Estimated mean ± SD NAA concentrations at each institution.
| Institution | Subjects | Scanner Field, Manufacturer, Model | Mean WBNAA (mmol/L) | SD (Unadjusted) (mmol/L) | SD (adjusted) |
|---|---|---|---|---|---|
| First | n = 23 | 1.5 T, Siemens, Vision | 11.7 | 1.3 | 1.3 |
| Second | n = 31 | 1.5 T, Siemens, SP63 | 12.3 | 1.1 | 1.1 |
| Third | n = 24 | 1.5 T, Siemens, Vision | 12.6 | 1.2 | 1.2 |
| n = 12 | 3.0 T, Siemens, Trio | 11.7 | 1.1 | 1.1 | |
| Fourth | n = 11 | 4.0 T, GE, Signa 5.x | 12.8 | 1.5 | 1.5 |
| Total | n = 101 | 12.2* | 1.2* | 1.2 |
Note:—WBNAA indicates whole-brain N-acetylaspartate. The SDs are presented as both unadjusted and adjusted with respect to confounding effects from age and gender (differences were in second decimal digit or smaller).
* Average of all subjects at all institutions.