טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentKievitski Rena
SubjectRisk Assessment and Safety Measures in Ultrasonics
DepartmentDepartment of Quality Assurance and Reliability
Supervisor Dr. Phineas Dickstein


Abstract

Ultrasonic, which is a branch of acoustics, deals with vibratory waves at frequencies above those within the hearing range of the average person, i.e., at frequencies above 16 kHz. The practical upper limit for concern as to human exposure is about 20 MHz. Since the Second World War, considerable progress has been made in the development of new materials and technique, and the applications of ultrasound have increased and diversified, particularly in recent years. Low-power applications of ultrasound are used in non-destructive testing and medical diagnoses. This work deals with applications of low-intensity ultrasound for medical diagnostic purposes. It was found that low-power ultrasound was capable of producing a wide range of biological effects. These effects of ultrasound are mainly thermal, resulting in elevated temperatures in the exposed organ. It is obvious, that the heat production is undesirable in diagnostic ultrasound (especially for fetal diagnosis). The effects may be nonthermal as well. Chief among these is cavitation, an activity that involves bubbles or cavities, containing gas or vapor. Other aspects of a sound wave include steady (time-averaged) forces and torques exerted on bodies, and steady circulations set up in fluids. This work surveys many animal and epidemiological studies, which have been conducted to examine the possible biological effects and potential risks associated with the exposure of humans to ultrasound. Critical levels of ultrasound quantities, which were determined from laboratory experiments, are the basis for safety advice and guidelines recommended or being considered by national and international organizations.