Diffusion effect on T2 relaxometry in triple-echo steady state free precession sequence.

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biophysics
• Medical Physics

Background:

• Steady-state Free Precession (SSFP) sequences are widely used in MRI.
• Accurate T2 relaxometry is crucial for quantitative MRI.
• The influence of diffusion on SSFP signals is not fully understood.

Purpose of the Study:

• To evaluate the effect of diffusion on SSFP signals within the triple-echo steady state (TESS) sequence.
• To assess the impact of diffusion on the accuracy of T2 relaxometry using TESS.
• To develop methods for correcting diffusion-induced errors in T2 quantification.

Main Methods:

• Utilized the extended phase graph (EPG) algorithm for simulating SSFP signals under varying diffusion conditions.
• Validated simulation results using a commercial phantom and in vivo MRI studies.
• Developed and tested a correction scheme to mitigate T2 underestimation caused by diffusion.

Main Results:

• Diffusion was found to cause significant T2 underestimation in TESS, particularly with small flip angles and large unbalanced gradient moments.
• The T2 underestimation was primarily attributed to the diffusion sensitivity of SSFP-echoes.
• The proposed correction scheme successfully corrected T2 underestimation, confirming the role of diffusion effects.
• Diffusion effects were deemed negligible in TESS for tissues with short T2, like cartilage and muscle.

Conclusions:

• Diffusion effects are a primary source of T2 underestimation in TESS T2 quantification, especially under specific sequence parameters (small flip angle, large unbalanced gradient moment).
• Neglecting diffusion can lead to inaccurate T2 values, particularly in tissues with high T2 and diffusion coefficients.
• The developed correction scheme provides a method to improve the accuracy of T2 relaxometry in TESS sequences.