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Measuring chemical exchange saturation transfer exchange rates in the human brain using a particle swarm optimisation
Andrew J Carradus1, Joe M P Bradley1, Penny A Gowland1
1Sir Peter Mansfield Imaging Centre and NIHR Nottingham Biomedical Research Centre, Nottingham University Hospitals NHS Trust, School of Physics and Astronomy, University of Nottingham, Nottingham, UK.
NMR in Biomedicine
|July 15, 2023
Summary
This study characterizes proton pools in the human brain using 7T MRI and particle swarm optimization (PSO). White matter shows larger magnetisation transfer and NOE pools, aiding future MRI experiment design.
Area of Science:
- Biophysics
- Magnetic Resonance Imaging (MRI)
- Neuroimaging
Background:
- Z-spectra analysis in MRI is complex due to multiple proton pools with varying exchange rates and T2 values.
- Interpreting in vivo data and designing specific MRI experiments are challenging.
- Characterizing these pools is crucial for understanding brain tissue and developing targeted imaging techniques.
Purpose of the Study:
- To characterize the main proton pools observable in the human brain at 7 Tesla (7T) using MRI.
- To optimize particle swarm optimization (PSO) for fitting z-spectrum data.
- To investigate differences in proton pool parameters between grey and white matter.
Main Methods:
- Acquisition of z-spectra at multiple saturation powers in the human brain at 7T.
- Optimization and validation of particle swarm optimization (PSO) using simulations and creatine phantoms.
- Fitting of z-spectra from grey and white matter to determine pool size, exchange rate (k), and T2 for five proton pools and water.
Main Results:
- Significantly larger magnetisation transfer and NOE-3.5ppm pool sizes were measured in white matter compared to grey matter.
- No significant differences in other measured parameters (pool size, exchange rate, T2) were found between grey and white matter.
- PSO successfully fitted z-spectra, providing information on peak position, amplitude, exchange rate, and T2 in vivo.
Conclusions:
- Particle swarm optimization (PSO) is a viable method for fitting complex z-spectra acquired at various B1 powers in the human brain.
- The characterized proton pools offer potential for increased sensitivity to changes in clinical conditions.
- These findings provide essential data for the design of future, more sensitive MRI experiments.
