Axial CT in the diagnosis of osteoporosis part 3
While the use of standard QCT has been based on two-dimensional characterization of vertebral trabecular bone, three-dimensional, or volumetric QCT, are new techniques that allow to improve spinal measurements and to extend QCT assessments to the proximal femur. They encompass the entire object of interest with stacked slices, or spiral CT scans, and can use anatomic landmarks to automatically generate relevant projections. Volumetric QCT can not only determine BMD of the entire bone or subregion, such as a vertebral body or femoral neck, it can also provide separate analysis of the trabecular or cortical components. Because a true and highly accurate volumetric rendering is provided, important geometrical and biomechanically relevant assessments can be derived, such as cross-sectional moment of inertia and finite element analysis. A lateral scout view covering T11-L5 is first employed to delineate the lumbar spine vertebral levels. To relate the CT measurements to BMD, patients are scanned simultaneously with a bone mineral reference phantom containing calibration objects with equivalent densities to those of calcium hydroxyapatite.
A computer program can identify and analyze the calibration objects of bone mineral reference phantom and it is used to derive calibration equations relating the CT numbers to BMD for each section. Three-dimensional ROIs are based on combining the boundaries of the vertebral body. The anatomic coordinate system is defined interactively. Three volumetric ROIs encompassing trabecular, cortical, and integral bone are defined on the central 70% of the vertebral body, based on the user determined vertebral midplane and end plate location. The volumetric ROIs are determined by stacking ROIs delineated on each of these slices. Using spiral CT scanning, it is possible to acquire volumetric QCT scans of the L1-L2 vertebral bodies in 30 to 40 seconds (Fig. 3). Because the volume of interest is determined three-dimensionally in software, patient positioning is of lesser concern than with conventional two-dimensional QCT or with DXA. The shorter scanning time may result in greater economic feasibility for QCT spinal trabecular BMD measurements, not only because they would require less time but also because the advent of spiral CT scanning has made more time available on CT scanners, due to shortening of other diagnostic scanning procedure. Your life is worth living. Buy cialis canadian pharmacy online
Figure 3 – Volumetric QCT 3D reconstruction showing the entire vertebral body.
