Electromagnetic modalities lec

what are Electromagnetic Modalities ?

• diathermy

• photobiomodulation (LASER)

what is Diathermy ?

• The application of high-frequency electromagnetic energy

  • primarily used to generate heat in body tissues

• Can be delivered continuously or through regular pulses or bursts of radiofrequency energy

what diathermy heat is produced by?

• Resistance of the tissue to the passage of the energy

• By friction between two surfaces which converts kinetic energy to thermal energy

Diathermy may also be used to produce ?

nonthermal effects

As a therapeutic agent may be classified as two distinct modalities:

o Shortwave
o Microwave

• A shortwave diathermy unit is basically a radio transmitter
• The Federal Communications Commission (FCC) assigns three frequencies to shortwave diathermy units:

o 27.12 MHz with a wavelength of 11 m
o 13.56 MHz with a wavelength of 22 m
o 40.68 MHz with a wavelength of 7.5 m (rarely used)

• A __ unit consists of a power supply that provides power to a radio frequency oscillator

• oscillator provides stable, drift-free oscillations at the required frequency

shortwave diathermy

The output resonant tank tunes in the patient as part of the circuit allowing?

maximum power to be transferred to the patient

The power amplifier generates the power required to drive the

different types of electrodes

Two types of SWD:

o Capacitive (Electric field method)
o Inductive (Magnetic Field Method)

SWD Can be delivered to body tissues either:

o Continuously
o Pulsed

• Uses an applicator system that requires that the patient’s tissues become part of a capacitor

• Uses a rapidly alternating high-frequency current (AC) that creates a voltage differential between two electrodes

• Electrodes are placed either one on each side

  • Or both on the same side of the part of the body

• Each of the two electrodes has a different polarity

• The patient is placed between two electrodes or plates and becomes part of the circuit

Capacitive SWD

Capacitive SWD Uses a rapidly alternating high-frequency current (AC) that creates a

voltage differential between two electrodes

for capacitive SWD electrodes are placed where?

• either one on each side

• Or both on the same side of the part of the body

• Each of the two electrodes has a different polarity

• The patient is placed between two electrodes or plates and becomes part of the circuit

• Have adjustable arms with metal plates (electrodes) at their ends that deliver electromagnetic radio wave

• Resistance to this current flow in the tissues results in tissue heating

• Have a glass or plastic guard surrounding each metal plate to prevent contact between the electrode and the patient’s skin

• An electrical burn may occur if either the therapist’s or the patient’s skin contacts the bare metal plate of the diathermy device

• A single layer of terrycloth toweling should be placed between the plate guards and the patient’s skin to prevent concentration of the electric field on perspiration that may accumulate on the skin.

Capacitive SWD Application

Capacitive SWD Application Have adjustable arms with metal plates (electrodes) at their ends that deliver ?

electromagnetic radio wave

Resistance to this current flow in the tissues results in

tissue heating 

Have a glass or plastic guard surrounding each metal plate to prevent contact between

the electrode and the patient’s skin

An __ may occur if either the therapist’s or the patient’s skin contacts the bare metal plate of the diathermy device

electrical burn

A single layer of __ should be placed between the plate guards and the patient’s skin to prevent concentration of the electric field on perspiration that may accumulate on the skin.

terrycloth toweling

The plastic plate guard should be located about __ from the skin for optimal heating

2 to 10 cm (1 to 3 inches)

Proper positioning of the plate and guard in relation to the skin provides effective absorption of thermal energy and safe heating of tissues

As the plate-to-skin distance increases, heat perception decrease

fat tissue may be heated considerably more than muscle when both tissues are exposed to the capacitive SWD electric field

Capacitive plates should not be placed over areas of thick subcutaneous fat

Capacitive SWD plates can be positioned in two possible arrangements:

o Contraplanar
o Coplanar

what is contraplanar?

The plates are placed on each side of the body part so that the body part creates a biological capacitor

what is coplanar?

The plates be positioned parallel on the same body surface rather than placing the body part between the plates

Coplanar arrangement is best for treating:

o Lumbar Spine
o Pelvis

Contraplanar arrangement is best for treating

extremities

Shortwave Diathermy Inductive Method requires an?

inductive applicator that creates an oscillating magnetic field that induces “eddy” currents in body tissue

Eddy currents flow along pathways of higher conductivity causing?

heating in these tissues

The greatest density of eddy current activity occurs in low-impedance (high-conductivity) tissues containing the highest electrolyte content

Causes greatest heating in skeletal muscle and blood

Less heating occurs in

high-impedance tissues such as skin and fat

What is an Eddy Current?

• A magnetic field generates small circular electrical fields

• Fields vibrate and increase cell membrane permeability, which causes heat.

• Creates a stronger magnetic field than an electrical field.

•  Induction diathermy relies primarily on a magnetic field to produce changes in tissue

• Friction between the rotating dipoles results in an increase in kinetic energy, which results in heat (thermal effects)

• With inductor electrodes the patient is in a magnetic field and is not part of the circuit

Shortwave Diathermy Inductor Electrodes

Shortwave Diathermy Inductor Electrodes creates a?

stronger magnetic field than an electrical field.

Induction diathermy relies primarily on a

magnetic field to produce changes in tissue

Friction between the rotating dipoles results in an

increase in kinetic energy, which results in heat (thermal effects)

Two types of inductive coil applicators can be used:

o Drums
o Sleeves

There are two types of drum applicators:

• monode 

• diode

A monode is a drum used to

• treat a single body surface

• Requires a single layer of terrycloth toweling to create additional spacing and moisture absorption from the skin

The diplode is a

• hinged drum that allows one or more body part surfaces to be treated simultaneously.

• Approximately 1 cm of terrycloth toweling is recommended to separate the diplode applicator from the patient’s skin because the coil is closer to the treatment surface

• An induction sleeve is a new method of delivering diathermy to a patient

• Deliver shortwave diathermy at a power of 35 W and a frequency of 13.56 MHz

• Sleeves are designed to fit around a body part

  • Heating ability is limited to moderate tissue temperature increases

• Increases ease of application

• It is important that the cables not touch each other because they will short out and cause excessive heat buildup

SWD Inductive Coils

__ on shortwave diathermy units vary  considerably from one unit to another

control panels 

Most modern shortwave diathermy units allow the clinician to select:

o average power
o pulse width
o frequency

The amount of energy absorbed by the tissue determines

change in tissue temperature

• Most diathermy devices today are either PSWD or have both continuous and pulsed modes

  • use the inductive method with a drum electrode

• Bursts of electromagnetic waves are created by interrupting the flow of continuous waves generated by the device

  • Pulse duration is in a range usually from 20 to 400 microseconds
    (μsec).

• The peak pulse power (the power in watts delivered during a pulse) ranges between 100 and 1,000 W in most devices that provide PSWD

• The interpulse interval or off time depends on the pulse repetition rate, which ranges between 100 and 800 Hz

• Average power output >38 W will cause increase in temperature

Pulsed Shortwave Diathermy (PSWD)

Pulsed diathermy is claimed to have

therapeutic value

• produces nonthermal effects with minimal thermal physiologic effects

Pulsed shortwave diathermy can also have

thermal effects

• When used with intensities that create an increase in tissue temperature

It has been suggested that a measurable heating effect can occur at power levels which are greater than

5 watts mean power

• In clinical practice, the heating effect on the body’s tissues depends on the average power of the device. The average power can be determined by the following equation:

• peak power (W)×pulse duration (s) ×pulse frequency=average power

• Example: if the peak power of a PSWD device is 250 W, the pulse duration is .0004 second, and the pulse frequency is set at 145 Hz, the average power is 14.5 W

Calculating Mean Power

• is seldom used as a clinical treatment modality by clinicians

• Has two FCC-assigned frequencies in this country

  • 2456 MHz (requires airspace b/w electrode and skin)

  • 915 MHz

Microwave Diathermy

Microwave has a much higher frequency and a

• shorter wavelength than shortwave diathermy

  • will not penetrate as deep as SWD or ultrasound

Microwave diathermy cannot penetrate the

fat layer as well as shortwave diathermy

SWD is preferred over MWD because of

greater depth of heating and a more predictable heat distribution pattern.

Selecting Diathermy Parameters

• The most critical factor that determines whether a shortwave diathermy unit will increase tissue temperature is the amount of energy absorbed by the tissue

• The power output of a shortwave diathermy unit should produce sufficient energy to raise the tissue temperature into a therapeutic range

• As pulse rate, pulse width, and average watts increase, tissue temperature increases as follows during a 15–20 minute treatment time:

• A 1°C increase occurs with an average power output of 12 W, pulse rate 800 pps, burst duration 100 μs, and interburst interval 850 μs.

• A 2°C increase occurs with an average power output of 24 W, 800 pps, burst duration 200 μs, and interburst interval 850 μs.

• A 3°C increase occurs with an average power output of 36 W, 800 pps, burst duration 300 μs, and interburst interval 850 μs.

• 4°C increase occurs with an average power output of 48 W, 800 pps, burst duration 400 μs, and interburst interval 850 μs.

Selecting Diathermy Parameters

• A 20-minute treatment all that is necessary to reach vigorous heating in deep tissue

• Vigorous heating = 104°F, or 40°C, from a baseline temperature of (98.6°F or 37°C)

• When a vigorous heating protocol was applied for 20 minutes, average tissue temperature in the center of the treatment area increased an average of 4.5°C

• average temperature 5 cm toward the periphery only increased an average of 3°C

Treatment Time

__ treatment all that is necessary to reach vigorous heating in deep tissue

20 minute 

Vigorous heating =

104°F, or 40°C, from a baseline temperature of (98.6°F or 37°C)

__ in the radiofrequency range are nonionizing radiation

Electromagnetic waves

__ delivers only a fraction of the energy level required to produce ionization in tissue

Radiofrequency energy

Energy at a frequency of 100 MHz (in the FM radiofrequency band)

approximately 300 million times too weak to produce ionization

• Increased tissue temperature
• Heats deeper than superficial agents (such as hot packs), and heats larger and deeper areas compared to ultrasound
• Increase blood flow
• Vasodilation
• Relaxation
• Increased metabolism
• Decreased muscle spasm
• Reduced pain
• Realignment of collagen fibers and collagen content to increase tensile strength

SWD thermal Effects

• Pulsed shortwave diathermy at a very low power (10 watts) has also been used for its nonthermal effects in the treatment of soft tissue injuries and wounds

• Facilitate tissue healing by inducing a magnetic field which reactivates the sodium-potassium pump

  • restoring cell membrane potential which reestablishes normal polarity by returning normal ionic balance

Diathermy Nonthermal Physiological Effects

• Repolarization of damage cells
• Acceleration of cell growth
• Reestablishment of sodium pump
• Increased microvascular perfusion
• Improved cell function
• Increased white blood cells at wound site

SWD Nonthermal Effects

Precautions to Diathermy

Contraindications to Diathermy

• magnetic field effect 

• electrical field 

  • cell membrane permeability owing to electrical effect on cell Ca+ gating

PSWD

• acoustic streaming

• stable cavitation 

• micromassage 

• cell membrane permeability owing to mechanical effect on cell Ca+ gating

ultrasound

• a few more contraindications 

• no couplant needed 

• can be applied over most clothing 

• easy to use 

• less affordable clinician can attend to other duties 

• heats large areas 

• retain heat two to three times longer 

SWD

• a few contraindications

• couplant required 

• possible disrobing 

• easy to use 

• affordable 

• monitoring by clinician 

• heats small areas 

• retain heat

ultrasound

• can heat tissues 3-5 cm deep to > 40 degrees celsius 

• heat large areas 

• long stretch /thermal window 

  • 5-10 minutes 

• less mess 

• can apply over some clothing

PSWD

• can heat tissues 3-5 cm deep to > 40 degrees celsius 

• heats small areas 

• short stretch/thermal window 

  • 5-10 minutes

ultrasound

• Increased Angiogenesis and Neovascularization-Oxygen to injured tissue

• Increased Collagen Production-good alignment reduces internal scar and enhances elasticity

• Muscle regeneration-repair of damaged fibers leading to regeneration

• Decreases inflammation and edema-increases macrophages

• Nerve Regeneration, Cartilage Production, and Bone Formation-growth factors, chondrocytes and osteocyte development

Indications for LASER

What are approved indications?

• Indications that are approved by the FDA (Very Specific)
o Increase in local circulation
o Relief of minor muscle and joint ache, pain, and stiffness
o Relaxation of muscle tissue
o Relief of spasms
o Relief of arthritis associated minor pain/stiffness

• Therapeutic use is based upon photons being absorbed into body tissues, triggering biochemical effects in cells

  • Examples: laser, light-emitting diode (LED), and superluminescent diode (SLD)

• Light exposure has been shown to stimulate the production of ATP and augment RNA synthesis in body cells

Electromagnetic Radiation: Lasers and Light

Light exposure is also believed to

• Affect calcium channels in body cells
•Promote the formation of collagen by stimulating fibroblasts
•Control inflammation by decreasing inflammatory cells
• Inhibit growth of microorganisms
• Promote vasodilation and formation of granulation tissue
•Affect nerve conduction velocity
•Affect nerve regeneration

Photobiomodulation Other terms are used synonymously

o Phototherapy
o Biostimulation
o Laser Therapy
• LASER = Light Amplification by Stimulated Emission Radiation

• A form of electromagnetic energy that has wavelengths and frequencies that fall within the infrared and visible light portions of the electromagnetic spectrum

• Electromagnetic light energy is transmitted through space as waves that contain tiny “energy packets” called photons

• Wavelengths are typically between 600-1200 nm

  • Longer wavelengths penetrate better

• Water has a high absorption between 1200-2000 nm

• Melanin has high absorption between 400-600 nm

Physics of LASERs

The laser light is emitted in an organized manner

Differing from the random pattern from incandescent and fluorescent light sources

Three properties distinguish the laser:

o Conherence
o Monochromaticity
o Collimation

what is Coherence?

The individual light waves are in phase and aligned with one another in space and in time

what is Monochromaticity?

o Refers to the specificity of light in a single, defined wavelength
o If on the visible light spectrum, it is only one color

what is collimation?

o There is minimal divergence of the photons in the laser beam
o photons move in a parallel fashion

The four most commonly used lasers are:

o Helium neon (HeNe)
o gallium arsenide (GaAs)
o gallium aluminum arsenide (GaAlAs)
o neodymium-doped yttrium aluminum garnet (Nd:YAG)

• Classification is by risks associated with exposure-higher the higher the risk

• PTs typically use low level lasers

  • High level Class 4 are an option (>500mW)

• Class 3B<500mW is consider low level

  • Lasers are a point or cluster

classification of LASERs?

• Wavelength (nm)
• Duty cycle (%) and frequency (Hz)
• Beam size (cm)
• Power and irradiance (W/cm2)
• Treatment time (s)
• Fluence (J/cm2)
• Total energy (J)

Photobiomodulation Treatment Parameters

• Wavelength determines the color of light
• Is constant for device

wavelength (nm)

• Duty cycle is similar to ultrasound or diathermy

• Duty cycle equals the on-time and off-time of the light

  • (Time on/(Time on + Time off))/100

• If the light is pulsed, the light’s frequency should be reported

  • Current clinical trials suggest that pulsed light may be superior to continuous PBM

Duty cycle (%) and frequency (Hz)

• It’s the radius of the light aperture.

• Size of the beam effects PBM irradiance.

  • Irradiance = Device Power (W)/Beam Size (cm2)

beam size (cm)

Irradiance = Device Power (W)/Beam Size (cm2)
o Usually reported in W/cm2

Power and irradiance (W/cm2)

• Reported in seconds

• Maybe reported in seconds/spot or total treatment time during a scanning mode

• Should be determined for each device based on the device’s irradiance and the desired fluence

Treatment time (s)

• Often referred to as the PBM dose

• Represents the number of photons delivered per unit area of tissue

  • Fluence (J/cm2) = Irradiance (W/cm2) × Time (s)

Fluence (J/cm2)

• The total energy delivered to the tissue

• Total energy (J) = fluency (J/cm2) x beam size (cm2)

• Currently, there is no consistency in reporting fluency or total energy.

  • World Association of Laser Therapy (WALT) has created specific guidelines based on 780- to 860-nm and 904-nm wavelengths

Total energy (J)

laser precuations

LASER Contraindications

• Class II and higher can cause damage to eye

• Class 3b and IV lasers require both the clinician and patient to wear protective eyewear when devices are being used

  • Treatments should be performed in private room that protects others

• Eyewear is unit specific and is made for the associated wavelength

  • DO NOT wear protective eyewear designed for other units

LASER Safety

• The laser, parameters, and treatment technique selected will depend on the desired treatment effect

• The wavelength of the laser will impact the penetration depth of the light

• The laser’s power intensity and the tissue properties of the chosen treatment area play a role in the light being reflected or absorbed.

LASER Parameters

• The goal of laser therapy is to supply a sufficient amount of light energy to the designated treatment area for a period of time

• It is important when setting up or documenting a treatment you consider all the parameters

• The power output of a laser device is measured in watts (W) or milliwatts (mW), which is 10 −3 watts

• A watt describes the amount of energy released by the laser device per second

• W = J/Sec

• Laser energy density is determined by knowing the surface area of the applicator probe tip and would be measured in J/cm2

• Laser dosimetry is often measured as total joules per treatment session or in joules per treatment point or body surface area depending on the mode of application

LASER Parameters

• The World Association for Laser Therapy (WALT) has published recommendations to help clinicians determine appropriate parameters for different pathologies

  • They recommend daily treatments for 2 weeks or laser treatments every other day for 3–4 weeks.

• The current WALT guidelines indicate greater energy is needed for the GaAlAs lasers from 780 to 860 nm compared to the superpulsed GaAs lasers at 904 nm

Selecting Dose