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Multi-frequency Harmonic Acoustography for Tissue Identification and Border Detection


Tissue identification and border delineation of diseased regions are essential for surgeons during surgical operations in tumor excisions. In the absence of an imaging technique that provides quantitative well-defined margins by identifying diseased from healthy regions, palpation of the tissue during surgery is the only practical option. To ensure complete resection of the diseased region, surgeons typically require large margins surrounding the suspect tissue in order to reduce the possibility of leaving behind any unhealthy tissue. The goal of this project is to develop an imaging modality that utilizes vibroacoustography (VA) technique to spatially map the contrast in mechanical and acoustic properties between malignant and normal tissue for abnormal tissue identification and border delineation. By enhancing boundary regions between malignant and healthy tissue, with this novel imaging technique, surgical margins are decreased and as a result, the resection of healthy tissue is potentially minimized. Some approaches that are used in the detection of tumor regions include conventional ultrasound, manual palpation, and CT scan. However, they suffer from limitations such as lack of sensitivity, subjectivity, and low contrast. As an alternative, VA provides an enhanced image of the boundary lines using the mechanical and acoustic properties of the target as the main mechanism of contrast. This work outlines the development of a VA medical imaging system for enhanced border detection as well as:

• Construction, improvement, and advancement of the VA system

• Characterization and optimization of VA system parameters such as point spread function (PSF), modulation transfer function (MTF), lateral and axial resolution of the imaging beam, and sensitivity and specificity specifications for biomedical imaging applications

• Investigation of VA feasibility in imaging mechanical properties of targets

• Design of a compact VA system for in vivo applications to enhance tissue characterization and boundary detection

The imaging system includes a dual electrode transducer, which possesses a confocal, piezoelectric element that produces two relatively close ultrasonic tones. When the two tones overlap at the point of interest, the beat frequency of the two tones is generated in a non-linear regime. The long-term goal of VA medical imaging is to provide a quantitative, intra-operative method of detecting the border between malignant and healthy tissue during surgical procedures. In the scope of this dissertation work, this study aims to culminate with in vivo system design and determination of tissue mechanical properties in pre-clinical models.

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