Which type of imaging study would use 25-50 mg of captopril prior to scanning?

Captopril, an angiotensin-converting enzyme (ACE) inhibitor, is primarily utilized in renal imaging studies to assess the function of the kidneys, particularly in the context of evaluating renal artery stenosis. When administered prior to the imaging, captopril can enhance the differentiation of renal function by inhibiting the effects of angiotensin II, which plays a role in the regulation of renal blood flow and glomerular filtration rate.

In renal imaging, particularly with radiopharmaceuticals used for dynamic renal scans, captopril causes a reduction in renal blood flow in stenotic arteries while allowing the unaffected kidney to maintain or even enhance perfusion. This contrast aids in identifying and assessing the presence of renal artery stenosis and helps to accurately evaluate renal function and perfusion.

Other imaging modalities like cardiac, thyroid, or liver imaging do not commonly involve the administration of captopril for their evaluations, as their focus lies on different physiological processes that are not influenced by ACE inhibition in the same manner as renal function assessments. This specificity makes the use of captopril prior to renal imaging the appropriate choice in this context.