Other imaging modalities Renal angiography is the most accurate test for an- atomic diagnosis of RAS, but it uses potentially nephrotoxic contrast agents and its associated radi- ation dose is high compared with other modalities. CT angiography (CTA), magnetic resonance angiog- raphy (MRA), and Doppler sonography (DS) are new noninvasive approaches for the diagnosis of re- nal artery stenosis. DS can be used to monitor recur- rent stenosis after corrective therapy and is effective for classifying patients as responders or nonre- sponders to therapy. Unfortunately, US criteria for RAS based on evaluation of renal peak systolic ve- locity and renal/aortic ratio are controversial. CTA and MRA provide anatomic information about re- nal artery stenosis. CTA has higher spatial resolu- tion than MRA and can be used to evaluate the calcium content of atherosclerotic lesions before treatment; however, the associated radiation dose is high and potentially nephrotoxic contrast agents are required. In contrast, MRA does not expose pa- tients to ionizing radiation or directly nephrotoxic contrast agents. Recently, Eklof and colleagues [92] compared DS, MRA, CTA, DS, and captopril re- nography for assessing renal artery disease and con- cluded that MRA and CTA were significantly better than duplex US and captopril renography for de- tecting hemodynamically significant RAS. A meta- analysis performed by Vasbinder and colleagues [93] supports these findings. Future prospects Although captopril renography can play an impor- tant role in the evaluation of renovascular hyperten- sion, the use of this test is decreasing. Recently, the clinical use of ACEI renography changed in two ways. First, with the introduction of other new noninvasive imaging techniques, ACEI renography Fig. 2. Renal study with MAG3 in a patient who had suspected obstruction of the right kidney. The upper row of images demonstrates rapid clearance of tracer from a small left kidney but delayed clearance from the normal- sized right kidney. The time-activity curves demonstrate a marked acceleration of clearance after furosemide ad- ministration in the left kidney. In contrast, the drug effect is blunted significantly in the right kidney, consistent with partial obstruction. Nuclear Imaging in the Genitourinary Tract 31 Interventional Ur oradiology Raul N. Uppot, MD * , Debra A. Gervais, MD, Peter R. Mueller, MD Percutaneous urologic interventions comprise a wide range of techniques, including biopsies, drainages, stone management, ureteral stenting, re- nal vascular interventions, and tumor ablations. With advances in imaging capabilities and percuta- neous instruments, many urologic diseases that were once managed surgically are now managed with minimally invasive image-guided techniques, using only conscious sedation. Interventional uroradiology has evolved from simple renal biopsies for diagnostic confirmation, to percutaneous management of stones, to ablation of renal and adrenal tumors. Central to this evolu- tion is the close cooperation with the urologist and nephrologist, each of whom provides specific skill sets and knowledge that can be used to successfully manage the patient. The purpose of this article is to detail the wide range of image- guided interventional techniques, including a dis- cussion of indications, methods, success rates, and complications. Imaging modalities Advances in imaging capabilities have spurred the evolution of minimally invasive techniques. Com- pared with open surgery, image guidance allows one to target the pathology of interest while avoid- ing injury to adjacent normal tissue. Modalities used in interventional uroradiology include ultra- sound, fluoroscopy, angiography, CT, and MR imaging. RADIOLOGIC CLINICS OF NORTH AMERICA Radiol Clin N Am 46 (2008) 45–64 Division of Abdominal Imaging and Interventional Radiology, Department of Radiology, Massachusetts Gen- eral Hospital, 55 Fruit Street; White #270, Boston, MA 02114, USA * Corresponding author. E-mail address: ruppot@partners.org (R.N. Uppot). - Imaging modalities Ultrasound Fluoroscopy Angiography Computed tomography Interventional MR imaging - Preprocedure planning Conscious sedation - Interventional urologic procedures Biopsy Nonfocal renal biopsy Focal renal biopsy Renal cyst aspiration biopsy Adrenal biopsy Prostate biopsy Transvaginal biopsy - Image-guided percutaneous drainage and aspiration Percutaneous nephrostomy Suprapubic tube insertion Stone management Percutaneous ureteral lithotripsy Ureteral stents Ureteral embolization - Renal vascular interventions Management of renal artery stenosis Renal embolization - Ablation Radiofrequency or cryoablation Renal ablation Adrenal ablation - Summary - References 45 0033-8389/08/$ – see front matter ª 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.rcl.2008.01.010 radiologic.theclinics.com . Radiology, Massachusetts Gen- eral Hospital, 55 Fruit Street; White #270, Boston, MA 02114, USA * Corresponding author. E-mail address: ruppot@partners.org (R.N. Uppot). - Imaging modalities Ultrasound Fluoroscopy Angiography Computed. embolization - Renal vascular interventions Management of renal artery stenosis Renal embolization - Ablation Radiofrequency or cryoablation Renal ablation Adrenal ablation - Summary - References 45 0 03 3-8 38 9/08/$. significantly in the right kidney, consistent with partial obstruction. Nuclear Imaging in the Genitourinary Tract 31 Interventional Ur oradiology Raul N. Uppot, MD * , Debra A. Gervais, MD, Peter R.