Flat-panel System Research Articles

Edge Response and Defect Detectability in Flat Panel Digital Radiography

Defect detectability studies are used in nondestructive testing to ascertain the reliability of the method of inspection. In digital radiography, with the growing prevalence of automation of quality control processes by image processing and machine learning, a threshold detection criterion based on quantifiable data from the digital radiograph could be explored. The use of the parameter contrast-to-noise ratio (CNR) of defect signal as a probability of detection (POD) threshold criterion is explored in this paper. A stainless steel block containing artificial defects of known dimensions and location is radiographed by a flat panel detector, and an empirical POD curve is constructed. Before the POD study, the edge response of the flat panel system is studied to ensure noninterference of adjacent defect signals, gain insights about the lateral spread of the defect signal, and provide information to choose the region of interest for CNR calculation. The effect of noise on the POD using CNR as the threshold criterion is also included in the present study. The use of CNR-based POD models for digital radiography to aid the comparison and development of automatic defect detection models is also discussed.

Parametric Analysis of Flat Slab with Shear Wall Lateral Resisting System Subjected to Dynamic Loading

Abstract: In the present project 20 storey structure is modelled using ETABS and loadings are considered as per IS codes. The models were analysed for both static and dynamic time history analysis the results are extracted, graphs are plotted. Models were compared and conclusions are drawn. The conclusions drawn from the analysis are, The Static analysis and dynamic analysis are having different values and time history analysis seems to be more accurate due to consideration of modal analysis and sitespecific analysis. The displacement is the main parameter in terms of serviceability criteria, the time history analysis shows lesser values than static analysis. It indicates that the static analysis may be on higher side for high rise structures. The comparatively huge displacement in case of Model M02 for both static and dynamic analysis proves the flat slab structure without drop panel and shear wall is not acceptable for lateral loading. From the overall analysis, it is found that the Column beam system with shear wall is best system to adopt, however in case of project demand, it is better to adopt flat slab drop panel system with shear wall located at centre as preference. In case of difficulty of shear wall at centre, the shear wall at corners can be adopted.

COMPARISON OF PHOTON-COUNTING AND FLAT-PANEL DIGITAL MAMMMOGRAPHY FOR THE PURPOSE OF 3D IMAGING USING A NOVEL IMAGE PROCESSING METHOD

The purpose of the present work was to compare the quality of low-dose projections from a photon-counting with a flat-panel system, and to evaluate a novel image processing method. Images were acquired of phantoms in both systems at average glandular doses ranging from ~ 0.15 to 1.4mGy. Automated detection of low-contrast features and modulation transfer functions were evaluated in phantom images. The novel image processing method was compared with standard processing in a series of clinical cases. At low-doses (~0.15) the photon-counting system out-performed the flat-panel system with a much higher detectability of low-contrast features. The novel algorithm was superior to both manufacturers' processing in terms of conspicuity of soft-tissue lesions (p>0.05), whereas it was not significantly different in calcification conspicuity. Photon-counting should allow more low-dose projections to be acquired at the same total dose. The novel image enhancer can help to further increase the image quality.

Nanoparticles: Untying the Gordian Knot in Conventional Computed Tomography Imaging

X-ray computed tomography (CT) imaging plays an essential role in disease diagnosis due to its noninvasive, painless mode and superior penetration depth. However, the resolution of the soft tissue ...

Techno-economics of algae production in the Arabian Peninsula

The Arabian Peninsula’s advantageous climate, availability of non-arable land, access to seawater and CO2-rich flue gas, make it an attractive location for microalgae biomass production. Despite these promising aspects, the region has seen very few studies into the commercial feasibility of algae-based value chains. This work aims to address this gap through a techno-economic feasibility study of algae biomass production costs, comparing different photobioreactor types, locations, and production scales. Flat panel and raceway pond cultivation systems were found to be the most economically attractive cultivation systems, with biomass production costs as low as 2.9 €·kg−1. Potential cost reductions of up to 42.5% and 25% could be accomplished with improvements in photosynthetic efficiencies and increased culture temperatures, respectively. As of such, efforts to source local thermo- and photo- tolerant strains could be the key to unlock the potential of the region for algae commercialization, linking into food, feed and nutraceutical industries.

Using seawater-based Na2CO3 medium for scrubbing the CO2 released from Bio-CNG plant for enhanced biomass production of Pseudanabaena limnetica

The concentration of CO2, one of the most important greenhouse gases (GHG), has reached to 409.8 ± 0.1 ppm in 2019. Although there are many carbon capture and storage (CCS) methods, they are very costly and their long term use raises concern about environmental safety. Alternatively, bio-sequestration of CO2 using microalgal cell factories has emerged as a promising way of recycling CO2 into biomass via photosynthesis. In the present study, Indigenous algal strain Pseudanabaena limnetica was cultivated in pneumatically agitated 60-L flat-panel photobioreactor system. The gas was released from Bio-CNG plant as by-product into Na2CO3-rich medium and cultivated in semicontinuous mode of operation. It was observed that when CO2 was sparged in seawater-based 0.02 M Na2CO3 solution, maximum CO2 was dissolved in the system and was used for algal cultivation. Control system produced 0.64 ± 0.035 g/L of biomass at the end of 15 days, whereas CO2 sparged Na2CO3 medium produced 0.81 ± 0.046 g/L of biomass. When CO2 from Bio-CNG station was fed, it resulted in biomass production of 1.62 ± 0.070 g/L at the end of 18 days compared to 1.46 ± 0.066 g/L of biomass produced in control system which was not fed with gas released from Bio-CNG plant as by-product. Thus, feeding CO2 directly into Na2CO3 medium and operating the system semicontinuously would be efficient for scrubbing CO2 from commercial Bio-CNG plant. This study proves that feeding CO2 gas from Bio-CNG plant into Na2CO3-rich alkaline system can be used to feed algae for enhanced biomass production.

Fluid structure interaction based structure stress and modal analysis of a flat type solar panel supporting system

Solar panel supporting systems are often affected by strong wind loads, especially in typhoon-intensive areas such as Southeast Asia. This paper focuses on the study of flat-panel solar energy system. The numerical model of solar panel supporting system has been built by using the fluid flow control equations. Firstly, the numerical simulation of aerodynamic characteristics of the solar panel supporting system are conducted, and then the pressure results gained from CFD are loaded and coupled to the front and back of the solar panels. Lastly, the stress, strain and the modal analysis results of the support system under four different directional wind loads are achieved. The conclusions include: (1) under the condition of same wind speed, the wind pressure and distribution of the solar panel are different with different wind directions, and the wind load perpendicular to the solar panel has the greatest influence on the solar supporting system. (2)The modal frequency of flat panel solar supporting system is little affected by wind directions and average wind pressure. In the structure design, low order vibration should be considered mainly in the supporting part of the system, while the high order vibration should be generally considered in vibrating risk of solar panel. (3)The first six modal frequencies coupled with fluid-structure interaction of the flat panel solar supporting system are all slightly lower than the free modal frequencies.

EXPOSURE DOSE INDEX BASED ON NOISE FACTOR ANALYSIS IN DIGITAL MAMMOGRAPHY: VERIFICATION USING DIRECT-TYPE FLAT-PANEL DETECTOR SYSTEM.

In this study, the development of a reasonable index of optimized exposure dose is attempted. Using a direct-type flat-panel system, noise factors contained in the image are analyzed based on the relative standard deviation method, and it is verified that the proposed index conforms with the appropriate standards regarding minimum exposure dose. The findings indicate that Poisson noise is dominant in the general clinical dose range; this noise fraction formed 90% of the total noise in the system considered in this study. Considering the results of previous surveys, it is estimated that the point at which the content rate of the Poisson noise starts to decrease can be considered as the lower limit, below which the dose cannot be reduced further without compromising on image quality. As the 'index' obtained by this method can be easily measured, it is useful as a quantitative indicator for dose determination and optimization.

Estimation of radiation exposure of children undergoing superselective intra-arterial chemotherapy for retinoblastoma treatment: assessment of local diagnostic reference levels as a function of age, sex, and interventional success

PurposeThis study aims to determine local diagnostic reference levels (LDRLs) of intra-arterial chemotherapy (IAC) procedures of pediatric patients with retinoblastoma (RB) to provide data for establishing diagnostic reference levels (DRLs) in pediatric interventional radiology (IR).MethodsIn a retrospective study design, LDRLs and achievable dose (AD) were assessed for children undergoing superselective IAC for RB treatment. All procedures were performed at the flat-panel angiography systems (I) ArtisQ biplane (Siemens Healthineers) and (II) Allura Xper (Philips Healthcare). Patients were differentiated according to age (A1: 1–3 months; A2: 4–12 months; A3: 13–72 months; A4: 73 months–10 years; A5: > 10 years), sex, conducted or not-conducted chemotherapy.Results248 neurointerventional procedures of 130 pediatric patients (median age 14.5 months, range 5–127 months) with RB (68 unilateral, 62 bilateral) could be included between January 2010 and March 2020. The following diagnostic reference values, AD, and mean values could be determined: (A2) DRL 3.9 Gy cm2, AD 2.9 Gy cm2, mean 3.5 Gy cm2; (A3) DRL 7.0 Gy cm2, AD 4.3 Gy cm2, mean 6.0 Gy cm2; (A4) DRL 14.5 Gy cm2, AD 10.7 Gy cm2, mean 10.8 Gy cm2; (A5) AD 8.8 Gy cm2, mean 8.8 Gy cm2. Kruskal-Wallis-test confirmed a significant dose difference between the examined age groups (A2–A5) (p < 0.001). There was no statistical difference considering sex (p = 0.076) and conducted or not-conducted chemotherapy (p = 0.627). A successful procedure was achieved in 207/248 cases.ConclusionWe report on radiation exposure during superselective IAC of a pediatric cohort at the German Retinoblastoma Referral Centre. Although an IAC formally represents a therapeutic procedure, our results confirm that radiation exposure lies within the exposure of a diagnostic interventional procedure. DRLs for superselective IAC are substantially lower compared with DRLs of more complex endovascular interventions.

Comparison between Visualization of Microcalcifications by Digital Breast Tomosynthesis and Full-Field Digital Mammography

Objective: To date, few studies have compared the diagnostic performance and visibility of microcalcifications obtained using digital breast tomosynthesis (DBT) with those obtained from full-field digital mammography (FFDM). The visualization and characterization of microcalcifications with DBT remain controversial. The purpose of this study was to compare the visibility of microcalcifications and determine whether DBT exhibits a diagnostic advantage for visualizing microcalcifications over FFDM. Methods: We retrospectively reviewed 120 cases including DBT and FFDM imaging (60 histologically verified as breast cancers and 60 as benign microcalcifications or normal). DBT images with a wide scan-angle of 50° and FFDM images were obtained using a flat-panel system (MAMMOMAT Inspiration, Siemens). Images were independently reviewed by four board-certified radiologists and evaluated for the presence of microcalcifications, probability of malignancy (BI-RADS classification), and visibility. Results: In predicting the malignancy of detected microcalcifications, no significant difference was found between readers’ areas under the receiver operating characteristic curve for DBT and FFDM (p = 0.068). The visibility scores of detected microcalcifications were 3.74 ± 1.06 for DBT and 3.46 ± 0.93 for FFDM, respectively. The visibility of microcalcifications when using DBT was found to be significantly superior to that of FFDM (p < 0.05). Conclusion: Our results suggest that the image quality of DBT with a wide scan-angle is comparable or superior to that obtained with FFDM in terms of both visibility and assessment of microcalcifications.

Optimisation of on-board imaging fluoroscopy

On-board imaging fluoroscopy is used for localisation of the target immediately prior to external beam radiotherapy. The feature is clinically used for lung stereotactic ablative radiotherapy involving a moving target and high dose per fraction. Use of fluoroscopy is clearly justified, allowing verification that the target is within the field over its range of motion, ensuring the tumour is not under-treated and there is not excessive dose to normal tissue. Commissioning the fluoroscopy features on Varian Clinacs and Varian Truebeams demonstrated that systems are not optimal at installation. The ability to adjust the automatic brightness control settings is not readily available and access required extensive discussions with the manufacturer. The TrueBeam linear accelerator had additional dose reduction features not available on the Clinac. Such features available in clinical mode included the ability to adjust pulse rate settings and add additional titanium filtration This paper will detail the potential for significant patient dose reduction (35 mGy/min to 16 mGy/min Clinac, 75 mGy/min to 8 mGy/min Truebeam) without a clinically significant reduction in image quality. The doses post optimisation are below what would be expected from an image intensifier and slightly higher than what would be typical for a modern flat-panel interventional system. The dose comparisons are made to interventional systems due to the lack of published data in radiotherapy systems. Historically the focus has been on the considerably higher radiotherapy dose, but recent developments and increased use of imaging in therapy has seen increased attention to imaging doses.

Pilot scale flat panel photobioreactor system for mass production of Ulva lactuca (Chlorophyta)

Conventional open-sea cultivation constrained by environmental factors is singly incompetent to sustain the rising seaweed demand. This necessitates a complementary strategy to reinforce the existing cultivation system and expand the global seaweed industry. Present study proposes cultivation of Ulva lactuca in temperature controlled flat panel photobioreactors under natural illumination. Adaptability of U. lactuca to the flat panel system is apparent through growth studies and photosynthetic performance (Fv/Fm) across individual panels. Evident effect of annual variation in irradiance on daily growth rates, biomass productivity and composition is portrayed. Significance of initial stocking density and harvesting frequency is highlighted. Poultry litter extract was used as an alternative N-source for sustainable cultivation. The maximum achievable productivity was 303gm−2d−1 (fresh weight) expanding to 910tonsha−1yr−1 including biomass composition consistent with the control media. The present pilot scale study delivers valuable information for commercial scale photobioreactors for seaweed cultivation.

Information Loss Via Visual Assessment of Radiologic Images Using Modified Version of the Low-Contrast Detailed Phantom at Direct DR System

IntroductionQuality in radiology images can be assessed by determining the levels of information retained or lost in an image. Information loss in images has been recently assessed via a method based on information theory and the employment of a contrast-detail (CD) phantom. In this study, the traditional CD phantom (air-Perspex) and a modified CD phantom were used. MethodsUsing the Agfa DX-D 600 digital flat panel system, six phantom radiographs were acquired at 70 kVp and 20 mAs. Three x-ray images were acquired for each phantom. ResultsOur results demonstrate that the material within the CD phantom influences total information loss (TIL) and image quality figure (IQF) measurements. The modified CD phantom provides a more realistic account of TIL and IQF for soft tissue radiology imaging. ConclusionIt is recommended that a low inherent subject contrast phantom, such as this modified CD phantom, be added to the image quality assessment processes of radiology departments. In addition, use of both IQF and TIL to assess image quality will provide radiology departments with greater evidence on which to base decisions.

Patient effective dose during pacemaker implantation at a flat panel and image intensifier angiography system

Introduction Pacemaker implantation is a minimally invasive technique performed under fluoroscopic guidance. Purpose This study aims to compare effective dose (ED) delivered to patients at pacemaker implantation procedures by two angiographic systems of different image capture technology; one with flat panel detector (FPD) and one with image intensifier (II). Materials and methods A retrospective analysis of 62 procedures performed at Attikon University Hospital of Athens has been conducted. Data concerning dose area product (DAP), fluoroscopy time and patient’s weight and height have been collected. The ED has been calculated, multiplying DAP with a conversion factor of 0.2 mSv/(Gy ∗ cm 2 ) and the results have been divided in categories accordingly to patients’ BMI and fluoroscopy time. Results ED, presented as median and range values, for normal, over weighted and obese patients that have been operated under a FPD X-ray system, in a fluoro time less than five minutes was 0.49 mSv (0.09–1.1 mSv), 0.67 mSv (0.4–1.2 mSv) and 1.18 mSv (1–1.3 mSv) respectively. The corresponding values for an II system were 0.50 mSv (0.5–0.8 mSv), 2.49 mSv (1.86–3.58 mSv) and 1.70 mSv (0.8–3.3 mSv). For fluoro time greater than five minutes in FPD imaging, ED for the three BMI categories was 1.57 mSv (0.7–3.7 mSv), 0.74 mSv (0.45–1.26 mSv) and 2.93 mSv (1.78–3.45 mSv), while for the II angiography system ED was 12.29 mSv (1.88–49.27 mSv), 28.36 mSv (6.27–15.43 mSv) and 35.27 mSv (5.84–158,73 mSv). Conclusion Obtained results indicate statistically significant higher radiation burden associated with II system compared to FPD system used for pacemaker’s implantations ( p Disclosure All authors confirm that none relationship may bias this presentation.

Patient radiation dose during atrial septal defect occluder

Introduction Atrial septal defect (ASD) is an abnormal opening in the wall between the two atrias of the heart. A catheter-based treatment in a heamodynamic room is a well established procedure. International literature has extremely limited data on related radiation dose levels. Purpose To determine radiation dose (RD) fluoroscopy time (FT) and Number of images (I) in ASD treatment in both paediatric and adult patients in a major cardiosurgery center in Greece. Materials and methods A sample of 161 patients were included in the study, divided in the following age categories: (1) 5–10 y, (2) 10–15 y, (3) 15–18;y and (4) >18 y. The X-ray machine used was a Siemens Artis Zee digital flat panel system. Various clinical (weight, body mass index, (BMI), etc.) and radiation related data (Kerma Area Product (KAP), fluoroscopy time (T) and number of images (F)) were recorded. Results Median W (kg), BMI (kg/m 2 ), KAP (Gycm 2 ), T (min) and F for the 4 weight categories were: (1) 25, 15.5, 5.8, 6.6 and 639, (2) 50, 21.5, 9.3, 4.6 and 409 (3) 58.5, 21.2, 11.6, 5.7 and 575 and finally (4) 58.0, 19.5, 5.8, 3.2 and 639. The correlation of various factors with KAP was investigated. Apart from fluoroscopy time there was no other factor that significantly correlated with radiation dose. Conclusion This study presents age-stratified radiation data for ASD occluder heart catheterizations. Fluoroscopy time or number of images are not adequate measures for monitoring radiation exposure. These values will be used as baseline for our future research on the subject.

A comprehensive model for quantum noise characterization in digital mammography

A version of cascaded systems analysis was developed specifically with the aim of studying quantum noise propagation in x-ray detectors. Signal and quantum noise propagation was then modelled in four types of x-ray detectors used for digital mammography: four flat panel systems, one computed radiography and one slot-scan silicon wafer based photon counting device. As required inputs to the model, the two dimensional (2D) modulation transfer function (MTF), noise power spectra (NPS) and detective quantum efficiency (DQE) were measured for six mammography systems that utilized these different detectors. A new method to reconstruct anisotropic 2D presampling MTF matrices from 1D radial MTFs measured along different angular directions across the detector is described; an image of a sharp, circular disc was used for this purpose. The effective pixel fill factor for the FP systems was determined from the axial 1D presampling MTFs measured with a square sharp edge along the two orthogonal directions of the pixel lattice. Expectation MTFs were then calculated by averaging the radial MTFs over all possible phases and the 2D EMTF formed with the same reconstruction technique used for the 2D presampling MTF. The quantum NPS was then established by noise decomposition from homogenous images acquired as a function of detector air kerma. This was further decomposed into the correlated and uncorrelated quantum components by fitting the radially averaged quantum NPS with the radially averaged EMTF2. This whole procedure allowed a detailed analysis of the influence of aliasing, signal and noise decorrelation, x-ray capture efficiency and global secondary gain on NPS and detector DQE. The influence of noise statistics, pixel fill factor and additional electronic and fixed pattern noises on the DQE was also studied. The 2D cascaded model and decompositions performed on the acquired images also enlightened the observed quantum NPS and DQE anisotropy.

Comparison of image quality and radiation dose between an image-intensifier system and a newer-generation flat-panel detector system — technical phantom measurements and evaluation of clinical imaging in children

Many image-intensifier fluoroscopy systems have been replaced by flat-panel detectors in recent years. To compare the level of contrast, image resolution and radiation dose between an image-intensifier and a newer-generation flat-panel detector system in a pediatric radiology unit. We compared two systems — a conventional image intensifier and a newer-generation flat-panel system. We measured image quality and radiation dose using a technical phantom. Additionally, we retrospectively compared age-matched fluoroscopic pediatric voiding cystourethrography (n = 15) and upper gastrointestinal investigations (n = 25). In phantom studies image contrast was equal while image resolution was higher and mean radiation dose lower using the flat-panel system (P < 0.0001). In pediatric investigations, mean dose area product was significantly reduced on the flat-panel system for upper gastrointestinal investigation (45 ± 38 μGy*m2 vs. 11 ± 9 μGy*m2; P < 0.0001) and for voiding cystourethrography (18 ± 20 μGy*m2 vs. 10 ± 12 μGy*m2; P = 0.04). The newer flat-panel system performs at lower dose levels with equal to better image quality and therefore seems to be the more suitable technique for pediatric fluoroscopy in comparison to image-intensifier systems.

A generalized reconstruction framework for unconventional PET systems.

Quantitative estimation of the radionuclide activity concentration in positron emission tomography (PET) requires precise modeling of PET physics. The authors are focused on designing unconventional PET geometries for specific applications. This work reports the creation of a generalized reconstruction framework, capable of reconstructing tomographic PET data for systems that use right cuboidal detector elements positioned at arbitrary geometry using a regular Cartesian grid of image voxels. The authors report on a variety of design choices and optimization for the creation of the generalized framework. The image reconstruction algorithm is maximum likelihood-expectation-maximization. System geometry can be specified using a simple script. Given the geometry, a symmetry seeking algorithm finds existing symmetry in the geometry with respect to the image grid to improve the memory usage/speed. Normalization is approached from a geometry independent perspective. The system matrix is computed using the Siddon's algorithm and subcrystal approach. The program is parallelized through open multiprocessing and message passing interface libraries. A wide variety of systems can be modeled using the framework. This is made possible by modeling the underlying physics and data correction, while generalizing the geometry dependent features. Application of the framework for three novel PET systems, each designed for a specific application, is presented to demonstrate the robustness of the framework in modeling PET systems of unconventional geometry. Three PET systems of unconventional geometry are studied. (1) Virtual-pinhole half-ring insert integrated into Biograph-40: although the insert device improves image quality over conventional whole-body scanner, the image quality varies depending on the position of the insert and the object. (2) Virtual-pinhole flat-panel insert integrated into Biograph-40: preliminary results from an investigation into a modular flat-panel insert are presented. (3) Plant PET system: a reconfigurable PET system for imaging plants, with resolution of greater than 3.3 mm, is shown. Using the automated symmetry seeking algorithm, the authors achieved a compression ratio of the storage and memory requirement by a factor of approximately 50 for the half-ring and flat-panel systems. For plant PET system, the compression ratio is approximately five. The ratio depends on the level of symmetry that exists in different geometries. This work brings the field closer to arbitrary geometry reconstruction. A generalized reconstruction framework can be used to validate multiple hypotheses and the effort required to investigate each system is reduced. Memory usage/speed can be improved with certain optimizations.

24. Contemporary Outcomes For Autogenous Infrainguinal Bypass In the Endovascular Era

Objective: To report our initial experience of using intraoperative C-arm Cone beam CT (DynaCT ) image fusion guidance along with steerable robotic endovascular catheter navigation to facilitate visceral vessel cannulation procedures. Methods: Between October 2012 and August 2014, 11 patients underwent endovascular procedures using DynaCT image fusion technique along with HansenMagellan vascular robotic catheter. All patients had pre-operative contrast enhanced multi-slice CT imaging (MSCT). For case planning, relevant landmarks and centerlines were electronically marked and stored. At the beginning of each procedure, a non-contrast DynaCT was acquired in the hybrid operating room equipped with a flat-panel robotic C-arm angiographic system. Pre-operative images were co-registered to intra-operative DynaCT images using bony structures. Stored landmarks were overlaid on 2D fluoroscopic images as virtual markers. Vascular access and the robotic catheter were setup and performed per standard. Vessel cannulation was attempted based on virtual markers using robotic catheter. The impact of these virtual markers from image fusion on vessel cannulation was evaluated retrospectively. Results: All 14 vessels were cannulated successfully in 11 patients’ attempted using image fusion guidance. Median vessel diameter at origin was 5.1 mm (2.3 to 13mm), while 10/14 vessels had either calcified/stenosed origin from parent vessel, accounting for the range of vessel diameters. 8/14 vessels (57.1%) were cannulated without any contrast injection. Median number of angiograms required before cannulation was 0 (0 2). On qualitative assessment, 11/12 vessels (91.7%) had grade1⁄41 accuracy (guide-wire inside virtual ostial marker). 11/11 vessels had grade1⁄41 accuracy (virtual centerlines that matched with the actual vessel trajectory during cannulation). Conclusion: Our initial experience with using DynaCT image fusion guidance along with steerable endovascular robotic navigation indicates that such strategies enhance intra-operative 2D fluoroscopy and could play a role in reducing contrast agent use therebymaximizing the versatility of endovascular robotic technology.

Parallelizing a Matched Pair of Ray-Tracing Projector and Backprojector for Iterative Cone-Beam CT Reconstruction

Iterative reconstruction methods in X-ray CT can provide better image quality than analytical methods but their applications in practice are still limited due to computationally expensive calculations of repeated projection and backprojection operations. In the past decade, GPU-accelerated methods have been successfully used to reduce the computation time for projection and backprojection. However, it has been of a difficult problem to overcome a trade-off between the accuracy of reconstructed images and the efficiency of parallel computations. For example, when the size of the voxel in the reconstructed volume is larger than that of the detector bin, the use of the conventional unmatched projector-backprojector pair can lower the accuracy of reconstructed images due to the error caused by the mismatch between the projector and backprojector. In this paper, we propose a new GPU-accelerated scheme for the most widely used ray-tracing method (RTM) to perform projection and backprojection operations. Unlike the previous works that accelerate the computation of backprojection by using approximations, our method does not use any approximations for parallelizing the projection and backprojection operations. Since our method is exact, the results are as accurate as those obtained from the nonaccelerated method. We apply our method to iterative reconstruction for dental cone-beam CT systems and test its performance using both the simulated data using a 3-D digital phantom and the real data acquired from an offset flat-panel X-ray CT system. Our experimental results show that, the proposed method achieves a substantially high acceleration rate while retaining the accuracy of the RTM for both projection and backprojection.