Grosser Oliver S, Klutzny Marcus, Wissel Heiko, Kupitz Dennis, Finger Michael, Schenke Simone, Wuestemann Jan, Lohmann Christoph H, Hoeschen Christoph, Pech Maciej, Staerke Christian, Kreissl Michael C
Department of Radiology and Nuclear Medicine, University Hospital Magdeburg and Medical Faculty of Otto-von-Guericke University, Leipziger Strasse 44, 39120, Magdeburg, Germany.
Research Campus STIMULATE, Otto-von-Guericke University, Magdeburg, Germany.
EJNMMI Phys. 2021 Feb 17;8(1):15. doi: 10.1186/s40658-021-00360-z.
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 Tc). 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.
使用放射性标记膦酸盐的SPECT-CT被认为是评估骨代谢的标准方法（例如，用于膝关节骨关节炎患者）。然而，SPECT可能会受到由假体导致的CT中的金属伪影的影响，这会影响衰减校正。本研究考察了特定假体设计的CT中的金属伪影对定量混合SPECT-CT成像的影响。将植入物放置在均匀填充有放射性活度（955 MBq锝）的体模内。针对不同的X射线管电流（I = 10、40、125 mA）和床速（p = 0.562和1.375）进行CT成像。所有扫描的X射线管电压（U = 120 kVp）和准直器（16×0.625 mm）保持恒定。使用五种不同的重建核进行CT重建（层厚1.25 mm和3.75 mm，均为512×512矩阵）。针对不同的CT扫描和重建方案分析金属伪影的影响。对代表相对于假体的目标结构典型位置（例如，股骨和胫骨）的两个切片位置/体积进行CT和SPECT数据的感兴趣区（ROI）分析。分析一个参考区域（不受金属伪影影响的均匀放射性活度浓度）以作比较。
对于不同的切片位置、CT数据的重建层厚、使用的床速和CT重建核，均观察到CT金属伪影对衰减校正后的SPECT产生显著影响（所有p < 0.0001）。基于优化，确定了一组三种方案，可将CT金属伪影对SPECT数据的影响降至最低。关于参考区域，解剖学相关体积内的放射性活度浓度被低估了8.9 - 10.1%。在区域内检测到重建的放射性活度浓度存在轻微不均匀性，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，在定量和CT辐射剂量之间取得了平衡。
本研究结果表明在假体成像中需要评估SPECT-CT方案。体模实验证明了在特定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数据造成的系统偏差。
