Comparison of SMS-EPI and 3D-EPI at 7T in an fMRI localizer study with matched spatiotemporal resolution and homogenized excitation profiles

• Published in: PloS one Vol. 14; no. 11; p. e0225286
• Main Authors: Le Ster, Caroline, Moreno, Antonio, Mauconduit, Franck, Gras, Vincent, Stirnberg, Ruediger, Poser, Benedikt A., Vignaud, Alexandre, Eger, Evelyn, Dehaene, Stanislas, Meyniel, Florent, Boulant, Nicolas
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 21.11.2019; Public Library of Science (PLoS)
• Subjects: Acceleration; Adult; Auditory tasks; Bioengineering; Biology and Life Sciences; Brain; Brain - physiology; Brain mapping; Brain Mapping - methods; Calibration; Cognitive ability; Cognitive Sciences; Comparative analysis; Diagnostic imaging; Echo-Planar Imaging - methods; Excitation; Female; Functional magnetic resonance imaging; Humans; Image Processing, Computer-Assisted; Imaging; Life Sciences; Magnetic resonance imaging; Magnetic Resonance Imaging - methods; Male; Medical imaging; Medicine and Health Sciences; Neuroimaging; Neurons and Cognition; Neurosciences; NMR; Noise; Nuclear magnetic resonance; Physical Sciences; Physiology; Research and Analysis Methods; ROC Curve; Sensitivity and Specificity; Sensorimotor integration; Sensorimotor system; Sensory integration; Sequences; Signal-To-Noise Ratio; SMS (Short messaging service); Social Sciences; Visual tasks; Young Adult; France
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0225286

The simultaneous multi-slice EPI (SMS-EPI, a.k.a. MB-EPI) sequence has met immense popularity recently in functional neuroimaging. A still less common alternative is the use of 3D-EPI, which offers similar acceleration capabilities. The aim of this work was to compare the SMS-EPI and the 3D-EPI sequences in terms of sampling strategies for the detection of task-evoked activations at 7T using detection theory. To this end, the spatial and temporal resolutions of the sequences were matched (1.6 mm isotropic resolution, TR = 1200 ms) and their excitation profiles were homogenized by means of calibration-free parallel-transmission (Universal Pulses). We used a fast-event "localizer" paradigm of 5:20 min in order to probe sensorimotor functions (visual, auditory and motor tasks) as well as higher level functions (language comprehension, mental calculation), where results from a previous large-scale study at 3T (N = 81) served as ground-truth reference for the brain areas implicated in each cognitive function. In the current study, ten subjects were scanned while their activation maps were generated for each cognitive function with the GLM analysis. The SMS-EPI and 3D-EPI sequences were compared in terms of raw tSNR, t-score testing for the mean signal, activation strength and accuracy of the robust sensorimotor functions. To this end, the sensitivity and specificity of these contrasts were computed by comparing their activation maps to the reference brain areas obtained in the 3T study. Estimated flip angle distributions in the brain reported a normalized root mean square deviation from the target value below 10% for both sequences. The analysis of the t-score testing for the mean signal revealed temporal noise correlations, suggesting the use of this metric instead of the traditional tSNR for testing fMRI sequences. The SMS-EPI and 3D-EPI thereby yielded similar performance from a detection theory perspective.