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Interference of Scalp and Skull with External Measurements of Brain Isotope Content: Part 2. Absorption by Skull of Gamma Radiation Originating in Brain

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

The broad-beam absorption of thick and thin wet human skull regions was measured. Isotope sources producing a range of photon energies were used. The absorption of gamma radiation rises sharply below about 100 keV. The radiation of ¹³³Xe is 20–30% absorbed and of ¹²⁵I is 60–80% absorbed. In external measurements of brain in which scalp contains isotope, skull absorption should be considered, particularly when counting photons less than 100 keV.