RFShort Wave vs. Microwave vs. Ultrasonic Diathermy: Key Differences
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This article compares Short Wave Diathermy, Microwave Diathermy, and Ultrasonic Diathermy, highlighting the differences between these three types of diathermy treatments.
Introduction:
Diathermy, meaning “electrically induced heat,” is used in medicine for physiotherapy and surgery. High-frequency current (~100 KHz) generates heat to treat body tissues and muscles. Diathermy is considered a low-risk procedure. In physiotherapy, diathermy utilizes different waves, including short wave, microwave, and ultrasonic waves. The primary function of diathermy in physiotherapy is to heat tissues without significantly raising skin temperature. Diathermy is also valuable in neurosurgery and eye surgery.
Short Wave Diathermy
Figure 1: Short wave diathermy treatment method.
Short wave diathermy employs capacitor plates (pads) or an inductor coil to generate short waves for heating tissues.
Capacitor Method: Two pads or electrodes are placed on either side of the treatment area. The body part acts as a dielectric, forming a capacitor circuit. Applying short waves causes the capacitor to produce heat due to dielectric losses in the tissues.
Inductor Method: The body part being treated is placed inside a coil. Applying a short wave current to the coil heats the tissues.
Short wave diathermy is used to relieve pain and heal deep-seated sports-related injuries and generally doesn’t cause discomfort during or after treatment.
Microwave Diathermy
Figure 2: Microwave diathermy treatment method.
Microwave diathermy uses microwave frequencies ranging from 300 to 30000 MHz. The most common frequency is 2450 MHz. It utilizes a magnetron device with an antenna to generate microwave frequency waves. These waves are transmitted towards the body area being treated.
The technique is simple and doesn’t require pads, electrodes, or coils, as in short wave diathermy. Microwave frequency waves are absorbed to heat tissues to the desired depth.
Ultrasonic Diathermy
Figure 3: Ultrasonic diathermy treatment method.
Ultrasonic diathermy produces heat through the absorption of ultrasonic energy by certain tissues. This absorption creates high-speed mechanical vibrations within the cells of absorptive tissues, providing a micro-level massage.
A piezoelectric crystal generates ultrasonic energy when an oscillator output is applied. The depth of penetration can be controlled, enabling treatment of specific tissues.
Difference Between Short Wave, Microwave, and Ultrasonic Diathermy
The following table outlines the differences between Short Wave Diathermy, Microwave Diathermy, and Ultrasonic Diathermy:
| Comparison Parameters | Short wave diathermy | Microwave diathermy | Ultrasonic diathermy |
|---|---|---|---|
| Wave type | Electrostatic field (in capacitive method) and Electromagnetic field (in inductor method) | Electromagnetic (EM) waves | Ultrasound waves |
| Frequency and Wavelength | Frequency of 10 to 100 MHz at wavelength of 3 to 30 meters | Frequency of 300 to 30000 MHz at wavelength of 1 m to 1 mm | Frequency of 1 to 3 MHz range |
| Working principle | In capacitor-based diathermy, pads or electrodes are placed such that the body part to be treated is sandwiched between them and acts as a dielectric. Short waves are applied to produce heat due to dielectric losses in the tissues. In the inductor coil method, the body part to be treated is placed in an inductive coil. The current flowing within the coil produces a rotating field which generates eddy currents in the tissues. The eddy currents cause friction, and heat is produced. | A magnetron is used to generate microwave frequencies/wavelengths at specific values to focus on a target area for treatment. 2450 MHz with 12.33 cm, 915 MHz with 32.7 cm, and 433.9 MHz with 69 cm are used by microwave diathermy devices. | High-frequency sound waves (at 1 MHz and 3 MHz) are used to treat deep tissues. |
| Circuit components | As shown in Figure 1, it uses an inductor coil or capacitor-based circuits. | As shown in Figure 2, it uses a magnetron, transducer, timer circuit, etc. | As shown in Figure 3, it uses a piezo-electric transducer, timer, and intensity/frequency control circuit, etc. |
| Depth of penetration | Deep, up to 50 mm or 7 cm | More superficial than short wave type, up to 3 to 4.5 cm (depends on tissues with high or low fluid content) | 1 MHz for deep penetration up to 5 cm, 3 MHz for superficial penetration up to 2 cm |
| Test duration | 5 to 20 minutes depending on indications and dosage | 20 to 30 minutes | N/A |
