We propose a 3-D-printed breast phantom for use in preclinical experimental microwave imaging studies. The phantom is derived from an MRI of a human subject; thus, it is anthropomorphic, and its interior is very similar to an actual distribution of fibroglandular tissues. Adipose tissue in the breast is represented by the solid plastic (printed) regions of the phantom, while fibro glandular tissue is represented by liquid-filled voids in the plastic. The liquid is chosen to provide a biologically relevant dielectric contrast with the printed plastic. Such a phantom enables validation of microwave imaging techniques. We describe the procedure for generating the 3-D-printed breast phantom and present the measured dielectric properties of the 3-D-printed plastic over the frequency range 0.5-3.5 GHz. We also provide an example of a suitable liquid for filling the fibroglandular voids in the plastic.

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MRI-Derived 3-D-Printed Breast Phantom for Microwave Breast Imaging Validation

We present a technique for fabricating realistic breast phantoms for microwave imaging experiments. Using oil-in-gelatin dispersions that mimic breast tissue dielectric properties at microwave frequencies, we constructed four heterogeneous phantoms spanning the full range of volumetric breast densities. We performed CT scans and dielectric properties measurements to characterize each phantom.

Heterogeneous Anthropomorphic Phantoms with Realistic Dielectric Properties for Microwave Breast Imaging Experiments.

This work introduces new, stable, and broadband skin-equivalent semisolid phantoms for mimicking interactions of millimeter waves with the human skin and skin tumors. Realistic skin phantoms serve as an invaluable tool for exploring the feasibility of new technologies and improving design concepts related to millimeter-wave skin cancer detection methods. Normal and malignant skin tissues are separately mimicked by using appropriate mixtures of deionized water, oil, gelatin powder, formaldehyde, TX-150 (a gelling agent, widely referred to as “super stuff”), and detergent. The dielectric properties of the phantoms are characterized over the frequency band of 0.5–50 GHz using a slim-form open-ended coaxial probe in conjunction with a millimeter-wave vector network analyzer. The measured permittivity results show excellent match with ex vivo , fresh skin (both normal and malignant) permittivities determined in our prior work over the entire frequency range. This work results in the closest match among all phantoms reported in the literature to surrogate human skin tissues. The stability of dielectric properties over time is also investigated. The phantoms demonstrate long-term stability (up to 7 months was investigated). In addition, the penetration depth of millimeter waves into normal and malignant skin phantoms is calculated. It is determined that millimeter waves penetrate the human skin deep enough (0.6 mm on average at 50 GHz) to affect the majority of the epidermis and dermis skin structures.

Ultrawideband, Stable Normal and Cancer Skin Tissue Phantoms for Millimeter-Wave Skin Cancer Imaging

A four-shell head phantom has been built and characterized. Its structure is similar to that of nonhomogeneous concentric shell domains used by numerical solvers that better approximate current distribution than phantoms currently used to validate electrical impedance tomography systems. Each shell represents a head tissue, namely, skin, skull, cerebrospinal fluid, and brain. A novel technique, which employs a volume conductive impermeable film, has been implemented to prevent ion diffusion between different agar regions without affecting current distribution inside the phantom. Comparisons between simulations and phantom measurements performed over four days are given to prove both the adherence to the model in the frequency range between 10 kHz and 1 MHz and its long-term stability.

A Four-Shell Diffusion Phantom of the Head for Electrical Impedance Tomography

There has recently been considerable interest in detecting and managing different types of cancer by using nonionizing electromagnetic waves. These methods rely on the inherent contrast between the electrical properties of malignant and normal tissues. It has been shown that cancer changes the water content as well as the biochemistry (e.g., metal concentration) of tissues [1]-[3], so it changes dielectric properties. In this regard, microwaves have been used to image breast cancer and lung cancer in the frequency range of 300 MHz-10 GHz [4]-[6]. Compared to microwaves, millimeter waves (mm-waves) (30-300 GHz) have shorter wavelengths and penetrate from 700 um to 1.3mm into the body [7], making them highly effective for sensing pathological changes in the tissue layers of excised organs or different skin layers from which most skin tumors originate [8], [9]. As the frequency increases further (>300 GHz), electromagnetic waves barely penetrate the tissues' surface [10], [11] and therefore have a limited ability to detect early-stage tumors that reside in deeper tissue layers.

Tumor Detection Using Millimeter-Wave Technology: Differentiating Between Benign Lesions and Cancer Tissues

Phantom model of the breast which has actual shape and size has been developed for evaluation of microwave imaging by Chirp Pulse Microwave Computed Tomography (CP-MCT). This phantom model will also be successfully used for hyperthermia experiments using microwaves. This phantom model is consisted of four kinds of tissue mimicking materials, that is, the skin-, breast fat-, muscle-, and tumor-simulators. The principal ingredients of the phantom are water, liquid paraffin, super stuff (TX-150), sugar, and salt. It is easy to simulate permittivity of the real breasts in addition to the shape and size. This is the advantage of this non-homogeneous phantom. CP-MCT is a modality for microwave imaging of a human body using chirp pulse microwaves to extract the component which transmits the straight path between two antennas. Possibility of tumor detection by CP-MCT has been demonstrated by using the higher frequency model of CP-MCT and the non-homogeneous breast phantom.

Kenta Inotsume

Papers

Development of non-uniform breast phantom and its microwave imaging for tumor detection by CP-MCT