Detection Of Acute Myocardial Infarction By Diffusion Weighted Magnetic Resonance Imaging

Objective: The aim of this research was to study the signal evolution of ischemic myocardium on a diffusion weighted imaging sequence (DWI) after acute myocardial infarction (AMI) using a porcine model. Changes in the diffusion ability and anisotropic diffusion of ischemic myocardium were studied using a diffusion tensor magnetic resonance imaging sequence (DT-MRI) after AMI in an in vitro porcine model.Methods: Eight Chinese miniature pigs underwent balloon-induced left anterior descending artery (LAD) or left circumflex artery (LCX) occlusion for 90 min followed by reperfusion to induce an AMI. A DWI sequence was used to image pre-operation and at four time points post-operation. Turbo inversion recovery magnitude T2 weighted imaging sequence (TIRM T2WI) and late gadolinium enhancement (LGE) was acquired using the same slices used for the DWI. The serum myocardial necrosis markers were detected at the same time points as MRI scanning. DT-MRI was used to image the hearts of the experimental and control groups. Histochemical staining with 2,3,5-triphenyltetrazolium chloride (TTC) was used as the gold standard to confirm injury. The in vivo images were analysed qualitatively. Contrast to noise ratio (CNR, the contrast between infarcted and healthy myocardium) and relative signal index (RSI) were used for quantitative image analysis. In vitro image analysis included a comparison of the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) between infarcted and normal myocardium. A fibre tracking (FT) technique showed the distribution and arrangement of myofibres in infarcted and normal hearts. Dependent on the characteristic of datas, Normal distribution datas were compared using paired-samples t-tests or one-way analysis of variance. Nonparametric Wilcoxon tests were used for the datas that were not normally distributed. P-values<0.05 were considered significant.Results: For in vivo image analysis:DWI sequencing was shown to identify myocardial signal abnormity early (< 4 h) after AMI. DWI identified the infarcted related high signal more frequently than TIRM T2WI (7/8=87.5% vs.3/8=37.5%, P=0.046). Quantitative image analysis indicated that the differences of CNR and RSI between DWI and TIRM T2WI were significant at 4 timepoints. However, within 4 hours after infarction, serological myocardial injury markers were not significantly positive. For in vitro image analysis:The ADC values of the infarcted myocardium increased and the FA value decreased significantly. FT revealed that the normal myofibres were arranged in laminar, helical, well-ordered patterns, whereas infarcted myocardial fibre structure was shortened, shrunken, and distorted. Myocardial fibres in the ischemic area were shorter, and the number of fibres was slightly reduced.Conclusions: DWI sequencing can be used for the detection of myocardial signal abnormalities in an early phase after AMI. This method can identify AMI earlier than TIRM T2WI and widely used clinical serological biomarkers. DT-MRI provides robust visualisation of normal myofibre anatomy and the changes in 3-dimensional (3D) myofibre architecture in infarcted hearts.