A computerized technique for the display and comparison of regional cerebral blood flow data

A technique is described by which the sizes, shape and orientation of the brain with respect to detector positioning can be reproduced by computerized simulation. Head size is estimated from the distance between the external acoustic meatus (EAM) and the outer canthus and head shape is determined from the length and height of the skull. These values are used to magnify and alter the shape of a standard brain outline to comply with individual patient measurements. The location of the EAM and nasion are used to establish the displacement and rotation of the orbito-meatal base line with respect to the detector holding assembly. The corrected brain outline is then rotated, centered and displayed superimposed on the regional flow data. Comparison of flow data from 2 studies is accomplished by mapping each probe location onto the standard brain and projecting these brain coordinates onto the second study. Flow data from the nearest detectors are averaged to obtain the interpolated flow value for that brain region. This method corrects for differences in head size and shape between patients and for changes in head positioning and rotation between studies. Computer simulation studies demonstrated that this correction procedure can significantly reduce the variance of flow measurements for expected ranges of head size and orientation.