Dxa scanner

A 2D bone density mapping was generated for each nano‐CT VOI (n = 30) by projecting all bone voxels onto a planar FN ROI. The anatomical location, orientation, and width of the FN ROI were consistent with the Hologic DXA scanner used for the validation study. The 2D mapping was called the pseudo‐DXA image (Fig. 1C). This analysis focused exclusively on the number of bone voxels, since the X‐ray attenuation giving rise to BMC and the associated image reflects primarily the mineral component.⁽³³⁾ The contributions of marrow and X‐ray scattering to the pseudo‐DXA image were not assessed, as this initial study focused on the relative contributions of cortical and trabecular tissues to the DXA parameters.
The parameters calculated from the pseudo‐DXA images included the ROI area (pseudo‐DXA area), number of cortical bone voxels, number of trabecular bone voxels, total number of bone voxels (pseudo‐DXA BMC), and total number of bone voxels/area (pseudo‐DXA BMD). The numbers of cortical and trabecular bone voxels above (superior) and below (inferior) the FN ROI midline were also calculated. The average FN width and minimum FN width were measured directly from the pseudo‐DXA image. All terms preceded by pseudo‐DXA designate traits defined from the projected nano‐CT images, whereas terms preceded by DXA refer to traits determined by the DXA system.

Body mass index (BMI) was calculated as body mass in kilograms divided by height in meters squared (kg/m²). Body fat mass (kg), body muscle mass (kg), and body fat percentages (%) were estimated using DXA (Hologic QDR-4500, DXA Scanner, Hologic Inc., Newark, DE, USA) by a recognized technologist. The average systolic blood pressure (SBP) and diastolic blood pressure (DBP) of ankle and arm were measured using a non-invasive vascular screening device (BP-203RPE II device; Omron Healthcare, Kyoto, Japan).
Physical activity information was obtained using the long form of the International Physical Activity Questionnaire (IPAQ), except for when participants were attending the exercise program. Metabolic equivalent task (MET) values in minutes/week were calculated [26 (link)]. The mean weekly sunlight exposure score was calculated from sun exposure time and exposed skin area. Additional details are provided elsewhere [27 (link)]. The above indicators were determined at t1 and t2.

Height and body mass were assessed prior to a dual energy X-ray absorptiometry (DXA) scan (Hologic DXA Scanner, Hologic Horizon^TM; Danbury, CT). One noninvasive whole-body scan, anteroposterior view of the total body lying supine was performed. Testing was completed according to the manufacturer’s instructions and specifications. Results were analyzed with APEX software, version 4.5.2.1 (Hologic Inc.). The quality analysis for the densitometer was conducted daily using a standard aluminum spine block (Hologic Phantom) provided by the manufacturer. Measurements of the phantom fell within the manufacturer’s precision standard with a coefficient of variation <0.5%. Test-retest interclass coefficient of variation (CV; %) using DXA for LM (kg) and FM (kg) was 1.1% and 0.69%, respectively. The minimum detectable difference using DXA for LM (kg) and FM (kg) were 0.27 and 0.21 respectively. Total body water (TBW) was assessed via InBody scan (In-Body 270). Participants removed their socks and had their hands and feet wiped clean prior to standing on the InBody platform and grabbing the handles. Participants stood on the testing platform while holding hand electrodes for approximately 45 seconds. The minimal detectable difference using InBody for TBW (kg) was 0.19.