Personnel
Peter Damsgaard Jensen, PhD Student
Johan Jacob Mohr, PhD, Associate Professor
Vitaliy Zhurbenko, PostDoc
Period
1 June 2010 – 31 May 2013
Funding
Technical University of Denmark
Villum Kann Rasmussen Foundation
Background
This project is a continuation of the project Microwave Imaging for Breast Cancer Detection.
Worldwide, more than a million people are diagnosed with breast cancer every year. Breast cancer is the second leading cause of cancer death among women today. Early detection is important for effective treatment, and greatly improves the chances for survival. To this end, women after the age of 40 or 50 years are offered regular mammography screening in most developed countries. Mammography uses X-rays to image the densities of a compressed breast. Lesions in the breast will be seen in the image (called a mammogram), however, it may be difficult to discriminate between cancerous and non-cancerous lesions without additional imaging or biopsy. Also, not all lesions may be detected, and it is difficult to image women who have dense breasts. Lastly, many women find mammography uncomfortable or painful, and there are health concerns related to exposure to ionizing radiation such as x-rays. The current alternatives, ultrasound and magnetic resonance imaging (MRI), are unfortunately not suitable for large-scale screening programs because they are too expensive, time-consuming and require highly specialized doctors to perform the screenings. In resent years, an increased number of research groups have proposed microwave imaging as another alternative to X-ray mammography. Potential advantages of microwave imaging systems, which presently are in a developing phase, are the use of non-ionizing radiation, better sensitivity to cancer tissue in young women, and a lower cost of the system.
Description
The project aims at designing and building a three-dimensional microwave tomography system including its preparation for clinical tests. The current prototype with 32 antennas and transceiver modules has on, non-biological phantoms, provided a resolution better than 1 cm3 at 1.5 GHz. Compared to the work of other research groups, the DTU system is a true 3-D system; it has good discrimination between materials with different permittivity and conductivity.
The system applies inverse scattering techniques. The term inverse scattering is used to describe techniques in which the images are created by inverting a model of the scattering mechanisms derived from Maxwell's equations. By using Maxwell’s equations, an exact solution to the forward scattering problem can be determined. The forward model, however, is often too complex to efficiently be inverted and certain approximations and assumptions must therefore be applied. Consequently, the application of physically viable assumptions and simplifications to the forward model is as important in inverse scattering as the pure mathematical procedure of inverting the model.
The PhD project has three components. The first concerns establishment of a test facility and conduct of extensive tests including phantoms and biological tissue. This will a) allow for a comparison with other system designs at other universities, b) provide insight into the strengths and weaknesses of the present inverse scattering algorithm and system configuration and c) provide a basis for cooperation with medical doctors. The long-term goal will be clinical tests including comparison with X-ray and/or ultrasound.
The second component concerns improvements of the imaging algorithm. The tests would be used to select the most promising line of work. Already now, several candidate tasks have been identified. These include simultaneous use of multiple frequencies and investigation of alternatives to the currently used log-phase formulation, which has proven efficient, but may not necessarily be optimal. Also, adaption of a commercial electromagnetic forward solver to substitute the Method of Moment (MoM) solver, developed in-house, could be addressed.
The third component concerns improvement of the antenna design and/or system configuration and data acquisition strategy. Again, the tests are anticipated to guide towards the most promising line of work. The limiting factor, though, is anticipated to be loss in coupling liquid so development of a directive antenna, with a reduced back-lobe, and good matching over a large frequency interval is a candidate task. The challenge here is that the antennas are submerged in a lossy liquid, giving currents not present in free space conditions. This implies that most of the antenna designs available in the literature cannot be used in the system.
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