Simulation-based quantification of native T1 and T2 of the myocardium using a modified MOLLI scheme and the importance of Magnetization Transfer
Section snippets
Background
Quantitative cardiovascular Magnetic Resonance Imaging (MRI) techniques are gaining acceptance within the MR community because of their potential not only to diagnose non-localized disease but also to guide therapy and improve patient outcome [1]. Quantification of the longitudinal (T1) and transverse (T2) relaxation times in the myocardium enables tissue characterization and identification of various cardiomyopathies [2], [3]. T1 mapping has been used for calculating important myocardial
Pulse sequence design
A conventional MOLLI pulse sequence with a 5s(3s)3s acquisition scheme [14] was modified so as to increase its T2 sensitivity. An increased T2 sensitivity can be achieved through RF pulses of longer duration and of higher excitation flip angles. However, for a given duration of the excitation RF pulse of the bSSFP readout, higher excitation flip angles increase the on-resonance RF power deposition of bSSFP on the macromolecular pool which, in turn, reduces the steady-state signal through the MT
Phantom study
Table 1 shows the reference T1 and T2 values of all the phantoms along with the mass concentrations of their elements and the T1 and T2 estimates given by the conventional mapping techniques (conventional MOLLI, SASHA and T2prep-bSSFP). The SQUAREMR results from the application of all the variants of the modified MOLLI on the three phantom sets are shown in Fig. 2. Fig. 2 presents the T1 and T2 differences of the SQUAREMR-estimated values from the reference values for each individual phantom,
Discussion
In this study, a new simulation-based quantitative MR technique for simultaneous T1 and T2 mapping of the myocardium without the incorporation of advanced pulse sequence design and iterative reconstruction workflow was presented. Moreover, this study presented for the first time the importance of examining the effect of Magnetization Transfer on the estimation of T1 and T2 values using simulation-based quantitative MR techniques.
During the last decade, significant progress has been made in
Conclusion
In conclusion, a new simulation-based quantitative MR technique for simultaneous T1 and T2 mapping of the myocardium was presented. The proposed technique is based on the incorporation of advanced MR simulations of a MOLLI pulse sequence that has been modified so as to present combined high T2 sensitivity and low MT effect. The current implementation does not require the design of an advanced pulse sequence since it is based on a commercially available pulse sequence and does not require a
Acknowledgement
The authors would like to express their gratitude to Dr. Gunther Helms for the fruitful discussions around Magnetization Transfer and to Dr. Frederik Testud for the fruitful discussions around pulse sequence design. Funding was provided by the Swedish Heart and Lung Foundation (2015-201), the Swedish Research Council (2012-4944) and (2016-01617), the Medical Faculty at Lund University and Region of Skåne (2014/354).
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