Finite-difference time-domain analysis of microwave heart monitoring

Life signal detection is an old concept with contemporary applications, including predicting cardiac arrhythmia from heart signals, and helping in the search for lost survivors. The underlying principle of the microwave heart monitoring is based on detecting the changes in the reflected microwaves caused by the movement of the chest wall in response to respiration and ventricular activities. This thesis seeks to analyze the induced current distribution and specific-absorption rate (SAR) using the finite-difference time-domain (FDTD) method on an accurate two-dimensional thoracic model provided by the Visual Human Project (VHP).Additional test cases are analyzed which model the two-dimensional heart model in different media, such as air, water, and lungs. The signal used in all simulations is a 1V/m 10GHz TM plane wave. The discussion of the two-dimensional results yields a preliminary assessment of microwave-tissue interaction in the process of heart monitoring at microwave frequencies

Cardiovascular magnetic resonance guided ablation and intra-procedural visualization of evolving radiofrequency lesions in the left ventricle

Abstract Background Radiofrequency (RF) ablation has become a mainstay of treatment for ventricular tachycardia, yet adequate lesion formation remains challenging. This study aims to comprehensively describe the composition and evolution of acute left ventricular (LV) lesions using native-contrast cardiovascular magnetic resonance (CMR) during CMR-guided ablation procedures. Methods RF ablation was performed using an actively-tracked CMR-enabled catheter guided into the LV of 12 healthy swine to create 14 RF ablation lesions. T2 maps were acquired immediately post-ablation to visualize myocardial edema at the ablation sites and T1-weighted inversion recovery prepared balanced steady-state free precession (IR-SSFP) imaging was used to visualize the lesions. These sequences were repeated concurrently to assess the physiological response following ablation for up to approximately 3 h. Multi-contrast late enhancement (MCLE) imaging was performed to confirm the final pattern of ablation, which was then validated using gross pathology and histology. Results Edema at the ablation site was detected in T2 maps acquired as early as 3 min post-ablation. Acute T2-derived edematous regions consistently encompassed the T1-derived lesions, and expanded significantly throughout the 3-h period post-ablation to 1.7 ± 0.2 times their baseline volumes (mean ± SE, estimated using a linear mixed model determined from n = 13 lesions). T1-derived lesions remained approximately stable in volume throughout the same time frame, decreasing to 0.9 ± 0.1 times the baseline volume (mean ± SE, estimated using a linear mixed model, n = 9 lesions). Conclusions Combining native T1- and T2-based imaging showed that distinctive regions of ablation injury are reflected by these contrast mechanisms, and these regions evolve separately throughout the time period of an intervention. An integrated description of the T1-derived lesion and T2-derived edema provides a detailed picture of acute lesion composition that would be most clinically useful during an ablation case