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Subject: search.filters.subject.Bone densitometry

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    Measurement of bone quality in growing male rats using dual energy x-ray absorptiometry and bone ash content : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science in Animal Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2001) Brown, Katherine Elizabeth
    Growing male rats have been considered and used as a model for bone growth and prevention of osteoporosis because of their high bone turnover and demand for calcium. Dual Energy X-ray Absorptiometry (DEXA) is a useful tool for identifying minimal changes in bone mineral density and has recently been adapted for use in small animal models. The objective of this trial was to identify the changes in Bone Mineral Density (BMD) in relation to age and to identify how BMD varies from site to site. Sixty male Sprague-Dawley rats were split into six groups to allow measurements at one, two, three, four, five and six months of age (n=10 per group). At each time point a group of rats was scanned using a QDR4000 DEXA machine from Hologic. Duplicate BMD measurements were obtained for the whole body, spine and both femurs in vivo. The rats were then euthanased and the spine and both femurs were excised for ex vivo DEXA scanning and ashed calcium analysis. BMD increased almost linearly to four months and then formed a plateau. This indicates that from weaning to four months is an especially sensitive time for manipulating bone growth in male rats. There was a significant difference in BMD between groups (P<0.001), which is to be expected in growing rats. There was also a significant difference in BMD within groups (p<0.001), believed to be due to variation at two and five months of age. There was a very strong positive correlation between weight and BMD and age and BMD at all sites, indicating that BMD is a strongly related to both weight and age. All sites were strongly correlated to each other and to the ashed calcium values. The excised femur had a lower BMD value than the in vivo femur, although the two values were strongly correlated. This is believed to be due to differences in positioning and indicates that the two methods cannot be used interchangeably. These results indicate that bone mineral density is the gold standard for following changes in bone growth over time in the growing rat. Alternatively, ashed bone calcium content can be used, but only as a once off endpoint.
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    The quantitative assessment of photodensity of the third carpal bone in the horse : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2000) Secombe, Cristy Jane
    The purpose of this study was to determine if a method of non-invasive bone mineral analysis could be adapted to quantitatively assess photodensity in the third carpal bone of the horse. The technique chosen was radiographic absorptiometry which determines bone mineral density from a radiograph that includes a control (usually a wedge) of known photodensity. When taken correctly the tangential view of the distal row of carpal bones allows visualisation of the dorsal aspect of the third carpal bone, without superimposition of overlying structures. The method is technically demanding, because the angle at which the x-ray beam penetrates the third carpal bone can not be exactly replicated in a clinical situation, as it is affected by the x-ray beam angle and the limb flexion angle. To utilise radioabsorptiometry in the tangential view assessment of the effect of variation in x-ray beam angle was required. Fourteen isolated distal rows of carpal bones were radiographed varying the x-ray beam angle in 5° increments over 15° from the base angles of 60° and 90°. The radiographs were digitised and processed to determine the photodensity of specific regions of interest in terms of millimetres of aluminium, using the wedge as reference. The results indicated that small variations in x-ray beam angle significantly affect photodensity. Quantitative assessment of the photodensity of the fourth carpal bone showed changes associated with exercise, similar to those in the third carpal bone. Changing the size of the region of interest when x-ray beam angle was varied by 30° did not affect photodensity of the region of interest. Although conversion from photodensity to bone mineral density was not possible within this project, the findings supported other authors who have studied bone mineral density of the third carpal bone. There are two tangential views of the distal row of carpal bones. The two methods affect the radiographic image differently because the magnification and distortion changes are different in each and this precluded accurate comparison. Therefore, it was impossible to determine which method would more accurately assess the photodensity of the third carpal bone. The study concluded that quantitative assessment of photodensity of the third carpal bone using either tangential view was clinically inapplicable at this time, because of the significant effect of very small changes in angle on photodensity. This is unfortunate, because the current practice of visual subjective assessment of photodensity of the third carpal bone remains unsatisfactory, in particular the differentiation between grades of sclerosis.