Measuring tissue shear wave properties using one excitation pulse and excitation pulses having different widths and shapes
Ultrasound radiation using a single tone burst pulse is applied to a selected location in a tissue region. The induced shear wave is detected in the region and its spectral distribution is calculated and analyzed. This detection may be repeated with other excitation pulses having different widths or different shapes at the same location. The spectral analysis of the detected shear wave is performed according to a nonlinear shear model for solving nonlinearity and viscoelasticity of the tissue at a single location. The detection location can be at one point at a time for imaging two-dimensional or three-dimensional tissue nonlinearities and shear wave properties including nonlinear magnitude variations, nonlinear phase variations, nonlinear coefficients, and viscoelasticity. The induced shear wave are detected at multiple locations along the shear propagation directions for calculating different shear group velocities and different shear phase velocities using different excitation pulses, and calculating nonlinearity and viscoelasticity.
1. A method for measuring a nonlinearity and viscoelasticity of a subject, the method comprising:
a) generating ultrasound excitation pulses that have prescribed pulse shapes and a center frequency;
b) applying the ultrasonic excitation pulses using an ultrasonic transducer to a vibration origin in the subject to induce a shear wave motion in the subject;
c) applying ultrasonic detection pulses to a detection location in the subject to detect the shear wave motion;
d) performing spectral analysis of the detected shear wave motion and the excitation pulses;
e) determining the nonlinearity of the subject at the detection location based at least in part on the spectral analysis;
f) determining the viscoelasticity of the subject at the detection location based at least in part on the nonlinearity using a nonlinear model.
2. The method as recited in claim 1 wherein the excitation pulses are gated tone burst pulses having a prescribed frequency and different prescribed numbers of periods and different pulse widths.
3. The method as recited in claim 1 wherein the excitation pulses are periodical pulses with a prescribed period and a prescribed duty cycle.
4. The method as recited in claim 1 wherein the determining the viscoelasticity of the subject includes determining elasticity and viscosity of the subject.
5. The method as recited in claim 4 wherein the elasticity at multiple locations of multiple dimensions of the subject is color coded for displaying a nonlinearity image of the subject.
6. The method as recited in claim 1 wherein the determining nonlinearity of the subject includes determining nonlinear coefficient SNEC, α, by fitting shear wave measurements to
Y
i
(
ω
)
=
P
i
α
(
ω
)
A
0
(
μ
1
+
j
ω
μ
2
)
α
,
where α is the shear nonlinear exponent coefficient (SNEC), P i (ω) is Fourier transform of the excitation pulses, Y i (ω) is Fourier transform of shear wave y i (t), H(ω) is a transfer function, A 0 is a scaling constant, μ 1 is elasticity of the subject, μ 2 is viscosity of the subject.
7. The method as recited in claim 1 wherein the determining nonlinearity of the subject includes determining nonlinear coefficients SNEC, α and SNCC, β, by fitting shear wave measurements to
Y i (ω)= A 1 {P i (ω)/(μ 1 +jωμ 2 )+β P i α (ω)/(μ 1 +jωμ 2 ) α },
where α is the shear nonlinear exponent coefficient (SNEC), β is defined as the shear nonlinear content coefficient (SNCC), P i (ω) is Fourier transform of the excitation pulses, Y i (ω) is Fourier transform of shear wave y i (t), H(ω) is a transfer function, A 1 is a scaling constant, μ 1 is elasticity of the subject, and μ 2 is viscosity of the subject.
8. The method as recited in claim 1 wherein the determining nonlinearity of the subject includes determining a distribution of phase shifts of shear waves versus excitation pulse widths.
9. The method as recited in claim 1 wherein the determining nonlinearity of the subject includes determining differences of phase shifts of shear waves induced by difference excitation pulses versus different frequencies.
10. The method as recited in claim 1 wherein the determining nonlinearity of the subject includes determining a distribution of group shifts of shear waves versus excitation pulse widths.
11. The method as recited in claim 1 wherein the determining nonlinearity of the subject includes determining differences of group shifts of shear waves induced by difference excitation pulses versus different frequencies.
12. The method as recited in claim 1 wherein the nonlinearity at multiple locations of multiple dimensions of the subject is color coded for displaying a nonlinearity image of the subject.
13. The method as recited in claim 1 wherein the viscoelasticity are labeled by pulse widths.
14. The method as recited in claim 1 wherein the nonlinearity are labeled by pulse widths.
15. A method for measuring a nonlinearity and viscoelasticity of a subject, the method comprising:
a) generating an ultrasound excitation pulse having a prescribed pulse shape and a center frequency;
b) applying the ultrasonic excitation pulse using an ultrasonic transducer to a vibration origin in the subject to induce a shear wave motion in the subject;
c) applying ultrasonic detection pulses to a detection location in the subject to detect the shear wave motion;
d) performing spectral analysis of the detected shear wave motion and the excitation pulse;
e) determining the nonlinearity of the subject at the detection location based at least in part on the spectral analysis;
f) determining the viscoelasticity of the subject at the detection location based at least in part on the nonlinearity using a nonlinear model.