Preface

A technology that began as a navigation and warfare tool in submarines during the First World War, ultrasound has grown to be a formidable, noninvasive, computerized visual tool to peer into the internal organs of the human body. Health care professionals can better interpret the images and make more accurate diagnoses by understanding the physics behind how ultrasound waves are generated, transmitted, and received. The increasing demand for the use of ultrasound technology in various biomedical fields points to a future in which medical professionals will be required to possess a general knowledge of ultrasound technology. While currently, most medical professionals rely on technicians to perform imaging studies, there can be a high degree of operator-dependent results; therefore, a solid foundation of the technological properties of ultrasound would give health care providers a competitive advantage in the future.

The discovery of ultrasound is credited to Italian physiologist Lazzaro Spallanzani, who first deduced that bats use ultrasound to navigate through echolocation. In 1938, Donald R. Griffin confirmed experimentally that bats use ultrasound for navigation. In 1826, Swiss physicist Jean-Daniel Colladon determined the speed and characteristics of sound in Lake Geneva using an underwater church bell. He successfully showed that sound waves travel faster in water than through the air. Another breakthrough came in 1880, when Pierre and Jacques Curie discovered the piezoelectric effect—the ability of certain materials to generate an electric charge in response to applied mechanical stress. In 1842, Austrian physicist Christian Doppler proposed that the frequency of a wave changes for an observer moving relative to its source, a process now called the Doppler effect. Both the piezoelectric effect and Doppler effect form the basis of the ultrasound technology used in diagnosis and therapy.

Due to the increasing need to detect icebergs and enemy submarines during the First World War, Paul Langevin developed an ultrasound transducer based on the piezoelectric effect. Karl Dussik, a neurologist and psychiatrist, started using ultrasound transducers to diagnose brain tumors in 1942.^[1] Thereafter, ultrasound technology use was extended to other medical specialties as well. For example, George D. Ludwig,^[2] in 1948, used it in internal medicine for diagnosing gallstones, and Donald et al.,^[3] in 1962, pioneered the use of ultrasound in obstetrics and gynecology. The 1950s marked the beginning of the use of digital 2D B-mode ultrasound. Today, ultrasound technology has expanded to medical imaging in various specialties: anesthesiology, cardiology, critical care, emergency medicine, general pediatrics, internal medicine, obstetrics and gynecology, pediatric emergency medicine, physiatry, sports medicine, and surgery.

This textbook provides the theoretical and practical concepts of ultrasound and its medical applications. It focuses on sound wave concepts, transducers, imaging formation, tissue mechanics, artifacts, the Doppler effect, bioeffects, and safety. It also discusses the different uses of ultrasound for clinical and medical purposes. We believe that premedical and medical students, as future clinicians, will immensely benefit from having knowledge of ultrasound physics and instrumentation in their early university life. The authors have carefully balanced theoretical concepts with practical aspects of ultrasound biomedical applications to ensure clarity on the knowledge relevant to the medical profession.