Cardiovascular magnetic resonance by non contrast T1-mapping allows assessment of severity of injury in acute myocardial infarction

Abstract

Background: Current cardiovascular magnetic resonance (CMR) methods, such as late gadolinium enhancement (LGE) and oedema imaging (T2W) used to depict myocardial ischemia, have limitations. Novel quantitative T1-mapping techniques have the potential to further characterize the components of ischemic injury. In patients with myocardial infarction (MI) we sought to investigate whether state-of the art pre-contrast T1-mapping (1) detects acute myocardial injury, (2) allows for quantification of the severity of damage when compared to standard techniques such as LGE and T2W, and (3) has the ability to predict long term functional recovery.

Methods: 3T CMR including T2W, T1-mapping and LGE was performed in 41 patients [of these, 78% were ST elevation MI (STEMI)] with acute MI at 12-48 hour after chest pain onset and at 6 months (6M). Patients with STEMI underwent primary PCI prior to CMR. Assessment of acute regional wall motion abnormalities, acute segmental damaged fraction by T2W and LGE and mean segmental T1 values was performed on matching short axis slices. LGE and improvement in regional wall motion at 6M were also obtained.

Results: We found that the variability of T1 measurements was significantly lower compared to T2W and that, while the diagnostic performance of acute T1-mapping for detecting myocardial injury was at least as good as that of T2W-CMR in STEMI patients, it was superior to T2W imaging in NSTEMI. There was a significant relationship between the segmental damaged fraction assessed by either by LGE or T2W, and mean segmental T1 values (P < 0.01). The index of salvaged myocardium derived by acute T1-mapping and 6M LGE was not different to the one derived from T2W (P = 0.88). Furthermore, the likelihood of improvement of segmental function at 6M decreased progressively as acute T1 values increased (P < 0.0004).

Conclusions: In acute MI, pre-contrast T1-mapping allows assessment of the extent of myocardial damage. T1-mapping might become an important complementary technique to LGE and T2W for identification of reversible myocardial injury and prediction of functional recovery in acute MI.

Figure 1

Panels A and B. Representative CMR images. Oedema T2W images (left column), acute LGE images (center), and ShMOLLI T1-mapping (right column) are displayed. Two sets of images (Panel A and Panel B) corresponding to two separate patients are shown. Top panels (A): a case of transmural inferior STEMI:both oedema (T2W) and LGE depict an area of increased signal intensity; in the same region T1-mapping depicts significantly increased T1 values (shown in red) compared to the remote unaffected myocardium (normal T1 values shown in green). Lower panels (B), a case of subendocardial NSTEMI : Although the T2 W images show only a mild increase in brightness, there is an area of increased T1 values exceeding the area of LGE enhancement. Of note the peak troponin I was significantly different in the two patients (peak troponin I 50 mg/mL in the STEMI patient vs7 mg/mL in the NSTEMI patient). Panels C and D: Correlation between T1 values and T2W normalized SI (Panel C) and between T1 values and LGE normalized SI (Panel D). The SI of T2W (on the × axis, panel C) and LGE (on × axis Panel D), both normalized to the remote unaffected myocardium, are shown to correlate strongly with T1 values.

Figure 2

Receiver Operating Curves showing the diagnostic performance of T1-mapping compared toT2W in detecting acute injury in ACS as derived from late gadolinium enhancement (LGE) scoring. The area under the curve forT2W (dashed line) was not significantly different from T1-mapping (solid line) in patients with STEMI (Panel A); In NSTEMI patients, the area under the curve forT2W (dashed line) was significantly smaller than that for T1-mapping (p = 0.004).

Figure 3

Assessment of severity of injury by T1-mapping: relationship withT2W and LGE. T1 values increase for increasing segmental extent of injury, assessed by either LGE (panel A) or T2W (panel B). The overall relationships are significant: however for T2W, there is an overlap in T1 values for segments with segmental damaged fraction between 41 and 80%. Lesions with MO have been excluded for this analysis.

Figure 4

Assessment of severity of injury by T1-mapping: relationship with regional and global function. Panel A shows the relationship between T1 values and the extent of regional wall motion abnormalities (P < 0.01). A highly significant negative correlation between mean LV T1 values and LV ejection fraction was also found (Panel B).

Figure 5

Quantitative assessment of microvascular obstruction by T1-mapping. Panel A shows a case of microvascular obstruction as depicted by LGE. The corresponding T1-map is shown in Panel B. The dark core of MO in the LGE image (arrows) is depicted by T1 values (Panel B) in the color range similar to remote myocardium (green). The surrounding injured myocardium (bright on LGE) shows high T1 values (red). Panel C shows quantitative analyses of the 7 cases with MO. T1 values in the MO regions are significantly lower than in the surrounding LGE-positive myocardium.

Figure 6

Likelihood of functional improvement at 6 m by T1-mapping and acute LGE in dysfunctional segments. Data are shown for 198 segments, which were dysfunctional acutely. Panel A shows the significant relationship between the likelihood of recovery of function of acutely dysfunctional segments and the T1 values in acute (P < 0.0004). Panel B shows the relationship between the likelihood of recovery of function of acutely dysfunctional segments and the segmental damaged fraction by LGE in acute (P < 0.004). While the relationship between functional recovery and T1 was essentially linear, by using acute LGE (Panel B) the likelihood of improvement for segments with intermediate LGE did not correlate with the amount of damage. No MO segments were included in this analysis.