Selective ablation of atherosclerotic lesions with less thermal damage by controlling the pulse structure of a quantum cascade laser in the 5.7-μm wavelength range

Cholesteryl esters are the main components of atherosclerotic plaques, and they have an absorption peak at the wavelength of 5.75 mu m. To realize less-invasive ablation of the atherosclerotic plaques using a quasi-continuous wave (quasi-CW) quantum cascade laser (QCL), the thermal effects on normal vessels must be reduced. In this study, we attempted to reduce the thermal effects by controlling the pulse structure. The irradiation effects on rabbit atherosclerotic aortas using macro pulse irradiation (irradiation of pulses at intervals) and conventional quasi-CW irradiation were compared. The macro pulse width and the macro pulse interval were determined based on the thermal relaxation time of atherosclerotic and normal aortas in the oscillation wavelength of the QCL. The ablation depth increased and the coagulation width decreased using macro pulse irradiation. Moreover, difference in ablation depth between the atherosclerotic and normal rabbit aortas using macro pulse irradiation was confirmed. Therefore, the QCL in the 5.7-mu m wavelength range with controlling the pulse structure was effective for less-invasive laser angioplasty.