Improved Detection and Localization of Lower Gastrointestinal Hemorrhage Using Subtraction Scintigraphy: Clinical Evaluation

Abstract

Does subtraction scintigraphy improve the diagnostic utility of scintigraphic evaluation in acute lower gastrointestinal hemorrhage? Methods: This research was a retrospective clinical study using a repeat-measures design of randomized control and experimental groups. A single patient dataset provided both the control group (conventional scintigraphy) and the experimental group (conventional and subtraction techniques). Forty-nine raw 99m Tc-red blood cell studies were randomized and interpreted by 4 independent physicians as conventional scintigraphy data only (round 1). The conventional scintigraphy studies were combined with subtraction images and randomized for reinterpretation (round 2). Results: Although there was a decrease in the mean, no statistically significant difference was noted between the mean time to bleed detection between interpretive rounds 1 and 2 (P 5 0.524). The addition of subtraction scintigraphy to the interpretation process changed the outcome from ''probably present'' to ''absent'' for 14% of patients and from ''equivocal'' to ''absent'' for another 12%, and this change had a marked effect on the false-positive rate. The false-positive rate decreased from 9.6% in round 1 to 3.6% in round 2. Receiver operator characteristic analysis showed that combining conventional scintigraphy with subtraction scintigraphy improved test performance. Conclusion: False-positive studies can be reduced by using subtraction scintigraphy in conjunction with conventional scintigraphy in the interpretive process.

The SNMMI Procedure Standard/EANM Practice Guideline for Gastrointestinal Bleeding Scintigraphy 2.0

“…Since intraluminal blood promotes rapid bowel peristalsis and movement of blood antegrade or retrograde from the bleeding site, faster frame rates such as 1 frame per 10-20 s allow for higher temporal resolution to better localize the gastrointestinal bleeding site (51). On the other hand, a small volume of intraluminal blood or slow gastrointestinal bleeding may be more difficult to detect when fast frame rates are used because of lower count densities (51).…”

“…On the other hand, a small volume of intraluminal blood or slow gastrointestinal bleeding may be more difficult to detect when fast frame rates are used because of lower count densities (51). This shortcoming can be compensated by reformatting the acquired study into longer frames (51,52). Therefore, reformatting is recommended when using fast frame rates.…”

“…Computer subtraction of background activity of early images from later frames in the imaging sequence has the following limitations: the patient must remain still during the examination or motion correction software must be applied, and the biodistribution of the 99m Tc-RBCs should be similar between the early frames and any image to be subtracted (51,(58)(59)(60)(61)(62). Failure to control these factors can cause false-positive findings.…”

Cost-Effectiveness Analysis of Subtraction Scintigraphy in Patients with Acute Lower Gastrointestinal Tract Hemorrhage

“…Subtraction scintigraphy has been used in the evaluation of acute LGIH (5). Subtraction scintigraphy should allow the elimination of background activity, providing high target-tobackground images of the extravasated blood.…”

“…Subtraction scintigraphy should allow the elimination of background activity, providing high target-tobackground images of the extravasated blood. In short, a dataset that theoretically offers the advantages of both conventional 99m Tc-sulfur colloid scintigraphy and 99m Tclabeled RBC scintigraphy is produced (5).…”