Assessment of [11C]-L-methionine transport into the human brain.
Neutral amino acid transport into human brain was measured using a dual-probe positron detection system or positron emission tomography (PET). Rate constants (ml/min/cc) for brain accumulation of [11C]L-methionine measured with the dual detector ranged from 0.012 to 0.078 (average 0.031) under baseline conditions and from 0.010 to 0.017 (average 0.014) after administration of nonradioactive L-phenylalanine (100 mg/kg). The net rate of brain accumulation of L-methionine ranged from 0.42 to 2.89 (average 1.28) nmol/min/cc, and decreased by 27.5-91.2% (average 53.9%) after L-phenylalanine. PET-estimated accumulation rates (ml/min/cc) of [11C]L-methionine ranged from 0.004 to 0.028 (average 0.016) baseline and from 0.010 to 0.021 (average 0.017) after L-phenylalanine. Initial volumes of distribution (ml/cc) of [11C]L-methionine (dual detector) were 0.044-0.070 (average 0.058) baseline and 0.032-0.074 (average 0.051) after phenylalanine and (PET) 0.026-0.098 (average 0.051) baseline and 0.021-0.061 (average 0.042) after phenylalanine. PET permits more accurate measurement of tracer accumulation by brain, excluding noncerebral regions included in dual-detector measurements. The dual-detector system permits better temporal resolution, facilitating kinetic analysis, and requires only one-fortieth the dose of tracer needed for PET. Multiple studies in the same patient are thus possible at low cost.
O'Tuama
L A
LA
Division of Nuclear Medicine, Johns Hopkins Medical Institutions, Baltimore, MD 21205-2179.
Guilarte
T R
TR
Douglass
K H
KH
Wagner
H N
HN
Wong
D F
DF
Dannals
R F
RF
Ravert
H T
HT
Wilson
A A
AA
LaFrance
N D
ND
Bice
A N
AN
D001692:Biological Transport; D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism*; D002250:Carbon Radioisotopes; D006801:Humans; D008715:Methionine / Q000097:blood / Q000378:metabolism*; D008959:Models, Neurological; D010649:Phenylalanine / Q000494:pharmacology; D014055:Tomography, Emission-Computed
D002250:Carbon Radioisotopes; D010649:Phenylalanine; D008715:Methionine