2015

Accelerating modified Look-Locker inversion recovery (MOLLI): Shortened inversion-recovery-based myocardial T1 mapping schemes
Li Huang1, Radhouene Neji1,2, Muhammad Sohaib Nazir1, John Whitaker1, Filippo Bosio1, Amedeo Chiribiri1, Reza Razavi1, and Sébastien Roujol1

1School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom, 2MR Research Collaborations, Siemens Healthcare Limited, Frimley, United Kingdom

Synopsis

Abnormal native myocardial T1 times are associated with a variety of cardiomyopathies, and are widely measured by inversion-recovery-based myocardial T1 mapping techniques such as modified Look-Locker inversion recovery (MOLLI). These sequences are limited in patients with severe breathholding difficulties for relatively long duration of breathholds. In this work, we sought to develop and characterize shortened schemes using less amount of T1-weighted images to reduce their sensitivity to imperfect breathholds.

Introduction

Abnormal native myocardial T1 times are associated with several cardiomyopathies1. Inversion-recovery-based myocardial T1 mapping techniques, such as modified Look-Locker inversion recovery (MOLLI)2,3, are widely used because of their high precision, reproducibility and map quality2-7. These techniques use ECG-triggered acquisition of 7-13 images with different T1 weightings of the same slice succeeding inversion preparation to generate one T1 map in a single breathhold of 9-17 heartbeats2-7. However, they may be limited in patients with severe breathholding difficulties. In this work, shortened inversion-recovery-based myocardial T1 mapping schemes were developed and characterized.

Methods

(1) Shortened schemes: In the proposed shortened schemes, 2-5 T1-weighted images were acquired after only one inversion pulse. For T1 fitting, a novel one-parameter (OP) fitting model as well as a standard three-parameter (TP) fitting model2 with Look-Locker and inversion factor corrections2,8 were used, respectively. These schemes were thus defined as OPn (n=2-5) and TPn (n=3-5) where n represents the image amount. They were compared to a conventional 5-(3)-3 MOLLI scheme, which is denoted as TP8.

(2) OP reconstruction: Dictionary matching was performed using the OP fitting model created for a 100-2200ms T1 range and defined as S(TI)=1-(1+δ)e-TI/T1 with δ being the inversion factor8 of the applied inversion pulse (non-selective hyperbolic-tangent) and TI the inversion time between the inversion preparation and image acquisition. Assuming typical B0/B1 inhomogeneities of ±150Hz/80-100% and myocardial T1/T2=400-1600/45ms, Bloch simulations of the inversion slice profiles were performed to determine δ=0.96. Signal polarity restoration9 and magnitude scaling to each dictionary entry were performed for dictionary matching.

(3) Computational validation: Accuracy and precision of all schemes were evaluated using Bloch simulations with added noise. Inversion and excitation slice profiles were calculated using the same B0/B1 inhomogeneities and myocardial T1/T2 as mentioned above, and then used in these Bloch simulations.

(4) Experimental validation: Imaging in a 9-vial phantom10 (5 repetitive scans) and 16 healthy volunteers (2 repetitive scans) were performed on a 1.5T scanner (MAGNETOM Aera, Siemens Healthcare, Erlangen, Germany) using a conventional 5-(3)-3 MOLLI acquisition scheme with 2D bSSFP readout: TR/TE/α 2.70ms/1.12ms/35°, FOV 360×306mm2, 1.4×2.1mm2 pixel, 3 slices with thickness 8mm, GRAPPA factor 2, partial Fourier factor 7/8, bandwidth 1085Hz/px, first inversion time 100ms. Slices were in the short-axis orientation in the healthy volunteer study. T1 times/spatial variability/repeatability of all schemes were measured in each vial (phantom) and each myocardial segment11 (healthy volunteers). Kruskal-Wallis and ANOVA as well as Wilcoxon rank sum tests and Student’s t-tests with Bonferroni correction were used to compare schemes in phantom and in healthy volunteers, respectively. Additionally, OP2 and MOLLI were compared using subjective assessment of native T1 map quality and Pearson correlation analysis. 5-point-scale qualitative scoring (1-non-diagnostic/5-excellent) was undergone by consensus of 2 experienced cardiac MRI readers with respect to image artifacts, myocardium/blood pool border delineation and myocardium homogeneity12.

Results

Both simulation and phantom studies showed limited penalty of accuracy, precision and spatial invariability of all shortened schemes compared to MOLLI, as shown in Fig. 1 and Fig. 2 (although statistically insignificant with p>0.71), respectively. Repeatability remained similar for all schemes in phantom (p=0.75). Fig. 3 shows representative example native T1 maps using all schemes. In the healthy volunteer study (Fig. 4), all schemes led to similar native T1 times and repeatability for myocardium (977-997ms, p=0.21 and 14-18ms, p=0.87) and blood (1583-1623ms, p=0.79 and 7-15ms, p=0.41), while all shortened schemes yielded limited increase of spatial variability for myocardium (56-59ms vs. 48ms, p<0.01) and blood (60-105ms vs. 49ms, p<0.01) compared to MOLLI. OP2 and MOLLI yielded high linear correlation between native myocardial T1 times (Pearson correlation coefficient=0.95) and similar scores of subjective T1 map quality (4.8±0.2 vs. 4.8±0.2, p=1.00).

Discussion

All proposed shortened schemes combined with the OP fitting model resulted in similar native T1 range, limited reduction of precision and spatial invariability, similar repeatability and similar map quality. Two-heartbeat myocardial T1 mapping has been proposed, but was based on saturation recovery and considerably increased spatial variability for native myocardial T1 mapping by a factor of 2.5 when compared to MOLLI13. The mild increase by a factor of 1.2 in spatial variability of all proposed shortened schemes compared to MOLLI for native myocardial T1 mapping was in the same magnitude as yielded by ShMOLLI7 (note TP5 can be seen as an approximation of ShMOLLI for native myocardial T1 mapping).

Conclusion

Compared to MOLLI, the proposed two-heartbeat OP2 scheme yields highly linearly correlated native T1 times, similar repeatability, similar map quality and mild loss in spatial invariability for native myocardial T1 mapping at 1.5T. This approach may be a valuable alternative for myocardial T1 mapping in patients with limited breathholding abilities.

Acknowledgements

This work was supported by the Health Innovation Challenge Fund (grant number HICF-R10-698), a parallel funding partnership between the Department of Health and the Wellcome Trust, the Wellcome Engineering and Physical Sciences Research Council (EPSRC) Centre for Medical Engineering at King's College London (WT 203148/Z/16/Z) and the EPSRC grant (EP/R010935/1). This research was also supported by the National Institute for Health Research (NIHR) Biomedical Research Centre based at Guy's and St Thomas' National Health Service (NHS) Foundation Trust in partnership with King's College London, and by the NIHR Healthcare Technology Co-operative for Cardiovascular Disease at Guy’s and St Thomas' NHS Foundation Trust. The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health.

References

  1. Moon JC, Messroghli DR, Kellman P, Piechnik SK, Robson MD, Ugander M, Gatehouse PD, Arai AE, Friedrich MG, Neubauer S, Schulz-Menger J, Schelbert EB. Myocardial T1 mapping and extracellular volume quantification: a Society for Cardiovascular Magnetic Resonance (SCMR) and CMR Working Group of the European Society of Cardiology consensus statement. J Cardiovasc Magn Reson. 2013;15(1):92.
  2. Messroghli DR, Radjenovic A, Kozerke S, Higgins DM, Sivananthan MU, Ridgway JP. Modified Look-Locker inversion recovery (MOLLI) for high-resolution T1 mapping of the heart. Magn Reson Med. 2004;52(1):141-146.
  3. Messroghli DR, Niendorf T, Schulz-Menger J, Dietz R, Friedrich MG. T1 mapping in patients with acute myocardial infarction. J Cardiovasc Magn Reson. 2003;5(2):353-359.
  4. Roujol S, Weingärtner S, Foppa M, Chow K, Kawaji K, Ngo LH, Kellman P, Manning WJ, Thompson RB, Nezafat R. Accuracy, precision, and reproducibility of four T1 mapping sequences: a head-to-head comparison of MOLLI, ShMOLLI, SASHA, and SAPPHIRE. Radiology. 2014;272(3):683-689.
  5. Kellman P, Hansen MS. T1-mapping in the heart: accuracy and precision. J Cardiovasc Magn Reson. 2014;16(1):2.
  6. Weingärtner S, Meßner NM, Budjan J, Loßnitzer D, Mattler U, Papavassiliu T, Zöllner FG, Schad LR. Myocardial T 1-mapping at 3T using saturation-recovery: reference values, precision and comparison with MOLLI. J Cardiovasc Magn Reson. 2017;18(1):84.
  7. Piechnik SK, Ferreira VM, Dall'Armellina E, Cochlin LE, Greiser A, Neubauer S, Robson MD. Shortened Modified Look-Locker Inversion recovery (ShMOLLI) for clinical myocardial T1-mapping at 1.5 and 3 T within a 9 heartbeat breathhold. J Cardiovasc Magn Reson. 2010;12(1):69.
  8. Kellman P, Herzka DA, Hansen MS. Adiabatic inversion pulses for myocardial T1 mapping. Magn Reson Med. 2014;71(4):1428-1434.
  9. Xue H, Greiser A, Zuehlsdorff S, Jolly MP, Guehring J, Arai AE, Kellman P. Phase-sensitive inversion recovery for myocardial T1 mapping with motion correction and parametric fitting. Magn Reson Med. 2013;69(5):1408-1420.
  10. Captur G, Gatehouse P, Keenan KE, Heslinga FG, Bruehl R, Prothmann M, Graves MJ, Eames RJ, Torlasco C, Benedetti G, Donovan J, Ittermann B, Boubertakh R, Bathgate A, Royet C, Pang W, Nezafat R, Salerno M, Kellman P, Moon JC. A medical device-grade T1 and ECV phantom for global T1 mapping quality assurance-the T1 mapping and ECV standardization in cardiovascular magnetic resonance (T1MES) program. J Cardiovasc Magn Reson. 2016;18:58.
  11. Cerqueira MD, Weissman NJ, Dilsizian V, Jacobs AK, Kaul S, Laskey WK, Pennell DJ, Rumberger JA, Ryan T, Verani MS. Standardized myocardial segmentation and nomenclature for tomographic imaging of the heart. A statement for healthcare professionals from the Cardiac Imaging Committee of the Council on Clinical Cardiology of the American Heart Association. Circulation. 2002;105(4):539-542.
  12. Kellman P, Wilson JR, Xue H, Ugander M, Arai AE. Extracellular volume fraction mapping in the myocardium, part 1: evaluation of an automated method. J Cardiovasc Magn Reson. 2012;14:63.
  13. Fitts M, Breton E, Kholmovski EG, Dosdall DJ, Vijayakumar S, Hong KP, Ranjan R, Marrouche NF, Axel L, Kim D. Arrhythmia insensitive rapid cardiac T1 mapping pulse sequence. Magn Reson Med. 2013;70(5):1274-1282.

Figures

Fig. 1. Accuracy and precision of all T1 mapping schemes obtained in numerical simulations. T1-dependent accuracy (a) and precision (b) are shown using a typical myocardial T2=45ms for all evaluated schemes. T1-T2 dependent accuracy (c) and precision (d) are shown for OP2 and MOLLI.

Fig. 2. Accuracy (a), spatial variability (b) and repeatability (c) of all evaluated schemes in the phantom study. There were no statistically significant differences between all schemes in terms of accuracy (p=1.00), spatial variability (p=0.71) and repeatability (p=0.75).

Fig. 3. Example native T1 maps of a 29yr male healthy volunteer along the short axis using all evaluated schemes. Similar image quality and native T1 range were obtained across all slices using all schemes.

Fig. 4. Native T1 times, spatial variability and repeatability for myocardium (a-c, respectively) and blood (d-f, respectively) obtained using all evaluated schemes in 16 healthy volunteers. Average (bar plots) and standard deviation (error bars) over all healthy volunteers are presented. All schemes had similar native myocardial and blood T1 times (p=0.21 and p=0.79, respectively) and repeatability (p=0.87 and 0.41, respectively). All shortened schemes led to increased myocardial and blood T1 spatial variability with respect to MOLLI (p<0.01).

Proc. Intl. Soc. Mag. Reson. Med. 27 (2019)
2015