Antenna and system design for controlled delivery of microwave thermal ablation

Doctor of PhilosophyDepartment of Electrical and Computer EngineeringPunit PrakashMicrowave ablation is an established minimally invasive modality for thermal ablation of unresectable tumors and other diseases. The goal of a microwave ablation procedure is to deliver microwave power in a manner localized to the targeted tissue, with the objective of raising the target tissue to ablative temperatures (~60 °C). Engineering efforts in microwave applicator design have largely been focused on the design of microwave antennas that yield large, near-spherical ablation zones, and can fit within rigid needles or flexible catheters. These efforts have led to significant progress in the development and clinical application of microwave ablation systems, particularly for treating tumors in the liver and other highly vascular organs. However, currently available applicator designs are ill-suited to treating targets of diverse shapes and sizes. Furthermore, there are a lack of non-imaging-based techniques for monitoring the transient progression of the ablation zone as a means for providing feedback to the physician. This dissertation presents the design, implementation, and experimental evaluation of microwave ablation antennas for site-specific therapeutic applications with these issues in mind. A deployable 915 MHz loop antenna is presented, providing a minimally-invasive approach for thermal ablation of the endometrial lining of the uterus for treatment of heavy menstrual bleeding. The antenna incorporates a radiating loop, which can be deployed to adjustable shapes within the uterine cavity, and a passive element, to enable thermal ablation, to 5.7–9.6 mm depth, of uterine cavities ranging in size from 4–6.5 cm in length and 2.5–4.5 cm in width. Electromagnetic–bioheat transfer simulations were employed for design optimization of the antennas, and proof-of-concept applicators were fabricated and extensively evaluated in ex vivo tissue. Finally, feasibility of using the broadband antenna reflection coefficient for monitoring the ablation progress during the course of ablation was evaluated. Experimental studies demonstrated a shift in antenna resonant frequency of 50 MHz correlated with complete ablation. For treatment of 1–2 cm spherical targets, water-cooled monopole antennas operating at 2.45 and 5.8 GHz were designed and experimentally evaluated in ex vivo tissue. The technical feasibility of using these applicators for treating 1–2 cm diameter benign adrenal adenomas was demonstrated. These studies demonstrated the potential of using minimally-invasive microwave ablation applicators for treatment of hypertension caused by benign aldosterone producing adenomas. Since tissue dielectric properties have been observed to change substantially at elevated temperatures, knowledge of the temperature-dependence of tissue dielectric properties may provide a means for estimating treatment state from changes in antenna reflection coefficient during a procedure. The broadband dielectric properties of bovine liver, an established tissue for experimental characterization of microwave ablation applicators, were measured from room temperature to ablative temperatures. The measured dielectric data were fit to a parametric model using piecewise linear functions, providing a means for readily incorporating these data into computational models. These data represent the first report of changes in broadband dielectric properties of liver tissue at ablative temperatures and should help enable additional studies in ablation system development

Terminal Deoxynucleotidyl Transferase (TdT) Inhibiti on of Cord Blood Derived B and T Cells Expansion

Purpose: Terminal deoxynucleotidyl transferase(TdT) is a DNA polymerase that is present in immature pre-B and pre-T cells. TdT inserts N-nucleotides to the V (D) J gene segment during rearrangements of genes, therefore, it plays a vital role in the development and variation of the immune system in vertebrates. Here we evaluated the relationship between cytokines like interleukin-2 (IL-2), interleukin-7 (IL-7), and interleukin-15 (IL-15) and TdT expression in cord blood mononuclear cells and also effect of inhibition in the expansion of B and T cells derived from cord blood. Methodes: The cord blood mononuclear cells were cultured with different combination of cytokines for 21days, which they were harvested in definite days (7, 14 and 21) and evaluated by flow cytometry. Results: Our data indicated that TdT expression increased in cord blood mononuclear cells using immune cell key cytokines without being dependent on the type of cytokines. TdT inhibition reduced both the expansion of B and T cells derived from cord blood and also declined the apoptosis and proliferation. Considered together, TdT played an important role in the control of the expansion of B and T cells derived from cord blood. Conclusion: considered together, it was observed that TdT expression was increased by cytokines and TdT inhibition not only reduced B and Tcells derived from cord blood, but it also affected the rate of apoptosis and proliferation

Technological requirements for microwave ablation of adrenal masses

Microwave thermal ablation is under consideration for minimally invasive treatment of bilateral adrenal adenomas, symptomatic of Conn's syndrome. Currently available microwave technologies are ill-suited to precise ablation of small adrenal targets. We report on our preliminary computational and experimental efforts towards the design of microwave ablation systems for targeting adrenal masses. Broadband dielectric properties of ex vivo bovine adrenal glands were experimentally measured. Computer simulations demonstrated the feasibility of achieving precise ablation of adrenal lesions with 2.45 GHz systems. Experiments in ex vivo adrenal tissue using a water-cooled 2.45 GHz antenna illustrated the feasibility of heating 10-20 mm adrenal targets with 40 W power applied for 1 min. These preliminary results warrant further investigation and development of microwave technology for precise ablation of adrenal masses.The research leading to these results has received funding from the European Research Council under the European Union's Horizon 2020 Programme/ERC Grant Agreement BioElecPro n. 637780. We also acknowledge funding through the KSU Johnson Cancer Research Center and the support of COST Action TD1301 and BM1309 EMF-MED for the convened session.peer-reviewe

Technological requirements for microwave ablation of adrenal masses

Microwave thermal ablation is under consideration for minimally invasive treatment of bilateral adrenal adenomas, symptomatic of Conn\u27s syndrome. Currently available microwave technologies are ill-suited to precise ablation of small adrenal targets. We report on our preliminary computational and experimental efforts towards the design of microwave ablation systems for targeting adrenal masses. Broadband dielectric properties of ex vivo bovine adrenal glands were experimentally measured. Computer simulations demonstrated the feasibility of achieving precise ablation of adrenal lesions with 2.45 GHz systems. Experiments in ex vivo adrenal tissue using a water-cooled 2.45 GHz antenna illustrated the feasibility of heating 10-20 mm adrenal targets with 40 W power applied for 1 min. These preliminary results warrant further investigation and development of microwave technology for precise ablation of adrenal masses.The research leading to these results has received funding from the European Research Council under the European Union\u27s Horizon 2020 Programme/ERC Grant Agreement BioElecPro n. 637780. We also acknowledge funding through the KSU Johnson Cancer Research Center and the support of COST Action TD1301 and BM1309 EMF-MED for the convened session