Introduction

Traditionally, total body (TB) DXA scans to assess body composition include the entire body, however novel abbreviated scan acquisition methods are available in new software. For example, total body less head (TBLH) is recommended given the head contains lean mass that cannot be altered by intervention. Recently, to reduce scan time and radiation exposure, a neck to knee (N-K) acquisition option is available. Finally, scans limited to the lower extremity might be useful to evaluate regional mass change after surgery/injury and in sarcopenia assessment.

Objectives

The purpose of this study was to evaluate comparability of measured and estimated body composition results using TBLH, N-K and lower extremity (LE; pelvis to toes) acquisition techniques. We hypothesized that body composition data with the 3 novel methods would not differ from the traditional TB method.

Methods

Each subject had 4 scans: TB, TBLH, N-K and LE. A subset of 30 had repeat N-K and LE scans with repositioning between. A Lunar iDXA (GE, Madison, WI) with enCORE v18.0 was used to acquire and analyze scans. TB scans were acquired per ISCD guidance. TBLH and N-K scans were acquired using automated software features that limited the anatomy scanned; N-K estimates non-scanned leg mass. LE scans were started at L3 and auto stopped past the toes. Automated analysis, with manual correction, was used for all but LE scans which were analyzed manually by compressing all upper body ROIs above the pelvis then placing lower body ROIs at the top of pelvis, bisecting the femur neck and separating the legs. Pearson Correlation and Bias plots were used to compare regional lean, fat and BMC measurements from the 3 novel scans to TB. Precision determined by the ISCD Precision Calculator was compared to TB historical control by F-test.

Results

The study sample included 82 subjects, 41F/41M mean (SD) age 51.0 (18.4) years and BMI 25.5 (3.7) kg/m2. Mean lean, fat and bone mass were very similar among all approaches with some statistical, but likely not clinical, differences (Tables 1&3). Composition from all regions with the 3 novel methods was highly correlated with TB measurement, r=0.99-1.0, p< 0.001 with mean bias of 14-237g lean, 7-121g fat and 0.3-13.3g BMC (Table 2). N-K and LE precision was excellent ranging from 0.45-2.31 %CV (Table 3).

Conclusions

These 3 novel approaches to either measure or estimate regional body composition are consistent with traditional TB measurement and may be considered as substitutes when appropriate.

中文翻译：

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DXA 的新身体成分方法：与经典全身扫描的比较

介绍

传统上，用于评估身体成分的全身 (TB) DXA 扫描包括整个身体，但是新软件中提供了新颖的简化扫描采集方法。例如，鉴于头部包含无法通过干预改变的瘦体重，建议使用全身少头 (TBLH)。最近，为了减少扫描时间和辐射暴露，可以使用颈对膝 (NK) 采集选项。最后，仅限于下肢的扫描可能有助于评估手术/损伤后的区域肿块变化和肌肉减少症评估。

目标

本研究的目的是评估使用 TBLH、NK 和下肢（LE；骨盆到脚趾）采集技术测量和估计的身体成分结果的可比性。我们假设 3 种新方法的身体成分数据与传统的 TB 方法没有区别。

方法

每个受试者进行 4 次扫描：TB、TBLH、NK 和 LE。30 个子集进行重复 NK 和 LE 扫描，并在其间重新定位。带有 enCORE v18.0 的 Lunar iDXA (GE, Madison, WI) 用于采集和分析扫描。根据 ISCD 指南获得 TB 扫描。TBLH 和 NK 扫描是使用限制扫描解剖结构的自动化软件功能获得的；NK 估计非扫描腿部质量。LE 扫描在 L3 开始并自动停止超过脚趾。除 LE 扫描外，所有扫描均使用自动分析和手动校正，LE 扫描通过压缩骨盆上方的所有上半身 ROI 然后将下半身 ROI 放置在骨盆顶部、平分股骨颈和分离腿来进行手动分析。Pearson 相关和偏差图用于比较来自 3 次新扫描的区域瘦、脂肪和 BMC 测量值与 TB。

结果

研究样本包括 82 名受试者，41F/41M 平均 (SD) 年龄 51.0 (18.4) 岁和 BMI 25.5 (3.7) kg/m2。所有方法的平均瘦肉、脂肪和骨量非常相似，有一些统计学差异，但可能不是临床差异（表 1 和 3）。采用 3 种新方法的所有地区的成分与 TB 测量高度相关，r=0.99-1.0，p<0.001，平均偏差为 14-237g 瘦肉、7-121g 脂肪和 0.3-13.3g BMC（表 2）。NK 和 LE 精度在 0.45-2.31 %CV 范围内非常出色（表 3）。

结论

这 3 种测量或估计区域身体成分的新方法与传统的 TB 测量一致，可在适当时考虑作为替代方法。