Mistretta C A, Wieben O, Velikina J, Block W, Perry J, Wu Y, Johnson K, Wu Y
Department of Medical Physics, The University of Wisconsin-Madison, USA.
Magn Reson Med. 2006 Jan;55(1):30-40. doi: 10.1002/mrm.20772.
Recent work in k-t BLAST and undersampled projection angiography has emphasized the value of using training data sets obtained during the acquisition of a series of images. These techniques have used iterative algorithms guided by the training set information to reconstruct time frames sampled at well below the Nyquist limit. We present here a simple non-iterative unfiltered backprojection algorithm that incorporates the idea of a composite image consisting of portions or all of the acquired data to constrain the backprojection process. This significantly reduces streak artifacts and increases the overall SNR, permitting decreased numbers of projections to be used when acquiring each image in the image time series. For undersampled 2D projection imaging applications, such as cine phase contrast (PC) angiography, our results suggest that the angular undersampling factor, relative to Nyquist requirements, can be increased from the present factor of 4 to about 100 while increasing SNR per individual time frame. Results are presented for a contrast-enhanced PR HYPR TRICKS acquisition in a volunteer using an angular undersampling factor of 75 and a TRICKS temporal undersampling factor of 3 for an overall undersampling factor of 225.
近期在k-t BLAST和欠采样投影血管造影方面的工作强调了使用在一系列图像采集过程中获得的训练数据集的价值。这些技术使用了由训练集信息引导的迭代算法，来重建采样频率远低于奈奎斯特极限的时间帧。我们在此提出一种简单的非迭代无滤波反投影算法，该算法纳入了由部分或全部采集数据组成的合成图像的概念，以约束反投影过程。这显著减少了条纹伪影并提高了整体信噪比，使得在采集图像时间序列中的每幅图像时可以使用更少的投影数。对于欠采样二维投影成像应用，如电影相位对比（PC）血管造影，我们的结果表明，相对于奈奎斯特要求，角度欠采样因子可以从目前的4提高到约100，同时提高每个单独时间帧的信噪比。给出了一名志愿者使用角度欠采样因子75和TRICKS时间欠采样因子3进行对比增强PR HYPR TRICKS采集的结果，整体欠采样因子为225。
