目的： 评估基于光子计数CT（photon-counting computed tomography， PCCT）的胰腺低剂量动态容积灌注CT（volume perfusion computed tomography， VPCT）扫描中单期图像的图像质量及其对胰腺导管腺癌（pancreatic ductal adenocarcinoma， PDAC）进行形态学评估的可行性。 方法： 2024年4月至8月，前瞻性收集疑似PDAC的患者，术前行胰腺VPCT扫描，纳入经组织病理学确诊为PDAC的55例患者，记录并计算检查辐射剂量。分析灌注时间衰减曲线，分别基于T3D、55 keV和70 keV虚拟单能量图像（virtual monoenergetic image， VMI），提取最佳胰腺实质期和门静脉期单期图像，用于临床诊断和PDAC的形态学评估。对图像进行主观评分，并测量图像中病灶、正常胰腺实质、胰周血管及腹壁脂肪CT值，以腹壁脂肪CT值标准差为图像噪声值，计算病灶、正常胰腺实质、胰周血管信噪比以及病灶、胰周血管对比噪声比（contrast-to-noise ratio， CNR）。采用Cohen’s kappa系数评估观察者主观评价一致性，采用单因素重复测量方差分析和Friedman H检验对各组图像定量评价指标及主观评分进行比较。 结果： VPCT扫描平均有效辐射剂量为（18.0 ± 4.9） mSv。基于重建图像提取的胰腺实质期和门静脉期单期图像均符合临床诊断质量标准，图像主观质量评分均≥3分。55 keV VMI重建图像提取的胰腺实质期单期图像中，PDAC病灶CNR为11.1±4.4，T3D为9.1±3.7，70 keV VMI为8.0±3.2；门静脉期55 keV VMI中，PDAC病灶CNR为6.3±3.0，T3D为5.7±3.0，而70 keV VMI为4.9±2.7。55 keV VMI重建提取单期图像表现出最高PDAC病灶CNR（P<0.001），表现出最高正常胰腺实质和胰周血管信噪比、胰周血管CNR，以及最佳PDAC病灶对比度主观评分。55 keV VMI和T3D重建单期图像的图像噪声［胰腺实质期（8.3±2.1）比（8.2±2.1），门静脉期（8.4±2.1）比（8.3±2.2）］差异无统计学意义（P=0.599、0.683），两者的图像噪声均高于70 keV VMI（胰腺实质期7.1±1.9，门静脉期7.3±1.8）（P<0.001）。 结论： 基于PCCT低剂量胰腺动态VPCT成像方案所获得的灌注扫描单期图像，可用于PDAC成像及形态学评估，55 keV VMI重建能够进一步优化PDAC的图像质量。

Objective This study aims to evaluate the image quality of single-phase images in low-dose pancreatic dynamic volume perfusion computed tomography (VPCT) scans based on photon-counting computed tomography (PCCT) and assess their feasibility for morphological evaluation of pancreatic ductal adenocarcinoma (PDAC). Methods From April to August 2024, participants suspected of PDAC were prospectively enrolled and underwent preoperative pancreatic VPCT scans. A total of 55 patients with pathologically confirmed PDAC were included, and radiation doses were recorded and calculated. Perfusion time-attenuation curves were analyzed, and optimal single-phase images of pancreatic parenchymal phase and portal venous phase were extracted from T3D, 55 keV, and 70 keV virtual monoenergetic images (VMIs) for clinical diagnosis and morphological evaluation of PDAC. Subjective scoring of images was performed, and CT values of lesions, normal pancreatic parenchyma, peripancreatic vessels, and abdominal wall fat were measured. The standard deviation of the CT value of abdominal wall fat was used as the image noise value. Signal-to-noise ratios (SNRs) of lesions, normal pancreatic parenchyma, and peripancreatic vessels, as well as contrast-to-noise ratios (CNRs) of lesions and peripancreatic vessels were calculated. Inter-observer agreement of subjective evaluations was evaluated using Cohen's kappa coefficient. One-way repeated measures ANOVA and Friedman H tests were used to compare the quantitative evaluation indicators and subjective scores among groups. Results The VPCT scanning achieved an average effective radiation dose of (18.0±4.9) mSv. The single-phase images of pancreatic parenchymal phase and portal venous phase extracted from reconstructed images met clinical diagnostic quality standards, with all subjective image quality scores above 3 points. In the single-phase images of pancreatic parenchymal phase reconstructed at 55 keV VMI, the CNR of PDAC lesions was 11.1±4.4, while for T3D it was 9.1±3.7 and for 70 keV VMI it was 8.0±3.2. In images of portal venous phase reconstructed at 55 keV VMI, the CNR of PDAC lesions was 6.3±3.0, while for T3D it was 5.7±3.0 and for 70 keV VMI, it was 4.9±2.7. Single-phase images reconstructed from 55 keV VMI showed the highest CNR of PDAC lesions (P<0.001), along with the highest SNR of normal pancreatic parenchyma and peripancreatic vessels, the highest CNR of peripancreatic vessels, and optimal subjective contrast scores of PDAC lesions. There was no significant difference in image noise between 55 keV VMI and T3D reconstructed single-phase images [parenchymal phase: (8.3±2.1) vs. (8.2±2.1), portal venous phase: (8.4±2.1) vs. (8.3±2.2)] (P=0.599, 0.683). Both had higher image noise than that of 70 keV VMI (parenchymal phase: 7.1±1.9, portal venous phase: 7.3±1.8) (P<0.001). Conclusion Single-phase images obtained from perfusion scanning PCCT-based low-dose pancreatic dynamic VPCT imaging protocols can be used for PDAC imaging and morphological evaluation. The 55 keV VMI reconstruction can further optimize the image quality of PDAC.