AN ANTHROPOMORPHIC PHANTOM STUDY ON THE EFFECT OF MIDVERTEBRAL SLICE PLACEMENT AND REGION-OF-INTEREST POSITIONING ON THE REPRODUCIBILITY OFSINGLE-ENERGY QUANTITATIVE CT (QCT) OF THE SPINE

Purpose: The purpose of our study was to develop an anthropomorphic ph antom with a 3D external reference system capable of geometrically des cribing the region of interest (ROI) of single-energy quantitative CT (QCT) scans and to study the reproducibility of ROI placement (volume) and bone mineral density (BMD) after operator-defined and algorithm-s upported midvertebral slice (MVS) placement. Method: In three vertebra e (L1-3) of 10 human cadaveric spines placed in a water phantom, MVSs were defined by an operator and an algorithm-supported technique on la teral digital CT radiographs, and QCT scans were performed accordingly . The measurements were repeated once after repositioning the phantom on the CT table. ROIs of the trabecular bone were determined with a st andard technique. The percentage of bone volume was calculated for one ROI not covered by the repetition (volume mismatch percent). Results: Reproducibility with algorithm-supported MVS placement was superior t o that of operator-defined positioning with regard to volume mismatch (mean +/- SD): 10.6 +/- 8.4 vs. 7.9 +/- 5.3%; and mean of paired BMDs (mean of three vertebral bodies): 2.7 vs. 1.5% (p < 0.05). Conclusion: The ROI volume mismatch of repeated QCT scans, which is similar to 10 % of ROI volume, can be quantified with an external reference system. Automated placement is superior to the manual technique and should be used in clinical practice.