Department of Biomedical Imaging and Radiological Sciences, School of Medicine, National Yang-Ming University, and Department of Radiology, Taipei Veterans General Hospital, Taipei 112, Taiwan.
Comput Math Methods Med. 2013;2013:157040. doi: 10.1155/2013/157040. Epub 2013 Apr 24.
Magnetic resonance (MR) imaging provides a noninvasive, in vivo imaging technique for studying respiratory and cardiac pulsations in human brains, because these pulsations can be recorded as flow-related enhancement on dynamic MR images. By applying independent component analysis to dynamic MR images, respiratory and cardiac pulsations were observed. Using the signal-time curves of these pulsations as reference functions, the magnitude and phase of the transfer function were calculated on a pixel-by-pixel basis. The calculated magnitude and phase represented the amplitude change and temporal delay at each pixel as compared with the reference functions. In the transfer function analysis, near constant phases were found at the respiratory and cardiac frequency bands, indicating the existence of phase delay relative to the reference functions. In analyzing the dynamic MR images using the transfer function analysis, we found the following: (1) a good delineation of temporal delay of these pulsations can be achieved; (2) respiratory pulsation exists in the ventricular and cortical cerebrospinal fluid; (3) cardiac pulsation exists in the ventricular cerebrospinal fluid and intracranial vessels; and (4) a 180-degree phase delay or inverted amplitude is observed on phase images.
磁共振（MR）成像是一种非侵入性的、体内成像技术，可用于研究人类大脑中的呼吸和心脏搏动，因为这些搏动可以在动态 MR 图像上作为与血流相关的增强而被记录下来。通过对动态 MR 图像应用独立成分分析，可以观察到呼吸和心脏搏动。使用这些搏动的信号-时间曲线作为参考函数，逐像素计算传递函数的幅度和相位。计算出的幅度和相位表示与参考函数相比，每个像素的幅度变化和时间延迟。在传递函数分析中，在呼吸和心脏频率带附近发现了几乎恒定的相位，这表明存在相对于参考函数的相位延迟。在使用传递函数分析分析动态 MR 图像时，我们发现：（1）可以很好地描绘这些搏动的时间延迟；（2）心室和皮质脑脊液中存在呼吸性搏动；（3）心室脑脊液和颅内血管中存在心脏搏动；（4）相位图像上观察到 180 度的相位延迟或幅度反转。
