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Published in Harald Paganetti, Proton Therapy Physics, 2018
In fact, the first implementation of a scanning beam was demonstrated in Japan using a novel system, including a range modulator wheel to modulate the beam range while scanning the beam transversely with magnetic dipoles [1]. As implied earlier, the beam size used in scanning can be varied. An unmodified beam (nonscattered or tightly focused) beam is sometimes called a “Pencil Beam”, although sometimes this term is used for a beam that has a dimension on the order of a few millimeters. It is possible to obtain a raw, unmodified (unscattered and uncollimated) beam which is on the order of several millimeters or even a centimeter, in which case, one can consider using the term “crayon beam,” owing to the larger size. In any case, it is more important to define the terms and understand the regime being considered than to rely on unclear acronyms. The longest (period of time) implementations of the scanning modality have been ongoing at research institutions such as the Paul Scherrer Institute (PSI) [2] and until it closed for clinical application, at the Gesellschaft fur Schwerionenforschung (GSI) [3]. Implementation outside the research environment began with commercial and academic hospital collaborations at MD Anderson and Massachusetts General Hospital (MGH) in 2008. Currently, many particle therapy facilities are using beam scanning as the primary beam delivery modality.
X-Ray Diffraction Tomography: Methods and Systems
Published in Joel Greenberg, Krzysztof Iniewski, X-Ray Diffraction Imaging, 2018
The use of polycapillary collimators would directly localize sources of scatter signals, unfortunately, at the expense of the collection efficiency. Also, due to the small scatter angle θ, the resolution along the beam illumination direction is lower than that along the perpendicular direction. By rotating the sample in the illumination plane and performing reconstruction similar to conventional CT, an improved resolution can be achieved along the illumination direction. Similar to the first-generation CT, pencil beam angular dispersive XDT uses a pencil beam to probe the sample, and a one-dimensional or two-dimensional array collects the diffracted photons. The major advantage of using pencil beam is that the collimation can be completely eliminated, making the highest collection efficiency possible. The pencil beam setup is ideal for observing samples with small scatter cross section. To achieve the resolution similar to the detector pixel size, the pencil beam has to have a diameter on the order of 0.1 ~ 1 mm, which would greatly reduce the efficiency of the source [22,23].
MicroCT Systems and Their Components
Published in Stuart R. Stock, MicroComputed Tomography, 2019
In the first-generation or pencil beam systems (Fig. 4.1a), a pinhole collimator C and a point-like source P produce a narrow, pencil-like beam across which the object O is scanned along x1; the successive measurements comprise a view (projection) of that physical slice of the specimen; successive views are obtained by rotation about x2. Only a simple zero-dimensional x-ray detector D is required, perhaps with some scatter shielding S. Energy-sensitive detectors are readily available and, if used instead of gas proportional or scintillation detectors, allow reconstruction with very accurate values of linear attenuation coefficients. Successive views are obtained by rotating the sample and repeating the translation. Obtaining volumetric data (i.e., a set of adjacent slices) borders on infeasible because of the long scan times required, but this is balanced by the inherent simplicity and flexibility of such apparatus and by a relatively greater immunity to degradation of contrast due to scatter. Pencil beam microCT continued to be used with laboratory x-ray sources through the 1990s (Elliott and Dover 1982, 1984, 1985, Borodin, Dementyev et al. 1986, Bowen, Elliott et al. 1986, Stock, Guvenilir et al. 1989, Breunig, Elliott et al. 1990, 1992, Breunig, Stock et al. 1993, Elliott, Anderson et al. 1994a, 1994b, Stock, Dollar et al. 1994, Mummery, Derby et al. 1995, Davis and Wong 1996), but, except for x-ray fluorescence tomography and for x-ray scattering tomography, it is now rare to find studies done using first-generation instruments. Very high spatial resolution has been achieved in small samples using synchrotron radiation (Spanne and Rivers 1987, Connor, Webb et al. 1990, Ferrero, Sommer et al. 1993).
Autonomous underwater vehicles - challenging developments and technological maturity towards strategic swarm robotics systems
Published in Marine Georesources & Geotechnology, 2019
N. Vedachalam, R. Ramesh, V. Bala Naga Jyothi, V. Doss Prakash, G. A. Ramadass
The Polar Regions cover about 12% of the Earth’s surface. The seasonally changing Polar ice cover modulates the heat and momentum between the high-latitude Oceans and the atmosphere, and the ice melt determines the upper ocean fresh water budget which is a crucial driver for the global ocean circulation. Coupling between the sea ice, ocean circulation and biogeochemical cycles results in the positive feedbacks that drive the climate change. Hence, scientific investigations in the challenging Polar Regions covered by ice almost throughout the year provide answers to vital questions on climate change, ecosystem responses, strengthening the predictive models for environmental management and to enact appropriate policy reforms. Understanding the strategic importance, funded by the Office of the Naval Research and developed by the University of Washington, the first under ice AUV unmanned arctic research submersible weighing about 400 kg and equipped with pencil beam upward-looking sonar was deployed through an ice hole near ice island T2 in the Beaufort Sea in 1972 for carrying out under-ice elevation mapping (Bellingham et al. 1995). Subsequently a number of specialized underwater vehicles are developed for the demanding Polar applications (Figure 1) making the previously inaccessible areas open to the scientific investigations.
Sparse non-convex Lp regularization for cone-beam X-ray luminescence computed tomography
Published in Journal of Modern Optics, 2018
Haibo Zhang, Guohua Geng, Shunli Zhang, Kang Li, Cheng Liu, Yuqing Hou, Xiaowei He
XLCT imaging can be achieved by narrow-beam XLCT, pencil-beam XLCT (PB-XLCT) (10) or cone-beam XLCT (CB-XLCT) (12). Similar to first-generation X-ray attenuation CT scanning strategy, Xing et al. first proposed the XLCT imaging modality with a narrow-beam X-ray (3). Then, Li et al. (13) used a collimated pencil-beam X-ray based on selective excitation scheme to image deep targets with good spatial resolution. However, long data acquisition time (typically, s) of PB-XLCT limits its application in drug processes and clinical experiments (14). In order to improve the scanning speed and fully utilize the X-ray dose, Tian et al. first designed a CB-XLCT system which can dramatically reduce the imaging time (134 s) (12). Then, Chen et al. (10) proposed a hybrid cone beam XLT/XCT system to accomplish quantitative imaging. With the development of X-ray-excitable nanophosphors (15–17), CB-XLCT extended the application of XLCT to the study of metabolic processes of nanophosphors-based drugs in small animals in vivo.
Feasibility of a New Moving Collimator for Industrial Backscatter Imaging
Published in Research in Nondestructive Evaluation, 2018
Ahmed Balamesh, Mohammad Salloum, Samir Abdul-Majid
Several other techniques that use lightweight X-ray machines have been described. They vary by collimation, scanning, and detection instruments [25,26]. These include radiography by selective detection (RSD), lateral migration radiography (LMR), and computed image backscatter radiography (CIBR). CIBR, as described by Meng [26], uses a fan beam X-ray source instead of a pencil beam, and rotational instead of two-dimensional scanning. Images are generated by using image reconstruction methods designed for computed tomography. These systems have different sizes, weights, image acquisition times, and electronics. Applications of the prototypes for field NDT work need to be proven. The digital array used with these techniques improved resolution and shortened exposure time [27,28]. It has been shown [29] that in backscatter counting, the rise time of the pulse from light materials is slower than that from heavy materials, and it has been suggested that the difference in time behavior can be used as a complementary analysis tool in addition to the pulse height discrimination method.