Closed-form solution for T2 mapping with nonideal refocusing of slice selective CPMG sequences

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Quantitative MRI techniques
• Biophysical modeling

Background:

• T2 quantification using multiecho MRI sequences is often inaccurate.
• Errors arise from stimulated echoes, B1+ inhomogeneity, and slice profile effects.
• Existing methods like monoexponential fitting can lead to significant T2 errors.

Purpose of the Study:

• To present a compact signal model using the generating functions (GF) approach for accurate T2 quantification.
• To account for errors caused by stimulated echoes, B1+ inhomogeneity, and slice profile effects.
• To improve the reliability of T2 measurements in MRI.

Main Methods:

• Utilized the generating functions (GF) approach to solve for transverse magnetization evolution in the z-domain.
• Incorporated flip angle distribution across refocusing slice profiles.
• Tested the GF model with simulated data, phantom, and in vivo measurements, comparing it to monoexponential fitting.

Main Results:

• Simulations showed monoexponential fitting can cause T2 errors up to 30% in clinical settings.
• The GF approach yielded accurate T2 quantification results.
• Experimental data demonstrated good agreement between GF values and spectroscopic/single-echo spin-echo sequences.

Conclusions:

• Correction for stimulated echoes is essential for accurate T2 value computation.
• The presented generating functions approach offers a robust solution for T2 quantification.
• This method enhances the comparability and reliability of MRI-derived T2 values.