T₂ relaxation-time mapping in healthy and diseased skeletal muscle using extended phase graph algorithms

Area of Science:

• Magnetic Resonance Imaging
• Biomedical Engineering
• Medical Physics

Background:

• Multi-echo spin-echo (MSE) transverse relaxometry is crucial for assessing T2 of the myocytic component (T2water) in neuromuscular diseases.
• Current extended phase graph (EPG) algorithms struggle with fat fractions >50%, and T2fat calibration inaccuracies are not well understood.

Purpose of the Study:

• To enhance EPG fitting methods for improved T2water accuracy across a wide range of fat fractions.
• To investigate the impact of slice-selection flip angle profiles, chemical-shift displacement, and T2fat calibration on T2water measurements.

Main Methods:

• Simulation experiments evaluated the influence of flip angle profiles, chemical-shift, and T2fat estimations.
• In vivo data from four neuromuscular disease cohorts were analyzed using various T2fat calibration and T2water estimation techniques.

Main Results:

• Excluding flip angle profiles or chemical-shift correction introduced up to 10 ms bias in T2water.
• Incorrect T2fat calibration led to a bias of up to 4 ms in T2water.
• In vivo data revealed decreasing T2water with increasing fat fractions, with two-component T2fat calibration outperforming one-component.

Conclusions:

• Optimized EPG models with two-component T2fat calibration and inclusion of flip angle profiles/chemical-shift correction are recommended for accurate T2water fitting from MSE data.
• Observed T2water decline with increasing fat fractions has significant implications for multicenter clinical studies.