Why bladder emptying reduces the false-positive results of dynamic renal scintigraphy?

Dynamic renal scintigraphy (DRS) is an imaging modality of choice for diagnosing the structural and functional obstruction in the urinary tract after intravenous injection of radiotracers such as Tc-99 m diethylenetriaminepentaacetic acid (DTPA). While upper urinary tract obstruction can prolong the elimination half-life > 20 min of Tc-99 m DTPA, false-positive diagnosis of upper urinary tract obstruction can also result from lower renal excretion of Tc-99 m DTPA due to reduced urinary production in dehydrated individuals, and reduced renal excretion increases the reabsorption of Tc-99 m DTPA from the bladder. Here, we dissected the purported cause for the false-positive results of prolonged elimination half-life > 20 min of Tc-99 m DTPA during dynamic image acquisition for DRS before bladder emptying. The prevalent view in nuclear medicine implicates back pressure of bladder as the purported cause of false positive results and ignores the contribution of kidney recycling Tc-99 m DTPA reabsorbed from bladder. Here, we distilled published clinical evidence to draw a mechanistic insight into the role of Tc-99 m DTPA reabsorption from the bladder in DRS.