More Than Ninety Percent of the Light Energy Emitted by Near-Infrared Laser Therapy Devices Used to Treat Musculoskeletal Disorders Is Absorbed Within the First Ten Millimeters of Biological Tissue

Abstract

There is increasing interest in the application of near-infrared (NIR) laser light for the treatment of various musculoskeletal disorders. The present study thoroughly examined the physical characteristics of laser beams from two different laser therapy devices that are commercially available for the treatment of musculoskeletal disorders. Then, these laser beams were used to measure the penetration depth in various biological tissues from different animal species. The key result of the present study was the finding that for all investigated tissues, most of the initial light energy was lost in the first one to two millimeters, more than 90% of the light energy was absorbed within the first ten millimeters, and there was hardly any light energy left after 15 – 20 mm of tissue. Furthermore, the investigated laser therapy devices fundamentally differed in several laser beam parameters that can have an influence on how light is transmitted through tissue. Overall, the present study showed that a laser therapy device that is supposed to reach deep layers of tissue for treatments of musculoskeletal disorders should operate with a wavelength between 800 nm and 905 nm, a top-hat beam profile, and it should emit very short pulses with a large peak power.

Spread of the Optical Power Emission of Several Units of the Same Laser Therapy Devices Used in Sports Medicine, Which Cannot Be Assessed by the Users, Shown by Means of High-Fidelity Laser Measurement Technology

“…The 660 nm diode of the K-lasers was not measured individually since the maximum power of this diode was only 0.1 W (c.f. [7]).…”

“…Camera images of the EMS lasers (Figure 3d-f) show that all three devices had an almost ideal flat-top beam shape (c.f. [7]), although the beam width varied between the three devices.…”

“…During the course of a recent study, we investigated the penetration depth of nearinfrared laser light into biological tissue emitted by two different LTDs [7]. When performing the experiments for this study, we realized that one of the used LTDs showed large deviations between the set and the actual measured power [7]. In order to see whether this behavior was due to a single broken laser diode, we measured two more units of the same LTD.…”

“…In addition to the average power, further laser beam characteristics such as the pulse shape, pulse length and the spatial intensity distributions were investigated. To compare the findings from the three units of this LTD, we also measured the beam parameters of three units of the other LTD that was used in the previous study [7]. All tested units of the LTDs were in clinical use before they were characterized in the present study.…”

“…Among these reasons is the fact that infrared light is invisible to the human eye. Furthermore, a thorough assessment of the characteristics of the laser beam of an LTD, which comprises the emitted power, pulse shapes and lengths as well as spatial intensity distributions, must be performed using professional, high-fidelity laser measurement equipment whose operation requires expert knowledge at the level of an engineer or a physicist [7,8].…”