Commercialized university research—a study of antecedents and outcomes and the innovation leading practices of entrepreneurs

Michael J Rivera, Purdue University

Abstract

X-ray mammography is the most widely used breast cancer imaging technique. Although mammography has met with success, over 400,000 women newly diagnosed each year are still misdiagnosed and undergo a biopsy. Current mammography techniques are limited by: (1) low image contrast of lesions in dense breasts; (2) difficulty in diagnosing and detecting lesions close to the chest wall and in women with radiographically dense breasts; (3) structural overlap onto a two-dimensional (2D) image plane; and (4) patient discomfort due to breast compression. Therefore, three-dimensional (3D) tomographic breast imaging approaches for pendant, uncompressed breasts have been explored to overcome these limitations and improve the detection of breast lesions. The goal of this thesis is to implement and characterize a dual-modality SPECT-CT dedicated breast imaging system that can overcome these limitations and integrate both metabolic and anatomical information to further improve the visual quality and quantitative accuracy over independent systems alone. Initial work on this thesis started out with characterizing the modulation transfer function (MTF) in 3D for the independent dedicated SPECT and CT systems. Using a novel phantom to measure the MTF at different locations in a 3D reconstructed volume, results indicated that acquiring images with a step-and-shoot mode and using trajectories (i.e. path the system travels as it moves around the object) that met the sampling criteria, uniform resolution throughout a 3D reconstructed volume can be obtained. The effects of cone-beam sampling and system geometry on the reconstructed CT images were investigated. As expected, constraining the x-ray source and detector to a circular tilt yielded insufficiently sampled reconstructed images, which contained geometric distortions, reconstruction inaccuracies, and cupping artifacts. Although beam hardening and scatter are considered to be the main causes of cupping artifacts in the reconstructed CT images, this study suggested that insufficient sampling might be a third cause to cupping artifacts in the reconstructed images. An additional finding in this study was that despite the insufficient sampling in the reconstructed CT images, high frequency information (edges, small objects) was preserved more than low frequency information (uniform area, large objects). Using a lateral offset geometry in CT, in which the system was shifted laterally from the center-of-rotation (COR), had been shown to introduce circular and cylindrical artifacts in the reconstructed coronal and sagittal CT slices, respectively. Monte Carlo studies showed that these artifacts were due to mechanical detector misalignment. However, cropping the projections, such that there was less of an overlap between conjugate projections, or placing the system in a centered geometry could eliminate these artifacts. Next, an integrated dual-modality SPECT-CT scanner was designed and built. The performance of this scanner was evaluated with geometric and anthropomorphic phantoms. Despite only having nearly complete sampling from both systems, results illustrated that SPECT and CT images can be registered and fused with minimal error. The feasibility of using the reconstructed CT images to quantify different tissue components was also investigated by using different materials as well as a cadaver (i.e., human breast). By implementing scatter correction using a developed beam stop approach, scatter corrected reconstructed images yielded attenuation coefficient values only with 7% error. Finally, four clinical studies were done to evaluate the effectiveness of the dual-modality scanner. Although the CT is currently limited in the amount of breast volume that can be imaged, reconstructed images appeared to have minimal distortion and reconstruction inaccuracy. Fused SPECT-CT images also illustrated the significance of using functional information from SPECT to help localize the lesion in the anatomical CT images. The dual-modality SPECT-CT scanner has successfully demonstrated its capability to uniformly sample an uncompressed breast with 3D complex trajectories that meet the sampling criteria and provide tissue quantification and localization information. This system has the potential to be a clinically useful imaging tool in detecting cancer, especially in women with high risk of breast cancer, monitoring treatment therapies, and improving surgical biopsy guidance.

Degree

Ph.D.

Advisors

Homan, Purdue University.

Subject Area

Entrepreneurship|Higher education

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