M Klopfer

TiO2 nanotubes as a cold cathode for x-ray generation

Here we report on an x-ray source based on titanium dioxide (TiO2) nanotubes grown by electrochemical oxidation. From the analysis of current-voltage characteristics of TiO2 electron emitter field emission nature of the current was confirmed. The threshold voltage and field enhancement factors were derived to be ∼1.8 V/μm and ∼8363, respectively. The current density was ∼4.0 mA/cm2 at ∼2.4 V/μm. The stability tests showed that the current stayed stable within 6% for more than 720 h. TiO2 nanotubes were used as a cold cathode in x-ray tube and it was demonstrated that TiO2 nanotubes could be a good candidate for such applications.

Effect of TiO2 nanotube parameters on field emission properties

The dependence of field emission properties of titanium dioxide (TiO(2)) nanotubes (NTs) has been studied as a function of NT diameter (D) and height (h), which varied in the ranges 18-500 nm and 500-12,000 nm, respectively. The studies showed a strong dependence of the field emission on these parameters. With an increase of NT diameter, the field enhancement factor increased monotonically from 120 to 3800; the current density also increased until D = 320 (current density ∼ 3.8 mA cm( - 2)), with subsequent decrease for larger diameters. The field emission properties initially improved with NT height until h = 5 µm, and later remained unchanged with further increases in h.

Volumetric lean percentage measurement using dual energy mammography.

PURPOSE Currently, there is no accepted standard for measuring breast density. Dual energy mammography, which has demonstrated accurate measurement in phantoms, has been proposed as one possible method. To examine the use of chemical analysis as a possible means to validate breast density measurements from dual energy mammography, a bovine tissue model was investigated. Known quantities of lean and adipose tissue were compared with composition values measured from dual energy images and chemical analysis. METHODS Theoretical simulations were performed to assess the impact variations in breast composition would have on measurement of breast density from a single calibration. Fourteen ex-vivo tissue samples composed of varying amounts of pure lean tissue and pure adipose tissue (lean percentage) from 0 to 100%, in increments of 10%, were imaged using dual energy mammography. This was followed by chemical analysis based on desiccation, trituration, and fat extraction with petroleum ether to determine water, lipid, and protein content. The volumetric lean percentage (VLP) as measured from images (VLP(I)) and as derived from chemical analysis data (VLP(CA)) were compared with the VLP calculated from measurements of sample mass with a scale (VLP(M)). Finally, data from the bovine tissue model in this study were compared to compositional data from a previous report of human tissue composition. RESULTS The results from simulation suggest a substantial impact on measuring breast density is likely due to changes in anatomical breast composition. VLP(I) was related to the VLP(M) by VLP(I) = 1.53 VLP(M) + 10.0 (r2 > 0.99). VLP(CA) was related to VLP(M) by VLP(CA) = 0.76 VLP(M) + 22.8 (r2 > 0.99). VLP(I) was related to VLP(CA) by VLP(I) = 2.00 VLP(CA) - 35.6 (r2 > 0.99). Bovine adipose tissue was shown to be very similar to human adipose tissue in terms of water, lipid, and protein content with RMS differences of 1.2%. Bovine lean tissue was shown to be very similar to human skeletal muscle tissue and somewhat similar to human mammary gland tissue with RMS differences of 0.4 and 22.2%, respectively. CONCLUSIONS The results of this study show strong linear relationships between volumetric lean percentage measurements using dual energy mammography, chemical analysis and the actual mass. Determining the existence of a relationship between VLP(I) and VLP(CA) was necessary before comparing density results from the dual energy technique to composition data from chemical analysis for samples of unknown composition.

Enhanced field emission from clustered TiO2 nanotube arrays

Field emission properties of clustered titanium dioxide (TiO2) nanotube arrays have been studied and compared with those of dense, highly aligned TiO2 nanotube arrays. It was found that clustered nanotube arrays showed significant increase of field emission current density (sevenfold) and field enhancement factor (fivefold) compared to regular shape, highly aligned forest-like TiO2 nanotube arrays, which can be explained by the reduction of electric field screening effects. Clustered TiO2 nanotubes arrays were achieved by electrochemical oxidation of titanium sheet in electrolyte consisting of diethylene or ethylene glycol solvents and ammonium fluorine, while the well aligned nanotube arrays were grown using glycerol.

Breast Tissue Characterization with Photon-counting Spectral CT Imaging: A Postmortem Breast Study

PURPOSE To investigate the feasibility of breast tissue characterization in terms of water, lipid, and protein contents with a spectral computed tomographic (CT) system based on a cadmium zinc telluride (CZT) photon-counting detector by using postmortem breasts. MATERIALS AND METHODS Nineteen pairs of postmortem breasts were imaged with a CZT-based photon-counting spectral CT system with beam energy of 100 kVp. The mean glandular dose was estimated to be in the range of 1.8-2.2 mGy. The images were corrected for pulse pile-up and other artifacts by using spectral distortion corrections. Dual-energy decomposition was then applied to characterize each breast into water, lipid, and protein contents. The precision of the three-compartment characterization was evaluated by comparing the composition of right and left breasts, where the standard error of the estimations was determined. The results of dual-energy decomposition were compared by using averaged root mean square to chemical analysis, which was used as the reference standard. RESULTS The standard errors of the estimations of the right-left correlations obtained from spectral CT were 7.4%, 6.7%, and 3.2% for water, lipid, and protein contents, respectively. Compared with the reference standard, the average root mean square error in breast tissue composition was 2.8%. CONCLUSION Spectral CT can be used to accurately quantify the water, lipid, and protein contents in breast tissue in a laboratory study by using postmortem specimens.

Hybrid pyroelectric/nanotube LiNbO3/TiO2 X-ray source

LiNbO3/TiO2 pyroelectric/nanotube system was fabricated by bonding electrochemically grown TiO2 nanotubes on −z face of pyroelectric LiNbO3 crystal and X-ray emission properties of such system were studied. The hybrid LiNbO3/TiO2 system had both higher electron energy and output X-ray flux compared to LiNbO3 without nanotubes. The endpoint energy increased from 38–45 keV to 55–74 keV, and the maximum X-ray flux increased by a factor of 3.6. The improved output energy and flux are thought to be due to the electric field amplification of nanotube tips increasing the efficiency of ionization of residual gas.

A fluid collection system for dermal wounds in clinical investigations

In this work, we demonstrate the use of a thin, self adherent, and clinically durable patch device that can collect fluid from a wound site for analysis. This device is manufactured from laminated silicone layers using a novel all-silicone double-molding process. In vitro studies for flow and delivery were followed by a clinical demonstration for exudate collection efficiency from a clinically presented partial thickness burn. The demonstrated utility of this device lends itself for use as a research implement used to clinically sample wound exudate for analysis. This device can serve as a platform for future integration of wearable technology into wound monitoring and care. The demonstrated fabrication method can be used for devices requiring thin membrane construction.

Flexible, transparent electronics for biomedical applications

The development and integration of flexible biocompatible electronics is of considerable interest in the biomedical community. Electronic and fluidic based monitoring and therapeutic platforms can be contoured into comfortable, low profile devices suitable for implanting in the body or for wearing on the body or in clothing. Truly integrated bioflexible devices would incorporate electronics, optics, photonics, wireless, fluidics, mechanical components, and power systems on a single flexible biocompatible substrate. Continued development of applications of this technology requires further development of biocompatible, flexible films with integrated electronics which can be mass produced at low cost. In this work, we demonstrate the fabrication of flexible printed circuits on Cyclo Olefin Polymer (COP) thermoplastic as a substrate material. COP is an attractive polymer for integrated bioflexible devices due to demonstrated biocompatibility and excellent material properties, such as high transparency over a wide band of wavelengths, low water absorption, and good mechanical properties. On significant challenge to building bioflxible devices on polymer films (such as COP) is the need for metalizing and patterning traces on these materials at low cost, and in a scalable manner. In this paper, we report work that utilizes a new technique for patterning metals on polymers that can result in low cost manufacturing of electronic circuits on biocompatible films such as COP. The process uses high intensity UV light that is directed through a quartz mask to selectively irradiate a film of COP. After processing, the material can be treated and subsequently metalized using electroless plating techniques. The great benefit of this approach is that no photoresists steps are needed-no coating, exposing, developing, etching, or stripping is required for the creation of the final device. Furthermore, the process can pattern traces at high resolution (<;2 microns) and can coat the insides of through hole vias, allowing multi-layer electronics to be produced. This greatly simplifies the manufacture of the circuits and reduces production cost considerably, when compared to conventional processes such as sputtering and etch. We demonstrate the production of electronic circuits on COP for the purpose of making bioelectronic devices and characterize some of the main properties of the device. We discuss the advantages of this approach and identify some of the manufacturing pitfalls.

SU‐E‐T‐344: Practicality of Pyroelectric X‐Ray Sources for Grenz and Conventional Radiotherapy

Purpose:Pyroelectric crystals can be used as a compact and low cost source for electrons and high energy photons. Only periodic heating cycles are required for energy input. In this study we examine the performance of a simulated pyroelectric x‐ray source in delivering a single 2Gy dose fraction for soft x‐ray (Grenz) and dermatological conventional x‐ray radiotherapy. Grenz radiotherapy applications include the treatment of persistent dermatitis and psoriasis. Methods:Dosedelivery was calculated as the energy deposited per photon in soft tissue for a monoenergetic x‐ray source with a beam area of 1.0cm2. Monoenergetic x‐ray photon energies between 1 and 30keV were plotted for delivered tissue dose between 1 and 3 mm tissue depth in 100 micron volume recording elements. From prior experimentation 5×1013 electrons emitted are assumed to be converted to 5.84×1010 photons per pyroelectric crystal heating cycle. Absorbed photons are assumed to deliver full energy dose upon absorption.Delivered volume element dose, average dose, heating cycles per fractional dose, and energy absorption efficiency are used as metrics for application performance. Results:Deliveredphotons between 8−15KeV produced the lowest number of cycles for delivereddoses to 2 and 3mm tissue depth. At 10keV a 2Gy fractional dose can be delivered at 2mm depth in 11 heating cycles. At energies below 6keV, nearly 100% energy deposition occurs within 1 mm, and the dose is delivered to shallow to cover treatment volume depth. Above 15keV, dosedelivery efficiency decreases, requiring 106 cycles at 80keV to deliver 2Gy at 3mm. Conclusions: Further study in device design will seek to maximize pyroelectric output x‐ray flux, decrease cycle time, and increase treatment coverage area using tiled sources. With decreased cycle times and increased flux, pyroelectricsources can be practical for photonradiotherapy applications.

TU‐F‐18C‐01: Breast Tissue Decomposition Using Spectral CT After Distortion Correction

PURPOSE To investigate the feasibility of accurate breast tissue compositional characterization by using spectral-distortion-corrected dual energy images from a photon-counting spectral CT. METHODS Thirty eight postmortem breasts were imaged with a Cadmium-Zinc-Telluride (CZT)-based photon-counting spectral CT system at beam energy of 100 kVp. The energy-resolved detector sorted photons into low and high energy bins with a splitting energy of 42 keV. The estimated mean glandular dose (MGD) for each breast was approximately 2.0 mGy. Dual energy technique was used to decompose breast tissue into water, lipid, and protein contents. Two image-based methods were investigated to improve the accuracy of tissue compositional characterization. The first method simply limited the recorded spectra up to 90 keV. This reduced the pulse pile-up artifacts but it has some dose penalty. The second method corrected the spectral information of all measured photons by using a spectral distortion correction technique. Breasts were then chemically decomposed into their respective water, lipid, and protein contents, which was used as the reference standard. The accuracy of the tissue compositional measurement with spectral CT was evaluated by the root-mean-square (RMS) errors in percentage composition. RESULTS The errors in quantitative material decomposition were significantly reduced after the appropriate image processing methods. As compared to the chemical analysis as the reference standard, the averages of the RMS errors were estimated to be 15.5%, 3.3%, and 2.8% for the raw, energy-limited, and spectral-corrected images, respectively. CONCLUSION Spectral CT can be used to accurately quantify the water, lipid, and protein contents in breast tissues by implementing a spectral distortion correction algorithm. The tissue compositional information can potentially improve the sensitivity and specificity for breast cancer diagnosis.