Estimation of bone mineral density in children from diagnostic CT images: a comparison of methods with and without an internal calibration standard.

We investigated the feasibility and potential limitations of estimating bone mineral density (BMD) from standard diagnostic computed tomography (dCT). We analyzed three sets of BMD measurements for L1 and L2, each performed by a novice and an expert, for intra- and interobserver variance (n=43 studies from 38 patients; median age, 13.2 years) using one BMD quantification system with (conventional quantitative computed tomography (QCT)) and two without (QCT and dCT) an external calibration phantom. Using ANOVA model, means of three sets of BMD measurements analyzed by the expert differed by 2.5mg/cm(2); for the novice, by less than 1mg/cm(2). Variation of measurement differences was less for the expert. Mean intra- and interobserver absolute standardized differences (ASD) were 1.77% and 1.8%, respectively. The mean ASD between phantom and phantom-less methods of QCT studies were 3.3%; mean ASD of phantom QCT versus phantom-less dCT was 14.3%. Regression modeling suggested compensation for sources of dCT BMD measurement bias can reduce the mean ASD of phantom QCT versus phantom-less dCT to 6.5%. Thus, phantom-less QCT of dCT adds clinically useful BMD information not typically attained from dCT, thereby augmenting patient care and presenting important possibilities for research without need for additional study.