Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA.
Department of Radiology, William Beaumont University Hospital, Royal Oak, Michigan, USA.
J Appl Clin Med Phys. 2023 Jul;24(7):e14074. doi: 10.1002/acm2.14074. Epub 2023 Jun 19.
To determine the suitability of a quality assurance (QA) program based on the American College of Radiology's (ACR) CT quality control (QC) manual to fully evaluate the unique capabilities of a clinical photon-counting-detector (PCD) CT system.
A daily QA program was established to evaluate CT number accuracy and artifacts for both standard and ultra-high-resolution (UHR) scan modes. A complete system performance evaluation was conducted in accordance with the ACR CT QC manual by scanning the CT Accreditation Phantom with routine clinical protocols and reconstructing low-energy-threshold (T3D) and virtual monoenergetic images (VMIs) between 40 and 120 keV. Spatial resolution was evaluated by computing the modulation transfer function (MTF) for the UHR mode, and multi-energy performance was evaluated by scanning a body phantom containing four iodine inserts with concentrations between 2 and 15 mg I/cc.
The daily QA program identified instances when the detector needed recalibration or replacement. CT number accuracy was impacted by image type: CT numbers at 70 keV VMI were within the acceptable range (defined for 120 kV). Other keV VMIs and the T3D reconstruction had at least one insert with CT number outside the acceptable range. The limiting resolution was nearly 40 lp/cm based on MTF measurements, which far exceeds the 12 lp/cm maximum capability of the ACR phantom. The CT numbers in the iodine inserts were accurate on all VMIs (3.8% average percentage error), while the iodine concentrations had an average root mean squared error of 0.3 mg I/cc.
Protocols and parameters must be properly selected on PCD-CT to meet current accreditation requirements with the ACR CT phantom. Use of the 70 keV VMI allowed passing all tests prescribed in the ACR CT manual. Additional evaluations such an MTF measurement and multi-energy phantom scans are also recommended to comprehensively evaluate PCD-CT scanner performance.
根据美国放射学院（ACR）的 CT 质量控制（QC）手册，确定基于质量保证（QA）程序的适用性，以充分评估临床光子计数探测器（PCD）CT 系统的独特功能。
建立了日常 QA 程序，以评估标准和超高分辨率（UHR）扫描模式的 CT 数准确性和伪影。根据 ACR CT QC 手册，使用常规临床方案扫描 CT 认证体模并重建 40 至 120keV 之间的低能阈值（T3D）和虚拟单能量图像（VMI），对完整的系统性能进行评估。通过计算 UHR 模式的调制传递函数（MTF）评估空间分辨率，通过扫描包含四个碘浓度在 2 至 15mg I/cc 之间的体模评估多能量性能。
日常 QA 程序确定了需要重新校准或更换探测器的情况。图像类型会影响 CT 数准确性：70keV VMI 的 CT 数在可接受范围内（定义为 120kV）。其他 keV VMI 和 T3D 重建至少有一个插入物的 CT 数超出可接受范围。根据 MTF 测量，分辨率的限制接近 40lp/cm，远远超过 ACR 体模的 12lp/cm 最大能力。所有 VMI 的碘插入物的 CT 数都准确（平均百分比误差为 3.8%），而碘浓度的平均均方根误差为 0.3mg I/cc。
在 PCD-CT 上必须正确选择协议和参数，以满足当前 ACR CT 体模的认证要求。使用 70keV VMI 可以通过 ACR CT 手册规定的所有测试。还建议进行其他评估，如 MTF 测量和多能量体模扫描，以全面评估 PCD-CT 扫描仪的性能。
