1. 1. .Gonobishwabidyalay(GonoUniversity,Mirzanagar,Nayerhat,Savar,Dhaka-1344,Bangladesh.April 2010.1 Dept.of Medical Radiation Physics,Kreiskrankenhaus Gummersbach, Teaching Hospital of the University ofCologne, 51643 Gummersbach, Germany.2Dept. of Medical Physics and Biomedical Engineering, Gono-Bishwabidyalay (Gono University), Nayarhat,Savar, Dhaka- 1344, Bangladesh.3Department of Orthopedic and Traumatology, Shaheed Suhrawardy Medical College Hospital, Dhaka-1207, Bangladesh.1|Page
2. 2. DeclarationI declare that I am the sole author of this thesis and that the work presentedhere has not previously been submitted as an exercise for a degree or otherqualification at any university.It consists entirely of my own work, except where references indicateotherwise.2|Page
3. 3. DedicationTo my parents, Mr. Alauddin Sikder & Ms. Munira Begum- for fostering andencouraging my interest in science &Mother in-law, late Ms. Anowara Begum and my wife Ms. Habiba IslamHappy for their tremendous and unbelievable mental support during my post-graduate period. Sponsored by-This research project is jointly sponsored by-Lab-Nucleon & Acme Laboratories Ltd., Dhaka, Bangladesh.3|Page
4. 4. I wish to express my deepest gratitude and thanks to my guide and thesis supervisor Professor Golam AbuZakaria, for his kind directions, inspiring guidance, and invaluable discussion throughout the course. Without hispatience and encouragement, this work would never be fulfilled. I also express my heartfelt respect to my co-guides Prof. F. H. Sirazee , ex. head of the department, and Associate professor, Dr. P C Debenarh, Departmentof Orthopedic & Traumatology, Shaheed Suhrawardy Medical College Hospital. Dhaka-1207, Prof. Nurul Islamdept. of Medical Physics and Biomedical Engineering, and Md. Delwar Hossain, registrar,GonoBishwabidyalay (Gono University) Nayarhat, Savar, Dhaka for heartiest co -operation and advicethroughout the whole research period.I would also like to express my profoundest gratitude to my thesis advisory board / working team members,Associate Prof. Dr Sheikh Abbasuddin Ahmed, assistant Prof Dr. Kazi Shamimuzzaman, Dr. Zia Uddin,consultant,Dr. Subir Hossain Shuvro, assistant registrar, Dr. Abdul Hannan of Orthopedic & Tramatology Department,assistant Prof Dr. Quamrul Akter Sanju of Surgry department, Shaheed Suhrawardy Medical College Hospital andDr. Sayed Shaheedul Islam Assistant professor, NITOR, Dhaka.Special thanks are due to Prof. Khadiza Begum, ex-director, Prof. A. K.M Mujibur Raman, director, Dr. MirMahamuda Khanam, assistant director of SsMCH, Prof. S. M. Idris Ali, ex. head of the department and vice-principal,SSMC and Prof. Abdul kader Khan, ex-principal and head of the department, surgery, SSMC/ SsMCH,associate professor, Dr. Mostaq Hossain Tuhin of Surgery department, assistant. Prof. Asraf Uddin, head o f thedepartment ,Radiology & Imaging department of SsMCH, and to all my friends and well-wishers, specially to Mr.Sinha Abu Khalid CEO, LabNucleon, Md. Masud Rana, medical Physicist, National Cancer Institute & Hospital,Md. Anwarul Islam, medical physicist, Squrae Hospital & Mr. Kumaresh Chandra Pal, medical physicist of GonoBiswabidyalay, Dhaka-1344, and Md Shakilur Rahman, senior scientific officer of Bangladesh Atomic EnergyCommission for their kind and nice co-operation throughout the course of this work.My deepest admiration and sincerest love to and my laser machine technician Mr. Mamun, laser operator Ms.Jannant & Ms. Chewty of LabNucleon, and Md. Abdul Aziz, Mr. Polash, Mr. Abul- kasem, Ms. Fatema, Ms Farida,Mr. Malek of Orthopedic and Traumatology Department, and Kazi Murad Hossain of Shaheed SuhrawardyMedical Hospital, Dhaka-1207, Bangladesh for their continuous efforts to successfully complete this project.Finally, I owe much and pay my heartiest thanks, especially to those who rendered their hind assistance during mystudy period. Words cannot be expressed my feeling of love, I am deeply indebted to my wife Habiba Islam, myloving sons- Sayem Islam labib & Talaat Islam Syiam for all their support and understanding. In the whole courseof this work, they gave me a sweet working atmosphere, which I cant find words to express. 4|Page
5. 5. BY-DR. MD NAZRUL ISLAMLaser (Semiconductor diode, Ga-Al-As, 830nm) is effective in human bone regeneration,i.e. it enhances bone fracture healing.Tissue healing is a complex process that involves both local and systemic responses, and the healing process of bone ismuch slower than that of soft tissues which is a great challenge of medical science. The use of Laser Therapy (LLLT) forwound healing has been shown to be effective in modulating both local and systemic response by enhancing- cellular &mitochondrial ion exchange, bone mineralization, nitric oxide formation, lymphatic circulation, osteoblast proliferation, effectson osteoblast gene expression, osteoclast inhibition (prevents bone mineral resorption) and by bone engraftment onsynthetic materials.40 (Twenty in laser & Twenty in control group) otherwise healthy men and women with, closed appendicular bone fracture(Radius/ ulna, or Femur / Tibial shaft /Clavicle / Meta carpal /Meta-tarsal) was enrolled for fracture management by lasertherapy adjunctive to regular management, and was assed by clinical and radiological findings (X-ray)/at 2nd , 3rd, 4th and6th week post fracture: assessment included fracture line/margins, fracture gap, external callus appearance, callus-to-cortexratio, bridging, and radiologic union as well as clinical assessment of the fracture- compliance of patient, and onwardsfollow-up of patients, in comparison to controlled group.Early significant bone regeneration /callus formation achieved by early application of Low Level laser therapy (Ga-Al-As, 830nm) on human fractured long (appendicular) bone.Treatment with 830 nm diode laser has substantially reduced the fracture healing time as well as improved thequality/quantity of callus formation of the patient, thus enhancing fracture healing. Laser biostimulative effects on bone couldbe a new dimension for bone regeneration which significantly reduce healing period, lessen cost of treatment, and enhancepatient compliance in medical science.5|Page
6. 6. 1.1 Introduction1.2 Background1.3 Literature review2.1 Cell2.2 Bone2.3 Bone Fracture2.4 Healing of fracture3.1 Laser3.2 Laser principle3.3 Components of a laser system3.4 Laser Machine3.5 Measurement of Laser Energy4.1 Biophysical Aspects & light transport theory4.2 Laser - Tissue Interaction4.3 The Mechanisms of Low Level Laser Therapy4.4: Effects of Laser on Biological Cell/Tissue healing Laser on hard tissue & Bone stimulation/ Regeneration4.5 Medical application of Low Level Laser5.1 Materials5.2 Methods10.1 Figure & Table list10.2 Laser Books & Articles10.3 Datasheet.10.4 Publications & Presentation:10.5 Biography & pictures 6|Page
7. 7. Chapter-1 Page- 7- 121.1 Introduction1.2 Background1.3 Literature reviewOptimizing the results of fracture treatment requires a holistic view of both patients and treatment. The nature of the patientdetermines the priority targets for outcome, which differ widely between the elderly and the young, and between the victimsof high and low energy trauma. The efficacy of treatment depends on the overall process of care and rehabilitation as wellas the strategy adopted to achieve bone healing.The rational basis for fracture treatment is the interaction between three elements, (I) the cell biology of bone regeneration,(ii) the revascularization of devitalized bone and soft tissue adjacent to the fracture; and (iii) the mechanical environment ofthe fracture. The development of systems for early fracture stabilization has been an advance. However, narrow thinkingcentered only on the restoration of mechanical integrity leads to poor strategy - the aim is to optimize the environment forbone healing. Future advances may come from the adjuvant use of molecular stimuli to bone regeneration.Restoring function to a patient who has had a fracture requires the physician/ surgeon to handle a heady mix of mechanicaland biological issues. In real life, it also requires considerable input of time into practice organization, given the largenumbers of patients and the almost universal inadequacy of resource, if each individual patient is to receive timely andappropriate intervention.There is a perception, not least among fracture surgeons themselves, that the mechanical issues have been over-emphasized in the past. The bonesetters art consisted basically of- providing- anatomical realignment and external supportfor as long as nature then took to restore internal structural competence by bone healing. This was slow and unkind to softtissues, particularly neighboring joints, so the development of materials, bio-mechanical understanding and surgicaltechnique launched a swing towards invasive interventions aimed at immediate restoration of internal structural integrity.The principles of AO treatment, drummed into a generation of orthopedic trainees, were anatomical open reduction, rigidinternal fixation and early rehabilitation of soft tissues without- external splint. But the scale of invasion required to achievethese aims brought a steady trickle of serious problems - most notably infected non-unions, sometimes in cases whichsurgeons knew they could safely have treated by simpler methods.Furthermore, there was increasing realization that the abolition of inter-fragmentary motion implied a commitment to primarycortical union as the only route for healing and a closure of the natural routes of callus formation. From various directions,less invasive alternatives were developed: functional bracing, external fixation (including the remarkable Ilizarov circularfixator developed in the USSR, which evades the bone only with fine wires) and closed intra-medullary nailing.Now the science is taking another step, further in the direction from mechanics to biology. If the mechanical environmentinfluences bone regeneration and hence fracture healing, how, at a cellular- level, does it do so? - What molecular signals-produce the response? If we know the signals, can we deliver them in the form of recombinant growth factors and hurry the-cellular response down the right path? 7|Page
8. 8. The evolution has been first to use nature, then to ignore her, then to remember her, and now to outdo her.Optimal fracturetreatment requires the following: (I) a definition of what optimal treatment means and a way of measuring the extent to whichit is achieved; (ii) a review of what we know about- the natural healing process that we want to harness or improve upon;and (iii) analysis of how to apply the above to clinical practice.During the last decade, it was discovered that low-power laser irradiation has stimulatory effects on bone tissue, in themicroscopic (cell proliferation [1-5] and gene expression [6]) and macroscopic [1, 2, 4, 12, 13-20] biological systems.In order to understand the effects of laser therapy, its mechanism of action in the cell needs to be established. Manyexplanations have been proposed {7-11]. Studies have shown that porphyrins and cytochromes, natural photoacceptorslocated in the cell, are the main contributors to laser-tissue interaction [7-11]. Porphyrins and cytochromes absorb the light intothe cell, resulting in the production of singlet 1O2. The singlet oxygen then stimulates the redox activity in the mitochondria,enhances chemiosmosis, DNA production and calcium-ion influx into the cytoplasm, thereby causing mitosis and cellproliferation.The purpose of this review is to analyze the effects of low power laser irradiation on bone cells and bone fracture repair,examine what has been done so far, and propose areas warranting further exploration.8|Page
9. 9. Bone and fracture healing is an important homeostatic process that depends on specialized cell activation andbone immobility during injury repair [1, 2]. Fracture reduction and fixation are a prerequisite to healing but a varietyof additional factors such as age, nutrition, and medical co-morbidities can mediate the healing process [3,4]..Different methods have been investigated in attempts to accelerate the bone-healing process. Most studieshave concentrated on drugs, fixation methods or surgical techniques; however, there is a potential role foradjunctive modalities that affect the bone-healing process.Laser is an acronym for Light Amplification by stimulated Emission of Radiation [5].The first laser wasdemonstrated in 1960 and since then it has been used for surgery, diagnostics, and therapeutic medicalapplications [6]. The physiological effects of low level lasers occur at the cellular level[7, 8], and can stimulate orinhibit biochemical and physiological proliferation activities by altering intercellular communication [9]. Early workon physical agents as mediators of bone healing was performed by Yasuda, Noguchi and Sata who studied theelectrical stimulation effects on bone healing in the mid 1950s[1, 10]. In subsequent years, others repeated thiswork in humans [1, 11] and a variety of physical agents have been investigated as potential mediators of bonehealing [12, 23, 14, 15, and 16]. With increasing availability of lasers in the early 1970s, the potential to investigate its useas a modality to affect the healing of different connective tissues became possible[17, 18, and 19]. In 1971, a shortreport by Chekurov stated that laser is an effective modality in bone healing acceleration[19]. Subsequently, otherresearchers studied bone healing after laser irradiation using histological, histochemical, and radiographicmeasures[18, 19, 20, 21, 22, 23, and 24]. These studies have demonstrated mixed results where some observed anacceleration of fracture healing [19, 21, 22, 23, 24], while others reported delayed fracture healing after low-level laserirradiation [20, 25]. 9|Page
10. 10. As far as is known, the first attempt at treating bone fracture with infrared light was reported by Shugaharov and Voronkov.In 1974 they used low level laser radiation (infrared wavelengths) on fracture sites observing intramedullary osteosynthesis.1Gatev studied the effect of stimulating repair of fractures with He-Ne laser. The majority of patients had fractures of the distalradius treated with a plaster cast. On the 5th to 8th day after injury a hole was cut out of the cast over the fracture site andlaser radiation applied at 632 nm, 2 mW/ cm2. Evaluations were made based on radiographic evidence and clinicalassessment. Results showed statistically significant differences [p He +Ne*An excited helium atom meets a ground-state neon atom and transfers its energy while decaying.Figure 3.2.6 also showsthat the lower levels of the laser transitions are far from the ground state, which favours population inversion (no thermalpopulation).Figure 3.2.6: A Helium-Neon Laser System. 37 | P a g e
11. 38. 3.3. Components of a laser system Laser-ComponentsFigure: 3.3.7: Diagram of Components of laser SystemAll lasers are composed of four basic components: oThe lasing medium oThe optical cavity oThe pumping system oThe delivery systemThere are three different vital parts to a Ga-Al-As laser: 1. an energy source, 2. a laser material that absorbs this energyemits it as light, and 3. a cavity that makes the light resonate and channels it in to narrow beam. Within the cavity very highcirculating photon densities stimulate the emission of light from the energized laser material. This design creates a powerfulbeam of billions of photons, unlike to laser and differentiating them from lower intensity light sources like LEDs.3.4 Laser MachineFigure: 3.4.8: schematic diagram of interior of a laser machine. 38 | P a g e
12. 39. There are five (5) basic components that make up the laser system, the control panel, the motherboard, the DC powersupply, the laser tube assembly, and the motion system. A. DC Power Supply. B. Motherboard C. Control Panel D. Laser Tube Assembly E. Motion SystemFigure: 3.4.9: schematic diagram of the control panel of a laser machine39 | P a g e
13. 40. 3.5 Measurement, Parameter & Protocol of Laser3.5.1 Calculating Laser and Treatment Parameters-Laser Therapy devices are generally specified in terms of the average output power (milliwatts) of the laser diode,and the wavelength (nanometers) of light they emit. This is necessary information, but not enough with which toaccurately define the parameters of the laser system. To do this, one must also know the area of the laser beam(cm2) at the treatment surface (usually the tip of the hand piece when in contact with the skin).If the output power (mW) and beam area (cm 2) are known, it is a reasonably straight-forward exercise to calculatethe remaining parameters which allow the precise dosage measurement and delivery.The output power of a laser,measured in milliwatts, refers to the number of photons emitted at the particular wavelength of the laser diode.Power Density measures the potential thermal effect of those photons at the treatment area. It is a function of LaserOutput Power and Beam area, and is calculated as:Laser Output Power (W) 1) Power Density (W/cm2) =Beam area (cm2)Beam area can be calculated by either: 2) Beam Area (cm2) = Diameter(cm)2 x 0.7854 or: Beam Area (cm2) =Pi x Radius(cm)2The total photonic energy delivered into the tissue by a laser diode operating at a particular output power over a certain period is measured inJoules, and is calculated as follows: Laser Output Power (Watts) x Time (Secs) 3) Energy (Joules) =It is important to know the distribution of the total energy over the treatment area, in order to accurately measuredosage. This distribution is measured as Energy Density (Joules/cm 2). "For a given wavelength of light, energydensity is the most important factor in determining- the tissue reaction"(Baxter, 1994). Energy Density is a functionof Power Density and Time in seconds, and is calculated as:Laser Output Power (Watts) x Time (Secs) 4) Energy Density (Joule/cm2) =Beam Area (cm2) OR: Energy Density (Joule/cm2) = Power Density (W/cm2) x Time (Secs)To calculate the treatment time for a particular dosage, you will need to know the Energy Density (J/cm 2) or Energy (J), as well as the OutputPower (mW), and Beam Area (cm 2 ). First, calculate the Output Power Density (mW/cm 2) as per Equation 1, then:Energy Density (Joules/cm2) 5) Treatment Time (Seconds) =Output Power Density (W/cm2)Energy (Joules) or: Treatment Time (Seconds) =Laser Output Power (Watts)Finally:Laser Output Power (mW) Laser Output Power (Watts) =100040 | P a g e
14. 41. OutputBeam TreatmentEnergyEnergy DensityPower Spot SizeTime (Secs)(Joules)(Joules/cm 2 )(mW)(cm2 )5 0.18.00.040.4500.18.00.4 4.0125 0.28.01.0 5.0250 0.28.02.0 10.0500 0.28.04.0 20.0Table: 3. 5.10: Various Laser Parameters v Dosage/Time: Illustrates thedifference in Joules and Joules/cm 2 dosages for differing output parameters.The calculation of these parameters is explained above.3.5.2 Laser Parameters for Effective Treatment"For a given wavelength of light, energy density is the most important factor in determining the tissue reaction"(Baxter, 1994). Research indicates that Energy Densities in the range 0.5 to 4 Joules/cm 2 are most effective intriggering a photobiological response in tissue (e.g. Mester & Jaszagi-Nagy, 1973; Mester & Mester, 1989; Mashikoet al, 1983; Haina, 1982), with 4 Joules/cm 2 having the greatest effect on wound healing (Mester et al, 1973; Mesteret al, 1989).Australian research suggests that this therapeutic window of biostimulation may be extended to include10/Joules/cm 2 (Laakso et al, 1994), and has applications in other areas of practice, such as Myofascial Trigger Pointtherapy and pain control and tissue healing. Dosages above 10J/cm 2 is proved to be bioinhibitive, and the resultingbioinhibition, may also have therapeutic applications, such as in the treatment of keloid scarring and painmanagement. Many practitioners have found straight Joules dosages - up to 20 J/cm 2 in some cases 94.7J/cm2, tobe effective in the treatment of a number of common musculoskeletal disorders. This is possibly due to thecombined action of the pain attenuating properties of laser bioinhibition at high dosages, and the biostimulatoryeffect of the lower-powered halo around the target treatment point. However, the same effect may not be elicitedfrom a different laser unit, due to differences in laser parameters (esp. Power Density) and configura tion.It is the Output Power Density which determines the time required delivering a particular Energy Density(Joules/cm 2) dosage, and the Output Power which determines the corresponding Energy (Joules) delivered duringthat time. Results obtained from particular dosages and treatments are likely to vary between individual practitionersand patients, therefore, practitioner discretion is recommended in determining the applicable wavelength and -dosage parameters for- each patient. It is important to note- that the appropriate- configuration of a laser unit willdepend primarily upon the types of conditions most commonly treated, and so specific requirements will generallydiffer between practitioners. 41 | P a g e
15. 42. 3.5.3 Treatment Protocol, Frequency, and ResponseTo maximize irradiance at the target tissue, the laser probe should be held in contact with, and perpendicular to, thetissue surface. When treating open wounds, the probe should be held slightly away from the tissue surface, whilststill maintaining a 90 o angle. The probe tip may be covered with plastic cling film, in order to reduce the likelihood ofcross-contamination.In treating musculoskeletal conditions, laser therapy should be carried out following cryotherapy as thevasoconstriction caused by cooling the tissue will increase the penetration depth of the laser irradiation. Lasertherapy helps to relax muscles, and so manipulations should be carried out following laser irradiation. Heattherapies and various creams and lotions can be applied after laser therapy.Laser treatments can be carried out by irradiating daily for the first week, then gradually increasing the intervalbetween treatments over successive weeks, according to the progression of the condition being treated. The totaldosage should not exceed 100-200 J in any single treatment session.Laser dosage is cumulative, and so overtreatment causing a degradation of LLLT effectiveness can come fromoverly-high dosages in one treatment session, or too many treatment sessions in close succession. In dividualpractitioner discretion is to be used to determine the appropriate maximum session dosage, and the frequency oftreatment, for each particular patient.Patients may report a number of sensations, such as localized feelings ofwarmth, tingling, or an increase or decrease in symptoms, within the period immediately following laser therapy.Other sensations that may be experienced in response to laser therapy are nausea or dizziness. It is good practiceto advice patients of this possibility.Treatment reactions, if they occur, are often reported after initial laser treatments, however, they generally diminishafter the second or third treatment. If a severe reaction is experienced during treatment, stop immediately.To reiterate, optimal biostimulation is affected by the application of smaller dosages-per-point to more points at thetreatment site. Optimal bioinhibition is achieved through applying higher dosages-per-point, but to less treatmentpoints.When treating acute musculoskeletal injuries, the initial desired outcome of laser therapy is the reduction of painand inflammation. It is very effective when used in conjunction with cryo-therapy, rest and elevation of the injury site.Ideally treatment will begin as soon as possible after the injury occurs, with relatively high, inhibitory dosages (8-12Joules per- point, up to 10 points) being used to attenuate the pain and reduce the initial inflammatory response. Atreatment frequency of 1-2 sessions per day may be used for the first 2-4 days post-injury.As the time post-injury progresses, dosages and treatment frequency may be reduced. In the period 5 -10 days post-injury, dosages of 6-8 Joules per point may be useful in promoting the rate of the inflammatory process and inclearing its products from the injury site, thus allowing healing to begin sooner.Moving into the healing phase, dosages are lowered and treatment frequency is reduced further. Throughout thehealing and rehabilitation phase of an injury, biostimulatory dosages (1-4 Joules per point) are used to promotetissue repair and- reduce scarring and adhesions. Higher doses may be used as required to alleviate any pain thatresults from over-working the injured body part during rehabilitation.When treating chronic injuries or pain, it is best to start with lower doses and then work up to the most effective dosefor that particular patient, as a high initial dose may cause an unpleasant exacerbation of symptomatic pain. 42 | P a g e
16. 43. Page- 43-70 4.1 Biophysical Aspects & light transport theory4.2 Laser - Tissue Interaction4.3 The Mechanisms of Low Level Laser Therapy4.4 Effects of Laser on Biological Cell/Tissue healing Laser on hard tissue & Bone stimulation/ Regeneration4.5 Medical application of Low Level Laser4.1a- Biophysical Aspects of Low Level Laser Therapy (By Courtesy of-Herbert Klima, Atomic Institute of the AustrianUniversities, Vienna, Austria) Biophysical aspects of low level laser therapy will be discussed from two points of view: The electromagnetic point of view, and The thermodynamical point of view. From electromagnetic point of view,Living systems are mainly governed by the electromagnetic interaction whose interacting particles are called photons. Eachinteraction between molecules, macromolecules or living cells is basically electromagnetic and governed by photons. Forthis reason, we must expect that electromagnetic influences like laser light of proper wavelength will have remarkable impacton the regulation of living processes. An impressive example of this regulating function of various wavelengths of light isfound in the realm of botany, where photons of 660 nm are able to trigger the growth of plants which leads among otherthings to the formation of buds. On the other hand, irradiation of plants by 730 nm photons may stop the growth and theflowering. Human phagocyting cells are natively emitting light which can be detected by single photon counting methods.Singlet oxygen molecules are the main sources of this light emitted at 480, 570, 633, 760, 1060 and 1270 nm- wavelengths.On the other hand, human cells (leukocytes, lymphocytes, stem cells, fibroblasts, etc) can be stimulated by low power laserlight of just these wavelengths. From thermodynamical point of view,Living systems - in contrast to dead organisms - are open systems which need metabolism in order to maintain their highlyordered state of life. Such states can only exist far from thermodynamical equilibrium thus dissipating heat in order tomaintain their high order and complexity. Such nonequilibrium systems are called dissipative structures proposed by theNobel laureat I. Prigogine. One of the main feature of dissipative structures is their ability to react very sensibly on weakinfluences, e.g. they are able to amplify even very small stimuli.Therefore, we must expect that even weak laser light of proper wavelength and proper irradiation should be able to influencethe dynamics of regulation in living systems. For example, the transition from a cell at rest to a dividing one will occur duringa phase transition already influenced by the tiniest fluctuations. External stimuli can induce these phase transitions whichwould otherwise not even take place. These phase transitions induced by light can be impressively illustrated by variouschemical and- physiological reactions as special kinds of dissipative systems. One of the most important biochemicalreaction localized in mitochondria is the oxidation of NADH in the respiratory chain of aerobic cells. 43 | P a g e
17. 44. A similar reaction has been found to be a dissipative process showing oscillating and chaotic behavior capable to absorband amplify photons of proper wavelength.A great variety of experimental and clinical results in the field of low level laser therapy supports these two biophysicalpoints of view concerning the interaction between life and laser light. Our former, but also our recent experimental results onthe effects of low level- laser light on human cells are steps in this direction.By using cytometric, photometric and radiochemical methods it is shown that the increase or decrease of cells growthdepends on the applied wavelengths (480, 570, 633, 700, 760, 904, 1060, 1270 nm), on the irradiance (100 - 5000 J/m2),on the pulse sequence modulated to laser beams (constant, periodic, chaotic pulses), on the type of cells- (leukocytes,lymphocytes, fibroblasts, normal and cancer cells) and on the density of the cells in tissue cultures.Our experimental results support our hypothesis which states that triplet oxygen molecules are able to absorb proper laserlight at wavelength at wavelengths 480, 570, 633, 700, 760, 904, 1060, 1270 nm thus producing singlet oxygen molecules.Singlet oxygen takes part in many metabolic processes, e.g. catalytic oxidation of NADH which has been shown to be adissipative system far from thermodynamical equilibrium and sensitive even to small stimuli. Therefore, laser light of properwavelength and irradiance in low level laser therapy is assumed to be able- to excite oxygen molecules thus influencing oramplifying metabolism and consequently influencing and supporting fundamental healing processes. 44 | P a g e
18. 45. 4.1b- Light transport theoryWhen light is sent into biological tissue, different processes can occur. While most of the light enters the tissue, a small partof it can be reflected off the tissue surface. The amount of reflected light depends on the angle of incidence and the index ofrefraction. Inside the tissue, the light can be absorbed or scattered. Both processes are highly wavelength dependent. In thelower part of the visible wavelength region, the scattering probability is comparable to the absorption. In the red and near-infrared wavelength region light penetrates tissue better. This region is called the optical window. Based on measurementsof optical properties, physiological or structural information about the probed tissue can be extracted. Here will outline themathematical basis of light transport in tissues and describe the tissue features that affect this transport.The process of light transport in turbid media may be described mathematically either by analytical theory, based directly onMaxwells equations, or by transport theory. Maxwells equations can describe the interaction between light and tissue as anelectromagnetic wave propagating through a medium with random dielectric fluctuations. However, due to the complexstructure of tissue it is in principle impossible to obtain a formulation that takes all its dielectric properties into account (A.Ishimaru 1978). Transport theory, on the other hand, treats the problem as a flow of power through a scattering medium.Transport theory is less mathematically- rigorous than electromagnetic theory and does not in itself include effects such asdiffraction or interference. However, it has proven useful for calculating photon transport in tissue. It is usually expressed forthe radiance L(r,s,t) [Wm-2sr-1], which is the radiant power per unit area and unit solid angle in direction s, at a position inspace r. It is obtained by multiplying the light distribution function, N(r,s,t) [m-3sr-1], with the speed and energy of thephotons in the medium. Radiance is the quantity used to describe the propagation of photon power. The transport equationcan be formulated as Where c is the speed of light in the tissue, c = c0/n/ is the speed of light in vacuum and n is the refractive index of themedium. The scattering and absorption coefficients s and a describe the probability of a scattering or absorption eventper unit length. The phase function, p(s, s) denotes the probability that a scattered photon initially travelling in direction scontinues in direction s after the scattering event. The integral of the probability density function over all- solid angles d isequal to one. The transport equation describes the energy balance in an infinitesimal volume element in the tissue.The left-hand side of Equation (8) is the change in number of photons at position r, with direction s at time t. On the right-hand side, the first two terms describe the loss of- photons, due to escape over the volume boundaries, scattering into otherdirections or- absorption. The third term represents the gain through photons that are scattered from- other directions intodirection s, while the last term is gain due to a light source. It is assumed that all photons have the same energy and that allscattering is elastic. 45 | P a g e
19. 46. It is further assumed that the scattering is symmetric about the incident wave, which means that the phase function is afunction of the scattering angle alone, such that p(s,s)= p(), where is the angle- between the incident and the scatteredphoton. It is often useful to have an analytic expression for the phase function.The most popular phase function for light transport in biological tissue is the Henyey-Greenstein function(L.G Henyey,J.LGreenstein 1941)Where g, the anisotropy factor, is the mean cosine of the scattering angle . For nearly isotropic scattering, the value of g isclose to zero, while a g close to unity indicates a strongly forward directed scattering. Tissue is in general highly forwardscattering. Analytic solutions to the transport equation are only known for a few special cases (K.M Case andP.F Zwiefel1978). In practise, either numerical methods such as Monte Carlo simulations or expansion in spherical harmonics. TheMonte Carlo method simulates a migration of photon packages in a scattering and absorbing medium. The simulatedinteraction events of these photon packages are based on random samplings from probability distributions of the step sizebetween interaction events and scattering angles. For each scattering event, the light is also attenuated due to absorption.The trajectory of the photon package is followed until it exits through a boundary or is totally lost by absorption. The MonteCarlo method is useful in that it can be used for any geometry, including layered and inhomogeneous media, and for anyoptical properties. The main disadvantage is that, due to the statistical nature of the method, a large number of photonpackages have to be simulated, and requiring long computation times.46 | P a g e
20. 47. 4.2 Laser - Tissue InteractionFigure-4.2.1-Schematic diagram of laser-tissue interaction Laser follows Lambert Beer law when it inter-acts with biological tissues. Lambert Beer law I = Io 10-aX = absorption coefficient X = thickness of material/tissue Io = incident intensity I = transmitted intensity Extinction length = 1/ = L; where 90% of the intensity is absorbed, when light energy is reflected, transmitted, absorbed and scattered by interacting with biological tissues. Laser light can have the following effects with biological tissue: 1) Photochemical /Photodynamic effects 2) Photothermal effects 3) Mechanical effects 4) Photoablative effect. PhotochemicalLaser energy can interact directly or indirectly with chemical structures within tissue. Photobiomodulation (laserbiostimulation, "cold laser" therapy): Low level laser or narrowband light has been used with varying success to modulatecellular activity to achieve a biological effect such as stimulation of hair growth, collagen remodeling, accelerated woundhealing, etc. In most cases the mechanism of action remains unclear, although changes in mitochondrial activity or cellmembrane permeability may be responsible.47 | P a g e