Ann P. O'Rourke

Dielectric properties of human normal, malignant and cirrhotic liver tissue : in vivo and ex vivo measurements from 0.5 to 20 GHz using a precision open-ended coaxial probe

Hepatic malignancies have historically been treated with surgical resection. Due to the shortcomings of this technique, there is interest in other, less invasive, treatment modalities, such as microwave hepatic ablation. Crucial to the development of this technique is the accurate knowledge of the dielectric properties of human liver tissue at microwave frequencies. To this end, we characterized the dielectric properties of in vivo and ex vivo normal, malignant and cirrhotic human liver tissues from 0.5 to 20 GHz. Analysis of our data at 915 MHz and 2.45 GHz indicates that the dielectric properties of ex vivo malignant liver tissue are 19 to 30% higher than normal tissue. The differences in the dielectric properties of in vivo malignant and normal liver tissue are not statistically significant (with the exception of effective conductivity at 915 MHz, where malignant tissue properties are 16% higher than normal). Also, the dielectric properties of in vivo normal liver tissue at 915 MHz and 2.45 GHz are 16 to 43% higher than ex vivo. No statistically significant differences were found between the dielectric properties of in vivo and ex vivo malignant tissue (with the exception of effective conductivity at 915 MHz, where malignant tissue properties are 28% higher than normal). We report the one-pole Cole-Cole parameters for ex vivo normal, malignant and cirrhotic liver tissue in this frequency range. We observe that wideband dielectric properties of in vivo liver tissue are different from the wideband dielectric properties of ex vivo liver tissue, and that the in vivo data cannot be represented in terms of a Cole-Cole model. Further work is needed to uncover the mechanisms responsible for the observed wideband trends in the in vivo liver data.

A floating sleeve antenna yields localized hepatic microwave ablation

We report a novel coaxial antenna for hepatic microwave ablation. This device uses a floating sleeve, that is, a metal conductor electrically isolated from the outer connector of the antenna coaxial body, to achieve a highly localized specific absorption rate pattern that is independent of insertion depth. This floating sleeve coaxial dipole antenna has low power reflection in the 2.4-GHz IMS band. Ex vivo experiments confirm our numerical simulation results.

Current status of liver tumor ablation devices

The liver is a common site of disease for both primary and metastatic cancer. Since most patients have a disease that is not amenable to surgical resection, tumor ablation modalities are increasingly being used for treatment of liver cancer. This review describes the current status of ablative technologies used as alternatives for resection, clinical experience with these technologies, currently available devices and design rules for the development of new devices and the improvement of existing ones. It focuses on probe design for radiofrequency ablation, microwave ablation and cryoablation, and compares the advantages and disadvantages of each ablation modality.

Taser Blunt Probe Dart-To-Heart Distance Causing Ventricular Fibrillation in Pigs

The maximum distance between the heart and a model Taser stimulation dart, called the dart-to-heart distance, at which the Taser can directly cause ventricular fibrillation (VF), was measured in pigs. A 9-mm-long blunt probe was advanced snugly through the surrounding tissues toward the heart. Five animals [pig mass = 61.2plusmn6.23 standard deviation (SD) kg] for ten dart-to-heart distances where the Taser caused VF were tested. The dart-to-heart distances where the Taser caused VF of the first stimulation site ranged from 4 to 8 mm with average 6.2 mmplusmn1.79 (SD) and of the second stimulation site ranged from 2 to 8 mm with average 5.4 mmplusmn2.41 (SD). The results help inform the evolving discussion of risks associated with Tasers.

The Sumatra-Andaman Earthquake and Tsunami of 2004: The Hazards, Events, and Damage

The Sumatra-Andaman Earthquake and subsequent Asian Tsunami of 26 December 2004 affected multiple countries in the Indian Ocean and beyond, creating disasters of a scale unprecedented in recorded history. Using the Conceptual Framework and terminology described in the Disaster Health Management: Guidelines for Evaluation and Research in the Utstein Style, the hazard, events, and damage associated with the Earthquake and Tsunami are described. Many gaps in the available information regarding this event are present. Standardized indicators and reporting criteria are necessary for research on future disasters and the development of best practice standards internationally.

Finite-Element Analysis of Ex Vivo and In Vivo Hepatic Cryoablation

Cryoablation is a widely used method for the treatment of nonresectable primary and metastatic liver tumors. A model that can accurately predict the size of a cryolesion may allow more effective treatment of tumor, while sparing normal liver tissue. We generated a computer model of tissue cryoablation using the finite-element method (FEM). In our model, we considered the heat transfer mechanism inside the cryoprobe and also cryoprobe surfaces so our model could incorporate the effect of heat transfer along the cryoprobe from the environment at room temperature. The modeling of the phase shift from liquid to solid was a key factor in the accurate development of this model. The model was verified initially in an ex vivo liver model. Temperature history at three locations around one cryoprobe and between two cryoprobes was measured. The comparison between the ex vivo result and the FEM modeling result at each location showed a good match, where the maximum difference was within the error range acquired in the experiment (< 5 degC). The FEM model prediction of the lesion size was within 0.7 mm of experimental results. We then validated our FEM in an in vivo experimental porcine model. We considered blood perfusion in conjunction with blood viscosity depending on temperature. The in vivo iceball size was smaller than the ex vivo iceball size due to blood perfusion as predicted in our model. The FEM results predicted this size within 0.1-mm error. The FEM model we report can accurately predict the extent of cryoablation in the liver.

Finite-Element Analysis of Hepatic Cryoablation Around a Large Blood Vessel

Cryoablation is a minimally invasive ablation technique for primary and metastatic hepatic tumors. Inadequate freezing around large blood vessels due to the warm blood flow can lead to local recurrence, and thus, necessitates close application of a cryoprobe to the large blood vessels. In this study, we constructed a perfusion model with an ex vivo bovine liver and ablated the tissue around a large blood vessel with one or two cryoprobes applied to the side of the vessel. The finite-element computer model developed in our previous study was modified to include a blood vessel and its convective heat transfer to the vicinity of the blood vessel. We compared the predicted simulation results to those acquired from this ex vivo perfusion model. The results indicate that blood vessels act as a heat source and generate steep temperature profiles in the area next to the large blood vessel. After validation, the maximum allowable distance between the cryoprobe and the large blood vessel for successful cryoablation was presented. The results of this study should be considered when placing cryoprobes in the vicinity of large blood vessels.

Research and Evaluations of the Health Aspects of Disasters, Part II: The Disaster Health Conceptual Framework Revisited.

A Conceptual Framework upon which the study of disasters can be organized is essential for understanding the epidemiology of disasters, as well as the interventions/responses undertaken. Application of the structure provided by the Conceptual Framework should facilitate the development of the science of Disaster Health. This Framework is based on deconstructions of the commonly used Disaster Management Cycle. The Conceptual Framework incorporates the steps that occur as a hazard progresses to a disaster. It describes an event that results from the changes in the release of energy from a hazard that may cause Structural Damages that in turn, may result in Functional Damages (decreases in levels of function) that produce needs (goods and services required). These needs can be met by the goods and services that are available during normal, day-to-day operations of the community, or the resources that are contained within the communitys Response Capacity (ie, an Emergency), or by goods and services provided from outside of the affected area (outside response capacities). Whenever the Local Response Capacity is unable to meet the needs, and the Response Capacities from areas outside of the affected community are required, a disaster occurs. All responses, whether in the Relief or Recovery phases of a disaster, are interventions that use the goods, services, and resources contained in the Response Capacity (local or outside). Responses may be directed at preventing/mitigating further deterioration in levels of functions (damage control, deaths, injuries, diseases, morbidity, and secondary events) in the affected population and filling the gaps in available services created by Structural Damages (compromise in available goods, services, and/or resources; ie, Relief Responses), or may be directed toward returning the affected community and its components to the pre-event functional state (ie, Recovery Responses). Hazard Mitigation includes interventions designed to decrease the likelihood that a hazard will cause an event, and should an event occur, that the amount of energy released will be reduced. Capacity Building consists of all interventions undertaken before an event occurs in order to increase the resilience of the community to an event related to a hazard that exists in an area-at-risk. Resilience is the combination of the Absorbing, Buffering, and Response Capacities of a community-at-risk, and is enhanced through Capacity-Building efforts. A disaster constitutes a failure of resilience.

Number of rib fractures thresholds independently predict worse outcomes in older patients with blunt trauma.

Background. There have been conflicting reports regarding whether the number of rib fractures sustained in blunt trauma is associated independently with worse patient outcomes. We sought to investigate this risk‐adjusted relationship among the lesser‐studied population of older adults. Methods. A retrospective review of the National Trauma Data Bank was performed for patients with blunt trauma who were ≥65 years old and had rib fractures between 2009 and 2012 (N = 67,695). Control data were collected for age, sex, injury severity score, injury mechanism, 24 comorbidities, and number of rib fractures. Outcome data included hospital mortality, hospital and intensive care unit durations of stay, duration of mechanical ventilation, and the occurrence of pneumonia. Multiple logistic and linear regression analyses were performed. Results. Sustaining ≥5 rib fractures was associated with increased intensive care unit admission (odds ratio: 1.14, P < .001) and hospital duration of stay (relative duration: 105%, P < .001). Sustaining ≥7 rib fractures was associated with an increased incidence of pneumonia (odds ratio: 1.32, P < .001) and intensive care unit duration of stay (relative duration: 122%, P < .001). Sustaining ≥8 rib fractures was associated with increased mortality (odds ratio: 1.51, P < .001) and duration of mechanical ventilation (relative duration: 117%, P < .001). Conclusion. In older patients with trauma, sustaining at least 5 rib fractures is a significant predictor of worse outcomes independent of patient characteristics, comorbidities, and trauma burden.

Research and Evaluations of the Health Aspects of Disasters, Part VI: Interventional Research and the Disaster Logic Model

Disaster-related interventions are actions or responses undertaken during any phase of a disaster to change the current status of an affected community or a Societal System. Interventional disaster research aims to evaluate the results of such interventions in order to develop standards and best practices in Disaster Health that can be applied to disaster risk reduction. Considering interventions as production functions (transformation processes) structures the analyses and cataloguing of interventions/responses that are implemented prior to, during, or following a disaster or other emergency. Since currently it is not possible to do randomized, controlled studies of disasters, in order to validate the derived standards and best practices, the results of the studies must be compared and synthesized with results from other studies (ie, systematic reviews). Such reviews will be facilitated by the selected studies being structured using accepted frameworks. A logic model is a graphic representation of the transformation processes of a program [project] that shows the intended relationships between investments and results. Logic models are used to describe a program and its theory of change, and they provide a method for the analyzing and evaluating interventions. The Disaster Logic Model (DLM) is an adaptation of a logic model used for the evaluation of educational programs and provides the structure required for the analysis of disaster-related interventions. It incorporates a(n): definition of the current functional status of a community or Societal System, identification of needs, definition of goals, selection of objectives, implementation of the intervention(s), and evaluation of the effects, outcomes, costs, and impacts of the interventions. It is useful for determining the value of an intervention and it also provides the structure for analyzing the processes used in providing the intervention according to the Relief/Recovery and Risk-Reduction Frameworks.