Validation of calcaneus trabecular microstructure measurements by HR-pQCT

• Published in: Bone (New York, N.Y.) N.Y.), 2018-01, Vol.106, p.69-77
• Main Authors: Metcalf, Louis M., Dall'Ara, Enrico, Paggiosi, Margaret A., Rochester, John R., Vilayphiou, Nicolas, Kemp, Graham J., McCloskey, Eugene V.
• Format: Article
• Language: English
• Subjects: Aged, 80 and over; Calcaneus; Calcaneus - diagnostic imaging; Female; High-resolution peripheral quantitative computed tomography; Humans; Micro computed tomography; Tibia - diagnostic imaging; Tomography, X-Ray Computed - methods; Trabecular microstructure; X-Ray Microtomography - methods
• ISSN: 8756-3282; 1873-2763
• DOI: 10.1016/j.bone.2017.09.013

Assessment of calcaneus microstructure using high-resolution peripheral quantitative computed tomography (HR-pQCT) might be used to improve fracture risk predictions or to assess responses to pharmacological and physical interventions. To develop a standard clinical protocol for the calcaneus, we validated calcaneus trabecular microstructure measured by HR-pQCT against ‘gold-standard’ micro-CT measurements. Ten human cadaveric feet were scanned in situ using HR-pQCT (isotropic 82μm voxel size) at 100, 150 and 200ms integration times, and at 100ms integration time following removal of the calcaneus from the foot (ex vivo). Dissected portions of these bones were scanned using micro-computed tomography (micro-CT) at an isotropic 17.4μm voxel size. HR-pQCT images were rigidly registered to those obtained with micro-CT and divided into multiple 5mm sided cubes to evaluate and compare morphometric parameters between the modalities. Standard HR-pQCT measurements (derived bone volume fraction (BV/TVd); trabecular number, Tb.N; derived trabecular thickness, Tb.Thd; derived trabecular spacing, Tb.Spd) and corresponding micro-CT voxel-based measurements (BV/TV, Tb.N, Tb.Th, Tb.Sp) were compared. A total of 108 regions of interest were analysed across the 10 specimens. At all integration times HR-pQCT BV/TVd was strongly correlated with micro-CT BV/TV (r2=0.95–0.98, RMSE=1%), but BV/TVd was systematically lower than that measured by micro-CT (mean bias=5%). In contrast, HR-pQCT systematically overestimated Tb.N at all integration times; of the in situ scans, 200ms yielded the lowest mean bias and the strongest correlation with micro-CT (r2=0.61, RMSE=0.15mm−1). Regional analysis revealed greater accuracy for Tb.N in the superior regions of the calcaneus at all integration times in situ (mean bias=0.44–0.85mm−1; r2=0.70–0.88, p