Introduction to B-mode imaging

Press. © Cambridge University Press 2010. principles of its formation. In essence, these principles are still used in modern B-mode systems, although they may be used within more complex arrangements designed to enhance performance. A B-mode image is a cross-sectional image representing tissues and organ boundaries within the body (Figure 1.1). It is constructed from echoes, which are generated by reflection of ultrasound waves at tissue boundaries, and scattering from small irregularities within tissues. Each echo is displayed at a point in the image, which corresponds to the relative position of its origin within the body cross section, resulting in a scaled map of echo-producing features. The brightness of the image at each point is related to the strength or amplitude of the echo, giving rise to the term B-mode (brightness mode). Usually, the B-mode image bears a close resemblance to the anatomy, which might be seen by eye, if the body could be cut through in the same plane. Abnormal The application of ultrasound to medical diagnosis has seen continuous development and growth over several decades. Early, primitive display modes, such as A-mode and static B-mode, borrowed from metallurgical testing and radar technologies of the time, have given way to high-performance, real-time imaging. Moving ultrasound images of babies in the womb are now familiar to most members of the public through personal experience of antenatal scanning or via television. Modern ultrasound systems do much more than produce images of unborn babies, however. Modern ultrasound systems are able to make detailed measurements of blood movements in blood vessels and tissues, visualize moving structures in 3D, and make measurements related to the stiffness of tissues. Improvements in technology have been followed by widespread acceptance and use of ultrasound in medical diagnosis. Applications have progressed from simple measurements of anatomical dimensions, such as biparietal diameter, to detailed screening for fetal abnormalities, detection of subtle changes in tissue texture and detailed study of blood flow in arteries. In many areas, ultrasound is now chosen as the first line of investigation, before alternative imaging techniques. This book describes the physics and technology of diagnostic ultrasound systems in use at the time of writing. The book may be divided into four sections; basic physics and B-mode imaging in Chapters 1–6; Doppler ultrasound in Chapters 7–10; quality assurance and safety in Chapters 11–12, and recent technology in Chapters 13–15. This chapter covers the very basic concepts involved in B-mode imaging.