Simultaneous T 2 and T 2 ∗ mapping of multiple sclerosis lesions with radial RARE-EPI

Carl J J Herrmann, Antje Els, Laura Boehmert, Joao Periquito, Thomas Wilhelm Eigentler, Jason M Millward, Sonia Waiczies, Joseph Kuchling, Friedemann Paul, Thoralf Niendorf
Magnetic Resonance in Medicine 2021 May 5

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 <mml:math xmlns:mml=""&gt; <mml:msubsup> <mml:mi>T</mml:mi> <mml:mn>2</mml:mn> <mml:mo>∗</mml:mo> </mml:msubsup> </mml:math> 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 <mml:math xmlns:mml=""&gt; <mml:msubsup> <mml:mi>T</mml:mi> <mml:mn>2</mml:mn> <mml:mo>∗</mml:mo> </mml:msubsup> </mml:math> 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 <mml:math xmlns:mml=""&gt; <mml:msubsup> <mml:mi>T</mml:mi> <mml:mn>2</mml:mn> <mml:mo>∗</mml:mo> </mml:msubsup> </mml:math> mapping was examined in a phantom study mimicking T2 and <mml:math xmlns:mml=""&gt; <mml:msubsup> <mml:mi>T</mml:mi> <mml:mn>2</mml:mn> <mml:mo>∗</mml:mo> </mml:msubsup> </mml:math> 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 / <mml:math xmlns:mml=""&gt; <mml:msubsup> <mml:mi>T</mml:mi> <mml:mn>2</mml:mn> <mml:mo>∗</mml:mo> </mml:msubsup> </mml:math> values derived from 2in1-RARE-EPI and T2 / <mml:math xmlns:mml=""&gt; <mml:msubsup> <mml:mi>T</mml:mi> <mml:mn>2</mml:mn> <mml:mo>∗</mml:mo> </mml:msubsup> </mml:math> reference values obtained from MSE and MGRE in both phantoms and healthy subjects. In patients, MS lesions in T2 and <mml:math xmlns:mml=""&gt; <mml:msubsup> <mml:mi>T</mml:mi> <mml:mn>2</mml:mn> <mml:mo>∗</mml:mo> </mml:msubsup> </mml:math> 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 <mml:math xmlns:mml=""&gt; <mml:msubsup> <mml:mi>T</mml:mi> <mml:mn>2</mml:mn> <mml:mo>∗</mml:mo> </mml:msubsup> </mml:math> mapping in MS patients.

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