S.M. Larson

MR imaging and positron emission tomography of cortical heterotopia

Heterotopia of the gray matter is a developmental malformation in which ectopic cortex is found in the white matter of the brain. A case of a 33-year-old man with cortical heterotopia who had a lifelong history of seizures and psychomotor retardation is reported, including the results of cerebral CT, magnetic resonance imaging, and positron emission tomography using 18F-2-deoxyglucose.

Human Cerebral Glucose Metabolism Determined by Positron Emission Tomography: A Revisit:

The cerebral glucose utilization rate was studied for 27 normal volunteers with 18F-deoxyglucose positron emission tomography (PET). The scanner has a spatial resolution of 6–7 mm and contains corrections for scatter, attenuation, and random coincidences. The lumped constant (tracer-to-glucose dynamic uptake ratio) was determined by comparing the average global uptake of tracer in representative slices with average glucose utilization rates measured by the Kety-Schmidt method as reported in the literature. The resulting value of 0.50 is in excellent agreement with a recent direct determination done by arterial and jugular bulb blood sampling. Gray and white matter values of glucose utilization in various areas of the brain were determined by placing small regions of interest over various cortical, basal, and white matter structures. These values are within 20% of published autoradiographic data on the macaque monkey. The average ratio of gray to white glucose utilization was 2.9, compared with a range of 3–5 for the monkey study and 1.6–2.2 reported in previous PET studies. The effect of instrumental errors on the results is analyzed and discussed.

Descent of Cerebrospinal Fluid to Spinal Subarachnoid Space

Scintigraphy has been used extensively to investigate the bulk flow of the cerebrospinal fluid (CSF) in human beings (DI CHIRO & ASHBURN 1971, DI CHIRO et call. 1964, HARBERT et call. 1972, KIEFFER et call. 1971). External scintillation scans of the head performed at various time intervals after the intraventricular or intrathecal introduction of different isotopes, have proven beyond any doubt the existence of an active ascending transport of the injected tracer toward the hemispheric cerebral convexities (DI CHIRO 1964, 1966). The descending path of the CSF to the spinal subarachnoid space, on the other hand, has been only briefly commented upon, mostly in reference to isotope ventriculography in abnormal conditions (DI CHIRO 1966, LARSON et coll. 1972, MILHORAT & HAMMOCK 1971). This report deals with the downward progression in the spinal subarachnoid space of isotopes injected into the ventricular system, or the basal cisterns, of normal Rhesus monkeys.