Improvement of the MR visualisation of Prosthetic Heart Valves

Erwin Immel, INSITE med. & Dept. of Physical engineering University of Applied Sciences, Gelsenkirchen and Biophan Europe, Castrop Rauxel, Germany

Jan Spillner, Dept. of Cardiac Surgery, RWTH Aachen Germany

Andreas Melzer, INSITE med. & Dept. of Physical engineering University of Applies Sciences Gelsenkirchen and Biophan Europe, Castrop Rauxel, Germany

Background

The purpose was to improve visualization of a percutaneously implantable heart valves under MRI. Through the use of a resonant circuit on the stent the visualization of intraluminal substrates should be improved.

Material & Methods

A resonant circuit comprising of a helical coil with a non-magnetic capacitor was attached to a Nitinol stent (Memotherm, Bard Angiomed) and tuned to the Larmor frequency of the 1T (42.58MHz) and 1.5T (64MHz) MRT (Philips). The coil was made from copper or gold wire. The resonant structure was insulated with silicon or parylene. Pulmonal and aortic heart valve were excised from a fresh pig heart and sutured in the Nitinol stent with 4-0 Prolene. The MR-tests were made in 0.9% NaCl solution at 21° Celsius in a Tupper ware box in the standard head coil. As MRI sequences Fast-Field-Echo, TR=200ms, TE=6ms with low flip angles (15°-25°) have been applied.

Results

The newly developed valve comprises of a fresh porcine heart valve that was sewed in to a Nitinol stent. The heart valve could be visualized in the MRI by low flip angle (15°). The signal difference of substrate and test liquid was significant. The shielding of the Nitinol stent could be over come.

Conclusion

The results demonstrate that the use of resonant structure on the stents could minimize or avoid the negative shielding effects of the stent based heart valve. This enables direct and improved MRI examination of the valve function with MRI.

Keywords

heart valve, resonant circuit