<s>[INST] context: Asymmetrical kidneys on usg in a pt of Renovascular hypeension suggests Renal Aery stenosis and Gold standard is renal Angiography. Perfusion Studies to Assess Differential Renal Blood Flow Captoril-renograpy with technetium 99m Tc meiatide (99mTcMAG3) Captopril -mediated fall in filtration pressure amplifies differences in renal perfusion Normal study excludes renovascular hypeension Multiple limitations in patients with advanced atherosclerosis or creatinine >2.0 mg/dL C/I In bilateral RAS Vascular Studies to Evaluate the Renal Aeries Duplex Ultrasonography Shows the renal aeries and measures flow velocity as a means of assessing the severity of stenosis Inexpensive and good screening test Heaviy dependent on operator's experience; Less useful than invasive angiography for the diagnosis of fibromuscular dysplasia and Magnetic resonance Angiography Shows the renal aeries and perirenal aoa Not nephrotoxic, but concerns for gadolinium toxicity exclude use in GFR<30/mL/min/1.73 m2 Expensive; Gadolinium excluded in renal failure, Unable to visualize stented vessels Computed tomographic Angiography Shows the renal aeries and perirenal aoa Provides excellent image Moderate volume of contrast required, Potentially nephrotoxic Intraaerial angiograhy Shows location and severity to vascular lesion Gold standard" for dx of large-vessel disease, Expensive,associated hazard of atheroembolism Contrast toxicity, Procedure-related complications [/INST] question: Gold standard investigation for renovascular hypeension in a patient showing asymmetrical kidneys on Ultrasound? | options: A: Captopril radionuclide scan B: Spiral CT C: MRI D: Angiography | answer: D </s>