Ruttimann U E, Unser M, Rawlings R R, Rio D, Ramsey N F, Mattay V S, Hommer D W, Frank J A, Weinberger D R
Laboratory of Clinical Studies, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892-1256, USA.
IEEE Trans Med Imaging. 1998 Apr;17(2):142-54. doi: 10.1109/42.700727.
The use of the wavelet transform is explored for the detection of differences between brain functional magnetic resonance images (fMRI's) acquired under two different experimental conditions. The method benefits from the fact that a smooth and spatially localized signal can be represented by a small set of localized wavelet coefficients, while the power of white noise is uniformly spread throughout the wavelet space. Hence, a statistical procedure is developed that uses the imposed decomposition orthogonality to locate wavelet-space partitions with large signal-to-noise ratio (SNR), and subsequently restricts the testing for significant wavelet coefficients to these partitions. This results in a higher SNR and a smaller number of statistical tests, yielding a lower detection threshold compared to spatial-domain testing and, thus, a higher detection sensitivity without increasing type I errors. The multiresolution approach of the wavelet method is particularly suited to applications where the signal bandwidth and/or the characteristics of an imaging modality cannot be well specified. The proposed method was applied to compare two different fMRI acquisition modalities. Differences of the respective useful signal bandwidths could be clearly demonstrated; the estimated signal, due to the smoothness of the wavelet representation, yielded more compact regions of neuroactivity than standard spatial-domain testing.
探讨了小波变换在检测两种不同实验条件下获取的脑功能磁共振成像（fMRI）差异中的应用。该方法得益于这样一个事实，即平滑且空间局部化的信号可以由一小组局部化小波系数表示，而白噪声的能量则均匀分布在整个小波空间中。因此，开发了一种统计程序，该程序利用所施加的分解正交性来定位具有大信噪比（SNR）的小波空间分区，随后将对显著小波系数的测试限制在这些分区内。这导致了更高的SNR和更少的统计测试次数，与空间域测试相比产生了更低的检测阈值，从而在不增加I型错误的情况下具有更高的检测灵敏度。小波方法的多分辨率方法特别适用于信号带宽和/或成像模态特征无法很好确定的应用。所提出的方法被应用于比较两种不同的fMRI采集模态。可以清楚地证明各自有用信号带宽的差异；由于小波表示的平滑性，估计信号产生的神经活动区域比标准空间域测试更紧凑。
