This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Medicine
Which of the following is the most specific and sensitive screening test for renovascular hypeension? 
Select and explain. 
A. HRCT, B. CT Angiography, C. Captopril enhanced radionucleotide scan, D. Doppler ultrasound of renal aeries
B: CT Angiography
Answer: B: CT Angiography 
Explanation: Hypeension due to an occlusive lesion of a renal aery is renovascular hypeensionIn the initial stages, the mechanism of hypeension generally is related to activation of the renin-angiotensin system. Obstruction of the renal aery leads to decreased renal perfusion pressure, thereby stimulating renin secretion. Over time, possibly as a consequence of secondary renal damage, this form of hypeension may become less renin-dependent.As a screening test, renal blood flow may be evaluated with a radionuclide -ohoiodohippurate (OIH) scan, or glomerular filtration rate may be evaluated with a - diethylenetriamine pentaacetic acid (DTPA) scan before and after a single dose of captopril (or another ACE inhibitor).Contrast aeriography remains the "gold standard" for evaluation and identification of renal aery lesions.Harrison 19e pg: 1618