Number Of Angular Projections Research Articles

CERN breakthrough technologies for non-invasive, in vivo, image-guided diagnosis

CERN, the largest laboratory for particle physics worldwide is at the forefront of detector technology development for many different applications. Over recent decades, many important medical diagnostic and therapeutic techniques have been developed from CERN’s fundamental research results or from technological progresses in these areas. A short description of these technologies and their application to medicine will be given. Focus will be made on new, higher performance imaging tools with multimodal capabilities including PET. These tools introduce breakthrough technologies for novel endoscopic procedures in diagnostic and therapeutic endoscopy and in surgical oncology aiming at diagnosing more patients with earlier tumour stages and improving patient outcome and therapy, as well as reducing health costs. Technical objectives include: a very high sensitivity allowed by the endoscopic approach and the proximity of the target. A spatial resolution of 1 mm to delineate early tumours. A time resolution of 200 ps corresponding to a spatial resolution of 3 cm along the Line of Response (LOR) in a dual-head system, allowing a direct (and therefore fast) 3-dimensional reconstruction through a limited number of angular projections only, and an efficient rejection of background coming from outside of the few cubic centimetres region of interest (ROI). The presentation will also emphasize on the number of challenges that have been addressed, both technically and clinically, which have led to the development and introduction of cutting edge technologies in three technological areas: scintillator performances and production methods, light transport and photo-detectors.

A virtual trial framework for quantifying the detectability of masses in breast tomosynthesis projection data

Digital breast tomosynthesis (DBT) is a promising breast cancer screening tool that has already begun making inroads into clinical practice. However, there is ongoing debate over how to quantitatively evaluate and optimize these systems, because different definitions of image quality can lead to different optimal design strategies. Powerful and accurate tools are desired to extend our understanding of DBT system optimization and validate published design principles. The authors developed a virtual trial framework for task-specific DBT assessment that uses digital phantoms, open-source x-ray transport codes, and a projection-space, spatial-domain observer model for quantitative system evaluation. The authors considered evaluation of reconstruction algorithms as a separate problem and focused on the information content in the raw, unfiltered projection images. Specifically, the authors investigated the effects of scan angle and number of angular projections on detectability of a small (3 mm diameter) signal embedded in randomly-varying anatomical backgrounds. Detectability was measured by the area under the receiver-operating characteristic curve (AUC). Experiments were repeated for three test cases where the detectability-limiting factor was anatomical variability, quantum noise, or electronic noise. The authors also juxtaposed the virtual trial framework with other published studies to illustrate its advantages and disadvantages. The large number of variables in a virtual DBT study make it difficult to directly compare different authors' results, so each result must be interpreted within the context of the specific virtual trial framework. The following results apply to 25% density phantoms with 5.15 cm compressed thickness and 500 μm(3) voxels (larger 500 μm(2) detector pixels were used to avoid voxel-edge artifacts): 1. For raw, unfiltered projection images in the anatomical-variability-limited regime, AUC appeared to remain constant or increase slightly with scan angle. 2. In the same regime, when the authors fixed the scan angle, AUC increased asymptotically with the number of projections. The threshold number of projections for asymptotic AUC performance depended on the scan angle. In the quantum- and electronic-noise dominant regimes, AUC behaviors as a function of scan angle and number of projections sometimes differed from the anatomy-limited regime. For example, with a fixed scan angle, AUC generally decreased with the number of projections in the electronic-noise dominant regime. These results are intended to demonstrate the capabilities of the virtual trial framework, not to be used as optimization rules for DBT. The authors have demonstrated a novel simulation framework and tools for evaluating DBT systems in an objective, task-specific manner. This framework facilitates further investigation of image quality tradeoffs in DBT.

Optimized image acquisition for breast tomosynthesis in projection and reconstruction space

Breast tomosynthesis has been an exciting new development in the field of breast imaging. While the diagnostic improvement via tomosynthesis is notable, the full potential of tomosynthesis has not yet been realized. This may be attributed to the dependency of the diagnostic quality of tomosynthesis on multiple variables, each of which needs to be optimized. Those include dose, number of angular projections, and the total angular span of those projections. In this study, the authors investigated the effects of these acquisition parameters on the overall diagnostic image quality of breast tomosynthesis in both the projection and reconstruction space. Five mastectomy specimens were imaged using a prototype tomosynthesis system. 25 angular projections of each specimen were acquired at 6.2 times typical single-view clinical dose level. Images at lower dose levels were then simulated using a noise modification routine. Each projection image was supplemented with 84 simulated 3 mm 3D lesions embedded at the center of 84 nonoverlapping ROIs. The projection images were then reconstructed using a filtered backprojection algorithm at different combinations of acquisition parameters to investigate which of the many possible combinations maximizes the performance. Performance was evaluated in terms of a Laguerre-Gauss channelized Hotelling observer model-based measure of lesion detectability. The analysis was also performed without reconstruction by combining the model results from projection images using Bayesian decision fusion algorithm. The effect of acquisition parameters on projection images and reconstructed slices were then compared to derive an optimization rule for tomosynthesis. The results indicated that projection images yield comparable but higher performance than reconstructed images. Both modes, however, offered similar trends: Performance improved with an increase in the total acquisition dose level and the angular span. Using a constant dose level and angular span, the performance rolled off beyond a certain number of projections, indicating that simply increasing the number of projections in tomosynthesis may not necessarily improve its performance. The best performance for both projection images and tomosynthesis slices was obtained for 15-17 projections spanning an angular are of approximately 45 degrees--the maximum tested in our study, and for an acquisition dose equal to single-view mammography. The optimization framework developed in this framework is applicable to other reconstruction techniques and other multiprojection systems.

中性子ＣＴの改良研究

The images of neutron radiography (NRG) have been able to be digitally analyzed recently. Following it, neutron computed tomography (NCT) attracts people's attention of non-destructive testing field. In our laboratory, the study of NCT technology has been carried out for 5 years. We utilize NRG as a method to obtain projection data. One of the NRG's demerits is to take a long time for measuring film density, and to input it into a computer system. Then, by making use of the image input equipment, instead of micro-densitometer, the data proceeding time is amazingly shortened.This makes it possible to increase the number of projections remarkably. We made an experiment, in which the number of angular projections is 200 (0.9) degree interval, at Kyoto University Reactor (KUR). The quality of obtained CT images is sufficiently good. FWHM of the line spread function for air-stainless steel was 130μm. Resolution power was 400μm for both airstainless steel and aluminum-paraffin. By using image input equipment, it became easy to chase the 3-dimensional shape of an inspected object. We obtained 41 CT images for one object axially at interval of 120-240μm, attempted 3-dimensional reconstruction of the object. Comparing to the real object, the 3-dimensional reconstructed images were satisfactory on shape and dimension.

A non-linear truncation scheme for the Ornstein-Zernike equation for dipolar fluids

A non-linear truncation method is proposed to represent the solution of the Ornstein-Zernike equation for dipolar fluids in terms of a finite number of angular projections. This method, which becomes exact at low densities, can be applied to the Percus-Yevick and hypernetted chain closures, and has the potential to study angular projections beyond the usual three angular projections that arise in the mean spherical approximation. Some numerical results for the hypernetted chain closure for hard sphere dipolar fluids will be given.