Microwave tomography of extremities: 1. Dedicated 2D system and physiological signatures

Abstract

Microwave Tomography (MWT) is a novel imaging modality which might be applicable for non-invasive assessment of functional and pathological conditions of biological tissues. The imaging of the soft tissue of extremities is one of its potential applications. The feasibility of this technology for such applications was demonstrated earlier. This is the first of two companion papers focused on an application of MWT for imaging of the extremity’s soft tissues. The goal of this study is to assess the technical performance of the developed 2D MWT system dedicated for imaging of functional and pathological conditions of the extremity’s soft tissues. Specifically, the system’s performance was tested by its ability to detect signals associated with physiological activity and soft tissue interventions (circulatory related changes, blood flow reduction and a simulated compartmental syndrome) – so called “physiological signatures”. The developed 2D MWT system dedicated for an imaging of animal extremities demonstrates good technical performance allowing for stable and predictable data acquisition with reasonable agreement between experimentally measured electromagnetic (EM) field and simulated EM field within a measurement domain. Using the system we were able to obtain physiological signatures associated with systolic vs diastolic phases of circulation in an animal extremity, reperfusion vs occlusion phases of the blood supply to the animal’s extremity and the a compartment syndrome. The imaging results are presented and discussed in the second companion paper.

Analysis of Incident Field Modeling and Incident/Scattered Field Calibration Techniques in Microwave Tomography

“…Monopoles [9] and open-ended loaded waveguides [10] seem to be the most popular, probably because they can be replaced by relatively accurate simple models in the inversion algorithm. Nonetheless, we have used more complicated antennas successfully: Our air-based system utilizes 24 co-resident double-layered Vivaldi antennas (DLVA) [11] encircling the OI on the periphery of a plexiglas chamber.…”

“…Due to the heavy computational cost, antennas are not fully modeled in MWT algorithms [3], [10], even for more sophisticated 3-D inversions [9], [12]. Thus, one must determine an acceptably accurate incident field to be used in the imaging algorithm and determine calibration factors that convert the measured quantities to field values at particular positions.…”

3D Microwave Breast Imaging Based on Multistatic Radar Concept System

“…The 2D MT system, which was created at the University of Keele, UK [5], [16], [17] applies a circular array of 24 Tx/Rx ceramic filled waveguides with opened ends. This array is attached to a metallic bath with the coupling liquid.…”

“…This array is attached to a metallic bath with the coupling liquid. The system operates in the 1.0～2.3 GHz frequency band and has been used to investigate imaging in soft animals tissues, like pig's extremities [16], [17].…”

A Multiprobe-Per-Collector Modulated Scatterer Technique for Microwave Tomography

“…The majority of experimental MWT measurement systems utilize co-resident antennas that measure the field directly, and thus we refer to such systems as direct measurement systems. The number of antenna elements used in these systems varies, e.g., 16 in the work reported in [2], 24 in [3] and [4], or 64 in [5]. Co-resident antenna direct systems are preferable to mechanical scanning systems for speed and accuracy of data acquisition.…”