Nuclear Medicine - Radiology of the Urinary Tract: Techniques and Normal Anatomy

 Nuclear Medicine

In general, the value of nuclear imaging in the urinary tract is severalfold: functional information related to the quantifiable collecteddata, lower radiation dose than traditional radiographic tech-niques, and very low incidence of complications. Renal eval-uation is typically performed by intravenous bolus injection of renal specific agents such as technetium-labeled mercap-toacetyltriglycine (Tc-MAG3). Images are acquired every few seconds demonstrating renal blood flow with additional im-ages obtained over several minutes showing renal uptake and excretion. The recorded data can be used to produce images, but it also is quantifiable and is employed to generate time-activity curves (Figure 9-13). Information about renal perfu-sion, morphology, relative function of each kidney, and excretion can be extremely useful in evaluation of conditions such as renovascular hypertension, obstruction, and renal transplant examination. Although anatomically oriented data can be obtained with other radioisotopes that aggregate more in the renal parenchyma, in general, nuclear medicine renal studies suffer from fairly low spatial resolution and are therefore often used in conjunction with other imaging stud-ies. Radionuclide cystography is another useful test used to diagnose and monitor vesicoureteral reflux. Here, tech-netium pertechnetate is mixed with saline and infused into the bladder with subsequent images obtained over the uri-nary tract. This study is quite sensitive for the detection of significant reflux, but at a considerably lower radiation dose than conventional cystography, making it particularly useful in children, especially in those needing follow-up and repeated imaging. Another important study is the radioactive iodine labeled metaiodobenzylguanidine (MIBG) examina-tion. MIBG collects in adrenal medullary tissue and is useful in diagnosis and evaluation of pheochromocytoma. Positron emission tomography (PET) is evolving as a powerful imag-ing tool, especially when combined with CT (PET/CT), com-bining the functional data of PET with the anatomic CT information. Unfortunately, fluorine-labeled deoxyglucose (FDG), which is the primary agent used in PET/CT, is nor-mally excreted by the kidneys, obscuring urinary tract pathology and limiting utilization. PET/CT has, however, shown promise in evaluation of possible metastatic disease.