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OBJECTIVE: There is disagreement over the reliability of technetium Tc 99m (99mTc)-labeled erythrocyte scintigraphy in the localization of active lower gastrointestinal hemorrhage. A previous study at The New York Hospital-Cornell Medical Center that showed a superior sensitivity for localization of scintigraphy versus angiography in surgical patients led the authors to emphasize scintigraphy as the diagnostic test of first choice in the clinical diagnostic algorithm. The authors hypothesized that tagged erythrocyte scintigraphy can be used accurately as the primary diagnostic modality in localizing acute bleeding and guiding surgical intervention. METHODS: The authors conducted a 5-year, retrospective analysis of 224 inpatients who underwent scintigraphic imaging for diagnosis and localization of active lower gastrointestinal bleeding. Using scintigraphy as the primary diagnostic test, with colonoscopy, upper endoscopy, and angiography as adjunctive studies, 99mTc-labeled erythrocyte scans were performed at the clinician's discretion and were reviewed again for study purposes by two nuclear radiologists who were blinded to clinical outcome. Adjunctive diagnostic tests also were ordered for clinical indications. RESULTS: Using delayed periodic scintigraphic imaging, results of 115 scans (51.3%) demonstrated bleeding, with 96 scans (42.9%) localizing to a specific anatomic site. Patients with positive scans were five times more likely to require surgery (p < 0.005) than patients with negative scans, and surgical patients were twice as likely to localize by scintigraphy (p < 0.0001). Fifty patients (22.3%) required surgical intervention to control hemorrhage and had a bleeding site confirmed by both clinical and pathologic examinations. Forty-eight of those patients (96%) had a bleeding site determined preoperatively. For 37 patients with bleeding sites localized preoperatively by scintigraphy, 36 (97.3%) had correct localization based on surgical pathology. Only one patient required a subtotal colectomy solely because of nonlocalized bleeding. No patient bled postoperatively, and there was no mortality in either operated or nonoperated patients. The mean volume of transfused erythrocytes was similar in both scan-localized and nonlocalized surgical patients. CONCLUSION: When performed correctly and interpreted conservatively, scintigraphy is a useful and safe means of guiding segmental resection, and should be the primary tool used in the diagnosis of patients with active lower gastrointestinal bleeding.

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Although magnetic resonance imaging (MRI) is a valuable aid in the initial diagnosis of multiple sclerosis (MS), quantitatively MRI has been disappointing in staging and evaluating therapy protocols by means of serial examinations. In this study, image processing algorithms were developed for the global analysis of MR images of the cerebrum. Limited three-dimensional segmentation was achieved through histogram analysis by these algorithms, which are essentially operator independent. The effects of coil response and tip angles, patient positioning, and interslice gap thicknesses were examined for 10 MS patients with repeated examinations for a total of 72 images. Effects of technique and instrumentation errors were approximately 6%, and agreement between two independent operators for measuring the total MR pixel sum from periventricular effusions and intense MS plaques was better than 97% with a standard deviation of 2.9%.

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Three patients, two of whom had histories of episodic hepatic encephalopathy, were shown by magnetic resonance imaging (MRI) to have occult spontaneous portosystemic shunts. The multiplanar imaging capabilities of MRI provided an optimal, noninvasive method of visualization of collateral anatomy in each case.

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In a patient with primary amyloidosis, we compared T2 values and relative signal intensity ratios of involved organs to those of normal patients. T2 was significantly decreased in the spleen and adrenals, while significantly increased in the pancreas. T2 values were insignificantly changed in the liver, subcutaneous fat, bone marrow, or kidney. Ratios may facilitate detection of relative changes in T2 values.

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The MR images and CT scans of 14 patients with surgically verified pyogenic cerebral abscesses were reviewed. The MR findings correlated well with those seen on CT and were believed to be sufficiently characteristic to allow early and accurate diagnosis with MR alone. These features include (1) peripheral edema producing mild hypointensity on short TR/short TE and marked hyperintensity on long TR/intermediate to long TE scans; (2) central necrosis with abscess fluid hypointense relative to white matter and hyperintense relative to CSF on short TR/short TE scans and hyperintense relative to gray matter on long TR/intermediate to long TE scans (the fluid had concentric zones of varying intensity in seven cases, a finding not previously identified in other lesions); (3) extraparenchymal spread (intraventricular or subarachnoid), which was detected more easily on MR than on CT and was manifested by increased intensity relative to normal CSF on both short TR/short TE and long TR/intermediate TE scans; and (4) visualization of the abscess capsule, which was iso- to mildly hyperintense relative to brain on short TR/short TE scans and iso- to hypointense relative to white matter on long TR/intermediate to long TE scans. On the long TR scans, the relative hypointensity of the rim allowed for visualization of the typical morphologic features of the capsule, which in turn aided in differentiation of abscesses from other lesions (as it does on CT). To investigate the cause of the capsular intensity, pathologic studies of the capsules were reviewed when available (10 cases). Fibrosis was identified in all mature abscess capsules, but the combination of the intensities seen on short TR/short TE and long TR/intermediate to long TE scans as well as the temporal changes in intensity were believed to be incompatible with fibrosis as a cause of the capsular changes. Intensity patterns were suggestive of hemorrhage, but neither acute nor chronic hemorrhage was identified on routine H and E stains, while iron stain revealed scant hemorrhage in only two of the eight patients in whom these stains were used. We believe the capsular intensity (in particular the hypointense rims on long TR scans) may reflect paramagnetic T1, and to a greater extent T2, shortening, possibly due to the presence of heterogeneously distributed free radicals that are products of the respiratory burst produced by actively phagocytosing macrophages in the capsule wall. Distinctive MR features of pyogenic abscesses should afford early and accurate diagnosis.

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