Coronary stent as a tubular flow heater in magnetic resonance imaging

Abstract

Abstract Background A coronary stent is an artificial metallic tube, inserted into a blocked coronary artery to keep it open. In magnetic resonance imaging (MRI), a stented person is irradiated by the radio-frequency electromagnetic pulses, which induce eddy currents in the stent that produce Joule (resistive) heating. The stent in the vessel is acting like a tubular flow heater that increases the temperature of the vessel wall and the blood that flows through it, representing a potential hazard for the stented patient. Methods Heating of a metallic coronary stent in MRI was studied theoretically and experimentally. An analytical theoretical model of the stent as a tubular flow heater, based on the thermodynamic law of heat conduction, was developed. The model enables to calculate the time-dependent stent’s temperature during the MRI examination, the increase of the blood temperature passing through the stent and the distribution of the temperature in the vessel wall surrounding the stent. The model was tested experimentally by performing laboratory magnetic resonance heating experiments on a non-inserted stainless-steel coronary stent in the absence of blood flow through it. The model was then used to predict the temperature increase of the stainless-steel coronary stent embedded in a coronary artery in the presence of blood flow under realistic MRI conditions. Results The increase of the stent’s temperature and the blood temperature were found minute, of the order of several tenths of a degree, because the blood flow efficiently cools the stent due to a much larger heat capacity of the blood as compared to the heat capacity of the stent. However, should the stent in the vessel become partially re-occluded due to the restenosis problem, where the blood flow through the stent is reduced, the stent’s temperature may become dangerously high. Conclusions In the normal situation of a fully open (unoccluded) stent, the increase of the stent temperature and the blood temperature exiting the stent were found minute, of less than 1°C, so that the blood flow efficiently cools the stent. However, should the problem of restenosis occur, where the blood flow through the stent is reduced, there is a risk of hazardous heating.