A guide for using NIH Image J for single slice cross-sectional area and composition analysis of the thigh from computed tomography

Reports using computed tomography (CT) to estimate thigh skeletal muscle cross-sectional area and mean muscle attenuation are often difficult to evaluate due to inconsistent methods of quantification and/or poorly described analysis methods. This CT tutorial provides step-by-step instructions in using free, NIH Image J software to quantify both muscle size and composition in the mid-thigh, which was validated against a robust commercially available software, SliceOmatic. CT scans of the mid-thigh were analyzed from 101 healthy individuals aged 65 and older. Mean cross-sectional area and mean attenuation values are presented across seven defined Hounsfield unit (HU) ranges along with the percent contribution of each region to the total mid-thigh area. Inter-software correlation coefficients ranged from R2 = 0.92–0.99 for all specific area comparisons measured using the Image J method compared to SliceOmatic. We recommend reporting individual HU ranges for all areas measured. Although HU range 0–100 includes the majority of skeletal muscle area, HU range -29 to 150 appears to be the most inclusive for quantifying total thigh muscle. Reporting all HU ranges is necessary to determine the relative contribution of each, as they may be differentially affected by age, obesity, disease, and exercise. This standardized operating procedure will facilitate consistency among investigators reporting computed tomography characteristics of the thigh on single slice images.Trial Registration: ClinicalTrials.gov NCT02308228.以往利用计算机断层扫描（CT，computed tomography）评估大腿骨骼肌横截面积与平均肌肉衰减值的相关研究，常因量化方法缺乏统一标准，或分析方法描述模糊，导致结果难以评估。 本CT教程将提供分步操作指南，讲解如何使用免费的美国国立卫生研究院Image J软件（NIH Image J）对大腿中段的肌肉体积与成分进行量化分析；该方法已通过性能优异的商用软件SliceOmatic完成验证。 本次分析共纳入101名65岁及以上健康个体的大腿中段CT扫描影像，研究呈现了7个预设亨氏单位（Hounsfield unit，HU）区间内的平均横截面积与平均衰减值，以及各区域对大腿中段总横截面积的占比。 与SliceOmatic软件的测量结果相比，Image J方法在所有特定区域面积的比对中，软件间相关系数R²介于0.92至0.99之间。 我们建议对所有测量区域分别报告其对应HU区间的结果。 尽管HU区间0–100可覆盖绝大多数骨骼肌面积，但量化大腿总肌肉量时，HU区间-29至150的覆盖范围最为全面。 由于年龄、肥胖、疾病与运动对各HU区间的影响存在差异，因此需报告所有HU区间的结果，以明确各区间的相对贡献。 本标准化操作流程将有助于不同研究者在报告单幅断层图像的大腿CT特征时保持分析方法的一致性。 试验注册：ClinicalTrials.gov NCT02308228。