Bone mineral measurement: automated determination of midvertebral CT section.

The selection of the computed tomographic (CT) section can introduce errors in reproducibility of several percent for bone mineral measurements. An algorithm for automated determination of the midvertebral CT section from survey radiographs was developed; it is based on ridge-line tracking of the vertebral end plates. The midvertebral section is defined by all points with equal perpendicular distance to the regression lines fitted through these end-plate contours. The algorithm can be corrected by manual interaction in case of failure. It was tested on T-12 to L-4 vertebrae on 25 randomly selected localizer radiographs. Of the 250 endplate contours, 223 (89.2%) were tracked automatically; the remaining 27 (10.8%) required user interaction for successful completion.