CT procedures and contrast

44 Gulf Prometric Radiographer (DHA, DOH, MOH, SCFHS, QCHP) practice questions on CT procedures and contrast, part of CT. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Hard

   A power injector extravasates about 120 mL of contrast into the forearm. An hour later the hand is cool, with worsening pain, numbness and slow capillary refill. What is the correct management?

   1. AElevation and cold packs only, with review the next day
   2. BUrgent surgical review for possible compartment syndrome
   3. CAspiration of the swelling through the same cannula site
   4. DMassage of the forearm to spread the contrast away

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   Answer: B · Urgent surgical review for possible compartment syndrome

   Most extravasations settle with elevation and cold or warm compresses, but the ACR Manual lists signs that need urgent surgical consultation: progressive swelling or pain, altered sensation, reduced capillary refill, and skin blistering or ulceration. These suggest compartment syndrome, which can cause permanent damage within hours.

   • A: Elevation and compresses suit mild cases, not signs of compartment syndrome.
   • C: Aspiration is not a reliable treatment and does not relieve compartment pressure.
   • D: Massage can spread the injury and does not treat raised compartment pressure.

   Remember this

   Extravasation with worsening pain, numbness or poor perfusion needs urgent surgical review.

2. Question 2 · Hard

   A patient with a previous moderate contrast reaction needs an emergency contrast CT within 5 hours and cannot complete the 13-hour oral scheme. Which accelerated regimen does the ACR Manual describe?

   1. ATwo doses of IV methylprednisolone 1 hour apart, with no antihistamine
   2. BIV diphenhydramine 50 mg alone, 1 hour before
   3. CIV methylprednisolone 40 mg (or hydrocortisone 200 mg) now and every 4 hours until contrast, plus IV diphenhydramine 50 mg 1 hour before
   4. DA single oral prednisone 50 mg dose given 30 minutes before the examination, with no antihistamine, because oral steroid acts within a few minutes

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   Answer: C · IV methylprednisolone 40 mg (or hydrocortisone 200 mg) now and every 4 hours until contrast, plus IV diphenhydramine 50 mg 1 hour before

   In emergencies, steroid is given IV straight away and repeated every 4 hours until the examination, with diphenhydramine 50 mg IV one hour before the injection. Steroid needs several hours to work, so short oral or single-drug schemes offer little protection. Where the scan cannot wait, the team treats reactions if they occur.

   • A: Two doses an hour apart are too short for steroid effect.
   • B: An antihistamine alone gives limited protection.
   • D: One late oral dose is too late to help.

   Remember this

   Accelerated premedication is IV steroid every 4 hours plus IV diphenhydramine at 1 hour.

3. Question 3 · Medium

   In CT pulmonary angiography, where is the bolus-tracking region of interest normally placed?

   1. AIn the right atrium wall only
   2. BIn the liver
   3. CIn the main pulmonary artery
   4. DIn the descending abdominal aorta

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   Answer: C · In the main pulmonary artery

   Contrast reaches the pulmonary arteries within seconds of injection, so the monitoring region sits in the main pulmonary artery. The scan begins once the threshold is reached, about 100 HU in many protocols, and finishes before enhanced blood returns to the left side.

   • A: The atrial wall is not a reliable region.
   • B: The liver is used for portal venous timing.
   • D: The abdominal aorta is for aortic or mesenteric angiography.

   Remember this

   For CT pulmonary angiography, trigger from a region in the main pulmonary artery.

4. Question 4 · Medium

   Why is iodinated contrast often warmed to body temperature before power injection?

   1. ATo lower its viscosity and ease injection at high flow rates
   2. BTo prevent allergic reactions
   3. CTo make the contrast radioactive
   4. DTo increase its iodine content, so that less volume is needed for the same enhancement

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   Answer: A · To lower its viscosity and ease injection at high flow rates

   Contrast viscosity falls as temperature rises, so warmed contrast flows more easily at high rates and the injector pressure is lower. This reduces the risk of cannula failure. The iodine content does not change.

   • B: Warming does not prevent allergy.
   • C: Contrast is not radioactive.
   • D: Warming does not change iodine concentration.

   Remember this

   Warming contrast to body temperature lowers viscosity and eases high-rate injection.

5. Question 5 · Medium

   A high-resolution CT (HRCT) of the lungs is requested for suspected air trapping. Which additional acquisition is most useful?

   1. AExpiratory images
   2. BImages at 10 mm slice thickness
   3. CImages with IV contrast only
   4. DA scan with the arms down only

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   Answer: A · Expiratory images

   Air trapping appears as areas that fail to increase in density on expiration, so expiratory images are added to the inspiratory ones. Prone images help separate dependent density from early fibrosis. Thin slices and a sharp kernel are used for HRCT.

   • B: HRCT requires thin sections, about 1 mm.
   • C: IV contrast is not needed for the lung parenchyma.
   • D: Arm position does not show air trapping.

   Remember this

   Add expiratory images to HRCT to show air trapping.

6. Question 6 · Easy

   What is the main purpose of a saline flush (chaser) after the contrast bolus?

   1. ATo dilute contrast and reduce its osmolality in the blood, so that fewer allergic reactions occur in the vein
   2. BTo prevent allergic reactions
   3. CTo push the contrast out of the veins and tubing, which saves volume and reduces streak artefact
   4. DTo lower the patient's blood pressure

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7. Question 7 · Hard

   An 80 kg patient receives contrast at 1.5 mL/kg for a portal venous abdominal scan, injected at 3 mL/s, with the scan planned at 70 s after the start of injection. How long does the injection last, and when does the scan begin relative to its end?

   1. A40 s, with the scan starting at the end of injection
   2. B40 s, with the scan starting 30 s after the end of injection
   3. C27 s, with the scan starting 43 s after the end of injection
   4. D120 s, with the scan starting before the end of injection

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8. Question 8 · Medium

   A CT angiogram at 5 mL/s is planned for a patient in Abu Dhabi. Which intravenous access is best?

   1. AAn 18 gauge cannula in the antecubital fossa, tested with saline before injection
   2. BAny cannula, without a saline test
   3. CA cannula in the foot
   4. DA 24 gauge cannula in the hand, because a smaller needle causes less pain and less vein damage

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9. Question 9 · Medium

   A CT myelogram is booked for a patient who cannot have MRI. Which contrast medium is injected into the lumbar thecal sac?

   1. AA gadolinium-based agent at the usual intravenous dose
   2. BA non-ionic iodinated agent licensed for intrathecal use, such as iohexol
   3. CA dilute barium sulphate suspension
   4. DAn ionic high-osmolar iodinated agent such as diatrizoate

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10. Question 10 · Medium

    During a CT in a Doha hospital, a patient develops a few itchy hives on the chest and no other symptoms five minutes after the injection. How is this reaction classified, and what is the usual action?

    1. ASevere: give epinephrine intramuscularly
    2. BDelayed: send the patient home immediately
    3. CMild: observe and reassure, as treatment is often not required
    4. DModerate: call the arrest team

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11. Question 11 · Hard

    A patient on regular haemodialysis with no residual kidney function needs an IV contrast CT. According to the ACR Manual, how should the timing of dialysis be handled?

    1. ADialysis must be done within 1 hour of the scan
    2. BNo change; urgent post-contrast dialysis is not needed
    3. CContrast is contraindicated in dialysis patients
    4. DDialysis must be held for 48 hours afterwards

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12. Question 12 · Medium

    A low-dose CT for lung cancer screening in a heavy smoker is planned. Which statement describes the technique?

    1. ANo IV contrast, with a standard-size CTDIvol of about 3 mGy or less
    2. BContrast-enhanced scan at 25 seconds
    3. COral contrast followed by delayed images
    4. DIV contrast at 100 mL and a CTDIvol of 30 mGy

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13. Question 13 · Hard

    A CT angiogram protocol delivers contrast of 370 mgI/mL at 4 mL/s. The hospital switches to 300 mgI/mL contrast and wants to keep the same iodine delivery rate. What injection rate is needed?

    1. AAbout 4.9 mL/s
    2. BAbout 4.0 mL/s
    3. CAbout 3.2 mL/s
    4. DAbout 1.5 mL/s

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14. Question 14 · Easy

    For a routine abdominal CT, the portal venous phase of the liver is usually acquired after about:

    1. A5 minutes
    2. B70 seconds
    3. C10 seconds
    4. D25 seconds

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15. Question 15 · Easy

    Under the ACR Manual on Contrast Media, the risk of contrast-associated kidney injury after IV iodinated contrast becomes significant when eGFR falls below:

    1. A15 mL/min/1.73 m²
    2. B90 mL/min/1.73 m²
    3. C60 mL/min/1.73 m²
    4. D30 mL/min/1.73 m²

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16. Question 16 · Medium

    In suspected acute ischaemic stroke, a CT angiogram of the head and neck is requested. What should the scan range include?

    1. AThe aortic arch to the vertex
    2. BThe chest and abdomen
    3. CThe skull base to the vertex only
    4. DThe neck only

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17. Question 17 · Medium

    A patient reports a shellfish allergy and asks whether it makes iodinated contrast unsafe. What is the correct reply?

    1. AShellfish allergy is an absolute contraindication to all iodinated contrast agents, with no exceptions
    2. BIodine in shellfish causes the reaction
    3. CShellfish allergy is not a specific risk factor and does not by itself need premedication
    4. DContrast contains shellfish protein

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18. Question 18 · Medium

    A patient had a moderate hive-and-wheeze reaction to iodinated contrast two years ago and now needs an elective contrast CT. Which standard oral premedication scheme is used according to the ACR Manual?

    1. AOral metformin 1 hour before
    2. BA single paracetamol tablet on the morning of the scan, to reduce any fever or discomfort afterwards
    3. CCalcium gluconate 10 mL IV before
    4. DPrednisone 50 mg at 13, 7 and 1 hour before, plus diphenhydramine 50 mg 1 hour before

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19. Question 19 · Medium

    A breastfeeding mother needs an IV contrast CT at a Riyadh hospital and asks whether she must stop feeding. What does the ACR Manual advise?

    1. ABreastfeeding is a contraindication to contrast
    2. BThere is no need to stop breastfeeding, as very little contrast enters the milk and infant gut
    3. CDiscard milk for 24 hours
    4. DStop breastfeeding for one week, because a large part of the contrast dose passes into the breast milk

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20. Question 20 · Hard

    A 58-year-old diabetic patient on metformin has an eGFR of 42 mL/min/1.73 m² and no acute kidney injury. A ward requests CT abdomen with IV contrast. Which plan matches the ACR Manual?

    1. AHold metformin for 48 hours and give IV hydration, since all diabetic patients need both before contrast
    2. BGive the contrast, continue metformin, and no routine prophylactic hydration is needed
    3. CGive contrast only after dialysis
    4. DCancel the contrast and use an unenhanced scan

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21. Question 21 · Easy

    Which drug and route is first-line for a severe allergic-like reaction with laryngeal oedema and hypotension after IV contrast?

    1. AOral antihistamine
    2. BEpinephrine (adrenaline) intramuscularly
    3. CNebulised saline
    4. DIntravenous hydrocortisone only

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22. Question 22 · Medium

    A 66-year-old non-dialysis patient with eGFR 24 mL/min/1.73 m² needs urgent IV contrast CT. What is the ACR-recommended preparation if the study is judged necessary?

    1. ANo preparation, since the risk of kidney injury is nil when the examination is urgent
    2. BProphylactic IV isotonic saline hydration, after weighing risk and benefit
    3. COral furosemide
    4. DStopping all fluids

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23. Question 23 · Medium

    A patient taking metformin has eGFR 55 mL/min/1.73 m² and no acute kidney injury and receives IV contrast. According to the ACR Manual, what should be done about metformin?

    1. ADouble the dose after the scan
    2. BStop it for 24 hours before the scan only
    3. CStop it for one week
    4. DContinue it, with no need to stop before or after

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24. Question 24 · Medium

    For a CT angiogram of the thoracic aorta, a region of interest is placed in the descending aorta. This technique is called:

    1. AA test bolus, performed three days earlier on a different scanner to measure the patient's circulation time
    2. BA fixed 10-minute delay
    3. CA timing chart based on weight alone
    4. DBolus tracking, starting the scan once a threshold of about 100 to 150 HU is reached

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25. Question 25 · Easy

    Which type of contrast medium is standard for intravenous use in CT today?

    1. AIonic, high-osmolar iodinated contrast
    2. BBarium sulphate suspension
    3. CNon-ionic, low- or iso-osmolar iodinated contrast
    4. DA gadolinium-based chelate

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