Quantitative first-pass MRI measures increased myocardial perfusion after vasodilation in mice
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KeywordsMyocardial Perfusion Slew Rate Gadolinium Injection Tissue Enhancement Separate Scan
We used first-pass contrast-enhanced MRI to quantatively measure the myocardial Ktrans, a parameter indicating myocardial perfusion and vascular permeability, in mice with or without vasodilation. We measured a significant increase in myocardial Ktrans with vasodilation. We believe this may be the first report showing that first-pass imaging can quantify increased myocardial perfusion in mice relative to baseline.
First-pass contrast-enhanced MRI is a well-established technique for quantifying myocardial perfusion in humans and large animals and has recently emerged as a viable tool for quantifying myocardial perfusion in mice [1, 2, 3]. Applied in mice, first-pass MRI could be used to assess the roles of individual genes in perfusion and vascular permeability. The purpose of this study was test the hypothesis that first-pass contrast-enhanced MRI can measure increased myocardial perfusion after administration of a vasodilator in mice.
Imaging was performed on a 7T Clinscan MR system equipped with a gradient system having a full strength of 650mT/m and a slew rate of 6666 mT/m/ms, and using a 30mm diameter birdcage RF coil. A saturation-recovery spiral sequence was employed, with TE = 0.36 ms, TR = 3.9ms, interleaves = 14, FOV = 25.6 x 25.6mm, matrix = 128x128, saturation delay = 40 ms, alpha = 20°, and slice thickness = 1mm. Data acquisition required 55 ms/image, approximately 40% of the murine R-R interval, and was placed in the latter part of the cardiac cycle. C57Bl6/J mice were imaged with (n=5) and without (n=5) an intraperitoneal bolus injection of the vasodilator ATL313 (Adenosine Therapeutics, Charlottesville, VA). First-pass images were acquired for one mid-ventricular short-axis slice. A dual-bolus gadolinium injection technique was used, acquiring the arterial input and tissue functions (AIF and TF) in separate scans. Myocardial Ktrans, the product of myocardial perfusion and the first-pass extraction fraction of gadolinium, was quantified using a standard Kety model deconvolution method.
These findings indicate that first-pass MRI in mice can quantitatively measure increased myocardial Ktrans with a vasodilator. Taken together with our previous studies quantifying perfusion after myocardial infarction1, these results indicate that first-pass imaging can accurately measure myocardial perfusion in mice in a variety of flow conditions.
Funding was provided by NIH R01 EB 001763.
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