SPEX SPEX Radiology and Imaging 4 — Questions and Answers
Question 1: A patient with a GFR of 28 mL/min requires contrast-enhanced CT. Which strategy best minimizes the risk of contrast-induced nephropathy?
- Prehydrate with IV normal saline and use the lowest effective iodine dose (Correct answer)
- Administer furosemide immediately after contrast injection
- Use double the standard contrast volume to ensure diagnostic quality
- Withhold metformin for 24 hours but give standard contrast dose without hydration
Correct answer: Prehydrate with IV normal saline and use the lowest effective iodine dose
IV hydration with isotonic saline before and after contrast administration and minimizing contrast volume are the cornerstones of CIN prevention in patients with reduced GFR.
Question 2: On a PA chest radiograph, which finding is most consistent with a left lower lobe collapse?
- Elevation of the left hemidiaphragm with leftward mediastinal shift and a triangular retrocardiac opacity (Correct answer)
- Widening of the right paratracheal stripe
- Hyperlucency of the left hemithorax with contralateral mediastinal shift
- Flattening of the left hemidiaphragm with increased left lung volume
Correct answer: Elevation of the left hemidiaphragm with leftward mediastinal shift and a triangular retrocardiac opacity
Left lower lobe collapse produces a triangular retrocardiac density, elevated left hemidiaphragm, and ipsilateral mediastinal shift due to volume loss.
Question 3: Which MRI sequence is most sensitive for detecting acute cerebral ischemia within the first 6 hours of symptom onset?
- Diffusion-weighted imaging (DWI) (Correct answer)
- T1-weighted imaging with gadolinium
- T2 FLAIR
- Gradient echo (GRE)
Correct answer: Diffusion-weighted imaging (DWI)
DWI detects cytotoxic edema from restricted water diffusion within minutes of ischemia onset, making it the most sensitive early sequence.
Question 4: During fluoroscopy-guided lumbar spine injection, the operator notices the C-arm beam is delivered in a steep oblique angle for extended periods. The most appropriate dose-reduction measure is to:
- Use pulsed fluoroscopy at the lowest frame rate that provides adequate visualization (Correct answer)
- Increase the source-to-image distance to reduce magnification
- Keep the patient table as far from the image intensifier as possible
- Collimate the beam to the widest field to capture more anatomy per frame
Correct answer: Use pulsed fluoroscopy at the lowest frame rate that provides adequate visualization
Pulsed fluoroscopy reduces cumulative dose by delivering radiation only in pulses rather than continuously, with minimal loss of procedural guidance.
Question 5: A 35-year-old pregnant woman at 28 weeks gestation presents with right flank pain. What is the preferred initial imaging modality?
- Renal ultrasound (Correct answer)
- Non-contrast CT of the abdomen and pelvis
- MRI with gadolinium
- Intravenous pyelogram (IVP)
Correct answer: Renal ultrasound
Ultrasound is the first-line modality in pregnancy because it carries no ionizing radiation and can diagnose hydronephrosis and renal calculi without fetal risk.
Question 6: Which ultrasound artifact is responsible for the appearance of a hyperechoic line with posterior acoustic shadowing deep to a gallstone?
- Acoustic shadowing (Correct answer)
- Posterior acoustic enhancement
- Side-lobe artifact
- Reverberation artifact
Correct answer: Acoustic shadowing
Gallstones reflect and absorb nearly all incident sound, producing a dense hyperechoic surface and clean anechoic shadow posterior to the stone.
Question 7: A radiation worker's monthly whole-body dosimeter reading is 420 mrem. Which statement about this result is most accurate?
- The reading exceeds the NRC monthly guidance level but remains below the annual occupational limit if not repeated (Correct answer)
- This reading mandates immediate removal of the worker from all radiation areas
- The NRC annual occupational limit is 5 rem, so this single reading is already over the limit
- Monthly dosimetry readings above 100 mrem automatically trigger a formal ALARA investigation regardless of annual totals
Correct answer: The reading exceeds the NRC monthly guidance level but remains below the annual occupational limit if not repeated
The NRC annual occupational whole-body limit is 5,000 mrem (5 rem); one month at 420 mrem is elevated and warrants investigation but does not by itself exceed the annual limit.
SPEX SPEX Radiology and Imaging 4
A patient with a GFR of 28 mL/min requires contrast-enhanced CT.
Which strategy best minimizes the risk of contrast-induced nephropathy?