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C.E. Girasol1, J.M.A.F. Moraes1, D.M.N. Alfredo1, R.I. Barbosa2, L. Bachmann3, E.C.d.O. Guirro1, R.R.d.J. Guirro1
1University of São Paulo, Department of Health Sciences, Ribeirão Preto, Brazil, 2Federal University of Santa Catarina, Department of Health Sciences, Ararangua, Brazil, 3University of São Paulo, Department of Physics, Ribeirão Preto, Brazil
Background: Physical factors and tissue characteristics determine the transmissivity of light through tissues. Thus, one of the significant clinical limitations of photobiomodulation is the amount of energy deposited in the points of application, since the depth of optical transmissivity is not established in the literature. Also, its value is difficult to measure in vivo, and the distance between the points of application that is given empirically.
Purpose: To analyze the influence of melanin in the transmission and scattering of the 660nm and 830nm laser on the skin and tendon in vivo.
Methods: 30 young individuals of both sexes were recruited, divided into two groups based on melanin concentration, submitted to photobiomodulation protocols in the posterior region of the elbow (skin-skin), and the calcaneus tendon (skin-tendon-skin). The irradiation area was evaluated using five sensors aligned in the same plane.
Results: Significant values of the transmitted power attenuation for different melanin concentrations and wavelengths (p<0.0001) were found. Also, other equipment can generate significant differences in the transmitted power at 830nm wavelength. Average spread values are 13mm and 14mm for 660nm, in higher and lower melanin concentration, respectively. For 830nm, values of 15 and 17mm are indicated.
Conclusion(s): Laser transmission and scattering in vivo tissues are related to wavelength, beam diameter, thickness, and target tissue type, as well as melanin concentration. The 830nm laser presents higher transmission and lowers scattering on the skin when compared to 660nm. It is suggested the distances between 12mm and 18mm between the application points, considering the red and infrared spectra, melanin concentration, and characteristics of the light-emitting source, to have a uniformity of the radiated power. For the “skin-tendon-skin” irradiation, no significant penetration of the 660 and 830nm lasers in the tissues was observed.
Implications: Know the real transmission and, mainly, the lateral scattering is necessary for adequate therapeutic intervention. Also, the definition, along with different levels of melanin concentration, may help in parameters previously considered as empirical.
Funding, acknowledgements: The work was supported by The Sao Paulo Research Foundation, Coordination for the Improvement of Higher Education Personnel, and INAGBE/Angola.
Keywords: photobiomodulation, penetration, physical therapy
Topic: Electrophysical & isothermal agents
Did this work require ethics approval? Yes
Institution: Medical School of Ribeirão Preto
Committee: Hospital das Clinicas of the Medicine School in Ribeirão Preto
Ethics number: 2748430
All authors, affiliations and abstracts have been published as submitted.
