Wearable Electromagnetic Belt for Steatotic Liver Detection Using Multivariate Energy Statistics

Abstract

A wearable electromagnetic belt system for the detection of hepatic steatosis (lipid accumulation within the major liver cells, hepatocytes), is proposed. To satisfy the requirements of the belt system, an array of body matched antennas is designed. The belt, which goes around the lower chest and over the liver, requires compact, wideband, unidirectional antennas that operate at low microwave frequencies. To avoid using conventional bulky reflector structures, the designed antenna utilizes the loop-dipole combination concept. To enhance electromagnetic wave penetration, the antenna is designed to match the human body. Thus, thanks to the high dielectric loading from the human body, the dipole element of the antenna is easily miniaturized. Since the same principle does not apply on the loop structure, meandered arc-shapes are employed to increase the effective electrical length of the loop. The final antenna design has a measured wide operating bandwidth of 0.58-1.6 GHz with a compact size of 0.096×0.048×0.048λ 3 . The proposed structure is effective in irradiating the torso, where the signal can reach center of the liver at a depth of 90 mm, with 64% of the peak radiated power. An electromagnetic belt is built using twelve elements of the designed antennas. The belt is then tested on a 3D printed torso phantom that includes models of the lungs and liver. Due to close dielectric properties of the other tissues inside the torso, these are represented using an average tissue mimicking mixture with permittivity of 46. Measured data are analyzed using multivariate energy statistics method. A peak measured dissimilarity of 15.1% between steatotic and healthy liver is attained. These initial tests and obtained results indicate the potential of the proposed system as a method to diagnose hepatic steatosis.INDEX TERMS Body-matched antenna, electromagnetic belt, fatty liver disease, statistical based analysis, wearable system.

Electromagnetic Torso Scanning: A Review of Devices, Algorithms, and Systems

“…Hence, this method is more suitable for surface or subsurface abnormalities [ 29 ]. In the multi-static system, an array of antennas, at least two, are used to transmit and receive signals [ 24 , 30 , 31 , 32 ]. This process continues sequentially until all the antennas in the array have received signals from each other.…”

“…To overcome the complications of finding the exact location of the antenna with respect to the body, wearable systems can be used [ 13 , 24 , 39 , 40 ]. As shown in Figure 6 , in these systems the antenna array is located on the body, and depending on the utilized detection algorithm, the antennas can be located locally adjacent to the subject [ 40 ] or surround the circumference of the imaged body [ 24 ]. These systems can utilize multi or mono static data acquisition methods and can accommodate larger number of antennas as antenna size can be significantly reduced due to the body loading on the antenna.…”

“…This is attributed to a wider distribution of EM field at longer distances compared to the focused distribution at closer distances [ 43 ]. Studying torso scanning systems reveals that using a 1 mW (0 dBm) transmitted power results in SAR values between 0.004–0.04 W/kg at 0.6–0.9 GHz [ 18 , 24 , 29 , 33 , 34 ]. Lower values are obtained when antennas are located farther from body [ 29 , 33 ] and higher values are attributed to antennas closer to body [ 18 , 24 , 34 ].…”

“…Investigating EM scanning systems reveals that two broad categories of radiators are used to scan the human torso; (1) on-body matched antennas [ 24 , 30 , 31 , 53 , 54 ], and (2) free-space antennas [ 55 , 56 , 57 , 58 , 59 , 60 ]. Different methods were proposed to design these antennas that are detailed in this section.…”

“…The advances in computational methods and artificial intelligence open new horizons in research that were not feasible before. For example, a statistical analysis was adopted to predict changes in fat levels inside the liver [ 24 ]. This method is based on the high symmetry between the right and left sides of the body and analysis of the correlation between signals from these areas at several frequency points.…”