Accelerated and motion‐robust in vivo T₂ mapping from radially undersampled data using bloch‐simulation‐based iterative reconstruction

Abstract

Purpose Development of a quantitative T2-mapping platform that operates at clinically feasible timescales by employing advanced image-reconstruction of radially undersampled multi spin-echo (MSE) datasets. Methods Data was acquired on phantom and in vivo at 3 Tesla using MSE protocols employing radial k-space sampling trajectories. In order to overcome the non-trivial spin evolution associated with MSE protocols a numerical signal model was pre-calculated based on Bloch simulations of the actual pulse-sequence scheme used in the acquisition process. This signal model was subsequently incorporated into an iterative model-based image reconstruction process, producing a T2 and proton-density maps. Results T2 maps of phantom and in vivo brain were successfully constructed, closely matching values produced by a single spin-echo reference scan. High-resolution mapping was also performed for the spinal cord in vivo, differentiating the underlying gray/white matter morphology. Conclusion The presented MSE data processing framework offers reliable mapping of T2 relaxation values in a ~5 minutes timescale, free of user- and scanner-dependent variations. The use of radial k-space sampling provides further advantages in the form of high immunity to irregular physiological motion, as well as enhanced spatial resolutions owing to its inherent ability to perform alias-free limited field-of-view imaging.

New Clinically Feasible 3T MRI Protocol to Discriminate Internal Brain Stem Anatomy

“…This allows the quantification of T2 and PD values in a manner that is independent to the scanner and parameter values, and at clinically feasible time scales [25]. These maps can be used to increase anatomical contrast by emphasizing subtle tissue property differences over a dynamic range that remain compressed on standard T2-weighted images.…”

“…These contrasts have been validated using histology in animal models [20, 21]. We have combined a track density approach with recently developed simultaneous multislice acquisition diffusion MRI [22] to obtain TDI maps of brainstem structures in living subjects with clinically feasible scan times at 3-T. We also have applied a new robust method for quantitating T2 and proton density in brain tissue based on multislice multiecho spin echo acquisitions and a novel echo modulation curve software package [23–25]. We demonstrate the advantages of combining these two techniques to generate detailed in-vivo depiction of internal brain stem anatomy with clinically feasible acquisition times at 3-T MRI.…”

Advances in Spinal Functional Magnetic Resonance Imaging in the Healthy and Injured Spinal Cords

“…Major imaging challenges exist, however, such as magnetic field inhomogeneity and increased vulnerability to physiological motion – hindering the imaging modality’s potential to transition into the clinic. Fortunately, the advent of cutting edge shimming methods (20–22) and pulse sequences (23,24) that are optimized for spinal imaging has led to a body of recent research which suggest that detecting neural activity in the spinal cord using spinal fMRI may not only be feasible, but also reliable (13,14,32,33). Furthermore, the technical advances in the field have also enabled the application of rsfMRI in the spinal cord, allowing the use of an identical imaging protocol for all study participants regardless of their degree of cognitive or physical limitations.…”

“…Fortunately, such image artifacts can be reduced by adopting advanced shimming methods (20–22) and pulse sequences (23,24) that are optimized for spinal imaging. One can also attempt to minimize the magnetic field variation within the imaging field of view itself by obtaining transverse imaging slices – i.e., by placing the imaging plane parallel to the spinal cord’s cross-section.…”

Single‐shot T2 mapping using overlapping‐echo detachment planar imaging and a deep convolutional neural network

“…Quantitative MR mapping can provide quantitative information for characterizing specific tissue properties and help to remove unrelated influences, such as different sequence parameters, different scanners, and experimental conditions, on disease diagnosis and make the comparison available across different sites, MRI protocols, and scanner vendors. Quantitative T 2 mapping has drawn more and more attention in clinical MRI . Neurologic and psychiatric diseases demonstrate variations on T 2 values in brain, such as stroke, multiple sclerosis, and epilepsy .…”