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Interference of Scalp and Skull with External Measurements of Brain Isotope Content: Part 1. Isotope Content of Scalp and Skull

Wadsworth Hospital, Veterans Administration Center and UCLA Center for the Health Sciences, Los Angeles, California

Correspondence: For reprints contact: W. H. Oldendorf, Wadsworth V.A. Hospital, V.A. Center, Wilshire and Sawtelle Blvds., Los Angeles, Calif. 90073.

ABSTRACT

Tissue volumes and weights of brain, scalp and skull were estimated from postmortem radiography in ten subjects. The isotope distribution in animal tissues for ^99mTc-pertechnetate and ¹³¹I-IHSA were defined as a function of time. The brain isotope concentration was low relative to other tissues. Blood volumes were calculated using ¹²⁵I-IHSA in the animal tissues. The percentage of total cranial counts originating in brain were calculated for a total cranial head counting geometry. Restriction of collimation in total-head counting to exclude the vertex scalp and skull would improve the brain-to-nonbrain tissue count ratio. Isotope data described here suggest an explanation for the "halo" seen on ^99mTc head scans. A difference was shown between calvarial scalp and lumbar skin isotope content for both ^99mTc-pertechnetate and ¹³¹I-IHSA. Brain mechanisms for keeping most "foreign" or externally introduced solutes low in concentration are briefly discussed. The effect of scalp and skull on external counting of a nondiffusible bolus passage is discussed in relation to the first derivative method of measuring brain blood pool transit time. A tracer technique is suggested which would allow correction for the superficially originating count in scalp and skull.