Weaver Ashley A, Beavers Kristen M, Hightower R Caresse, Lynch Sarah K, Miller Anna N, Stitzel Joel D
a Virginia Tech-Wake Forest University Center for Injury Biomechanics , Winston-Salem , North Carolina.
b Wake Forest School of Medicine , Winston-Salem , North Carolina.
Traffic Inj Prev. 2015;16 Suppl 2(0 2):S153-60. doi: 10.1080/15389588.2015.1054029.
Low bone quality is a contributing factor to motor vehicle crash (MVC) injury. Quantification of occupant bone mineral density (BMD) is important from an injury causation standpoint. The first aim of this study was to validate a technique for measuring lumbar volumetric BMD (vBMD) from phantomless computed tomography (CT) scans. The second aim was to apply the validated phantomless technique to quantify lumbar vBMD in Crash Injury Research and Engineering Network (CIREN) occupants for correlation with age, fracture incidence, and osteopenia/osteoporosis diagnoses.
Quantitative CT (qCT) and dual-energy X-ray absorptiometry (DXA) were collected prospectively for 50 subjects and used to validate a technique to measure vBMD from 281 phantomless CT scans of CIREN occupants. Hounsfield unit (HU) measurements were collected from the L1-L5 vertebrae, right psoas major muscle, and anterior subcutaneous fat for all subjects and from 3 phantom ports with known mg/cc calcium hydroxyapatite values for the validation group. qCT calibration was accomplished using regressions between the phantom HU and mg/cc values to convert L1-L5 HU values to mg/cc. A phantomless calibration technique was developed where the fat and muscle HU values were linearly regressed against fat (-69 mg/cc) and muscle (77 mg/cc) to establish a conversion for L1-L5 HU measurements to mg/cc. vBMD calculated from qCT versus the phantomless method was compared for the 50 subjects to assess agreement and a mg/cc osteopenia threshold was established using DXA T-scores. CIREN HU measurements were converted to mg/cc using the phantomless technique and the mg/cc osteopenia threshold was used to compare vBMD to age, fracture incidence, and osteopenia comorbidity classifications in CIREN.
Linear regression of lumbar vBMD derived from the qCT versus phantomless calibrations showed excellent agreement (R(2) = 0.87, P <.0001). A 145 mg/cc threshold for osteopenia was established (sensitivity = 1, specificity = 0.57) and 44 CIREN occupants had vBMD below this threshold. Of these 44 occupants, 64% were not classified as osteopenic in CIREN, but vBMD suggested undiagnosed osteopenia. Age was negatively correlated with vBMD in both sexes (P <.0001) and CIREN occupants with less than 145 mg/cc vBMD sustained an average 1.7 additional rib/sternum fractures (P =.036).
Because lumbar vBMD was estimated from phantomless CT scans with accuracy similar to qCT, the phantomless technique can be broadly applied to both prospectively and retrospectively assess patient bone quality for research and clinical studies related to MVCs, falls, and aging.
低骨质量是机动车碰撞（MVC）损伤的一个促成因素。从损伤因果关系的角度来看，对乘员骨矿物质密度（BMD）进行量化很重要。本研究的首要目的是验证一种从无体模计算机断层扫描（CT）测量腰椎体积骨密度（vBMD）的技术。第二个目的是应用经过验证的无体模技术来量化碰撞损伤研究与工程网络（CIREN）乘员的腰椎vBMD，以与年龄、骨折发生率和骨质减少/骨质疏松诊断进行关联。
前瞻性收集了50名受试者的定量CT（qCT）和双能X线吸收法（DXA）数据，并用于验证一种从CIREN乘员的281次无体模CT扫描测量vBMD的技术。收集了所有受试者L1 - L5椎体、右侧腰大肌和前皮下脂肪的Hounsfield单位（HU）测量值，以及验证组中3个具有已知毫克/立方厘米羟基磷灰石钙值的体模端口的测量值。通过体模HU值与毫克/立方厘米值之间的回归来完成qCT校准，以将L1 - L5的HU值转换为毫克/立方厘米。开发了一种无体模校准技术，其中脂肪和肌肉HU值与脂肪（-69毫克/立方厘米）和肌肉（77毫克/立方厘米）进行线性回归，以建立将L1 - L5的HU测量值转换为毫克/立方厘米的转换关系。比较了50名受试者通过qCT和无体模方法计算得到的vBMD，以评估一致性，并使用DXA T值建立毫克/立方厘米的骨质减少阈值。使用无体模技术将CIREN的HU测量值转换为毫克/立方厘米，并使用毫克/立方厘米的骨质减少阈值来比较CIREN中vBMD与年龄、骨折发生率和骨质减少合并症分类。
qCT与无体模校准得出的腰椎vBMD的线性回归显示出极好的一致性（R(2) = 0.87，P <.0001）。建立了145毫克/立方厘米的骨质减少阈值（敏感性 = 1，特异性 = 0.57），44名CIREN乘员的vBMD低于此阈值。在这44名乘员中，64%在CIREN中未被归类为骨质减少，但vBMD表明存在未诊断出的骨质减少。年龄在两性中均与vBMD呈负相关（P <.0001），vBMD低于145毫克/立方厘米的CIREN乘员平均多发生1.7处肋骨/胸骨骨折（P =.036）。
由于从无体模CT扫描估计的腰椎vBMD与qCT具有相似的准确性，因此无体模技术可广泛应用于前瞻性和回顾性评估患者的骨质量，以用于与MVC、跌倒和衰老相关的研究和临床研究。
