Simulations of magnetization reversal in FM/AFM bilayers with THz frequency pulses.

It is widely known that antiferromagnets (AFMs) display a high frequency response in the terahertz (THz) range, which opens up the possibility for ultrafast control of their magnetization for next generation data storage and processing applications. However, because the magnetization of the different sublattices cancel, their state is notoriously difficult to read. One way to overcome this is to couple AFMs to ferromagnets-whose state is trivially read via magneto-resistance sensors. Here we present conditions, using theoretical modelling, that it is possible to switch the magnetization of an AFM/FM bilayer using THz frequency pulses with moderate field amplitude and short durations, achievable in experiments. Consistent switching is observed in the phase diagrams for an order of magnitude increase in the interface coupling and a tripling in the thickness of the FM layer. We demonstrate a range of reversal paths that arise due to the combination of precession in the materials and the THz-induced fields. Our analysis demonstrates that the AFM drives the switching and results in a much higher frequency dynamics in the FM due to the exchange coupling at the interface. The switching is shown to be robust over a broad range of temperatures relevant for device applications.

RF ablation of intestinal metaplasia (Barrett esophagus).

Esophageal intestinal metaplasia, otherwise known as Barrett's Esophagus, is a pre-cancerous condition that afflicts over 1 million Americans annually. Barrett's Esophagus is caused by chronic esophageal exposure to stomach acid which can occur in patients afflicted with Gastro Esophageal Reflux Disease (GERD). The lining of the esophagus undergoes a metaplastic change, from normal squamous cell epithelium to columnar cell epithelium. Over time, this condition can progress to dysplasia and ultimately to adenocarcinoma. Currently, there are no widely practiced therapies for Barrett's Esophagus. Patients diagnosed with this disease are routinely screened to ensure do not have cancer, yet. It has been shown that if the GERD is controlled (i.e. a normal esophageal pH is maintained) and the metaplastic lining of the esophagus is carefully removed, i.e. no damage to underlying tissues), the normal squamous epithelial cells will repopulate the esophagus. A system has been designed to couple radiofrequency (RF) energy to the epithelial lining of the esophagus to effectively ablate the metaplastic cells and allow normal squamous cell repopulation. The design principles of this system and the resulting effects are the subject of this presentation.

Complete ablation of esophageal epithelium with a balloon-based bipolar electrode: a phased evaluation in the porcine and in the human esophagus.

BACKGROUND: The aim of this study was to evaluate the endoscopic and the histologic effects of a balloon-based bipolar radiofrequency electrode for ablation of porcine and human esophageal epithelium. METHODS: All procedures were performed with a balloon-based, bipolar radiofrequency system that creates a circumferential, thin-layer epithelial ablation zone within the esophagus. In Phase I, multiple ablations were created in 10 farm swine, followed by acute euthanasia and histologic assessment for completeness of epithelial removal and ablation depth. In Phase II, multiple ablations were created in 19 farm swine, with varying power and energy density, followed by endoscopy at 2 and 4 weeks to assess stricture formation. In Phase III, 3 ablations were created in 12 farm swine, with varying energy density (5, 8, 10, 12, 15, or 20 J/cm 2 ) at 350 W. Animals were euthanized at 48 hours. Histologic examination determined the percentage of epithelium removed and the ablation depth. In Phase IV, 3 patients underwent esophageal epithelial ablation before esophagectomy, creating separate lesions proximal to the tumor. Completeness of epithelial ablation and ablation depth was quantified histologically. RESULTS: In Phase I, complete removal of esophageal epithelium was achieved at energy density settings of 9.7 to 29.5 J/cm 2 . In Phase II, 9.7 and 10.6 J/cm 2 produced no stricture, whereas more than 20 J/cm 2 produced a stricture in every case. In Phase III, 8-20 J/cm 2 resulted in 100% epithelial ablation. Five and 8 J/cm 2 spared the muscularis mucosae, whereas 10 J/cm 2 caused injury to the muscularis mucosae but preserved the submucosa. In Phase IV, histologic examination demonstrated full-thickness epithelial removal in areas of electrode contact. Ablation extended only to the muscularis mucosae, without injury to submucosa. CONCLUSIONS: In the porcine and the human esophagus, circumferential, full-thickness ablation of epithelium without direct injury to the submucosa is possible and was well tolerated. In all cases, depth of ablation was linearly related to energy density of treatment.