Modalities, Contrast & Physics MCQs

Radiology · 5 free questions with answers & explanations.

1. During a fluoroscopy procedure, the radiographer notes that doubling the distance from the X-ray tube to the patient reduces the radiation dose rate to the patient by a factor of four. This relationship is an example of which physical law?
2. A 70-year-old man with diabetic nephropathy (eGFR 25 mL/min/1.73m²) requires IV contrast-enhanced CT for staging of a newly diagnosed renal mass. Serum creatinine is 250 µmol/L. Which statement best reflects the risk-benefit consideration and recommended precaution for iodinated contrast administration in this patient?
3. On a T2-weighted MRI sequence, free fluid (such as CSF or urine in the bladder) appears as bright (high signal intensity), while fat appears intermediate, and rapidly flowing blood appears dark (signal void). What property of free fluid accounts for its high T2 signal?
4. A 25-year-old pregnant woman at 18 weeks gestation requires investigation for suspected appendicitis. Ultrasound is inconclusive. Which statement best reflects the safety and guidance on further imaging in this clinical scenario?
5. During abdominal ultrasound, the operator increases the frequency of the transducer from 3.5 MHz to 7 MHz to improve image resolution. What is the inevitable trade-off of using higher frequency ultrasound?