Validity of PET studies in brain tumors
- Max-Planck-Institut fuer Neurologische Forschung, Koeln (Germany, F.R.)
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 constant, which relates the kinetics of FDG to those of glucose. Most experimental data indicate a considerable increase of the lumped constant in malignant tumors, resulting in overestimation of glucose metabolism if the standard value is used. In spite of these limitations, measurements of glucose metabolism with FDG are useful clinically to evaluate the prognosis of patients with brain tumors and to differentiate between late radiation necrosis and recurrent tumor. New tracers for measurement of protein synthesis, cell proliferation, and uptake of cytostatic drugs are of high clinical interest. 154 refs.
- OSTI ID:
- 6273979
- Journal Information:
- Cerebrovascular and Brain Metabolism Reviews; (USA), Journal Name: Cerebrovascular and Brain Metabolism Reviews; (USA) Vol. 2:3; ISSN 1040-8827; ISSN CEMRE
- Country of Publication:
- United States
- Language:
- English
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62 RADIOLOGY AND NUCLEAR MEDICINE
ACCURACY
ALDEHYDES
ANIMALS
BETA DECAY RADIOISOTOPES
BETA-PLUS DECAY RADIOISOTOPES
BLOOD FLOW
BLOOD-BRAIN BARRIER
BODY
BRAIN
CARBOHYDRATES
CENTRAL NERVOUS SYSTEM
COMPUTERIZED TOMOGRAPHY
DIAGNOSIS
DIAGNOSTIC TECHNIQUES
DISEASES
EMISSION COMPUTED TOMOGRAPHY
FLUORINE 18
FLUORINE ISOTOPES
GLUCOSE
HEXOSES
HOURS LIVING RADIOISOTOPES
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
LIGHT NUCLEI
MAMMALS
MAN
MEMBRANE TRANSPORT
METABOLISM
MONOSACCHARIDES
NEOPLASMS
NERVOUS SYSTEM
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANS
PERMEABILITY
POSITRON COMPUTED TOMOGRAPHY
PRIMATES
RADIOISOTOPES
SACCHARIDES
TOMOGRAPHY
VERTEBRATES