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Cardiac motion resolved Magnetic Resonance Fingerprinting with joint reconstruction: jMORE-MRF
Olivier Jaubert1, Gastao Cruz1, Aurelien Bustin1, Torben Schneider2, Peter Koken3, Mariya Doneva3, Rene M. Botnar1, and Claudia Prieto1

1School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom, 2Philips Healthcare, Guilford, United Kingdom, 3Philips Research Europe, Hamburg, Germany

Synopsis

ECG-triggered cardiac Magnetic Resonance Fingerprinting (cMRF) has been proposed to provide simultaneous myocardial T1 and T2 mapping from a single scan. A “free-running” motion-resolved cardiac MRF (MORE-MRF) approach has been recently introduced to provide T1 and T2 myocardial characterization over the entire cardiac cycle. Here we propose to improve MORE-MRF by exploiting redundancy between the different cardiac phases within a novel motion resolved multi-contrast reconstruction framework. The feasibility of this joint MORE-MRF approach (jMORE-MRF) was evaluated in phantom and healthy subjects and compared against conventional T1 and T2 mapping techniques.

Introduction

Cardiac MRI is currently the gold standard for the assessment of left ventricular volumes and function. Quantitative myocardial T1 and T2 mapping is an emerging technique that enables assessment of diffuse fibrosis (T1), edema and inflammation (T2)1. In current clinical practice, these images are acquired sequentially under several breath-holds, resulting in long scan times and potentially misaligned images and motion corrupted parametric maps. ECG-triggered cardiac MR fingerprinting (MRF)2–4 has been proposed to simultaneously measure T1 and T2 maps in a single scan at the diastolic cardiac phase. A “free-running” motion-resolved cardiac MRF (MORE-MRF)5 approach has been recently introduced to provide T1 and T2 myocardial characterization over the entire cardiac cycle, thus enabling simultaneous assessment of cardiac tissue viability and function in a single breath-hold scan. However, MORE-MRF is limited to a reduced number of cardiac phases. Here we propose to improve MORE-MRF reconstruction by exploiting redundancy between the different cardiac phases within a novel motion resolved multi-contrast reconstruction framework. The feasibility of this joint MORE-MRF approach (jMORE-MRF) was evaluated in phantom and five healthy subjects and compared against conventional T1 and T2 mapping techniques.

Methods

MORE-MRF consists of a continuous bSSFP MRF acquisition with inversion (IR) pulses followed by a variable flip angle pattern5,6 that is repeated every 2.95s. Acquisition is performed with a tiny golden angle (~23o) radial trajectory7. The reconstruction process uses ECG-based retrospective soft-gating and a novel multi contrast patch based undersampled reconstruction (HD-PROST8,9). HD-PROST for MORE-MRF alternates the optimization of 2 steps: 1) low-rank inversion(LRI)10 regularised with denoised images from step 2 as prior, and 2) a higher-order tensor-based denoising that assumes low rankness along 3 dimensions: locally (within a patch)11,12, non-locally (between similar patches) and along different contrasts. Singular images, resulting from the temporal compression (based on the dictionary) of the time-points images, are reconstructed with this approach. In this study, we extend HD-PROST to exploit low rankness also in the cardiac motion dimension by searching for similar patches in all cardiac phases simultaneously, thus providing implicit motion compensation of multi contrast data and joint reconstruction of multiple cardiac phases (Fig.1). A matching step and the generation of a synthetic cine are performed between steps 1) and 2) to obtain same contrast reference images for patch selection throughout the cardiac phases.

Experiments

2D free-running cardiac MRF acquisitions were performed on a standardised phantom13 and five healthy subjects using a 1.5T MR scanner (Ingenia, Philips Healthcare) using anterior and posterior coils (28-channels). Acquisition parameters included: TR/TE=4/1.99ms, 7300 time-points, one radial spoke per time-point, 2x2mm2 resolution, FOV=288x288mm2, 10 mm slice thickness, 10 repetitions of IR and flip angle train, 29.5s breath-hold. Eight and sixteen cardiac phases were reconstructed with MORE-MRF (independent reconstruction of each cardiac phase) and jMORE-MRF (joint reconstruction). Reconstruction parameters were set empirically and equally for both methods. For comparison purposes, 2D T1-MOLLI14, T1-SASHA15 and T2-GRASE16 maps were acquired with matching acquisition parameters.

Results

T1 and T2 phantom measurements for 8 phases reconstructed with jMORE-MRF are shown in Fig.2, demonstrating good agreement with the reference values provided by the vendor and consistency across different phases. MORE-MRF and jMORE-MRF reconstructions for 8 cardiac phases are compared in Fig.3 for a representative healthy subject. T1, T2 parametric maps and a synthetic bSSFP cine are included in Fig.3. Exploiting redundancy in the cardiac dimension allows for improved reconstruction of the time-point images with jMORE-MRF leading to more detailed parametric maps. Comparison between diastolic maps obtained with T1-MOLLI, T1-SASHA, T2-GRASE, MORE-MRF and jMORE-MRF are shown in Fig.4. Although good qualitative correspondence can be observed between the techniques, some blurring can be observed with MORE-MRF which is resolved with jMORE-MRF. Average diastolic T1 measurement and standard deviation on 5 subjects for SASHA, MOLLI, MORE-MRF and joint MORE-MRF are 1132±100ms, 1025±37ms, 1174±73ms and 1138.4±69ms respectively. T2 values for T2GRASE, MORE-MRF and jMORE-MRF are 52±5ms, 45±5ms and 44±5ms. A comparison between MORE-MRF and jMORE-MRF for 16 cardiac phases is shown in Fig.5. Temporal profiles show improved map quality using jMORE-MRF compared to MORE-MRF. Dynamic T1 map, T2 map and synthetic bSSFP cine are also included in Fig. 5 for jMORE-MRF.

Conclusions

Improvements of a continuous 2D free-running myocardial MRF framework have been demonstrated with the proposed jMORE-MRF reconstruction. This novel motion resolved multi-contrast reconstruction framework enables simultaneous cardiac function and quantitative tissue characterisation, with high image quality, by exploiting redundancies between the different cardiac phases. jMORE-MRF doubled the number of achievable cardiac phases with respect to the previously proposed MORE-MRF. Future work will further validate the proposed approach in healthy subjects and patients with cardiovascular disease.

Acknowledgements

This work was supported by EPSRC (EP/L015226/1, EP/P001009/1, EP/P032311/1) and Wellcome EPSRC Centre for Medical Engineering (NS/ A000049/1).

References

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8. Bustin A, Cruz G, Jaubert O, Lopez K, Botnar RM, Prieto C. High-Dimensionality Undersampled Patch-Based Reconstruction (HD-PROST) for Accelerated Multi-Contrast Magnetic Resonance Imaging. Proc. 27th Annu. Meet. ISMRM Montr. Canada. 2019.

9. Bustin A, Ginami G, Cruz G, et al. Five-minute whole-heart coronary MRA with sub-millimeter isotropic resolution, 100% respiratory scan efficiency, and 3D-PROST reconstruction. Magn. Reson. Med. 2018 doi: 10.1002/mrm.27354.

10. Assländer J, Cloos MA, Knoll F, Sodickson DK, Hennig J, Lattanzi R. Low rank alternating direction method of multipliers reconstruction for MR fingerprinting. Magn. Reson. Med. 2018;79:83–96 doi: 10.1002/mrm.26639.

11. Zhang T, Pauly JM, Levesque IR. Accelerating parameter mapping with a locally low rank constraint. Magn. Reson. Med. 2015;73:655–661 doi: 10.1002/mrm.25161.

12. Cruz G, Bustin A, Jaubert O, Schneider T, Botnar RM, Prieto C. Locally Low Rank Regularization for Magnetic Resonance Fingerprinting. Proc. 26th Annu. Meet. ISMRM Paris,France. 2018.

13. Captur G, Gatehouse P, Kellman P, et al. A T1 and ECV phantom for global T1 mapping quality assurance: The T1 mapping and ECV standardisation in CMR (T1MES) program. J. Cardiovasc. Magn. Reson. 2016;18:W14 doi: 10.1186/1532-429X-18-S1-W14.

14. Messroghli DR, Radjenovic A, Kozerke S, Higgins DM, Sivananthan MU, Ridgway JP. Modified Look-Locker inversion recovery (MOLLI) for high-resolutionT1 mapping of the heart. Magn. Reson. Med. 2004;52:141–146 doi: 10.1002/mrm.20110.

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Figures

Figure 1. Cardiac motion resolved jMORE-MRF reconstruction framework. Step 1: Regularised low-rank inversion reconstruction with denoised images from step 2 as prior. A matching step and generation of synthetic cine is performed between steps 1 and 2 to obtain same contrast reference images for patch selection throughout the cardiac phases. Step 2: higher-order tensor-based denoising that assumes low rankness along 3 dimensions: locally (within a patch), non-locally (between similar patches) and along different contrasts. For the search of similar patches (local similarity) MORE-MRF defines a spatial neighbourhood within each cardiac phase whereas jMORE-MRF defines a spatial-temporal neighbourhood throughout the whole cardiac cycle.

Figure 2.Comparison of joint MORE-MRF and MORE-MRF T1 and T2 maps and synthetic cine images (8 cardiac phases) for a representative subject. Reconstructions were performed using the same parameters. Sharper maps are obtained with jMORE-MRF exploiting redundancies throughout the entire cardiac cycle.

Figure 3. T1 and T2 phantom measurements for 8 phases reconstructed with jMORE-MRF in comparison to reference vendor values. A maximum normalised root mean square error on the myocardial vial (T1/T2=1090/48ms) of 5.5% (T1) and 5.6% (T2) across all cardiac phases was obtained.

Figure 4. 2D T1-MOLLI, T1-SASHA and T2-GRASE maps are compared to a diastolic phase of MORE-MRF and jMORE-MRF maps for a representative healthy subject. Although good correspondence is seen in all cases, some blurring can be observed with MORE-MRF which is resolved with jMORE-MRF

Figure 5. Comparison between MORE-MRF and jMORE-MRF for 16 cardiac phases reconstruction. The corresponding temporal profiles from images reconstructed with MORE-MRF (a) and jMORE-MRF (b) are shown in c) and d). Improved map quality, with less blurring, is achieved using jMORE-MRF compared to MORE-MRF. Dynamic T1 map, T2 map and synthetic bSSFP cine are included in e) for jMORE-MRF showing good quality across all cardiac phases.

Proc. Intl. Soc. Mag. Reson. Med. 27 (2019)
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