be assessed in real time on a monitor.
Cathode
Negatively charged side of the x-ray tube that produces electrons from a metal filament when it is heated.
Computed radiography
Similar to digital radiography except that an x-ray receiver similar to a film cassette is used and must be processed in a special machine. The special cassette contains a photostimulable phosphor that changes x-ray photons into a latent electronic image when read by a laser.
Contrast
Density or opacity differences between neighboring areas on the radiographic image. Large differences result in high-contrast images, whereas small differences result in low-contrast images.
Density
Degree of blackness of a radiographic image. Denser areas are blacker and are noted in areas of the image where little x-ray absorption occurred. Whiter areas are less dense and are noted in areas of greater x-ray absorption.
DICOM
Digital Imaging and Communications in Medicine
A standard for handling, storing, and transmitting medical images.
Digital radiography
A digital imaging technique in which the x-ray tube is coupled to a specialized receiver that changes x-rays into electrical signals. The analogue image is digitalized and is displayed on the integrated computer screen.
Fluoroscopy
Presentation of a continuous x-ray image, which involves directing the x-ray beam through the patient and onto an image intensifier.
Grid(s)
A thin sheet of lead strips with radiolucent spacers encased in an aluminum cover, giving the appearance of a thin, flat rectangular tray. A grid is placed between the patient and the film cassette to absorb scatter radiation so it does not reach the cassette and affect image quality.
Heel effect
The x-ray beam produced through interactions with the anode has a spectrum of x-ray energies. The x-ray beam is more intense at the side of the cathode than in the center of the beam or on the anode side.
Hertz (Hz)
Hertz (Hz) cycles per second
Unit of measurement used to quantify the frequency of ultrasound waves.
Hyperechoic
Structure in the ultrasound image that appears bright or white compared with adjacent structures.
Hypoechoic
Structure in the ultrasound image that appears darker that adjacent structures.
Ionizing radiation
Any radiation that is capable of displacing electrons from atoms or molecules, thereby producing ions. Examples include alpha particles, beta particles, gamma rays or x-rays, and cosmic rays. In medicine, ionizing radiation arises from radiotherapy, x-ray machines, and radioactive substances. Ionizing radiation also enters the atmosphere of the earth from outer space. At high doses, ionizing radiation increases specific types of chemical activity inside cells. This effect can be used to treat cancer, but it also leads to health risks such as the induction of cancer.
Isoechoic
Structure in the ultrasound image that is of equal echogenicity to another structure.
Kilovoltage
Quality factor that regulates the energy of the x-ray beam. the higher the kVp (kilovoltage), the higher the energy of the x-ray photons. Regulates contrast in the radiographic image. The higher the kVp, the lower the contrast.
Milliamperage
The milliamperage setting controls the quantity of electrons boiled off the filament in the x-ray tube.
M-mode
Time-motion ultrasound imaging mode wherein motion of the body, usually the heart, is observed by scanning a thin slice of it over time.
PACS
Picture Archiving and Communication System, Picture Archival Computing System
A computer system used to store, transmit, and access digital medical images.
Rad
Unit of absorbed dose of ionizing radiation.
Rem
Abbreviation for roentgen equivalent man; it is the product of the dose in rads and the relative biological effectiveness of the radiation used.
Rotating anode(s)
Anode plate in an x-ray tube that rotates around a stem made of molybdenum to aid in heat dissipation.
Stationary anode(s)
Anode block in an x-ray tube that does not move and is embedded in copper to aid in heat dissipation. Found exclusively in portable equipment used in fieldwork.
Teleradiology
Transmission of digital images from one hospital to the next via computer cable connections. Teleradiology allows rapid turnaround in assessment of images and improves access to expert opinions on patient findings.
X-rays
Form of electromagnetic radiation that can be used in diagnostic imaging to produce radiographs or computed tomographic images.
Radiographs are part of the legal medical record and must be?
Correctly identified and carefully labeled.
Always place the thickest part of the area being x-rayed toward?
Toward the cathode side of the x-ray tube.
What is the main source of radiation exposure for the veterinary technician?
Scatter radiation coming from the area of the PT exposed during radiography.
Name the three factors that must be set correctly for production of a properly exposed radiograph.
Kilovoltage
Milliamperage
Time of exposure
What will decrease motion blur on the radiograph?
Always use the highest milliamperage setting and the lowest time setting to arrive at a particular mAs.
How can you increase radiographic density or film blackness?
By increasing the energy level of x-ray photons (kVp) or the total number of x-ray photons (mAs).
What happens to the x-ray beam intensity, if you double the film distance from the x-ray source?
You will decrease the x-ray beam intensity to 1/4th of the original strength.
Small changes in focal-film distance can result in big changes in radiographic density.
What are technique charts developed for?
They are developed for a specific focal-film distance, film, cassette screen, and development process.
If you change any one of these factors within your practice, the technique chart will need to be updated.
Why are rare earth screens advantageous for veterinary radiography?
Because they require fewer x-rays to produce a diagnostic radiograph.
Lower exposures mean lower radiation doses to the PT and technician, fewer retakes because of patient motion, and longer x-ray tube life.
What do you need to ensure before using x-ray film?
Be sure that the x-ray film you are using is maximally sensitive to the spectrum of light that the screens are emitting.
What should you always use when the body part being x-rayed is greater than 10 cm thick?
Always use a grid between the PT and the film cassette.
Remembering that all film and safelights are not created equal, what should you make sure of?
Make sure the wavelength or color of light to which your film is sensitive is completely blocked by your safelight filter.
Name the “big three” of radiation safety.
Time
Distance
Shielding
What is the most commonly used contrast study of the kidney?
The intravenous pyelogram (IVP).
What is essential if diagnostic radiographs are to be obtained?
Proper positioning
Why has chemical restraint greatly contributed to the progress made in radiology?
It allows positioning that otherwise would be impossible to achieve.
Piezoelectric effect (ultrasonography)
Ultrasound production and reception are based on the piezoelectric effect.
A piezoelectric crystal will change shape or thickness when subjected to a voltage pulse.
Why is good patient preparation so critical for ultrasonography?
Hair traps air, and if not clipped, most of the beam would be reflected before it ever enters the animal.
Why should you use a transducer with the highest possible frequency?
To maximize resolution while allowing penetration to the necessary depth.
Why is it important to have a thorough understanding of the normal appearance of various abdominal organs?
In order to be better able to identify abnormalities associated with disease.
What is the current treatment of hyperthyroidism and thyroid tumors?
Currently, veterinary therapeutic nuclear medicine involves the administration of radioactive iodine (131I) for the treatment of hyperthyroidism and thyroid tumors.
What is the primary route of radionuclide administration to veterinary PTs?
Intravenous!
Latex examination gloves should be worn and careful injection techniques should be used to ensure that the entire dose is delivered IV and not perivascularly.
When CT studies are performed, what contrast agents are used?
The same contrast agents are used as for radiographic contrast procedures, but at a much lower concentration, because CT is much more sensitive than radiography for detecting the presence of contrast agents.
How does MRI differ from CT?
MRI differs from CT in that it uses no ionizing radiation to create the image.
MRI is superior to CT in image resolution, anatomic definition, and sensitivity to tissue composition differences. Because of this, MRI is vastly superior to CT for imaging of the brain and spinal cord and is currently the state of the art modality for head and spine evaluation.
Why is it never safe to bring anything made of a ferromagnetic metal close to the MRI machine?
Because the magnetic field in an MRI unit is always on.
