Sonoelastographic shear velocity imaging using crawling wave excitation
Vibration sources are applied to a body or other object to image a region of interest. The mechanical vibrations introduced by the sources interfere in the region of interest to produce a crawling wave, which is detected by an ultrasound probe A relationship between crawling wave phase derivatives and local shear wave velocity is derived with phase derivatives estimated using either one-dimensional (1D) or two-dimensional (2D) autocorrelation-based techniques to image the region of interest.
1. A system for forming an image of a region of interest in an object, the region of interest comprising areas having differing elastic properties, the system comprising:
a plurality of vibration sources to generate a sinusoidal steady state interference-based crawling wave in the object;
a vibration detector that detects an interference field of the crawling wave; and
a processor, coupled to the detector, characterized in that the processor controls the formation of the crawling wave, and determines a shear wave speed distribution from the crawling wave by deriving an interference field of the crawling wave and performing a two-dimensional spatial autocorrelation on the interference field.
2. A method for determining a local shear wave velocity in a sample, comprising the steps of:
a) generating a crawling wave in the sample from a sinusoidal steady state shear wave interference;
b) detecting an interference field of the crawling wave;
c) performing a two-dimensional spatial autocorrelation on the interference field;
d) using the autocorrelation to estimate a phase derivative of the crawling wave; and
e) using the phase derivative of the crawling wave to estimate the local shear wave velocity in the sample.
3. The method of claim 2 , further involving obtaining a two-dimensional (2-D) shear wave velocity spatial distribution in a given sample region by performing a one sample shifting of the crawling wave interference field and generating a resultant matrix.
4. The method of claim 3 , further involving generating a shear wave sonoelastogram by imaging the resultant matrix.
5. The method of claim 2 , wherein step (c) further involves performing the two-dimensional spatial autocorrelation on the detected crawling wave interference field to estimate the local shear wave velocity in two dimensional space in the sample.
6. The method of claim 5 , further involving independently estimating a mean axial shear velocity and a mean lateral shear velocity relative to respective, orthogonal axial (vertical) and lateral (horizontal) axes.
7. The method of claim 6 , further involving combining the axial and the lateral shear wave velocity estimates to obtain a 2-D mean shear velocity estimate.
8. The method of claim 7 , further involving performing a one sample shifting of the crawling wave interference field and generating a resultant matrix.
9. The method of claim 8 , further involving generating a shear wave sonoelastogram by imaging the resultant matrix.
10. The method of claim 2 , further comprising using a received Doppler spectral variance to calculate the crawling wave interference field.
11. The method of claim 2 , further comprising using a pair of vibrational sources having different frequencies to generate the crawling wave.
12. The method of claim 2 , further comprising using a pair of vibrational sources having different frequencies and continuously phase shifting at least one sample excitation signal to generate the crawling wave.
13. The method of claim 2 , wherein step (a) comprises applying the pair of vibrational sources to the object on opposite sides of the region of interest.