Precision and Accuracy of a Transportable Dual-Energy X-ray Absorptiometry Unit for Bone Mineral Measurements in Guinea Pigs

Dual energy X-ray absorptiometry (DXA) is a valuable tool for measuring bone mineral content (BMC) and bone mineral density (BMD) in small-animal research. The present study was devised to establish guidelines and to define sites for bone mineral measurements in guinea pigs and to evaluate the accuracy of a new transportable research DXA unit. Repeated scans were performed on 30 guinea pig hindlimbs (in situ) as well as the isolated bones from these limbs (ex situ). Nine exactly specified regions of interest (ROIs) were analyzed twice for BMC and BMD by three different observers. Additionally, the BMC of whole bones and bone segments as measured by DXA was correlated to ash weights of bone in a subset of five animals to determine the accuracy of the DXA measurements. On ex situ scans, intra-observer variability for BMD ranged from 0.09% to 2.33% and inter-observer variability from 0.23% to 5.86% depending on the site studied, with smaller ROIs exhibiting more variability. Coefficients of variance (CV) for BMC measurements were slightly higher than for BMD. However, BMC offered a better correlation between in situ and ex situ values than BMD. On in situ scans, observer variability for BMD and BMC for comparable sites was higher than the ex situ variability. The results of this study indicate that DXA provides an accurate measurement of BMC even in small specimens. The precision of BMC and BMD measurements in situ can be improved considerably by using specific, well-defined ROIs and by careful placement of the bones to be scanned in close proximity to the scanning surface.