SPECT-CT using radiolabeled phosphonates is considered a standard for assessing bone metabolism (e.g., in patients with osteoarthritis of knee joints). However, SPECT can be influenced by metal artifacts in CT caused by endoprostheses affecting attenuation correction. The current study examined the effects of metal artifacts in CT of a specific endoprosthesis design on quantitative hybrid SPECT-CT imaging. The implant was positioned inside a phantom homogenously filled with activity (955 MBq 99mTc). CT imaging was performed for different X-ray tube currents (I = 10, 40, 125 mA) and table pitches (p = 0.562 and 1.375). X-ray tube voltage (U = 120 kVp) and primary collimation (16 × 0.625 mm) were kept constant for all scans. The CT reconstruction was performed with five different reconstruction kernels (slice thickness, 1.25 mm and 3.75 mm, each 512 × 512 matrix). Effects from metal artifacts were analyzed for different CT scans and reconstruction protocols. ROI analysis of CT and SPECT data was performed for two slice positions/volumes representing the typical locations for target structures relative to the prosthesis (e.g., femur and tibia). A reference region (homogenous activity concentration without influence from metal artifacts) was analyzed for comparison. Significant effects caused by CT metal artifacts on attenuation-corrected SPECT were observed for the different slice positions, reconstructed slice thicknesses of CT data, and pitch and CT-reconstruction kernels used (all, p < 0.0001). Based on the optimization, a set of three protocols was identified minimizing the effect of CT metal artifacts on SPECT data. Regarding the reference region, the activity concentration in the anatomically correlated volume was underestimated by 8.9–10.1%. A slight inhomogeneity of the reconstructed activity concentration was detected inside the regions with a median up to 0.81% (p < 0.0001). Using an X-ray tube current of 40 mA showed the best result, balancing quantification and CT exposure. The results of this study demonstrate the need for the evaluation of SPECT-CT protocols in prosthesis imaging. Phantom experiments demonstrated the possibility for quantitative SPECT-CT of bone turnover in a specific prosthesis design. Meanwhile, a systematic bias caused by metal implants on quantitative SPECT data has to be considered.

中文翻译：

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单室关节卸载膝关节植入物（ATLAS膝关节系统）患者的骨重塑定量成像-基于SPECT-CT定量的金属假象的影响

使用放射标记的膦酸酯的SPECT-CT被认为是评估骨代谢的标准（例如，在膝关节骨关节炎患者中）。但是，SPECT可能会受到内假体影响衰减校正的CT中的金属伪影的影响。当前的研究检查了特定的内置假体设计的CT中的金属假象对定量混合SPECT-CT成像的影响。将植入物放置在均质充满活动性的体模内（955 MBq 99mTc）。针对不同的X射线管电流（I = 10、40、125 mA）和工作台间距（p = 0.562和1.375）进行了CT成像。所有扫描的X射线管电压（U = 120 kVp）和一次准直（16×0.625 mm）保持恒定。使用五个不同的重建内核（切片厚度1.25 mm和3.75 mm，每个512×512矩阵）。针对不同的CT扫描和重建方案分析了金属伪影的影响。对两个切片位置/体积进行了CT和SPECT数据的ROI分析，这两个切片位置/体积代表相对于假体（例如股骨和胫骨）的目标结构的典型位置。分析参考区域（不受金属伪影影响的均匀活性浓度）以进行比较。对于不同的切片位置，CT数据的重构切片厚度以及所使用的螺距和CT重构内核，观察到了CT金属伪影对衰减校正后的SPECT产生的显着影响（全部，p <0.0001）。基于优化，确定了三个协议的集合，以最小化CT金属伪影对SPECT数据的影响。关于参考区域，解剖相关体积中的活动浓度被低估了8.9–10.1％。在区域内部检测到重建活动浓度略有不均匀，中位数最高为0.81％（p <0.0001）。使用40 mA的X射线管电流显示出最佳结果，平衡了定量和CT曝光。这项研究的结果表明，需要在假体成像中评估SPECT-CT方案。幻影实验证明了在特定的假体设计中定量定量SPECT-CT骨转换的可能性。同时，必须考虑金属注入对定量SPECT数据造成的系统性偏差。在区域内部检测到重建活动浓度略有不均匀，中位数最高为0.81％（p <0.0001）。使用40 mA的X射线管电流显示出最佳结果，平衡了定量和CT曝光。这项研究的结果表明，需要在假体成像中评估SPECT-CT方案。幻影实验证明了在特定的假体设计中定量定量SPECT-CT骨转换的可能性。同时，必须考虑金属注入对定量SPECT数据造成的系统性偏差。在区域内部检测到重建的活性浓度存在轻微的不均匀性，中位数高达0.81％（p <0.0001）。使用40 mA的X射线管电流显示出最佳结果，平衡了定量和CT曝光。这项研究的结果表明，需要在假体成像中评估SPECT-CT方案。幻影实验证明了在特定的假体设计中定量定量SPECT-CT骨转换的可能性。同时，必须考虑金属注入对定量SPECT数据造成的系统性偏差。幻影实验证明了在特定的假体设计中对骨转换进行定量SPECT-CT的可能性。同时，必须考虑金属植入物对定量SPECT数据造成的系统性偏差。幻影实验证明了在特定的假体设计中定量定量SPECT-CT骨转换的可能性。同时，必须考虑金属注入对定量SPECT数据造成的系统性偏差。