Heating of fat-muscle layers by electromagnetic and ultrasonic diathermy

IN CLINICAL practice, it is frequently desirable to produce heat in the muscular tissue which lies below subcutaneous layers of fat. Until recently short-wave diathermy provided the most satisfactory answer to the general problem of deep heating. However, biophysical research1 has shown that, when electric currents pass through alternate layers of fat and muscle, the fatty tissue is selectively heated. Although the ratio of heat developed in fat to that in muscle becomes smaller as the frequency increases, even at the highest practical frequencies the ratio is still greater than unity. It was in part to overcome this difficulty that electromagnetic and ultrasonic radiation were introduced as forms of diathermy following the second World War. The heating of homogeneous tissues by radiant energy has previously been discussed.2 However, the important fat-muscle problem as it applies to the new forms of radiation diathermy has not, up to now, been given quantitative consideration.