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Radionuclide Evaluation of the Lower Gastrointestinal Tract^*

¹ Regional Center of Nuclear Medicine, University of Pisa Medical School, Pisa, Italy; ² Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands; ³ Gastroenterology Unit, Department of Internal Medicine, University of Pisa Medical School, Pisa, Italy; ⁴ Fourth Division of General Surgery, "S. Chiara" University Hospital, Pisa, Italy; ⁵ PET Center, Nuclear Medicine Service, "S. Maria della Misericordia" Hospital, Rovigo, Italy; and ⁶ Division of Nuclear Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York

View larger version (24K): [in this window] [in a new window]   FIGURE 1.  Diagrammatic representation of geometric center approach for estimating colonic transit time. According to Temple University protocol, colon is subdivided into 6 regions with weighting factors increasing from 1 to 6 proximally to distally (cecum and ascending colon to rectosigmoid). Highest weighting factor (7) is assigned to radioactivity unaccounted for in images, which is therefore assumed to have been evacuated in stools. Each black dot represents 1% (or 0.01 fraction) of radioactivity that has reached colon. Examples of calculation are given in inserts for 2 different geometric centers, 2.50 on left and 5.62 on right. In actual colonic transit study performed on healthy individual, most radioactivity would be seen in transverse colon at 24 h (geometric center, approximately 3), progressing to descending colon at 48 h (geometric center, about 5), and being mostly evacuated at 72 h (geometric center, about 6–7). In patient with colonic inertia, radioactivity would not significantly progress past hepatic flexure at 48 h or at 72 h (geometric centers, about 1.5–2 and 2–3, respectively). In patient with functional rectosigmoid obstruction, progression of radioactivity would be nearly normal until 48 h after ingestion, combined however with little further progression at 72 h (geometric center, about 5–6), thus indicating obstructed defecation.

View larger version (34K): [in this window] [in a new window]   FIGURE 2.  (A) Sequential static 5-min images of abdominal area recorded at various times after 99mTc-RBC injection. Abnormal accumulation of radioactivity is obvious already in early images (elongated horizontal area in upper abdominal region). Although accumulation of radioactivity increases with time, no obvious progression along intestinal tract is detectable. Localization of bleeding site is equivocal in planar images, being possibly consistent either with transverse colon or with duodenal localization. (B) SPECT/CT images after 99mTc-RBC injection demonstrate that radioactivity accumulation is not localized in anterior abdominal area (as transverse colon would be) but rather in mid region, thus indicating duodenal localization of bleeding. (Courtesy of Dr. Elena Lazzeri, Regional Center of Nuclear Medicine, University of Pisa Medical School, Pisa, Italy.)

View larger version (74K): [in this window] [in a new window]   FIGURE 3.  Bleeding scintigraphy performed on 82-y-old man whose presenting symptom was intermittent bright rectal bleeding. (A) Early dynamic imaging sequence after intravenous administration of 99mTc-RBCs (each frame is summed image of 5-min sequence) shows no definite area of abnormal radioactivity accumulation. (B) Later dynamic sequence starting 60 min after injection of 99mTc-RBCs clearly shows abnormal accumulation of radioactivity initiating in proximal descending colon and extending to whole descending colon, as also confirmed by subsequent SPECT (image not shown).

View larger version (91K): [in this window] [in a new window]   FIGURE 4.  Meckel's diverticulum scintigraphy performed on 2-y-old boy with intermittent bleeding (bright red blood) and no other accompanying symptom. Sequential images obtained after injection of 99mTc-pertechnetate show obvious accumulation of radioactivity in right lower paraumbilical region, consistent with most frequent location of Meckel's diverticulum. Time-course pattern of radioactivity accumulation in possible Meckel's diverticulum mirrors pattern of tracer concentration in gastric region. Diagnosis of Meckel's diverticulum was confirmed at surgery, which was followed by complete disappearance of gastrointestinal bleeding. (Courtesy of Drs. Pham Thi Minh Bao and Le Ngoc Ha, Department of Nuclear Medicine, Tran Hung Dao General Hospital, Hanoi, Vietnam.)

View larger version (158K): [in this window] [in a new window]   FIGURE 5.  Planar imaging of abdomen performed on patient with active Crohn's disease approximately 45 min after injection of autologous 99mTc-HMPAO–labeled leukocytes. Accumulation of radioactivity is obvious in section of small bowel that can be identified as preterminal ileum.

View larger version (25K): [in this window] [in a new window]   FIGURE 6.  Planar imaging (A) and SPECT/CT (B) performed on patient with active Crohn's disease approximately 45–90 min after injection of autologous 99mTc-HMPAO–labeled leukocytes. Obvious accumulation of radioactivity in terminal ileum is seen on planar imaging. However, SPECT/CT also demonstrates IBD involvement of preterminal ileum, which was obscured on planar imaging because of superimposition with circulating blood pool and with accumulation in underlying bone marrow. (Courtesy of Dr. Paola A. Erba, Regional Center of Nuclear Medicine, University of Pisa Medical School, Pisa, Italy).

View larger version (55K): [in this window] [in a new window]   FIGURE 7.  18F-FDG PET/CT performed on patient with active Crohn's disease. Both transaxial sections (A) and coronal sections (B) show focally increased tracer uptake in region easily identified on CT images as section of small bowel (with increased thickness of intestinal wall), clearly distinct from tracer accumulation in urinary excretory routes. Standardized uptake value of small-bowel segment with highest radioactivity accumulation was 10.4 in this patient. (Courtesy of Dr. Paola A. Erba, Regional Center of Nuclear Medicine, University of Pisa Medical School, Pisa, Italy.)