Daniel P. Muffoletto

Preoperative Mapping of Nonmelanoma Skin Cancer Using Spatial Frequency Domain and Ultrasound Imaging

RATIONALE AND OBJECTIVES The treatment of nonmelanoma skin cancer (NMSC) is usually by surgical excision or Mohs micrographic surgery and alternatively may include photodynamic therapy (PDT). To guide surgery and to optimize PDT, information about the tumor structure, optical parameters, and vasculature is desired. MATERIALS AND METHODS Spatial frequency domain imaging (SFDI) can map optical absorption, scattering, and fluorescence parameters that can enhance tumor contrast and quantify light and photosensitizer dose. High frequency ultrasound (HFUS) imaging can provide high-resolution tumor structure and depth, which is useful for both surgery and PDT planning. RESULTS Here, we present preliminary results from our recently developed clinical instrument for patients with NMSC. We quantified optical absorption and scattering, blood oxygen saturation (StO2), and total hemoglobin concentration (THC) with SFDI and lesion thickness with ultrasound. These results were compared to histological thickness of excised tumor sections. CONCLUSIONS SFDI quantified optical parameters with high precision, and multiwavelength analysis enabled 2D mappings of tissue StO2 and THC. HFUS quantified tumor thickness that correlated well with histology. The results demonstrate the feasibility of the instrument for noninvasive mapping of optical, physiological, and ultrasound contrasts in human skin tumors for surgery guidance and therapy planning.

Characterization of nonmelanoma skin cancer for light therapy using spatial frequency domain imaging

The dosimetry of light-based therapies critically depends on both optical and vascular parameters. We utilized spatial frequency domain imaging to quantify optical and vascular parameters, as well as estimated light penetration depth from 17 nonmelanoma skin cancer patients. Our data indicates that there exist substantial spatial variations in these parameters. Characterization of these parameters may inform understanding and optimization of the clinical response of light-based therapies.

Partial discharge analysis of prestretched and unstretched acrylic elastomers for Dielectric Elastomer Actuators (DEA)

Partial discharges (PD) occur in solid insulating materials when the insulating material is partially bridged by an electrical discharge in response to an applied voltage stress. PDs typically occur at localized points of high field stresses or at voids and other inhomogeneities within the insulator. The applied fields effect on the frequency of occurrence and intensity of PDs can be used to assess the electrical breakdown strength and aging characteristics of insulating materials. PD testing is therefore a promising characterization method to understand the insulating properties of the elastomers and geometries commonly used in DEAs. Prestretched (~100% and ~230% biaxial) and unstretched acrylic elastomers (3M VHB tapes) with solid metal electrodes have been tested. We have found the number and intensity of PDs increase with applied field, and that a significant number of PDs are detected before any actuation was visibly observed, implying that the fields required for actuation will cause material aging and degradation over time. Most interestingly, the number of PDs steadily increase as the applied voltage increases up to a sufficiently high voltage, where the PDs suddenly cease. Since internal voids can cause PDs, this may indicate that the Maxwell stress minimized the thickness of or eliminated these voids, which could explain how prestretching improves performance.

Temporal Analysis of Exploding Film Burst Phenomenon

A technique to determine the time of burst for exploding aluminum metallized films has been studied. An experimental approach has been taken to determine the burst time relative to the discharge current, voltage, resistance, and power waveforms. A microphone transducer was employed to detect the time of burst from the sound produced by the bursting of the film and was compared to the calculated burst times. A theoretical discussion on the energy needed to melt and vaporize the film is also presented and compared to the experimental results.

Anticipating electrical breakdown in dielectric elastomer actuators

The output strain of a dielectric elastomer actuator is directly proportional to the square of its applied electric field. However, since the likelihood of electric breakdown is elevated with an increased applied field, the maximum operating electric field of the dielectric elastomer is significantly derated in systems employing these actuators so that failure due to breakdown remains unlikely even as the material ages. In an effort to ascertain the dielectric strength so that stronger electric fields can be applied, partial discharge testing is used to assess the health of the actuator by detecting the charge that is released when localized instances of breakdown partially bridge the insulator. Pre-stretched and unstretched samples of VHB4910 tape were submerged in dielectric oil to remove external sources of partial discharges during testing, and the partial discharge patterns were recorded just before failure of the dielectric sample.

Partial discharge monitoring in dielectric elastomer actuators

Dielectric elastomer actuators represent an interesting use of dielectric materials for two reasons. First, being a soft material that is designed to exert mechanical strains, the aging and dielectric breakdown mechanisms are often the result of mechanical phenomena less common in other high voltage insulating systems that use rigid dielectrics selected solely for their electrical properties. Secondly, these systems are rather unique in that realtime insulation health monitoring can provide meaningful insights to extend the working life of the system. Like most high voltage systems, dielectric breakdown results in the irreversible and catastrophic failure of the system. However, since the system can be used at lower operating voltages, albeit at a lower effectiveness, if the operating voltage can be lowered as the dielectric shows signs of aging, the useful life of the system can be extended. Partial discharge testing has been used to assess the health of the polymer films used in these systems, and the procedures for real-time monitoring of partial discharges are explored in this paper.

Examination of Initial Strike and Restrike Modes in Exploding Metallized Films

The discharge modes of a capacitive exploding metallized film setup are discerned. Long exposure still images of the plasma formation during the initial strike and restrike are presented.

High power ceramic resistors square wave pulse and impulse testing

Ceramic resistors are used for many pulsed power applications and the accuracy of the performance is vital information. There were two different experiments used to determine the performance of this resistor: a square-wave pulse voltage and an impulse voltage. High voltage ceramic resistors were tested towards its maximum impulse limitations during these experiments. The pulse or impulse duration time was adjusted to maximize the energy and power delivered to the resistor. From these experiments, the amount of average power and energy absorbed by the resistor determined its limits regardless of the voltage profile curve during the pulse. The resistors were analyzed through a model initially, and then physically investigated. The ratings and results from the experiments are also represented graphically.

Repetitive pulse testing and modeling of a high power ceramic resistor

In an effort to understand the failure mechanisms of ceramic resistors when used above their stated limits, a series of pulsed load profiles were applied to an epoxy coated ceramic resistor. A dependent relationship between the pulsed load profiles and the temperature of the epoxy was shown through the series of experiments. From these experiments a safe operating range was found beyond the stated limits. The load profiles that cause failure are evaluated and compared to the results of a lumped element numerical model, which models the thermal characteristics of such a resistor under test and allows for the heating profiles during operation to be predicted.

Nonthermal Plasma Torch Surface Attachment in Fluidic Environments

The plasma jet of a nonthermal plasma torch was studied under various flow rates as it interacted with cell culture media. As the flow rate of the plasma working gas increases, the surface area of the attachment changes considerably. Effects in appearance range from a fine “jet” to a broad “skirt” that flutters in a disorganized pattern.