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WIREs Nanomed Nanobiotechnol
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An update on carbon nanotube‐enabled X‐ray sources for biomedical imaging

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A new imaging technology has emerged that uses carbon nanotubes (CNT) as the electron emitter (cathode) for the X‐ray tube. Since the performance of the CNT cathode is controlled by simple voltage manipulation, CNT‐enabled X‐ray sources are ideal for the repetitive imaging steps needed to capture three‐dimensional information. As such, they have allowed the development of a gated micro‐computed tomography (CT) scanner for small animal research as well as stationary tomosynthesis, an experimental technology for large field‐of‐view human imaging. The small animal CT can acquire images at specific points in the respiratory and cardiac cycles. Longitudinal imaging therefore becomes possible and has been applied to many research questions, ranging from tumor response to the noninvasive assessment of cardiac output. Digital tomosynthesis (DT) is a low‐dose and low‐cost human imaging tool that captures some depth information. Known as three‐dimensional mammography, DT is now used clinically for breast imaging. However, the resolution of currently‐approved DT is limited by the need to swing the X‐ray source through space to collect a series of projection views. An array of fixed and distributed CNT‐enabled sources provides the solution and has been used to construct stationary DT devices for breast, lung, and dental imaging. To date, over 100 patients have been imaged on Institutional Review Board‐approved study protocols. Early experience is promising, showing an excellent conspicuity of soft‐tissue features, while also highlighting technical and post‐acquisition processing limitations that are guiding continued research and development. Additionally, CNT‐enabled sources are being tested in miniature X‐ray tubes that are capable of generating adequate photon energies and tube currents for clinical imaging. Although there are many potential applications for these small field‐of‐view devices, initial experience has been with an X‐ray source that can be inserted into the mouth for dental imaging. Conceived less than 20 years ago, CNT‐enabled X‐ray sources are now being manufactured on a commercial scale and are powering both research tools and experimental human imaging devices. WIREs Nanomed Nanobiotechnol 2018, 10:e1475. doi: 10.1002/wnan.1475 This article is categorized under: Diagnostic Tools > Diagnostic Nanodevices Diagnostic Tools > In Vivo Nanodiagnostics and Imaging
(a) A sealed carbon nanotube (CNT)‐enabled X‐ray source. This source contains an array of 31 CNT cathodes. The X‐ray window, access ports, and ion pumps are visible. (b) Schematic of an individual CNT‐enabled X‐ray source. (c) Scanning electron micrograph of a CNT cathode.
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A new stationary intraoral tomosynthesis device being prepared for human use. The carbon nanotube‐enabled X‐ray source is shown as it will appear in the dental examination room (a) and surrounded by the equipment used to characterize its performance prior to implementation in the clinic (b).
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A representative slice from the reconstructed image stack obtained by stationary digital chest tomosynthesis, demonstrating the conspicuity of thoracic anatomy.
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Sample mediolateral‐oblique views obtained by stationary digital breast tomosynthesis. These slices are a part of the reconstructed image stack generated from 15 X‐ray projections. The reader scrolls through the slices to visualize the three‐dimensional anatomy and pathology.
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Representative images of the chest of an anesthetized but free‐breathing mouse obtained by carbon nanotube‐enabled micro‐computed tomography. Prospective gating allowed the information to be captured at end expiration (low point on the respiratory pressure waveform) and systole (R wave on ECG), which was then reconstructed in the (a) axial and (b) coronal planes. (Reprinted with permission from Ref . Copyright 2012 American Association of Physicists in Medicine)
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