P4F-7 Integration of a Pressure Sensing Array Into Ultrasound Elastography

Mechanical in vitro tests and in vivo elasticity imaging have shown differences between breast tissue types in their nonlinear stress/strain behavior, which could be utilized to differentiate between benign and malignant lesions potentially reducing the benign biopsy rate. Stress and strain measurements are required for absolute measures of this non-linear behavior in vivo. A variety of tests were performed with a prototype pressure sensor array to gauge its stability, sensitivity and calibration in reference to its application in ultrasound elastography. Measurements on elastographic phantoms were also performed and compared to finite element analysis (FEA) simulations. In addition, data was collected from patients undergoing ultrasound elasticity imaging at the University of Wisconsin Breast Center. Initial tests show that the pressure sensor array is stable in an ultrasound imaging environment. A reliable calibration technique was also developed, with reproducibility to within 5% for most elements. Tests also show a wide disparity in sensitivity among elements. The best performing elements are capable of detecting pressure as low as about 100 Pa. The average minimum detectable pressure was about 800 Pa. This suggests that the array is capable of detecting initial contact and measuring the contact force during a deformation of the breast - a critical task for quantifying stress/strain nonlinearities. The preliminary clinical trial confirmed this prediction. However, surface pressure distribution measurements on phantoms have shown only modest agreement with FEA simulations. Geometric uncertainties on the surface of the sensor as well as the variability of the absolute calibration make the array ill suited to measure accurate maps of the surface pressure distribution which might limit its utility for elastic modulus reconstructions.