Modulation of ultrasound to produce multifrequency radiation force

Abstract

Dynamic radiation force has been used in several types of applications, and is performed by modulating ultrasound with different methods. By modulating ultrasound, energy can be transmitted to tissue, in this case a dynamic force to elicit a low frequency cyclic displacement to inspect the material properties of the tissue. In this paper, different types of modulation are explored including amplitude modulation ͑AM͒, double sideband suppressed carrier amplitude modulation AM, linear frequency modulation, and frequency-shift keying. Generalized theory is presented for computing the radiation force through the short-term time average of the energy density for these various types of modulation. Examples of modulation with different types of signals including sine waves, square waves, and triangle waves are shown. Using different modulating signals, multifrequency radiation force with different numbers of frequency components can be created, and can be used to characterize tissue mimicking materials and soft tissue. Results for characterization of gelatin phantoms using a method of vibrating an embedded sphere are presented. Different degrees of accuracy were achieved using different modulation techniques and modulating signals. Modulating ultrasound is a very flexible technique to produce radiation force with multiple frequency components that can be used for various applications.

Ultrasonic method to characterize shear wave propagation in micellar fluids

“…Another limitation is that the frequency BW of generated shear waves with ultrasound radiation force (>100 Hz) is considerably different to the conventional shear oscillatory test (<16 Hz) where micellar fluids are highly viscous. 28 Modulated ultrasound methods could be employed to generate acoustic radiation force to investigate other frequencies, but would require a more involved experimental setup. Nonetheless, micellar fluids offer a unique material to model semi-solid biological tissue such as cyst or fat, thus, its advantages to validating and developing new ultrasound shear wave imaging methods are valuable.…”

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

“…(13) is estimated using theory detailed by Urban and co-workers for repeated tone bursts. 4,20 For curve fitting, a weighted least-squares curve fitting algorithm (LSQCURVEFIT) was used in MATLAB (The Mathworks, Natick, MA). The weights used were the normalized values of the velocity spectrum.…”

“…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.…”

A Review of Vibro-acoustography and its Applications in Medicine

“…Other techniques have used an embedded sphere or bubble excited by radiation force to characterize the surrounding medium. This type of application has been studied for both elastic and viscoelastic media [55–63]. …”