Department of Radiology, Mayo Clinic, Rochester, MN, United States of America.
Phys Med Biol. 2020 Aug 31;65(17):17NT01. doi: 10.1088/1361-6560/ab99e4.
Multi-energy CT imaging of large patients with conventional dual-energy (DE)-CT using an energy-integrating-detector (EID) is challenging due to photon starvation-induced image artifacts, especially in lower tube potential (80-100 kV) images. Here, we performed phantom experiments to investigate the performance of DECT for morbidly obese patients, using an iodine and water material decomposition task as an example, on an emulated dual-source (DS)-photon-counting-detector (PCD)-CT, and compared its performance with a clinical DS-EID-CT. An abdominal CT phantom with iodine inserts of different concentrations was wrapped with tissue-equivalent gel layers to emulate a large patient (50 cm lateral size). The phantom was scanned on a research whole-body single-source (SS)-PCD-CT (140 kV tube potential), a DS-PCD-CT (100/Sn140 kV; Sn140 indicates 140 kV with Sn filter), and a clinical DS-EID-CT (100/Sn140 kV) with the same radiation dose. Phantom scans were repeated five times on each system. The DS-PCD-CT acquisition was emulated by scanning twice on the SS-PCD-CT using different tube potentials. The multi-energy CT images acquired on each system were then reconstructed, and iodine- and water-specific images were generated using material decomposition. The root-mean-square-error (RMSE) between true and measured iodine concentrations were calculated for each system and compared. The images acquired on the DS-EID-CT showed severe artifacts, including ringing, reduced uniformity, and photon starvation artifacts, especially for low-energy images. These were largely reduced in DS-PCD-CT images. The CT number difference that was measured using regions-of-interest across field-of-view were reduced from 20.3 ± 0.9 (DS-EID-CT) to 2.5 ± 0.4 HU on DS-PCD-CT, showing improved image uniformity using DS-PCD-CT. Iodine RMSE was reduced from 3.42 ± 0.03 mg ml (SS-PCD-CT) and 2.90 ± 0.03 mg ml (DS-EID-CT) to 2.39 ± 0.05 mg ml using DS-PCD-CT. DS-PCD-CT out-performed a clinical DS-EID-CT for iodine and water-based material decomposition on phantom emulating obese patients by reducing image artifacts and improving iodine quantification (RMSE reduced by 20%). With DS-PCD-CT, multi-energy CT can be performed on large patients that cannot be accommodated with current DECT.
使用能量积分探测器（EID）对常规双能（DE）-CT 中的大患者进行多能量 CT 成像是具有挑战性的，因为光子饥饿引起的图像伪影，尤其是在较低的管电压（80-100 kV）图像中。在这里，我们使用碘和水材料分解任务作为示例，在模拟的双源（DS）-光子计数探测器（PCD）-CT 上进行了病态肥胖患者的 DECT 性能研究，并将其性能与临床 DS-EID-CT 进行了比较。一个带有不同浓度碘插入物的腹部 CT 体模用组织等效凝胶层包裹，以模拟大患者（50 cm 侧尺寸）。该体模在研究型全身单源（SS）-PCD-CT（140 kV 管电压）、DS-PCD-CT（100/Sn140 kV；Sn140 表示带 Sn 滤波器的 140 kV）和相同辐射剂量的临床 DS-EID-CT 上进行了扫描。每个系统上的体模扫描重复五次。DS-PCD-CT 采集通过在 SS-PCD-CT 上使用不同的管电压进行两次扫描来模拟。然后对每个系统采集的多能量 CT 图像进行重建，并使用材料分解生成碘和水特异性图像。计算了每个系统的真实和测量碘浓度之间的均方根误差（RMSE）并进行了比较。DS-EID-CT 采集的图像显示出严重的伪影，包括振铃、不均匀性降低和光子饥饿伪影，尤其是低能量图像。这些在 DS-PCD-CT 图像中得到了很大程度的减少。使用整个视场的感兴趣区域测量的 CT 数差异从 DS-EID-CT 上的 20.3 ± 0.9（DS-EID-CT）减少到 DS-PCD-CT 上的 2.5 ± 0.4 HU，表明 DS-PCD-CT 提高了图像均匀性。使用 DS-PCD-CT，碘的 RMSE 从 SS-PCD-CT（3.42 ± 0.03 mg ml）和 DS-EID-CT（2.90 ± 0.03 mg ml）降低到 2.39 ± 0.05 mg ml。DS-PCD-CT 通过减少图像伪影和提高碘定量（RMSE 降低 20%），在模拟肥胖患者的情况下，在碘和水基材料分解方面优于临床 DS-EID-CT。使用 DS-PCD-CT，可以对目前 DECT 无法容纳的大患者进行多能量 CT 检查。
