Timothy Raynolds

Parallel-detection microwave spectroscopy system for breast imaging

A liquid-coupled, noncontacting, broadband microwave imaging system has been designed and fabricated. Extension of the operating bandwidth allows us to exploit the potential of new clinical information for breast cancer diagnosis at frequencies higher than previously achieved. The new system design implements a parallel-detection scheme that allows signals to be simultaneously sampled at multiple receiving antenna sites (in 8 s for a single tomographic slice at a single frequency). It also has important features such as high cross-channel isolation (>120 dB), smooth broad bandwidth receiver response, and adjustable intermediate frequency signal amplification factors of 1 to 2000 to ensure successful realization of a large linear dynamic range which is especially important to counteract the increased signal loss at the higher operating frequencies. The new system is capable of recovering dielectric properties of breastlike phantoms with tumor inclusions over the frequency range from 0.5 to 2.1 GHz when embedded in an 87%/13% glycerin/water background. Errors in the measurement data are less than 0.5% in signal amplitude and 1° in phase, on average.

A broadband microwave breast imaging system

A liquid-coupled, non-contacting, broadband (0.5 - 3 GHz) microwave imaging system has been designed and fabricated to exploit new clinical information for breast cancer diagnosis. Ultimately this system may complement conventional X-ray mammography by reducing the number of false negatives and false positives, especially in challenging cases such as patients with radiographically dense breast tissue.

3-Point support mechanical steering system for high intensity focused ultrasound.

We have developed a simple approach for mechanically scanning a focused bowl ultrasound (US) transducer for either hyperthermia or tissue ablation therapies called the 3-point support (3PS) mechanical steering technique. The scanning involves translation of the required 3D motion of the ultrasound transducer to the more manageable linear movement of three support rods. It is a cost-effective alternative, especially compared with electronic scanning and other previous implementations of mechanically scanned systems. The 3PS approach is particularly well suited for integration with our microwave breast imaging technique--the combination of which could be an effective, low-cost thermal therapy/monitoring approach. The results show that the US focus can be moved laterally in a spiral pattern 3 cm below the surface in a gel phantom and that similar patterns can be moved to multiple locations within the phantom volume in succession. The feasibility of simultaneously acquiring microwave thermal images is also demonstrated.

Microwave breast imaging with an under-determined reconstruction parameter mesh

Microwave imaging has been proposed as a method for detecting breast tumors because of the high electrical property contrast between tumors and normal tissue. We are currently developing a tomographic system which can generally be treated as an ill-conditioned inverse problem and utilize a Gauss-Newton iterative algorithm to handle its nonlinear nature. The ill-conditioning is generally related to the number of parameters being reconstructed with respect to the amount of measurement data. Our initial implementation restricted the number of parameters to close to that of the measurement data. However, this sparse discretization of the imaging zone severely limited the resolution and required a high degree of spatial filtering to stabilize the algorithm convergence. We are currently exploring significantly increasing the number of reconstruction parameters to the point of making the problem considerably under-determined. Initial results indicate that the benefit in terms of increased degrees of freedom has resulted in dramatically improved resolution without compromising stability.

Spectrum analysis of microwave breast examination data and reconstructed images

A broadband microwave tomographic imaging system is being developed for breast cancer detection which exploits the significant electrical property contrast between normal and malignant tissue. The improved image reconstruction algorithm directly processes the log-magnitude and phase values of the measured fields with the frequency rich data set being utilized to acquire the absolute scattered phase terms, especially when multiple wrapping has occurred. In addition, a lower contrast coupling medium has been selected which alleviates certain problems associated with the phase unwrapping task but also appears to reduce artifacts associated with higher permittivity contrasts between the surrounding coupling medium and the breast. Sequences of multi-plane image sets from a low contrast medium examination of a 53 year old woman over a broad frequency range are presented to illustrate the general consistency of the images over the range and to demonstrate the improved resolution at the higher frequencies.

Analysis of maximum phase projection data for improvement of microwave imaging background media

Scattered phase values measured at receiver sites in our microwave breast tomographic imaging system can be considerable when the dielectric properties of an object being imaged vary significantly from those of the background coupling medium. A focus of study for the improvement of our microwave breast imaging system has been to devise a background solution that more closely matches the dielectric properties of the breast in order to reduce the magnitude of scattered phase projections. Analysis of phase projection simulation and measurement data has provided important insight in the permittivity requirements for an optimal background solution.

A scanned focused ultrasound device for hyperthermia: numerical simulation and prototype implementation

We are developing a scanned focused ultrasound system for hyperthermia treatment of breast cancer. Focused ultrasound has significant potential as a therapy delivery device because it can focus sufficient heating energy below the skin surface with minimal damage to intervening tissue. However, as a practical therapy system, the focal zone is generally quite small and requires either electronic (in the case of a phased array system) or mechanical steering (for a fixed bowl transducer) to cover a therapeutically useful area. We have devised a simple automated steering system consisting of a focused bowl transducer supported by three vertically movable rods which are connected to computer controlled linear actuators. This scheme is particularly attractive for breast cancer hyperthermia where the support rods can be fed through the base of a liquid coupling tank to treat tumors within the breast while coupled to our noninvasive microwave thermal imaging system. A MATLAB routine has been developed for controlling the rod motion such that the beam focal point scans a horizontal spiral and the subsequent heating zone is cylindrical. In coordination with this effort, a 3D finite element thermal model has been developed to evaluate the temperature distributions from the scanned focused heating. In this way, scanning protocols can be optimized to deliver the most uniform temperature rise to the desired location.