Department of Radiology, University Hospitals Cleveland Medical Center, Cleveland, OH, USA; Department of Radiology, Case Western Reserve University, Cleveland, OH, USA; Department of Radiology, Universitair Ziekenhuis Brussel, Brussels, Belgium; Vrije Universiteit Brussel, Brusssels, Belgium.
Department of Radiology, Case Western Reserve University, Cleveland, OH, USA; Case Center for Imaging Research, Case Western Reserve University, Cleveland, OH, USA.
J Clin Densitom. 2019 Jul-Sep;22(3):374-381. doi: 10.1016/j.jocd.2018.10.004. Epub 2018 Oct 26.
Bone mineral density (BMD) analysis by Dual-Energy x-ray Absorptiometry (DXA) can have some false negatives due to overlapping structures in the projections. Spectral Detector CT (SDCT) can overcome these limitations by providing volumetric information. We investigated its performance for BMD assessment and compared it to DXA and phantomless volumetric bone mineral density (PLvBMD), the latter known to systematically underestimate BMD. DXA is the current standard for BMD assessment, while PLvBMD is an established alternative for opportunistic BMD analysis using CT. Similarly to PLvBMD, spectral data could allow BMD screening opportunistically, without additional phantom calibration.
Ten concentrations of dipotassium phosphate (K2HPO4) ranging from 0 to 600 mg/ml, in an acrylic phantom were scanned using SDCT in four different, clinically-relevant scan conditions. Images were processed to estimate the K2HPO4 concentrations. A model representing a human lumbar spine (European Spine Phantom) was scanned and used for calibration via linear regression analysis. After calibration, our method was retrospectively applied to abdominal SDCT scans of 20 patients for BMD assessment, who also had PLvBMD and DXA. Performance of PLvBMD, DXA and our SDCT method were compared by sensitivity, specificity, negative predictive value and positive predictive value for decreased BMD.
There was excellent correlation (R2 >0.99, p < 0.01) between true and measured K2HPO4 concentrations for all scan conditions. Overall mean measurement error ranged from -11.5 ± 4.7 mg/ml (-2.8 ± 6.0%) to -12.3 ± 6.3 mg/ml (-4.8 ± 3.0%) depending on scan conditions. Using DXA as a reference standard, sensitivity/specificity for detecting decreased BMD in the scanned patients were 100%/73% using SDCT, 100%/40% using PLvBMD provided T-scores, and 90-100%/40-53% using PLvBMD hydroxyapatite density classifications, respectively.
Our results show excellent sensitivity and high specificity of SDCT for detecting decreased BMD, demonstrating clinical feasibility. Further validation in prospective clinical trials will be required.
双能 X 射线吸收法（DXA）的骨密度（BMD）分析可能由于投影中的重叠结构而出现一些假阴性。光谱探测器 CT（SDCT）可以通过提供体积信息来克服这些限制。我们研究了它在 BMD 评估中的性能，并将其与 DXA 和无骨 Phantom 体积骨密度（PLvBMD）进行了比较，后者已知系统地低估了 BMD。DXA 是目前用于 BMD 评估的标准，而 PLvBMD 是一种已建立的 CT 机会性 BMD 分析替代方法。与 PLvBMD 类似，光谱数据可以在没有额外的 Phantom 校准的情况下，有机会进行 BMD 筛查。
十种浓度的磷酸二氢钾（K2HPO4），浓度范围为 0 至 600mg/ml，在一个丙烯酸体模中，使用 SDCT 在四个不同的、具有临床相关性的扫描条件下进行扫描。对图像进行处理以估计 K2HPO4 浓度。扫描一个代表人类腰椎的模型（欧洲脊柱 Phantom），并通过线性回归分析进行校准。校准后，我们的方法通过灵敏度、特异性、阴性预测值和阳性预测值，对 20 名患者的腹部 SDCT 扫描进行了回顾性 BMD 评估，这些患者还进行了 PLvBMD 和 DXA 检查。通过降低 BMD 的灵敏度、特异性、阴性预测值和阳性预测值，比较了 PLvBMD、DXA 和我们的 SDCT 方法的性能。
所有扫描条件下，真K2HPO4 浓度与实测 K2HPO4 浓度之间均存在极好的相关性（R2>0.99，p<0.01）。总的平均测量误差范围为-11.5±4.7mg/ml（-2.8±6.0%）至-12.3±6.3mg/ml（-4.8±3.0%），具体取决于扫描条件。以 DXA 为参考标准，SDCT 检测到扫描患者的 BMD 降低的灵敏度/特异性为 100%/73%，提供 T 评分的 PLvBMD 为 100%/40%，使用 PLvBMD 羟磷灰石密度分类的灵敏度/特异性分别为 90-100%/40-53%。
我们的结果表明 SDCT 检测 BMD 降低具有极好的灵敏度和高特异性，证明了临床可行性。需要进一步的前瞻性临床试验验证。
