Quality Assurance
The Shepherd Research Lab serves as a DXA (dual-energy X-ray absorptiometry) quality-assurance site for NIH-funded studies, CDC research programs, and other large multi-site studies. Dr. Shepherd holds the patent that Hologic uses for body-composition measurement and has served as past president of the ISCD, participating in every ISCD Position Development Conference.
Technical infrastructure
The lab maintains workstations for both Hologic and GE systems with rights to use their software on external scans. Our QA work involves:
- Reviewing and revising DXA image data to ensure consistency by defining regions of interest within and among participants
- Harmonizing data from Lunar DXA systems with subsequent Hologic scanner acquisitions through cross-calibration equations and longitudinal corrections
- Performing quality-control checks on participant alignment, region positioning, and DXA-scan accuracy
- Defining protocols for consistency within and among participants’ scans
- Establishing procedures for continued QC, reanalysis, and data generation — with site manuals and training materials
Current QA engagements
NHANES 2018–2022
Analysis and quality-control review of DXA scans (hip, spine, VFA spine, whole body) at mobile examination centers, including longitudinal calibrations and cross-calibrations.
IMPAACT 2009 & 2010
Monitoring bone-mineral-density changes through central analysis of spine, femur, and whole-body DXA scans in HIV prevention and treatment studies.
HANDLS
DXA analysis and quality control for body-composition and bone-mineral-density data examining health disparities across socioeconomic groups in Baltimore.
Extended use of NHANES Visceral Adiposity Cancer Risk Factors to GE Systems
Determining relationships between Hologic and GE systems for visceral-adiposity measurements; providing cutoff points for cancer and metabolic risk.
Past QA work
Previously completed studies include TODAY (type 2 diabetes in youth), BMDCS (bone-mineral density in childhood), BeMyKids (bone-mineral accrual in young children), the TiP Study (tenofovir safety in pregnancy), and IMPAACT P1084s (maternal and infant monitoring).