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A calibration methodology of QCT BMD for human vertebral body with registered micro‐CT images
Author(s) -
Dall'Ara E.,
Varga P.,
Pahr D.,
Zysset P.
Publication year - 2011
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3582946
Subject(s) - voxel , quantitative computed tomography , bone mineral , calibration , nuclear medicine , grayscale , tomography , materials science , mathematics , biomedical engineering , medicine , radiology , osteoporosis , physics , optics , statistics , pixel , endocrinology
Purpose : The accuracy of QCT‐based homogenized finite element (FE) models is strongly related to the accuracy of the prediction of bone volume fraction (BV/TV) from bone mineral density (BMD). The goal of this study was to establish a calibration methodology to relate the BMD computed with QCT with the BV/TV computed with micro‐CT (μCT) over a wide range of bone mineral densities and to investigate the effect of region size in which BMD and BV/TV are computed.Methods : Six human vertebral bodies were dissected from the spine of six donors and scanned submerged in water with QCT (voxel size: 0.391 × 0.391 × 0.450 mm 3 ) and μCT (isotropic voxel size: 0.018 3 mm 3 ). The μCT images were segmented with a single level threshold. Afterward, QCT‐grayscale, μCT‐grayscale, and μCT‐segmented images were registered. Two isotropic grids of 1.230 mm (small) and 4.920 mm (large) were superimposed on every image, and QCT BMD was compared both with μCT BMD and μCT BV/TV for each grid cell.Results : The ranges of QCT BMD for large and small regions were 9–559 mg/cm 3 and −90 to 1006 mg/cm 3 , respectively. QCT BMD was found to overestimate μCT BMD . No significant differences were found between the QCT BMD –μCT BV/TV regression parameters of the two grid sizes. However, the R 2 was higher, and the standard error of the estimate (SEE) was lower for large regions when compared to small regions. For the pooled data, an extrapolated QCT BMD value equal to 1062 mg/cm 3 was found to correspond to 100% μCT BV/TV .Conclusions : A calibration method was defined to evaluate BV/TV from QCT BMD values for cortical and trabecular bone in vitro . The QCT BMD –μCT BV/TV calibration was found to be dependent on the scanned vertebral section but not on the size of the regions. However, the higher SEE computed for small regions suggests that the deleterious effect of QCT image noise on FE modelling increases with decreasing voxel size.