Choice of reference measurements affects quantification of long diffusion time behaviour using stimulated echoes

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Diffusion Tensor Imaging (DTI)
• Quantitative MRI

Background:

• Diffusion-weighted stimulated echo acquisition mode (DW-STEAM) is used for long diffusion time measurements.
• Accurate quantification of the apparent diffusion coefficient (ADC) is crucial in diffusion MRI.
• Reference data acquisition in DW-STEAM presents challenges due to the inability to achieve a true b=0 value.

Purpose of the Study:

• To investigate the impact of reference data b-values on ADC quantification in long diffusion time DW-STEAM.
• To identify and address the contribution of crusher gradients in DW-STEAM measurements.
• To propose a modification for improved ADC quantification by avoiding crusher gradient artifacts.

Main Methods:

• Two reference data acquisition strategies were evaluated: constant diffusion weighting (fixed-b0) and constant gradient area (fixed-q0).
• Signal calculations were performed for systems with one and two diffusion coefficients.
• Experimental validation was conducted using postmortem human corpus callosum samples.

Main Results:

• Underestimation of ADC was observed for reference images with b>0, leading to apparent time-dependence with fixed-q0.
• Restricted diffusion systems were also affected by this phenomenon.
• Experimental results showed that fixed-q0 exaggerated diffusion time-dependent effects by 62% (longitudinal) and 35% (radial) compared to fixed-b0 in white matter.

Conclusions:

• Variations in reference measurement b-values in DW-STEAM can introduce artificial diffusion time dependence in ADC.
• This artifact occurs even in the absence of diffusion restriction.
• The findings highlight the importance of careful reference data selection for accurate ADC quantification in long diffusion time MRI.