Evaluation of Lunar small animal software for measuring bone mineral content in excised rat bones

The purpose of this study was to evaluate software from Lunar Corporation (Madison, WI) designed for the measurement of bone mineral content ([BMC],g) in excised rat femurs using dual-energy X-ray absorptiometry (DXA). Femurs were harvested from intact 2- to 12-mo-old female Sprague-Dawley rats, stripped of soft tissues, wrapped in saline-soaked gauze, and frozen at -20 degrees F. Thawed bones were scanned in air on a 1.7-cm-thick Lucite plate that was laid on the manufacturer's supplied Delrin platform. Bones were in an anteroposterior position and scanned in a proximal-to-distal manner. Small animal software version 1.0d was used with a Lunar DPX-L densitometer. Regions of interest (ROIs) were the middle one-third of the diaphysis, a small central area of the distal metaphysis, and the total bone. Precision (n = 6 femurs) was calculated for each region of interest. After DXA scanning, one group of bones (n = 10 femurs) was dried and incinerated in a muffle furnace to obtain bone ash. The ash was then digested in acid and aliquots assayed for calcium using atomic absorption spectrophotometry. This group of bones was used to correlate BMC with ash weight and areal bone mineral density (BMD) with calcium concentration. A second group of bones (n = 14 femurs) was used to correlate BMC with maximal load to failure (N), a biomechanical variable that provides information about bone strength. Precision of repetitive measurements for the three ROIs was 1.2, 3.0, and 0.65%, respectively. Total femur BMC and total femur ash weights were significantly correlated (r = 0.974, p <0.0001). Total femur area BMD (g/cm2) was significantly correlated with calcium concentration (microM) of the bone hydrolysate (r = 0.686, p = 0.029). Total femur BMC and maximum load to midshaft fracture were also significantly correlated (r = 0.914, p<0.0001). The greatest problem with the software was with edge detection: operator intervention was necessary to place edges manually during scan analyses. We conclude that the small animal software from Lunar Corporation accurately and precisely measured BMC in excised rat femurs. However, poor edge detection resulted in tedious and time-consuming analyses.