Abstract

Mapping the longitudinal relaxation time T 1 has widespread applications in clinical MRI as it promises a quantitative comparison of tissue properties across subjects and scanners. Due to the long scan times of conventional methods, however, the use of quantitative MRI in clinical routine is still very limited. In this work, an acceleration of Inversion-Recovery Look-Locker (IR-LL) T 1 mapping is presented. A model-based algorithm is used to iteratively enforce an exponential relaxation model to a highly undersampled radially acquired IR-LL dataset obtained after the application of a single global inversion pulse. Using the proposed technique, a T 1 map of a single slice with 1.6mm in-plane resolution and 4mm slice thickness can be reconstructed from data acquired in only 6s. A time-consuming segmented IR experiment was used as gold standard for T 1 mapping in this work. In the subsequent validation study, the model-based reconstruction of a single-inversion IR-LL dataset exhibited a T 1 difference of less than 2.6% compared to the segmented IR-LL reference in a phantom consisting of vials with T 1 values between 200ms and 3000ms. In vivo, the T 1 difference was smaller than 5.5% in WM and GM of seven healthy volunteers. Additionally, the T 1 values are comparable to standard literature values. Despite the high acceleration, all model-based reconstructions were of a visual quality comparable to fully sampled references. Finally, the reproducibility of the T 1 mapping method was demonstrated in repeated acquisitions. In conclusion, the presented approach represents a promising way for fast and accurate T 1 mapping using radial IR-LL acquisitions without the need of any segmentation.

Highlights

  • Quantitative evaluation of T1 relaxation times is desirable in many clinical MRI applications

  • A comparison of the two reference measurements shows a small deviation between the segmented Inversion-Recovery LookLocker (IR-LL) and the segmented inversion recovery (IR) method increasing with T1

  • The noisier appearance of the IR-MAP reconstruction is confirmed by a lower signal-to-noise ratio (SNR) especially in comparison to the segmented IR-LL acquisition, and to the segmented IR acquisition

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Summary

Introduction

Quantitative evaluation of T1 relaxation times is desirable in many clinical MRI applications. One of the most prominent ways to perform T1 mapping is to track the spin-lattice relaxation process after a suitable magnetization preparation. The resulting images and a relaxation model according to the type of preparation applied are used for a fit of the relaxation parameters. For short relaxation times, which occur in many clinically relevant types of tissue, this can be difficult and measurements have to be performed in segmented fashion or with low spatial resolution [1,2,3]. PLOS ONE | DOI:10.1371/journal.pone.0122611 April 10, 2015

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