SONIC AND ULTRASONIC THERAPY 63 



(2) Based on the same principle, the rate of blood flow through the ar- 

 terial system can now be measured by reflected ultrasound, in a nondestruc- 

 tive experiment in which all instrumentation is external to the body. 



(3) Dentists have begun to apply sound to the ears of patients during 

 drilling, because it has been found that the brain cannot perceive pain from 

 the teeth and sound from the ear at the same time. The sound in this case 

 acts as a local anesthetic. 



(4) "Rapid massage" heat therapy is now quite common, with an assort- 

 ment of low-frequency vibrator pads and belts available, and experimental 

 models operating in the 12,000 to 50,000 cps region. For deep "massage" 

 higher frequency ultrasound is used; it has the added advantage of comfort 

 from noise. 



(5) Certain skin diseases can be treated with beamed and focused ultra- 

 sound. Thus viruses are destroyed (literally shaken into little bits!) by 

 ultrasound, and a future in sterilization seems assured. In this application 

 its competitor is soft X rays. 



(6) "Neurosonic surgery" is now well advanced on animals, and has re- 

 ceived some experimental evaluation on humans. The most spectacular suc- 

 cess so far has been achieved in treatment of Parkinson's disease, the shaking 

 palsy. Because of its future importance,*** some details will now be given. 



"Neurosonic Surgery" 



The ultrasonic radiation reaches the brain through a hole cut in the skull, 

 and the matter waves are beamed and focused on that part, deep in the 

 brain, in which involuntary movements are controlled (Figure 3-6 (b)). The 

 energy dissipated by the beam is concentrated at the focus of the beam, and 

 gently destroys the metabolic activity at the site (the substantia nigra). The 

 method, when used carefully, has the advantage over all others that it pro- 

 duces lesions at the focus of the ultrasonic energy without interfering with 

 the normal blood flow from one part of the brain to another through the 

 region irradiated. Of course this is a great advantage from the medical point 

 of view. The techniques were worked out first on hundreds of cats and 

 monkeys, and are now very cautiously being applied to man. Functional 

 disruption of nervous conduction occurs within a few seconds of exposure to 

 ultrasound of sufficient dosage to produce lesions: 980,000 cps, 1.8- to 3-sec 

 duration, and particle velocity amplitude of 350 cm/sec, from a generator 

 with the capability of 20 to 1000 w/cm 2 . From the therapeutic viewpoint it 

 has been found possible to irradiate simultaneously the four small parts of 

 the brain which are active with respect to Parkinsonism in the four limbs. 



***In spite of the fact that Parkinsonism may be dying out. Thus the average age of these 

 patients is steadily increasing, in North America, a trend which, if it continues, would indicate 

 that the disease may have died out naturally by 1985. 



