Motion Optimized Conformal Microwave Imaging for Biomedical Applications

Investigations into alternative breast cancer (BC) imaging techniques have become increasingly popular based on the limitations of traditional imaging modalities: X-ray mammography uses ionizing radiation, has limited intrinsic contrast and is associated with high false-positive and false-negative rates. Microwave tomographic imaging (MTI) has the ability to detect a wide range of dielectric property (DP) values, and due to the contrast that exists between the DPs of normal and abnormal breast tissue, MTI has shown promise as an alternative BC imaging modality. This thesis reports on a third generation system currently used in clinical trials at Dartmouth Hitchcock Medical Center. This system's improvements include increased data acquisition speeds and capabilities due to upgraded microwave electronic components and motion control hardware, respectively. Part I of this work will evaluate the system's microwave electronics in terms of channel isolation, system sensitivity and measurement repeatability in an effort to define an optimal operational bandwidth. The system's antenna array is composed of two interwoven sub-arrays (SAs) that can independently move to a number of positions. We have found that incorporating measurement data obtained at larger SA separation spacing during 3D acquisition results in unwanted artifacts in the reconstructed images. S-parameter studies have indicated that signals transmitted at these larger separation distances fall below the noise floor (NF) of the system's receiving channels. Part II of this thesis will focus on analyzing measurement sensitivity as a function of increasing SA spacing. The analysis has resulted in the creation of a motion optimized imaging system; increasing examination speeds by eliminating measurements positions where signals fall below the NF. Additionally, we have seen that our reconstruction algorithm has benefited from the incorporation of boundary information regarding the object under test (OUT). An optical-scanning system that can capture the boundary of the OUT while submerged in the system imaging chamber has been developed and mounted to the new imaging prototype. Conforming the reconstruction property mesh to the boundary of the OUT has increased the accuracy of recovered DPs. Part III of this thesis evaluates the boundary conformed microwave reconstruction process utilizing information obtained from the integrated optical-scanner.