Multifrequency vibro-acoustography

Abstract

Elasticity imaging is a burgeoning medical imaging field. Many methods have been proposed that impart a force to tissue and measure the mechanical response. One method, vibro-acoustography, uses the ultrasound radiation force to harmonically vibrate tissue and measure the resulting acoustic emission field with a nearby hydrophone. Another method, vibrometry, uses the ultrasound radiation force accompanied with a measurement of the resulting velocity or displacement of the vibrating tissue or object has also been used for different applications. An extension of the vibro-acoustography method using a multifrequency stress field to vibrate an object is described. The objective of this paper is to present the image formation theory for multifrequency vibro-acoustography. We show that the number of low-frequency components created by this multifrequency method scales with the square of the number of ultrasound sources used. We provide experimental validation of the point-spread function of the multifrequency stress field and show examples of both vibrometry and vibro-acoustography imaging applications. This method holds the potential for a large gain of information with no increase in scanning time compared to conventional vibro-acoustography systems.

Generalized response of a sphere embedded in a viscoelastic medium excited by an ultrasonic radiation force

“…This method has been used in later studies for quantification of the viscoelastic material properties of gelatin materials. 3,4 Norris studied the impedance of a vibrating sphere in an elastic medium when slip was present or absent by adding an interfacial impedance to account for this condition. 5 Ilinskii et al derived relationships for the static and transient displacement responses of a sphere and a bubble embedded in an elastic medium.…”

Modulation of ultrasound to produce multifrequency radiation force

“…Vibro-acoustography has taken advantage of this multifrequency radiation force using DSB-SC AM waveforms to create multiple images from one scan. 28 Another method called shear wave dispersion ultrasound vibrometry ͑SDUV͒ uses square wave modulation to transmit multiple tonebursts of ultrasound at the frequency of the square wave f r , and then elicits shear waves with components at harmonics of f r . 25 The shear wave velocity is estimated at f r and several of its harmonics to estimate the shear wave velocity dispersion and characterize the viscoelastic material properties of the tissue or medium.…”

“…28. We modulated an ultrasound signal with different functions and derived the radiation force with the pressure from the needle hydrophone measurements.…”

Portable vibro-acoustic testing system for in situ microstructure characterization and metrology

“…VA is an imaging modality based on ultrasound-stimulated acoustic emission [1][2][3][4][5]. VA uses the force caused by the beating of two frequencies to generate an acoustic emission signal, (Fig.…”

“…In order to form a 2D image, the whole area is covered by raster scanning motion of the confocal transducer. Whereas, the stimulation frequency is generally on the order of MHz, the difference frequency (acoustic [5]. However, there is no theoretical limitation on difference frequency, and it can be adjusted to suit the application.…”