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

## TL;DR

This paper presents a case series showing how combining 99mTc-RBC scans with SPECT/CT improves diagnosis of unclear gastrointestinal bleeding.

## Contribution

The study highlights the added diagnostic value of SPECT/CT in complex gastrointestinal bleeding cases.

## Key findings

- SPECT/CT imaging improved identification of active bleeding or non-bleeding causes of tracer accumulation.
- Hybrid imaging provided better diagnostic clarity compared to planar imaging alone.
- Imperfect red blood cell labeling occasionally caused misinterpretation but was mostly overcome with SPECT/CT.

## Abstract

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.