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Published on: February 10, 2012
Evaluation of rat heart microvasculature with high-spatial-resolution susceptibility-weighted MR imaging
Eléonore Blondiaux1, Laetitia Pidial, José Vilar
1Paris Cardiovascular Research Center, INSERM U970, Université Paris Descartes, Sorbonne Paris Cité, 56 rue Leblanc, 75015 Paris, France; Biostatistics and Epidemiology Unit, Assistance Publique-Hôpitaux de Paris, Hôtel-Dieu, Université Paris Descartes,Paris, France.
Purpose:
To demonstrate that strandlike hypointense signals seen in the myocardium of normal rat hearts correspond to myocardial microvessels with high-spatial-resolution susceptibility-weighted (SW) magnetic resonance (MR) imaging without injection of contrast medium.
Materials And Methods:
Animal experiments were performed with institutional animal care committee approval. Ex vivo cardiac MR imaging was performed in 10 normal Wistar rats with a 4.7-T imager and a cryogenic probe. The hypothesis that thin tubular hypointense signals in the myocardium of rat hearts at SW MR imaging sequences (group 1, n = 6; in-plane resolution, 39 μm) represent intramyocardial microvessels was tested. A superparamagnetic intravascular contrast agent (ferumoxsil; Lumirem) was used to explore the distribution of the intramyocardial microvessels (group 2, n = 4; three-dimensional fast imaging with steady-state free precession sequences). Nonparametric Mann-Whitney tests were performed to compare groups 1 and 2 both for microvascular densities (MVD) on histologic sections and for MR imaging signal intensities (SIs). Wilcoxon signed rank tests were used for paired comparison of subepicardial and subendocardial MVD and SI within groups.
Results:
Ferumoxsil opacified the coronary microvasculature (group 2) on MR-matched histologic sections. No statistically significant difference was found between groups 1 and 2 for either MVD or MR imaging SI expressed as ratios between subendocardium and subepicardium (P = .40 and P = .46, respectively). The comparison of mean subendocardial and subepicardial SI within groups revealed significantly more microvessels in the subepicardium with MR (group 1: P = .01; group 2: P = .004).
Conclusion:
Myocardial microvessels appear as strandlike structures on high-spatial-resolution SW MR images without the aid of contrast medium injection.
Insights
High-spatial-resolution susceptibility-weighted (SW) magnetic resonance (MR) imaging can visualize myocardial microvessels in rat hearts without contrast agents. These microvessels appear as distinct strandlike hypointense signals on SW MR images.
Area of Science:
- Cardiovascular imaging
- Magnetic Resonance Imaging
- Microvascular research
Background:
- Myocardial microvessels are crucial for heart function.
- Visualizing microvasculature non-invasively aids in diagnosing cardiac conditions.
- Current methods often require contrast agents, limiting their application.
Purpose of the Study:
- To confirm that strandlike hypointense signals in rat myocardium on susceptibility-weighted (SW) magnetic resonance (MR) imaging represent microvessels.
- To achieve this visualization without injecting contrast medium.
- To utilize high-spatial-resolution SW MR imaging for detailed microvascular assessment.
Main Methods:
- Ex vivo cardiac MR imaging of 10 Wistar rats using a 4.7-T imager.
- Hypothesis testing for SW MR imaging signals representing intramyocardial microvessels (Group 1).
- Use of a superparamagnetic contrast agent (ferumoxsil) to map microvessel distribution (Group 2).
Main Results:
- Ferumoxsil successfully opacified the coronary microvasculature in Group 2.
- No significant differences in microvascular density (MVD) or MR imaging signal intensity (SI) ratios between subendocardium and subepicardium were found between groups.
- Significantly more microvessels were detected in the subepicardium compared to the subendocardium using MR imaging in both groups.
Conclusions:
- High-spatial-resolution SW MR imaging can visualize myocardial microvessels without contrast agents.
- Strandlike hypointense signals on SW MR images correspond to intramyocardial microvessels.
- This technique offers a non-contrast method for assessing cardiac microvasculature.
