Improving diffusion-weighted imaging of post-mortem human brains: SSFP at 7 T

Area of Science:

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

Background:

• Post-mortem diffusion imaging is crucial for validating and investigating human brain anatomy.
• Diffusion-weighted steady-state free precession (DW-SSFP) shows promise over conventional methods at 3 Tesla (3T) by mitigating signal losses due to tissue fixation.
• Tissue fixation decreases T2 and apparent diffusion coefficient (ADC), impacting conventional diffusion imaging quality.

Purpose of the Study:

• To compare the efficacy of DW-SSFP at 3T and 7 Tesla (7T) for post-mortem human brain imaging.
• To evaluate the impact of different effective b-values (b(eff)) at 7T on diffusion contrast and signal quality.
• To assess the resulting improvements in white matter tractography fidelity.

Main Methods:

• Acquired diffusion-weighted data from four post-mortem human brains at 3T and 7T.
• Utilized DW-SSFP with comparable effective b-values (b(eff)~5150 s/mm(2)) for inter-field strength comparisons.
• Acquired additional DW-SSFP data at 7T with higher b(eff) (~8550 s/mm(2)) for intra-field strength analysis.

Main Results:

• 7T datasets exhibited significantly higher signal-to-noise ratio (SNR) and diffusion contrast compared to 3T data.
• Higher b(eff) at 7T resulted in improved diffusion contrast.
• Tractography of major white matter pathways (corpus callosum, corticospinal tract, superior longitudinal fasciculus) showed improved accuracy and projection fidelity at 7T.

Conclusions:

• DW-SSFP at 7T is the preferred method for diffusion-weighted imaging of post-mortem human brains.
• This technique is particularly advantageous for investigating complex white matter structures and crossing fibers.
• Enhanced image quality at 7T leads to more reliable and high-fidelity tractography results.