In-Situ Monitoring of Reciprocal Charge Transfer and Losses in Graphene-Silicon CCD Pixels.

Charge-coupled devices (CCD) allow imaging by photodetection, charge integration, and serial transfer of the stored charge packets from multiple pixels to the readout node. The functionality of CCD can be extended to the non-destructive and in-situ readout of the integrated charges by replacing metallic electrodes with graphene in the metal-oxide-semiconductors (MOS) structure of a CCD pixel. The electrostatic capacitive coupling of graphene with the substrate allows the Fermi level tuning that reflects the integrated charge density in the depletion well. This work demonstrates the in-situ monitoring of the serial charge transfer and interpixel transfer losses in a reciprocating manner between two adjacent Gr-Si CCD pixels by benefitting the electrostatic and gate-to-gate couplings. We achieved the maximum charge transfer efficiency (CTE) of 92.4%, which is mainly decided by the inter-pixel distance, phase clock amplitudes, switching slopes, and density of surface defects. The discussion on overcoming transfer losses and improving CTE by realizing a graphene-electron multiplication CCD is also presented. The proof of the concept of the in-situ readout of the out-of-plane avalanche in a single Gr-Si CCD pixel is also demonstrated, which can amplify the photo packet in a pre-transfer manner.

A new detector for sub-millisecond EXAFS spectroscopy at the European Synchrotron Radiation Facility.

A new FReLoN (Fast-Readout Low-Noise) high-frame-rate detector adopted for the fast continuous collection of X-ray absorption spectra is presented. The detector is installed on the energy-dispersive X-ray absorption beamline ID24 at the ESRF and is capable of full time-resolved EXAFS spectra collection with over 4 kHz repetition rate and 0.2 ms exposure time. An example of the in situ kinetic study of the high-temperature oxidation of metallic iron is presented.

Extreme Value Theory Applications to Space Radiation Damage Assessment in Satellite Microelectronics.

Calculations of the first and second moments of displacement damage energy distributions from clastic collisions and from nuclear reactions, at proton energies ranging from 10 MeV to 300 MeV, are incorporated into a model describing the probability of damage as a function of the proton fluence and the size of the sensitive micro-volume in Si. Comparisons between the predicted and measured leakage currents in Si imaging arrays illustrate how the Poisson distribution of higher energy nuclear reaction recoils affects the pixel-to-pixel variance in the damage across the array for proton exposures equivalent to mission duration of a few years within the earth's trapped proton belts. Extreme value statistics (EVS) quantify the largest expected damage extremes following a given proton fluence, and an analysis derived from the first-principle damage calculations shows excellent agreement with the measured extremes. EVS is also used to demonstrate the presence of high dark current pixels, or "spikes," which occur from different mechanisms. Different sources of spikes were seen in two different imager designs.

Cameras for digital microscopy.

This chapter reviews the fundamental characteristics of charge-coupled devices (CCDs) and related detectors, outlines the relevant parameters for their use in microscopy, and considers promising recent developments in the technology of detectors. Electronic imaging with a CCD involves three stages--interaction of a photon with the photosensitive surface, storage of the liberated charge, and readout or measurement of the stored charge. The most demanding applications in fluorescence microscopy may require as much as four orders of greater magnitude sensitivity. The image in the present-day light microscope is usually acquired with a CCD camera. The CCD is composed of a large matrix of photosensitive elements (often referred to as "pixels" shorthand for picture elements, which simultaneously capture an image over the entire detector surface. The light-intensity information for each pixel is stored as electronic charge and is converted to an analog voltage by a readout amplifier. This analog voltage is subsequently converted to a numerical value by a digitizer situated on the CCD chip, or very close to it. Several (three to six) amplifiers are required for each pixel, and to date, uniform images with a homogeneous background have been a problem because of the inherent difficulties of balancing the gain in all of the amplifiers. Complementary metal oxide semiconductor sensors also exhibit relatively high noise associated with the requisite high-speed switching. Both of these deficiencies are being addressed, and sensor performance is nearing that required for scientific imaging.

Ratio imaging: practical considerations for measuring intracellular Ca2+ and pH in living cells.

This chapter discusses the use of ratiometric fluorescent probes for measuring intracellular pH (pHi) and Cai(2+) concentration at the single cell level. The development of sensitive and stable probes for monitoring pHi and Cai(2+) in living cells has provided the scientists with invaluable tools for studying a multitude of cellular processes. These probes afford a noninvasive and semiquantitative assessment of pHi and Cai(2+), eliminating the need to impale cells with microelectrodes. The development and availability of membrane permeant Cai(2+)- and pH-specific fluorescent probes coupled to major advances in the technology and design of low-light-level charge-coupled devices geared toward biological applications, and improved microscope optics, have made it possible to visualize a two-dimensional fluorescence signal that is related to Cai(2+) and pHi. The chapter describes the basis for using dual excitation ratio imaging and tries to provide a framework for understanding and developing the technique for investigating the roles of Cai(2+) and pHi in cellular processes. The technique of quantitative ratio imaging for the measurement of pHi and Cai(2+) has revolutionized the field of cell physiology. Using the proper equipment and choosing the right dyes for the experimental needs should provide reliable and reproducible results. More importantly, the amount of data produced from each experiment, when analyzing pHi and Cai(2+) on an individual cell basis, yields valuable information on the heterogeneity of cellular responses.

SU-E-J-164: Verification of Commercial Respiratory Tracking System Using Scintillation Screen.

PURPOSE: The accuracy of the tracking system is critical for the result of four-dimensional radiation therapy. The objective of this study is to propose the method of verifying the accuracy of respiratory tracking system. METHODS: The scintillation screen and the light marker between the transparent acrylic plates were designed to move according to the prerecorded respiratory organ motion of volunteers. A vertical circle photon beam with 3 cm diameters from the cyberknife unit was planned to track the motion of the scintillation screen with the plates. In dark room, the CCD camera outside of the phantom captured the scintillation from the screen and the light marker in 30 frames per second when the photon beam was incident. The pictures were captured by the CCD camera were analyzed frame by frame, and the discrepancy between the scintillating circle on the scintillation screen and the light marker depending on the time was measured. The discrepancy of the motions of the delivered photon beam and the light marker was analyzed. RESULTS: In the preliminary study, the maximum discrepancy was measured less than 1.5 mm in normal breathing pattern as the manufacturer specified it. CONCLUSIONS: As the speed of the motion was increased, the discrepancy between the position of the beam and internal marker increased. However, the error was clinically acceptable. The further study will be performed for the irregular respiratory motion patterns. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (20110004848).

SU-E-T-95: Investigation of 3D Dosimetry for an Anthropomorphic Spine Phantom.

PURPOSE: To evaluate 3D dosimetry for a spinal cord treatment plan delivery using the Radiological Physics Center's (RPC) anthropomorphic spine phantom. METHODS: The RPC's spine phantom currently uses radiochromic film and thermoluminescent dosimeters (TLD) to evaluate spinal metastases treatments. A second dosimetry insert for the phantom was created to hold a PRESAGE® 3D dosimeter which matched the location of the TLD and film in the original insert. The phantom was CT imaged with each insert and an IMRT treatment plan was developed. The IMRT plan was delivered to the phantom twice; once with each insert. The film and PRESAGE® were scanned on a CCD microdensitometer and optical-CT system, reconstructed to a 2 mm slice width, respectively. The measured dose distributions were compared to the treatment plan calculated dose distribution using RPC in-house developed software or the Computational Environment for Radiotherapy Research (CERR). Film and PRESAGE® dose profiles were taken across several planes and compared for agreement. The distance to agreement (DTA) between the measured data and treatment plan, within the high dose gradient region, was quantified. RESULTS: The PRESAGE® and plan dose profiles agreed to within 2and 1 mm in the AP and SI directions, respectively. The film and plan also agreed to within 2 mm across all profiles. CONCLUSIONS: The PRESAGE® 3D dosimeter, based on these preliminary data, shows potential as a dosimeter for the RPC's phantom irradiation studies. Future work will add markers to the PRESAGE® insert to allow for a reproducible registration in CERR and a an optical-CT system, reconstructed to a 2 mm slice width dose calibration protocol will be created. CA 100835.

SU-E-T-277: Hypothesis and Design of an Integrated X-Ray/Bioluminescent Imaging (BLI) and Tomography (BLT) System for the Study of Radiation and Treatment in Small Animals.

PURPOSE: Design and construct an integrated x-ray/bioluminescent tomography (BLT) system (with BLT being our initial focus) that can function as a standalone research apparatus and also on-board the SARRP to guide focal irradiation. In addition, it is aimed to enhance the BLT of the system to improve target localization by incorporating multi-projection, multi-spectral BL images, as well as CT 'priors'. METHODS: The SARRP system integrates a portable robotic translational/rotational stages system and an x-ray source which in the new system development the x-ray source is replaced with the PXS10-65 W model rated at maximum 130 kV having a variable small focal. A high performance, low noise, CCD camera mounted on a light-tight housing along is used for the aim of the BL imaging and tomography. In the new setup of the BLI system, the camera-filter-mirror assembly is attached to a motorized gantry to acquire images in angles between to while the position of the camera does not block the path of the x- ray beam. Innovatively, a 3-mirror arrangement is implemented to eliminate the need to rotate the CCD camera for capturing images. Furthermore, the robotic stage can be vertically adjusted to allow BLI imaging of multiple animals. RESULTS: To validate the accuracy with the on-board x-ray and BL tomography can be used to localize a BL tumor target and the minimum beam expansion to ensure radiation coverage of the target. The validation will employ phantoms and immunohistochemistry analysis of radiation damage in irradiated BL tumor models in vivo. The proposed system is currently under development and envisioned to be calibrated and evaluated along with the stand-alone radiation system. CONCLUSIONS: The novelty of embedded BLI guidance system is to enable the unprecedented focal irradiation of the small volumes of tumors which are more realistic in human disease.

SU-E-I-99: An Ultra-High Resolution Small Field-Of-View Solid State X-Ray Imaging Detector Based on an Electron Multiplying CCD.

PURPOSE: To demonstrate the ultra-high resolution capability of a small field-of-view (FOV) solid state x-ray imaging detector based on an EMCCD sensor. METHODS: A micro-solid state x-ray image intensifier (micro-SSXII) was developed to serve as an ultra-high resolution region-of-interest (ROI) imaging detector. It is based on an 8 micron, 1004 by 1002 pixel electron multiplying CCD (EMCCD) optically coupled to a 100 micron thick CsI(Tl) phosphor through a fiber optic window resulting in a FOV of 8 mm. The modulation transfer function (MTF) of the micro-SSXII was measured by the slanted edge method. A cast of a rat kidney (made by mixing resin and iodine for contrast) and a mammography line pair test object were imaged at 50 kVp to demonstrate the detector's ultra-high resolution capability visually. RESULTS: The MTF was determined and was 5% at 20 cycles/mm. This is consistent with the clear visualization of the maximum 20 lp/mm group in the image of the mammography test object. Also, iodine bubbles with diameters as small as 25 microns, which are formed by the non-uniform mixing of the iodine in the resin cast, can be clearly identified in the rat kidney vessels. CONCLUSIONS: The ultra-high resolution capability (>20 lp/mm) but small FOV (8 mm) of the micro-SSXII in combination with a low-energy x-ray source may have application for investigations of vascular specimen details and other fine structures where optical or other surface imagers would be unsuited for evaluating features below the surface. Contact radiography with this imager combined with a large higher-load focal spot x-ray tube may be a promising substitute for magnification radiography which is limited by the use of specialized low output microfocus x-ray tubes and geometric un-sharpness for large magnifications. Supported in part by: NIH Grants R01-EB008425, R01-EB002873 and an equipment grant from Toshiba Medical Systems Corp.

SU-E-I-112: Pre-Clinical Imaging with an Ultra-High Resolution X-Ray Detector.

PURPOSE: To explore the possible applications for a newly developed ultra-high resolution, small field-of-view (FOV) micro-solid state x-ray image intensifier (micro-SSXII) detector. METHODS: The micro-SSXII is based on an 8 micron, 1004 by 1002 electron-multiplying CCD (EMCCD) optically coupled to a 100-micron thick CsI(Tl) phosphor through a fiber optic window resulting in a FOV of 8 mm with a resolution limit of more than 20 lp/mm. The system has the capability of providing real-time images at low exposures because of the high variable gain of the EMCCD. Several phantoms were prepared by filling catheter tubes of 470 micron internal diameter with separate mixtures of a casting resin with different ratios of three different contrast agents (Omnipaque 350, barium sulphate, tantalum powder). These were imaged with the micro-SSXII at 50 kVp to help select the best mixture for use in making a cast of a rat kidney whose vasculature would then be made radiopaque and visualized. RESULTS: The images of all phantoms showed clumping of these contrast agents within the resin resulting in a non-uniform mix. The image of the phantom filled with Omnipaque and resin in a 1:4 ratio showed the best mixture although large bubble formation of the iodine was observed. This combination was used to make a cast of a rat kidney vasculature and imaged with the micro-SSXII. Small iodine bubbles with diameters as small as 25 microns were clearly delineated in the rat kidney vessels confirming the sharp detail capability of the micro-SSXII. CONCLUSIONS: The micro-SSXII in combination with a soft x-ray spectrum can provide excellent images of small animal casts prepared with an appropriate radiopaque resin to study finer details of the vasculature. This new imager has the potential to be used for region-of-interest x-ray image guidance for interventional studies in small animals. Supported in part by: NIH Grants R01-EB008425, R01-EB002873 and an equipment grant from Toshiba Medical Systems Corp.

SU-E-T-168: Development of a Liquid Scintillation Detector for External Beam Dosimetry.

PURPOSE: The goal of this research was to design a liquid scintillation dosimeter that could be used forrelative dosimetry of linear accelerator fields. The project emphasized minimization of cost and ease of use. METHODS: The scintillator that was used in this research was BETAMAX- ES scintillation cocktail from MPBiomedical. This particular scintillator was selected due to its relatively high scintillation yield and lowcost. The entirety of the scintillator used the measurements was supplied free of cost. The housing for the liquid was constructed from PVC and is cylindrical with one tapered end. One fiber of the dual optical fibers transmits the generated photons to the CCD while the other fiber is used for Cerenkovsubtraction.The detector used comes from a Philips SPC880NC webcam. The plastic casing of the webcamwas removed so that only the printed circuit board, USB cable and lens eyepiece holder remained. Thesensor employed is the Sony ICX098QB CCD, which is 3.2mm by 2.4mm and each pixel is 5.6mm by 5.6mm. A small cylindrical insert was manufactured that was inserted into the lens eyepiece holder to get adequate mechanical coupling of the fibers to the CCD face. Images were acquired with a freeware image acquisition tool, SharpCap, and analyzed with theMatlab commercial math package from Mathworks. RESULTS: Measurements have been performed that show that the detector is able to accurately measuretissue maximum ratio and the relative dose factor. The detector was able to accurately measurephysical wedge factors and made good predictions of the modulation factor for a patient's 7-field IMRT plan. CONCLUSIONS: This work has shown that relative dosimetry can be performed using an inexpensive liquidscintillation detector. This could be expanded to include an array of liquid scintillator cells formeasurement of beam profiles and other more complex problems.

SU-E-T-161: SOBP Beam Analysis Using Light Output of Scintillation Plate Acquired by CCD Camera.

PURPOSE: To analyze Bragg-peak beams in SOBP (spread-out Bragg-peak) beam using CCD (charge-coupled device) camera - scintillation screen system. We separated each Bragg-peak beam using light output of high sensitivity scintillation material acquired by CCD camera and compared with Bragg-peak beams calculated by Monte Carlo simulation. METHODS: In this study, CCD camera - scintillation screen system was constructed with a high sensitivity scintillation plate (Gd2O2S:Tb) and a right-angled prismatic PMMA phantom, and a Marlin F-201B, EEE-1394 CCD camera. SOBP beam irradiated by the double scattering mode of a PROTEUS 235 proton therapy machine in NCC is 8 cm width, 13 g/cm2 range. The gain, dose rate and current of this beam is 50, 2 Gy/min and 70 nA, respectively. Also, we simulated the light output of scintillation plate for SOBP beam using Geant4 toolkit. RESULTS: We evaluated the light output of high sensitivity scintillation plate according to intergration time (0.1 - 1.0 sec). The images of CCD camera during the shortest intergration time (0.1 sec) were acquired automatically and randomly, respectively. Bragg-peak beams in SOBP beam were analyzed by the acquired images. Then, the SOBP beam used in this study was calculated by Geant4 toolkit and Bragg-peak beams in SOBP beam were obtained by ROOT program. The SOBP beam consists of 13 Bragg-peak beams. The results of experiment were compared with that of simulation. CONCLUSIONS: We analyzed Bragg-peak beams in SOBP beam using light output of scintillation plate acquired by CCD camera and compared with that of Geant4 simulation. We are going to study SOBP beam analysis using more effective the image acquisition technique.

WE-G-BRB-06: Real-Time Radiation Field Tracking Using Long Scintillating Fibers.

PURPOSE: To ensure the quality assurance of small field, dynamic radiotherapy, we present and validate a radiation tracking system based on long scintillating fibers that allows for the real-time measurement of the position and energetic fluence of a small incident radiation field. METHOD: We aligned 60 parallel scintillating fibers on a thin grooved acrylic slab with a 100-cm source-to-fibers distance. Both ends of each scintillating fiber were coupled to clear optical fibers to enable light collection by a single CCD camera using an f/0.95, 50 mm focal length lens. Using a small, static photon radiation field of 2×2 cm2 of a Varian Clinac iX, we changed the interaction position on the prototype using the linac treatment couch. The interaction position parallel and perpendicular to the scintillating fiber array were deduced using the optical attenuation of the scintillating fibers. The energetic fluence of the incident field was calculated from the fibers light fluxes, corrected for the position dependent optical attenuation and scintillation efficiency. RESULTS: Considering a treatment couch positioning error of ±0.5 mm, the system was able to measure the field position with a mean error of 0.1 mm perpendicular and 0.8 mm parallel to the scintillating fiber array. The maximum error measured using this setup was of 0.13 mm perpendicular and 3.2 mm parallel to the scintillating fiber array. The energetic fluence was determined with a mean error of 0.5% and a maximum error of 2.2%. CONCLUSIONS: This work demonstrates the capacity of a long scintillating fibers array to detect in real-time both the position and the energetic fluence of an incident small radiation field. Such methodology would allow for the real-time tracking of small field in both photon and particle radiation therapy.

Poster - Thurs Eve-37: Energy and irradiation modality independence of calibration coefficients for water equivalent plastic scintillation detectors in the megavoltage range.

PURPOSE: To demonstrate that the independence of the calibration coefficients of plastic scintillation detector (PSD) for both photon and electron beams in the megavoltage energy range. METHOD AND MATERIALS: The PSD consists in a small 1 mm diameter and 2 mm long plastic scintillating fiber made of a polystyrene core (BCF-12, Saint-Gobain, inc.). The scintillator was coupled to a 2 meters long non-scintillating plastic optical fiber and a color CCD camera (Apogee instruments inc.) was used as photodetector. The calibration coefficients of the PSD where extracted for 6 MV, 23 MV photon beams and 9,12,15 and 18 MeV electron beams using a Farmer ionization chamber (Exradin). Complete removal of the Cerenkov radiation produced in the optical fiber was performed with a chromatic discrimination technique using the blue and green channel of the CCD camera. All measurements were performed according to the recommendations of the AAPM TG-51 protocol for clinical dosimetry. RESULTS: The PSD exhibits a maximum deviation of less than 1.7 % (about the mean) of its calibration coefficients over the measured energy range for both irradiation modalities. CONCLUSION: The energy independence of the calibration coefficients for PSD was demonstrated experimentally for the first time for both photons and electrons. PSDs have the potential to simplify and improve accuracy of dose measurements in clinical situations where photons and electrons are both present in the beam such as electron contamination in photon beams or bremsstrahlung contaminated electron beams.

Sci-Thurs PM: Delivery-02: Improving image quality produced by CCD cameras exposed to stray radiation from a medical linac.

PURPOSE: Charge coupled devices (CCDs) are increasingly used in radiation therapy. CCDs are ideal for applications such as two-dimensional dosimetry of scintillator sheets or to read arrays of miniature scintillation detectors. However, CCDs are sensitive to stray radiation. Radiation-induced noise strongly alters images and limits their quantitative analysis. We have characterized radiation-induced noise and developed filtration algorithms to restore image quality. METHOD AND MATERIALS: Two models of CCD cameras were used for measurements in linac environments. Images were acquired with and without radiation. The structure of the transient noise was characterized. Then, four methods of noise filtration were compared: median filtering of a time series of images, uniform median filtering of single images, an adaptive filter with switching mechanism and a modified version of the adaptive filter. RESULTS: The intensity distribution of noisy pixels was similar in both cameras. However, the spatial distribution of the noise was different: the average noise cluster size was 1.2±0.6 and 3.2±2.7 pixels for each of the two cameras. The median of a time series of image resulted in the best filtration and minimal image distortion. For applications where time series is impractical, adaptive filtration must be used to reduce image distortion. CONCLUSION: We have characterized the transient noise produced in CCDs by scattered radiation from a linac and have developed an efficient filtration scheme to remove this noise and restore image quality. Use of our filtration scheme allows detailed quantitative analysis of an image even when subjected to scattered radiation.

Precise radiochromic film dosimetry using a flat-bed document scanner.

In this study, a measurement protocol is presented that improves the precision of dose measurements using a flat-bed document scanner in conjunction with two new GafChromic® film models, HS and Prototype A EBT exposed to 6MV photon beams. We established two sources of uncertainties in dose measurements, governed by measurement and calibration curve fit parameters contributions. We have quantitatively assessed the influence of different steps in the protocol on the overall dose measurement uncertainty. Applying the protocol described in this paper on the Agfa Arcus II flat-bed document scanner, the overall one-sigma dose measurement uncertainty for an uniform field amounts to 2% or less for doses above around 0.4Gy in the case of the EBT (Prototype A), and for doses above 5Gy in the case of the HS model GafChromic® film using a region of interest 2×2mm2 in size.