Conventional Detector Arrays Research Articles

Numerical Studies on Primary Ionization in TPC

Identification followed by directionality measurement using reconstruction of tracks is very crucial for studying the reaction vertex kinematics. In the field of low-energy nuclear physics, Active-Target Time Projection Chambers (AT-TPCs) can be used to study the nuclear reaction kinematics through tracking of the reaction products which is important for cross-section measurement. Ions produced in primary ionization by any charged particle along their track in the active gas volume of TPC can be utilized for track reconstruction with position-sensitive electron collection system placed inside an electric field. The TPC gas volume acts as the tracker of the reaction products and the target for the reaction with the incoming projectile simultaneously which is advantageous to conventional detector arrays. In this context, the design of the electric field in the drift volume of the TPC is an important criterion for precise tracking as the tracking capability of the TPC is strongly governed by the homogeneity of the electric field. Due to the lesser mobility of positive ions produced in primary ionization, their accumulation in the drift volume can distort the local electric field. In low-energy nuclear physics, this effect may be substantial due to the significant amount of ionization produced by the low-energy projectile and reaction products. Here we report the spatial information of primary space charges produced by cosmic muon and alpha particle obtained with geant4 [1] and Heed [2] simulation packages. We have used photo absorption and ionization physics lists in geant4 for the simulation and compared the results with that of the Heed. The simulation results for the change in pressure of gas volume will be reported. These results can be used for finding the distortion of the electric field due to the space charge in the drift region of the TPC which can be helpful for designing an AT-TPC for low-energy nuclear reaction experiments.

Transit and non-transit 3D EPID dosimetry versus detector arrays for patient specific QA.

PurposeDespite their availability and simplicity of use, Electronic Portal Imaging Devices (EPIDs) have not yet replaced detector arrays for patient specific QA in 3D. The purpose of this study is to perform a large scale dosimetric evaluation of transit and non‐transit EPID dosimetry against absolute dose measurements in 3D.MethodsAfter evaluating basic dosimetric characteristics of the EPID and two detector arrays (Octavius 1500 and Octavius 1000SRS), 3D dose distributions for 68 VMAT arcs, and 10 IMRT plans were reconstructed within the same phantom geometry using transit EPID dosimetry, non‐transit EPID dosimetry, and the Octavius 4D system. The reconstructed 3D dose distributions were directly compared by γ‐analysis (2L2 = 2% local/2 mm and 3G2 = 3% global/2 mm, 50% isodose) and by the percentage difference in median dose to the high dose volume (%∆HDVD 50).ResultsRegarding dose rate dependency, dose linearity, and field size dependence, the agreement between EPID dosimetry and the two detector arrays was found to be within 1.0%. In the 2L2 γ‐comparison with Octavius 4D dose distributions, the average γ‐pass rate value was 92.2 ± 5.2%(1SD) and 94.1 ± 4.3%(1SD) for transit and non‐transit EPID dosimetry, respectively. 3G2 γ‐pass rate values were higher than 95% in 150/156 cases. %∆HDVD 50 values were within 2% in 134/156 cases and within 3% in 155/156 cases. With regard to the clinical classification of alerts, 97.5% of the treatments were equally classified by EPID dosimetry and Octavius 4D.ConclusionTransit and non‐transit EPID dosimetry are equivalent in dosimetric terms to conventional detector arrays for patient specific QA. Non‐transit 3D EPID dosimetry can be readily used for pre‐treatment patient specific QA of IMRT and VMAT, eliminating the need of phantom positioning.

Imaging using hyperuniform sampling with a single-pixel camera.

Digital cameras use detector arrays with regular geometry for optical sampling. Though regular arrangement was demonstrated to be optimal for two-dimensional sampling, it causes aliasing at high frequencies exceeding its Nyquist limit. Here, we proposed a randomization procedure to generate 2D hyperuniform patterns that can be used to suppress aliasing in image retrieval. Experiments are performed using a single-pixel camera, where the sampling patterns do not necessarily follow a fixed Cartesian geometry. Results demonstrate that the images reconstructed by hyperuniform patterns have a lower root mean squared error and exhibit less moiré fringes at high frequencies than the images reconstructed by regular square patterns do. Furthermore, the same conclusion can be applied to the production of conventional detector arrays, where manufacturing imperfection could be utilized to suppress frequency aliasing in image retrieval.

Three‐dimensional optoacoustic tomography using a conventional ultrasound linear detector array: Whole‐body tomographic system for small animals

Optoacoustic imaging relies on the detection of ultrasonic waves induced by laser pulse excitations to map optical absorption in biological tissue. A tomographic geometry employing a conventional ultrasound linear detector array for volumetric optoacoustic imaging is reported. The geometry is based on a translate-rotate scanning motion of the detector array, and capitalizes on the geometrical characteristics of the transducer assembly to provide a large solid angular detection aperture. A system for three-dimensional whole-body optoacoustic tomography of small animals is implemented. The detection geometry was tested using a 128-element linear array (5.0∕7.0 MHz, Acuson L7, Siemens), moved by steps with a rotation∕translation stage assembly. Translation and rotation range of 13.5 mm and 180°, respectively, were implemented. Optoacoustic emissions were induced in tissue-mimicking phantoms and ex vivo mice using a pulsed laser operating in the near-IR spectral range at 760 nm. Volumetric images were formed using a filtered backprojection algorithm. The resolution of the optoacoustic tomography system was measured to be better than 130 μm in-plane and 330 μm in elevation (full width half maximum), and to be homogenous along a 15 mm diameter cross section due to the translate-rotate scanning geometry. Whole-body volumetric optoacoustic images of mice were performed ex vivo, and imaged organs and blood vessels through the intact abdominal and head regions were correlated to the mouse anatomy. Overall, the feasibility of three-dimensional and high-resolution whole-body optoacoustic imaging of small animal using a conventional linear array was demonstrated. Furthermore, the scanning geometry may be used for other linear arrays and is therefore expected to be of great interest for optoacoustic tomography at macroscopic and mesoscopic scale. Specifically, conventional detector arrays with higher central frequencies may be investigated.

New developments in particle characterization by laser diffraction: size and shape

Abstract Laser diffraction has become a popular technique in many fields for measuring particle size distributions (PSDs). It is not only one of the standard techniques for laboratory measurements but is also gaining importance for on-line process monitoring and process control. This article reports some developments of this technique while recognizing the potential that still exists. In this report both particle size and shape are taken into account. For optimum results, both effective sensing and analysis of the diffraction pattern are required. This is the goal of our present study with a special interest in on-line application. In this paper, a statistical approach — principal component analysis (PCA) — to the scattered light signals from a conventional detector array is shown to improve the sensitivity to a few large particles relative to the main size distribution. For determining particle shape, a wedge-type photo-detector for sensing the azimuthal light intensity has been applied together with the procedures of cross-correlation, sweep selection for single particle presence and Fourier analysis. Finally, a novel light scattering sensor is presented, which enables the measurement of both size and shape and which offers even more promising applications for on-line process control.