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

Abstract

. 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/cm 3 , 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/cm 3 ) by use of the bone-density phantom and linear regression analysis (r 2 >0.95). The mean tBMD value of the thoracic vertebrae (369.4 ± 31.8 mg/cm 3 ) was significantly higher than that of the lumbar vertebrae (285 ± 58.1 mg/cm 3 ). 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. KEY WORDS: bone mineral density, feline, quantitative computed tomography, trabecular bone. doi: 10.1292/jvms.11-0579; J. Vet. Med. Sci. 74(11): 1461-1467, 2012 Bone mineral density (BMD) decreases in accordance with normal aging and metabolic or systemic disease. The turnover rates for cancellous bone are 4 to 8 times greater than for cortical bone, so cancellous bone is more sensitive to disease-induced changes [25]. Therefore, in humans with osteoporosis, BMD has been primarily investigated in cancellous bone.On the basis of this relationship, several techniques have been developed to noninvasively measure bone mineralization at various skeletal sites. These include radioabsorptiometry (RA), single photon absorptiometry (SPA), dual photon absorptiometry (DPA), quantitative ultrasound (QUS), dual-energy x-ray absorptiometry (DEXA), quantitative computed tomography (QCT) and peripheral QCT (pQCT). Among these, DEXA, QCT and pQCT have become the established methods for evaluating skeletal status, assessing osteoporosis, determining fracture risk and monitoring metabolic diseases and therapies in humans [8,[10][11][12][13].Feline diseases affecting BMD include mucopolysaccharidosis, osteopetrosis, osteogenesis imperfect and osteopenia related to primary hyperparathyroidism and secondary to renal or nutritional hyperparathyroidism. Reports in cats have been limited to the studies for BMD evaluation using DEXA [17] and a few peer-reviewed studies that measured BMD in clinically normal cats and abnormal cats using DEXA [3,23]. DEXA has been accepted as the gold standard method of BMD measurement, and it requires less X-ray exposure for the patient...

Cervical Vertebral Trabecular Bone Mineral Density in Great Danes With and Without Osseous‐Associated Cervical Spondylomyelopathy

“…In people, anatomic differences in BMD can be explained by the fact that individual vertebrae are subjected to different in vivo loads; such that in areas where loading is highest, bone density would also be highest in accordance with Wolff's Law . Anatomic variations in trabecular BMD values have also been described in the thoracolumbar spine of normal cats . In human studies, part of this variation has been attributed to the shape and overall volume of bone sampled, such that BMD measures within hypertrophied or abnormally shaped bone may result in the final measurement of a lower BMD …”

“…Bone mineralization can be noninvasively measured, by using dual‐energy x‐ray absorptiometry, quantitative computed tomography (CT), and peripheral quantitative CT . CT utilizing calibration phantoms is considered the gold standard for measuring BMD in vivo . Its superior spatial resolution, allows for discrimination between trabecular and cortical bone, facilitating noninvasive BMD measurement .…”

“…To detect small differences between and within subjects, it is essential that the same volume is analyzed for each ROI. A few studies have evaluated BMD in clinically normal dogs and cats, and dogs with OA of the appendicular skeleton . No data are available on the use of CT to examine BMD in dogs with osseous‐associated CSM.…”

“…[7][8][9][10][11][12][13][14][15][16] Bone mineralization can be noninvasively measured, by using dual-energy x-ray absorptiometry, quantitative computed tomography (CT), and peripheral quantita-tive CT. 8,9,11,17,18 CT utilizing calibration phantoms is considered the gold standard for measuring BMD in vivo. 13,19,20 Its superior spatial resolution, allows for discrimination between trabecular and cortical bone, facilitating noninvasive BMD measurement. 12,20,21 This is especially important in trabecular bone, where measurement changes are more sensitive than in cortical bone.…”

“…A few studies have evaluated BMD in clinically normal dogs and cats, and dogs with OA of the appendicular skeleton. 19,[24][25][26] No data are available on the use of CT to examine BMD in dogs with osseous-associated CSM.…”