Limitations of line-scan MRI for directly measuring neural activity

Motivation: There are reports that line-scan MRI methods can directly measure neural activity (the DIANA response). Goal(s): In light of replication failures, we sought to understand the noise profile of the line-scan acquisition. Approach: Using the line-scan protocol (3T GE UHP scanner, N=5) we measured human visual cortex while subjects viewed a blank screen. Results: The noise has a 1/f temporal spectrum that can be confused with certain stimulus-driven responses. This noise spreads into the surrounding volume in the phase-encoding direction. We explain the pattern of results with a model of the sequence that incorporates time-varying contrast fluctuations. Impact: Line-scan MRI is particularly susceptible to physiological noise because of its long acquisition time to create a single image. For this reason, the sequence will have difficulty measuring small contrast fluctuations due to neural electrical activity.