Optimizing cardiac diffusion tensor imaging in vivo: More directions or repetitions?

Area of Science:

• Cardiovascular MRI
• Diffusion Tensor Imaging
• Medical Imaging Physics

Background:

• Cardiac diffusion tensor imaging (cDTI) is sensitive to imaging parameters.
• Optimization of parameters like diffusion encoding directions (ND) and repetitions (NR) is crucial for clinical application.
• Current clinical guidance for cDTI parameter optimization is lacking.

Purpose of the Study:

• To assess the impact of varying ND and total acquisitions (NA_all) on cDTI accuracy and precision.
• To provide data-driven recommendations for optimizing cDTI acquisition protocols.
• To guide the harmonization of cDTI across different clinical settings.

Main Methods:

• Acquired spin echo cDTI data in 10 healthy volunteers on a 3T scanner.
• Subsampled data to create 96 schemes with varying ND (6-30) and NA_all (33-180).
• Used stratified bootstrapping with robust fitting to evaluate accuracy (RMSD) and precision (SD) of cDTI metrics.

Main Results:

• Increasing ND from 6 to 30 significantly reduced RMSD and SD for MD, FA, HA, and |E2A| at fixed acquisition times.
• Acquiring sufficient low b-value data showed a trend towards improved MD and FA accuracy and precision.
• Longer acquisition times (quadrupling NA_all) substantially improved accuracy and precision across all metrics.

Conclusions:

• Prioritizing the number of diffusion encoding directions over repetitions is beneficial for fixed scan times.
• Sufficient low b-value data and longer protocols enhance cDTI accuracy and precision.
• Recommended clinically relevant protocols include ND=30 and a low to high b-value acquisition ratio (NA_b50:NA_b500) of at least 1/3.