FDG PET may be useful for differentiating common enhancing malignant brain tumors, particularly lymphoma versus high-grade glioma and metastatic tumor. FDG PET can provide useful information for distinguishing between lymphoma and other malignant enhancing brain tumors and is recommended when differential diagnoses are difficult to narrow using MRI alone.

Purpose To clarify the components primarily responsible for diffusion abnormalities in pancreatic cancerous tissue. Materials and Methods Subjects comprised 10 patients with surgically confirmed pancreatic cancer. Diffusion‐weighted (DW) echo‐planar imaging (b value = 0, 500 s/mm2) was employed to calculate the apparent diffusion coefficient (ADC). ADC values of cancer and noncancerous tissue were calculated. Furthermore, ADC values of the cancer were compared with histopathological results. Results The mean (±standard deviation) ADC value was significantly lower for tumor (1.27 ± 0.52 × 10−3 mm2/s) than for noncancerous tissue (1.90 ± 0.41 × 10−3 mm2/s, P < 0.05). Histopathological examination showed similar proportions of fibrotic area, cellular component, necrosis, and mucin in each case. Regarding the density of fibrosis in cancer, three cases were classified in the loose fibrosis group and the remaining seven cases were classified in the dense fibrosis group. The mean ADC value was significantly higher in the loose fibrosis group (1.88 ± 0.39 × 10−3 mm2/s) than in the dense fibrosis group (1.01 ± 0.29 × 10−3 mm2/s, P < 0.05). In quantitative analysis, ADC correlated well with the proportion of collagenous fibers (r = −0.87, P < 0.05). Conclusion Collagenous fibers may be responsible for diffusion abnormalities in pancreatic cancer. J. Magn. Reson. Imaging 2008;27:1302–1308. © 2008 Wiley‐Liss, Inc.

Anisotropy of water diffusion in axon tracts, as determined by diffusion-weighted MRI, has been assumed to reflect the restriction of water diffusion across axon membranes. Reduction in this anisotropy has been interpreted as degeneration of axons. These interpretations are based primarily on a priori reasoning that has had little empirical validation. We used the experimental advantages of the sea lamprey spinal cord, which contains several very large axons, to determine whether intraaxonal diffusion is isotropic and whether anisotropy is attributable to restriction of water mobility by axon surface membranes. Through the application of magnetic resonance microimaging, we were able to measure the purely intraaxonal diffusion characteristics of the giant reticulospinal axons (20 -40 m in diameter). The intraaxonal apparent diffusion coefficients of water parallel (longitudinal ADC, l-ADC) and perpendicular (transverse ADC, t-ADC) to the long axis were 0.98 ؎ 0.06 (10 ؊3 mm 2 ͞sec) and 0.97 ؎ 0.11 (10 ؊3 mm 2 ͞sec), respectively. In white matter regions that included multiple axons, l-ADCs were almost identical regardless of axon density in the sampled axon tract. By comparison, t-ADCs were reduced and varied inversely with the number of axons (and thus axolemmas) in a fixed cross-sectional area. Thus, diffusion was found to be isotropic when measured entirely within a single axon and anisotropic when measured in regions that included multiple axons. These findings support the hypothesis that the cell membrane is the primary source of diffusion anisotropy in fiber tracts of the central nervous system. MR microimaging ͉ diffusion-weighted imaging ͉ giant axon ͉ intraaxonal apparent diffusion coefficient ͉ axolemma D iffusion-weighted MRI (DWI) techniques have been widely applied in the white matter (WM) for detection of damage to axons (1-4) and more recently for determining the orientation of fiber tracks (5, 6) in the brain and spinal cord. These applications invoke diffusional anisotropy, a larger apparent diffusion coefficient (ADC) in longitudinal (l-ADC) orientation than in transverse (t-ADC) orientation, in the WM (7).Possible causes of the diffusional anisotropy have been subjects of many studies for over a decade (8-10). To date, although these inferences have been derived from simulation and experimental studies, there have been few studies (11,12) in which the diffusion characteristics of axons have been related directly to axonal anatomy or physiology. This is due largely to limitations in spatial resolution of magnetic resonance (MR) compared with histological methods. In short, it has been possible to obtain MR images of relatively large fields of view, which must be related to the small fields of view achieved with high-power microscopy. Bringing the spatial resolution of MR closer to that of microscopy for diffusion studies will improve correlations of ADCs with histological changes.The nervous system of the sea lamprey (Petromyzon marinus) is unmyelinated. In the spinal cord, the Mauthner and Müll...

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The CT appearance of pulmonary sarcoidosis suggests that the large nodules arise from a coalescence of small nodules. The large nodules are surrounded by many tiny satellite nodules. These findings were considered to simulate the appearance of a galaxy. This observation was supported by radiologic-pathologic correlation. The sarcoid galaxy sign may be a useful adjunct in the diagnosis of pulmonary sarcoidosis.