Ideal imaging modality for Renal aeria hypeension-

A number of investigations may be abnormal in patients with renovascular disease. Renal function may be impaired and plasma renin activity may be elevated, sometimes with hypokalaemia due to hyperaldosteronism. Ultrasound may reveal a discrepancy in size between the two kidneys. Unfounately, these simple non-invasive tests are insufficiently sensitive for screening in hypeensive patients and vascular imaging is required to diagnose renovascular disease. Such imaging is usually undeaken only in patients in whom intervention to improve renal perfusion would be contemplated; this is usually limited to young patients and those in whom blood pressure cannot be controlled with antihypeensive agents ('resistant hypeension'), those who have a history of 'flash' pulmonary oedema or accelerated phase ('malignant') hypeension, or those in whom renal function is deteriorating. CT and MRI angiographic techniques have largely replaced Doppler ultrasound or renal isotope scanning (including 'captopril renography') in diagnosing renal aery stenosis. Conventional renal aery cannulation and aeriography is now usually undeaken for therapeutic rather than diagnostic purposes. CT angiography entails large intravenously administered doses of contrast medium which may be nephrotoxic. ref:Harrison's principles of internal medicine,ed 18,pg no 2045