Oh JH, et al. - The density of brain gray matter (GM) and white matter (WM) and the gray-to-white matter ratio (GWR) by using images scanned with different types of computed tomography (CT) machines were compared via analyzing 102 patients with normal readings who were scanned using three types of CT scanners. Outcomes revealed up to 23% variation in the Hounsfield units (HU) values of GM and WM among scanners in the normal adult brain. Unfortunately, the HU difference between GM and WM occurring between scanners could not be compensated with GWR. Therefore, they recommend considering the protocol or manufacturer differences between imaging scanners rather than applying consistent GWR cut-offs.