Dr David C Somerville 
guide to Ultrasound and Other Contact Electrotherapies and Underpinning Science 

While some varieties of electrotherapy equipment available to the professional therapist can safely be used with few contra-indications, those discussed in this book require special consideration. They transfer energy directly into the target tissue, requiring direct contact application on, or very close to, the area of injury. Safe application is paramount and giving an understanding of both the technicalities, application and effect of such therapies is this book’s main objective.