Hadzic's Regional Anesthesia > Part V. Ultrasound-Guided Regional Anesthesia > Chapter 50. Introduction to Ultrasound-Assisted Regional Anesthesia Techniques Andrew T. Gray, MD, PhD

Ultrasound Imaging

"Ultrasound imaging utilizes high-frequency sound waves (3–17 MHz). Because the speed of sound in soft tissue is fairly constant (1540 m/sec), the position of objects can be inferred from the time of flight of their received echoes. The product of wavelength and frequency is the speed of sound, so high-frequency sound waves have shorter wavelengths, and therefore provide better axial resolution. Attenuation of sound waves is frequency-dependent (approximately 0.75 dB/cm/MHz), so penetration of high-frequency sound waves into deep tissue is limited. For interventional guidance, one of the biggest advantages of ultrasound over other imaging modalities is the real-time acquisition of images. Frame rates of 30 Hz or higher are common in clinical practice...."