SeHCAT retention measurements may be compromised by traces of 177 Lu/ 177m Lu more than 90 days after 177 Lu-DOTATATE was administered.

[ 75 Se]tauroselcholic acid (SeHCAT) retention measurement provides a noninvasive test for bile acid diarrhea (BAD); however, it is sensitive to the presence of other radionuclides. Two SeHCAT patients at the Royal Free Hospital (RFH) had significant discrepancies between the lower photopeak (111-159 keV) and central photopeak (242-296 keV) windows, indicating contamination with a radionuclide other than 75 Selenium. These patients had received lutetium-177 oxodotreotide ( 177 Lu-DOTATATE) therapy 98 and 151 days before their SeHCAT tests.

Uncollimated gamma camera measurements at two metres to the patient provide a practical and statistically robust method for SeHCAT retention calculation.

[75Se]tauroselcholic acid (SeHCAT) retention studies may be performed using a collimated or uncollimated (intrinsic) gamma camera, with trade-offs between counting sensitivity, collision risk, and stray source influence. In this work, we evaluate the uncertainty in SeHCAT studies performed in 'outer room' mode, where the patient sits or stands two metres away from the uncollimated camera face. 768 SeHCAT studies performed at the Royal Free Hospital were analysed retrospectively, and in all cases, the absolute uncertainty was found to be well within the clinically acceptable limit of ±1 percentage point at 15% retention.