G Currie, J Wheat
lgih, rbc, subtraction scintigraphy
G Currie, J Wheat. Confirmation Of A Gastrointestinal Bleed Detected On Subtraction Scintigraphy: Case Studies. The Internet Journal of Nuclear Medicine. 2006 Volume 3 Number 2.
This article reports the role of subtraction techniques in two interesting cases of lower gastrointestinal haemorrhage (LGIH) using 99mTc red blood cell (RBC) scintigraphy.
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
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.
The dynamic data for the 82 year old male demonstrated marked 99mTc RBC accumulation centrally in the lower abdomen suggestive of a small bowel bleed (Fig. 3). Superimposition of the bleed on blood vessels obscures the bleed origin (Fig. 4). While not particularly problematic in this patient, an obscured bleed site may delay detection and result in less accurate localisation; hindering successful management. Subtraction scintigraphy was used to further evaluate the data. Using ASSS (Fig. 4) allowed convincing evidence of the bleed origin.
These cases highlight the interpretation difficulties associated with 99mTc RBC scintigraphic evaluation of LGIH. The high background activity of 99mTc RBCs and the normal biodistribution in vascular structures confounds interpretation on occasion which may result in either false positive or false negative findings. Subtraction scintigraphy offers an interpretive aid that combines the high contrast of 99mTc sulphur colloid imaging in LGIH with the extended time for imaging using 99mTc RBCs. These cases highlight the potential role of subtraction scintigraphy in aiding conventional scintigraphy for earlier bleed detection and more accurate bleed localisation.
Geoff Currie School of Clinical Sciences Locked Bag 588 Charles Sturt University Wagga Wagga 2678 Australia Telephone: 61 2 69332822 Facsimile: 61 2 69332866 Email: email@example.com