OBJECTIVES To determine the best compromise between low radiation dose and suitable image quality for the detection of lytic and sclerotic bone lesions of the lumbar spine and pelvis. METHODS A phantom was scanned using the routine protocol (STD, 13 mGy) and six decreasing dose levels. Raw data were reconstructed using level 3 of iterative reconstruction (IR3) with 1-mm slice thickness for the STD protocol and highest IR levels with 3-mm slice thickness for the others. CTDIvol was used for radiation dose assessment. Quantitative criteria (noise power spectrum [NPS], task-based transfer function [TTF], and the detectability index [d']), as well as qualitative analysis, were used to compare protocols. NPS and TTF were computed using specific software (imQuest). d' was computed for two imaging tasks: lytic and sclerotic bone lesions. A subjective analysis was performed to validate the image quality obtained on the anthropomorphic phantom with the different dose values. RESULTS Similar d' values were found for CTDIvol from 3 to 4 mGy with IR4 and from 1 to 2 mGy for IR5 compared with d' values using the STD protocol. Image quality was validated subjectively for IR4 but rejected for IR5 (image smoothing). Finally, for the same d', the dose was reduced by 74% compared with the STD protocol, with the CTDIvol being 3.4 mGy for the lumbar spine and for the pelvis. CONCLUSION A dose level as low as 3.4 mGy, in association with high levels of IR, provides suitable image quality for the detection of lytic and sclerotic bone lesions of the lumbar spine and pelvis. KEY POINTS • A CTDI volof 3.4 mGy, in association with high iterative reconstruction level, provides suitable image quality for the detection of lytic and sclerotic bone lesions, both at objective and subjective analysis. • Compared with the standard protocol, radiation dose can be reduced up to 74% for the lumbar spine and pelvis. • A task-based image quality assessment using the detectability index represents an objective method for the assessment of image quality and bridges the gap between complex physical metrics and subjective image analysis.

中文翻译：

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CT检测溶血性和硬化性骨病变的放射剂量的优化：一项幻像研究。

目的确定低辐射剂量和合适的图像质量之间的最佳折衷，以检测腰椎和骨盆的溶解性和硬化性骨病变。方法使用常规方案（STD，13 mGy）和六种降低剂量水平扫描体模。原始数据使用3级迭代重建（IR3）重建，STD协议的切片厚度为1毫米，其他IR级别最高的切片厚度为3毫米。CTDIvol用于辐射剂量评估。使用定量标准（噪声功率谱[NPS]，基于任务的传递函数[TTF]和可检测性指标[d']）以及定性分析来比较协议。使用特定软件（imQuest）计算NPS和TTF。d'用于两个成像任务：溶解性和硬化性骨病变。进行主观分析以验证在具有不同剂量值的拟人化体模上获得的图像质量。结果与使用STD协议的d'值相比，使用IR4的CTDIvol从3-4 mGy和IR5的1-2 mGy得出了相似的d'值。主观上对IR4验证了图像质量，但对IR5拒绝了图像质量（图像平滑）。最后，对于相同的d'，与STD方案相比，剂量减少了74％，对于腰椎和骨盆CTDIvol为3.4 mGy。结论低至3.4 mGy的剂量水平与高水平的IR结合可为检测腰椎和骨盆的溶解性和硬化性骨病变提供合适的图像质量。要点•CTDI阈值为3.4 mGy，并具有较高的迭代重建水平，无论是客观分析还是主观分析，均可提供合适的图像质量，以检测溶骨和硬化性骨病变。•与标准方案相比，腰椎和骨盆的辐射剂量最多可降低74％。•使用可检测性指标的基于任务的图像质量评估代表了评估图像质量的客观方法，并弥合了复杂的物理指标和主观图像分析之间的差距。