Dosage / Dosimetry

Sci Rep. 2018 Mar 9;8(1):4251. doi: 10.1038/s41598-018-22634-w.

An optical system via liquid crystal photonic devices for photobiomodulation.

Chang CM1, Lin YH2, Srivastava AK3, Chigrinov VG3.

Author information

National Chiao Tung University, Department of Photonics, Hsinchu, 30010, Taiwan, Republic of China.
National Chiao Tung University, Department of Photonics, Hsinchu, 30010, Taiwan, Republic of China.
Hong Kong University of Science and Technology, Department of Electronic and Computer Engineering, Hong Kong, China.


Photobiomodulation or low-level light therapy (LLLT) has extensive applications based on light-induced effects in biological systems. Photobiomodulation remains controversial because of a poorly understood biochemical mechanism limited by the well-known biphasic dose response or Arndt-Schulz curve. The Arndt-Schulz curve states that an optimal dose of light is a key factor for realizing a therapeutic effect. In this report, we demonstrate a tunable optical system for photobiomodulation to aid physicians in overcoming the constraints of light due to biphasic dose response. The tunable optical system is based on a white light-emitting diode and four liquid crystal (LC) photonic devices: three LC phase retarders, and one LC lens. The output light of the tunable optical system exhibits electrical tunability for the wavelength, energy density and beam size. The operating principle is introduced, and the experimental results are presented. The proposed concept can be further extended to other electrically tunable photonic devices for different clinical purposes for photobiomodulation.

J Biomed Opt. 2018 Jan;23(1):1-4. doi: 10.1117/1.JBO.23.1.010503.

Flexible nine-channel photodetector probe facilitated intraspinal multisite transcutaneous photobiomodulation therapy dosimetry in cadaver dogs.

Piao D1,2, Sypniewski LA2, Bailey C1, Dugat D2, Burba DJ2, De Taboada L3.

Author information

Oklahoma State University, School of Electrical and Computer Engineering, Stillwater, Oklahoma, United States.
Oklahoma State University, Department of Veterinary Clinical Sciences, Center for Veterinary Health, United States.
LiteCure LLC, Carlsbad, California, United States.


Noninvasive photobiomodulation therapy (PBMT) of spinal cord disease remains speculative due to the lack of evidence for whether photobiomodulatory irradiances can be transcutaneously delivered to the spinal cord under a clinically acceptable PBMT surface irradiation protocol. We developed a flexible nine-channel photodetection probe for deployment within the spinal canal of a cadaver dog after hemilaminectomy to measure transcutaneously transmitted PBMT irradiance at nine sites over an eight-cm spinal canal length. The probe was built upon a 6.325-mm tubular stem, to the surface of which nine photodiodes were epoxied at approximately 1 cm apart. The photodiode has a form factor of 4.80??mm×2.10??mm×1.15??mm (length×width×height). Each photodiode was individually calibrated to deliver 1 V per 7.58???W/cm2 continuous irradiance at 850 nm. The outputs of eight photodiodes were logged concurrently using a data acquisition module interfacing eight channels of differential analog signals, while the output of the ninth photodiode was measured by a precision multimeter. This flexible probe rendered simultaneous intraspinal (nine-site) measurements of transcutaneous PBMT irradiations at 980 nm in a pilot cadaver dog model. At a surface continuous irradiance of 3.14??W/cm2 applied off-contact between L1 and L2, intraspinal irradiances picked up by nine photodiodes had a maximum of 327.48???W/cm2 without the skin and 5.68???W/cm2 with the skin.

Lasers Med Sci. 2016 Mar 10. [Epub ahead of print]

The dark art of light measurement: accurate radiometry for low-level light therapy.

Hadis MA1, Zainal SA2, Holder MJ2, Carroll JD3, Cooper PR2, Milward MR2, Palin WM4.

Author information

  • 1Biomaterials Unit, School of Dentistry, College of Medical and Dental Sciences, University of Birmingham, St Chads Queensway, Birmingham, UK, B4 6NN.
  • 2Oral Biology, School of Dentistry, College of Medical and Dental Sciences, University of Birmingham, St Chads Queensway, Birmingham, UK, B4 6NN.
  • 3THOR Photomedicine Ltd, Chesham, UK.
  • 4Biomaterials Unit, School of Dentistry, College of Medical and Dental Sciences, University of Birmingham, St Chads Queensway, Birmingham, UK, B4 6NN.


Lasers and light-emitting diodes are used for a range of biomedical applications with many studies reporting their beneficial effects. However, three main concerns exist regarding much of the low-level light therapy (LLLT) or photobiomodulation literature; (1) incomplete, inaccurate and unverified irradiation parameters, (2) miscalculation of ‘dose,’ and (3) the misuse of appropriate light property terminology. The aim of this systematic review was to assess where, and to what extent, these inadequacies exist and to provide an overview of ‘best practice’ in light measurement methods and importance of correct light measurement. A review of recent relevant literature was performed in PubMed using the terms LLLT and photobiomodulation (March 2014-March 2015) to investigate the contemporary information available in LLLT and photobiomodulation literature in terms of reporting light properties and irradiation parameters. A total of 74 articles formed the basis of this systematic review. Although most articles reported beneficial effects following LLLT, the majority contained no information in terms of how light was measured (73 %) and relied on manufacturer-stated values. For all papers reviewed, missing information for specific light parameters included wavelength (3 %), light source type (8 %), power (41 %), pulse frequency (52 %), beam area (40 %), irradiance (43 %), exposure time (16 %), radiant energy (74 %) and fluence (16 %). Frequent use of incorrect terminology was also observed within the reviewed literature. A poor understanding of photophysics is evident as a significant number of papers neglected to report or misreported important radiometric data. These errors affect repeatability and reliability of studies shared between scientists, manufacturers and clinicians and could degrade efficacy of patient treatments. Researchers need a physicist or appropriately skilled engineer on the team, and manuscript reviewers should reject papers that do not report beam measurement methods and all ten key parameters: wavelength, power, irradiation time, beam area (at the skin or culture surface; this is not necessarily the same size as the aperture), radiant energy, radiant exposure, pulse parameters, number of treatments, interval between treatments and anatomical location. Inclusion of these parameters will improve the information available to compare and contrast study outcomes and improve repeatability, reliability of studies.

Sci Rep. 2015 Jun 1;5:10581. doi: 10.1038/srep10581.

Molecular pathway of near-infrared laser phototoxicity involves ATF-4 orchestrated ER stress.

Khan I1, Tang E1, Arany P1.

Author information

  • 1Cell Regulation and Control Unit, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda MD.


High power lasers are used extensively in medicine while lower power applications are popular for optical imaging, optogenetics, skin rejuvenation and a therapeutic modality termed photobiomodulation (PBM). This study addresses the therapeutic dose limits, biological safety and molecular pathway of near-infrared (NIR) laser phototoxicity. Increased erythema and tissue damage were noted in mice skin and cytotoxicity in cell cultures at phototoxic laser doses involving generation of reactive oxygen species (ROS) coupled with a rise in surface temperature (>45°C). NIR laser phototoxicity results from Activating Transcription Factor-4 (ATF-4) mediated endoplasmic reticulum stress and autophagy. Neutralizations of heat or ROS and overexpressing ATF-4 were noted to rescue NIR laser phototoxicity. Further, NIR laser mediated phototoxicity was noted to be non-genotoxic and non-mutagenic. This study outlines the mechanism of NIR laser phototoxicity and the utility of monitoring surface temperature and ATF4 expression as potential biomarkers to develop safe and effective clinical applications.

Photomed Laser Surg. 2013 May;31(5):225-9. doi: 10.1089/pho.2012.3434.

Laser phototherapy at high energy densities do not stimulate pre-osteoblast growth and differentiation.

Pacheco PS1, de Oliveira FA, Oliveira RC, Sant’ana AC, de Rezende ML, Greghi SL, Damante CA.

Author information

  • 1Bauru School of Dentistry, Bauru, SP, Brasil.



The aim of this study is to evaluate the effects of red and infrared lasers at high energy densities on pre-osteoblast MC3T3 proliferation and differentiation. Background data: The acceleration of bone regeneration by low intensity laser irradiation may hold potential benefits in clinical therapy in orthopedics and dentistry.


Cells were irradiated with red (660?nm) and infrared (780?nm) lasers (90 and 150?J/cm2, 40?mW). The control group did not receive irradiation. Cell growth was assessed by a colorimetric test (MTT) (24, 48, 72, 96?h) and cell differentiation was evaluated by alkaline phosphatase (ALP) quantification after growth in osteogenic medium (72, 96?h; 7, 14 days).


None of the irradiation groups had an enhancement in cell growth (p<0.05). The production of ALP was not influenced by irradiation at any period of time (p>0.05).


The low intensity laser stimulated neither cell growth nor the production of alkaline phosphatase.

Photmed Laser Surg.  2012 Jun 29. [Epub ahead of print]

Meta-Analysis of Pain Relief Effects by Laser Irradiation on Joint Areas.

Jang H, Lee H.


Department of Information and Communications, Gwangju Institute of Science and Technology , Gwangju, Republic of Korea.


Abstract Background: Laser therapy has been proposed as a physical therapy for musculoskeletal disorders and has attained popularity because no side effects have been reported after treatment. However, its true effectiveness is still controversial because several clinical trials have reported the ineffectiveness of lasers in treating pain.

Methods: In this systematic review, we investigate the clinical effectiveness of low-level laser therapy (LLLT) on joint pain. Clinical trials on joint pain satisfying the following conditions are included: the laser is irradiated on the joint area, the PEDro scale score is at least 5, and the effectiveness of the trial is measured using a visual analogue scale (VAS). To estimate the overall effectiveness of all included clinical trials, a mean weighted difference in change of pain on VAS was used.

Results: MEDLINE is the main source of the literature search. After the literature search, 22 trials related to joint pain were selected. The average methodological quality score of the 22 trials consisting of 1014 patients was 7.96 on the PEDro scale; 11 trials reported positive effects and 11 trials reported negative effects. The mean weighted difference in change of pain on VAS was 13.96?mm (95% CI, 7.24-20.69) in favor of the active LLLT groups. When we only considered the clinical trials in which the energy dose was within the dose range suggested in the review by Bjordal et al. in 2003 and in World Association for Laser Therapy (WALT) dose recommendation, the mean effect sizes were 19.88 and 21.05?mm in favor of the true LLLT groups, respectively.

Conclusions: The review shows that laser therapy on the joint reduces pain in patients. Moreover, when we restrict the energy doses of the laser therapy into the dose window suggested in the previous study, we can expect more reliable pain relief treatments.

Photomed Laser Surg.  2011 Nov 22. [Epub ahead of print]

How to Report Low-Level Laser Therapy (LLLT)/Photomedicine Dose and Beam Parameters in Clinical and Laboratory Studies.

Jenkins PA, Carroll JD.


1 SpectraMedics Pty Ltd , Oakbank, SA, Australia ; SpectraVET Inc., Irradia LLC, and Irradia Education Inc., Lawndale, North Carolina; and Immunophotonics Inc., Columbia, Missouri.


Abstract Dose and beam parameters are critical for successful laser, LED, and other light therapy treatments, however, in our experience, researchers frequently make critical errors and omissions when submitting papers for publication. Journals frequently publish studies with missing data, mathematical errors, and no reported verification of beam parameters. This makes reproducibility impossible, and further confounds an already complex subject. This article is intended to be a reference document for non-physicist researchers conducting low-level laser therapy (LLLT) laboratory studies and clinical trials to help them design and report the beam and dose aspects of their trials. It provides a checklist to help LLLT researchers understand and report all the necessary parameters for a repeatable scientific study. It includes the eight most important beam parameters to report, which are: wavelength, power, irradiation time, beam area at the skin or culture surface (this is not necessarily the same as the aperture size), pulse parameters, anatomical location, number of treatments, and interval between treatments. The three commonly used dose parameters are time, energy, and energy density. In addition, more thorough reporting would include coherence, application technique (contact, projection, scanning, pressure), beam profile, and spectral width, as these may also be considered important. Beam power often decreases as the device warms up and as the device ages; therefore, this should be checked routinely during an experiment/trial. Measurements of beam area and beam power require special instruments and trained technicians to operate them. Power measurements should be taken before, after, and at frequent intervals during research trials.

Dose Response. 2011;9(4):602-18. doi: 10.2203/dose-response.11-009.Hamblin. Epub 2011 Sep 2.

Biphasic dose response in low level light therapy – an update.

Huang YY1, Sharma SK, Carroll J, Hamblin MR.

Author information

Wellman Center for Photomedicine, Massachusetts General Hospital; Department of Dermatology, Harvard Medical School, Boston MA; and Aesthetic and Plastic Center of Guangxi Medical University, China.


Low-level laser (light) therapy (LLLT) has been known since 1967 but still remains controversial due to incomplete understanding of the basic mechanisms and the selection of inappropriate dosimetric parameters that led to negative studies. The biphasic dose-response or Arndt-Schulz curve in LLLT has been shown both in vitro studies and in animal experiments. This review will provide an update to our previous (Huang et al. 2009) coverage of this topic. In vitro mediators of LLLT such as adenosine triphosphate (ATP) and mitochondrial membrane potential show biphasic patterns, while others such as mitochondrial reactive oxygen species show a triphasic dose-response with two distinct peaks. The Janus nature of reactive oxygen species (ROS) that may act as a beneficial signaling molecule at low concentrations and a harmful cytotoxic agent at high concentrations, may partly explain the observed responses in vivo. Transcranial LLLT for traumatic brain injury (TBI) in mice shows a distinct biphasic pattern with peaks in beneficial neurological effects observed when the number of treatments is varied, and when the energy density of an individual treatment is varied. Further understanding of the extent to which biphasic dose responses apply in LLLT will be necessary to optimize clinical treatments.


biphasic dose response; low level laser therapy; nitric oxide; photobiomodulation; reactive oxygen species; traumatic brain injury

Lasers Surg Med.  2010 Nov;42(9):656-64.

Laser photobiostimulation of wound healing: defining a dose response for splinted wounds in diabetic mice.

Chung TY, Peplow PV, Baxter GD.

Department of Anatomy & Structural Biology, University of Otago, Dunedin, New Zealand.


BACKGROUND AND OBJECTIVES: We have used a 660 nm, 80 mW laser diode in genetic diabetic mice to stimulate the healing of wounds covered with a Tegaderm HP dressing that causes a retardation of contraction (splinted wounds). The purpose of our study was to examine the effects of irradiating the wounds for different time intervals in order to determine a dose response relationship.

MATERIALS AND METHODS: A circular excisional wound was made on the left flank of diabetic mice using a 5-mm skin punch, and covered with a Tegaderm HP dressing. Mice were allocated to four groups in which wounds were irradiated 660 nm, 80 mW for 0, 10, 20, or 40 seconds each day for 7 days. In total, 51 mice were used. Wounds were harvested on day 14 and the healing assessed from hematoxylin-eosin stained sections examined by light microscopy.

RESULTS: The wounds were splinted in 40 of the mice, and splinting caused a retardation of healing. The findings for the four treatments showed that irradiation for 20 second/day for 7 days brought about the greatest extent of healing. The wounds healed mainly by re-epithelization and granulation tissue formation. This duration of irradiation represents an energy dose of 1.6 J per irradiation and, for an estimated area of irradiation of 32-43 mm², corresponds to an energy density of 3.7-5.0 J/cm².

CONCLUSION: Irradiation with 660 nm, 80 mW at an energy density of 3.7-5.0 J/cm² each day for 7 days caused the maximal stimulation of healing in splinted wounds of diabetic mice.

Photomed Laser Surg. 2010 Aug;28 Suppl 1:S157-65.

Red-light light-emitting diode irradiation increases the proliferation and osteogenic differentiation of rat bone marrow mesenchymal stem cells.

Li WT, Leu YC, Wu JL.

Department of Biomedical Engineering, Chung Yuan Christian University, Chung-Li, Taiwan, Republic of China.


OBJECTIVE: The objective of this study was to investigate the effects on the proliferation and osteogenic differentiation of rat mesenchymal stem cells (MSCs) by using red-light light-emitting diode (LED) irradiation.

BACKGROUND DATA: Low-level light irradiation (LLLI) has been shown to enhance proliferation and cytokine secretion of a number of cells. MSCs are capable of regenerating various mesenchymal tissues and are essential in supporting the growth and differentiation of hematopoietic stem cells within the bone marrow.

MATERIALS AND METHODS: Rat bone marrow MSCs were treated with single or multiple doses of LLLI from an LED array (630 nm) at the irradiances of 5 and 15 mW/cm(2), and radiant exposures of 2 and 4 J/cm(2). The proliferation, clonogenic potential, and osteogenic differentiation of MSCs were evaluated after illumination.

RESULTS: The growth of MSCs was enhanced by red-light LLLI, and the effect became more obvious at low cell density. A single dose of LLLI led only to a short-term increase in MSCs proliferation. A maximal increase in cell proliferation was observed with multiple exposures of LLLI at 15 mW/cm(2) and 4 J/cm(2). The number of colony-forming unit fibroblasts increased when cells were illuminated under the optimal parameter. During osteogenesis, significant increases (p < 0.01) in both alkaline phosphatase and osteocalcin expressions were found in the MSCs that received light irradiation.

CONCLUSION: Our data demonstrated that MSCs proliferation was enhanced by multiple exposures to LLLI from 630-nm LEDs, and cell growth depended on the plating density. Furthermore, multiple dose of LLLI could enhance the osteogenic potential of rat MSCs.

Photomed Laser Surg. 2010 Jun;28(3):411-6.

Effect of biostimulation on healing of bone defects in diabetic rats.

Akyol UK, Güngörmü? M.

Ataturk University, Faculty of Dentistry, Department of Oral and Maxillofacial Surgery, Erzurum, Turkey.


BACKGROUND AND OBJECTIVE: The aim of this study was to investigate the effects of biostimulation on healing of bone defects in diabetic rats.

STUDY DESIGN/MATERIAL AND METHODS: Twenty-eight Wistar rats weighting 250 to 300 g were used for this study. Diabetes was chemically induced with streptozotocin, and 14 nondiabetic and 14 diabetic rats were included in the study. The distal epiphysis of the right and left femurs of the diabetic rats were perforated with a surgical bone drill. This surgical procedure was performed on the left femurs of normal rats too. The wound on the right side of each diabetic rat received laser stimulation. The left femur of each nondiabetic (normal) rat served as a control. The rats were assigned to three experimental groups: (1) normal bur (control group); (2) diabetic bur; (3) diabetic bur + biostimulation.

RESULTS: There was a significant difference among all groups in substantia spongiosa formation on day 10. According to the Mann-Whitney U test, there was a difference between Groups 1 and 2. A significant difference was noted between Groups 2 and 3 as well as between Groups 1 and 3 and between Groups 2 and 3 in union at 20 d of healing.

CONCLUSIONS: Substantia spongiosa formation was slightly more evident in Groups 1 and 3 than in Group 2. Also, there was more union in Group 3 than in the other groups on day 20. As a result, it can be concluded that low-level laser therapy (808 nm laser at 10 J/cm(2)) can have a beneficial effect on spongiosa in diabetic bone repair when five treatments are administered with 2 d intervals between treatments.

Photomed Laser Surg. 2009 Sep 21. [Epub ahead of print]

Low-Level Laser Irradiation (InGaAlP-660 nm) Increases Fibroblast Cell Proliferation and Reduces Cell Death in a Dose-Dependent Manner.

Frigo L, Fávero GM, Campos Lima HJ, Maria DA, Bjordal JM, Joensen J, Iversen VV, Marcos RL, Parizzoto NA, Lopes-Martins RA.

1 Biological Sciences and Health Center, Cruzeiro do Sul University , São Paulo, Brazil .

Abstract Background and Objective: Impaired cell metabolism and increased cell death in fibroblast cells are physiological features of chronic tendinopathy. Although several studies have shown that low-level laser therapy (LLLT) at certain parameters has a biostimulatory effect on fibroblast cells, it remains uncertain if LLLT effects depend on the physiological state. Study

Design/Material and Methods: High-metabolic immortal cell culture and primary human keloid fibroblast cell culture were used in this study. Trypan blue exclusion and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test were used to determine cell viability and proliferation. Propidium iodide stain was used for cell-cycle analysis by flow cytometry. Laser irradiation was performed daily on three consecutive days with a GaAlAs 660-nm laser (mean output: 50 mW, spot size 2 mm(2), power density =2.5 W/cm(2)) and a typical LLLT dose and a high LLLT dose (irradiation times: 60 or 420 s; fluences:150 or 1050 J/cm(2); energy delivered: 3 or 21 J). Results: Primary fibroblast cell culture from human keloids irradiated with 3 J showed significant proliferation by the trypan blue exclusion test (p < 0.05), whereas the 3T3 cell culture showed no difference using this method. Propidium iodide staining flow cytometry data showed a significant decrease in the percentage of cells being in proliferative phases of the cell cycle (S/g(2)/M) when irradiated with 21 J in both cell types (hypodiploid cells increased). Conclusions: Our data support the hypothesis that the physiological state of the cells affects the LLLT results, and that high-metabolic rate and short- cell-cycle 3T3 cells are not responsive to LLLT. In conclusion, LLLT with a dose of 3 J reduced cell death significantly, but did not stimulate cell cycle. A LLLT dose of 21 J had negative effects on the cells, as it increased cell death and inhibited cell proliferation.

Photomed Laser Surg. 2009 Dose Response.;7(4):358-83.

Biphasic dose response in low level light therapy.

Huang YY, Chen AC, Carroll JD, Hamblin MR.

Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA; Department of Dermatology, Harvard Medical School, Boston, MA; Aesthetic and Plastic Center of Guangxi Medical University, Nanning, P.R. China.

The use of low levels of visible or near infrared light for reducing pain, inflammation and edema, promoting healing of wounds, deeper tissues and nerves, and preventing cell death and tissue damage has been known for over forty years since the invention of lasers. Despite many reports of positive findings from experiments conducted in vitro, in animal models and in randomized controlled clinical trials, LLLT remains controversial in mainstream medicine. The biochemical mechanisms underlying the positive effects are incompletely understood, and the complexity of rationally choosing amongst a large number of illumination parameters such as wavelength, fluence, power density, pulse structure and treatment timing has led to the publication of a number of negative studies as well as many positive ones. A biphasic dose response has been frequently observed where low levels of light have a much better effect on stimulating and repairing tissues than higher levels of light. The so-called Arndt-Schulz curve is frequently used to describe this biphasic dose response. This review will cover the molecular and cellular mechanisms in LLLT, and describe some of our recent results in vitro and in vivo that provide scientific explanations for this biphasic dose response.

Lasers Med Sci. 2009 Jul;24(4):539-47. Epub 2008 Aug 21.

Effect of equal daily doses achieved by different power densities of low-level laser therapy at 635 nm on open skin wound healing in normal and corticosteroid-treated rats.

Gál P, Mokrý M, Vidinský B, Kilík R, Depta F, Harakalová M, Longauer F, Mozes S, Sabo J.Department of Medical Biophysics, Pavol Jozef Safárik University, Kosice, Slovak Republic.

Optimal parameters of low-level laser therapy (LLLT) for wound healing are still discussed. Hence, our study was aimed to compare effects of different power densities of LLLT at 635 nm in rats. Four, round, full-thickness, skin wounds were made on the backs of 48 rats that were divided into two groups (non-steroid laser-treated and steroid laser-treated). Three wounds were stimulated daily with a diode laser (daily dose 5 J/cm(2)) each with different power density (1 mW/cm(2), 5 mW/cm(2), and 15 mW/cm(2)), whereas the fourth wound served as a control. Two days, 6 days, and 14 days after surgery, eight animals from each group were killed and samples were removed for histological evaluation. In the non-steroid laser-treated rats, significant acceleration of epithelization and collagen synthesis 2 days and 6 days after surgery was observed in stimulated wounds. In steroid laser-treated rats, 2 days and 14 days after surgery, a decreased leucocyte/macrophage ratio and a reduction in the area of granulation tissue were recorded, respectively. In conclusion, LLLT, by the method we used, improved wound healing in the non-steroid laser-treated rats, but it was useless after corticosteroid treatment.

Photomed Laser Surg. 2009 Jun;27(3):387-93.

Intricacies of dose in laser phototherapy for tissue repair and pain relief.

Enwemeka CS.

School of Health Professions, New York Institute of Technology, Old Westbury, NY 11568, USA.


Inaccurate measurement and incorrect reporting of dosages are major shortcomings of phototherapy articles. As many as 30% of published reports in the field either lack relevant information needed to determine a dosage or report dosages that are altogether inaccurate. The high prevalence of dosage-related mistakes in published reports suggests that dosage determination errors are common among clinicians and other end-users. This special article is designed to advance understanding of the relevant parameters used in phototherapy for tissue repair and pain relief, particularly among clinicians and others who may not be completely familiar with the technology. I define and discuss five key parameters that influence dosage, including 1) radiant power, 2) radiant energy, 3) power density, 4) energy density, and 5) wavelength, and use hypothetical cases to demonstrate how factors such as beam spot size, size of lesion, mode of treatment (contact, noncontact, or scanning), frequency of treatment, dose per treatment, and cumulative dose affect dosages and treatment outcomes. The potential effects of patient-related factors, such as etiology, pathology, tissue optical density, depth of target tissue, and skin pigmentation are discussed concurrently and strategies are suggested to improve dosage determination.

Lasers Med Sci. 2007 Oct 31; [Epub ahead of print]

Relevance of laser irradiance threshold in the induction of alkaline phosphatase in human osteoblast cultures.

Haxsen V, Schikora D, Sommer U, Remppis A, Greten J, Kasperk C.

Faculty of Science, Biophotonics Group, University of Paderborn, Paderborn, Germany,

Induction of matrix synthesis by low-level laser has been demonstrated extensively. However, the question of dose- or power intensity-dependency is under-investigated. To address this issue we chose human osteoblast cell cultures and measured their alkaline phosphatase (ALP) activity after laser irradiation. The cell cultures were irradiated periodically by 690 nm radiation via optical transmission fiber-based laser needles, reaching into the culture dishes. The osteoblasts showed no induction of ALP activity when we used a single laser needle stimulation with a laser irradiance of 51 mW/cm(2), an increase of approximately 43% at 102 mW/cm(2) irradiance (two needles per well) and a ninefold increase at 204 mW/cm(2) irradiance (four needles per well), leaving the temperature of the culture medium unaffected. We concluded that the osteoblastic response in ALP activity to a laser stimulus shows a logarithmic relationship, with a distinct threshold, rather than a linear dose-dependency. Secondly, the laser irradiance, rather than the dose, is relevant for the impact of the laser.

Lasers Surg Med. 2007 Jul;39(6):543-50.

Low-level laser therapy for zymosan-induced arthritis in rats: Importance of illumination time.

Castano AP, Dai T, Yaroslavsky I, Cohen R, Apruzzese WA, Smotrich MH, Hamblin MR.

Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.


BACKGROUND: It has been proposed for many years that low-level laser (or light) therapy (LLLT) can ameliorate the pain, swelling, and inflammation associated with various forms of arthritis. Light is thought to be absorbed by mitochondrial chromophores leading to an increase in adenosine triphosphate (ATP), reactive oxygen species and/or cyclic AMP production and consequent gene transcription via activation of transcription factors. However, despite many reports about the positive effects of LLLT in arthritis and in medicine in general, its use remains controversial. For all indications (including arthritis) the optimum optical parameters have been difficult to establish and so far are unknown.

METHODS: We tested LLLT on rats that had zymosan injected into their knee joints to induce inflammatory arthritis. We compared illumination regimens consisting of a high and low fluence (3 and 30 J/cm(2)), delivered at high and low irradiance (5 and 50 mW/cm(2)) using 810-nm laser light daily for 5 days, with the positive control of conventional corticosteroid (dexamethasone) therapy.

RESULTS: Illumination with 810-nm laser was highly effective (almost as good as dexamethasone) at reducing swelling and a longer illumination time (10 or 100 minutes compared to 1 minute) was more important in determining effectiveness than either the total fluence delivered or the irradiance. LLLT induced reduction of joint swelling correlated with reduction in the inflammatory marker serum prostaglandin E2 (PGE2).

CONCLUSION: LLLT with 810-nm laser is highly effective in treating inflammatory arthritis in this model. Longer illumination times were more effective than short times regardless of total fluence or irradiance. These data will be of value in designing clinical trials of LLLT for various arthritides.

Photomed Laser Surg. 2007 Jun;25(3):197-204.

Effect of laser therapy on bone tissue submitted to radiotherapy: experimental study in rats.

Da Cunha SS, Sarmento V, Ramalho LM, De Almeida D, Veeck EB, Da Costa NP, Mattos A, Marques AM, Gerbi M, Freitas AC.

Federal University of Bahia, Salvador, Bahia, Brazil.


OBJECTIVE: The aim of this study was to investigate the effect of laser therapy (lambda = 780 nm) on bone tissue submitted to ionizing radiation.

BACKGROUND DATA: The biostimulation effect of laser in normal bone tissue has already been demonstrated successfully; however its effect on bone tissue submitted to radiotherapy has not yet been studied.

METHODS: Twenty-two Wistar rats were randomly divided into four groups: group I, control (n = 4), submitted only to radiotherapy; group II, laser starting 1 day prior to radiotherapy (n = 6); group III, laser started immediately after radiotherapy (n = 6); group IV, laser 4 weeks after radiotherapy (n = 6). The source of ionizing radiation used was Cobalt 60, which was applied in a single dose of 3000 cGy on the femur. The laser groups received seven applications with a 48-h interval in four points per session of DE = 4 J/cm(2), P = 40 mW, t = 100 sec, and beam diameter of 0.04 cm(2). All animals were killed 6 weeks after radiotherapy.

RESULTS: Clinical examination revealed cutaneous erosions on experimental groups (II, III, and IV) starting at the 6th week after radiotherapy. The radiographic findings showed higher bone density in groups II and IV (p < 0.05) compared to the control group. The results further showed an increase of bone marrow cells, and number of osteocytes and Haversian canals in experimental groups II and IV (p < 0.05). It was also found an increase of osteoblastic activity, in groups II, III, and IV (p < 0.05).

CONCLUSION: Laser therapy on bone tissue in rats presented a positive biostimulative effect, especially when applied before or 4 weeks after radiotherapy. However, the use of laser in the parameters above should be used with caution due to epithelial erosions.

Conf Proc IEEE Eng Med Biol Soc. 2007;2007:5830-33.

Effects of low level red-light irradiation on the proliferation of mesenchymal stem cells derived from rat bone marrow.

Li WT, Leu YC.

Department of Biomedical Engineering, Chung-Yuan Christian University, Chung-Li, 32023 Taiwan, ROC.


Mesenchymal stem cells (MSCs) are capable of regenerating various mesenchymal tissues and are essential in supporting the growth and differentiation of hematopoietic stem cells within the bone marrow microenvironment in vivo. To achieve clinically meaningful numbers of cells, many approaches have been used to maintain the differentiation potentialities and expand enough cells for clinical treatments. Previously, we have reported that low level light irradiation (LLLI) using 630 nm light emitting diodes (LEDs) could enhance replicative and colony formation potentials of MSCs derived from human bone marrow. The purpose was to study the effect on the proliferation of MSCs derived from the rat bone marrow by red light LLLI (630 nm) under different parameters of irradiation. The irradiance used was 5, 10 or 15 mW/cm2, and the radiant exposure was 2 or 4 J/cm2. Rat MSCs were irradiated at room temperature with single and multiple exposures. The results showed that the proliferation of MSCs plated at the low density (100 cells/well) and high density (1000 cells/well) was enhanced by multiple exposures of red-light LED treatment. The rate of proliferation of MSCs plated at the high density was not as high as those plated at the low density. The optimal parameter for LLLI was at irradiance of 15 mW/cm2, and radiant exposure of 4 J/cm2. The effect on the proliferation of cells by single dose irradiation was temporary. Multiple stimuli may be necessary for the enhancement of cell growth.

Photomed Laser Surg. 2006 Dec;24(6):705-14

Effect of multiple exposures of low-level laser therapy on the cellular responses of wounded human skin fibroblasts.

  • Hawkins D,
  • Abrahamse H.

Laser Research Unit, Group of Health Sciences, University of Johannesburg, Doornfontein, Johannesburg, South Africa.

Objective: This study aimed to establish the behavior of wounded human skin fibroblasts (HSF) after heliumneon (HeNe) (632.8 nm) laser irradiation using one, two, or three exposures of different doses, namely, 2.5, 5.0, or 16.0 J/cm(2) on each day for 2 consecutive days. Background Data: Low-level laser therapy (LLLT) is a form of phototherapy used to promote wound healing in different clinical conditions. LLLT at than adequate wavelength, intensity, and dose can accelerate tissue repair. However, there is still conflicting information about the effect of multiple irradiations on the cellular responses of wounded cells. Methods: Cellular responses to HeNe laser irradiation were evaluated by measuring changes in cell morphology, cell viability, cell proliferation, and damage caused by multiple irradiations. Results: A single dose of 5.0 J/cm(2), and two or three doses of 2.5 J/cm(2) had a stimulatory or positive effect on wounded fibroblasts with an increase in cell migration and cell proliferation while maintaining cell viability, but without causing additional stress or damage to the cells. Multiple exposures at higher doses (16 J/cm(2)) caused additional stress, which reduces cell migration, cell viability, and ATP activity, and inhibits cell proliferation. Conclusion: The results show that the correct energy density or fluence (J/cm(2)) and number of exposures can stimulate cellular responses of wounded fibroblasts and promote cell migration and cell proliferation by stimulating mitochondrial activity and maintaining viability without causing additional stress or damage to the wounded cells. Results indicate that the cumulative effect of lower doses (2.5 or 5 J/cm(2)) determines the stimulatory effect, while multiple exposures at higher doses (16 J/cm(2)) result in an inhibitory effect with more damage.

J Cosmet Laser Ther. 2006 Dec;8(4):177-83.

Cutaneous effects compared between higher fluence with fewer treatments and lower fluence with more treatments in a combined IR laser/radio frequency system.

Trelles MA, Mordon S.

Instituto Médico Vilafortuny/Antoni de Gimbernat Foundation, Cambrils, Spain.

BACKGROUND AND AIMS: A combined infrared (IR) laser/radio frequency (RF) system has recently been reported to create rejuvenation-related cutaneous effects, but was associated with high levels of pain and some complications. The present study was designed to evaluate the cutaneous effects of the same system with a lower fluence and more treatments. METHODS: Twenty patients were randomly assigned into two groups of 10 individuals each: Group A was treated at 50 J/cm2/100 J/cm3 (laser/RF), respectively, two passes, three treatment sessions 30 days apart; Group B at 30 J/cm2/50 J/cm3, three passes, five treatment sessions 15 days apart. Objective comparisons were made at the same time points with a computer program based on the clinical photography. RESULTS: Group A noted more improvement in wrinkles than Group B at the first assessment, but both groups showed slight and progressive deterioration at the 2- and 6-month assessments. Improved skin appearance was maintained throughout in both groups. The authors recognize that the comparatively small number of subjects possibly limits the statistical power of the study. CONCLUSIONS: Lower fluences and more treatment sessions with the combined 900 nm laser/RF system were complication-free, produced improvements in the overall skin condition and less pain during sessions, suggesting that this combination may produce better patient compliance. Further treatment sessions may improve the results with implications in skin rejuvenation.

Photomed Laser Surg. 2006 Aug;24(4):458-66.

Effects of power densities, continuous and pulse frequencies, and number of sessions of low-level laser therapy on intact rat brain.


Ilic S, Leichliter S, Streeter J, Oron A, DeTaboada L, Oron U.

Photothera Inc., Carlsbad, California, USA.

OBJECTIVE: The aim of the present study was to investigate the possible short- and long-term adverse neurological effects of low-level laser therapy (LLLT) given at different power densities, frequencies, and modalities on the intact rat brain.

BACKGROUND DATA: LLLT has been shown to modulate biological processes depending on power density, wavelength, and frequency. To date, few well-controlled safety studies on LLLT are available.

METHODS: One hundred and eighteen rats were used in the study. Diode laser (808 nm, wavelength) was used to deliver power densities of 7.5, 75, and 750 mW/cm2 transcranially to the brain cortex of mature rats, in either continuous wave (CW) or pulse (Pu) modes. Multiple doses of 7.5 mW/cm2 were also applied. Standard neurological examination of the rats was performed during the follow-up periods after laser irradiation. Histology was performed at light and electron microscopy levels.

RESULTS: Both the scores from standard neurological tests and the histopathological examination indicated that there was no long-term difference between laser-treated and control groups up to 70 days post-treatment. The only rats showing an adverse neurological effect were those in the 750 mW/cm2 (about 100-fold optimal dose), CW mode group. In Pu mode, there was much less heating, and no tissue damage was noted.

CONCLUSION: Long-term safety tests lasting 30 and 70 days at optimal 10x and 100x doses, as well as at multiple doses at the same power densities, indicate that the tested laser energy doses are safe under this treatment regime. Neurological deficits and histopathological damage to 750 mW/cm2 CW laser irradiation are attributed to thermal damage and not due to tissue-photon interactions.

J Biomed Mater Res A. 2005 Apr 1;73(1):55-62.

Determining optimal dose of laser therapy for attachment and proliferation of human oral fibroblasts cultured on titanium implant material.

Khadra M, Lyngstadaas SP, Haanaes HR, Mustafa K.

Department of Oral Surgery and Oral Medicine, Faculty of Dentistry, University of Oslo, P.O. Box 1109 Blindern, N-0317 Oslo, Norway.


The purpose of this study was to investigate the influence of single or multiple doses of low-level laser therapy (LLLT) on attachment and proliferation of human gingival fibroblasts in a standardized, reproducible in vitro model. Titanium discs were randomly allotted to one of three groups: group I served as a control, group II was exposed to a single laser dose of 3 J/cm2, and the three subgroups in group III were exposed to laser doses of 0.75, 1.5, and 3 J/cm2. To examine the possible thermal effects of laser exposure on the cell culture, the temperature in the Petri dish was measured for every dose used, before and during irradiation. For attachment assays, groups II and III were exposed to laser irradiation and then seeded onto titanium discs. In group III, the exposures were repeated after 3 and 6 h. Cells were cultured for 6 and 24 h and stained with Hoechst and Propidium. Attached cells were counted under a light microscope. To investigate the effect of LLLT on cell proliferation after 48 h, 72 h, and 7 days, cells were cultured on titanium discs for 24 h and then exposed to laser irradiation for 1 day and 3 consecutive days, respectively. Cell proliferation was determined by counting cells under the microscope and by a cell proliferation enzyme-linked immunosorbent assay system. No increase of temperature of the cell cultures occurred before or during laser exposure at any of the doses tested. Both single and multiple doses of LLLT significantly enhanced cellular attachment (p<0.05). The proliferation assays showed higher cell proliferation (p<0.05) in group III at doses of 1.5 and 3 J/cm2 after 72 h and 7 days, with agreement between staining and enzyme-linked immunosorbent assay. It is concluded that, in this cellular model, the attachment and proliferation of human gingival fibroblasts are enhanced by LLLT in a dose-dependent manner.

J Photochem Photobiol B.  2004 May 27;74(2-3):101-7.

Effects of different protocol doses of low power gallium-aluminum-arsenate (Ga-Al-As) laser radiation (650 nm) on carrageenan induced rat paw ooedema.

Albertini R, Aimbire FS, Correa FI, Ribeiro W, Cogo JC, Antunes E, Teixeira SA, De Nucci G, Castro-Faria-Neto HC, Zângaro RA, Lopes-Martins RA.


Research Group of Fluorescence, IP&D UNIVAP R, Shishima Hifumi, 2911, 12244-000 São José dos Campos, SP, Brazil.


The purpose of the present study was to investigate the effect of the low power laser therapy on the acute inflammatory process. Male Wistar rats were used. The rat paw oedema was induced by sub-plantar injection of carrageenan, the paw volume was measured before and 1, 2, 3 and 4 h after the injection using a hydroplethysmometer. To investigate the mechanism action of the Ga-Al-As laser on inflammatory oedema, parallel studies were performed using adrenallectomized rats or rats treated with sodium diclofenac. Different laser irradiation protocols were employed for specific energy densities (EDs), exposure times and repetition rates. The rats were irradiated with the Ga-Al-As laser during 80 s each hour. The ED that produced an anti-inflammatory effect were 1 and 2.5 J/cm(2), reducing the oedema by 27% (P<0.05) and 45.4% (P<0.01), respectively. The ED of 2.5 J/cm(2) produced anti-inflammatory effects similar to those produced by the cyclooxigenase inhibitor sodium diclofenac at a dose of 1 mg/kg. In adrenalectomized animals, the laser irradiation failed to inhibit the oedema. Our results suggest that low power laser irradiation possibly exerts its anti-inflammatory effects by stimulating the release of adrenal corticosteroid hormones.

J Clin Laser Med Surg. 2004 Feb;22(1):19-25.

Dose and wavelength of laser light have influence on the repair of cutaneous wounds.

Mendez TM, Pinheiro AL, Pacheco MT, Nascimento PM, Ramalho LM.

IP&D, Univap & School of Dentistry, Universidade do Vale do Paraíba, São José dos Campos, São Paulo, Brazil.

OBJECTIVE: The objective of the present study was to compare histologically the effect of GaAlAs (lambda 830 nm, phi approximately 2 mm(2), 35 mW) and InGaAlP (lambda 685 nm, phi approximately 2 mm(2), 35 mW) lasers, alone or in association with doses of 20 or 50 J/cm(2) on cutaneous wounds in the dorsum of the Wistar rat. Background Data: The healing time of surgical wounds is of extreme importance and it is usually associated with a post-operative period free of infection and with less pain and inflammation.

MATERIALS AND METHODS: Sixty Wistar rats were divided into seven groups: Group I – control (non-irradiated); Group II – lambda 685 nm, 20 J/cm(2); Group III – lambda 830 nm, 20 J/cm(2); Group IV – lambda 685 nm and lambda 830 nm, 20 J/cm(2); Group V – lambda 685 nm, 50 J/cm(2)); Group VI – lambda 830 nm, 50 J/cm(2); and Group VII – lambda 685 nm and 830 nm, 50 J/cm(2). The animals were sacrificed 3, 5, and 7 days after surgery.

RESULTS: Light microscopic analysis using H&E and Picrosírius stains showed that, at the end of the experimental period, irradiated subjects showed increased collagen production and organization when compared to non-irradiated controls. Inflammation was still present in all groups at this time.

CONCLUSION: Group IV (lambda 830 nm and lambda 685 nm, 20 J/cm(2)) presented better results at the end of the experimental period. It is concluded that low-level light therapy (LLLT) can have a positive biomodulatory effect on the repair of cutaneous wounds.

J Clin Laser Med Surg. 2001 Feb;19(1):29-33.

Biostimulatory windows in low-intensity laser activation: lasers, scanners, and NASA’s light-emitting diode array system.

Sommer AP, Pinheiro AL, Mester AR, Franke RP, Whelan HT.

Central Institute of Biomedical Engineering, Department of Biomaterials, University of Ulm, Germany.

OBJECTIVE: The purpose of this study was to assess and to formulate physically an irreducible set of irradiation parameters that could be relevant in the achieving reproducible light-induced effects in biological systems, both in vitro and in vivo.

BACKGROUND DATA: Light-tissue interaction studies focusing on the evaluation of irradiation thresholds are basic for the extensively growing applications for medical lasers and related light-emitting systems. These thresholds are of central interest in the rejuvenation of collagens, photorefractive keratectomy, and wound healing.

METHODS: There is ample evidence that the action of light in biological systems depends at least on two threshold parameters: the energy density and the intensity. Depending on the particular light delivery system coupled to an irradiation source, the mean energy density and the local intensity have to be determined separately using adequate experimental methods.

RESULTS: From the observations of different research groups and our own observations, we conclude that the threshold parameters energy density and intensity are biologically independent from each other.

CONCLUSIONS: This independence is of practical importance, at least for the medical application of photobiological effects achieved at low-energy density levels, accounting for the success and the failure in most of the cold laser uses since Mester’s pioneering work.

Lasers Surg Med. 2001;28(1):18-26.

Lightdosimetric quantitative analysis of the human petrous bone: experimental study for laser irradiation of the cochlea.

Tauber S, Baumgartner R, Schorn K, Beyer W.

Department of Otolaryngology, Head and Neck Surgery, University of Munich, Germany.


BACKGROUND AND OBJECTIVE: Application of laser irradiation targeting the inner ear has to be investigated for therapeutic effectiveness in cochlear injury and dysfunction. In vitro data demonstrate low-level laser-induced photochemical and photobiologic cell response, depending on cell type and irradiation parameters such as light dose. The aim of the presented study was to determine the light dose received by the cochlear hair cells by using different irradiation modalities for the human petrous bone.

STUDY DESIGN/MATERIALS AND METHODS: Lightdosimetric assessment was performed in human cadaver temporal bones (n = 13) after removing the cochlear membranous labyrinth. The external auditory meatus, the tympanic membrane (quadrants), and the mastoid bone were illuminated by a helium-neon laser (lambda = 593 nm) and diode lasers of different wavelengths (lambda = 635, 690, 780, and 830 nm). The spatial distribution of transmitted light in the cochlear windings was measured by means of a retrocochlearly positioned endoscopic CCD camera for image processing and was assigned to acoustic frequencies according to the tonotopic organization of the cochlea. For an estimation of the corresponding space irradiance in an intact cochlea, correction factors have been calculated by a Monte Carlo procedure on the basis of experimentally determined optical properties of skull bone.

RESULTS: The transmission of light across the tympanic cavity and the promontory depends strongly on wave-length of the laser and the position of the radiator. Transtympanal irradiation results in spatial intensity variations of a factor 4 to 10 within the cochlear windings. The space irradiance in an intact cochlea is 10 to 20 times the measured irradiance. For an irradiation of the mastoid, the light transmission within the cochlea is 10(3) to 10(5) times smaller compared with an irradiation of the tympanic membrane and is extremely variable for different specimens.

CONCLUSION: The strong dependence of the cochlear light distribution on various irradiation parameters demonstrates the impact of preclinical lightdosimetric investigations for effective individual laser irradiation of the human cochlea. Because of the observed spatial intensity variations, the optimal external light dose has to be chosen with regard to the tonotopy of the human cochlea. The obtained results are enabling us to apply defined laser light doses to different cochlear winding areas. Mastoidal irradiation leads to therapeutically insufficient light doses within reasonable treatment times, whereas transmeatal irradiation is recommendable. Further studies are mandatory for development of clinical devices for transmeatal irradiation of the cochlea.