Gray-Scale, Color Doppler, Spectral Doppler, and Contrast-Enhanced Renal Artery Ultrasound: Imaging Techniques and Features

Renal artery stenosis (RAS) is increasingly being detected in elderly patients as life expectancy increases. RAS induces hypertension or reduces renal function. Computed tomography or magnetic resonance angiography are objective in detecting RAS but may cause iodine-induced nephrotoxicity or nephrogenic systemic fibrosis in patients with RAS. Ultrasound (US) is, by contrast, a noninvasive and real-time imaging modality useful in patients with reduced renal function. Renal US is not as sensitive for detecting RAS because this technique indirectly assesses the renal artery by analyzing intrarenal hemodynamic changes. Although, ideally, US would be used to directly evaluate the renal artery, its current utility for RAS detection remains unclear. The purpose of this review is to introduce how to assess renal artery with US, to describe imaging features of renal artery US, to compare renal artery US and renal US, and to show how to perform work-up in patients in whom RAS is suspected.