BOLD sensitivity and SNR characteristics of parallel imaging-accelerated single-shot multi-echo EPI for fMRI

• Published in: NeuroImage (Orlando, Fla.) Vol. 84; pp. 65 - 75
• Main Authors: Bhavsar, Saurabh, Zvyagintsev, Mikhail, Mathiak, Klaus
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.01.2014; Elsevier; Elsevier Limited
• Subjects: Adult; Biological and medical sciences; BOLD sensitivity; Brain Mapping - methods; Cerebral Cortex - physiology; Cerebrovascular Circulation - physiology; Echo-Planar Imaging - methods; Female; fMRI; Fundamental and applied biological sciences. Psychology; Humans; Image Enhancement - methods; Image Interpretation, Computer-Assisted - methods; Inter-subject covariance; Magnetic Resonance Imaging - methods; Male; Measurement techniques; Multi-echo EPI; Multimodal Imaging - methods; Nerve Net - physiology; Neural networks; Neurosciences; Noise; Oxygen Consumption - physiology; Parallel imaging; Reproducibility of Results; Sensitivity and Specificity; Signal-To-Noise Ratio; Studies; Temporal SNR; Vertebrates: nervous system and sense organs; Young Adult; fMRI; Temporal SNR; Multi-echo EPI; BOLD sensitivity; Parallel imaging; Inter-subject covariance; Human; Sensitivity; Imaging; Nuclear magnetic resonance imaging; Functional imaging
• ISSN: 1053-8119; 1095-9572; 1095-9572
• DOI: 10.1016/j.neuroimage.2013.08.007

Echo-planar imaging (EPI) is a standard procedure in functional magnetic resonance imaging (fMRI) for measuring changes in the blood oxygen level-dependent (BOLD) signal associated with neuronal activity. The images obtained from fMRI with EPI, however, exhibit signal dropouts and geometric distortions. Parallel imaging (PI), due to its short readout, accelerates image acquisition and might reduce dephasing in phase-encoding direction. The concomitant loss of signal-to-noise ratio (SNR) might be compensated through single-shot multi-echo EPI (mEPI). We systematically compared the temporal SNR and BOLD sensitivity of single echoes (TE=15, 45, and 75ms) and contrast-optimized mEPI with and without PI and mEPI-based denoising. Audio-visual stimulation under natural viewing conditions activated distributed neural networks. Heterogeneous SNR, noise gain, and sensitivity maps emerged. In single echoes, SNR and BOLD sensitivity followed the predicted dependency on echo time (TE) and were reduced under PI. However, the combination of echoes with mEPI recovered the quality parameters and increased BOLD signal changes at circumscribed fronto-polar and deep brain structures. We suggest applying PI only in combination with mEPI to reduce imaging artifacts and conserve BOLD sensitivity. •Parallel imaging reduces SNR in fMRI globally with local improvements.•Multi-echo EPI recovers quality parameters and yields locally improved BOLD signal.•Combined multi-echo and parallel imaging EPI optimizes BOLD imaging.•Natural viewing activates distributed networks for BOLD sensitivity mapping.•Multi-echo EPI can be used for denoising.