Quantitative computed tomography: Comparison of two calibration phantoms

Abstract

Vertebral trabecular mineral density of healthy Japanese (91 females and 67 males) was measured using the quantitative computed tomography (QCT) technique in a cross-sectional study. We compared estimates of vertebral bone density using two calibration phantoms: the Genant K₂HPO₄ phantom developed by Genant and a solid CaCO₃ phantom developed by Chugai Pharmaceutical. Using the CaCO₃ phantom, the rate of decrease of spinal trabecular mineral with age in control females averaged 1.1% per year from age 20 to 80, with an accelerated loss demonstrated at menopause (1.8%). Trabecular bone mass in male controls declined an average 0.9% per year. There was a highly significant correlation between the results obtained with each phantom (r=0.980, p<0.001). This relation was linear over the range of bone mass (60 –172 mg K₂HPO₄/cm³), and was expressed by the equation y(CaCO₃)=1.26×(K₂HPO₄)+12.3 There was, however, some dispersion of the data around the regression. The calibration phantom used for the measurement of the vertebral trabecular bone should need to be more consistent in longitudinal studies. Apart from this consideration, a solid Chugai phantom can be said to be useful having practical advantages in its flexibility.