Microwave Diathermy

By

Prof.Dr. Gehan Mosaad

At the end of the lecture the student should be able to

Understand physics and properties of MWD Know different directors of MWD Identify therapeutic effects, indications,

contraindications of MWD Recognize dangers and precautions with MWD Know the difference between SWD and MWD Analyze and discuss different cases

Properties of Microwaves Microwave diathermy (MWD), is a form of

electromagnetic radiations lying between shortwave and infrared waves.

Microwave diathermy does not penetrate as deep as shortwave diathermy.

The energy is first absorbed at the surface of the body (skin) and a part of it penetrate and absorbed in deep tissues.

It generates Strong Electrical Field and relatively Little Magnetic Field

Frequency and wavelength

Microwave has a much higher frequency and a shorter wavelength than shortwave diathermy.

The general frequency of microwave is between 300 MHz to 300 GHz with wave length of 10 mm to 1 meter.

The therapeutic microwave generators used frequency of 2450MHz with wave length of 122.5mm.

Microwave Production and Device

The generator used to produce microwaves has three main components:

1- A multi-cavity magnetron valve 2- A coaxial cable 3- A director.Mechanism of MW production The magnetron produces a high frequency alternating

current which is carried by coaxial cable to the transducer (director).

The coaxial cable transmits the energy to the director whereas a radiating system comprising an antenna within a reflector that is used to direct the microwave to the patient.

Microwave Production and Device

The alternating current in the antenna produces an electromagnetic field that is directed toward the tissue by a curved reflecting director surrounding the antenna.

The presence of a director and the short wavelength of microwave radiation allow this type of diathermy to be focused and applied to small, defined areas.

Therefore these devices can be useful during rehabilitation when only small areas of tissue are involved.

Production of microwave

Directors Used in Microwave Directors Used in Microwave ApplicationsApplications

Circular directors

- The heating pattern is more intense around the outer portion than the centre.

- There are small and large

Rectangular directors

The heating pattern tends to be more concentrated in the center of the treated area.

Biophysics of MWD MWD tend to be reflected and scattered at different

interfaces as air-skin, skin-fat, and the fat-muscle which limit its penetration into the tissues.

Because of the spreading of MW, the superficial tissues tend to be heated more than deeper tissues.

Depth of penetration depends on the frequency of the wave and the medium. The effective penetration of 2450MHz is approximately 3 cm.

Mechanism of heat production by MWD is the same as SWD

Therapeutic Effects of Microwave Therapeutic Effects of Microwave DiathermyDiathermy

Pain: MWD is useful in the treatment of traumatic and rheumatic conditions affecting superficial muscles, ligaments and small superficial joints.

Muscle spasm: which may be reduced directly by MWD or may be reduced by relieving of pain.

Inflammation: MWD reduces inflammation by increase blood supply that will increase venous return from the inflamed area and aids the reabsorption of edema exudates.

Therapeutic Effects (cont.)Therapeutic Effects (cont.)

Delayed healing: MWD promotes healing of open skin by increase cutaneous circulation.

Infection: MWD can control the chronic infection by increasing the circulation.

Fibrosis: The heating effect of MWD increase the extensibility of fibrous tissues such as tendons, joint capsules and scars.

Indications of MWDIndications of MWD- The clinical indications for MWD are, more or less, similar to

those for SWD. - MWD may be preferable to SWD when more concentrated or

localize heating is needed. Musculoskeletal disorders: - Sprain - Muscle & tendon tear - Strain - Degenerative joint disease - Joint stiffness in superficial joints - Capsular lesions. Superficial inflammatory or infective conditions : - Tenosynovitis - Bursitis - Synovitis - Abscess - Infected surgical incisions

Contra-indicationsContra-indications Over malignant tissues. Over ischemic tissues. Over wet dressings and adhesive tapes. Metal implants. Pacemaker. Over growing bone. Male gonads: repeated irradiation can cause

sterility. Hemorrhage. Impaired thermal sensation.

Contra-indications (cont.)Contra-indications (cont.) Recent radiotherapy. Hypersensitivity to heat. Acute infection or inflammation. Venous thrombosis or phlebitis. Pregnancy: heat applied to pelvis or hip in

pregnancy may cause hemorrhage or miscarriage.

Acute dermatological conditions. Severe cardiac conditions.

Precautions & DangersPrecautions & Dangers

The same as SWD, but it is recommended to avoid the presence of metal within the treatment field (4 feet) because of scattering and reflection of MWD

Due to scattering and reflection of MWD to the surrounding environment, it has been associated with high incidence of miscarriages among female therapists who regularly operate these units than SWD.

The eyes: MWD may cause cataract.

Precautions & Dangers(cont.)Precautions & Dangers(cont.)

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

Burn: There is an increasing of risk of excessive heating and burning with the using of MWD due to:

1. Shallow depth of penetration2. Reflection at tissue interfaces3. Potential standing waves

Dosage of MWDDosage of MWD

Duration of treatment: 20 minutes is the optimum.

Intensity: the patient should feel mild and comfortable warmth.

Frequency: daily or on alternating day.

Microwave Device

Comparison of different types of diathermy

TypeThermal SWDThermal MWD

Non thermal SWD

Frequency27,12MHZ2450MHZ27,12MHZ

ApplicatorInductive coilCapacitive plate

MagnetronInductive coil drum

Incident fieldElectromagneticElectricElectromagneticElectromagnetic

Tissues most affected

Deep and superficial

SuperficialSmall areasDeep and superficial

Comparison of heat distribution by different diathermy applicators and

ultrasoundTypeFatMuscleBone

Inductive coilMinimumMaximumNone

Capacitive plate

MaximumModerateLow

Magnetron MWD

MaximumMaximumNone

UltrasoundSlightMaximumNone

Case studyCase 1

MS is a 50-year-old female. She has been diagnosed with adhesive capsulitis of the right shoulder and has been referred to physical therapy. She complains of shoulders stiffness. The objective exam reveals restricted right shoulder active and passive range of motion.

Case 2

AB is a 24-year-old male, football player who suffered from left ankle inversion sprain approximately 48 hours ago. He complains of moderate pain and swelling at the lateral ankle.