Magnetic resonance imaging (MRI) was used to evaluate 22 histologically proven peripheral nerve sheath tumors, approximately two-thirds of which arose in the lower extremity. The histologic distribution was as follows: 12 schwannomas, 7 neurofibromas, and 3 malignant peripheral nerve sheath tumors (2 of which occurred in patients with neurofibromatosis). Most lesions demonstrated an intermediate to moderately bright signal on T1-weighted images and were minimally inhomogeneous. All lesions were moderately bright on proton-density-weighted images and bright on T2-weighted images, again with variable inhomogeneity. The extent of the tumor was best assessed on proton-density- and T2-weighted images. Smooth margins were noted in 19 lesions. Of the 3 remaining lesions, 2 were malignant (but had been subjected to biopsy prior to MRI), and the other lesion was a plexiform neurofibroma. MRI accurately determined the relationship between the lesion and the adjacent neurovascular structures and muscles, thereby assisting surgical management. On MRI, 5 lesions demonstrated coexistent subtle muscle atrophy along the longitudinal axis of surrounding or distally innervated musculature. This latter finding, together with the presence of a tumor in the vicinity of a large nerve trunk, suggests a peripheral nerve sheath neoplasm.
It is possible to use storage phosphor radiography (SR) devices in a manner that results in excess exposure to the patient without the operators knowledge. Because these SR systems have an automatic correction for the final optical density (OD) of the image, the technologist and radiologist will not be able to use excessive blackness of the image as a sign of overexposure. Tests reported here demonstrate that it is possible to obtain images of a chest phantom that appear acceptable with a 32 times difference in exposure (maximal exposure .86 R). It is possible to obtain exposures of a pelvis phantom that appear acceptable up to the tube limit of our machine (4.8R). Tests of the Fuji AC-i demonstrate that it will accept a much wider range of exposures than the AGFA ADC prototype which permits only a 7 times difference in exposure before The image is degraded.Exposure estimates, based on the dosimetry of the phantom, of the exposures actually used by our technologist when they obtain bedside chest radiographs initially demonstrated a range of estimated exposure of 8.5 TO 289 mR with an average exposure of 33 mR. When the exposure data was evaluated by the exposure techniques used by each individual technologist, the average exposure estimated to be used by each technologist ranged from 10 TO 289 mR, a 29 times difference in exposure. Based on this data, an educational program was commenced. Six months after the conclusion of the educational program, the range of average exposures used by the technologists on bedside chest radiographs varied from 24 to 121 mR, a 5 times range, with a mean of 55 mR. The 5 fold range of variation in exposure of beside chest radiographs is similar to that expected in conventional bedside chest radiographs.
We present two cases of isolated popliteal vein entrapment caused by the lateral head of the gastrocnemius muscle confirmed by both venography and magnetic resonance imaging of the knee.
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