A special purpose x-ray fan-beam CT scanner for trabecular bone density measurement in the appendicular skeleton

A special purpose x-ray CT scanner with the capability of scanning objects 75-220 mm in diameter with constant relative geometrical resolution has been developed. The data collection scheme for the scanner uses multiple rotations of a linearly shifted, asymmetric fan beam permitting user-defined variable resolution. Details of hardware and the calibration procedures for the scanner are described and the methods used to measure trabecular bone density (TBD) in the peripheral skeleton are outlined. The standard error of estimate (SEE) of a calibration line of pixel value as a function of K2HPO4 concentration was determined to be 0.07%. The short-term, in vivo precision of the TBD determination, by repeated measurements of a volunteer with repositioning between each measurement, was +/- 0.67% (coefficient of variation (CV] with a 50s scan time and a radiation dose of less than 20 mR per slice.