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DIAGNOSTIC IMAGING EXAM; QUESTIONS AND ANSWERS
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DIAGNOSTIC IMAGING EXAM; QUESTIONS ANDANSWERS
You are instructed to take a DLPMO radiograph of a horse's fetlock using a
portable X-ray device. Where will the x-ray device be, and where should the film
cassette be? - ANSWER In a DLPMO, or dorsolateral-palmar/plantar medial
oblique, the beam is aimed 45 degrees between the dorsal and lateral sides of the
limb, while the film is positioned 45 degrees between the medial and palmar (or
plantar) aspects.
What are the components of a standard X-ray cassette, from the front (where
X-rays enter) to the back? - ANSWER To expose the film, the intensifying screen
must be placed adjacent to it and not shielded with padding. Most cassettes feature
intensifying screens and cushioning on both sides of the film.
Some X-ray machines offer the option of using two different sized filaments at the
cathode. Which of the following are the benefits of utilizing a bigger filament? -
ANSWER A bigger filament creates a wider electron beam with a larger focal
point. This spreads out the heat-generating area of the target, allowing for longer
exposures. However, a broader focal spot reduces image quality and increases the
penumbra effect, both of which are drawbacks. The penumbra effect refers to the
blurring of edges caused by the geometry of the x-ray beam.
When performing a lateral thoracic radiograph on a dog, where should the field be
centered? - ANSWER To avoid overlaying the cranial thorax, take a lateral thoracic
radiograph with the forelimbs drawn forward. The film should be centered at the
5th rib and caudal border of the scapula, as well as collimated to include the
manubrium (as the cranial landmark) and halfway between the xiphoid and the last
rib (as the caudal landmark). The head and neck should be in a natural position,
neither extended or flexed, with the sternum and dorsal spinous processes parallel
to the table, suggesting that the animal is not rotated. All lung fields should be
included, and the film should be taken at full inspiration.
Which of the following diagnostic radiograph techniques will reduce the quantity
of scatter radiation that reaches a film? - ANSWER A Potter-Bucky diaphragm is a
,movable grid. A grid is a series of small strips of lead that are placed over the
cassette to absorb any radiation that does not pass between the strips. The strips are
geometrically structured to allow primary radiation through while absorbing any
radiation dispersed in other directions. This increases the resolution of structures on
the film. However, utilizing a grid causes grid lines to show on the film unless a
Potter-Bucky diaphragm is employed. Scatter can also be reduced by using the
"air-gap" approach, in which the cassette and film are moved away from the
patient. This will magnify the film and possibly reduce its clarity, but it will also
reduce the amount of scatter radiation that reaches it. The amount of scatter
radiation that reaches the film is unaffected by exposure duration, high-speed film,
or an amplifying screen.
What is the purpose of the screen on an X-ray cassette? - ANSWER The screen of
an X-ray cassette, also known as intensifying screens, is the cassette's shining white
inner surfaces. They are made of crystals that fluoresce and produce light when
exposed to xrays, resulting in the diagnostic image.
Which of the following can be easily altered by a technician to increase exposure
on a radiograph while maintaining contrast? - ANSWER: Milliamperage and
exposure duration are two parameters that impact exposure without changing
contrast. Increasing either of these will increase the film's exposure. The level of
contrast varies with kilovoltage (higher kVp produces less contrast and more
latitude, while lower kVp gives greater contrast but less latitude). Decreased field
size reduces scatter and may improve image quality, but it does not increase
exposure to film.
In radiation safety, what is the distinction between "rad" and "rem"? - ANSWER
Rad and rem are two old units of absorbed dose that can be used on either the
patient or the crew. More often, rem is utilized in radiation safety for personnel,
while rad is used in radiation therapy dosage calculations. The distinction between
the two is that rad is the fundamental unit of absorbed dose, whereas rem
incorporates a quality factor based on the type of radiation. For x-rays, rad equals
rem; however, for other forms of radiation, such as neutrons and protons, rem may
be larger. Rem exposure is more important in radiation protection than rad
exposure because the physiological effects of 10 rad of neutron exposure are
significantly greater than those of 10 rad of x-ray exposure. The Gray (Gy) and
Sievert (Sv) units should now be used for absorbed dosage and effective absorbed
dose, respectively, but many people continue to use rad and rem.
, The radiograph cassette is often placed on the tabletop to image which of the
following places in a medium-sized dog? The tabletop approach is ideal for
imaging structures under 10cm thick because to reduced dispersion and the absence
of the requirement for a grid or Bucky. The elbow is the only construction on this
list that is not thick enough to require the use of a grid and Bucky.
What is the maximum permitted dose of radiation that a veterinary X-ray
technician can receive in one year? - ANSWER There are numerous units of
radiation exposure and dose that are utilized. In the past, dosage was measured
using the rad unit. A "quality factor" is often multiplied by the dose to provide a
"dose equivalent" for radiation safety purposes. The radiation equivalent in man
(rem) is calculated by multiplying the dose in rad by a quality factor. Accepted
terminology has evolved throughout time, and the standard (SI) unit of dose is the
Gray (Gy). There are 100 rad for one Gy (1 rad = 1 cGy). The Sievert equals the
dose in Gy multiplied by the quality factor. The maximum allowable dose for a
radiation worker, as mentioned in this question, is 5 rem. (5,000 mrem). This yields
50 mSv, which is the correct solution to the question.
Which of the following radiographic faults will result in higher film density? -
ANSWER Focal-film distance is the distance between the film and the X-ray
source. The inverse-square law states that as the film moves closer to the source, its
density grows exponentially. The other answers given would all reduce film
density.
What will an area of the film look like if it does not come into touch with developer
but does go through fixer and the remaining processing steps? - ANSWER Films
are first processed in the developer, which converts exposed silver halide to
elemental metallic silver, which is black. If a section of the film does not come into
contact with the developer, there will be no black on the film, even if it has been
exposed. The leftover crystals would be transformed to a soluble state in the fixer
solution, dissolving and leaving a clear image.
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