Assessment of Trabecular Bone Mineral Density Using Quantitative Computed Tomography in Normal Cats

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The aim of this study was to assess age-related changes and anatomic variation in trabecular bone mineral density (tBMD) using quantitative computed tomography (QCT) in normal cats. Seventeen normal cats were included in this study and divided into the following 3 age groups: <6 months (n=4); 2–5 years (n=10); and >6 years (n=3). A computed tomographic scan of each vertebra from the 12th thoracic to the 7th lumbar spine, and the pelvis was performed with a bone-density phantom (50, 100, and 150 mg/cm3, calcium hydroxyapatite, CIRS phantom®). On the central transverse section, the elliptical region of interest (ROI) was drawn to measure the mean Hounsfield unit (HU) value. Those values were converted to equivalent tBMD (mg/cm3) by use of the bone-density phantom and linear regression analysis (r2>0.95). The mean tBMD value of the thoracic vertebrae (369.4 ± 31.8 mg/cm3) was significantly higher than that of the lumbar vertebrae (285 ± 58.1 mg/cm3). The maximum tBMD occurred at the T12, T13, and L1 levels in all age groups. There was a statistically significant difference in the mean tBMD value among the 3 age groups at the T12 (P<0.001), T13 (P<0.001), and L4 levels (P=0.013), respectively. The present study suggests that age-related changes and anatomic variation in tBMD values should be considered when assessing tBMD using QCT in cats with bone disorders.