Non‐contrast myocardial infarct scar assessment using a hybrid native T₁ and magnetization transfer imaging sequence at 1.5T

Abstract

Purpose To develop a gadolinium‐free cardiac MR technique that simultaneously exploits native T1 and magnetization transfer (MT) contrast for the imaging of myocardial infarction. Methods A novel hybrid T one and magnetization transfer (HYTOM) method was developed based on the modified look‐locker inversion recovery (MOLLI) sequence, with a train of MT‐prep pulses placed before the balanced SSFP (bSSFP) readout pulses. Numerical simulations, based on Bloch‐McConnell equations, were performed to investigate the effects of MT induced by (1) the bSSFP readout pulses, and (2) the MT‐prep pulses, on the measured, “apparent,” native T1 values. The HYTOM method was then tested on 8 healthy adult subjects, 6 patients, and a swine with prior myocardial infarction (MI). The resulting imaging contrast between normal myocardium and infarcted tissues was compared with that of MOLLI. Late gadolinium enhancement (LGE) images were also obtained for infarct assessment in patients and swine. Results Numerical simulation and in vivo studies in healthy volunteers demonstrated that MT effects, resulting from on‐resonance bSSFP excitation pulses and off‐resonance MT‐prep pulses, reduce the measured T1 in both MOLLI and HTYOM. In vivo studies in patients and swine showed that the HYTOM sequence can identify locations of MI, as seen on LGE. Furthermore, the HYTOM method yields higher myocardium‐to‐scar contrast than MOLLI (contrast‐to‐noise ratio: 7.33 ± 1.67 vs. 3.77 ± 0.66, P < 0.01). Conclusion The proposed HYTOM method simultaneously exploits native T1 and MT contrast and significantly boosts the imaging contrast for myocardial infarction.

Quantitative magnetization transfer imaging for non‐contrast enhanced detection of myocardial fibrosis

“…Our results did not show evidence of an increase of the bound pool in the presence of replacement fibrosis/collagen, that is, in the chronic MI patients. On the contrary, a reduction of the MT effects was observed, which is consistent with findings in chronic myocardial infarction in rats by Scholz et al, 35 findings of fibrosis in end‐stage renal disease (ESRD) patients by Stromp et al, 36 and reports from Duan et al 13 in 15‐mo (average) post MI patients using a hybrid T1/MT –weighted sequence. The proposed sequence may present advantages over Duan et al and Stromp et al in terms of quantification of the bound pool and potential specificity to fibrosis, since the cited approaches rely on combining the MT contrast with T1 and/or T2 weighting.…”

“…Previous studies have explored the use of MT ratio (MTR) for gadolinium‐free assessment of chronic or acute myocardial fibrosis. In vivo studies have shown reductions of the MT effects associated with both acute 11,12 and over 10‐mo old myocardial infarction (MI) 13 . A post‐mortem study 9 found correlation between increased MTR and fibrous tissue in histology, while some areas of decreased MTR were associated with inflammatory granulocyte infiltration at a microscopic level.…”

“…In vivo studies have shown reductions of the MT effects associated with both acute 11,12 and over 10-mo old myocardial infarction (MI). 13 A post-mortem study 9 found correlation between increased MTR and fibrous tissue in histology, while some areas of decreased MTR were associated with inflammatory granulocyte infiltration at a microscopic level. This shows that MTR results can be complex to interpret without knowledge of the dynamics of the free pool, as it can also be affected by edema and inflammation.…”

Role of Cardiac Magnetic Resonance to Improve Risk Prediction following Acute ST-elevation Myocardial Infarction

“…The clinical significance of gadolinium deposition remains to be determined [152]. Nevertheless, novel techniques that allow quantitative characterization of the infarcted and non-infarcted myocardium after myocardial infarction without the need of a gadolinium contrast agent have been investigated recently [97,[153][154][155][156][157]. CMR infarct characterization and prognostication without using contrast agents is an interesting concept, but the prognostic role of non-contrast CMR compared to contrast-enhanced CMR remains to be defined.…”

Development, validation, qualification, and dissemination of quantitative MR methods: Overview and recommendations by the ISMRM quantitative MR study group

“…Interestingly, MOLLI T 1 mapping, which is most common in clinical use, is known to exhibit a large bias. However, it has been suggested that certain confounders to MOLLI T 1 measurements may enhance clinical sensitivity 137 . As illustrated in Figure 7, this somewhat counter‐intuitive phenomenon arises because some confounders (e.g., magnetization transfer 84,137,138 ) are sensitive to pathological alterations, leading to inflated effect size in certain disease entities compared to unbiased measurements.…”