Diagnostic Imaging practice questions

Answer: C) Peak inspiration

• AIncorrect. Time it to breathing.
• BIncorrect. Lungs look denser then.
• CCorrect. Lungs are fully inflated.
• DIncorrect. Time it to inspiration.

Answer: A) At the thickest part of the anatomy included in the field, with the patient in the imaging position

Patient thickness is measured with calipers at the thickest part of the area being radiographed, with the patient in the imaging position. That value is then used with the technique chart.

• ACorrect. Measuring the thickest part of the region, with the patient positioned as for the exposure, makes sure the chosen technique penetrates the densest tissue in the field.
• BIncorrect. A technique based on the thinnest area would underpenetrate the thicker parts of the region.
• CIncorrect. Technique charts are set up for a single measurement at the thickest part, not an average of several points.
• DIncorrect. The measurement should be taken with the patient in the position used for the exposure, because that is the tissue thickness the beam actually passes through.

Answer: A) It lets the operator watch the needle enter a small or hard-to-palpate bladder

With ultrasound guidance, the bladder and needle are seen in real time, which helps with accurate placement when the bladder is small or hard to palpate. Any properly performed cystocentesis gives a culture-quality sample, and the bladder still has to contain urine.

• ACorrect. Seeing the bladder and needle in real time allows accurate placement. This is especially useful when the bladder is small or hard to palpate, such as in cats that void when handled.
• BIncorrect. A properly performed cystocentesis, guided or blind, gives an uncontaminated sample suitable for culture.
• CIncorrect. Microscopic hematuria is common in cystocentesis samples, especially when the bladder is inflamed. Ultrasound guidance does not prevent it.
• DIncorrect. The bladder must contain urine to be sampled. Ultrasound helps find a small volume of urine but cannot get urine from an empty bladder.

Answer: C) Extended caudally, parallel, and rotated inward so the patellae are centered

For the VD hip-extended view, the hind limbs are extended caudally with the femurs parallel and rotated inward so the patellae are centered over the femurs. The frog-leg view uses flexed, abducted limbs instead.

• AIncorrect. That is the frog-leg VD view, where the limbs are flexed and abducted. It is not the extended view used for hip dysplasia screening.
• BIncorrect. Rotating the limbs outward moves the patellae off center and distorts the coxofemoral joints. The stifles should be rotated inward.
• CCorrect. The femurs are extended caudally, parallel to each other and to the table, and rotated slightly inward. This centers the patellae over the femurs and gives a symmetric view of the hips.
• DIncorrect. The femurs should be parallel to each other and to the spine. Spreading them outward changes hip measurements such as the Norberg angle.

Answer: A) Soft tissue

• ACorrect. CT excels at bone.
• BIncorrect. CT is often better for bone.
• CIncorrect. MRI excels at soft tissue.
• DIncorrect. MRI excels at soft tissue.

Answer: B) The full tibia, including the stifle proximally and the tarsus distally

Radiographs of a long bone should include the joints proximal and distal to it (here the stifle and tarsus), taken in at least two orthogonal views, so that associated injuries are not missed.

• AIncorrect. Tight collimation lowers scatter, but leaving out the adjacent joints can miss joint involvement, luxations or other injuries next to the fracture.
• BCorrect. Long-bone studies should include the joint proximal and the joint distal to the injured bone so that the whole bone and any associated joint injuries can be assessed.
• CIncorrect. A contralateral view can help as a normal comparison, but it cannot replace imaging of the affected limb.
• DIncorrect. One view centered on the swelling can miss displacement and associated injuries. Two orthogonal views that include the adjacent joints are standard.

Answer: B) Dorsoventral projection with the patient in sternal recumbency

The DV projection is preferred for cardiac evaluation. In sternal recumbency the heart sits in a more natural, consistent position, and the pulmonary lobar vessels are shown well.

• AIncorrect. In dorsal recumbency the heart can tip and shift, widening the thorax and sometimes creating a false bulge in the cardiac outline. VD is often chosen for ventral lung and accessory lung lobe detail instead.
• BCorrect. In sternal recumbency the heart rests on the sternum in a more natural, consistent position. The dorsal lung fields, where the caudal lobar vessels lie, are also well aerated.
• CIncorrect. Horizontal-beam (decubitus) views are used to show pleural fluid or free gas moving with gravity. They are not a standard cardiac projection.
• DIncorrect. Oblique views are used to separate specific structures, such as the ribs or a lung mass, from overlying tissue. Rotation distorts the cardiac silhouette.

Answer: C) For body parts measuring more than about 10 cm thick

A grid is generally used for body parts thicker than about 10 cm, where scatter significantly reduces contrast. Its lead strips absorb angled scatter, but the exposure must be increased to compensate.

• AIncorrect. Thin extremities produce little scatter, so a grid adds little contrast while requiring a higher exposure. These parts are usually imaged on the tabletop without a grid.
• BIncorrect. Intraoral dental films and sensors are placed inside the mouth and used without a grid. The tissue imaged is thin and the beam is tightly collimated.
• CCorrect. Thicker tissue produces much more scatter radiation. A grid's lead strips absorb scattered photons that travel at an angle, while the primary beam passes between them, which improves image contrast.
• DIncorrect. A grid absorbs part of the primary beam as well as scatter, so exposure (mAs) must be increased when a grid is used, not decreased.

Answer: D) Wipe off gel and disinfect with an approved product

• AIncorrect. Clean it between patients.
• BIncorrect. That can damage it.
• CIncorrect. Heat damages probes.
• DCorrect. Follow the manufacturer's guidance.

Answer: A) About 40 inches (100 cm)

• ACorrect. Changing it alters exposure.
• BIncorrect. That's far too close.
• CIncorrect. That's too far.
• DIncorrect. Distance affects exposure.