COMPARISON OF THE PRECISION OF 2 STANDARDIZED COORDINATE SYSTEMS FOR THE QUANTITATION OF BRAIN ANATOMY - PRELIMINARY-RESULTS

We assessed reproducible definition of two standardized co-ordinate sy stems for intersubject analysis of brain images. The baselines in the two co-ordinate systems were a modification of the canthomeatal (mCM) line and the anterior-posterior commissural (AC-PC) line. Axial spin-e cho MR images of four subjects at 1.5T were used. Operator error was c omputed from the replicate analyses of two operators. The mCM line was determined by the lens of the eye and the inter nai auditory canal, a nd the AC-PC line was determined by the intersection of the AC and PC with the interhemispheric fissure. Reproducibility of the mCM markers (SD = 0.59 mm) did not differ significantly from that of the AC-PC lin e (SD = 0.68 mm). The measurement error of the angle of the baseline ( delta alpha), however, was more than 7 times as large for the AC-PC li ne as for the mCM line. An additional error affecting the rostrocaudal rotation of the co-ordinate systems, attributable to the distance bet ween the anatomic markers, was 2.1 and 3.6 degrees (3 mm and 5 mm slic e thickness) for the mCM co-ordinate system and 8.2 and 11.0 degrees ( 3 mm and 5 mm slice thickness) for the AC-PC system. The AC-PC line ba sed co-ordinate system is therefore, less reproducible than the mCM li ne based system. This could be improved if a combination of axial and sagittal images were used for the definition of the AC-PC line.