This chapter encompasses the process from which ultrasound images are optimally produced and interpreted by clinicians at the point of care. The science behind ultrasound image generation is a journey of discovery that began with the physical examination and ended with technology able to listen and see into the body. This journey includes the physical properties of human tissue described as solid, liquid, and gas. These concepts are built upon as we describe physics of mechanical wave production and the mathematical attenuation of these waves as they are impeded by various surfaces in tissue boundaries. The comparison of various types of medical images based on frequency can help the operator when trying to understand how images are generated and the safety profile of various medical imaging techniques. By developing techniques based on mathematical principles to optimally produce quality images and establishing a common language to manipulate the probe and image, the operator dependency of ultrasound can be reduced.
HISTORY OF IMAGE GENERATION
Artificial images of what lay beneath the surface of patients perhaps began when Joseph Leopold Auenbrugger observed his father tapping barrels in the 18th century to “picture” whether they were full or empty with fluid. A dull and low-pitched (low frequency) sound meant it was full of fluid. Leopold then used this observation to describe percussion as a key part of the physical examination of patients. Rene Laennec used his ear directly applied to a patient’s chest to imagine whether fluid, air, or disease lay under the surface. Due to modesty and the observation of children using solid pieces of wood and a pin to amplify sound, he “invented” stethoscopy.
Medical imaging advanced in the late 19th century on November 8, 1895, when William Roentgen observed the first instance of electromagnetic radiation that fluoresced a platinum plate. His first image a month later of his wife’s hand with a signet ring has become the genesis of the field of radiology and medical imaging. As radiology and fluoroscopy used electromagnetic radiation to image soft tissue, bone, gas, and fluid in the human body, the advent of computer processing set the stage for radiology to expand into computed tomography (CT) and use the power of computing to image clearly. The 20th century saw imaging science spread across the world and become a true global phenomenon. As X-rays became a modern miracle to enable clinicians to see beneath the surface, fluoroscopy allowed the imaging of structures such as the bowel, the ventricles of the brain and heart, and a myriad of anatomy and pathology in between.
CT was the intersection between the power of computers and the X-ray technology developed by Roentgen. Imaging the human bodies from multiple lines of sight and then compiling that data into “tomograms” started with first-generation scanners in the 1970s and now can be done in seconds to minutes and reconstructed to allow ...