Since its conception in 2005, irreversible electroporation (IRE), a non-thermal tumor ablation modality, was investigated for safety and efficacy in clinical applications concerning different organs. IRE utilizes high voltage (~3kV), short duration (~100us) pulses to create transient nanoscale defects in the plasma membrane to cause cell death due to irreversible defects, osmotic imbalances and ATP loss. More recently, high-frequency irreversible electroporation (H-FIRE), which employs narrow bipolar pulses (~0.5-10us) delivered in bursts (on time ~100us), was invented to provide benefits such as the mitigation of intense muscle contractions associated with IRE-based treatments. Furthermore, H-FIRE exhibits the potential to improve lesion predictability in homogeneous and heterogeneous tissue masses.
Therapeutic IRE and H-FIRE utilize source and sink electrodes inserted into or around the tumor to deliver the treatment. Prediction of the ablation size, for a set of parameters, can be achieved by the use of pre-treatment planning algorithms that calculate the induced electric field distribution in the target tissue. An electric field above a certain threshold induces cell death and parameters are tuned to ensure complete tumor coverage while sparing the nearby healthy tissue. IRE studies have shown that the underlying field is influenced by the increase in tissue conductivity due to enhanced membrane permeability, and treatment outcome can be improved when this nonlinearity is accounted for in numerical models.
Since IRE pulses far exceed the time constant of the cell (~1us), the tissue response can be treated as essentially DC a static approximation can be used to predict the field distribution. Alternately, as H-FIRE pulses are on the order of the time constant of the membrane, the tissue response can no longer be treated as DC. The complexity of the H-FIRE-induced field distribution is further enhanced due to the dispersion and non-linearity in biological tissue impedance during treatment.
In this dissertation, we have studied the electromagnetic fields induced in tissue during H-FIRE using several experimental and modeling techniques. In addition, we have characterized the nonlinearity and dispersion in tissue impedance during H-FIRE treatments and proposed simpler methods to predict the field distribution to enable easier translation to the clinic. / Ph. D. / Development within urbanized regions increase impervious surfaces, which further cause significant storm events in watersheds. The increased impervious surfaces result in hotter stormwater particularly during hot summers, which has diverse effects on aquatic health of downstream receiving streams. The main objective of the current study is to evaluate the thermal impact of urbanization on aquatic health habitats in Stroubles Creek Watershed, Blacksburg, Virginia. To aim this goal and achieve the thermal evaluation of the highly urbanized Stroubles Creek Watershed, a U.S. Environmental Protection Agency’s Storm Water Management Model (SWMM) and a Minnesota Urban Heat Export Tool (MINUHET) models from scratch of the Stroubles Creek watershed, using Town of Blacksburg and Virginia Tech Physical Facility information were developed. This necessitated combining information from a wide variety of sources, including geologic maps, geodatabases, hydraulic models, computer-aided design (CAD) files, and scanned as-built information. In addition to the models, a hybrid model was developed that combines SWMM and MINHET outputs. The temperatures and heat loads at the downstream of the watershed were predicted using SWMM, MINUHET, and Hybrid models for two summer periods of 2016 and 2015, and the predicted temperature were compared to the criteria for survival of aquatic health such as trout. Furthermore, a number of thermal mitigation strategies such as bioretentions systems, concrete pavements (which has lighter color compared to asphalt pavements), and increased vegetation canopies were simulated within the MINUHET and SWMM models configurations to reduce simulated temperatures and heat loads at the watershed scale. The simulated temperatures and heat loads represented that concrete pavements results in better performance of thermal mitigation within watersheds than bioretention systems, and increased vegetation canopies.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/91904 |
| Date | 27 January 2018 |
| Creators | Bhonsle, Suyashree P. |
| Contributors | Electrical Engineering, Safaai-Jazi, Ahmad, Davalos, Rafael V., Zhu, Yizheng, Verbridge, Scott, Zhu, Yunhui |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/x-zip-compressed |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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