6. Quantitative Computed Tomography
Abstract
Journal of the ICRU Vol 9 No 1 (2009) Report 81 Oxford University Press doi:10.1093/jicru/ndp009 6.1 Introduction The CT number displayed in a pixel actually represents a volume element or voxel. The size of this voxel, typically in mm3, is the pixel area times the thickness S of the investigated slice. Thus, in QCT, a mass concentration is determined and not an areal mass concentration as in absorptiometry. In clinical CT, the values of m(x, y, z) are calibrated relative to the x-ray attenuation of water (w) resulting in a so-called CT number measured in Hounsï¬eld units (HU): CT number ¼ In the context of the present Report, (QCT) is referred to as a dedicated computed tomography (CT) technique to determine bone mineral density (BMD). was introduced shortly after the ï¬rst CT scanner had been realized (Hounsï¬eld, 1973) and was developed in parallel for the lumbar spine (Genant and Boyd, 1977) using clinical scanners and for the proximal radius (Ruegsegger et al., 1974) using smaller dedicated ¨ forearm scanners. All of these scanners worked in single-slice mode. For each acquired slice, a CT image is reconstructed in which dedicated regions of interest (ROIs) are analyzed. The linear attenuation