QF1-005 - Histological validation of cardiac magnetic resonance T1 mapping for evaluating the extent of myocardial injury in swine with ST-segment–elevation myocardial infarction.

Background: Current cardiac magnetic resonance (CMR) T1 mapping is a quantitative imaging technique allowing the characterization of injured myocardium after myocardial infarction (MI) and the further assessment of the severity of myocardial damage. However, a key limitation of the present work is lack of histopathological confirmation of these findings. Our aims are to 1) detect whether the results from native T1 map and ECV map would be sufficient to assess the extent of myocardial injury after MI; 2) evaluate the relationship between ECV and native T1 against extracellular volume by histopathology.

Methods: A total of 15 MI pigs were induced successfully with left anterior descending coronary artery ligated. Meanwhile, 26 MI patients were also enrolled in this study. The CMR examination was performed on a 3T MR scanner (MAGNETOM Skyra, Siemens Healthcare, Erlangen, Germany) including protocols of cine, Modified Look-Lock Inversion (MOLLI) recovery for native T1 mapping and late gadolinium enhancement (LGE). In the experimental study, all of 15 pigs underwent serial CMR exams at 24h, 7 days, and 3 months after MI. Myocardium characterization was then compared with the histological findings after hematoxylin-eosin and Masson trichrome staining. The same CMR protocol was applied for the patients in order to keep the consistency. For the 26 patients, 14 of them were scanned at acute and chronic stage (3 months post-MI) and 12 of them underwent CMR exam at subacute stage as well as chronic stage. For all the subjects, the infarct size and the quantitative values of infarct, adjacent to infarct and remote zones at different time points were assessed by LGE and ECV/native T1, respectively.

Results: In pigs, both T1 and ECV values were higher in the infarct myocardium than in adjacent myocardium and remote myocardium at all evaluated time-points (all p < 0.05). Besides, ECV of infarct myocardium progressively increased with time (38.1 ± 2.7 % vs. 48.6 ± 2.8 % vs. 51.8 ± 3.6%, p < 0.001) (figure 1 B), while native T1 values were highest at day 7 after MI (1280.9 ± 16.3 ms vs. 1635.9 ± 50.3 ms vs. 1440.8 ± 54 ms, p = 0.032) (figure 1 A). The similar trend of the evaluation of these findings was also found in clinical study (Figure 1 C and D). Furthermore, both the native T1 and ECV values statistically correlated well with the histological findings in experimental model (figure 2).

Conclusion: The study shows that T1 mapping provides a non-invasive and comprehensive methods for quantification of the extent of myocardial injury in MI. Further studies are needed to study the effect of other factors on these variables.