Optimal repetition time reduction for single subject event‐related functional magnetic resonance imaging

• Published in: Magnetic resonance in medicine Vol. 81; no. 3; pp. 1890 - 1897
• Main Authors: McDowell, Amy R., Carmichael, David W
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.03.2019; John Wiley and Sons Inc
• Subjects: Adult; Algorithms; Autocorrelation; autoregressive model; Autoregressive models; Autoregressive processes; Brain Mapping - methods; Data processing; EEG‐fMRI; event related; Female; fMRI; Functional magnetic resonance imaging; Healthy Volunteers; Humans; Image Processing, Computer-Assisted - methods; Magnetic resonance imaging; Magnetic Resonance Imaging - methods; Male; Middle Aged; multiband; Neuroimaging; Notes—Imaging Methodology; Optimization; Photic Stimulation; Reduction; Regression Analysis; ROC Curve; Sensitivity; simultaneous multislice; Temporal lobe; Time Factors; Visual cortex; Visual Cortex - diagnostic imaging; Visual Cortex - physiology; Visual stimuli; Young Adult; event related; fMRI; multiband; EEG-fMRI; autoregressive model; simultaneous multislice
• DOI: 10.1002/mrm.27498
• ISSN: 0740-3194; 1522-2594

Purpose Short TRs are increasingly used for fMRI as fast sequences such as simultaneous multislice excitation become available. These have been associated with apparent sensitivity improvements, although greater temporal autocorrelation at shorter TRs can inflate sensitivity measurements leading to uncertainty regarding the optimal approach. Methods In volunteers (n = 10), the optimal TR was assessed at the single subject level for event‐related designs (visual stimulation) with 4 frequencies of presentation at 4 TR values (412‐2550 ms). T‐values in the visual cortex localized in each individual were obtained and receiver operating characteristics (ROC) analysis was performed by counting voxels within and outside expected task active regions at different thresholds. This analysis was repeated using 4 different autoregressive (AR) models; SPM AR(1) and SPM AR(fast) which globally estimate autocorrelation, and fMRIstat AR(1) and AR(5) that use a local estimate. Results The use of modest multiband factors of 2 or 3 with a reduction in TR to 1000 ± 200 ms had greater sensitivity and specificity as shown by higher T‐values in visual cortex and ROC analysis. At these TRs, the ROC analysis demonstrated that a local AR model fit improved performance while high order AR models were unnecessary. Conclusions Modest TR reductions (to 1000 ± 200 ms) optimally improved event‐related fMRI performance independent of design frequency. Autoregressive models with a local as opposed to global fit performed better, while low order autoregressive models were sufficient at the optimal TR.