RIU 320 Lecture Notes - Lecture 56: Rarefaction, Fundamental Frequency, Microbubbles

• School: GVSU
• Department: Radiation and Imaging - Ultrasound
• Course: RIU 320
• Professor: Angela Malone

Document Summary

Not present as sound leaves the transducer; they are created deeper in the tissues. Created by nonlinear behavior in the speed of sound. Sound in compressions travels faster than sound in rarefactions. Primarily created along the beam"s main axis. The beam contains no harmonic frequency sound at the skin"s surface, thereby avoiding distortion and reducing noise. Pulse inversion harmonics is an imaging technique specifically designed to utilize harmonic reflections, which are distortion free, while eliminating distorted fundamental reflections. Reflections contain both fundamental and harmonic frequencies. Fundamental imaging creates images from the portion of the reflected sound that has the same frequency of the transmitted sound. Originally, filters were used to separate the harmonic signal from the fundamental, but filtering was only moderately effective. Modern techniques, such as pulse inversion harmonics, separate the harmonics from the fundamental frequencies more successfully. With pulse inversion harmonics, two consecutive ultrasound pulses are transmitted down each scan line.