Microwave diathermy

microwave diathermy,physiotherapy

2. Definition

= Irradiation of tissues with radiation in the shorter wireless part of the spectrum (Hertzian
rays) ie. the wave length is between infra red and short wave diathermy,

= The general frequency of microwave is between 300 to 30000Hz with wave length of ı m
toamm.

= Frequently used frequency and wavelength are,

Frequency Wavelength
2450 MHz 12.25 cm
915 MHz 32.7cm

433-92 MHz 69 cm

3. (

generally not

Sreeraj SR

Non-ionising Radiation

so bad)

lonising
Radiation
(generally bad)

4. Production

Fan and cathode
Heater control
circuits

Magnetron

Reflector

Antenna

5. Magnetron

Output couplin:
loop \ 1l Resonating cavity

\
al

¡W,
cop EN
anode biock
®
Oi

ae

— Leads to cathode

cathode à heater

Resonant cavity magnetron high-power
high-frequency oscillator

Coramic-antenna

Shield-cup

Resonator Antenna’ Magnet

6. 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

7. 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

8. Applicators

= Circular Shaped Applicators
» Maximum Temperature At Periphery
= Rectangular Shaped Applicators

» Maximum Temperature At Center

Sreeraj S R

9. Physiological effects

= Consequence of tissue heating due to

o lonic movement
o Dipole rotation
o Molecular distortion

10. Physiological effects

= Effects on metabolism
Effects on blood supply
= Effects on nervous tissue

= Effects on muscular tissue
= Effects on sweat glands

11. Therapeutic Effects

= Relief of pain
= Reduce muscle spasm
= Promote healing

= Infection

= Increase the extensibilit:

12. 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.

13. 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.

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 thermal
sensation diminished.

Venous thrombosis.

Pregnancy: heat applied to pelvis
ip in pregnancy may cause

hemorrhage or miscarriage.

Menstruation.

Acute dermatological conditions.

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14. 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

15. Difference between SWD & MWD
Sw

Frequency and + Frequency of 10 to 100 MHz + Frequency of 300 to 30,000 MHz
wavelength + Wavelength of 3 to 30 m + Wavelength of 1m to1mm

Therapeutic frequency * Frequency of 27.12MHzand + Frequencies of 2450, 915 and 433.9 MHz
and wavelength + wavelength of greater than 11 + wavelengths of 122.5, 330 and 690 mm
m respectively

Circuits used + Machine circuit (produce HFC Magnetron
and amplify its intensity) Transducer circuit (with antenna &
+ Patient circuit reflector)

Fields used + Electrostatic and Electro- Electro-magnetic
magnetic

Factors affecting heat Water content + water content

absorption spacing + frequency
size ofthe condenser + Distance
laws of reflection, refraction, + laws of reflection, refraction, absorption
absorption and inverse square and inverse square

Depth of penetration deep, up to 50 mm or7 cm * more superficial than SWD, up to 3-4
cm.

Sreeraj SR

16. Difference between SWD & MWD
ES mm

Advantages

Limitations

Treatment time

and intensity

Factors
affecting heat
absorption

can heat through joints

Complex application
risk of deep tissue burn
intensity can't be monitored

+ 20 Minutes

+ Intensity - Mild comfortable

warmth

+ Frequency is daily or alternate

days

+ Water content

* spacing

+ size of the condenser

+ laws of reflection, refraction,
absorption and inverse square

can localize heat accurately

can do selective heating

Can't be used to heat deep
structures

a aspect of body can be treated at a
time

20 Minutes

Intensity - Mild comfortable
warmth

Frequency is daily or alternate days

water content

frequency

Distance

laws of reflection, refraction,
absorption and inverse square

Sreeraj S R

17. References

1. Electrotherapy Explained by Low and Reed
2. Textbook of Electrotherapy by Singh Jagmohan
http://en.wikipedia.org/wiki/Cavity magnetron

http://www. powershow.com/view/13fe42-
MzA2M/Shortwave and Microwave Diathermy powerpoint ppt present
ation

5. Microwave Diathermy by Sagar Naik. physiogall
http://hyperphysics.phy-astr.gsu.edu/hbase/ems2.html#c4

7. Sheila Kitchen, S. and Bazin, S. (1996). Clayton's electrotherapy (10 ed).
Philadelphia: W.B. Saunders Company.