Joint estimation of compartment-specific T₂ relaxation and tumor microstructure using multi-TE IMPULSED MRI

Area of Science:

• Biomedical Imaging
• Magnetic Resonance Imaging
• Cancer Research

Background:

• Magnetic Resonance Imaging (MRI) is crucial for non-invasive cancer diagnosis and monitoring.
• IMPULSED MRI techniques estimate tissue microstructure, but T2 relaxation effects can introduce biases.
• Understanding T2 heterogeneity is vital for accurate microstructural parameter estimation in tumors.

Purpose of the Study:

• To assess the impact of T2 heterogeneity on IMPULSED-derived microstructural metrics in solid tumors.
• To evaluate a novel method for simultaneous estimation of multi-compartmental T2 and microstructural parameters.

Main Methods:

• Computer simulations and in vivo multi-echo (TE) IMPULSED MRI were used across five tumor models.
• A T2+IMPULSED method was developed for simultaneous fitting of T2 and microstructural parameters.
• Bayesian model selection was employed voxel-wisely to assess the necessity of including T2 heterogeneity.

Main Results:

• T2 heterogeneity minimally affected cell size (d) estimation in high-density tissues but significantly biased it in low-density tissues.
• Most IMPULSED metrics were TE-independent, but some showed significant increases with longer TEs in specific tumor models.
• The T2+IMPULSED method yielded consistently smaller intracellular volume fractions than standard methods.

Conclusions:

• Echo time (TE) has a negligible impact on IMPULSED-derived cell size estimations.
• The TE-dependence of intracellular volume fractions is critical for T2+IMPULSED modeling accuracy.
• These findings advance non-invasive MRI techniques for precise cell size measurement in cancer.