Effects of blood flow on the heating of cardiac stents due to radio frequency fields

Nate Elder, Purdue University

Abstract

A safety concern during MRI scans with implanted medical devices is heating induced by the incident RF field. This research was performed to better understand the heating of cardiac stents during MRI. Heating of cardiac stents tends to occur at their ends. The temperature rise will be affected by blood flow through the lumen of the stent. In this work, an experiment was performed to simulate heating of a cardiac stent in the presence of blood flow during exposure to the electric field induced by a 64 MHz magnetic field, which corresponds to MRI at 1.5 T. The test procedure was based on the one specified in ASTM F2182-11a. The test article was a 3.5 mm diameter x 70 mm long stent. The rate of liquid flow through the stent was varied with a flow meter and the temperature rises at the ends and the middle of the stent were measured with fiber optic sensors. With no flow, temperature rise scaled to the local background SAR was 0.89 ºC/(W/kg). Temperature rise decreased as flow rate increased and reached the minimum value of 0.39 ºC/(W/kg) for the maximum flow rate of 251.4 m/h. Computer simulations of temperature rise for idealized stents in the form of cylindrical conducting shells yielded rises consistent with the experimental findings. It is concluded that in-vivo temperature rise of a coronary stent during MRI will be less than half of the value that would be predicted from in-vitro tests that do not incorporate the cooling effects of blood.

Degree

M.S.E.

Advisors

Nyenhuis, Purdue University.

Subject Area

Biomedical engineering|Electrical engineering

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