GE HealthCare, Waukesha, Wisconsin, USA.
GE HealthCare Technology & Innovation Center, Niskayuna, New York, USA.
Med Phys. 2024 Jul;51(7):4622-4634. doi: 10.1002/mp.17088. Epub 2024 May 16.
Four-dimensional (4D) wide coverage computed tomography (CT) is an effective imaging modality for measuring the mechanical function of the myocardium. However, repeated CT measurement across a number of heartbeats is still a concern.
A projection-domain noise emulation method is presented to generate accurate low-dose (mA modulated) 4D cardiac CT scans from high-dose scans, enabling protocol optimization to deliver sufficient image quality for functional cardiac analysis while using a dose level that is as low as reasonably achievable (ALARA).
Given a targeted low-dose mA modulation curve, the proposed noise emulation method injects both quantum and electronic noise of proper magnitude and correlation to the high-dose data in projection domain. A spatially varying (i.e., channel-dependent) detector gain term as well as its calibration method were proposed to further improve the noise emulation accuracy. To determine the ALARA dose threshold, a straightforward projection domain image quality (IQ) metric was proposed that is based on the number of projection rays that do not fall under the non-linear region of the detector response. Experiments were performed to validate the noise emulation method with both phantom and clinical data in terms of visual similarity, contrast-to-noise ratio (CNR), and noise-power spectrum (NPS).
For both phantom and clinical data, the low-dose emulated images exhibited similar noise magnitude (CNR difference within 2%), artifacts, and texture to that of the real low-dose images. The proposed channel-dependent detector gain term resulted in additional increase in emulation accuracy. Using the proposed IQ metric, recommended kVp and mA settings were calculated for low dose 4D Cardiac CT acquisitions for patients of different sizes.
A detailed method to estimate system-dependent parameters for a raw-data based low dose emulation framework was described. The method produced realistic noise levels, artifacts, and texture with phantom and clinical studies. The proposed low-dose emulation method can be used to prospectively select patient-specific minimal-dose protocols for functional cardiac CT.
四维（4D）宽覆盖计算机断层扫描（CT）是一种测量心肌机械功能的有效成像方式。然而，在多个心跳周期中进行重复 CT 测量仍然令人担忧。
提出了一种投影域噪声仿真方法，可从高剂量扫描中生成准确的低剂量（mA 调制）4D 心脏 CT 扫描，从而优化方案，在使用尽可能低的剂量（合理可行的最低剂量，ALARA）的同时，为心脏功能分析提供足够的图像质量。
给定目标低剂量 mA 调制曲线，所提出的噪声仿真方法在投影域中将适当幅度和相关性的量子和电子噪声注入到高剂量数据中。提出了一种空间变化（即通道相关）的探测器增益项及其校准方法，以进一步提高噪声仿真的准确性。为了确定 ALARA 剂量阈值，提出了一种基于探测器响应非线性区域下的投影射线数量的简单投影域图像质量（IQ）度量。使用体模和临床数据进行了实验，以验证噪声仿真方法在视觉相似性、对比噪声比（CNR）和噪声功率谱（NPS）方面的效果。
对于体模和临床数据，低剂量仿真图像的噪声幅度（CNR 差异在 2%以内）、伪影和纹理与真实低剂量图像相似。所提出的通道相关探测器增益项进一步提高了仿真的准确性。使用所提出的 IQ 度量，为不同体型患者的低剂量 4D 心脏 CT 采集计算了推荐的 kVp 和 mA 设置。
描述了一种用于基于原始数据的低剂量仿真框架的估计系统相关参数的详细方法。该方法通过体模和临床研究产生了逼真的噪声水平、伪影和纹理。所提出的低剂量仿真方法可用于前瞻性选择针对特定患者的心脏 CT 功能的最小剂量方案。
