Ghandour Abed, Sher Andrew, Rassouli Negin, Dhanantwari Amar, Rajiah Prabhakar
Philips Healthcare, Cleveland, OH.
J Comput Assist Tomogr. 2018 Nov/Dec;42(6):858-865. doi: 10.1097/RCT.0000000000000748.
To evaluate the ability of retrospectively generated virtual monoenergetic images (VMIs) from the detector-based spectral computed tomography (SDCT) to augment pulmonary artery enhancement in CT and if iodine map can predict the optimal monoenergetic level.
The study included 79 patients with contrast-enhanced chest CT scans on an SDCT scanner. Conventional 120-kVp images and VMI from 40 to 80 keV were generated. Attenuation, noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were measured at 7 different locations in the pulmonary arterial system. The iodine concentration (in milligrams per milliliter) was calculated using the iodine-density images. The overall image quality was subjectively graded on a 5-point scale, with 1 being the worst and 5 the best. Fifty-four patients with suboptimal pulmonary enhancement (<200 Hounsfield units [HU]) were then identified. From the VMIs, an ideal set was chosen that maintained mean vascular attenuation greater than 200 HU while maintaining at least diagnostically acceptable quality (ie, IQ score ≥3). At this ideal energy level, quantitative and qualitative parameters were compared with the standard 120-kVp polyenergetic study. Average iodine concentrations were correlated with the optimal keV levels used for salvaging suboptimal studies.
The mean attenuation of all the measured pulmonary arterial regions in the suboptimal cases was 136.1 ± 18.1 HU in conventional 120-kVp images. Attenuations of the VMIs at 40, 50, and 60 keV were significantly higher than conventional images measuring 357.5 ± 19.5, 243.6 ± 16.7, and 176.6 ± 15.0 HU, respectively (P < 0.001). Similar results were seen with SNR and CNR. In total, 50 studies can be salvaged, with 50 keV being the optimal energy for 21, 60 keV optimal for 17, and 40 keV optimal for 12 studies. At the optimal energy level, there were improvements of attenuation, SNR, and CNR by 71%, 63%, and 137% compared with conventional images. There was a positive correlation between iodine value and optimal reconstruction energy with a linear equation y = 5.9539x + 27.434 and R = 0.8093.
Suboptimal enhanced pulmonary arterial CT studies can be salvaged using low-energy VMI generated from the SDCT scanner. There were significant improvements of attenuation, SNR, and CNR at the optimal monoenergetic level.
评估基于探测器的光谱计算机断层扫描（SDCT）回顾性生成的虚拟单能图像（VMI）增强CT肺动脉强化的能力，以及碘图能否预测最佳单能水平。
本研究纳入79例在SDCT扫描仪上进行胸部增强CT扫描的患者。生成常规120 kVp图像和40至80 keV的VMI。在肺动脉系统的7个不同位置测量衰减、噪声、信噪比（SNR）和对比噪声比（CNR）。使用碘密度图像计算碘浓度（毫克/毫升）。整体图像质量采用5分制主观评分，1分为最差，5分为最佳。然后确定54例肺动脉强化欠佳（<200亨氏单位[HU]）的患者。从VMI中选择一组理想图像，使其平均血管衰减保持大于200 HU，同时保持至少可接受的诊断质量（即IQ评分≥3）。在这个理想能量水平下，将定量和定性参数与标准的120 kVp多能研究进行比较。平均碘浓度与用于挽救欠佳研究的最佳keV水平相关。
在常规120 kVp图像中，欠佳病例所有测量的肺动脉区域的平均衰减为136.1±18.1 HU。40、50和60 keV时VMI的衰减显著高于常规图像，分别为357.5±19.5、243.6±16.7和176.6±15.0 HU（P<0.001）。SNR和CNR也有类似结果。总共可以挽救50项研究，其中21项研究的最佳能量为50 keV，17项为60 keV，12项为40 keV。在最佳能量水平下，与常规图像相比，衰减、SNR和CNR分别提高了71%、63%和137%。碘值与最佳重建能量之间存在正相关，线性方程为y = 5.9539x + 27.434，R = 0.8093。
使用SDCT扫描仪生成的低能量VMI可以挽救欠佳的肺动脉CT增强研究。在最佳单能水平下，衰减、SNR和CNR有显著改善。
