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

Abstract

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 mapping (2in1-RARE-EPI). 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 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 mapping was examined in a phantom study mimicking T2 and 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. There was a good agreement between T2 / values derived from 2in1-RARE-EPI and T2 / reference values obtained from MSE and MGRE in both phantoms and healthy subjects. In patients, MS lesions in T2 and maps deduced from 2in1-RARE-EPI could be just as clearly delineated as in reference maps calculated from MSE/MGRE. This work demonstrates the feasibility of radially (under)sampled 2in1-RARE-EPI for simultaneous T2 and mapping in MS patients.