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While an accurate image reconstruction of digital breast tomosynthesis (DBT) is fundamentally impossible due to its limited data, the DBT is increasingly used in clinics for its rich image information at a relatively low dose. One of the dominant image artifacts in DBT that hinders a faithful diagnosis is high-density object artifact in conjunction with a limited angle problem. In this paper, we developed a very efficient method for reconstructing DBT images with much reduced high-density object artifacts. The method is based on backprojection filtration reconstruction algorithm, voting strategy, and image blending. Data derivatives were backprojected with appropriate weights to reduce ripple artifacts by use of the voting strategy. We generated another differentiated backprojection volume, where the edges of high-density objects are replaced by the background. After Hilbert transform, we blended the two images to reduce undershoot artifacts. Physical phantoms were scanned and we compared conventional filtered backprojection, filtered backprojection with weighted backprojection, and our proposed method. Ripple artifacts were dramatically suppressed and undershoot artifacts were also greatly suppressed in the proposed method.

Purpose Scatter contamination constitutes a dominant source of degradation of image quality in cone-beam computed tomography (CBCT). We have recently developed an analytic image reconstruction method with a scatter correction capability from the partially blocked cone-beam data out of a single scan. Despite its easy implementation and its computational efficiency, the developed method may result in additional image artifacts for a large cone angle geometry due to data inconsistency. To improve the image quality at a large cone angle, we propose a weighted rebinned backprojection-filtration (wrBPF) algorithm in conjunction with a hybrid type scatter correction approach. Methods The proposed method uses a beam-blocker array that provides partial data for scatter correction and image reconstruction and that only blocks the beam within a limited cone angle. This design allows a chance to keep the image quality at larger cone angles by use of data redundancy since the projection data corresponding to larger cone angles are not blocked. However, the scatter correction would not be straightforward. In order to correct for the scatter in the projections at larger cone angles, we propose a novel scatter correction method combining a measurement-based and a convolution-based method. We first estimated the scatter signal using a measurement-based method in the partially beam-blocked regions, and then optimized the fitting parameters of a convolution-kernel that can be used for scatter correction in the projections at larger cone angles. For image reconstruction, we developed a wrBPF with butterfly filtering. We have conducted an experimental study to validate the proposed algorithm for image reconstruction and scatter correction. Results The experimental results revealed that the developed reconstruction method makes full use of the benefits of partial beam-blocking for scatter correction and image reconstruction and at the same time enhances image quality at larger cone angles by use of an optimized convolution-based scatter correction. Conclusions The proposed method that enjoys the advantages of both measurement-based and convolution-based methods for scatter correction has successfully demonstrated its capability of reconstructing accurate images out of a single scan in circular CBCT.

Dual-energy X-ray inspection systems are widely used today for it provides X-ray attenuation contrast of the imaged object and also its material information. Material decomposition capability allows a higher detection sensitivity of potential targets including purposely loaded impurities in agricultural product inspections and threats in security scans for example. Dual-energy X-ray transmission data can be transformed into two basis material thickness data, and its transformation accuracy heavily relies on a calibration of material decomposition process. The calibration process in general can be laborious and time consuming. Moreover, a conventional calibration method is often challenged by the nonuniform spectral characteristics of the X-ray beam in the entire field-of-view (FOV). In this work, we developed an efficient material decomposition calibration process for a linear accelerator (LINAC) based high-energy X-ray cargo inspection system. We also proposed a multi-spot calibration method to improve the decomposition performance throughout the entire FOV. Experimental validation of the proposed method has been demonstrated by use of a cargo inspection system that supports 6 MV and 9 MV dual-energy imaging.

Cone-beam computed tomography (CBCT) is gaining widespread use in various medical and industrial applications but suffers from substantially larger amount of scatter than that in the conventional diagnostic CT resulting in relatively poor image quality. Various methods that can reduce and/or correct for the scatter in the CBCT have therefore been developed. Scatter correction method that uses a beam-blocker has been considered a direct measurement-based approach providing accurate scatter estimation from the data in the shadows of the beam-blocker. To the best of our knowledge, there has been no record reporting the significance of the scatter from the beam-blocker itself in such correction methods. In this paper, we identified the scatter from the beam-blocker that is detected in the object-free projection data investigated its influence on the image accuracy of CBCT reconstructed images, and developed a scatter correction scheme that takes care of this scatter as well as the scatter from the scanned object.

Purpose: A beam-blocker composed of multiple strips is a useful gadget for scatter correction and/or for dose reduction in cone-beam CT (CBCT). However, the use of such a beam-blocker would yield cone-beam data that can be challenging for accurate image reconstruction from a single scan in the filtered-backprojection framework. The focus of the work was to develop an analytic image reconstruction method for CBCT that can be directly applied to partially blocked cone-beam data in conjunction with the scatter correction. Methods: The authors developed a rebinned backprojection-filteration (BPF) algorithm for reconstructing images from the partially blocked cone-beam data in a circular scan. The authors also proposed a beam-blocking geometry considering data redundancy such that an efficient scatter estimate can be acquired and sufficient data for BPF image reconstruction can be secured at the same time from a single scan without using any blocker motion. Additionally, scatter correction method and noise reduction scheme have been developed. The authors have performed both simulation and experimental studies to validate the rebinned BPF algorithm for image reconstruction from partially blocked cone-beam data. Quantitative evaluations of the reconstructed image quality were performed in the experimental studies. Results: The simulation study revealed that the developed reconstructionmore » algorithm successfully reconstructs the images from the partial cone-beam data. In the experimental study, the proposed method effectively corrected for the scatter in each projection and reconstructed scatter-corrected images from a single scan. Reduction of cupping artifacts and an enhancement of the image contrast have been demonstrated. The image contrast has increased by a factor of about 2, and the image accuracy in terms of root-mean-square-error with respect to the fan-beam CT image has increased by more than 30%. Conclusions: The authors have successfully demonstrated that the proposed scanning method and image reconstruction algorithm can effectively estimate the scatter in cone-beam projections and produce tomographic images of nearly scatter-free quality. The authors believe that the proposed method would provide a fast and efficient CBCT scanning option to various applications particularly including head-and-neck scan.« less

The image of the current non-destructive testing system using a high energy accelerator is limited to conventional two-dimensional metaphysical information. Requirements for the present manufacturing industry are growing rapidly and include quantitative measurements, high-density component model extraction, reverse process development and precision inspection to meet the needs for the verification of manufactured goods. Therefore, industrial three-dimensional high-penetration tomography has emerged as the most promising method. In this study, in order to evaluate the applicability of a MeV-level high-energy accelerator, we developed a three-dimensional tomography system using a 450 kV X-ray generator. Evaluation of the three-dimensional tomography image is based on measurements of the penetration and the image resolution for high-energy X-rays.

We conducted a feasibility study using a total-variation minimization algorithm for image reconstruction in prospectively gated micro computed tomography (micro-CT). The total-variation (TV) minimization algorithm exploits the sparseness of the image’s gradient magnitude and can successfully reconstruct CT images from undersampled data for which conventional analytic reconstruction algorithms fail. We implemented the algorithm and applied it to sparsely-sampled data for a mouse by using a prospectively gated micro-CT system. The images were successfully reconstructed, and an image similarity index was quantitatively calculated with respect to the reference images reconstructed from fully-sampled data. Compared to a conventional image reconstruction algorithm, the TV-minimization algorithm substantially reduced image inaccuracy related to the image artifacts.

THE medical imaging technologies and the industrial ones have benefitted from each other. For a baggage inspection for example, multiple-detector helical CT scanning technology has been deployed that was originally developed for a fast volumetric imaging of a patient in clinics. In a helical CT, the detector array and the x-ray source are rotating continuously in a gantry with the slip-ring technology, and the object is moving along the rotation axis. With the slip-ring technology, an elaborate x-ray cable and drum system can be eliminated but may increase the production cost and instability of the system.

X-ray computed laminography is widely used in nondestructive testing of relatively flat objects using an oblique scanning configuration for data acquisition. In this work, a new scanning scheme is proposed in conjunction with the compressive-sensing-based image reconstruction for reducing imaging radiation dose and scanning time. We performed a numerical study comparing image qualities acquired by various scanning configurations that are practically implementable: single-arc, double-arc, oblique, and spherical-sinusoidal trajectories. A compressive-sensing-inspired total-variation (TV) minimization algorithm was used to reconstruct the images from the data acquired at only 40 projection views in those trajectories. It was successfully demonstrated that the proposed scanning scheme outperforms the others in terms of image contrast and spatial resolution, although the oblique scanning scheme showed a comparable resolution property. We believe that the proposed scanning method may provide a solution to fast and low-dose nondestructive testing of radiation-sensitive and highly integrated devices such as multilayer microelectronic circuit boards. (C) 2014 Optical Society of America

In computed tomography (CT) imaging, radiation dose delivered to the patient is one of the major concerns. Among many technical solutions to lowering radiation dose while preserving clinical utilities of the images, sparse-view CT is a promising technique. However, a fast power switching of an x-ray tube, which is needed for the sparse-view sampling, can be challenging in many CT systems. We have recently proposed a novel alternative approach to sparse-view circular CT that can be readily incorporated in the existing CT systems, and have successfully shown its feasibility. Instead of switching the x-ray tube power, one can place an oscillating multi-slit collimator between the x-ray tube and the patient to partially block the x-ray beam thereby reducing the radiation. In this study, we performed a preliminary study on the effects of dose reduction via using multi-slit collimators of varying sizes of slit-openings on the reconstructed image quality. MicroCT projection data of a mouse were used and a numerical collimation was applied in the form of multi-slits. We used a sinusoidal motion of the collimator to the perpendicular direction of the rotation axis for the purpose of obtaining more uniform spatial sampling of the image. For image reconstruction, we used a total-variation minimization (TV) algorithm which has shown its out-performance in many sparse-view CT applications. This study UQI value was calculated to investigate the dependence of image quality on slit-opening size. Additionally, a visual image quality assessment was made.

A high resolution micro computed tomography (micro-CT) system for live small animal imaging has been developed. The system consists of an x-ray source with micro focus spot and high brightness, rotating gantry with a x-ray tube and flat panel detector pair and a stationary and a horizontally positioned small animal bed to achieve a conebeam mode scan. The system is optimized for in vivo small animal imaging and the capability of administering respiratory anesthesia during scanning. The Feldkamp algorithm was adopted in image reconstruction with graphic processing unit (GPU). We evaluated the spatial resolution, image contrast, and uniformity of system using phantom. As the result, the spatial resolution of the system was the 56lp/mm at 10% of the MTF curve, and the radiation dose to the sample was 98mGy. The minimal resolving contrast was found to be less than 46 CT numbers on low-contrast phantom. We present the image test results of the bone and lung, and heart of the live mice.

Dual-energy cone-beam CT is an important imaging modality in diagnostic applications, and may also find its use in other applications such as therapeutic image guidance. Despite of its clinical values, relatively high radiation dose of dual-energy scan may pose a challenge to its wide use. In this work, we investigated a low-dose, pre-reconstruction type of dual-energy cone-beam CT (CBCT) using a total-variation minimization algorithm for image reconstruction. An empirical dual-energy calibration method was used to prepare material-specific projection data. Raw data acquired at high and low tube voltages are converted into a set of basis functions which can be linearly combined to produce material-specific data using the coefficients obtained through the calibration process. From much fewer views than are conventionally used, material specific images are reconstructed by use of the total-variation minimization algorithm. An experimental study was performed to demonstrate the feasibility of the proposed method using a micro-CT system. We have reconstructed images of the phantoms from only 90 projections acquired at tube voltages of 40 kVp and 90 kVp each. Aluminum-only and acryl-only images were successfully decomposed. A low-dose dual-energy CBCT can be realized via the proposed method by greatly reducing the number of projections.

In this work, we proposed a novel scatter correction method for a circular cone-beam computed tomography (CBCT) using a hardware-based approach that completes both data acquisition and scatter correction in a single rotation. We utilized (quasi-)redundancy in the circular cone-beam data, and applied the chord-based backprojection-filtration (BPF) algorithm to avoid the problem of filtering discontinuous data that would occur if conventional filtered-backprojection (FBP) algorithms were used. A single scan was performed on a cylindrical uniform phantom with beam-block strips between the source and the phantom, and the scatter was estimated for each projection from the data under the blocked regions. The beam-block strips (BBSs) were aligned parallel to the rotation axis, and the spacing between the strips was determined so that the data within the spaces constitute at least slightly more than the minimum data required for image reconstruction. The results showed that the image error due to scatter (about 30 % of the attenuation coefficient value) has been successfully corrected by the proposed algorithm.

We proposed a novel scanning method for low-dose computed tomography (CT) that uses an oscillating multi-slit collimator between the x-ray source and the patient. It can be thought as a realization of sparse data sampling that does not require a fast x-ray power switching. A simulation study was performed based on experimentally acquired microCT data of a mouse to demonstrate the feasibility of the proposed method. A numerical collimation was designed to leave only one-fourth of each projection data for use in image reconstruction. A total-variation minimization algorithm was implemented for image reconstruction from the sparely sampled data. We have successfully shown that the proposed method provides a viable option to low-dose CT.