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The value of positron emission tomography (PET) and magnetic resonance (MR) imaging in differentiating recurrent rectal cancer and scar was investigated. PET with fluorine-18 2-fluoro-2-deoxy-D-glucose (FDG) and MR imaging were performed in 15 patients with suspected recurrence. FDG accumulation in the mass was measured by means of the differential absorption ratio (DAR). All 11 patients with confirmed recurrent rectal cancer had increased accumulation of FDG in the mass (DAR = 4.73 +/- 2.28). Low FDG accumulation in the mass (DAR = 0.97 +/- 0.15) was noted in the remaining four patients, in whom the presence of a scar was proved by means of follow-up observation with or without biopsy. On the MR images, the recurrent tumor could be differentiated from scar in all but one case. The lesion-muscle signal intensity ratios on the T2-weighted images for the recurrent tumor and scar were 2.18 +/- 0.55 and 0.89 +/- 0.30, respectively. PET and MR imaging complement each other in the differential diagnosis between recurrent rectal cancer and scar. PET may also permit the evaluation of the effect of therapy.

We compared the efficacies of 18 F-FDG PET and 99m Tc-bone scintigraphy for the detection of bone metastases in patients with differentiated thyroid carcinoma (DTC). Methods: We examined 47 patients (32 women, 15 men; mean age 6 SD, 57.0 6 10.7 y) with DTC who had undergone total thyroidectomy and were hospitalized to be given 131 I therapy. All patients underwent both whole-body 18 F-FDG PET and 99m Tc-bone scintigraphy. The skeletal system was classified into 11 anatomic segments and assessed for the presence of bone metastases. Bone metastases were verified either when positive findings were obtained on .2 imaging modalities-201 Tl scintigraphy, 131 I scintigraphy, and CT-or when MRI findings were positive if vertebral MRI was performed. Results: Bone metastases were confirmed in 59 of 517 (11%) segments in 18 (38%) of the 47 study patients. The sensitivities (visualization rate) for bone metastases on a segment basis using 18 F-FDG PET and 99m Tcbone scintigraphy were 50 of 59 (84.7%) and 46 of 59 (78.0%), respectively; the difference between these values was not statistically significant. There were only 2 (0.4%) false-positive cases in a total of 451 bone segments without bone metastases when examined by 18 F-FDG PET, whereas 39 (8.6%) were falsepositive when examined by 99m Tc-bone scintigraphy. Therefore, the specificities of 18 F-FDG PET and 99m Tc-bone scintigraphy were 449 of 451 (99.6%) and 412 of 451 (91.4%), respectively; the difference between these values was statistically significant (P , 0.001). The overall accuracies of 18 F-FDG PET and 99m Tcbone scintigraphy were 499 of 510 (97.8%) and 458 of 510 (89.8%), respectively; the difference between these was also statistically significant (P , 0.001). Conclusion: The specificity and the overall accuracy of 18 F-FDG PET for the diagnosis of bone metastases in patients with DTC are higher than those of 99m Tc-bone scintigraphy, whereas the difference in the sensitivities of both modalities is not statistically significant. In comparison with 99m Tc-bone scintigraphy, 18 F-FDG PET is superior because of its lower incidence of false-positive results in the detection of bone metastases of DTC. Skel etal imaging by 18 F-FDG PET has been shown to be useful in the detection of bone metastases of breast (1-6), lung (1,4,7,8), thyroid (4), esophageal (4,9), gastric (4), colorectal (4), endemic nasopharyngeal (10), renal cell (11), prostate (1), ovarian (4), and testicular (4) carcinomas. In most of these studies, 18 F-FDG PET was proven to be superior to conventional scintigraphic imaging using 99m Tclabeled phosphate compounds ( 99m Tc-methylene diphosphonate [ 99m Tc-MDP] or 99m Tc-hydroxymethylene diphosphonate [ 99m Tc-HMDP]). For the detection and evaluation of bone metastases of various kinds of carcinomas, 99m Tc-bone scintigraphy has been used widely because of its overall high sensitivity and the easy evaluation of the entire skeleton (12). However, 99m Tc-bone scintigraphy leads often to falsepositive lesions and, consequently, its specificity is r...

Little is known about how ischemia affects hemodynamic responses to neural activation in the brain. We compare the effects of a motor activation task and a cerebral vasodilating agent, acetazolamide (ACZ), on regional cerebral blood flow (rCBF) in primary sensorimotor cortex (PSM) in six patients with major cerebral artery steno-occlusive lesions without paresis of the upper extremities. Quantitative rCBF was measured in all patients using H2(15)O autoradiographic method and positron emission tomography. The CBF was determined at rest, during a bimanual motor activation task, and 10 minutes after ACZ administration. With bimanual motor activation, rCBF increased significantly in both PSM compared with at rest (P < 0.01 on lesion side, and P < 0.02 on contralateral side). However, rCBF did not increase after ACZ injection in the PSM on the lesion side, whereas rCBF increased significantly in the contralateral PSM after ACZ injection compared with the level at rest. This result suggests that despite a decreased hemodynamic reserve, there is a nearly normal flow response to neural activation, indicating that the mechanism of vasodilation responsible for perfusion change is different for acetazolamide and neural activation. The relations among neural activation, hemodynamic status, and cerebral metabolism in the ischemic stroke patients are discussed.

Background and Purpose-In major cerebral arterial steno-occlusive diseases, there can be remarkably decreased hemodynamic reserve without marked neurological impairments. In such settings, it is not known whether the neural activity is well maintained or disturbed according to the severity of cerebral ischemia. The present study was therefore undertaken to examine the neural activity under mild cerebral ischemia resulting from major cerebral arterial occlusion. Methods-Seven patients with minor neurological impairment as well as either unilateral internal carotid artery or middle cerebral artery occlusion were studied. The severity of the cortical ischemia was assessed by measuring regional cerebral blood flow (rCBF) with positron emission tomography. The change in neural activity in the ischemic brain was then evaluated by means of somatosensory evoked magnetic field with magnetoencephalography. Results-The