MultiContrast Delayed Enhancement (MCODE) improves detection of subendocardial myocardial infarction by late gadolinium enhancement cardiovascular magnetic resonance: a clinical validation study

Abstract

Background: Myocardial infarction (MI) documented by late gadolinium enhancement (LGE) has clinical and prognostic importance, but its detection is sometimes compromised by poor contrast between blood and MI. MultiContrast Delayed Enhancement (MCODE) is a technique that helps discriminate subendocardial MI from blood pool by simultaneously providing a T2-weighted image with a PSIR (phase sensitive inversion recovery) LGE image. In this clinical validation study, our goal was to prospectively compare standard LGE imaging to MCODE in the detection of MI.

Methods: Imaging was performed on a 1.5 T scanner on patients referred for CMR including a LGE study. Prospective comparisons between MCODE and standard PSIR LGE imaging were done by targeted, repeat imaging of slice locations. Clinical data were used to determine MI status. Images at each of multiple time points were read on separate days and categorized as to whether or not MI was present and whether an infarction was transmural or subendocardial. The extent of infarction was scored on a sector-by-sector basis.

Results: Seventy-three patients were imaged with the specified protocol. The majority were referred for vasodilator perfusion exams and viability assessment (37 ischemia assessment, 12 acute MI, 10 chronic MI, 12 other diagnoses). Forty-six patients had a final diagnosis of MI (30 subendocardial and 16 transmural). MCODE had similar specificity compared to LGE at all time points but demonstrated better sensitivity compared to LGE performed early and immediately before and after the MCODE (p = 0.008 and 0.02 respectively). Conventional LGE only missed cases of subendocardial MI. Both LGE and MCODE identified all transmural MI. Based on clinical determination of MI, MCODE had three false positive MI's; LGE had two false positive MI's including two of the three MCODE false positives. On a per sector basis, MCODE identified more infarcted sectors compared to LGE performed immediately prior to MCODE (p < 0.001).

Conclusion: While both PSIR LGE and MCODE were good in identifying MI, MCODE demonstrated more subendocardial MI's than LGE and identified a larger number of infarcted sectors. The simultaneous acquisition of T1 and T2-weighted images improved differentiation of blood pool from enhanced subendocardial MI.

Figure 1

Simplified schematic of what data is acquired in MCODE: Within the same acquisition, MCODE produces both a LGE T1 image and a T2-weighted image at similar time points in the cardiac cycle. The LGE image is comparable to conventional methods with nulled, normal myocardium and bright MI. The T2-weighted image easily differentiates fluid (blood) from solid tissue (myocardium) but has minimal T1-weighting. Thus, the MI looks comparable to viable myocardium, and the endocardium is better delineated than on LGE images. Red arrows indicate the location of a MI on both the LGE T1 image (left) and the T2-weighted image (right).

Figure 2

Results: Timeline of image acquisition post-contrast: The mean time elapsed after contrast administration for each acquisition is summarized.

Figure 3

Example of an MCODE false positive MI: The above image is an example of one of MCODE’s false positive cases in a patient with an 80% circumflex stenosis but no clinical history of an MI or evidence of Q waves by EKG.

Figure 4

On a per sector basis, MCODE identified more infarcted sectors than LGE.

Figure 5

Fusion of MCODE T1 and T2 data: DICOM images from MCODE sequences can be loaded into a free open source software, OsiriX Imaging Software. From the MCODE sequence, the T2-weighted image is fused with the PSIR image with the Image Fusion function. No manual registration of the images is necessary since they were acquired during the same breath hold. When fused, the grey-scale T2-weighted image is then converted to the PET color look up table and overlays the grey-scale PSIR image. The image is then windowed and leveled to display areas with low T2 signal intensity (myocardium) to appear as dark red, and areas with high T2 signal intensity (blood pool) to appear as bright yellow.

Figure 6

Example comparison of LGE T1 and T2 signal intensity differences between normal myocardium, blood, and MI: In this example, LGE T1 signal intensities are similar between infarction and blood. On the MCODE T2 image, both normal and infarcted myocardium have similar signal intensities but are different from the blood pool such that one can better differentiate where the endocardial border of the infarction is relative to the blood pool.

Figure 7

Summary of signal intensity differences between blood, normal myocardium, and MI on LGE T1 and T2 images. On T1 images, the MI to blood pool difference is not significant which can be diagnostically challenging. On the T2 images, there is a significant difference between the MI and blood pool signal intensities.