Quantitative computed tomography: comparative study using different scanners with two calibration phantoms.

To assess computed tomography (CT) scanners in vertebral quantitative computed tomography (QCT) measurement, five cadaveric vertebrae fixed in a water phantom were measured using 16 CT scanners of 10 different models using two types (CaCO3 and K2HPO4) of reference phantom. Although the same reference phantoms were used, the QCT values varied markedly depending on the CT scanner employed. The differences in QCT values were greater in the equivalent amount of CaCO3 than in that of K2HPO4. The largest difference between CT scanners was 40 mg/cm3 in the equivalent amount of CaCO3 and 28 mg/cm3 in that of K2HPO4. These differences were reflected among CT scanners by different slopes and intercepts of the reference lines of CaCO3, K2HPO4 and ash density depending on the CT scanner used. However, good correlations (r greater than 0.97) were observed for the QCT values obtained by various CT scanners. These results show that QCT values on one machine can be compared more closely with those of another machine if conversion formulae, determined by using materials equivalent to human vertebral bone, are employed.