The Impact Of Vicarious Gallbladder Activity In Tc-99m Mag3 Diuretic Renography

3029 Introduction: The Impact of Vicarious Gallbladder Activity in Tc-99m MAG3 Diuretic Renography Background: Technetium(Tc)-99m Mercaptoacetyltriglycine (MAG3) is the preferred radiopharmaceutical used in renal scintigraphy. MAG3’s predominant uptake and excretion through the kidneys enables us to noninvasively evaluate renal function and urodynamic obstruction. After intravenous injection of Tc-99m MAG3, it is known that 90% of the dose is excreted through the renal system while the remaining 10% of radiotracer is excreted through the hepatobiliary system. The purpose of this study is to evaluate the frequency of vicarious gallbladder activity seen in Tc-99m MAG3 renal scintigraphy using our standard protocol and to highlight its impact in the evaluation of diuretic renography.\n Methods: In this IRB approved study, we retrospectively reviewed the MAG3 renal scintigraphy studies performed at our institution from Jan 01, 2019 to Dec 01, 2019. These studies were comprised of 97 renal scintigraphy scans for differential function, and 195 diuretic renography studies using furosemide challenge. The differential function protocol at our institution consists of 30 minutes of posterior dynamic imaging, and the diuretic renography includes an additional 30 minutes of imaging following the intravenous administration of 40 mg furosemide (Lasix). Additional right lateral static and/or abdominal SPECT/CT images were also performed in order to verify gallbladder radiotracer uptake. The imaging data was processed on MIM software (MIM Software Inc.) for calculation of differential split function, cortical emptying, and collecting system emptying - with re-processing at the discretion of the radiologist.\n Results: On all of the 292 renal scintigraphy studies performed at our institution, there was confirmed visualization of radiotracer excretion into the liver during the first 30 minutes of imaging. Of the 97 differential function studies, no gallbladder uptake was visualized resulting in no artifact and therefore no need to re-process the images. Of the 195 patients in whom furosemide was given, we observed 45 (23%) patients with gallbladder and/or small bowel activity, and 18 (9%) requiring image re-processing or manipulation for more accurate results. In addition, four SPECT/CTs were performed in order to confirm the presence of gallbladder and/or small bowel.\n Conclusions: Vicarious gallbladder uptake of Tc-99m MAG3 radiotracer is a frequently encountered phenomenon in diuretic renography utilizing the standard protocol at our facility. A lack of recognition could potentially result in the misevaluation of a patient’s urodynamic presentation, and has the potential to lead to misdiagnosis in the right kidney. A post-Lasix right lateral view image and/or SPECT/CT is able to confirm gallbladder radiotracer accumulation and should be considered after diuretic renography. The nuclear medicine technologist should be aware of this phenomenon in daily practice and take extreme caution when drawing regions of interest.