Atlas of ^99mTc-RBC scan for gastrointestinal bleeding with emphasis on SPECT/CT imaging: A case series

Diagnosing gastrointestinal bleeding (GIB) can be especially difficult when endoscopic evaluation do not reveal a clear source. In this report, we describe 20 patients with suspected GIB in whom initial evaluations were inconclusive. All underwent dynamic planar ^99mTc-RBC scintigraphy followed by SPECT/CT imaging. This combination proved valuable in either identifying active bleeding sites or clarifying non-bleeding causes of tracer accumulation. The added anatomical detail from SPECT/CT helped distinguish true bleeding from normal physiological activity, vascular landmarks, or postoperative alterations-areas where planar imaging is not enough. In some patients, imperfect red blood cell labeling introduced challenges in image interpretation, occasionally mimicking bleeding. Even so, the fusion of functional and anatomical data improved diagnostic clarity in most cases. This series emphasizes how hybrid nuclear imaging can provide critical insight when other diagnostic methods fail, enabling more accurate localization and better-informed clinical decisions. Our experience supports the broader use of SPECT/CT in evaluating complex or obscure GIB, offering clinicians a noninvasive yet highly informative diagnostic option.