Bone mineral density is the mean concentration of mineral in a bone structure, and osteopenia and osteoporosis are conditions in which BMD is decreased.1 Quantitative CT and dual energy x-ray absorptiometry have been used to measure BMD in veterinary medicine.2,3 Dual energy x-ray absorptiometry has an advantage of lower radiation exposure than quantitative CT, but dual energy x-ray absorptiometry nonselectively incorporates all tissues that x-rays penetrate in a 2-D image. Bone mineral density measured by dual energy x-ray absorptiometry is the sum of densities of soft tissue, trabecular bone, and cortical bone.4 Quantitative CT can distinguish between trabecular and cortical bone and measure the BMD of each part separately as a volumetric unit (g/cm3).2
The precision of measuring BMD with quantitative CT can be affected by apparatus instability, CT slice selection, and ROI selection.5 Among them, selection of the CT slice and the ROI setting can be highly influenced by the operator, and operator error is as high as 2.5% to 6% when an entirely manual ROI is used.5 Region of interest selection by the operator must be scrutinized because of a potential limit on reproducibility, particularly if different operators are involved in follow-up examinations.5 Even if the same shape and size of ROI are used, a small change in position can also result in significantly different values.5 Automatic software is used to reduce operator dependence and increase reproducibility when measuring BMD with quantitative CT in human medicine.5 When this software is used, the ROI is drawn automatically by use of vertebral anatomic landmarks, and only minor intervention is needed when the ROIs are not suitable for each patient.5
Osteopenia and osteoporosis are recognized more often as these abnormalities become more common in the aged population of dogs. Therefore, canine BMD should be estimated and monitored with accurate and reproducible methods. The purpose of the study reported here was to investigate the effect of ROI setting and slice thickness on vertebral trabecular BMDs measured with quantitative CT in dogs and to compare manual settings and automatic software for the ROI, which was designed for humans, to estimate the applicability of this software to dogs. We hypothesized that the automatic software would have reliability and applicability for setting the ROI for measurement of BMD in canine lumbar vertebrae.
Bone mineral density
Region of interest
Zoletil, Virbac, Carros, France.
Domitor, Orion Corp, Espoo, Finland.
Siemens Emotion 16, Siemens, Forchheim, Germany.
Calcium hydroxyapatite rod (0 and 200 mg/cm3), Siemens, Forchheim, Germany.
Syngo Osteo CT, Siemens, Forchheim, Germany.
SPSS Statistics, version 20, IBM Corp, Armonk, NY.
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