Abstract
BackgroundT1 mapping sequences such as MOLLI, ShMOLLI and SASHA make use of different technical approaches, bearing strengths and weaknesses. It is well known that obtained T1 relaxation times differ between the sequence techniques as well as between different hardware. Yet, T1 quantification is a promising tool for myocardial tissue characterization, disregarding the absence of established reference values. The purpose of this study was to evaluate the feasibility of native and post-contrast T1 mapping methods as well as ECV maps and its diagnostic benefits in a clinical environment when scanning patients with various cardiac diseases at 3 T.MethodsNative and post-contrast T1 mapping data acquired on a 3 T full-body scanner using the three pulse sequences 5(3)3 MOLLI, ShMOLLI and SASHA in 19 patients with clinical indication for contrast enhanced MRI were compared. We analyzed global and segmental T1 relaxation times as well as respective extracellular volumes and compared the emerged differences between the used pulse sequences.ResultsT1 times acquired with MOLLI and ShMOLLI exhibited systematic T1 deviation compared to SASHA. Myocardial MOLLI T1 times were 19% lower and ShMOLLI T1 times 25% lower compared to SASHA. Native blood T1 times from MOLLI were 13% lower than SASHA, while post-contrast MOLLI T1-times were only 5% lower. ECV values exhibited comparably biased estimation with MOLLI and ShMOLLI compared to SASHA in good agreement with results reported in literature. Pathology-suspect segments were clearly differentiated from remote myocardium with all three sequences.ConclusionMyocardial T1 mapping yields systematically biased pre- and post-contrast T1 times depending on the applied pulse sequence. Additionally calculating ECV attenuates this bias, making MOLLI, ShMOLLI and SASHA better comparable. Therefore, myocardial T1 mapping is a powerful clinical tool for classification of soft tissue abnormalities in spite of the absence of established reference values.
Highlights
T1 mapping sequences such as modified look-locker inversion-recovery protocols (MOLLI), shortened MOLLI (ShMOLLI) and SASHA make use of different technical approaches, bearing strengths and weaknesses
Mean T1 relaxation time of remote myocardium was lowest with ShMOLLI (1076 ± 100 ms) compared to MOLLI (1175 ± 72 ms) and SASHA (1460 ± 67 ms), with broadest distribution found in ShMOLLI
Native T1 time was remarkably higher in pathologic segments (ShMOLLI: 1264 ± 72 ms; MOLLI: 1356 ± 43 ms; SASHA: 1687 ± 68 ms; solid red)
Summary
T1 mapping sequences such as MOLLI, ShMOLLI and SASHA make use of different technical approaches, bearing strengths and weaknesses. Quantification of myocardial longitudinal relaxation (T1) times is a promising method in cardiovascular magnetic resonance, bearing the ability to characterize myocardial tissue and to identify abnormalities in the context of both acute and chronic events [1, 2]. Evaluation of T1 mapping before and after contrast administration further allows calculation of quantitative myocardial extracellular volume fraction (ECV) maps. This parameter may be superior for the assessment of diffuse extracellular myocardial pathologies like early disease stages of myocardial fibrosis or amyloidosis compared to the commonly used gold standard late gadolinium enhancement (LGE) [3,4,5]. Sensitivity to T2 and MT may enhance sensitivity to tissue abnormalities [14] while sensitivity to magnetic field inhomogeneities and inversion efficiency may reduce overall specificity
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