Department of Radiology and Biomedical Imaging at China Basin, University of California - San Francisco, 185 Berry Street, Suite 190, Lobby 6, San Francisco, CA 94107, USA.
Department of Medicine, University of California - San Francisco, 505 Parnassus Avenue, San Francisco, CA 94143, USA; Endocrine Research Unit, San Francisco Veterans Affairs Health Care System, 4150 Clement St, San Francisco, CA 94121, USA.
Bone. 2020 Sep;138:115505. doi: 10.1016/j.bone.2020.115505. Epub 2020 Jun 27.
Significant weight loss following treatments for obesity undermines bone metabolism and increases bone turnover and fracture incidence. High resolution peripheral quantitative computed tomography (HR-pQCT) is widely used in skeletal heath assessment research to provide noninvasive bone parameter measurement (e.g. volumetric bone mineral density (vBMD)) with minimal radiation exposure. However, variation in body composition among study groups or longitudinal variations within individuals undergoing significant weight change will generate artifacts and errors in HR-pQCT data. The purpose of this study is to determine the influence of these artifacts on the measurement of vBMD.
We designed a custom-made hydroxyapatite (HA)-polymer phantom surrounded by layers of reusable gel pack and hydrogenated fat to mimic the distal tibia and the surrounding lean and fat tissue. Four different thicknesses of fat were used to mimic the soft tissue of increasingly overweight individuals. We then evaluated how a change in soft tissue thickness influenced image quality and vBMD quantification within total, trabecular, and cortical bone compartments. Based on these data, we applied a data correction to previously acquired clinical data in a cohort of gastric bypass patients.
In the phantom measurements, total, trabecular, and cortical vBMD increased as soft tissue thickness decreased. The impact of soft tissue thickness on vBMD varied by anatomic quadrant. When applying the soft tissue data correction to a set of clinical data, we found that soft tissue reduction following bariatric surgery can lead to a clinically significant underestimation of bone loss in longitudinal data, and that the effect is most severe in the cortical compartment.
HR-pQCT-based vBMD measurement accuracy is influenced by soft tissue thickness and is spatially inhomogeneous. Our results suggest that variations in soft tissue thickness must be considered in HR-pQCT studies, particularly in studies enrolling cohorts with differing body composition or in studies of longitudinal weight change.
肥胖治疗后的显著体重减轻会破坏骨代谢，增加骨转换并增加骨折发生率。高分辨率外周定量计算机断层扫描（HR-pQCT）广泛用于骨骼健康评估研究中，以提供非侵入性的骨骼参数测量（例如体积骨矿物质密度（vBMD）），同时辐射暴露最小。然而，研究组之间的身体成分差异或经历显著体重变化的个体的纵向变化会在 HR-pQCT 数据中产生伪影和误差。本研究的目的是确定这些伪影对 vBMD 测量的影响。
我们设计了一种定制的羟磷灰石（HA）-聚合物体模，周围环绕着多层可重复使用的凝胶包装和氢化脂肪，以模拟远端胫骨和周围的瘦组织和脂肪组织。使用了四种不同厚度的脂肪来模拟超重个体的软组织。然后，我们评估了软组织厚度变化如何影响总骨、小梁骨和皮质骨腔内的图像质量和 vBMD 定量。根据这些数据，我们对胃旁路患者队列中先前获得的临床数据应用了数据校正。
在体模测量中，总骨、小梁骨和皮质骨的 vBMD 随着软组织厚度的减少而增加。软组织厚度对 vBMD 的影响因解剖象限而异。当将软组织数据校正应用于一组临床数据时，我们发现减重手术后软组织减少会导致纵向数据中骨丢失的临床显著低估，并且这种影响在皮质骨腔内最为严重。
基于 HR-pQCT 的 vBMD 测量准确性受软组织厚度的影响，并且具有空间不均匀性。我们的结果表明，在 HR-pQCT 研究中，必须考虑软组织厚度的变化，特别是在招募身体成分不同的队列的研究中，或者在纵向体重变化的研究中。
