Volumetric assessment of cerebral asymmetry from CT scans

The advent of computed tomography (CT) of the brain has facilitated the study of brain asymmetries in normal individuals and in patients with various diseases. A computerized volumetric approach to quantifying CT scan data is used to demonstrate that imperfect alignment of the subject's head in the CT scanner can be a major source of artifact in the assessment of cerebral asymmetry. An approach for estimating the extent of misalignment of the head in the scanner is described. This approach can be used to take variations in head alignment into account when studying cerebral asymmetries. When volumetric measures were used, left-handed subjects (n = 5) were found to have a significantly lower left/right ratio of total cerebral hemispheric tissue than right-handed subjects (n = 41). The amount of asymmetry in the lateral ventricles was found to depend on their total size. A method for controlling for the effect of size when measuring asymmetry of the lateral ventricles is described. In both right- and left-handed subjects, the left lateral ventricles were significantly larger than the right. A magnetic resonance (MR) scan was performed with standard alignment and with a deliberate 10 degrees misalignment, using a volunteer subject. These data are presented to demonstrate how artifactual cerebral asymmetries can be generated by head tilt and to test the quantification procedures developed.