Prof.Dr. Gehan Mosaad

At the end of this lecture the student must be able to:  Define electrotherapy, electric current and electromagnetic spectrum (EMS)  Understand the characteristics of electromagnetic radiation  Identify the different regions of EMS  List Physical laws governing application of electromagnetic radiation

Definitions  Electrotherapy can be defined as the treatment of patients by electrical means. It also means that electrical forces are applied to the body leading to physiological changes for therapeutic purpose.  Electric current is the flow of electric charge through a medium. This charge is carried by moving electrons in a conductor as wire, or by ions in electrolyte or by both ions and electrons as in a plasma. The unit for measuring the rate of flow of electric charge is the ampere.  Electromagnetism: Electric current produces a magnetic field which can be visualized as pattern of circular field lines surrounding the wire.

Electromagnetic Spectrum Electromagnetic spectrum It is the distribution of electromagnetic radiation according to the energy ( or according to wavelength or frequency). It is the distribution of electromagnetic radiation according to the energy ( or according to wavelength or frequency). Electromagnetic radiation  It is composed of electric and magnetic fields that are oriented perpendicular to each other and to the direction of travel or radiation.  It covers a broad spectrum of wavelengths and 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 space They 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 frequency  Wavelength: The horizontal distance from one wave beak to the same point on the next wave.  Frequency: The number of cycles that occurs in one second (cycle /second). It is measured in Hertz (Hz).  The relation between wavelength and frequency are governed by the formula: Speed of light = Wavelength X frequency Speed of light = Wavelength X frequency Because the velocity is constant, there is inverse relationship between the wavelength and frequency for electromagnetic wave( the higher the frequency the shorter the wavelength). Because the velocity is constant, there is inverse relationship between the wavelength and frequency for electromagnetic wave( the higher the frequency the shorter the wavelength).  The radiating energy is directly proportional to the frequency and inversely to the wavelength

Regions of electromagnetic spectrum Ionizing range Electromagnetic 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 range Low frequency electromagnetic radiation is non ionizing and can not break molecular bonds or produce ions and so can be used for therapeutic medical applications. Low frequency electromagnetic radiation is non ionizing and can not break molecular bonds or produce ions and so can be used for therapeutic medical applications. It includes: 1- Light spectrum as visible light, infrared & ultraviolet 1- Light spectrum as visible light, infrared & ultraviolet 2- Diathermy as shortwave and microwave 2- Diathermy as shortwave and microwave 3- Electric currents as electrical stimulating current 3- Electric currents as electrical stimulating current

Physical laws governing the application of electromagnetic radiation

1- Reflection   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.

2-Refraction Refraction refers to the change in direction of the radiation vector when it passes from one medium to another of a different density. It depends on the media involved and the angle of incidence of the rays So, the rays striking the surface at right angle continue in the same straight lines.

3- Absorption and penetration   Absorption 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

4- Scattering Radiation passing through non-homogenous matter may be partly scattered. The amount of scattering depends on the wavelength of radiation. Longer wavelength ( lower frequency) are scattered less than the shorter ones (higher frequency) ( lower frequency) are scattered less than the shorter ones (higher frequency)

5- Inverse square law   This 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.  E = Es / D²  According to the formula : 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.

6-Cosine 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.

7-The Arndt-Schulz law  no physiological changes can occur in body tissues, if the amount of energy absorbed is insufficient to stimulate the absorbing tissues.  This law state that, no physiological changes can occur in body tissues, if the amount of energy absorbed is insufficient to stimulate the absorbing tissues.  According to this law, a certain minimum intensity of electromagnetic radiation is needed to initiate a biological process.  Beyond a certain level, stronger intensity will have a progressively less positive effect and become inhibitory.