Reproducibility of the whole-brain N-acetylaspartate level across institutions, MR scanners, and field strengths.
OBJECTIVE
Radiologic markers in multicenter trials are often confounded by different instrumentation used. Our goal was to estimate the variance of the global concentration of the neuronal cell marker N-acetylaspartate (NAA) among research centers using MR imaging scanners of different models, from different manufacturers, and of different magnetic field strength.


METHODS
Absolute millimolar amounts of whole-brain NAA (WBNAA) were quantified with nonlocalizing proton MR spectroscopy in the brains of 101 healthy subjects (53 women, 48 men) aged 16-59 years (mean, 34.2 years). Twenty-three were scanned at 1 institute in a 1.5T Siemens Vision; 31 from another institute were studied with a 1.5T Siemens SP63; 36 were scanned at a third institute (24 with a 1.5T Vision, 12 with a 3T Siemens Trio); and 11 were obtained at a fourth institute using a 4T GE Signa 5.x. The NAA amounts were quantified with phantom-replacement and divided by the brain volume, segmented from MR imaging, to yield the concentration, a metric independent of brain size suitable for cross-sectional comparison.


RESULTS
The average WBNAA concentration among institutions was 12.2 +/- 1.2 mmol/L. The subjects' WBNAA distributions did not differ significantly (p > .237) among the 4 centers, regardless of scanner manufacturer, model, or field strength and irrespective of whether adjustments were made for age or sex.


CONCLUSIONS
Absolute quantification against a standard makes the WBNAA concentration insensitive to the MR hardware used to acquire it. This important attribute renders it a robust surrogate marker for multicenter neurologic trials.
Benedetti
B
B
Department of Radiology, New York University School of Medicine, New York, New York 10016, USA.
Rigotti
D J
DJ
Liu
S
S
Filippi
M
M
Grossman
R I
RI
Gonen
O
O
D000293:Adolescent; D000328:Adult; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000032:analysis; D001921:Brain / Q000473:pathology*; D015331:Cohort Studies; D004867:Equipment Design; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D009682:Magnetic Resonance Spectroscopy / Q000295:instrumentation*; D008297:Male; D008875:Middle Aged; D012015:Reference Standards; D015203:Reproducibility of Results
D001224:Aspartic Acid; C000179:N-acetylaspartate