Simultaneous spin‐echo and gradient‐echo BOLD measurements by dynamic MRS |
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| Authors: | Peng Cao Fahmeed Hyder Iris Y Zhou Jevin W Zhang Victor B Xie Adrian Tsang Ed X Wu |
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| Institution: | 1. Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong, SAR, China;2. Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong, SAR, China;3. Department of Radiology and Biomedical Imaging, University of California at San Francisco, San Francisco, CA, USA;4. Departments of Diagnostic Radiology and Biomedical Engineering, Yale University, New Haven, CT, USA |
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| Abstract: | This study aimed to dissociate the intravascular and extravascular contributions to spin‐echo (SE) and gradient‐echo (GE) blood oxygenation level‐dependent (BOLD) signals at 7 T, using dynamic diffusion‐weighted MRS. We simultaneously acquired SE and GE data using a point‐resolved spectroscopy sequence with diffusion weightings of 0, 600, and 1200 s/mm2. The BOLD signals were quantified by fitting the free induction decays starting from the SE center to a mono‐exponential decay function. Without diffusion weighting, BOLD signals measured with SE and GE increased by 1.6 ± 0.5% (TESE = 40 ms) and 5.2 ± 1.4% (nominal TEGE = 40 ms) during stimulation, respectively. With diffusion weighting, the BOLD increase during stimulation measured with SE decreased from 1.6 ± 0.5% to 1.3 ± 0.4% (P < 0.001), whereas that measured by GE was unaffected (P > 0.05); the post‐stimulation undershoots in the BOLD signal time courses were largely preserved in both SE and GE measurements. These results demonstrated the feasiblity of simultaneous SE and GE measurements of BOLD signals with and without interleaved diffusion weighting. The results also indicated a predominant extravascular contribution to the BOLD signal time courses, including post‐stimulation undershoots in both SE and GE measurements at 7 T. |
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| Keywords: | BOLD functional MRS gradient echo inferior colliculus spin echo |
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