Ultrasound. It is a common procedure because is not invasive and provides lot if information and it is cheap. Therefore widely use. When there is any suspicion of renal pathology most of the time an ultrasound is performed before a ct scan.
Renal artery. Stenosis can be a cause of hypertension. This is called renovascular hypertension. Sometimes a renal ultrasound with renal artery Doppler is performed to screen for this.