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Infarct delineation in patients with acute myocardial infarction using the tractographic propagation angle and late gadolinium enhancement
Journal of Cardiovascular Magnetic Resonance volume 17, Article number: P16 (2015)
Currently used techniques to quantify late gadolinium enhancement (LGE) include an intensity threshold 5 standard deviations (5-SD) above normal myocardium and the full width at half maximum (FWHM) of the histogram [1, 2]. Validation of these segmentation schemes can be performed ex vivo using tetrazolium tetrachloride (TTC). However, no analogous gold standard metric exists in vivo. We recently introduced the tractographic propagation angle (PA) , and showed that a PA threshold of 4° in infarcted hearts produces a distribution that corresponds very closely to that of TTC staining . Here, we use PA maps in patients with myocardial infarction (MI) to evaluate the standard FWHM and 5-SD metrics. In addition, we introduce a new metric based on a Gaussian fit of the LGE image histogram.
Patients with acute MI (n=3) were imaged at the diastolic sweet spot on a 1.5 T scanner with a diffusion-encoded stimulated echo EPI sequence using the following parameters: resolution 2x2x8 mm3, b-value of 500 s/mm2, 10 diffusion-encoding directions, and 8 averages. LGE was performed using a 2D inversion recovery gradient echo sequence. Mean diffusivity (MD), fractional anisotropy (FA), helix angle (HA), and PA were calculated from the dyadic diffusion tensor. LGE of 16 short-axis slices were available for analysis. In addition to computing the 5-SD and FWHM, a Gaussian fit of each image histogram was performed and a threshold applied in 10% increments (G10-G100) of the total area.
In normal myocardium PA is typically less than 4° (Figure 1A). Of all LGE-based metrics, G60 demonstrated the closest relationship to PA (Figures 1B-D). Figures 1E-H depict infarct segmentation by PA, G60, FWHM, and 5-SD; the latter two overestimating infarct size. Microstructural characterization of the infarct and remote zones was performed using DTI-tractography, color-coded by HA and PA (infarct zone: Figures 2A-B; remote zone: Figures 2C-D). PA, HAvariance, and MD were higher in the infarct compared to the remote zone, while FA was lower (Figures 2E-H).
A Gaussian fit using 60% of the LGE histogram area (G60) improves infarct segmentation and correlates well with a PA threshold of 4°. PA provides valuable information for infarct detection and microstructural characterization of the myocardium, can be assessed in vivo without exogenous contrast, and could prove valuable in a broad range of cardiovascular diseases.
Flett : JACC. 2011
Nguyen : J Cardiovasc Magn Reson. 2014
Mekkaoui : ISMRM. 2014
Mekkaoui : J Cardiovasc Magn Reson. 2013
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Mekkaoui, C., Jackowski, M.P., Stoeck, C.T. et al. Infarct delineation in patients with acute myocardial infarction using the tractographic propagation angle and late gadolinium enhancement. J Cardiovasc Magn Reson 17 (Suppl 1), P16 (2015). https://doi.org/10.1186/1532-429X-17-S1-P16
- Fractional Anisotropy
- Late Gadolinium Enhancement
- Mean Diffusivity
- Normal Myocardium
- Helix Angle