Medical imaging currently relies on several techniques, including X-rays, magnetic resonance, and echography. However, these techniques exhibit drawbacks, and alternative approaches are required. Microwave imaging has been proposed as a possible solution, especially for breast cancer imaging. However, most of these systems work with a central frequency of a few gigahertz, and this leads to a suboptimum resolution, which can jeopardize the image quality. Millimeter waves can provide superior resolutions, at the cost of a lower penetration depth within the breast tissue. In addition, a significant fraction of the power generated by a mm-wave imaging system would be reflected back from the skin. For these reasons, and also considering that mm-wave transmitters and receivers have been historically outperformed by microwave counterparts in terms of available power and sensitivity, mm-wave imaging has not been considered a possible solution. This paper contributes to demonstrate a paradigm shift toward the possible use of mm-waves for breast cancer imaging of targets a few centimeter below the skin, a useful penetration depth for several cases. All key points are addressed using analytical, full-wave, and multiphysics simulations, including the system architecture (linear and conformal), the safety aspects (power density, specific absorption rate, and temperature increase), and the use of realistic breast models derived from ex vivo measurements.

Millimeter (mm)-wave imaging has been recently proposed as a new technique for breast cancer detection, based on the significant dielectric contrast between healthy and tumor tissues. Here we propose a procedure to fabricate, electromagnetically characterize and preserve realistic breast tissue-mimicking phantoms for testing mm-wave imaging prototypes. Low-cost, non-toxic and easy-to-produce mixtures made of sunflower oil, water and gelatin were prepared and their dielectric properties were for the first time measured in the (0.5–50) GHz frequency range using a coaxial probe kit. Different oil and gelatin percentages were tested. An alternative recipe based on a waste-oil hardener was also proposed. Finally, water and sunflower oil were investigated as preservation media. The mixtures electromagnetic properties were in good agreement with those of human breast ex vivo samples. By changing the ingredient concentrations or using different solidifying agents it was possible to mimic different tissue types. Besides, we show that sunflower oil represents an effective preservation medium for the developed materials. The first breast phantom mimicking a tumor mass into healthy tissues up to 50 GHz was also successfully fabricated. Results demonstrated the potential of the designed recipes to mimic breast tissues with different biological characteristics, preserving dielectric properties over time. Thus, this study represents a fundamental step towards the development of heterogeneous breast phantoms able to mimic the electromagnetic behavior of healthy and tumor tissues for mm-wave imaging applications.

Breast cancer represents one of the main reasons of death among women. As an alternative to the gold standard techniques for breast cancer diagnosis, microwave imaging has been proposed from research community and many microwave systems have been designed mainly to work at low microwave frequencies. Based both on the results of recent dielectric characterization campaigns on human breast ex-vivo tissues up to 50 GHz and on the promising feasibility studies of mm-wave imaging systems, in this article, we propose and test inverse scattering techniques as effective tool to process mm-wave data to image breast cancer. Differently from the radar techniques so far adopted in conjunction with mm-wave imaging system, inverse scattering techniques turn out to be more versatile and robust with respect to the reduction of the number of processed frequencies and eventually also able to characterize the anomaly in terms of electromagnetic properties. In particular, in the above, two image reconstruction techniques, the Linear Sampling Method and the Born Approximation, are proposed and compared against both simulated and experimental data.

Objective: The potentialities of improving the penetration of millimeter waves for breast cancer imaging are here explored. Methods: A field focusing technique based on a convex optimization method is proposed, capable of increasing the field level inside a breast-emulating stratification. Results: The theoretical results are numerically validated via the design and simulation of two circularly polarized antennas. The experimental validation of the designed antennas, using tissue-mimicking phantoms, is provided, being in good agreement with the theoretical predictions. Conclusion: The possibility of focusing, within a lossy medium, the electromagnetic power at millimeter-wave frequencies is demonstrated. Significance: Field focusing can be a key for using millimeter waves for breast cancer detection.

Nowadays, breast cancer is the most diffused disease among women around the word. Statistics indicate an increase in incident rate, especially in Europe, North America, and Oceania. Currently, the set of diagnostic tools for breast cancer detection is wide. Nevertheless, these tools exhibit limitations, especially when aiming at cost-effective periodical mass screenings. Therefore, there is a growing interest toward microwave imaging systems for biomedical applications, and several microwave prototypes have been proposed worldwide. However, in order to have a satisfying resolution for earlydiagnosis, microwaves may be not sufficient, and a crucial point is the utilization of higher frequencies. To this aim, as the physical principle of all imaging techniques at these frequencies is based on the detection of the dielectric discontinuities between materials, the characterization of all breast tissues in the mmwave spectrum becomes fundamental. No experimental data were available beyond 20 GHz before the two extensive experimental campaigns performed at the European Institute of Oncology in 2014 and 2016. In this paper, the results concerning the full database (given by the fusion of the two datasets) of exvivo samples, are presented. In particular, a huge amount of data is considered, involving more than 330 samples, of which 237 healthy and 99 malignant, taken from around 100 women with an age spanning from 28 years up to 85 years.

Breast cancer is one of the leading causes of cancer death among women; to decrease the death rate for this disease, early detection plays a key role. Recently, microwave imaging systems have been proposed as an alternative to the current techniques, but they suffer from poor resolution due to the low frequencies involved. In this paper, for the first time, an innovative millimeter-wave imaging system for early-stage breast cancer detection is proposed and experimentally verified on different breast phantoms. This has the potential to achieve superior resolution for breasts with a high volumetric percentage of adipose tissue, and the merit to overcome the common misconception that millimeter-waves cannot achieve useful penetration depths for biological applications. Three phantoms were prepared according to the dielectric properties of human breast ex vivo tissues in the frequency range [0.5–50] GHz. Two cylindrical inclusions made by water and gelatin or agar, mimicking dielectric properties of neoplastic tissues, were embedded in the phantom at different depths up to 3 cm. Two double ridge waveguides, with mono-modal frequency band equal to [18–40] GHz, were used to synthetize a linear array of 24 elements in 28 positions, acquiring signals with a Vector Network Analyzer. The images were reconstructed by applying the Delay and Sum algorithm to calibrated data. The feasibility of a new imaging system with a central working frequency of about 30 GHz is experimentally demonstrated for the first time, and a target detection capability up to 3 cm within the phantom is shown. The presented results pave the way for a possible use of millimeter-waves to image non-superficial neoplasms in the breast.