Quantitative computed tomography (QCT) using body CT
Using QCT, bone mineral density (BMD; mg/cm3) measurements can be obtained in central and peripheral skeletal sites. Examinations are performed using an application-specific software package and a dedicated bone-equivalent calibration phantom imaged simultaneously with the patient to convert the CT numbers into bone-equivalent values (mg/cm3; g/l). QCT requires a lateral scout image of the lumbar spine. A typical single-slice 2D QCT protocol consists of a 10-mm section in the mid plane of each of three or four adjacent vertebrae (T12, L1, L2 and L3) acquired with 80-kVp tube potential and 125-mAs tube load. As this 2D technique has a limited precision, 3D volumetric QCT protocols have been developed based on multi-detector CT (MDCT) imaging. Using MDCT, 3D volume sets are acquired and from these BMD values and bone geometry can be measured [9, 10]. In spine multi-detector QCT (MDQCT) two or three vertebrae are usually imaged, L1–L2 or L1–L3, to reduce dose. Hip MDQCT is capable of analysing the main regions of the hip i.e. the femoral neck, the trochanter and the intertrochanteric region.