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Accuracy of infarct measurements by inversion recovery delayed-enhancement MRI during the hyper-acute phase of myocardial infarction in rats
© Cheung et al; licensee BioMed Central Ltd. 2010
Published: 21 January 2010
Quantification of infarct size is important in the assessment of myocardial infarction (MI) and is commonly performed by ex-vivo staining in experimental studies . Delayed-enhancement (DE) is an accurate method for assessing infarct in-vivo in humans, and is increasingly used in experimental studies of chronic MI where its accuracy has been well validated . However, the feasibility and accuracy of DE-MRI in measuring infarct during the hyperacute MI phase (i.e. hours) is less well-defined. Additionally, while inversion recovery (IR) is the MR sequence of choice clinically, its role has not been fully explored in small animal models.
To compare infarct measurements by IR-based DE-MRI against tetrazolium staining during the hyperacute phase of MI in rats.
Male Wistar rats (n = 13) were anaesthetised and underwent 30 minutes of myocardial ischaemia and 2 hours of reperfusion. Short-axis DE images of the infarcted heart were acquired using a 9.4 T system (Varian) with Gd-DTPA (0.6 mmol/kg, i.v.) and a dual ECG/respiratory-gated IR sequence  (α = 90°, TE = 1.5 ms, TR = 3.6 ms, TI~400 ms, FOV = 40 × 40 mm2, 192 × 192, ΔZ = 1 mm, 10-15 slices). Hearts were extracted following imaging for TTC staining and planimetry. Data were randomised and segmented by thresholding with manual corrections (ImageJ). Infarct size was expressed as a ratio to the LV (In/LV). Linear regression and Bland-Altman analysis were performed (SPSS) to compare the two methods.
The application of IR-based DE-MRI in small animals has mainly been in chronic MI at lower fields (1.5-3 T) [4, 5]. By employing a customised IR sequence at 9.4 T, we achieved excellent image contrast between normal and infarcted myocardium, and demonstrated that this technique can provide accurate infarct measurements during the hyper-acute phase of MI as validated by TTC planimetry. Therefore, IR-based DE-MRI may serve as a valuable tool in monitoring infarct progression and therapeutic outcome in small animal models.
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