Pleural effusion detection system using wideband slot-loaded loop antenna

Pleural effusion (PE) is the accumulation of fluids around the lungs due to various diseases, such as cancer, liver and heart failure. Given the fact that fluid provides a high contrast in terms of dielectric constant at microwave frequencies, a radar-based microwave imaging system is proposed to utilise that change in properties for the early detection of PE. The system uses a wideband slot-loaded loop antenna to scan the torso, a portable vector network analyser for signal generation and recording, and a laptop for signal processing and image formation using a frequency-based imaging algorithm. The utilised antenna is designed to have a compact size (in wavelengths) of 0.23 × 0.23 that is one-third the size of recent designs. By using proper slots in a conventional slot-loaded loop and adding a staircase-shaped patch to the loop´s perimeter, the antenna achieves a fractional bandwidth of 50% (0.72-1.19 GHz), and a peak gain of 4.9 dBi. The practicality of the proposed system is successfully tested by detecting a small amount of fluid (3 mL) around the lungs of a realistic life-size torso phantom.