Charlotte Curtis

Microwave Breast Imaging With a Monostatic Radar-Based System: A Study of Application to Patients

A prototype microwave breast imaging system is used to scan a small group of patients. The prototype implements a monostatic radar-based approach to microwave imaging and utilizes ultra-wideband signals. Eight patients were successfully scanned, and several of the resulting images show responses consistent with the clinical patient histories. These encouraging results motivate further studies of microwave imaging for breast health assessment.

Neighborhood-Based Algorithm to Facilitate the Reduction of Skin Reflections in Radar-Based Microwave Imaging

Radar-based microwave imaging is being investigated as a complementary diagnostic tool for breast cancer detection. One of the major challenges associated with radar-based breast imaging is the removal of the overwhelming re∞ection caused by the skin. This paper presents an algorithm that has been designed for realistic 3D scenarios. The algorithm is tested on a variety of realistic 3D numerical breast models, as well as measured data from a phantom and patient. In all cases, the re∞ections from the skin are signiflcantly reduced, facilitating detection of known tumors.

Evaluation of 3-D Acquisition Surfaces for Radar-Based Microwave Breast Imaging

This study investigates the impact that the acquisition surface has on the internal coverage of an object in the context of radar-based near-field microwave (MW) breast imaging. We define an acquisition surface as the surface over, which data are collected. Three different three-dimensional (3-D) data acquisition surfaces are investigated: 1) cylindrical, 2) hemispherical, and 3) patient specific. Three 3-D numerical breast models are used for the study. A realistic ultra-wideband (UWB) antenna generates incident fields and records the total fields. The responses from targets are analyzed, and object coverage is evaluated in terms of range distances, cross-range distances, and cumulative radiated power directed into the object by the antenna array embedded in the acquisition surface. Images are formed to verify these observations. We demonstrate that a patient-specific acquisition surface provides greater responses from targets, superior object coverage and improved images compared to the other acquisition surfaces studied.

Detailed evaluation of artifact removal algorithms for radar-based microwave imaging of the breast

One of the most important components of radar-based microwave imaging systems for breast cancer detection is the early-stage artifact removal algorithm. The early-stage artifact is composed of the input signal, the reflection from the skin-fat interface and any antenna reverberation present. This artifact is typically several orders of magnitude greater than the reflections from any tumours present within the breast. If the early-stage artifact is not removed and the tumour response effectively preserved, the artifact could potentially mask energy reflected from shallow tumours located close to the surface of the skin, and also hinder the identification of tumours located deeper within the breast.

Semiautomated Multimodal Breast Image Registration

Consideration of information from multiple modalities has been shown to have increased diagnostic power in breast imaging. As a result, new techniques such as microwave imaging continue to be developed. Interpreting these novel image modalities is a challenge, requiring comparison to established techniques such as the gold standard X-ray mammography. However, due to the highly deformable nature of breast tissues, comparison of 3D and 2D modalities is a challenge. To enable this comparison, a registration technique was developed to map features from 2D mammograms to locations in the 3D image space. This technique was developed and tested using magnetic resonance (MR) images as a reference 3D modality, as MR breast imaging is an established technique in clinical practice. The algorithm was validated using a numerical phantom then successfully tested on twenty-four image pairs. Dices coefficient was used to measure the external goodness of fit, resulting in an excellent overall average of 0.94. Internal agreement was evaluated by examining internal features in consultation with a radiologist, and subjective assessment concludes that reasonable alignment was achieved.

Near field radar imaging in the frequency domain with application to patient data

Radar imaging in the near field for biological applications has received considerable attention in recent years. Development of this new modality is motivated by differences in the dielectric properties of tissues; in particular, cancerous breast tissue has been found to be significantly different from healthy tissues (M. Lazebnik et al, Phys. Med. and Bio., 52(20), 6093115. 2007). These differences cause scattering of electromagnetic fields and by recording the scattered signals at many antenna positions, the locations of high contrast objects can be determined via image formation.

Characterizing the point spread function of a near field ultrawideband monostatic radar imaging system

Summary form only given. Near field microwave imaging has been gaining traction as a viable imaging technique for biomedical applications such as breast cancer detection. Microwave imaging systems, both radar and tomographic, have proven capable of accurately detecting inclusions in models, and results from initial patient studies are promising. However, little is known about the relationship between acquisition parameters and system response such as resolution and sensitivity.

Using X-ray mammograms to assist in microwave breast image interpretation

Current clinical breast imaging modalities include ultrasound, magnetic resonance (MR) imaging, and the ubiquitous X-ray mammography. Microwave imaging, which takes advantage of differing electromagnetic properties to obtain image contrast, shows potential as a complementary imaging technique. As an emerging modality, interpretation of 3D microwave images poses a significant challenge. MR images are often used to assist in this task, and X-ray mammograms are readily available. However, X-ray mammograms provide 2D images of a breast under compression, resulting in significant geometric distortion. This paper presents a method to estimate the 3D shape of the breast and locations of regions of interest from standard clinical mammograms. The technique was developed using MR images as the reference 3D shape with the future intention of using microwave images. Twelve breast shapes were estimated and compared to ground truth MR images, resulting in a skin surface estimation accurate to within an average Euclidean distance of 10 mm. The 3D locations of regions of interest were estimated to be within the same clinical area of the breast as corresponding regions seen on MR imaging. These results encourage investigation into the use of mammography as a source of information to assist with microwave image interpretation as well as validation of microwave imaging techniques.

An Analysis of the Assumptions Inherent to Near-Field Beamforming for Biomedical Applications

Microwave imaging for biomedical applications is a growing field that shows promise in early patient studies. Interpretation of preclinical imaging results is difficult, in part due to an incomplete understanding of the imaging operator. In this paper, near-field beamforming is demonstrated to be analogous to synthetic aperture radar, and both imaging methods are shown to depend on several simplifying assumptions. The influence of these assumptions is analyzed using analytical and simulated models, and the results are confirmed in an experimental setup. These observations are further explored in application to simulations of realistic breast models as well as patient data.

Performance of leading artifact removal algorithms assessed across microwave breast imaging prototype scan configurations

Microwave imaging is a promising imaging modality for the detection of early-stage breast cancer. One of the most important signal processing components of microwave radar-based breast imaging is early-stage artifact removal. Several artifact removal algorithms have been reported in the literature. However, the neighbourhood-based skin subtraction and hybrid artifact removal algorithms have shown particularly promising results in different realistic 3D breast phantoms. For the first time in this paper, both algorithms have been evaluated and compared using the scan approaches of the most common microwave breast imaging prototype systems. The tests include 3D numerical as well as experimental breast phantoms scanned with hemispherical, cylindrical and adaptive scanning patterns. The efficacy of both algorithms has been evaluated across a range of appropriate performance metrics.