Comparison of physiological noise at 1.5 T, 3 T and 7 T and optimization of fMRI acquisition parameters
Comparison of physiological noise at 1.5 T, 3 T and 7 T and optimization of fMRI acquisition parameters
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DOI：
10.1016/j.neuroimage.2005.01.007
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发表时间：
2005-05-15
期刊：
影响因子：
5.7
通讯作者：
Wald, LL
中科院分区：
文献类型：
--
作者：
Triantafyllou, C;Hoge, RD;Wald, LL
以往的研究表明，在某些条件下，噪声波动的fMRI时间过程中占主导地位的生理调制的图像强度与二次贡献的热图像噪声，这两个源的规模不同的信号强度，磁化率加权（TE）和场强。SNR的fMRI时程被发现是接近其渐近极限的中等空间分辨率测量在3 T，只有边际收益预期从收购在较高的场强。在这项研究中，我们调查的幅度的图像强度波动的fMRI时间过程中的磁场强度为1.5 T，3 T，和7 T的图像分辨率，翻转角和TE的函数。无论图像SNR是否由翻转角、图像分辨率或场强调制，时间过程SNR都是图像SNR的类似函数。对于目前在fMRI中使用的那些典型的空间分辨率（例如，3 x 3 x 3 mm（3）），从7 T采集获得的图像SNR增加仅导致时间过程SNR适度增加。在该空间分辨率下，1.5 T、3 T和7 T的生理噪声与热图像噪声的比值分别为0.61、0.89和2.23。然而，在1 x 1 x 3 mm（3）的分辨率下，对于T2* 附近的TE，1.5 T、3 T和7 T的生理热噪声比分别为0.34、0.57和0.91。因此，通过使用更高的图像分辨率来降低信号强度，生理噪声与图像噪声的比率可以被降低到这样的状态，在该状态下，由更高的场强度提供的增加的灵敏度仍然转化为fMRI时间序列中的改善的SNR。(c)2005年爱思唯尔公司All rights reserved.
Previous studies have shown that under some conditions, noise fluctuations in an fMRI time-course are dominated by physiological modulations of the image intensity with secondary contributions from thermal image noise and that these two sources scale differently with signal intensity, susceptibility weighting (TE) and field strength. The SNR of the fMRI time-course was found to be near its asymptotic limit for moderate spatial resolution measurements at 3 T with only marginal gains expected from acquisition at higher field strengths. In this study, we investigate the amplitude of image intensity fluctuations in the fMRI time-course at magnetic field strengths of 1.5 T, 3 T, and 7 T as a function of image resolution, flip angle and TE. The time-course SNR was a similar function of the image SNR regardless of whether the image SNR was modulated by flip angle, image resolution, or field strength. For spatial resolutions typical of those currently used in fMRI (e.g., 3 x 3 x 3 mm(3)), increases in image SNR obtained from 7 T acquisition produced only modest increases in time-course SNR. At this spatial resolution, the ratio of physiological noise to thermal image noise was 0.61, 0.89, and 2.23 for 1.5 T, 3 T, and 7 T. At a resolution of 1 x 1 x 3 mm(3), however, the physiological to thermal noise ratio was 0.34, 0.57, and 0.91 for 1.5 T, 3 T and 7 T for TE near T2*. Thus, by reducing the signal strength using higher image resolution, the ratio of physiologic to image noise could be reduced to a regime where increased sensitivity afforded by higher field strength still translated to improved SNR in the fMRI time-series. (c) 2005 Elsevier Inc. All rights reserved.