ARRT CT Practice Questions (2026) — Free Sample Questions with Answers

Answer: B

Proceed with the routine contrast dose, because nonionic low-osmolar agents carry no renal risk at any eGFR: Incorrect. Nonionic low-osmolar contrast reduces but does not eliminate risk; ACR guidance identifies eGFR below 30 as the group in whom contrast-associated AKI risk must be weighed.

Hold the injection and notify the radiologist, since an eGFR below 30 calls for a risk-benefit decision and possible IV hydration: Correct. Per the ACR Manual on Contrast Media, patients with eGFR <30 not on dialysis are the at-risk group; the radiologist/ordering provider decides whether to give contrast, adjust dose or order prophylactic IV hydration.

Inject the contrast, then arrange for hemodialysis within two hours to remove the agent and protect renal function: Incorrect. Scheduling urgent dialysis to remove contrast is not recommended for patients who are not already on dialysis and does not prevent AKI.

Substitute an equivalent dose of a gadolinium-based agent, which is the preferred option for patients with poor renal function: Incorrect. Gadolinium is not a CT substitute at diagnostic doses, and severe renal impairment raises the concern for nephrogenic systemic fibrosis with some GBCAs.

eGFR <30 mL/min/1.73 m² (not on dialysis) is the ACR threshold for elevated contrast-associated AKI risk: stop, notify the radiologist, and follow the prophylaxis decision.

Answer: D

0.18 mSv: Incorrect. This multiplies CTDIvol by k and omits the scan length, so it is not based on DLP.

32 mSv: Incorrect. This divides the DLP (480) by 15 instead of multiplying by 0.015.

480 mSv: Incorrect. 480 is the DLP in mGy·cm; it must be multiplied by k to estimate effective dose.

7.2 mSv: Correct. DLP = CTDIvol × length = 12 × 40 = 480 mGy·cm; E ≈ DLP × k = 480 × 0.015 = 7.2 mSv.

DLP (mGy·cm) = CTDIvol × scan length; effective dose (mSv) ≈ DLP × region-specific k-factor.

Answer: B

Ring artifact: Incorrect. Ring artifacts are circular, centered on the isocenter, and caused by a miscalibrated detector element, not linear streaks between bones.

Beam hardening: Correct. The polychromatic beam is preferentially stripped of low-energy photons by the dense petrous bones, producing dark streaks between them (the classic Hounsfield bar).

Motion artifact: Incorrect. Motion causes blurring, double contours or streaks from moving edges; the patient was still.

Partial volume averaging: Incorrect. Partial volume averaging blurs structures that only partly occupy a voxel; it is reduced with thinner slices and does not cause these dark bands.

Dark streaks between two dense objects (petrous ridges, shoulders, contrast-filled vessels) = beam hardening; reduce with bowtie filtration, correction algorithms or thinner sections and higher kVp.

Answer: D

0.24 mm: Incorrect. This would correspond to roughly a 125 mm DFOV or a 1024 matrix at 250 mm.

0.98 mm: Incorrect. This results from using a 256 matrix (250 ÷ 256) rather than 512.

2.05 mm: Incorrect. This inverts the formula (512 ÷ 250).

0.49 mm: Correct. Pixel size = DFOV ÷ matrix = 250 mm ÷ 512 ≈ 0.49 mm.

Pixel size = DFOV ÷ matrix size; a smaller DFOV or larger matrix gives smaller pixels and potentially better spatial resolution (with more noise per pixel).

Answer: C

56%; below the 60% cutoff, so the nodule is indeterminate: Incorrect. 56% is the relative washout ((80 − 35) ÷ 80), which should be compared with its own 40% cutoff; it is not the absolute washout.

25%; low washout, so the nodule is suspicious for malignancy: Incorrect. This divides delayed minus unenhanced (15) by enhanced minus unenhanced (60), which is the retained fraction, not washout.

75%; at least 60%, so the nodule is consistent with an adenoma: Correct. Absolute washout = (80 − 35) ÷ (80 − 20) × 100 = 45 ÷ 60 × 100 = 75%; a value of 60% or more supports a benign adenoma.

45%; between thresholds, so biopsy is required for diagnosis: Incorrect. 45 is the raw HU drop, not a percentage; it must be divided by the enhancement (60 HU).

Absolute washout = (enhanced − delayed) ÷ (enhanced − unenhanced) × 100 (≥60% = adenoma); relative washout = (enhanced − delayed) ÷ enhanced × 100 (≥40% = adenoma).

Answer: B

In the descending aorta at the diaphragm: Incorrect. Systemic arterial enhancement arrives after the pulmonary arteries peak, so triggering here would scan too late for a PE study.

In the main pulmonary artery (pulmonary trunk): Correct. Triggering from the pulmonary trunk times the scan to peak pulmonary arterial opacification.

In the superior vena cava near the right atrium: Incorrect. The SVC opacifies first with dense undiluted contrast and streak artifact, which would trigger the scan too early.

In the left ventricle at the level of the mitral valve: Incorrect. Left heart enhancement follows pulmonary transit, which again would trigger after the pulmonary arterial peak.

Place the bolus-tracking ROI in the vessel you want opacified: pulmonary trunk for PE, ascending/descending aorta for aortic and coronary studies.