Transmission of laser energy and assessment of target temperature in an experimental model of laser balloon angioplasty

The potential application of laser balloon angioplasty (LBA) is limited because of difficulties in temperature control and dosimetry during trans-balloon laser irradiation. An experimental model of LBA was designed to help understand the polymer membrane effects of two materials on tissue temperature. The durability of two types of polymer films with different optical properties, polyethylene terephthalate (PET), a low scattering polymer and polyetheretherketone (PEEK), a high scattering polymer, were examined as potential balloon material. The PEEK film (thickness: 50 μm) was melted and perforated by light from a diode laser (wavelength: 808±10 nm, irradiance: 1469 W cm⁻², mean exposure time: 30±7 s). On the other hand, the PET film with the same thickness was completely intact after 1 min exposure at the same irradiance. Diode laser irradiation was applied to indocyanine green stained human aortic media in three different exposure methods; directly, through the free PET and through the pressed PET film. Temperatures of laser-irradiated specimens were measured using an infra-red thermal camera with an 8–12 μm bandwidth, and corrected for the emissivity of the tissue and the PET film. Results demonstrated underestimation of surface temperature because of low transmittance of radiated intensity through the free PET film and a significant (p<0.001) increase of corrected temperature (δT=169±32°C) through the pressed-PET exposure compared with the direct exposure (ΔT=81±7°C), even though the same laser irradiance (18.6W cm⁻²) was applied for 5s. That is, the tightly PET-covered tissue develops a significantly higher temperature during diode laser irradiation, and this increased thermal effect can be advantageous for laser welding with less power in laser balloon angioplasty.