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Definition� Irradiation of tissues with radiation in the shorter wireless part of the spectrum (Hertzian

rays) i.e. the wave length is between infra red and short wave diathermy.

� The general frequency of microwave is between 300 to 30000MHz with wave length of 1 m

to 1 mm.

� Frequently used frequency and wavelength are,

Frequency Wavelength2450 MHz 12.25 cm915 MHz 32.7 cm433.92 MHz 69 cm

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Electromagnetic spectrum

1 101 102 103 104 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022

Radio & TV

Infra Red

Microwaves

Gamma-

Rays

X-Rays

Ultra

Violet

Microwaves

Non-ionising Radiation

(generally not so bad)

Ionising

Radiation

(generally bad)

Frequency (Hertz)Sreeraj S R

Fan and cathodeHeater controlcircuits

Powersupplyfrommains

Magnetron

MainsIntensity control

Reflector

Emitter

Antenna

Coaxial cable

Production

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Magnetron

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Microwave Diathermy Unit

� A= Power Switch

� B=Timer

� C=Output Meter (indicates output in watts)

� D= Power Output Level Knob

� E= Amber Light-Warming up / Red Light- Ready

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Physical behaviour

� Reflection

� Refraction

� Absorption, Grotthus Law

� the half-value depth for microwave is often

given as 3 – 4 cm.

� absorption of microwaves is much lower in fat

(half-value about 3.5 cm) and higher in the

vascular muscle tissue (half-value about 0.7

cm).Sreeraj S R

Applicators

� Circular Shaped Applicators

� Maximum Temperature At Periphery

� Rectangular Shaped Applicators

� Maximum Temperature At Center

� Contact applicators

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Physiological effects

� Consequence of tissue heating due to

o Ionic movement

o Dipole rotation

o Molecular distortion

� Strongly absorbed by tissues of high water

content

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Physiological effects

� Effects on metabolism

� Effects on blood supply

� Effects on nervous tissue

� Effects on muscular tissue

� Effects on sweat glands

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Therapeutic Effects

� Relief of pain

� Reduce muscle spasm

� Promote healing

� Infection

� Increase the extensibility

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Dosage

� 20 min for vascular adjustment

� If significant heating required 30 min would

be reasonable

� Intensity: the patient should feel mild and

comfortable warmth.

� Frequency: daily or on alternating day.

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Contra-indications

� Over malignant tissues.

� Over ischemic tissues

� Over wet dressings

� Metal implants.

� Pacemaker.

� Over growing bone.

� Male gonads: repeated irradiation can cause sterility.

� Hemorrhage.

� Tuberculous joints.

� Impaired thermal sensation.

� Unreliable patients.

� The eyes: cause cataract.

� Recent radiotherapy.

� Hypersensitivity to heat

� Acute infection or inflammation.

� Obesity: with 2450MHz microwave, there is danger of producing an excessive heat in the subcutaneous fat layer.

� Analgesic therapy: the thermalsensation diminished.

� Venous thrombosis.

� Pregnancy: heat applied to pelvisor hip in pregnancy may causehemorrhage or miscarriage.

� Menstruation.

� Acute dermatological conditions.

� Severe cardiac conditions.

� Blood pressure abnormalities.

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Principles of Application

� Preparation of patient

� Preparation of apparatus

� Preparation of part to be treated

� Setting up- Emitter should be positioned so that radiations strike the

surface at right angles

� Instruction and warning

� Application

� Termination

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Difference between SWD & MWD

SWD MWD

Frequency and

wavelength

• Frequency of 10 t0 100 MHz

• Wavelength of 3 to 30 m

• Frequency of 300 to 30,000 MHz

• Wavelength of 1 m to 1 mm

Therapeutic frequency

and wavelength

• Frequency of 27.12 MHz and

• wavelength of greater than 11

m

• Frequencies of 2450, 915 and 433.9 MHz

• wavelengths of 122.5, 330 and 690 mm

respectively

Circuits used • Machine circuit (produce HFCand amplify its intensity)

• Patient circuit

• Magnetron• Transducer circuit (with antenna &

reflector)

Fields used • Electrostatic and Electro-

magnetic

• Electro-magnetic

Factors affecting heat

absorption

• Water content

• spacing

• size of the condenser

• laws of reflection, refraction,

absorption and inverse square

• water content

• frequency

• Distance

• laws of reflection, refraction, absorption

and inverse square

Depth of penetration • deep, up to 50 mm or 7 cm • more superficial than SWD, up to 3-4

cm.

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Difference between SWD & MWD

SWD MWD

Advantages can heat through joints • can localize heat accurately• can do selective heating

Limitations • Complex application• risk of deep tissue burn• intensity can’t be monitored

• Can’t be used to heat deepstructures

• 1 aspect of body can be treated at atime

Treatment time and intensity

• 20 Minutes• Intensity - Mild comfortable warmth• Frequency is daily or alternate days

• 20 Minutes• Intensity - Mild comfortable

warmth • Frequency is daily or alternate days

Factors affecting heat absorption

• Water content• spacing• size of the condenser• laws of reflection, refraction,• absorption and inverse square

• water content• frequency• Distance• laws of reflection, refraction,

absorption and inverse square

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References

1. Electrotherapy Explained by Low and Reed

2. Textbook of Electrotherapy by Singh Jagmohan

3. http://en.wikipedia.org/wiki/Cavity_magnetron

4. http://www.powershow.com/view/13fe42-

MzA2M/Shortwave_and_Microwave_Diathermy_powerpoint_ppt_present

ation

5. Microwave Diathermy by Sagar Naik. physio4all

6. http://hyperphysics.phy-astr.gsu.edu/hbase/ems2.html#c4

7. Sheila Kitchen, S. and Bazin, S. (1996). Clayton’s electrotherapy (10th ed).

Philadelphia: W.B. Saunders Company.

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