4K-2 3D Acoustic Radiation Force Impulse (ARFI) Imaging using a 2D Matrix Array: Feasibility Study

Acoustic radiation force impulse (ARFI) imaging has been reported as a successful method of measuring mechanical properties of tissue. Current methods use linear arrays to obtain a 2D image of tissue displacement. In this study, we have modified our real-time 3D ultrasound system (Volumetrics Medical Imaging, Durham, NC) to acquire volumetric ARFI data and create 3D displacement images. To ensure that the pulse to pulse correlation values from a 2.5-MHz matrix array transducer with 440 transmit and 256 receive channels were sufficient for ARFI processing, we transmitted a series of 2-cycle pulses into a homogeneous 4 kPa tissue-mimicking phantom (CIRS, Norfolk, VA) and collected corresponding 16:1 parallel received RF lines spaced 1.2deg apart. We found pulse to pulse normalized cross-correlation values were greater than 0.995 for scan depths of 3.5 cm. Our 3D ARFI pulse sequence consists of 3 2-cycle reference pulses followed by a set of 3 256-cycle pushing pulses. A series of 42 2-cycle tracking pulses are then used to monitor the displacement of the sample volume. Displacements between the reference and tracking RF data are estimated with ultrasonic cross-correlation methods. When acquiring a single scan line in a tissue mimicking phantom with a Young´s modulus of 4 kPa, we measured maximum displacements of approximately 3 mum near the focus. 3D ARFI images were produced at depths of 0.5-3.5 cm using 9 transmit lines, which produced 144 receive lines to form a 12 line by 12 line 3D pyramid of 13.2deg yielding B-scan and C-scan planes of displacement data. System modifications are ongoing to the 3D Doppler processing algorithm (1D autocorrelation) to permit 3D ARFI processing to occur in realtime