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Quantitative evaluation of scar, area at risk, and wall thickening in a porcine model of sub-acute myocardial infarction (MI)
Journal of Cardiovascular Magnetic Resonance volume 15, Article number: P213 (2013)
Elevated signal intensity (SI) in T2w images is often designated as area-at-risk (AAR) following acute/sub-acute MI. While AAR has been qualitatively associated with reductions in wall thickening (WT), quantitative information between the two is not available [1–3]. Quantitative SI threshold for classifying regions as AAR, and its effect on regional WT have also been not reported.
In an animal model, quantify the:
Effect of SI threshold on estimating AAR,
Reduction in WT with AAR at increasing SI thresholds, and
Correlation between AAR and percent scar.
Acquisition Protocol: Basal, mid, and apical slices in short axis orientation were obtained in a pig (n=14) AMI model (LAD occlusion) at 3.0T (Ingenia, Philips Healthcare):
Cine SSFP: TR/TE/α = 3/1.5 ms/45°; acquired temporal resolution: 12 ms.
Delayed enhancement MRI (DE-MRI): 10 min after 0.2 mmol/kg of contrast, scar was visualized using a gated IR-TFE sequence with inversion delay (TI) adjusted to null normal myocardium.
Dual-IR T2W imaging (BB): Effective TE/TR: 80 ms/2*RR interval; TSE readout.
Data Analysis: Myocardial region was manually segmented from cine, DE-MRI, and BB images (Figure 1) using MATLAB™. Myocardial region was sub-divided into co-registered segments of equal mass for each animal to calculate the following quantitative parameters:
Normalized wall thickness (nWT) per segment = (WTES - WTED)/( WTED), where ED = End-Diastole, ES-End-Systole.
Segmental scar burden, defined as ratio of pixels designated as scar to total number of pixels in each segment of DE-MRI. Scar pixel is one with SI > [mean + 5*Standard Deviation (SD) of normal remote myocardium].
Segmental AAR, defined as regions in BB images with SI > mean + n*SD of normal remote myocardium (AAR with n = 2, 3, 4 are AAR_2SD, AAR_3SD, and AAR_4SD, respectively).
As a share of total myocardium, AAR burden was significantly higher (43 to 57 %) than scar burden (30 %) (Table 1). Although total AAR burden progressively declined with increasing T2w SI cut-offs, it was not lower than scar burden at any threshold evaluated (AAR_4SD > Scar burden).
Spatially, AAR overlapped, and extended beyond scar regions.
Reduction in segmental nWTwas lower in AAR regions that did not overlap scar region compared to those segments that did(108 ± 36 % vs 91 ± 29 %, Figure 2).
In sub-acute AMI, AAR is significantly larger than scar. In non-overlapping regions of AAR and scar, nWT, while diminished compared to normal remote myocardium, is significantly better than in regions of scar.
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Krishnamurthy, R., Li, K., Pednekar, A. et al. Quantitative evaluation of scar, area at risk, and wall thickening in a porcine model of sub-acute myocardial infarction (MI). J Cardiovasc Magn Reson 15, P213 (2013). https://doi.org/10.1186/1532-429X-15-S1-P213
- Normalize Wall Thickness
- Scar Burden
- Scar Region
- Short Axis Orientation
- Cine SSFP