TDOA-based microwave imaging algorithm for real-time microwave ablation monitoring

Abstract

Microwave ablation is widely recognized as a promising minimally invasive tool for treating cancer. Real-time monitoring of the dimensions of the ablation zone is indispensable for ensuring an effective and safe treatment. In this paper, we propose a microwave imaging algorithm for monitoring the evolution of the ablation zone. Our proposed algorithm determines the boundary of the ablation zone by exploiting the time difference of arrival (TDOA) between signals received before and during the ablation at external antennas surrounding the tissue, using the interstitial ablation antenna as the transmitter. A significant advantage of this method is that it requires few assumptions about the dielectric properties of the propagation media. Also the simplicity of the signal processing, wherein the TDOA is determined from a cross-correlation calculation, allows real-time monitoring and provides robust performance in the presence of noise. We investigate the performance of this approach for the application of breast tumor ablation. We use simulated array measurements obtained from finite-difference time-domain simulations of magnetic resonance imaging-derived numerical breast phantoms. The results demonstrate that our proposed method offers the potential to achieve millimeter-order accuracy and real-time operation in estimating the boundary of the ablation zone in heterogeneous and dispersive breast tissue.

Ultra-Wideband Temperature Dependent Dielectric Spectroscopy of Porcine Tissue and Blood in the Microwave Frequency Range

“…The dielectric properties determine how electromagnetic waves propagate within the MUT. The knowledge of these properties is essential for a wide variety of medical applications such as microwave breast cancer imaging [1,2,3,4,5,6] or microwave ablation and temperature monitoring [7,8,9,10,11]. The latter scenario is a promising approach to monitor the temperature distribution inside of the body during thermal therapies (e.g., hyperthermia), which support oncological treatments (e.g., chemotherapy or radiotherapy).…”

Towards a Microwave Imaging System for Continuous Monitoring of Liver Tumor Ablation: Design and In Silico Validation of an Experimental Setup

“…Moreover, the results also confirm that the envisaged device, while quite simple, being made by a single line of antennas, is capable of achieving real-time 3D imaging results conveying information on the position of the ablated area. It is worth noting that this is, in any case, remarkable, as monitoring liver ablation has a number of additional difficulties compared to monitoring other MWA treatments considered in the literature [ 20 , 21 , 22 ] due to the impossibility of measuring the signal all around the ROI and the high level of losses in the interested tissue. Moreover, it is worth noting here that to mimic actual clinal conditions, the pre-treatment scenario should consider tumor tissue rather than liver tissue.…”

“…By taking advantage of this contrast, which evolves during the treatment, it is possible to retrieve the changes in the permittivity of the ablated region and, hence, the temperature. For this reason, efforts have been addressed to develop MWI devices for real-time monitoring of thermal therapies in different anatomical regions such as liver [ 19 , 20 ], breast [ 21 ], and brain [ 22 ]. However, MWI shows drawbacks in terms of resolution and penetration depth.…”

Determining of Ablation Zone in Ex Vivo Bovine Liver Using Time-Shift Measurements

“…In this context, cold tissue represents the tissue before ablation with a permittivity of ε r_cold and hot tissue represents the tissue after ablation with a permittivity of ε r_hot . As shown in [23], the propagation of the ablation zone is determined by a mathematical model. To determine the ablation zone, the knowledge of the relative permittivity of the tissue before ablation and the relative permittivity of the ablated tissue is required.…”

“…This affects the propagation velocity in the tissue. Using the TDOA method, Equations (1)-( 4) from [23] can be used to calculate the extent of the ablation zone. The radial distance, denoted as 𝑟 , between points A and B serves as a representation of the size of the ablation zone.…”