**4. Imaging Studies and Their Limitations**

Technetium 99m (99mTc) mertiatide, 99mTc diethylene triamine penta-acetic acid, or 99mTc dimercaptosuccinic acid renal scans (with or without diuresis) are commonly used to evaluate the presence and severity of UUTO in patients with hydronephrosis. Patients are divided into those with no, partial, or complete obstruction and with or without renal function [21–23]. Urgent surgical relief of complete obstruction is essential, otherwise the kidney will rapidly become nonfunctional. A partial obstruction is a resistance to outflow that, if left untreated, will lead to a loss of kidney function. If renal function is lost, surgery is not considered unless the kidney may be infected. Although renal scans are the standard method of evaluating the presence and severity of UUTO, they are expensive and expose patients to radiation, and repeat scans should be avoided. Furthermore, they do not reveal kidney damage per se, and the equipment is not widely available.
