Optical properties of normal, diseased, and laser photocoagulated myocardium at the Nd:YAG wavelength

Abstract

Laser photocoagulation of the myocardium effectively destroys arrhythmogenic foci. The purpose of this study was 1) to compare the optical properties of canine myocardium before and after photocoagulation, 2) to compare the canine model with clinical cases by measuring the optical properties of human myocardium, and 3) to assess the optical properties of human myocardial scar and epicardial fat tissue. Measured optical properties were the absorption coefficient, mu a; scattering coefficient, mu s; and scattering anisotropy factor, g. Optical measurements were performed at 1064 nm wavelength on thin plane parallel tissue slices using the integrating sphere method with glass hemispheres on either side of the sample. The study showed 1) an increase of the scattering coefficient by 40% and a two- to threefold increase in reduced scattering coefficient as a result of photocoagulation; 2) that the mu a (0.035 +/- 0.024 mm-1) and mu s (17.9 +/- 3.8 mm-1) of human myocardium were not significantly different from mu a (0.043 +/- 0.021 mm-1) and mu s (17.3 +/- 2.2 mm-1) of canine myocardium, whereas the human g (0.964 +/- 0.005) was slightly different from the canine g (0.974 +/- 0.008); and 3) that the mu a (0.021 +/- 0.016 mm-1) of epicardial fat and mu s (13.8 +/- 1.1 mm-1) of myocardial scar were significantly lower than those of normal myocardium. A dynamic model of laser-tissue interaction incorporating these changes and inhomogeneities is necessary to better describe light distribution during laser photocoagulation.

Measurement of thermal effects on the optical properties of prostate tissue at wavelengths of 1,064 and 633 nm

“…Another study has reported a fourfold increase in the scattering coefficient (0.43-1.74 mm −1 ) of porcine myocardium during coagulation, whereas the absorption coefficient remained relatively unchanged (0.04 to 0.05 mm −1 ) [9]. Similar results have been demonstrated in canine and human coagulated myocardial tissue [5]. In rat liver, the scattering coefficient has been shown to increase while the absorption and anisotropy coefficients decrease during tissue heating [10].…”

“…No significant difference has been found between the optical properties of human and canine myocardium at 1,064 nm [5], but canine bladder tissue has been found to have a 70% higher scattering coefficient (5.08 mm −1 ) than human bladder (2.93 mm −1 ) at a wavelength of 633 nm [12]. It is apparent from these results that differences in the optical properties between human and animal tissue are organ dependent.…”

Optical properties of native and coagulated human liver tissue and liver metastases in the near infrared range

“…Pickering et al [39] obtained similar results on coagulated healthy rat liver. Splinter et al [30] showed that the optical parameters of myocardial tissue also changed and resulted in a reduction of the penetration depth from 3.9 to 2.9 mm (26 %). A possible reason for this is the alteration of the protein tertiary structure due to the destruction of absorbing chromophores such as hemoglobin or mitochondrial cytochromoxidase and the thermally induced break-down of disulfide bonds as described by Mirza et al [40].…”

Laser catheter coagulation of normal and scarred ventricular myocardium in dogs

“…However, argon laser effects are closely related to surface vaporization, whereas the Nd:YAG laser is more suitable for tissue coagulation [15]. Due to its low absorption in normal and coagulated myocardium, Nd:YAG laser light has the potential of reaching deep intramural sites from the endo-or the epicardial surface [16,17]. As suggested by the apical lesions produced during this study, laser light may penetrate through scarred tissue and coagulate myocardium even across fibrous tissue.…”