Simulated Cervical ARFI

Abstract

Every day, 1,300 children in the U.S. and an additional 34,000 children worldwide are born prematurely. This study acts as a feasibility study for a proposed ultrasonic technique for the identification of preterm birth risk factors using an acoustic technique known as Acoustic Radiation Force Impulse (ARFI) imaging. A 3D finite element model was constructed to optimize transducer ARFI parameters in a layered cervix structure prior to clinical evaluation. The transducer model optimized in this study was the AcuNavTM (Siemens Medical Solutions, Mountain View, CA). Cervix model structural geometry and material properties were varied according to anticipated pregnancy induced property fluctuation. Transmitted ARFI acoustic fields were generated by applying a Field II derived pulse to the 3D model[15]. Optimization procedures were performed in the following order: focal depth evaluation, transmit frequency optimization, effect of material property variation and the application of ARFI shear wave speed calculation algorithms to a layered cervical structure. Results indicated that ARFI evaluation of a layered cervix structure was most feasible using an 8MHz transmit frequency in the focal range of 5-10mm axial depth. It was observed that material property estimation errors were most likely when ARFI excitations were focused near a material boundary. A phenomenon was noted where shear waves initiated in stiffer media were slowed as a function of their relative proximity to a more compliant medium. Overall, these simulation studies demonstrate that ARFI shear wave imaging in the cervix is feasible; a model has been developed that can be used to evaluate the accuracy of shear stiffness estimates in the cervix to help address the important clinical problem of premature cervical ripening.