The experimental investigation of the micro-vibrations underlying Temporal Enhanced ultrasound
Temporal enhanced Ultrasound (TeUS) is a non-invasive imaging approach, recently proposed by our group. TeUS makes use of ultrasound time series for tissue classification, and it has been successfully applied to ex vivo prostate tissue classification, breast cancer detection, and prostate cancer grading. Of particular importance is the physical phenomenon underlying the tissue characterizing capability of TeUS. Our group previously proposed that physiological micro-vibrations are a source of tissue differentiation. These micro-vibrations are induced by blood perfusion (heart beat: ~ 1 Hz) and breathing (0.2-0.4 Hz). Our group then derived a theory that integrates the effect of micro-vibrations into the standard imaging equation. We validated this theory by digitally simulating micro-vibrations in benign and cancerous pathology and demonstrated that response to the micro-vibrations can be the basis for differentiating the tissues. This thesis aims to find experimental evidence to support the theory. Specifically, I accurately simulated and measured micro-vibrations; I then studied the mechanical properties of the tissue and their relationship to TeUS, through tissue mimicking phantom studies. First, I adapted a fiber optic sensor for micro-vibration detection. The sensor was shown to be capable of simultaneously capturing low frequency micro-vibration as well as megahertz ultrasound transmission waveforms. The sensor is expected to be an invaluable tool for studying micro-vibrations and developing advanced ultrasound tissue characterization technologies. I then developed and characterized tissue mimicking phantoms with an integrated micro-vibration mechanism. To investigate the effects of micro-vibrations on TeUS, I built the tissue mimicking phantoms that differed in ultrasound scatterer size and elasticity. I collected TeUS signals and showed that TeUS is sensitive to scatterer size and elasticity through micro-vibrations. These results provided experimental evidence to the hypothesis that physiological micro-vibrations are a cause of TeUS differentiation, as proposed by our group's previous work. They also warrant the translation of TeUS to other types of material characterization tasks.