Heismann Björn, Kreisler Björn, Fasbender Robert
Friedrich-Alexander-University of Erlangen-Nuremberg, Siemens Healthineers AG, Forchheim, Germany.
Siemens Healthineers AG, Forchheim, Germany.
Med Phys. 2025 Mar;52(3):1526-1535. doi: 10.1002/mp.17591. Epub 2024 Dec 19.
Photon counting computed tomography (PCCT) employs direct and spectrally resolved counting of individual x-ray quanta, enhancing image quality compared to the standard energy-integrating CT (EICT).
To evaluate the quantitative improvements in CT image quality metrics by comparing the first medical PCCT with a state-of-the-art EICT.
The PCCT versus EICT noise improvement ratio R was derived from the quantum statistics of the measurement process and measured across the clinical x-ray flux range for both systems. Detector and system modulation transfer functions (MTFs) were obtained using tilted-slit and wire phantom measurements. Image root mean square (RMS) noise, noise power spectrum (NPS), and x-ray patient dose were compared using a CatPhan phantom at two identical clinical target resolutions.
The measurement of the PCCT noise improvement ratio R showed an elimination of electronic noise and a 10% noise transfer advantage. The PCCT detector MTF exhibited 3x higher angular resolution limits in comparison to EICT and close to ideal sinc behavior due to the electromagnetic formation of pixels in the PCCT semiconductor detector. This translated to 3.5x enhancements in CT system MTF ratios at 10 LP/cm, reflecting a significant improvement in millimeter range CT imaging. Both the improved quantum detection and the system MTF ratio improvement contribute to the measured 3x enhancements in image NPS at 10 LP/cm for identical image target resolution. An improvement of up to 1.7x in RMS image noise was observed accordingly. For low and ultra-low dose imaging with image filtering, dose efficiency increased between 2x and 10x, demonstrating the PCCT's capability to advance CT ultra-low dose imaging.
The direct counting detection in PCCT has been shown to significantly improve sinogram noise and detector MTF ratios compared to energy integrating EICT. The observed translations into CT system MTF, image NPS, image noise, and dose ratios reflect a paradigm shift for CT image quality and dose efficiency.
光子计数计算机断层扫描（PCCT）采用对单个X射线量子进行直接和光谱分辨计数，与标准能量积分CT（EICT）相比，可提高图像质量。
通过将首台医用PCCT与最先进的EICT进行比较，评估CT图像质量指标的定量改善情况。
PCCT与EICT的噪声改善率R源自测量过程的量子统计，并在两个系统的临床X射线通量范围内进行测量。使用倾斜狭缝和线模体测量获得探测器和系统调制传递函数（MTF）。在两个相同的临床目标分辨率下，使用CatPhan模体比较图像均方根（RMS）噪声、噪声功率谱（NPS）和X射线患者剂量。
PCCT噪声改善率R的测量显示消除了电子噪声，并具有10%的噪声传递优势。与EICT相比，PCCT探测器MTF的角分辨率极限高出3倍，并且由于PCCT半导体探测器中像素的电磁形成，接近理想的辛格函数行为。这转化为在10LP/cm时CT系统MTF比率提高3.5倍，反映出毫米级CT成像有显著改善。对于相同的图像目标分辨率，改进的量子检测和系统MTF比率的提高共同促成了在10LP/cm时图像NPS测量提高3倍。相应地，观察到RMS图像噪声提高了1.7倍。对于采用图像滤波的低剂量和超低剂量成像，剂量效率提高了2至10倍，证明了PCCT推进CT超低剂量成像的能力。
与能量积分EICT相比，PCCT中的直接计数检测已显示出可显著改善正弦图噪声和探测器MTF比率。观察到的在CT系统MTF、图像NPS、图像噪声和剂量比率方面的变化反映了CT图像质量和剂量效率的范式转变。
