Magnetic resonance imaging (MRI) and computerized tomography (CT) scans of 18 patients with 20 chronic subdural hematomas were compared. In many ways, MRI was superior to CT for demonstrating the hematomas. In general, chronic subdural hematomas were hyperintense on both T1- and T2-weighted MRI. The T1 values of chronic subdural hematomas were significantly shorter than gray matter values and significantly longer than white matter values. The T2 values were significantly longer than both gray matter and white matter values. These findings were consistent with previous reports. However, six hematomas (30%) were iso- or hypointense on T1-weighted images. Possible mechanisms responsible for the difference in intensity of chronic subdural hematoma on MRI are discussed, and the important role of methemoglobin formation is emphasized.

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The clinical and radiological findings in a case of brain-stem encephalitis are described with special emphasis on the serial magnetic resonance imaging. This pathological condition should be differentiated from brain-stem tumors, which may present with similar symptoms.

Thirty-two cases of pineal cyst diagnosed by magnetic resonance imaging (MRI) were reviewed and are described. The pineal cyst was demonstrated to be an area with slightly less intensity than the surrounding tissue and with slightly greater intensity than the CSF on T1-weighted images. On the T2-weighted images this lesion was identified as a high-intensity area with smooth margins and was homogeneous in nature. In three cases presenting with headache, compression of the vein of Galen was identified, and compression of the quadrigeminal plate was demonstrated in five cases. No patients presented with both pineal and quadrigeminal lesions. Of the cases, 63% were not detected by CT scanning alone. There were two cases in which the cyst ruptured and collapsed spontaneously during follow-up. It is emphasized that the presence of this lesion, which was more frequent than previously expected, should be kept in mind when diagnosing pineal tumors and should not be misdiagnosed. Surgery should not be undertaken unless the lesion produces symptoms due to the compression of the quadrigeminal plate, aqueduct, or the vein of Galen.

The design and properties of thermal detectors constructed with multiple layers of polyvinylidene fluoride film are described. By use of these detectors, production of heat by the photoreceptors in the darkadapted bullfrog retina in response to brief pulses of very weak light was examined.In response to brief light pulses delivering an average of 1 photon per retinal rod, the retina was found to produce heat more-or-less abruptly after a latent period of 0.2 to 0.4 s. At this level of pulse intensity, the thermal energy produced by the retina was approximately 1,500,000times as large as the total radiant energy delivered to the retina for stimulation. It appears possible that a large number of disks in the rod outer segment are activated by absorption of a single photon.