On the dielectric and mechanical characterization of tissue-mimicking breast phantoms.

Objective. In this paper, we focus on the dielectric and mechanical characterization of tissue-mimicking breast phantoms.Approach. Starting from recipes previously proposed by our research group, based on easy-to-handle, cheap and safe components (i.e. sunflower oil, deionized water, dishwashing liquid and gelatin), we produced and tested, both dielectrically and mechanically, more than 100 samples. The dielectric properties were measured from 500 MHz to 14 GHz, the Cole-Cole parameters were derived to describe the dielectric behaviour in a broader frequency range, and the results were compared with dielectric properties of human breastex vivotissues up to 50 GHz. The macroscale mechanical properties were measured by means of unconfined compression tests, and the impact of the experimental conditions (i.e. preload and test speed) on the measured Young's moduli was analysed. In addition, the mechanical contrast between healthy- and malignant-tissue-like phantoms was evaluated.Main results. The results agree with the literature in the cases in which the experimental conditions are known, demonstrating the possibility to fabricate phantoms able to mimic both dielectric and mechanical properties of breast tissues.Significance. In this work, for the first time, a range of materials reproducing all the categories of breast tissues were experimentally characterized, both from a dielectric and mechanical point of view. A large range of frequency were considered for the dielectric measurements and several combinations of experimental conditions were investigated in the context of the mechanical characterization. The proposed results can be useful in the design and testing of complementary or supplementary techniques for breast cancer detection based on micro/millimetre-waves, possibly in connection with other imaging modalities.

Enhancement of Penetration of Millimeter Waves by Field Focusing Applied to Breast Cancer Detection.

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.

Combining Millimeter-Wave Imaging, Ultrasound and Elastography in a New Multimodal Approach for Breast Cancer Detection: Initial Experimental Results.

In this paper, for the first time, a triple-mode scan using electromagnetic waves, in the shape of millimeter waves, and ultrasound waves, to obtain B-mode and quasistatic elastography images of a phantom of human breast tissues is shown. A homogeneous phantom composed of nontoxic, low-cost and easy-to-handle materials (i.e. water, oil, gelatin and dishwashing liquid) was produced, with an inclusion made of water and agar. These are intended to mimic, in terms of dielectric properties, healthy adipose tissues and neoplastic tissues, respectively. A millimeter-wave imaging prototype was used to scan the phantom, by implementing a linear synthetic array of 24 antennas with a central working frequency of 30 GHz. The phantom was then scanned using an ultrasound research system and a linear-array probe at 7 MHz, acquiring both B-mode and quasi-static elastography images. The millimeter-wave system showed an excellent ability to detect the target placed at about 1.4 cm depth. Also in the ultrasound case the inclusion was correctly detected as a hypoechoic, stiff mass. This first experimental findings show that millimeter-wave, ultrasound and elasticity imaging can be used jointly to detect tumor-like targets into phantoms mimicking healthy breast tissues. Thus, they provide promising preliminary results to further study the application of this multimodal approach in all those critical cases in which such complementary imaging techniques could be exploited for an enhanced tumor detection, based on tissues dielectric, acoustic and elastic properties.

Tissue-mimicking materials for breast phantoms up to 50 GHz.

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.

Towards mm-wave spectroscopy for dielectric characterization of breast surgical margins.

PURPOSE: The evaluation of the surgical margin in breast conservative surgery is a matter of general interest as such treatments are subject to the critical issue of margin status as positive surgical margins can undermine the effectiveness of the procedure. The relatively unexplored ability of millimeter-wave (mm-wave) spectroscopy to provide insight into the dielectric properties of breast tissues was investigated as a precursor to their possible use in assessment of surgical margins. METHODS: We assessed the ability of a mm-wave system with a roughly hemispherical sensitive volume of ∼3 mm radius to distinguish malignant breast lesions in prospectively and consecutively collected tumoral and non-tumoral ex-vivo breast tissue samples from 91 patients. We characterized the dielectric properties of 346 sites in these samples, encompassing malignant, fibrocystic disease and normal breast tissues. An expert pathologist subsequently evaluated all measurement sites. RESULTS: At multivariate analysis, mm-wave dielectric properties were significantly correlated to histologic diagnosis and fat content. Further, using 5-fold cross-validation in a Bayesian logistic mixed model that considered the patient as a random effect, the mm-wave dielectric properties of neoplastic tissues were significantly different from normal breast tissues, but not from fibrocystic tissue. CONCLUSION: Reliable discrimination of malignant from normal, fat-rich breast tissue to a depth compatible with surgical margin assessment requirements was achieved with mm-wave spectroscopy.