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Microbeam radiation therapy (MRT) is a promising preclinical modality for cancer treatment, with remarkable preferential tumoricidal effects, that is, tumor eradication without damaging normal tissue functions. Significant lifespan extension has been demonstrated in brain tumor-bearing small animals treated with MRT. So far, MRT experiments can only be performed in a few synchrotron facilities around the world. Limited access to MRT facilities prevents this enormously promising radiotherapy technology from reaching the broader biomedical research community and hinders its potential clinical translation. We recently demonstrated, for the first time, the feasibility of generating microbeam radiation in a laboratory environment using a carbon nanotube x-ray source array and performed initial small animal studies with various brain tumor models. This new nanotechnology-enabled microbeam delivery method, although still in its infancy, has shown promise for achieving comparable therapeutic effects to synchrotron MRT and has offered a potential pathway for clinical translation.

RATIONAL AND OBJECTIVES: The objective of this study was to compare the stationary digital breast tomosynthesis (s-DBT) system to a conventional mammography system in a study of breast specimens. Radiologist evaluation of image quality was assessed in a reader study. This study represents the first human tissue imaging with the novel carbon nanotube-based s-DBT device. MATERIALS AND METHODS: Thirty-nine patients, with known breast lesions (Breast Imaging Reporting and Data System 4 or 5) by conventional mammography and scheduled for needle localization biopsy, were recruited under an institutional review board-approved protocol. Specimen images were obtained using a two-dimensional (2D) mammography system with a ×1.8 magnification factor and an s-DBT system without a high magnification factor. A reader study was performed with four breast fellowship-trained radiologists over two separate sessions. Malignancy scores were recorded for both masses and microcalcifications (MCs). Reader preference between the two modalities for MCs, masses, and surgical margins was recorded. RESULTS: The s-DBT system was found to be comparable to magnified 2D mammography for malignancy diagnosis. Readers preferred magnified 2D mammography for MC visualization (P < .05). However, readers trended toward a preference for s-DBT with respect to masses and surgical margin assessment. CONCLUSIONS: Here, we report on the first human data acquired using a stationary digital breast tomosynthesis system. The novel s-DBT system was found to be comparable to magnified 2D mammography imaging for malignancy diagnosis. Given the trend of preference for s-DBT over 2D mammography for both mass visibility and margin assessment, s-DBT could be a viable alternative to magnified 2D mammography for imaging breast specimens.

Microbeam radiation therapy (MRT) uses an array of high-dose, narrow (~100 μm) beams separated by a fraction of a millimeter to treat various radio-resistant, deep-seated tumors. MRT has been shown to spare normal tissue up to 1000 Gy of entrance dose while still being highly tumoricidal. Current methods of tumor localization for our MRT treatments require MRI and X-ray imaging with subject motion and image registration that contribute to the measurement error. The purpose of this study is to develop a novel form of imaging to quickly and accurately assist in high resolution target positioning for MRT treatments using X-ray fluorescence (XRF). The key to this method is using the microbeam to both treat and image. High Z contrast media is injected into the phantom or blood pool of the subject prior to imaging. Using a collimated spectrum analyzer, the region of interest is scanned through the MRT beam and the fluorescence signal is recorded for each slice. The signal can be processed to show vascular differences in the tissue and isolate tumor regions. Using the radiation therapy source as the imaging source, repositioning and registration errors are eliminated. A phantom study showed that a spatial resolution of a fraction of microbeam width can be achieved by precision translation of the mouse stage. Preliminary results from an animal study showed accurate iodine profusion, confirmed by CT. The proposed image guidance method, using XRF to locate and ablate tumors, can be used as a fast and accurate MRT treatment planning system.

We have recently demonstrated the feasibility of stationary digital chest tomosynthesis (s-DCT) using a dis- tributed carbon nanotube x-ray source array. The technology has the potential to increase the imaging resolution and speed by eliminating source motion. In addition, the flexibility in the spatial configuration of the individual sources allows new tomosynthesis imaging geometries beyond the linear scanning mode used in the conventional systems. In this paper, we report the preliminary results on the effects of the tomosynthesis imaging geometry on the image quality. The study was performed using a bench-top s-DCT system consisting of a CNT x-ray source array and a flat-panel detector. System MTF and ASF are used as quantitative measurement of the in-plane and in-depth resolution. In this study geometries with the x-ray sources arranged in linear, square, rectangular and circular configurations were investigated using comparable imaging doses. Anthropomorphic chest phantom images were acquired and reconstructed for image quality assessment. It is found that wider angular coverage results in better in-depth resolution, while the angular span has little impact on the in-plane resolution in the linear geometry. 2D source array imaging geometry leads to a more isotropic in-plane resolution, and better in-depth resolution compared to 1D linear imaging geometry with comparable angular coverage.

Current digital breast tomosynthesis (DBT) systems have been shown to have diminished microcalcification (MC) visibility compared to 2D mammography systems. Rotating gantry DBT systems require mechanical motion of the X-ray source which causes motion blurring of the focal spot, thus reducing spatial resolution. We have developed a stationary DBT (s-DBT) technology that uses a carbon nanotube (CNT) based X-ray source array in order to acquire all the projections images without any mechanical motion. It is capable of producing full tomosynthesis datasets with zero motion blur. It has been shown to have significantly higher spatial resolution than continuous motion DBT systems. An s-DBT system also allows for a wider angular span without increasing the acquisition time. A larger angular span covers a larger portion of the Fourier domain, thus decreasing the tissue overlap. In this study, we compare tomosynthesis imaging of MCs, in lumpectomy specimens, between an s-DBT system and a rotating gantry DBT system. Results show that s-DBT produces better MC sharpness and reduced tissue overlap compared to continuous motion DBT systems.

Stationary Digital Breast Tomosynthesis (sDBT) is a carbon nanotube based breast imaging device with fast data acquisition and decent projection resolution to provide three dimensional (3-D) volume information. To- mosynthesis 3-D image reconstruction is faced with the challenges of the cone beam geometry and the incomplete and nonsymmetric sampling due to the sparse views and limited view angle. Among all available reconstruction methods, statistical iterative method exhibits particular promising since it relies on an accurate physical and statistical model with prior knowledge. In this paper, we present the application of an edge-preserved regularizer to our previously proposed precomputed backprojection based penalized-likelihood (PPL) reconstruction. By using the edge-preserved regularizer, our experiments show that through tuning several parameters, resolution can be retained while noise is reduced significantly. Compared to other conventional noise reduction techniques in image reconstruction, less resolution is lost in order to gain certain noise reduction, which may benefit the research of low dose tomosynthesis.

The electronic structures and the work functions of pristine and Cs-intercalated single-walled carbon nanotube bundles were investigated by C 1 s and valence band photoemission spectroscopy. The C 1 s spectrum of the pristine material showed a Doniach–Sunjic type asymmetry, indicating the existence of metallic tubes. The work function of the pristine bundles was found to be 4.8 eV, which is about 0.2 eV larger than that of graphite. A drastic decrease of the work function to about 2.0 eV was observed in the Cs-intercalated sample. The Cs intercalation also caused a nearly two-order increase in the spectral intensity at the Fermi level.

The effects of processing on the structure and morphology of single-walled carbon nanotubes (SWNT) and their electrochemical intercalation with lithium were investigated. Purified SWNTs were processed by impact ball-milling and were electrochemically intercalated with lithium. The reversible saturation Li composition increased from Li 1.7 C 6 in purified SWNTs to Li 2.7 C 6 after 10 min of milling. The irreversible capacity decreased from Li 3.2 C 6 to Li 1.3 C 6 . Electron microscopy, Raman and X-ray diffraction measurements indicated that ball-milling induced disorder within the bundles and fractured the nanotubes.

Field emission properties of single-walled carbon nanotubes (SWNTs), deposited on n-type Si substrates, were investigated by a combination of classical I–V characterization and field emission energy distribution (FEED) measurements. I–V characterization showed that current densities on the order of 1 mA/cm2 could be obtained at nominal electric fields as low as 3 V/μm. A current density of up to 25 mA/cm2 was observed, and long-term current stability and reproducibility were excellent. FEED measurements revealed that at low current densities, the field emitted electrons originated from energy levels close to the Fermi level of the Si substrate. At larger applied voltages and larger current densities, I–V characterization of the field emitters showed primarily an ohmic behavior; FEED data taken under the same experimental conditions showed a shift of the main spectral peak toward lower kinetic energies with increasing applied voltages. This energy shift was found to be linear with the applied voltage and emission current over a wide range. Both FEED and I–V data thus indicated that the field emission current was primarily limited by the ohmic resistance of the nanotubes and/or the contact resistance between the nanotubes and the Si substrate; typical measured values for the cathode surface resistances were 100 kΩ cm2.

This article summarizes the current status of carbon nanotube intercalation compounds. It focuses on the structure and electrochemical properties of intercalated single-walled carbon nanotubes (SWNTs). Materials synthesis, purification and characterization methods are also discussed. This article draws mostly from works performed at UNC.

The electronic properties of single phase type-I clathrate compounds, ${\mathrm{Ba}}_{8}{\mathrm{Au}}_{6}(\mathrm{Si}\mathrm{}or\mathrm{}\mathrm{Ge}{)}_{40}$ and ${\mathrm{Ba}}_{8}{\mathrm{Ge}}_{46\ensuremath{-}x}$ have been investigated. The crystal structure, electrical resistivities, magnetic susceptibilities, the density of states at the Fermi level, and the band gap (where applicable) were determined. ${\mathrm{Ba}}_{8}{\mathrm{Au}}_{6}{\mathrm{Si}}_{40}$ and ${\mathrm{Ba}}_{8}{\mathrm{Au}}_{6}{\mathrm{Ge}}_{40}$ show a metallic behavior whereas ${\mathrm{Ba}}_{8}{\mathrm{Ge}}_{46\ensuremath{-}x}$ is semiconducting. On a basis of this work, a first evidence is presented of the existence of type-I mixed-clathrates containing both silicon and germanium.

Single-walled carbon nanotubes (SWNT) synthesized by laser ablation were electrochemically intercalated with lithium. As-grown SWNTs showed a reversible saturation composition of Li 1.2 C 6 (450 mAh g −1 ). After removing the impurity phases by filtration, the reversible saturation composition increased to Li 1.6 C 6 (600 mAh g −1 ), significantly higher than the ideal value of LiC 6 (372 mAh g −1 ) for graphite. All the SWNT materials showed large irreversible capacities and voltage hysteresis. Upon processing the nanotubes by ball-milling, the reversible Li capacity increased to 1000 mAh g −1 (Li 2.7 C 6 ) while the irreversible capacity decreased to 650 mAh g −1 .

(M=K or Cs). No crystalline structure was observed in the reacted materials by X-ray diffraction. In situ metal deposition, TEM, and electron energy loss spectroscopy (EELS) measurements were performed on individual SWNT bundles at 300 K. The results showed that alkali metals can be reversibly intercalated into the SWNT bundles. Although intercalation induced structural disorder, individual nanotubes and to a large extent the bundles maintained their structural integrity after intercalation and de-intercalation.

Single-walled carbon nanotubes (SWNTs) were reacted with HNO 3 solution. An expansion of the inter-nanotube spacing and increase in the amount of hydrogen in the material were observed by X-ray diffraction and proton NMR measurements after the SWNTs were immersed into the HNO 3 solution for less than 2 hours. The change in diffraction pattern was reversible, indicating intercalation of HNO 3 into the SWNT bundles. When the SWNTs were immersed in the HNO 3 solution for a longer period of time, the bundles became disordered and partially exfoliated. Isolated SWNTs and large nano-particles were often observed.

Cesium (Cs) or potassium (K) was deposited on single-walled carbon nanotube bundles in vacuum at room temperature. The deposited bundles were analyzed in-situ by transmission electron microscopy and electron energy loss spectroscopy techniques. The results indicate that both Cs and K can be reversibly intercalated with the bundles. The intercalants reside in-between the individual nanotubes within the bundles. Intercalation caused structural disorder to the two-dimensional lattice of the pristine nanotube bundles. The chemical compositions of the nanotube bundles intercalated with K and Cs were found to be about KC 24 and CsC 24 to CsC 8 .

Microbeam radiation therapy (MRT) is a promising experimental and preclinical radiotherapy method for cancer treatment. Synchrotron based MRT experiments have shown that spatially fractionated microbeam radiation has the unique capability of preferentially eradicating tumour cells while sparing normal tissue in brain tumour bearing animal models. We recently demonstrated the feasibility of generating orthovoltage microbeam radiation with an adjustable microbeam width using a carbon nanotube based x-ray source array. Here we report the preliminary results from our efforts in developing an image guidance procedure for the targeted delivery of the narrow microbeams to the small tumour region in the mouse brain. Magnetic resonance imaging was used for tumour identification, and on-board x-ray radiography was used for imaging of landmarks without contrast agents. The two images were aligned using 2D rigid body image registration to determine the relative position of the tumour with respect to a landmark. The targeting accuracy and consistency were evaluated by first irradiating a group of mice inoculated with U87 human glioma brain tumours using the present protocol and then determining the locations of the microbeam radiation tracks using γ-H2AX immunofluorescence staining. The histology results showed that among 14 mice irradiated, 11 received the prescribed number of microbeams on the targeted tumour, with an average localization accuracy of 454 µm measured directly from the histology (537 µm if measured from the registered histological images). Two mice received one of the three prescribed microbeams on the tumour site. One mouse was excluded from the analysis due to tissue staining errors.

We have developed a compact microbeam radiation therapy device using carbon nanotube cathodes to create a linear array of narrow focal line segments on a tungsten anode and a custom collimator assembly to select a slice of the resulting wedge-shaped radiation pattern. Effective focal line width was measured to be 131 μm, resulting in a microbeam width of ∼300 μm. The instantaneous dose rate was projected to be 2 Gy/s at full-power. Peak to valley dose ratio was measured to be >17 when a 1.4 mm microbeam separation was employed. Finally, multiple microbeams were delivered to a mouse with beam paths verified through histology.

Background We performed in vivo micro‐computed tomography (micro‐ CT ) imaging using a novel carbon nanotube ( CNT )–based x‐ray source to detect calcification in the aortic arch of apolipoprotein E (apoE)–null mice. Methods and Results We measured calcification volume of aortic arch plaques using CNT ‐based micro‐ CT in 16‐ to 18‐month‐old males on 129S6/SvEvTac and C57BL/6J genetic backgrounds (129‐apoE KO and B6‐apoE KO ). Cardiac and respiratory gated images were acquired in each mouse under anesthesia. Images obtained using a CNT micro‐ CT had less motion blur and better spatial resolution for aortic calcification than those using conventional micro‐ CT , evaluated by edge sharpness (slope of the normalized attenuation units, 1.6±0.3 versus 0.8±0.2) and contrast‐to‐noise ratio of the calcifications (118±34 versus 10±2); both P KO than in the B6‐apoE KO mice (0.90±0.18 versus 0.22±0.10 mm 3 , P KO than in the B6‐apoE KO mice (6.1±0.6 versus 3.7±0.4 mm 2 , P KO than in the B6‐apoE KO mice (16.9±2.0 versus 9.6±0.8%, P Conclusions A novel CNT ‐based micro‐ CT is a useful tool to evaluate vascular calcifications in living mice. Quantification from acquired images suggests higher susceptibility to calcification of the aortic arch plaques in 129‐apoE KO than in B6‐apoE KO mice.

Micro-beam radiation therapy (MRT) uses parallel planes of high dose narrow (10–100 um in width) radiation beams separated by a fraction of a millimeter to treat cancerous tumors. This experimental therapy method based on synchrotron radiation has been shown to spare normal tissue at up to 1000Gy of entrance dose while still being effective in tumor eradication and extending the lifetime of tumor-bearing small animal models. Motion during the treatment can result in significant movement of micro beam positions resulting in broader beam width and lower peak to valley dose ratio (PVDR), and thus can reduce the effectiveness of the MRT. Recently we have developed the first bench-top image guided MRT system for small animal treatment using a high powered carbon nanotube (CNT) x-ray source array. The CNT field emission x-ray source can be electronically synchronized to an external triggering signal to enable physiologically gated firing of x-ray radiation to minimize motion blurring. Here we report the results of phantom study of respiratory gated MRT. A simulation of mouse breathing was performed using a servo motor. Preliminary results show that without gating the micro beam full width at tenth maximum (FWTM) can increase by 70% and PVDR can decrease up to 50%. But with proper gating, both the beam width and PVDR changes can be negligible. Future experiments will involve irradiation of mouse models and comparing histology stains between the controls and the gated irradiation.

The recent commercialization of digital breast tomosynthesis systems realizes the clinical applications of this novel three-dimensional imaging technology. The total dosage of breast tomosynthesis for single patient is comparable to that of the traditional mammography. This paper presents our continuous work on image quality analysis for the optimization of a new multi-beam breast tomosynthesis system based on carbon nanotube X-ray emission technology. Several tomosynthesis reconstruction algorithms were implemented to reconstruct the phantom data. Noise power spectrum and modulation transfer function were investigated to evaluate the image quality.

Conventional mammography techniques used for imaging patients that have undergone augmentation mammoplasty produce substandard images, incomplete evaluation of breast tissue, and can cause discomfort to the patient. Typically, four images of each breast are acquired (double the amount of a patient without implants), two with the implant in view and two "pushback" views, which moves the implant posteriorly out of the field of view. The "pushback" view can be difficult to perform when there is encapsulation of the breast tissue around the implant. In severe cases, performing the technique can cause unwarranted pain to the patient. This technique can also result in up to a three times increase in procedure time which leads to lower patient throughput. Using 2D mammography, it is difficult to interpret tissue above and below implants due to the overlap of breast tissue and implant. Recently, Digital Breast Tomosynthesis (DBT) has been shown to aid in the localization and diagnosis of breast masses by removing underlying and overlying tissue from the plane of interest in 3D space. However, commercial DBT systems have motion blurring of the projection images associated with x-ray source motion. To overcome this limitation, stationary DBT (s-DBT) has been developed. Here we report the feasibility of using s-DBT as an effective screening tool for patients who have undergone augmentation mammoplasty. Qualitative image analysis is completed on reconstruction images of tomosynthesis phantoms combined with implants. Reconstruction images show that it is possible to locate lesions above and below the implant using a clinically relevant entrance dose.

XinRay Systems Inc has a rectangular x-ray computed tomography (CT) imaging setup using multibeam x-ray tubes. These multibeam x-ray tubes are based on cold cathodes using carbon nanotube (CNT) field emitters. Due to their unique design, a CNT x-ray tube can contain a dense array of independently controlled electron emitters which generate a linear array of x-ray focal spots. XinRay uses a set of linear CNT x-ray tubes to design and construct a stationary CT setup which achieves sufficient CT coverage from a fixed set of views. The CT system has no moving gantry, enabling it to be enclosed in a compact rectangular tunnel. The fixed locations of the x-ray focal spots were optimized through simulations. The rectangular shape creates significant variation in path length from the focal spots to the detector for different x-ray views. The shape also results in unequal x-ray coverage in the imaged space. We discuss the impact of this variation on the reconstruction. XinRay uses an iterative reconstruction algorithm to account for this unique geometry, which is implemented on a graphics processing unit (GPU). The fixed focal spots prohibit the use of an antiscatter grid. Quantitative measure of the scatter and its impact on the reconstruction will be discussed. These results represent the first known implementation of a completely stationary CT setup using CNT x-ray emitter arrays.

Chest tomosynthesis is an imaging modality that provides 3D sectional information of a patients thoracic cavity using limited angle x-ray projections. Studies show that tomosynthesis can improve the detection of subtle lung nodules comparing to conventional radiography at a lower radiation dose than CT. In the conventional design, the projection images are collected by mechanically moving a single x-ray source to different viewing angles. We investigated the feasibility of stationary chest tomosynthesis using the distributed CNT x-ray source array technology, which can generate a scanning x-ray beam without any mechanical motion. A proof-of-concept system was constructed using a short linear source array and a at panel detector. The performance of the source including the flux was evaluated in the context of chest imaging. The bench-top system was characterized and images of a chest phantom were acquired and reconstructed. The preliminary results demonstrate the feasibility of stationary chest tomosynthesis using the CNT x-ray source array technology.

Current practice for imaging surgical breast specimens is a single 2D magnification view on a mammography system, but 2D imaging overlaps the tissue in different planes causing distortion of lesion margins. Digital breast tomosynthesis (DBT) could be used as an alternative imaging modality for imaging breast specimens. DBT systems acquire multiple low dose projection images, over a small angular span, which are then reconstructed into a partial 3D volume. The reconstructed images can be used to increase visualization of lesion margins and extent of microcalcifications (MCs). Current commercial DBT systems use a single rotating X-ray source, the movement of which produces motion blur. Motion blur reduces visualization of small objects such as MCs. MCs, depending on size and structure, can be implicative of breast cancer. We have developed a stationary DBT (s-DBT) system using a linearly distributed, CNT Xray source array. S-DBT allows for rapid acquisition of projection images with no image degradation from X-ray source motion. Full tomosynthesis datasets can be acquired, allowing visualize of both masses and microcalcifications. Here we report the preliminary results of a reader study comparing breast specimen images from a 2D commercial mammography system and an s-DBT system. Preliminary results show that s-DBT is capable of producing equivalent image quality to 2D mammography, and in some cases is superior.

We have recently developed a method of using a distributed x-ray source array to obtain images with scatter correction for tomographic reconstruction of an object. The method consists of obtaining x-ray images of the object with and without the primary beam sampling apparatus. In this study, we report the results of applying the scatter correction method for breast tomosynthesis imaging using the carbon nanotube x-ray based stationary Digital Breast Tomosynthesis (s-DBT) system developed at UNC. The unique design of s-DBT system makes it possible to estimate the image of the scatter profile of the object with very low dose, and without significant increase in acquisition time. An anthropomorphic breast phantom was used for quantitative analysis of the change in contrast and scatter-to-primary ratio. Our results suggest that the scatter correction method is effective and can be used for enhanced contrast.

Microbeam radiation therapy (MRT) is an experimental and preclinical technique with demonstrated capability of eradicating tumors while sparing normal tissues from radiation damage. We have proposed the design of a microbeam radiation device using a carbon nanotube (CNT) field emission x-ray source. The key enabling technology is the CNT based spatially distributed x-ray technology. The proposed MRT system has a unique square system geometry with the radiations shining on the targeting tumor positioned at the center of the square. A high microbeam dose rate is achieved by distributing the electron energy over multiple elongated focal tracks with a significantly larger area and therefore higher heat capacity compared to a conventional x-ray source with a point focal spot. Meanwhile the efficiency of the xray photons going through the narrow microbeam collimator, thus the dose rate, is greatly increased by making the effective width of the focal track comparable to that of the microbeam collimator opening. In order to achieve the desired focal track on the anode, a commercial software package (Opera 3D, Cobham plc) was used to simulate and design the optimal line focusing lens. The finalized design was based on a two-electrode Einzel focusing lens configuration. The simulation shows the two-stage electrostatic focusing lens is capable of providing the 100μm effective focal spot size required for the proposed microbeam x-ray with 100μm beam width. The recent focal spot size measurement performed using a testing x-ray chamber has also verified the simulation results.

Conductivity and superconductivity of C60 fullerides are reviewed, and the specific features of these new materials are described from the viewpoint of electronic properties and structure.

Carbon nanotubes (CNTs) have attracted great attention as electron emitters. These field emission cathodes operate at room temperature without a heater, in contrast to thermionic emitters that often require considerable heater power for proper operation. Furthermore, CNTs have the advantage of large aspect ratios, allowing large local electric field enhancements at the nanotube tips, further increasing their attractiveness as field emitters. However, due primarily to materials issues such as limited emission site density, screening effects, and weak interfacial bonding, no large area cathodes have been operated at high current to date. In this paper, we report on the design, fabrication, and testing of a large-area CNT cathode operating at high-voltage (>200 kV) and high-current density (30 A/cm/sup 2/). The cathode lifetime exceeded four thousand pulses. The current density and voltage achieved represent a significant achievement and indicate that such a cathode design can prove valuable as a high-current, large-area emitter.

High-resolution electron field emission cathodes were fabricated at room temperature by a high throughput electrophoresis process using functionalized carbon nanotubes (CNTs). Well-defined and adherent CNT patterns with 20 μm feature size were achieved on a variety of substrates with fine control of the CNT morphology. The cathodes show uniform emission pattern across the entire surfaces and emission current with long-term stability. This room-temperature liquid-phase process is efficient and has no intrinsic limit on the deposition area. The emission characteristics of these cathodes compare favorably to those from other fabrication methods for CNT based field emission display applications.

We report the first direct study on the oxidation of carbon nanotubes at the resolution of an aberration-corrected environmental transmission electron microscope (ETEM), as we locate and identify changes in the same nanotubes as they undergo oxidation at increasing temperatures in situ in the ETEM. Contrary to earlier reports that CNT oxidation initiates at the end of the tube and proceeds along its length, our findings show that only the outside graphene layer is being removed and, on occasion, the interior inner wall is oxidized, presumably due to oxygen infiltrating into the hollow nanotube through an open end or breaks in the tube. We believe that this work provides the foundation for a greater scientific understanding of the mechanism underlying the nanotube oxidation process, as well as guidelines to manipulate the nanotubes' structure or prevent their oxidation.

We have investigated the synthesis, structure, and electronic properties of ${(\mathrm{N}{\mathrm{H}}_{3})}_{x}{\mathrm{K}}_{3}{\mathrm{C}}_{60}$ by exposing preformed ${\mathrm{K}}_{3}$${\mathrm{C}}_{60}$ to N${\mathrm{H}}_{3}$ vapor. Measurements were made on bulk powders and films with a variety of techniques including in-situ x-ray diffraction and monitoring of N${\mathrm{H}}_{3}$ pressure, Raman scattering and ac susceptibility. The reaction of N${\mathrm{H}}_{3}$ with ${\mathrm{K}}_{3}$${\mathrm{C}}_{60}$ is completely reversible and leaves the ${({\mathrm{C}}_{60})}^{3\ensuremath{-}}$ charge state intact, while allowing the distance between the ${\mathrm{C}}_{60}$ molecules to vary. We observe two different crystallographic structures at $x=1$ and $x=8\ensuremath{-}10$. The $x=1$ structure is face-centered orthorhombic with a single N${\mathrm{H}}_{3}$ on the octahedral interstitial site. It is single phase at 100\ifmmode^\circ\else\textdegree\fi{}C and N${\mathrm{H}}_{3}$ pressures \ensuremath{\ge}400 torr and remains single phase at 0 torr if the temperature is reduced to 25\ifmmode^\circ\else\textdegree\fi{}C. Although (N${\mathrm{H}}_{3}$)${\mathrm{K}}_{3}$${\mathrm{C}}_{60}$ exhibits no superconductivity at ambient pressure, superconductivity can be induced by hydrostatic pressure with an onset at 28 K. The details of the $x=8\ensuremath{-}10$ structure are uncertain, however it appears that this phase is body-centered tetragonal with N${\mathrm{H}}_{3}$ on both the octahedral and tetrahedral sites. It occurs at room temperature and N${\mathrm{H}}_{3}$ pressures \ensuremath{\ge}500 torr, but is not stable at lower N${\mathrm{H}}_{3}$ pressures. Resistivity measurements of N${\mathrm{H}}_{3}$-doped ${\mathrm{K}}_{3}$${\mathrm{C}}_{60}$ films show that the formation of the new structure results in a rapid increase of the resistivity to values exceeding 1 \ensuremath{\Omega} cm.

We report the synthesis of a new strontium ruthenium oxycarbonate, Sr2RuO4 · 0.25 CO2, and its use to synthesize Sr3Ru2O7, the n = 2 member of the (SrO)n+1 (RuO2)n Ruddlesden-Popper series. Like layered K2NiF4-type Sr2RuO4, and three-dimensional perovskite-type SrRuO3, Sr3Ru2O7 is a metallic conductor. In Sr3Ru2O7, the magnetic moments (d4, low spin) interact weakly with each other and develop strong antiferromagnetic correlations below 15 K. Small substitutions of Ir for Ru in Sr3Ru2O7 result in a metal-insulator transition.

C 60 films up to 1000 A in thickness have been grown by room-temperature sublimation onto Si(100) and Si(111) substrates that have been prepared with surfaces passivated against dangling bonds. X-ray diffraction measurements reveal that films deposited on such substrates have a high degree of (111)-textured crystallinity which is absent in films deposited on untreated Si. Examination of surface topographies with tapping mode atomic force microscopy shows a thickness-dependent increase in roughness which is greater for the treated samples. Our results are placed in context with respect to what is presently known about the growth of C 60 films on a variety of substrates. Implications for possible device applications will also be discussed.

We report superconductivity in Cs3C60 at 40K using ac susceptibility measurements under hydrostatic conditions up to 15 kbar. Cs3C60 was prepared by reaction of C60 with Cs in liquid ammonia, followed by heating at 150°C. This route circumvents formation of the energetically more stable Cs1C60 and Cs4C60 phases. We have studied the synthesis and phase formation by measuring the symmetric Ag pentagonal pinch mode of C60 using Raman spectroscopy. Whereas Raman spectroscopy indicates homogeneous charge transfer of three electrons, x-ray diffraction indicates two phases other than the commonly observed fcc structure. This superconducting transition temperature is considerably higher than for known doped C60 compounds and intermetallic compounds.

We recently developed a new spatially distributed x-ray source array technology utilizing the carbon nanotubes (CNTs) as the electron field emitters. The technology with flexible source configuration and digital control of radiation opens up new possibilities for designing x-ray tomography scanners with enhanced resolution and scanning speed, and for developing novel radiotherapy systems. Several imaging and radiation therapy systems are currently at different stages of development. A stationary digital tomosynthesis scanner for detection of human breast tumor has been demonstrated which offers a higher spatial resolution, a faster scanning speed, and potentially a higher sensitivity for micro-calcification compared to the current rotating-gantry tomosynthesis scanners. We have also initiated an effort on microbeam radiotherapy, which is an experimental and preclinical technique that has been shown in synchrotron based animal studies to be effective for eradication of brain tumor while sparing normal tissue. In this talk we will provide an update on the status of the CNT x-ray source technology and will introduce the stationary digital breast tomosynthesis and microbeam radiation therapy systems currently under development at UNC.

Purpose: The purpose of this study is to investigate the feasibility of increasing the system spatial resolution and scanning speed of Hologic Selenia Dimensions digital breast tomosynthesis (DBT) scanner by replacing the rotating mammography x-ray tube with a specially designed carbon nanotube (CNT) x-ray source array, which generates all the projection images needed for tomosynthesis reconstruction by electronically activating individual x-ray sources without any mechanical motion. The stationary digital breast tomosynthesis (s-DBT) design aims to (i) increase the system spatial resolution by eliminating image blurring due to x-ray tube motion and (ii) reduce the scanning time. Low spatial resolution and long scanning time are the two main technical limitations of current DBT technology. Methods: A CNT x-ray source array was designed and evaluated against a set of targeted system performance parameters. Simulations were performed to determine the maximum anode heat load at the desired focal spot size and to design the electron focusing optics. Field emission current from CNT cathode was measured for an extended period of time to determine the stable life time of CNT cathode for an expected clinical operation scenario. The source array was manufactured, tested, and integrated with a Selenia scanner. An electronic control unit was developed to interface the source array with the detection system and to scan and regulate x-ray beams. The performance of the s-DBT system was evaluated using physical phantoms. Results: The spatially distributed CNT x-ray source array comprised 31 individually addressable x-ray sources covering a 30 angular span with 1 pitch and an isotropic focal spot size of 0.6 mm at full width at half-maximum. Stable operation at 28 kV(peak) anode voltage and 38 mA tube current was demonstrated with extended lifetime and good source-to-source consistency. For the standard imaging protocol of 15 views over 14, 100 mAs dose, and 2 × 2 detector binning, the projection resolution along the scanning direction increased from 4.0 cycles/mm [at 10% modulation-transfer-function (MTF)] in DBT to 5.1 cycles/mm in s-DBT at magnification factor of 1.08. The improvement is more pronounced for faster scanning speeds, wider angular coverage, and smaller detector pixel sizes. The scanning speed depends on the detector, the number of views, and the imaging dose. With 240 ms detector readout time, the s-DBT system scanning time is 6.3 s for a 15-view, 100 mAs scan regardless of the angular coverage. The scanning speed can be reduced to less than 4 s when detectors become faster. Initial phantom studies showed good quality reconstructed images. Conclusions: A prototype s-DBT scanner has been developed and evaluated by retrofitting the Selenia rotating gantry DBT scanner with a spatially distributed CNT x-ray source array. Preliminary results show that it improves system spatial resolution substantially by eliminating image blur due to x-ray focal spot motion. The scanner speed of s-DBT system is independent of angular coverage and can be increased with faster detector without image degration. The accelerated lifetime measurement demonstrated the long term stability of CNT x-ray source array with typical clinical operation lifetime over 3 years.

The stationary Digital Breast Tomosynthesis System (s-DBT) has the advantage over the conventional DBT systems as there is no motion blurring in the projection images associated with the x-ray source motion. We have developed a prototype s-DBT system by retrofitting a Hologic Selenia Dimensions rotating gantry tomosynthesis system with a distributed carbon nanotube (CNT) x-ray source array. The linear array consists of 31 x-ray generating focal spots distributed over a 30 degree angle. Each x-ray beam can be electronically activated allowing the flexibility and easy implementation of novel tomosynthesis scanning with different scanning parameters and configurations. Here we report the initial results of investigation on the imaging quality of the s-DBT system and its dependence on the acquisition parameters including the number of projections views, the total angular span of the projection views, the dose distribution between different projections, and the total dose. A mammography phantom is used to visually assess image quality. The modulation transfer function (MTF) of a line wire phantom is used to evaluate the system spatial resolution. For s-DBT the in-plan system resolution, as measured by the MTF, does not change for different configurations. This is in contrast to rotating gantry DBT systems, where the MTF degrades for increased angular span due to increased focal spot blurring associated with the x-ray source motion. The overall image quality factor, a composite measure of the signal difference to noise ratio (SdNR) for mass detection and the z-axis artifact spread function for microcalcification detection, is best for the configuration with a large angular span, an intermediate number of projection views, and an even dose distribution. These results suggest possible directions for further improvement of s-DBT systems for high quality breast cancer imaging.

X-ray fluorescence molecular imaging (XFMI) can be a potential alternative to existing molecular imaging modalities providing high sensitivity and good spatial resolution. However, high sensitivity at a few tens of μg/mL can be reached only with monochromatic synchrotron x-rays; in typical laboratory setting using conventional x-ray sources XFMI has been reported to reach only about 10 mg/mL sensitivity. In this paper, we demonstrated the feasibility of simultaneously detecting x-ray fluorescence signals from a mouse-sized object containing iodine and indium solutions at 50 μg/mL concentration using a carbon nanotube (CNT) x-ray source. XFMI has the high potential to provide molecular imaging capability in small-animal models with high sensitivity, high spatial and temporal resolution, high multiplexing capacity, and at low radiation dose.

X-ray scatter may significantly degrade imaging performance in x-ray radiography applications, including flatpanel detector-based x-ray imaging, tomosynthesis, and cone-beam CT (CBCT), primarily due to their large projection field sizes. It results in soft tissue contrast reduction, potentially severe image artifacts, and increased patient dose. Several different approaches have been developed to reject the scatter contributions, including analytical calculation, empirical algorithms, Monte-Carlo simulation, blocker based measurement, and slot scan technique. We recently developed a new x-ray scatter rejection method based on nanotechnology-enabled frequency division multiplexing x-ray (FDMX) imaging technique. The key enabling technology is the carbon nanotube (CNT)-based multi-beam field emission x-ray (MBFEX) source technology. The proposed FDMX imaging system has a MBFEX source with an array of x-ray tubes. The x-ray radiation from each individual x-ray tube is modulated at a certain given frequency. The collimated x-ray beams passed through the object and were captured by a high speed x-ray detector. A demultiplexing algorithm was applied to reject the scatter radiation from the primary radiation based on their different modulation frequencies. The x-ray images generated by the FDMX imaging technique clearly demonstrated improved imaging quality in terms of lower scatter-to-primary-ratio (SPR) and higher contrast-to-noise-ratio (CNR). It shows great potential of improving x-ray imaging performance and reducing patient dose.

Carbon nanotube (CNT) micro-focus x-ray tubes have been demonstrated as a novel technology for in-vivo small animal imaging. It enables simultaneous respiratory and cardiac gated prospective CT imaging of free breathing animals with high temporal resolution. Operating the micro-focus CNT x-ray source at high power is required to achieve high temporal resolution. The thermal loading of the anode focal spot is a limiting factor in determining the maximum power of an x-ray tube. In this paper, we developed a reliable simulation model to quantitatively analyze the anode heat load of the CNT x-ray source operating in both DC and pulse modes. The anode temperature distribution is simulated using finite element analysis. The model is validated by comparing simulation results for the micro-focus x- ray tube with reported experimental results. We investigated the relationship between the maximum power and the effective focal spot size for CNT micro-CT system running in both DC and pulse modes. Our results show that when operating in pulse mode, the maximum power of the CNT x-ray source can be significantly higher than when operating in DC mode. In DC mode, we found that the maximum power scales non-linearly with the effective focal spot size as P(in W) = (0.25/ sin θ+1.6)f0.73 s (in μm), where 1/sin θ is the projection factor for a given anode angle θ. However, in pulse mode the maximum power linearly increases with the effective focal spot size asP(in W) = (0.20/ sin θ+0.35)fs(in μm), and is significantly higher than that in the DC mode. This implies that it is feasible to improve the micro-CT temporal resolution further without sacrificing the image quality. The simulation method developed here also enables us to analyze the thermal loading of the other CNT x-ray sources for other applications, such as the stationary digital breast tomosynthesis scanner and the CNT microbeam radiation therapy system.

A prototype stationary digital breast tomosynthesis (s-DBT) system has been developed by retrofitting a Hologic Selenia Dimension rotating gantry tomosynthesis scanner with a spatially distributed carbon nanotube (CNT) x-ray source array. The goal is to improve the system spatial resolution by removing the x-ray tube motion induced focal spot blurring. The CNT x-ray source array comprises 31 individually addressable x-ray beams covering 30° angular span. Each x-ray beam has a minimum focal spot size of 0.64×0.61mm (full-width-at-half-maximum), a stationary W anode operating up to 50kVp, and 1mm thick Al filter. The flux from each beam is regulated and varied using dedicated control electronics. The maximum tube current is determined by the heat load of the stationary anode and depends on the energy, pulse width and the focal spot size used. Stable operation at 28kVp, 27mA tube current, 250msec pulse width and 38mA tube current, 183msec pulse width per exposure was achieved with extended lifetime. The standard ACR phantom was imaged and analyzed to evaluate the image quality. The actual scanning speed depends on the number of views and the readout time of the x-ray detector. With the present detector, 6 second scanning time at either 15 views or 31 views can be achieved at 100mAs total imaging dose with a detector readout time of 240msec.

A cone beam micro-CT has previously been utilized along with a pressure-tracking respiration sensor to acquire prospectively gated images of both wild-type mice and various adult murine disease models. While the pressure applied to the abdomen of the subject by this sensor is small and is generally without physiological effect, certain disease models of interest, as well as very young animals, are prone to atelectasis with added pressure, or they generate too weak a respiration signal with this method to achieve optimal prospective gating. In this work we present a new fibre-optic displacement sensor which monitors respiratory motion of a subject without requiring physical contact. The sensor outputs an analogue signal which can be used for prospective respiration gating in micro-CT imaging. The device was characterized and compared against a pneumatic air chamber pressure sensor for the imaging of adult wild-type mice. The resulting images were found to be of similar quality with respect to physiological motion blur; the quality of the respiration signal trace obtained using the non-contact sensor was comparable to that of the pressure sensor and was superior for gating purposes due to its better signal-to-noise ratio. The non-contact sensor was then used to acquire in-vivo micro-CT images of a murine model for congenital diaphragmatic hernia and of 11-day-old mouse pups. In both cases, quality CT images were successfully acquired using this new respiration sensor. Despite the presence of beam hardening artefacts arising from the presence of a fibre-optic cable in the imaging field, we believe this new technique for respiration monitoring and gating presents an opportunity for in-vivo imaging of disease models which were previously considered too delicate for established animal handling methods.

Previous high-resolution electron microscopy (HREM) observations of the carbon nanotubes have led to a "Russian doll" structural model that is based on hollow concentric cylinders capped at both ends. The structures of the carbon nanotubes and particles were characterized here by bulk physical and chemical property measurements. The individual nanostructure is as compressible as graphite in the c axis, and such nanostructures can be intercalated with potassium and rubidium, leading to a saturation composition of "MC 8 ." These results are counter to expectations that are based on a Russian doll structure. HREM after intercalation with potassium and deintercalation indicates that individual nanoparticles are a "paper-mache" of smaller graphite layers. Direct current magnetization and electron spin resonance measurements indicate that the electronic properties of the nanostructures are distinctly different from those of graphite. Although the nanostructures have distinct morphologies and electronic properties, they are highly defective and have a local structure similar to turbostratic graphite.

Field emission offers an alternate method of electron production for Bremsstrahlung based X-ray tubes. Carbon nanotubes (CNTs) serve as very effective field emitters, allowing them to serve as electron sources for X-ray sources, with specific advantages over traditional thermionic tubes. CNT derived X-ray sources can create X-ray pulses of any duration and frequency, gate the X-ray pulse to any source and allow the placement of many sources in close proximity. We have constructed a number of micro-CT systems based on CNT X-ray sources for applications in small animal imaging, specifically focused on the imaging of the heart and lungs. This paper offers a review of the pre-clinical applications of the CNT based micro-CT that we have developed. We also discuss some of the current and potential clinical applications of the CNT X-ray sources.