Bone imaging modality precision and agreement between DXA, pQCT, and HR-pQCT

Quantifying precision error for DXA, peripheral QCT (pQCT), and HR-pQCT is crucial for monitoring longitudinal changes in body composition and musculoskeletal outcomes. Agreement and associations between bone variables assessed using pQCT and second-generation HR-pQCT are unclear. This study aimed to determine the precision of, and agreement and associations between, bone variables assessed via DXA, pQCT, and second-generation HR-pQCT. Thirty older adults (mean age: 64.2 ± 8.0 yr; women: 67%) were recruited. DXA scans were performed at the total hip, lumbar spine, and whole body. Distal (4%) and proximal (30%/33%/66%) skeletal sites at the radius and tibia were scanned with pQCT and/or HR-pQCT. Root-mean-squared coefficients of variation (%CVRMS) were calculated to define precision errors, and Bland–Altman plots assessed agreement between densitometric estimates. Pearson correlations and linear regression explored relationships between bone variables at different skeletal sites and proportional bias, respectively. Precision errors ranged between 0.55% and 1.6% for DXA, 0.40% and 4.8% for pQCT, and 0.13% and 30.7% for HR-pQCT. Systematic bias was identified between pQCT- and HR-pQCT-determined radius and tibia volumetric BMD (vBMD) estimates (all p<.001). Proportional bias was not observed between vBMD measures at any skeletal site (all p>.05). pQCT- and HR-pQCT-determined total, trabecular, and cortical vBMD and estimates of bone strength at the radius and tibia were strongly correlated (all p<.05). Precision error was low for most bone variables and within the expected range for all imaging modalities. We observed significant systematic bias, but no proportional bias, between pQCT- and second-generation HR-pQCT-determined vBMD estimates at the radius and tibia. Nevertheless, measures of bone density and strength were strongly correlated at all skeletal sites. These findings suggest that although bone density and strength estimates from both imaging modalities are not interchangeable, they are strongly related and likely have similar fracture prediction capabilities.

Lay Summary
Medical imaging machines, regardless of type, produce a random error called “precision error,” even under consistent conditions (eg, same operator, site, and patient). Despite advancements in medical imaging technologies, precision error still exists, making it challenging to collect reliable and consistent results. Understanding the degree of precision error that exists across different scanning facilities is important for accurately interpreting results and tracking changes over time. Additionally, comparing outcomes from different imaging machines measuring the same variables is essential to assess result interchangeability/agreement. This study assessed the precision of three bone imaging machines and evaluated agreement between two generations of 3D imaging machines. Our findings showed precision error was low and within expected ranges for all scanners. Although the 3D imaging machines had poor agreement, they had strong associations between measurements of the same bone variables on different machines. Collectively, these results suggest that machine operators effectively controlled factors influencing scan precision, leading to consistent scans. They also show that the two different generations of 3D imaging machines do not produce similar estimates of bone variables; however, if one machine identifies poor bone health and increased fracture risk based on certain bone variables, the other machine would likely produce similar findings.