1338944 - Optimized CMR protocol for evaluating bicuspid aortic valve (BAV) in small animals

Bicuspid Aortic Valve (BAV) is the most common congenital heart disease affecting 1-2% of all live births. Current clinical management includes periodic surveillance of aortic valve dysfunction, and only when the valve becomes stenotic is intervention recommended; however, relief is variable and largely suboptimal, and surgical procedures come with insuperable long-term outcomes. In this study, we used high-field CMR to develop an optimized and efficient protocol for comprehensive valvular assessment in a mouse model of BAV.

Methods:

The developed imaging protocol and pulse sequences were optimized on a small-animal Bruker 9.4T MRI scanner. The protocol includes sequences for imaging valvular structure, function, flow pattern, and tissue characterization for comprehensive assessment of BAV in a genetically modified mouse model (Nfatc1cre;Exoc5^fl/+). Proper animal setup is essential for ensuring adequate image quality and avoiding artifacts. Three-lead ECG patch electrodes were used due to their better performance compared to needle electrodes. The ECG wires were twisted and run along the center of the magnet bore to minimize signal noise. Valve structure and function information was obtained using cine imaging with either ECG gating or retrospective self-gating, where the latter allows for 3D imaging capability with improved temporal and spatial resolutions, albeit at the cost of increased scan time. Blood flow pattern through the valve was obtained using phase-contrast (PC) imaging with minimum repetition time (TR) to improve temporal resolution. Finally, multicontrast T1/T2/PD weighted spin-echo sequences were used to assess valvular tissue characterization. The multicontrast imaging parameters were optimized based on the animal’s heart and respiratory rates to acquire data at late diastole with minimal motion artifacts while improving imaging efficiency. Circle cvi42 software was used to process the resulting images.  

Results:

The optimized protocol produced clinically useful images in a reasonable scan time (1-2 hours depending on selected pulse sequences and type of acquisition (2D vs 3D)). Figure 1 shows a cross-section of BAV, showing clearly two leaflets compared to three leaflets in normal tricuspid aortic valve. Figure 2 shows PC magnitude and phase images across the aortic valve and generated flow pattern in BAV, which is distinguished from that in normal valve. Figure 3 shows multicontrast T1, T2, and PD weighted images of the aortic valve, where different signal intensities in the images  can be used to study valve tissue composition, e.g., lipid, fat, edema, and calcification.

Conclusion:

The developed optimized CMR protocol provides complementary cardiovascular information for biomechanical assessment of BAV. Therefore, children and adolescents with BAV would benefit from this comprehensive assessment of their risk profile during early stages of the disease to better predict outcomes and clinical management strategies.