  Brain CT has become a standard imaging tool for emergent evaluation of brain
condition, and measurement of midline shift (MLS) is one of the most important
features to address for brain CT assessment. We present a simple method to
estimate MLS and propose a new alternative parameter to MLS: the ratio of MLS
over the maximal width of intracranial region (MLS/ICWMAX). Three neurosurgeons
and our automated system were asked to measure MLS and MLS/ICWMAX in the same
sets of axial CT images obtained from 41 patients admitted to ICU under
neurosurgical service. A weighted midline (WML) was plotted based on individual
pixel intensities, with higher weighted given to the darker portions. The MLS
could then be measured as the distance between the WML and ideal midline (IML)
near the foramen of Monro. The average processing time to output an automatic
MLS measurement was around 10 seconds. Our automated system achieved an overall
accuracy of 90.24% when the CT images were calibrated automatically, and
performed better when the calibrations of head rotation were done manually
(accuracy: 92.68%). MLS/ICWMAX and MLS both gave results in same confusion
matrices and produced similar ROC curve results. We demonstrated a simple, fast
and accurate automated system of MLS measurement and introduced a new parameter
(MLS/ICWMAX) as a good alternative to MLS in terms of estimating the degree of
brain deformation, especially when non-DICOM images (e.g. JPEG) are more easily
accessed.
