Prof.Dr. Gehan MosaadProf.Dr. Gehan Mosaad

At the end of this lecture the student At the end of this lecture the student must be able tomust be able to::

Define electrotherapy, electric current and Define electrotherapy, electric current and electromagnetic spectrum (EMS)electromagnetic spectrum (EMS)

Understand the characteristics of Understand the characteristics of electromagnetic radiationelectromagnetic radiation

Identify the different regions of EMSIdentify the different regions of EMS List Physical laws governing application of List Physical laws governing application of

electromagnetic radiationelectromagnetic radiation

DefinitionsDefinitions ElectrotherapyElectrotherapy can be defined as the treatment of can be defined as the treatment of

patients by electrical means. It also means that electrical patients by electrical means. It also means that electrical forces are applied to the body leading to physiological forces are applied to the body leading to physiological changes for therapeutic purpose.changes for therapeutic purpose.

Electric currentElectric current is the flow of electric charge through a is the flow of electric charge through a medium. This charge is carried by moving electrons in a medium. This charge is carried by moving electrons in a conductor as wire, or by ions in electrolyte or by both conductor as wire, or by ions in electrolyte or by both ions and electrons as in a plasma. ions and electrons as in a plasma. The unitThe unit for for measuring the rate of flow of electric charge is the measuring the rate of flow of electric charge is the ampere. ampere.

Electromagnetism:Electromagnetism: Electric current produces a Electric current produces a magnetic field which can be visualized as pattern of magnetic field which can be visualized as pattern of circular field lines surrounding the wire. circular field lines surrounding the wire.

Electromagnetic SpectrumElectromagnetic Spectrum

Electromagnetic spectrum It is the distribution of electromagnetic It is the distribution of electromagnetic

radiation according to the energy ( or radiation according to the energy ( or according to wavelength or frequency).according to wavelength or frequency).

Electromagnetic radiation It is composed of electric and magnetic fields It is composed of electric and magnetic fields

that are oriented perpendicular to each other that are oriented perpendicular to each other and to the direction of travel or radiation. and to the direction of travel or radiation.

It covers a broad spectrum of wavelengths and It covers a broad spectrum of wavelengths and frequencies.frequencies.

Characteristics of electromagnetic radiation

All electromagnetic radiations have a constant velocity in space 300 million meters per second (speed of light) They transport energy through spaceThey are transmitted without the need of a medium or conductor (self propagating).They are transverse waves, may be absorbed, reflected and/or refracted depending on the medium that they strike.Their direction of travel is always in a straight line.Electromagnetic radiation is categorized according to its wavelength and frequency which are inversely proportional to each other.

The relation between wavelength and frequencyThe relation between wavelength and frequency

Wavelength:Wavelength: The horizontal distance from one The horizontal distance from one wave beak to the same point on the next wave.wave beak to the same point on the next wave.

Frequency:Frequency: The number of cycles that occurs The number of cycles that occurs in one second (cycle /second). It is measured in in one second (cycle /second). It is measured in Hertz (Hz).Hertz (Hz).

The relation between wavelength and frequency The relation between wavelength and frequency are governed by the formula: are governed by the formula:

Speed of light = Wavelength X frequencySpeed of light = Wavelength X frequency Because the velocity is constant, there is inverse Because the velocity is constant, there is inverse

relationship between the wavelength and relationship between the wavelength and frequency for electromagnetic wave( the higher frequency for electromagnetic wave( the higher the frequency the shorter the wavelength).the frequency the shorter the wavelength).

The radiating energy is The radiating energy is directlydirectly proportional to proportional to the the frequencyfrequency and and inverselyinversely to the to the wavelengthwavelength

Regions of electromagnetic spectrum

Ionizing rangeIonizing rangeElectromagnetic radiation such as x ray and gamma rays is ionized radiation.It can break molecular bonds to form ions and can easily penetrate the tissue and deposit its energy within the cell. If the energy is sufficiently high, ionizing radiation can also inhibit cell division and eventually killing the cell. Energy within the ionizing range is used in very small doses for imaging (diagnostically in X ray) or to destroy tissues (therapeutically in radiation treatment) for some forms of cancer.

Regions of electromagnetic spectrum

Non ionizing rangeNon ionizing range

Low frequency electromagnetic radiation is non Low frequency electromagnetic radiation is non ionizing and can not break molecular bonds or ionizing and can not break molecular bonds or produce ions and so can be used for therapeutic produce ions and so can be used for therapeutic medical applications.medical applications.

It includes: It includes: 1-1- Light spectrumLight spectrum as visible light, infrared & as visible light, infrared &

ultravioletultraviolet 2-2- DiathermyDiathermy as shortwave and microwaveas shortwave and microwave 3-3- Electric currentsElectric currents as electrical stimulating as electrical stimulating

current current

Physical laws governing the Physical laws governing the application of electromagnetic application of electromagnetic

radiationradiation

11 - -ReflectionReflection

Reflection is the return of the electromagnetic wave from an object. When electromagnetic radiations strike a surface part of the energy is reflected back in the same plane of the incident angle.

Incident angle = Reflected angle The amount of reflection decrease when the

radiation striking the surface at right angle.

22--RefractionRefraction

Refraction Refraction refers to the change in refers to the change in direction of the radiation vector when it direction of the radiation vector when it passes from one medium to another of passes from one medium to another of a different density.a different density.

It depends on the It depends on the mediamedia involved and involved and the the angle angle of incidence of the raysof incidence of the rays

So, the rays striking the surface at right So, the rays striking the surface at right angle continue in the same straight angle continue in the same straight lines.lines.

33 - -Absorption and penetrationAbsorption and penetrationAbsorption is reciprocal of penetration as the greater the penetration the lesser the absorption.

Radiation must be absorbed to facilitate the changes within the body tissue. Absorption depends on the nature and type of tissue

The penetration of energy into a medium is dependent upon: Wavelength and frequency Angle of incidence Nature of medium Intensity of radiation

44 - -ScatteringScattering

Radiation passing through non-homogenous Radiation passing through non-homogenous matter may be partly scattered. matter may be partly scattered.

The amount of scattering depends on the The amount of scattering depends on the wavelength of radiation. wavelength of radiation. LongerLonger wavelength wavelength

( lower frequency) are scattered ( lower frequency) are scattered less less than the than the shorter ones (higher frequency)shorter ones (higher frequency)

55 - -Inverse square lawInverse square lawThis law state that the intensity of radiation is

inversely proportional to the square of the distance between the source of the energy and the tissues.

The intensity of the energy striking the tissue depends on the distance between the source and the tissue.

According to the formula : E = Es / D² E = Es / D² where: E = the amount of energy received by the tissue Es = the amount of energy produced by the source D² = the square of the distance between the tissue

and the source.

66--Cosine lawCosine law This law state that the intensity of radiation varies

as the cosine of the angle of incidence.

Effective energy = Energy X cosine of the angle of incidence

Electromagnetic energy is most efficiently transmitted to the tissue when it strikes the body at right angle. As this angle of incidence deviates away from 90 degree, the intensity of radiation affecting the tissue decrease.

77--The Arndt-Schulz lawThe Arndt-Schulz lawThis law state that, no physiological changes no physiological changes

can occur in body tissues, if the amount of can occur in body tissues, if the amount of energy absorbed is insufficient to stimulate energy absorbed is insufficient to stimulate the absorbing tissues.the absorbing tissues.

According to this law, a certain According to this law, a certain minimum minimum intensityintensity of electromagnetic radiation is of electromagnetic radiation is needed to needed to initiate a biological process.initiate a biological process.

Beyond a certain level, Beyond a certain level, stronger intensity stronger intensity will will have a progressively less positive effect and have a progressively less positive effect and become inhibitorybecome inhibitory. .