Confirmation Of A Gastrointestinal Bleed Detected On Subtraction Scintigraphy: Case Studies

摘要

This article reports the role of subtraction techniques in two interesting cases of lower gastrointestinal haemorrhage (LGIH) using 99mTc red blood cell (RBC) scintigraphy. Introduction An 82 year old male and an 84 year old female independently presented for evaluation of suspected LGIH with 99mTc RBC scintigraphy. Acquisition parameters included a 128x128 matrix continuous dynamic acquisition over 60 minutes at 60 seconds per frame. A rapid 3 second blood flow dynamic preceded the 60 second dynamic. The study was performed using an in vitro 99mTc RBC label using a commercially available kit preparation. Blood pool data was displayed and interpreted as conventional 60 second frames and after summation to five minute frames. Findings The dynamic data for the 84 year old female demonstrated marked 99mTc RBC accumulation in the region of the stomach suggestive of an upper gastrointestinal haemorrhage (UGIH) (Fig. 1). Diffuse stomach activity, however, may be associated with 99mTc RBC breakdown with free pertechnetate demonstrating a similar gradual accumulation over time. The overlying vascular structure limits evidence of bleed transit on conventional scintigraphy (Fig. 2). Subtraction scintigraphy was used to further evaluate the data. Using alternate sequential subtraction scintigraphy (ASSS) (1), a new data set was created by replacing each frame in the dynamic sequence (f) with the result of subtracting each previous frame (f-1) from each subsequent frame (f+1). The resulting images represent altered biodistribution in the period between the two frames. Thus, a bleed should appear as an area of increased accumulation of the radiotracer. The ASSS study (Fig. 2) provides convincing evidence of activity transit in the duodenum providing confirmation of an UGIH.