Samei Ehsan, Richard Samuel
Carl E. Ravin Advanced Imaging Laboratories, Clinical Imaging Physics Group, Departments of Radiology, Physics, Biomedical Engineering, and Electrical and Computer Engineering, Medical Physics Graduate Program, Duke University, Durham, North Carolina 27710.
Carl E. Ravin Advanced Imaging Laboratories, Department of Radiology, Duke University, Durham, North Carolina 27710.
Med Phys. 2015 Jan;42(1):314-23. doi: 10.1118/1.4903899.
Different computed tomography (CT) reconstruction techniques offer different image quality attributes of resolution and noise, challenging the ability to compare their dose reduction potential against each other. The purpose of this study was to evaluate and compare the task-based imaging performance of CT systems to enable the assessment of the dose performance of a model-based iterative reconstruction (MBIR) to that of an adaptive statistical iterative reconstruction (ASIR) and a filtered back projection (FBP) technique.
The ACR CT phantom (model 464) was imaged across a wide range of mA setting on a 64-slice CT scanner (GE Discovery CT750 HD, Waukesha, WI). Based on previous work, the resolution was evaluated in terms of a task-based modulation transfer function (MTF) using a circular-edge technique and images from the contrast inserts located in the ACR phantom. Noise performance was assessed in terms of the noise-power spectrum (NPS) measured from the uniform section of the phantom. The task-based MTF and NPS were combined with a task function to yield a task-based estimate of imaging performance, the detectability index (d'). The detectability index was computed as a function of dose for two imaging tasks corresponding to the detection of a relatively small and a relatively large feature (1.5 and 25 mm, respectively). The performance of MBIR in terms of the d' was compared with that of ASIR and FBP to assess its dose reduction potential.
Results indicated that MBIR exhibits a variability spatial resolution with respect to object contrast and noise while significantly reducing image noise. The NPS measurements for MBIR indicated a noise texture with a low-pass quality compared to the typical midpass noise found in FBP-based CT images. At comparable dose, the d' for MBIR was higher than those of FBP and ASIR by at least 61% and 19% for the small feature and the large feature tasks, respectively. Compared to FBP and ASIR, MBIR indicated a 46%-84% dose reduction potential, depending on task, without compromising the modeled detection performance.
The presented methodology based on ACR phantom measurements extends current possibilities for the assessment of CT image quality under the complex resolution and noise characteristics exhibited with statistical and iterative reconstruction algorithms. The findings further suggest that MBIR can potentially make better use of the projections data to reduce CT dose by approximately a factor of 2. Alternatively, if the dose held unchanged, it can improve image quality by different levels for different tasks.
不同的计算机断层扫描（CT）重建技术提供了不同的分辨率和噪声图像质量属性，这对相互比较它们的剂量降低潜力提出了挑战。本研究的目的是评估和比较CT系统基于任务的成像性能，以便能够评估基于模型的迭代重建（MBIR）与自适应统计迭代重建（ASIR）和滤波反投影（FBP）技术的剂量性能。
在一台64层CT扫描仪（GE Discovery CT750 HD，威斯康星州沃基沙）上，对ACR CT体模（464型）在广泛的毫安设置范围内进行成像。基于先前的工作，使用圆形边缘技术并结合ACR体模中对比度插件的图像，根据基于任务的调制传递函数（MTF）评估分辨率。根据从体模均匀部分测量的噪声功率谱（NPS）评估噪声性能。将基于任务的MTF和NPS与任务函数相结合，以得出基于任务的成像性能估计值，即可检测性指数（d'）。针对分别对应于检测相对较小和相对较大特征（分别为1.5毫米和25毫米）的两项成像任务，将d'计算为剂量的函数。将MBIR在d'方面的性能与ASIR和FBP的性能进行比较，以评估其剂量降低潜力。
结果表明，MBIR在显著降低图像噪声的同时，相对于物体对比度和噪声表现出可变的空间分辨率。MBIR的NPS测量表明，与基于FBP的CT图像中典型的带通噪声相比，其噪声纹理具有低通特性。在可比剂量下，对于小特征和大特征任务，MBIR的d'分别比FBP和ASIR高至少61%和19%。与FBP和ASIR相比，MBIR根据任务的不同显示出46%-84%的剂量降低潜力，且不影响模拟的检测性能。
基于ACR体模测量提出的方法扩展了在统计和迭代重建算法所呈现的复杂分辨率和噪声特征下评估CT图像质量的现有可能性。研究结果进一步表明，MBIR有可能更好地利用投影数据将CT剂量降低约一半。或者，如果剂量保持不变，它可以针对不同任务在不同程度上提高图像质量。
