PMID: 2121212Jan 1, 1990Paper

Validity of PET studies in brain tumors

Cerebrovascular and Brain Metabolism Reviews
K HerholzW D Heiss

Abstract

Positron emission tomography (PET) in human brain tumors presents specific problems, such as tissue inhomogeneity and disruption of the blood-brain barrier (BBB), that are not present or at least not that important in normal brain. In addition, tracer metabolism may be different from normal brain. Mathematical arguments demonstrate that quantitation in inhomogeneous tissue is extremely difficult with tracers undergoing reversible metabolism, whereas irreversible metabolic steps can be quantified more easily. Even for metabolically inert tracers with reversible transport across the BBB, physiological identification of transport rate constants may be ambiguous, since diffusion processes within the tissue cannot be differentiated from slow transport components at the BBB. Mathematical analysis shows that transport is usually underestimated, whereas metabolism is usually overestimated in inhomogeneous tumor tissue. For accurate measurements of blood flow and BBB permeability, use of short measurement times is recommended. Measurements of tumor glucose consumption with [18F]2-fluoro-2-deoxy-D-glucose (FDG) are probably only little affected by tumor heterogeneity. There are, however, major problems caused by variation of the lumped c...Continue Reading

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