Quantitative computed tomography precision and accuracy for long-term follow-up of bone mineral density measurements: a five year in vitro assessment

The purpose of this work was to test the long-term precision of quantitative computed tomography (QCT) on a CT scanner partly used for the measurement of bone mineral density (BMD). A spine phantom (ESP), which simulates three lumbar vertebrae (Li, i = 2-4) with given mineral densities of 50, 100, and 200 mg hydroxyapatite equivalents (HAP)/cm(3), respectively, was measured periodically over more than 5 yr on a Elscint-Marconi CT-Twin scanner. A total of 80 measurements were taken. The measured BMDi values were 48.4 +/- 1.2, 101.3 +/- 1.1, and 212.6 +/- 1.7 mg HAP/cm3, respectively (coefficient of variation [CV%] = 2.4, 1.1, and 0.8), and they were linearly correlated with the given density values (r > 0.99). The mean BMD value of the three simulated vertebrae was 120.8 +/- 1.1 mg HAP/cms(3) (CV% = 0.9), a value that corresponds to the mean lumbar BMD value in normal 65-yr-old women. We concluded that QCT is a precise and accurate method for long-term follow-up of BMD assessment in the population affected by osteoporosis.