Simultaneous T₂ and mapping of multiple sclerosis lesions with radial RARE‐EPI

Abstract

Purpose The characteristic MRI features of multiple sclerosis (MS) lesions make it conceptually appealing to pursue parametric mapping techniques that support simultaneous generation of quantitative maps of 2 or more MR contrast mechanisms. We present a modular rapid acquisition with relaxation enhancement (RARE)‐EPI hybrid that facilitates simultaneous T2 and T2∗ mapping (2in1‐RARE‐EPI). Methods In 2in1‐RARE‐EPI the first echoes in the echo train are acquired with a RARE module, later echoes are acquired with an EPI module. To define the fraction of echoes covered by the RARE and EPI module, an error analysis of T2 and T2∗ was conducted with Monte Carlo simulations. Radial k‐space (under)sampling was implemented for acceleration (R = 2). The feasibility of 2in1‐RARE‐EPI for simultaneous T2 and T2∗ mapping was examined in a phantom study mimicking T2 and T2∗ relaxation times of the brain. For validation, 2in1‐RARE‐EPI was benchmarked versus multi spin‐echo (MSE) and multi gradient‐echo (MGRE) techniques. The clinical applicability of 2in1‐RARE‐EPI was demonstrated in healthy subjects and MS patients. Results There was a good agreement between T2/T2∗ values derived from 2in1‐RARE‐EPI and T2/T2∗ reference values obtained from MSE and MGRE in both phantoms and healthy subjects. In patients, MS lesions in T2 and T2∗ maps deduced from 2in1‐RARE‐EPI could be just as clearly delineated as in reference maps calculated from MSE/MGRE. Conclusion This work demonstrates the feasibility of radially (under)sampled 2in1‐RARE‐EPI for simultaneous T2 and T2∗ mapping in MS patients.

Monitoring kidney size to interpret MRI‐based assessment of renal oxygenation in acute pathophysiological scenarios

“…As KS can be readily obtained from T 2 *, T 2 maps without the need for additional scans, this should always accompany the assessment of MRI-derived oxygenation results. Driven by technical advances including simultaneous T 2 * and T 2 mapping, 61,73 renal MR oximetry can greatly support preclinical studies into the mechanisms of renal pathophysiology. Moreover, this non-invasive approach to probing renal oxygenation holds the promise of swift translation to human studies, for example, for the assessment of drug effects, and for clinically meaningful diagnosis.…”

Accelerated Simultaneous T2 and T2* Mapping of Multiple Sclerosis Lesions Using Compressed Sensing Reconstruction of Radial RARE-EPI MRI

“…It is therefore conceptually appealing to establish methods to simultaneously acquire multiple MR contrasts, and to explore approaches to accelerate this as much as possible. To realize this, we previously presented a radially-sampled RARE-EPI hybrid that facilitates simultaneous T 2 and T 2 * mapping (2in1-RARE-EPI) [ 4 ]. Similar to previously proposed RARE-EPI combined-acquisition-techniques [ 5 , 6 , 7 ], the MR signal in 2in1-RARE-EPI is acquired with a RARE module followed by an EPI module to capture the T 2 and T 2 * decay simultaneously after each excitation.…”

“…This limits the implementation of quantitative mapping in routine clinical practice and broader clinical studies. In our previous study, the acquisition time for simultaneous T 2 and T 2 * mapping was reduced to 77% of the comparable reference methods Multi-Spin-Echo (MSE) and Multi-Gradient-Recalled-Echo (MGRE) due to the use of the hybrid acquisition and a modest radial undersampling factor (R = 2) [ 4 ]. Unlike previous methods for simultaneous T 2 and T 2 * mapping, such as Spin- and Gradient-Echo (SAGE) [ 8 , 9 , 10 , 11 ] and 3D Echo Planar Time-Resolved Imaging (3D EPTI) [ 12 ], which utilize multiple EPI readouts before and after 180° refocusing pulses to obtain multiple images with different contrast weightings for T 2 and T 2 * mapping, 2in1-RARE-EPI samples k-space spokes in a hybrid acquisition in an echo train consisting of a RARE module followed by an EPI module.…”