Photobiomodulation therapy for osteoarthritis: Mechanisms of action

Table 1 Technical specifications

Device	Considerations
Manufacturer	Important to consider well known sellers in the market, making wise cost-effective decisions
Device ID	For reference and tracking of malfunctioning equipment
Year produced	It is always best to choose the latest and most recent models to guarantee long-term success
Beam delivery system	Light can be delivered into the tissue via manual probe apparatus, fiberoptic or free air/scanned
Number of emitters	Left to the practitioner’s decision
Emitter type	There are different types of laser such as KTP, LEDs, InGaAlP, and GaAlAs
Spatial distribution	Number of emitters and the distance between them as well as the pattern of distribution

KTP: Potassium-titanyl-phosphate; LEDs: Light emitting diodes; InGaAlP: Indium gallium aluminum and phosphorus; GaAlAs: Gallium-aluminum-arsenide.

Table 2 Photobiomodulation treatment parameters

Parameters	SI units	Additional notes
Exposure duration	Seconds (sec)	Some tissues may require more or less exposure duration, depending on the physical traits of the patient. For instance, obese individuals
Radiant exposure	Joules per centimeter squared (J/cm2)	Intensity of the equipment must be adequately regulated depending on the different points to be irradiated. If the power density is too low, extending the irradiation time to reach the ideal energy density may not give an adequate final result. This should not be confused with “dose”
Number of irradiated points	-	Left to practitioner’s decision depending on the treatment plan
Area irradiated	Centimeter squared (cm2)	Area of target tissue must be carefully measured with precision for optimal results
Manual technique	-	Physicians must keep consistent pressure against the target point to ensure optimal delivery and penetration into the target tissue
Total number of sesssions	-	Number may vary depending on how the patient responds to the treatment
Session intervals
Irradiance at target point	Milliwatts per centimeter squared (mW/cm2)	This parameter must be adequately regulated depending on the different points to be irradiated, otherwise, the absorption of photons will not be sufficient to attain the desired result. Additionally, very high intensities may generate excessive heat
Beam spot size at target point	Centimeter squared (cm2)	This must be carefully measured with precision for optimal results
Radiant energy	Joules (J)	Different tissues may require more or less energy according to the patient’s unique physical attributes (e.g. skin pigmentation and mass)
Total radiant energy	Joules (J)	The total accumulated energy delivered per session and over all sessions

SI Units: International System of Units.

Table 3 Irradiation

Parameters	SI units	Additional observations
Operating mode	-	Physicians may select a continuous or pulsed wave, for example
Pulse on duration	Seconds (sec)	It is important to equally distribute time intervals between pulse on and pulse off cycles
Pulse off duration	Seconds (sec)
Irradiance at aperture	Milliwatts per centimeter squared (mW/cm2)	Irradiance can be significantly affected by the angular aperture of the light guide. For instance, irradiance measured with an aperture is greater than that without an aperture. Physicians should always keep this in mind
Aperture diameter	Centimeters (cm)	Values may vary significantly across different manufacturers and specific devices are better suited for different application objectives
Beam divergence	Radians or degrees (rad/deg)	Beam divergence may be an important variable depending on the nature and localization of the target tissue
Beam shape	-	The beams may be circular or elliptical, for instance
Laser beam polarization	-	The electric field vibration can be simple, with only one direction along the beam path (linear polarization) or it can be complex
Beam profile	-	Depending on the scenario (clinical or laboratory study), a specific profile may be indicated, such as Gaussian or Top Hat
Peak radiant power	Milliwatts (mW)	This variable must be carefully adjusted according to the target sample being irradiated
Average radiant power	Milliwatts (mW)
Center wavelength (CW). And Spectral bandwidth (FWHM – range of wavelengths)	Nanometers (nm)	Practitioners must carefully select a suitable device with the appropriate wavelength and bandwidth specifications for the intended objectives. The FWHM (Full Width at Half Maximum) filter is important because outside the ideal bandwidth range light can be significantly attenuated
Frequency	Hertz (Hz)	The operator should always be aware of the frequency being applied to the area
Energy per pulse	Joules (J)	This parameter must be adequately regulated depending on the different points to be irradiated. Different tissues may require more or less energy per pulse. In clinical scenarios, the corporal density of each patient may vary significantly. In three-dimensional tissue cultures there are fewer layers of materials impeding light penetration and less scattering

SI Units: International System of Units.