Tactile resonance method for measuring stiffness in soft tissue - evaluation of piezoelectric elements and impression depth using a silicone model

Abstract: An instrument is being developed at the Department of Biomedical Engineering; Research and Development (MT-FoU), at the University Hospital of Umeå with the aim to detect prostate cancer ex vivo. Using a combination of tactile resonance technology and Raman spectroscopy the instrument is intended to be used in the operating room during radical prostatectomy to identify positive surgical margins. The hypothesis was that the length of the piezoelectric element used in the tactile resonance sensor affects the sensor's sensitivity and reproducibility when measuring the stiffness of soft tissue, and that there might be an optimal impression depth to measure at. The specific aim of this study was to evaluate two piezoelectric elements, of different lengths, by the sensitivity and reproducibility of the measurements they performed. Measurements were performed on five silicone samples of different stiffness, during a 2 mm impression. The standard deviation of the stiffness parameters, the R2 of the linear regression used to determine the stiffness parameter, and the depth at the which the most linear relationship between impression force and frequency shift was found were studied using linear mixed-effects models to identify any significant differences between the elements. The long element had a significantly higher R2 of 0.98 compared to 0.93 for the short element, and a higher measurement depth of 0.47 mm compared to 0.37 mm for the short element. No difference between the elements were found on accuracy as measured by standard deviation of the stiffness parameter. It was concluded that this was not enough to claim that one element was better than the other.