Yin Zhye, Wu Pengwei, Manohar Ashish, McVeigh Elliot R, Pack Jed D
GE HealthCare, Waukesha, WI, USA.
GE Research Healthcare, Niskayuna, NY, USA.
ArXiv. 2024 Mar 13:arXiv:2403.08486v1.
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）是测量心肌机械功能的一种有效成像方式。然而，在多个心跳周期内进行重复CT测量仍是一个问题。
提出一种投影域噪声模拟方法，用于从高剂量扫描生成准确的低剂量（毫安调制）4D心脏CT扫描，从而实现方案优化，在使用尽可能低的合理可达到剂量（ALARA）的同时，为心脏功能分析提供足够的图像质量。
给定目标低剂量毫安调制曲线，所提出的噪声模拟方法在投影域中将适当大小和相关性的量子噪声和电子噪声注入高剂量数据中。提出了一种空间变化（即与通道相关）的探测器增益项及其校准方法，以进一步提高噪声模拟精度。为了确定ALARA剂量阈值，提出了一种基于未落在探测器响应非线性区域内的投影射线数量的直接投影域图像质量（IQ）指标。进行了实验，从视觉相似性、对比度噪声比（CNR）和噪声功率谱（NPS）方面，使用体模和临床数据验证了噪声模拟方法。
对于体模和临床数据，低剂量模拟图像与真实低剂量图像相比，呈现出相似的噪声大小（CNR差异在2%以内）、伪影和纹理。所提出的与通道相关的探测器增益项使模拟精度进一步提高。使用所提出的IQ指标，计算了针对不同体型患者的低剂量4D心脏CT采集的推荐千伏峰值和毫安设置。
描述了一种为基于原始数据的低剂量模拟框架估计系统相关参数的详细方法。该方法在体模和临床研究中产生了逼真的噪声水平、伪影和纹理。所提出的低剂量模拟方法可用于前瞻性地选择针对患者的功能性心脏CT最小剂量方案。
