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Magnetic resonance imaging with submillisecond temporal resolution
Author(s) -
Zhong Zheng,
Sun Kaibao,
Karaman M. Muge,
Zhou Xiaohong Joe
Publication year - 2021
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.28588
Subject(s) - waveform , temporal resolution , raster scan , raster graphics , signal (programming language) , nuclear magnetic resonance , physics , eddy current , phase (matter) , optics , computer science , artificial intelligence , voltage , quantum mechanics , programming language
Purpose To demonstrate an MRI technique—Submillisecond Periodic Event Encoded Dynamic Imaging (SPEEDI)—for capturing cyclic dynamic events with submillisecond temporal resolution. Methods The SPEEDI technique is based on an FID or an echo signal in which each time point in the signal is used to sample a distinct k ‐space raster, followed by repeated FIDs or echoes to produce the remaining k ‐space data in each k ‐space raster. All acquisitions are synchronized with a cyclic event, resulting in a set of time‐resolved images of the cyclic event with a temporal resolution determined by the dwell time. In SPEEDI, spatial encoding is accomplished by phase encoding. The SPEEDI technique was demonstrated in two experiments at 3 T to (1) visualize fast‐changing electric currents that mimicked the waveform of an action potential, and (2) characterize rapidly decaying eddy currents in an MRI system, with a temporal resolution of 0.2 ms and 0.4 ms, respectively. In both experiments, compressed sensing was incorporated to reduce the scan times. Phase difference maps related to the dynamics of electric currents or eddy currents were then obtained. Results In the first experiment, time‐resolved phase maps resulting from the action potential–mimicking current waveform were successfully obtained and agreed well with theoretical calculations (normalized RMS error = 0.07). In the second experiment, spatially resolved eddy current phase maps revealed time constants (27.1 ± 0.2 ms, 41.1 ± 3.5 ms, and 34.8 ± 0.7 ms) that matched well with those obtained from an established method using point sources (26.4 ms, 41.2 ms and 34.8 ms). For both experiments, phase maps from fully sampled and compressed‐sensing–accelerated k ‐space data exhibited a high structural similarity (> 0.8) despite a two‐fold to three‐fold acceleration. Conclusions We have illustrated that SPEEDI can provide submillisecond temporal resolution. This capability will likely lead to future exploration of ultrafast, cyclic biomedical processes using MRI.