在120、100和80千伏峰值电压下，使用迭代图像重建技术（AIDR 3D）测定冠状动脉钙评分的校准。
Calibration of coronary calcium scores determined using iterative image reconstruction (AIDR 3D) at 120, 100, and 80 kVp.
作者信息
Blobel Joerg, Mews Juergen, Goatman Keith A, Schuijf Joanne D, Overlaet Willem
机构信息
Toshiba Medical Systems Europe BV, Zoetermeer 2718 RP, The Netherlands.
Toshiba Medical Visualization Systems Europe, Ltd., Edinburgh EH6 5NP, United Kingdom.
出版信息
Med Phys. 2016 Apr;43(4):1921. doi: 10.1118/1.4942484.
PURPOSE
Computed tomography (CT) radiation dose reduction is frequently achieved by applying lower tube voltages and using iterative reconstruction (IR). For calcium scoring, the reference protocol at 120 kVp with filtered back projection (FBP) is still used, because kVp and IR may influence the Agatston score (AS) and volume score (VS). The authors present a two-step method to optimize dose: first, to determine the lowest feasible exposure and highest noise thresholds; second, to define a calibration method that ensures that the AS and VS are similar to the reference protocol.
METHODS
AS and VS were measured for an anthropomorphic thoracic phantom that includes a calcium calibration module. The phantom was scanned on a 320-row CT scanner, at tube voltages of 120 kVp using FBP, and 120, 100, and 80 kVp using adaptive iterative dose reduction (AIDR 3D) reconstruction. The minimum CTDIs were determined based on three objective quality criteria. Calibration was performed to estimate adjusted CT number thresholds for the lower kVp acquisitions. Finally, the accuracies of the total and individual insert scores at dose level close to the minimum CTDI level were investigated and compared to low (FBPLD - 120) and high (FBPHD - 120) dose reference protocols (based on ten repeated acquisitions for each group).
RESULTS
IR allows the exposure to be reduced by 69% at 120 kVp, with no significant effect on the total scores when averaged over all included dose steps and compared to FBP-120 (AS: 693 vs 699, p = 0.182; VS: 588 vs 587 mm(3), p = 0.569). Also when averaged over ten repeated scans and compared to FBPHD - 120 (AS: 709 vs 704, p = 0.435; VS: 604 vs 601 mm(3), p = 0.479), there is no statistical significant effect. Reducing the peak tube voltage allows even greater dose reductions: 73% at 100 kVp and 76% at 80 kVp. The calibrated CT number thresholds for analysis at 120, 100, and 80 kVp were, respectively, 130, 133, and 160 HU for the Agatston score, and 130, 132, and 140 HU for the volume score. Following the calibration, the mean scores of the four groups with dose variation were not significantly different from the reference protocol, at 100 kVp (AS: 698 vs 699, p = 0.818; VS: 584 vs 587 mm(3), p = 0.365) or at 80 kVp (AS: 698 vs 699, p = 0.996; VS: 586 vs 587 mm(3), p = 0.827). Similarly, there was no significant score difference with FBPLD - 120 during repeated scanning: 100 kVp (AS: 690 vs 694, p = 0.394; VS: 579 vs 585 mm(3), p = 0.168) and 80 kVp (AS: 703 vs 694, p = 0.115; VS: 588 vs 585 mm(3), p = 0.613). Compared to FBPHD - 120 group, the relative score deviation for the accuracy of the 400 and 800 mg/cm(3) HA inserts with 3 and 5 mm diameter is less than 7%. However, the relative deviation of the smaller 1 mm inserts is poorer (up to 41% deviations for scores <3).
CONCLUSIONS
With iterative reconstruction using AIDR 3D, deviations of the total Agatston and volume scores remain within 4% of the reference protocol. The 1 mm inserts were detected as calcification, but scores less than ten tend to be underestimated. Following the calibration process, the application of IR in combination with reduced tube voltages allows up to 76% lower radiation dose.
目的
计算机断层扫描（CT）辐射剂量的降低通常通过采用较低的管电压和使用迭代重建（IR）来实现。对于钙化积分，120 kVp 结合滤波反投影（FBP）的参考方案仍在使用，因为 kVp 和 IR 可能会影响阿加斯顿积分（AS）和容积积分（VS）。作者提出了一种两步优化剂量的方法：首先，确定最低可行曝光量和最高噪声阈值；其次，定义一种校准方法，以确保 AS 和 VS 与参考方案相似。
方法
对包含钙化校准模块的人体胸部模型测量 AS 和 VS。该模型在 320 排 CT 扫描仪上进行扫描，管电压为 120 kVp 时使用 FBP 重建，管电压为 120、100 和 80 kVp 时使用自适应迭代剂量降低（AIDR 3D）重建。基于三个客观质量标准确定最小剂量长度乘积（CTDI）。进行校准以估计较低 kVp 采集时的调整 CT 数阈值。最后，研究了接近最小 CTDI 水平剂量下总积分和单个植入物积分的准确性，并与低剂量（FBPLD - 120）和高剂量（FBPHD - 120）参考方案进行比较（每组基于十次重复采集）。
结果
IR 可使 120 kVp 时的曝光量降低 69%，与 FBP - 120 相比，在所有纳入的剂量步骤中平均时，对总分无显著影响（AS：693 对 699，p = 0.182；VS：588 对 587 mm³，p = 0.569）。在十次重复扫描中平均并与 FBPHD - 120 相比时（AS：709 对 704，p = 0.435；VS：604 对 601 mm³，p = 0.479），也无统计学显著影响。降低管电压峰值可实现更大的剂量降低：100 kVp 时降低 73%，80 kVp 时降低 76%。用于 120、100 和 80 kVp 分析的校准 CT 数阈值，阿加斯顿积分分别为 130、133 和 160 HU，容积积分为 130、132 和 140 HU。校准后，剂量变化的四组平均积分与参考方案相比无显著差异，100 kVp 时（AS：698 对 699，p = 0.818；VS：584 对 587 mm³，p = 0.365）或 80 kVp 时（AS：698 对 699，p = 0.996；VS：586 对 587 mm³，p = 0.827）。同样，在重复扫描期间与 FBPLD - 120 相比积分无显著差异：100 kVp 时（AS：690 对 694，p = 0.394；VS：579 对 585 mm³，p = 0.168）和 80 kVp 时（AS：703 对 694，p = 0.115；VS：588 对 585 mm³،p = 0.613）。与 FBPHD - 120 组相比，直径为 3 和 5 mm 的 400 和 800 mg/cm³ 羟基磷灰石（HA）植入物准确性的相对积分偏差小于 7%。然而，较小的 1 mm 植入物的相对偏差较差（积分<3 时偏差高达 41%）。
结论
使用 AIDR 3D 进行迭代重建时，阿加斯顿总分和容积积分的偏差保持在参考方案的 4%以内。1 mm 植入物被检测为钙化，但积分小于 10 时往往被低估。在校准过程之后，IR 与降低管电压相结合可使辐射剂量降低高达 76%。
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