CONCLUSION 



65 



Q 



UJ 



or 



300 



250 



200 



co ~ 



*- 100- 



=5 h- 



150 



IRRADIATION TIME 



t (seconds) 



Figure 3-8. Threshold Energy for Paralysis as a Function of Ultrasonic Intensity, 

 curve shows data of W. J. Fry and F. Dunn, 1956. Broken curve shows how the th 

 is much higher than expected at very short irradiation times. 



Solid 

 reshold 



pressure 1 atm, starting temperature 10° C) by the simple expression 



t oc i/vTT 



the Dunn-Fry law, which says simply that the time to paralysis is shorter the 

 higher the intensity; but that the damage occurs relatively more slowly for 

 large intensities than for small intensities. 



This is one of the best rules-of-thumb so far worked out in biophysics of 

 ultrasound therapy. It remains to be seen whether it is of general applica- 

 bility. Intuitively one would think it should be. In any case it might be well 

 to state the following memory aid: Probably because of general heating and 

 of molecular excitation induced by absorbed ultrasound, metabolic, physio- 

 logic, and histologic changes occur in tissues. In otner words, tissues Fry 

 until Dunn! 



CONCLUSION 



"Like some other agents which have been introduced into the arma- 

 mentarium of clinical medicine, medical ultrasonics passed through the early 

 stages of enthusiasm, followed by a reactionary stage of pessimism, before 

 it achieved the stature presently accorded it. Currently there are promising 

 developments and interesting applications of ultrasound for medical diag- 

 nosis, for therapy, and for biologic measurement." (J. F. Herrick. 12 ) 



The next ten years should be interesting ones from this point of view. 



