Prostate vibro-elastography: Multi-frequency 1D over 3D steady-state shear wave imaging for quantitative elastic modulus measurement

Background, Motivation and Objective: This article describes a state of the art ultrasound system that is used to quantify tissue elasticity of the prostate. Statement of Contribution/Methods: The system involves the measurement of the steady-state multi-frequency response of tissue to transperineal excitation while imaging the gland using the sagittal array of the BK Medical 8848 trans-rectal ultrasound transducer. A roll motor rotates the transducer in discrete steps to create a volume sector of images. GPU Processing of raw in-phase/quadrature data streamed from the ultrasound machine is used to measure the axial (radial) spatial distribution of tissue motion and compute displacement phasors. Bandpass sampling is used to perform the reconstruction since the sampling frequency is below the Nyquist rate. Finally, a local frequency estimator is used to compute the Youngs Modulus from the three dimensional local spatial wavelengths of the shear wave that is created at each of the excitation frequencies. Results/Discussion: The system has been used in several clinical studies but its design and function has not been published before. Some of the study results have been published and include an area under receiver operating characteristic curve of 0.820.01 with regards to prostate cancer identification in the peripheral zone. The accuracy of the elastic modulus measurement was validated using a CIRS elastography phantom. Numerical and visual correlations between our elasticity measurements and pathology results demonstrate its clinical potential. The system has been expanded to a generic platform that can be used to provide real-time quantitative elasticity measurements in other organs.