Development of an Anthropomorphic Phantom of the Axillary Region for Microwave Imaging Assessment

Abstract

We produced an anatomically and dielectrically realistic phantom of the axillary region to enable the experimental assessment of Axillary Lymph Node (ALN) imaging using microwave imaging technology. We segmented a thoracic Computed Tomography (CT) scan and created a computer-aided designed file containing the anatomical configuration of the axillary region. The phantom comprises five 3D-printed parts representing the main tissues of interest of the axillary region for the purpose of microwave imaging: fat, muscle, bone, ALNs, and lung. The phantom allows the experimental assessment of multiple anatomical configurations, by including ALNs of different size, shape, and number in several locations. Except for the bone mimicking organ, which is made of solid conductive polymer, we 3D-printed cavities to represent the fat, muscle, ALN, and lung and filled them with appropriate tissue-mimicking liquids. Existing studies about complex permittivity of ALNs have reported limitations. To address these, we measured the complex permittivity of both human and animal lymph nodes using the standard open-ended coaxial-probe technique, over the 0.5 GHz–8.5 GHz frequency band, thus extending current knowledge on dielectric properties of ALNs. Lastly, we numerically evaluated the effect of the polymer which constitutes the cavities of the phantom and compared it to the realistic axillary region. The results showed a maximum difference of 7 dB at 4 GHz in the electric field magnitude coupled to the tissues and a maximum of 10 dB difference in the ALN response. Our results showed that the phantom is a good representation of the axillary region and a viable tool for pre-clinical assessment of microwave imaging technology.

A Simulation-Based Methodology of Developing 3D Printed Anthropomorphic Phantoms for Microwave Imaging Systems

“…As defined in the framework of the EMERALD project, the manufacturing process used to build up accurate ultra-wideband (UWB) phantoms has to be easily reproducible by an electrical engineer in a non-specific environment without extreme precautions, and to some extent at low cost. The specificity of the GeePs-L2S breast phantom and those suggested in our previous and current works on the head [ 19 , 32 ], breast [ 13 , 33 ], and thorax [ 34 , 35 ] phantoms, has been confirmed by the work of [ 14 , 15 , 16 , 17 , 18 ] and [ 36 , 37 , 38 , 39 ]. These phantoms composed of several 3D printed cavities are filled up with liquid mixtures made for example of Triton X-100 (TX-100, a non-ionic surfactant) and salt water, the concentrations are numerically adjusted so that the dielectric properties are close to the reference values over a wide frequency range.…”

Development of MRI‐based axillary numerical models and estimation of axillary lymph node dielectric properties for microwave imaging

“…We also used this methodology with a new objective: estimate dielectric properties of structures for which dielectric property information is still limited. As mentioned in Section 1, the assumptions behind our methodology limit the direct comparison of absolute dielectric property values with state‐of‐the‐art values measured with traditional methods, such as OECP 11,20 . Also, a comparison with the patients included in our study is not possible since no follow‐up of the patients was done.…”

“…In general, the authors observed that the complex permittivity results extracted from the measurements on the external surfaces are dominated by the fat layer surrounding the ALNs at the time of excision, resulting in lower permittivity and conductivity. A large variability of dielectric property values was observed in all measurements (5–55 at 4 GHz 11,20 ). More recently, Yu et al 21 measured human intrathoracic LNs removed from lung cancer surgeries and verified metastasized LNs presented significantly higher dielectric properties than healthy LNs.…”

“…A few studies carried dielectric property measurements of ALNs using the open-ended coaxial-probe (OECP) method, 11,16,19,20 both in animal and human ALNs. However, usually human ALN samples have to remain intact due to clinical constraints and only their surface is measured.…”

“…MWI is a low‐cost, low‐power and noninvasive technique which has already yielded promising results for early breast cancer diagnosis 8 and brain stroke detection 9 . MWI has been recently studied to work as a complementary diagnostic tool to detect metastasized ALNs 10–12 …”