X-ray Dose Reduction through Adaptive Exposure in Fluoroscopic Imaging

X-ray fluoroscopy is widely used for image guidance during cardiac intervention. However, radiation dose in these procedures can be high, and this is a significant concern, particularly in pediatric applications. Pediatrics procedures are in general much more complex than those performed on adults and thus are on average four to eight times longer1. Furthermore, children can undergo up to 10 fluoroscopic procedures by the age of 10, and have been shown to have a three-fold higher risk of developing fatal cancer throughout their life than the general population2,3

Compressed Sensing Based Reconstruction Algorithm for X-ray Dose Reduction in Synchrotron Source Micro Computed Tomography

Synchrotron computed tomography requires a large number of angular projections to reconstruct tomographic images with high resolution for detailed and accurate diagnosis. However, this exposes the specimen to a large amount of x-ray radiation. Furthermore, this increases scan time and, consequently, the likelihood of involuntary specimen movements. One approach for decreasing the total scan time and radiation dose is to reduce the number of projection views needed to reconstruct the images. However, the aliasing artifacts appearing in the image due to the reduced number of projection data, visibly degrade the image quality. According to the compressed sensing theory, a signal can be accurately reconstructed from highly undersampled data by solving an optimization problem, provided that the signal can be sparsely represented in a predefined transform domain. Therefore, this thesis is mainly concerned with designing compressed sensing-based reconstruction algorithms to suppress aliasing artifacts while preserving spatial resolution in the resulting reconstructed image. First, the reduced-view synchrotron computed tomography reconstruction is formulated as a total variation regularized compressed sensing problem. The Douglas-Rachford Splitting and the randomized Kaczmarz methods are utilized to solve the optimization problem of the compressed sensing formulation. In contrast with the first part, where consistent simulated projection data are generated for image reconstruction, the reduced-view inconsistent real ex-vivo synchrotron absorption contrast micro computed tomography bone data are used in the second part. A gradient regularized compressed sensing problem is formulated, and the Douglas-Rachford Splitting and the preconditioned conjugate gradient methods are utilized to solve the optimization problem of the compressed sensing formulation. The wavelet image denoising algorithm is used as the post-processing algorithm to attenuate the unwanted staircase artifact generated by the reconstruction algorithm. Finally, a noisy and highly reduced-view inconsistent real in-vivo synchrotron phase-contrast computed tomography bone data are used for image reconstruction. A combination of prior image constrained compressed sensing framework, and the wavelet regularization is formulated, and the Douglas-Rachford Splitting and the preconditioned conjugate gradient methods are utilized to solve the optimization problem of the compressed sensing formulation. The prior image constrained compressed sensing framework takes advantage of the prior image to promote the sparsity of the target image. It may lead to an unwanted staircase artifact when applied to noisy and texture images, so the wavelet regularization is used to attenuate the unwanted staircase artifact generated by the prior image constrained compressed sensing reconstruction algorithm. The visual and quantitative performance assessments with the reduced-view simulated and real computed tomography data from canine prostate tissue, rat forelimb, and femoral cortical bone samples, show that the proposed algorithms have fewer artifacts and reconstruction errors than other conventional reconstruction algorithms at the same x-ray dose

New technologies to reduce pediatric radiation doses

X-ray dose reduction in pediatrics is particularly important because babies and children are very sensitive to radiation exposure. We present new developments to further decrease pediatric patient dose. With the help of an advanced exposure control, a constant image quality can be maintained for all patient sizes, leading to dose savings for babies and children of up to 30%. Because objects of interest are quite small and the speed of motion is high in pediatric patients, short pulse widths down to 4 ms are important to reduce motion blurring artifacts. Further, a new noise-reduction algorithm is presented that detects and processes signal and noise in different frequency bands, generating smooth images without contrast loss. Finally, we introduce a super-resolution technique: two or more medical images, which are shifted against each other in a subpixel region, are combined to resolve structures smaller than the size of a single pixel. Advanced exposure control, short exposure times, noise reduction and super-resolution provide improved image quality, which can also be invested to save radiation exposure. All in all, the tools presented here offer a large potential to minimize the deterministic and stochastic risks of radiation exposure

X-ray dose reduction using additional copper filtration for abdominal digital radiography: Evaluation using signal difference-to-noise ratio

Purpose: X-ray dose reduction using additional copper filters (Cu-filters) for abdominal general radiography was indicated in a report using a simulation study. We validated the dose reduction effects using a clinical digital radiography system equipped with an indirect-type CsI detector and an automatic Cu-filter insertion function. Methods: The image qualities were evaluated using signal difference-to-noise ratio (SDNR) for different radiation qualities with and without Cu-filters for a 20-cm acrylic phantom. Acrylic and bone equivalent material plates were used for contrast measurements. The dose reduction using Cu-filters was estimated from the ratios of the SDNR2 values. Results: For the same entrance surface dose (ESD), Cu-filters with 0.1- and 0.2-mm thicknesses increased the image quality as evaluated by SDNR2 and the estimated dose reduction without degrading the image quality. For the acrylic contrast, the dose reductions with the 0.1- and 0.2-mm-thick Cu-filters were approximately 30% and 44% at 70kV and 29% and 35% at 80kV, respectively. For the bone contrast, the reduction rates were slightly reduced. Conclusions: We validated the dose reduction capability of additional Cu-filters without degrading the image quality for abdominal radiography. The estimated entrance surface dose reductions of the Cu-filters were approximately 30-40% and 20-30% for the acrylic and bone contrasts, respectively, and effective dose reductions for acrylic were nearly half of those for ESD. At these reduced dose conditions, the current time product values needed to be increased by factors of 1.4 and 1.8 for the 0.1- and 0.2-mm-thick Cu-filters, respectively. © 2017 Associazione Italiana di Fisica Medica.Embargo Period 12 month

Application of electron multiplying CCD technology in space instrumentation

Electron multiplying CCD (EMCCD) technology has found important initial applications in low light surveillance and photon starved scientific instrumentation. This paper discusses the attributes of the EMCCD which make it useful for certain space instruments, particularly those which are photon starved, and explores likely risks from the radiation expected in such instruments

Can Image Enhancement Allow Radiation Dose to Be Reduced Whilst Maintaining the Perceived Diagnostic Image Quality Required for Coronary Angiography?

Objectives: The aim of this research was to quantify the reduction in radiation dose facilitated by image processing alone for percutaneous coronary intervention (PCI) patient angiograms, without reducing the perceived image quality required to confidently make a diagnosis. Methods: Incremental amounts of image noise were added to five PCI angiograms, simulating the angiogram as having been acquired at corresponding lower dose levels (10-89% dose reduction). Sixteen observers with relevant experience scored the image quality of these angiograms in three states - with no image processing and with two different modern image processing algorithms applied. These algorithms are used on state-of-the-art and previous generation cardiac interventional X-ray systems. Ordinal regression allowing for random effects and the delta method were used to quantify the dose reduction possible by the processing algorithms, for equivalent image quality scores. Results: Observers rated the quality of the images processed with the state-of-the-art and previous generation image processing with a 24.9% and 15.6% dose reduction respectively as equivalent in quality to the unenhanced images. The dose reduction facilitated by the state-of-the-art image processing relative to previous generation processing was 10.3%. Conclusions: Results demonstrate that statistically significant dose reduction can be facilitated with no loss in perceived image quality using modern image enhancement; the most recent processing algorithm was more effective in preserving image quality at lower doses. Advances in knowledge: Image enhancement was shown to maintain perceived image quality in coronary angiography at a reduced level of radiation dose using computer software to produce synthetic images from real angiograms simulating a reduction in dose

CARDIOVASCULAR COMPUTED TOMOGRAPHY AND MAGNETIC RESONANCE IMAGING IN CONGENITAL HEART DISEASE

Cardiac magnetic resonance (CMR) is a non-invasive imaging modality highly reliable for studying cardiovascular morphology and function. Cardiac computed tomography (CCT) can give valuable anatomic information on CHD in children but implies radiation exposure, a relevant issue in children and newborns who are more radiosensitive than adult patients and have a longer lifetime to develop stochastic effects from radiation. We contributed to show the possibility to obtain an impressively low ionizing dose reduction in CHD patients also using standard 64-slice CT scanners. Conversely, CMR holds a pivotal role when functional and flow imaging is required. We showed the role of CMR in evaluating of patients percutaneously implanted with a pulmonary valve. Moreover, we proposed two new approaches for post-processing CMR images, regarding volume estimation of patients with a single ventricle, a rare CHD and a method for quantifying the paradoxical septal motion. CMR and CCT are two fundamental imaging techniques to evaluate patients with complex CHD. Both imaging modalities have limitations and advantages. CMR can evaluate heart function vessel flow but require a long acquisition time and in same patients a long sedation time. CCT has a very high spatial resolution and short acquisition time but implies ionizing radiation exposure. On the one side, we confirming the crucial role of CMR when function analysis is required but also showed the relevant possibilities of x-ray dose reduction in CCT, also using standard 64-slice scanners in the study of CHD patients