OMNISWD
®
USER MANUAL
15
COPYRIGHT © 2017, ACCELERATED CARE PLUS CORP., ALL RIGHTS RESERVED
MODES OF OPERATION
Thermal Effect Variables
I.
Tissue Energy Dissipation
The extent of the thermal effect in tissue is based on the tissue energy dissipation.
Specific Absorption Rate
(
SAR
)
is a measure of the rate at which energy is absorbed by the human body when exposed to a radio frequency (RF)
electromagnetic field. It is defined as the power absorbed per mass of tissue and has units of watts per kilogram
(W/kg).
ACP has performed testing on human subjects in the triceps Surae (Gastrocnemius) muscle group using to determine
the rate of heating and establish dosage for raising the tissue temperature by 1, 2, or 4 degrees C. This also allowed
the calculation of the SAR as follows:
In a
human tissue load consisting mainly of muscle the temperature of muscle at 2.5cm depth changes by 4 degrees
C over 15 minutes. This represents 900 seconds or a rate of .00444 degrees C per second.
Specific Heat of Water and Muscle
The specific heat of water is 4.181 Joules/gram (at 20
o
C), i.e. if 4.181 Joules are applied to 1 gram of water the
temperature will increase by 1 degree C. Muscle tissue specific heat is very similar to water and thus the specific
heat of water is used for the calculation of the SAR.
Estimate of in-vivo tissue volume heated under the shortwave field:
The area of the treatment area is estimated at 200 cm2 (based on the applicator coil diameter and field calculations)
for a depth of 2.5 cm (measured in prior research by BYU researchers
9,10
) for a total volume of 500 cm
3
or 0.5 Kg of
tissue.
Total Energy required to heat to 4
o
C in-vivo:
To raise tissue volume of 500 cm
3
by 4 degrees C would require a total of 500g x 4.181 x 4 = 8,362J (using the same
specific heat as water)
Power
= Joules/ Time = 8362/900 = 9.29W for 500g
SAR
= 18.58 W/Kg in-vivo
II.
Drum Inductive Applicator Design
The SAR is also controlled by the shape of the magnetic field, the drum inductive applicator design and the
positioning on the patient. Typical values for the OmniSWD
®
drum inductive applicator is 18.58 SAR in muscle
tissue and 4.57 in a saline water phantom. The higher the SAR value, the greater the thermal effect in the tissue.
III.
Treatment Time
In general treatment times for pulsed shortwave is 15 minutes. The dosage charts have been computed based on a 15
minute application time. The sensation of mild, moderate or vigorous warmth by the patient should be the final
indicator of obtaining the desired temperature in tissue. Start with the lowest dose capable of providing the desired
sensation of temperature to the patient. Increase the pulse rate and pulse duration to increase the dose as clinically