Li Ke, Chen Guang-Hong
Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705.
Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, WI 53792.
Proc SPIE Int Soc Opt Eng. 2016;9783. doi: 10.1117/12.2216293. Epub 2016 Mar 22.
Cerebral CT perfusion (CTP) imaging is playing an important role in the diagnosis and treatment of acute ischemic strokes. Meanwhile, the reliability of CTP-based ischemic lesion detection has been challenged due to the noisy appearance and low signal-to-noise ratio of CTP maps. To reduce noise and improve image quality, a rigorous study on the noise transfer properties of CTP systems is highly desirable to provide the needed scientific guidance. This paper concerns how noise in the CTP source images propagates to the final CTP maps. Both theoretical deviations and subsequent validation experiments demonstrated that, the noise level of background frames plays a dominant role in the noise of the cerebral blood volume (CBV) maps. This is in direct contradiction with the general belief that noise of non-background image frames is of greater importance in CTP imaging. The study found that when radiation doses delivered to the background frames and to all non-background frames are equal, lowest noise variance is achieved in the final CBV maps. This novel equality condition provides a practical means to optimize radiation dose delivery in CTP data acquisition: radiation exposures should be modulated between background frames and non-background frames so that the above equality condition is satisïňĄed. For several typical CTP acquisition protocols, numerical simulations and in vivo canine experiment demonstrated that noise of CBV can be effectively reduced using the proposed exposure modulation method.
脑CT灌注（CTP）成像在急性缺血性卒中的诊断和治疗中发挥着重要作用。同时，由于CTP图像噪声大、信噪比低，基于CTP的缺血性病变检测的可靠性受到了挑战。为了降低噪声并提高图像质量，非常需要对CTP系统的噪声传递特性进行严谨研究，以提供所需的科学指导。本文关注CTP源图像中的噪声如何传播到最终的CTP图像。理论偏差和后续的验证实验均表明，背景帧的噪声水平在脑血容量（CBV）图像的噪声中起主导作用。这与普遍认为的非背景图像帧的噪声在CTP成像中更重要的观点直接矛盾。研究发现，当施加到背景帧和所有非背景帧的辐射剂量相等时，最终的CBV图像中可实现最低的噪声方差。这种新的相等条件为优化CTP数据采集中的辐射剂量传递提供了一种实用方法：应在背景帧和非背景帧之间调节辐射曝光，以使上述相等条件得到满足。对于几种典型的CTP采集协议，数值模拟和犬体内实验表明，使用所提出的曝光调制方法可以有效降低CBV的噪声。
