In Vivo Meso-Scale Whole-Brain Quantitative Imaging With Tailored MRF on the NexGen 7T Scanner

To push the speed and resolution limit of in vivo quantitative imaging and enable estimation of quantitative tissue parameters of subtle brain structures that were previously difficult to assess.

This study implemented an efficient quantitative imaging approach, 3D-SPI MRF, on the NexGen 7T scanner equipped with a high-performance head-only gradient and 96-channel receiver array. To address challenges associated with performing rapid mesoscale MRF on this system, acquisition and reconstruction mitigation methods were developed and incorporated into the MRF framework, including: (i) flip-angle-aware dictionary fitting to account for both B₁ ⁺ inhomogeneity and voxel-specific RF frequency response, (ii) gradient imperfection corrections via Skope measurements that incorporates a new per-TR trajectory rewinder compensation, (iii) incorporation of rapid B₁ ⁺ and B₀ mappings into the MRF sequence, and (iv) high-temporal motion navigation.

Whole-brain T₁ and T₂ maps were obtained at 560-μm isotropic resolution within 4 min, where ablation studies demonstrated the necessity of the various mitigation methods implemented in removing bias and artifacts. For comparison, MRF data were acquired using current state-of-the-art method but limited to typical whole-body gradient specifications to demonstrate that the proposed developments resulted in ∼3× shorter scan time while producing more accurate parameter maps. Data were also acquired at ∼3.8× smaller voxel size, 360-μm isotropic, using the developed technique, to achieve mesoscale multi-parameter quantitative mapping in vivo.

Tailored 3D MRF acquisition and reconstruction were developed to enable fast and accurate T₁ and T₂ mapping across the whole-brain at mesoscale resolution on the NexGen 7T scanner.