Assessment of Tissue Biomechanical Properties Using Ultrasound Elastography and Optical Coherence Elastography

This dissertation reports several significant contributions that further the field of elastography as a whole. Each chapter also represents a key step toward the realization of quantitative compression elastography (QCE). First, motion estimation algorithms were analyzed in chapter 2 to determine which algorithm allowed for the most accurate measurement of motion and subsequent elastic wave speed. This is significant for the entire field of elastography, as motion estimation algorithms are used regardless of choice of imaging modality or method. Following this, ultrasound shear wave elastography and transient optical coherence elastography were compared under similar conditions in chapter 3 to determine if they gave comparable results. This analysis proves that the results obtained from both modalities are comparable and that they can be used interchangeably. While this is important for the field of elastography, i.e., measurements taken with one can and should be compared to the other, it is absolutely crucial for the development of QCE. If the two methods cannot give comparable results, it follows that techniques used to obtain quantitative information from one cannot be used in the other. Chapter 4 contains the most significant contribution, which is the development of QCE. QCE is a simple, multi-modal, quantitative elastography technique that borrows the idea of a compliant stress sensor from optical coherence elastography and improves upon it by removing the need for calibration. Because strain imaging and wave excitation can be performed without moving the transducer, ultrasound has the unique ability to essentially calibrate the sensor in place during the act of compression. Furthermore, this allows for a more accurate measurement than is typically possible when using a compliant sensor because the exact sensor conditions can be known at the time of measurement instead of assumed from uniaxial compression testing. Overall, the contributions of this work serve to increase accuracy in elastographic measurements, further multimodal elastography, and serve as the genesis of quantitative compression elastography methods in ultrasound.