Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, USA.
Department of Radiology, Johns Hopkins Medical Institutions, Baltimore, MD, USA.
Med Phys. 2018 Dec;45(12):5420-5436. doi: 10.1002/mp.13244. Epub 2018 Nov 13.
Indirect-detection CMOS flat-panel detectors (FPDs) offer fine pixel pitch, fast readout, and low electronic noise in comparison to current a-Si:H FPDs. This work investigates the extent to which these potential advantages affect imaging performance in mobile C-arm fluoroscopy and cone-beam CT (CBCT).
FPDs based on CMOS (Xineos 3030HS, 0.151 mm pixel pitch) or a-Si:H (PaxScan 3030X, 0.194 mm pixel pitch) sensors were outfitted on equivalent mobile C-arms for fluoroscopy and CBCT. Technical assessment of 2D and 3D imaging performance included measurement of electronic noise, gain, lag, modulation transfer function (MTF), noise-power spectrum (NPS), detective quantum efficiency (DQE), and noise-equivalent quanta (NEQ) in fluoroscopy (with entrance air kerma ranging 5-800 nGy per frame) and cone-beam CT (with weighted CT dose index, CTDI , ranging 0.08-1 mGy). Image quality was evaluated by clinicians in vascular, orthopaedic, and neurological surgery in realistic interventional scenarios with cadaver subjects emulating a variety of 2D and 3D imaging tasks.
The CMOS FPD exhibited 2-3× lower electronic noise and ~7× lower image lag than the a-Si:H FPD. The 2D (projection) DQE was superior for CMOS at ≤50 nGy per frame, especially at high spatial frequencies (2% improvement at 0.5 mm and ≥50% improvement at 2.3 mm ) and was somewhat inferior at moderate-high doses (up to 18% lower DQE for CMOS at 0.5 mm ). For smooth CBCT reconstructions (low-frequency imaging tasks), CMOS exhibited 10%-20% higher NEQ (at 0.1-0.5 mm ) at the lowest dose levels (CTDI ≤0.1 mGy), while the a-Si:H system yielded slightly (5%) improved NEQ (at 0.1-0.5 lp/mm) at higher dose levels (CTDI ≥0.6 mGy). For sharp CBCT reconstructions (high-frequency imaging tasks), NEQ was ~32% higher above 1 mm for the CMOS system at mid-high-dose levels and ≥75% higher at the lowest dose levels (CTDI ≤0.1 mGy). Observer assessment of 2D and 3D cadaver images corroborated the objective metrics with respect to a variety of pertinent interventional imaging tasks.
Measurements of image noise, spatial resolution, DQE, and NEQ indicate improved low-dose performance for the CMOS-based system, particularly at lower doses and higher spatial frequencies. Assessment in realistic imaging scenarios confirmed improved visibility of fine details in low-dose fluoroscopy and CBCT. The results quantitate the extent to which CMOS detectors improve mobile C-arm imaging performance, especially in 2D and 3D imaging scenarios involving high-resolution tasks and low-dose conditions.
与当前的非晶硅（a-Si:H）平板探测器相比，间接探测 CMOS 平板探测器（FPD）具有更精细的像素间距、更快的读出速度和更低的电子噪声。本研究旨在探讨这些潜在优势在移动 C 臂透视和锥形束 CT（CBCT）中对成像性能的影响程度。
在等效的移动 C 臂上为基于 CMOS（Xineos 3030HS，0.151mm 像素间距）或 a-Si:H（PaxScan 3030X，0.194mm 像素间距）传感器的 FPD 配备设备。二维和三维成像性能的技术评估包括电子噪声、增益、滞后、调制传递函数（MTF）、噪声功率谱（NPS）、探测量子效率（DQE）和噪声等效量子（NEQ）的测量，这些测量分别在透视（每个框架的入口空气比释动能为 5-800nGy 范围内）和 CBCT（加权 CT 剂量指数，CTDI，范围为 0.08-1mGy）中进行。临床医生在具有尸体受试者的现实介入场景中对血管、矫形和神经外科的图像质量进行了评估，这些场景模拟了各种二维和三维成像任务。
与 a-Si:H FPD 相比，CMOS FPD 的电子噪声低约 2-3 倍，图像滞后低约 7 倍。在 ≤50nGy/帧时，CMOS 的二维（投影）DQE 优于 a-Si:H，尤其是在高空间频率时（0.5mm 处的改进幅度约为 2%，≥2.3mm 处的改进幅度≥50%），而在中高剂量时略差（0.5mm 处的 CMOS DQE 低 18%）。对于平滑的 CBCT 重建（低频成像任务），在最低剂量水平（CTDI≤0.1mGy）下，CMOS 产生约 10%-20%更高的 NEQ（在 0.1-0.5mm 处），而 a-Si:H 系统在更高剂量水平（CTDI≥0.6mGy）下产生略高（5%）的 NEQ（在 0.1-0.5lp/mm 处）。对于锐利的 CBCT 重建（高频成像任务），在中高剂量水平下，CMOS 系统在 1mm 以上的 NEQ 高约 32%，在最低剂量水平（CTDI≤0.1mGy）时，NEQ 高≥75%。二维和三维尸体图像的观察者评估与各种相关介入成像任务的客观指标相符。
图像噪声、空间分辨率、DQE 和 NEQ 的测量表明，基于 CMOS 的系统在低剂量性能方面有了显著改善，尤其是在较低剂量和较高空间频率下。在现实的成像场景中的评估证实，低剂量透视和 CBCT 中精细细节的可见度得到了改善。这些结果量化了 CMOS 探测器在移动 C 臂成像性能方面的改进程度，尤其是在涉及高分辨率任务和低剂量条件的二维和三维成像场景中。
