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Time-division multiplexing (TDM) sequence removes bias in T2 estimation and relaxation-diffusion measurements
Qiang Liu1,2, Borjan Gagoski3,4, Imam Ahmed Shaik1
1Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
Magnetic Resonance in Medicine
|August 13, 2024
Summary
Time-division multiplexing (TDM) offers accurate accelerated relaxation-diffusion MRI (rdMRI) microstructure measures, outperforming multi-echo (ME) sequences. TDM provides reliable rdMRI data with 2-3x acceleration, unlike ME which shows significant biases.
Area of Science:
- Magnetic Resonance Imaging
- Biophysics
- Medical Physics
Background:
- Accelerated MRI techniques are crucial for reducing scan times in diffusion MRI (dMRI) and relaxation-based imaging.
- Relaxation-diffusion MRI (rdMRI) combines diffusion and T2 relaxation measurements to probe tissue microstructure.
- Comparing acquisition sequences is essential for optimizing rdMRI performance and reliability.
Purpose of the Study:
- To compare multi-echo (ME) and time-division multiplexing (TDM) sequences for accelerated rdMRI.
- To evaluate the accuracy and reliability of TDM and ME sequences in estimating rdMRI microstructure measures.
- To assess the impact of acceleration factors on sequence performance.
Main Methods:
- ME, TDM, and single-echo (SE) sequences were implemented using Pulseq with single-band (SB) and multi-band 2 (MB2) acceleration.
- Phantom and in-vivo brain scans were performed to compare image intensities and T2 estimates.
- Microstructure estimation was assessed using relaxation diffusion imaging moment (REDIM) and maximum-entropy relaxation diffusion distribution (MaxEnt-RDD).
Main Results:
- TDM performance closely matched the gold standard SE acquisition.
- ME sequences exhibited significantly larger biases (3-4x on phantom, 2x in-vivo) compared to SE.
- TDM provided comparable diffusion and relaxation parameters to SE, while ME showed substantial biases in R2 maps and relaxation-diffusion covariance.
Conclusions:
- Time-division multiplexing (TDM) sequences provide accurate and reliable relaxation-diffusion MRI microstructure measurements.
- TDM enables accelerated rdMRI acquisition with factors of 2-3x without compromising data quality.
- ME sequences are less reliable for accurate rdMRI microstructure estimation due to higher biases.
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