Diagnostic performance of 99mTc-labeled red blood cell SPECT/CT using a 360º CZT camera in patients with overt gastrointestinal bleeding and negative findings on multidetector CT

Gastrointestinal bleeding can contribute significantly to morbidity and result in life-threatening events. Multidetector computed tomography (MDCT) is widely utilized as a first-line diagnostic tool for patients presenting with gastrointestinal bleeding; however, it has limited detection capability when bleeding is intermittent. This study aimed to evaluate the diagnostic performance of 99m Tc-labeled red blood cell ( 99m Tc-RBC) single-photon emission computed tomography/computed tomography (SPECT/CT) using a full-ring 360º Cadmium-Zinc-Telluride (CZT) camera in patients presenting with overt gastrointestinal bleeding and negative findings on a MDCT. We retrospectively reviewed 65 patients who presented to our hospital with overt gastrointestinal bleeding and negative findings on initial multiphasic MDCT between April 2021 and December 2024. All patients subsequently underwent 99m Tc-RBC SPECT/CT that consisted of initial dynamic planar imaging using a dual-head gamma camera, followed by delayed static SPECT/CT imaging using a full-ring 360º CZT camera. Definitive clinical diagnosis was used as the reference standard, and the diagnostic performance of 99m Tc-RBC SPECT/CT was assessed. Of enrolled 65 patients, 49 (75.4%) were clinically diagnosed with a gastrointestinal bleeding focus. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of 99m Tc-RBC SPECT/CT for detecting gastrointestinal bleeding were 73.5%, 93.8%, 97.3%, 53.6%, and 78.5%, respectively. 99m Tc-RBC SPECT/CT accurately identified bleeding in 21 (80.8%) of 26 patients diagnosed with small bowel bleeding. Additionally, 99m Tc-RBC SPECT/CT successfully detected bleeding from the anastomosis site of prior surgeries in all five patients (100%). In patients with overt gastrointestinal bleeding and negative MDCT findings, 99m Tc-RBC SPECT/CT could be helpful for detecting bleeding sites, particularly in cases with suspected small bowel bleeding or bleeding from an anastomosis site.