Assessment of calibration methods for estimating bone mineral densities intrauma patients with quantitative CT: An anthropomorphic phantom study

Rationale and Objectives. Osteoporosis may contribute to the increased morb idity and mortality of elderly persons involved in motor vehicle accidents. Such patients commonly undergo whole-body computed tomographic (CT) studie s that may be analyzed with quantitative CT. Various quantitative CT calibr ation techniques were investigated for use with patients who have suffered trauma, who are typically scanned on a backboard. Materials and Methods. Lumbar simulator phantoms were used to simulate smal l and large patients. Vertebral spongiosa inserts with a wide range of bone and fat compositions were placed in the phantoms, and their bone mineral d ensities (BMDs) were measured by using calibration lines derived from the C T numbers of a calibration standard. Four calibration techniques were teste d. In three the lumbar simulator and the calibration standard were scanned simultaneously, with the standard placed beneath the backboard (method 1), on top of the backboard adjacent to the lumbar simulator (method 2), or on top of the abdomen region of the lumbar simulator (method 3). The fourth te chnique employed a single calibration line derived from a separate scan of the calibration standard beneath the small lumbar simulator without the bac kboard, with correction for patient body size. Results. The best overall results were obtained with the single calibration line method. The root mean square errors of the BMD values were 2.9-18.4, 2.5-7.5, 2.5-14.9, and 0.3-2.8 mg/cm(3) for methods 1, 2, 3, and 4, respect ively (ranges represent variations in the errors of the measured BMDs of th e inserts due to changes in scanner table height and lumbar simulator phant om size). Conclusion. The single calibration line method is an accurate means of meas uring BMD in trauma patients.