Energy Subtraction Methods as an Alternative to Conventional X-Ray Angiography

Digital subtraction angiography (DSA) is a technique that is widely used to enhance the visibility of small vessels obscured by background structures by subtracting a mask and contrast image. However, DSA is generally unsuccessful for imaging the heart due to the motion that occurs between mask and contrasted images which cause motion artifacts. An alternative approach known as energy subtraction angiography (ESA) exploits the iodine k-edge by acquiring contrast images with a low and high kV in rapid succession to bring the benefits of DSA without motion artifacts. However, it was concluded that image quality for ESA could not compete with DSA, and the approach was abandoned. In our work we show that conclusions about iodine SNR for ESA were based on limitations of early technical components that are no longer relevant. The goals of this thesis were to: 1) develop a theoretical model of iodine SNR that is independent of technology for DSA and ESA; 2) optimize the iodine SNR for ESA; 3) image ESA in an anthropomorphic phantom. It is concluded that, when these conditions are satisfied, ESA iodine SNR equal to that of DSA for low iodine mass loadings (artery sizes) for the same patient entrance exposure, and therefore may provide alternatives to DSA in situations where motion artifacts are expected to render a study as non-diagnostic, such as in coronary applications. In the future this will have important applications for subtraction imaging of the coronary arteries and other vessels where stenosis is vital to patient health

Image quality of energy-dependent approaches for x-ray angiography

Digital subtraction angiography (DSA) is an x-ray-based imaging method widely used for diagnosis and treatment of patients with vascular disease. This technique uses subtraction of images acquired before and after injection of an iodinated contrast agent to generate iodine-specific images. While it is extremely successful at imaging structures that are near-stationary over a period of several seconds, motion artifacts can result in poor image quality with uncooperative patients and DSA is rarely used for coronary applications. Alternative methods of generating iodine-specific images with reduced motion artifacts might exploit the energy-dependence of x-ray attenuation in a patient. This could be performed either by aquiring two or more post-injection images at different x-ray energies or from an analysis of the spectral shape of the transmitted spectrum. The first method, which we call energy-subtraction angiography (ESA), was introduced as a dual-energy alternative to DSA over two decades ago but technological limitations of the time resulted in poor image quality. The second potential method, energy-resolved angiography (ERA), requires energy-resolving photon-counting (EPC) x-ray detectors that are under development in a number of laboratories. The goals of this thesis were to: 1) develop a method of comparing image quality in terms of signal-to-noise ratio (SNR) obtained using ESA and ERA with DSA assuming ideal instrumentation for each; 2) develop a method of describing performance and image quality that can be obtained in practice with photon-counting detectors, and; 3) assess the potential of ESA and ERA by comparing the available iodine SNR with that of DSA including the effects of non-ideal detector performance. It is shown that using ideal instrumentation both ESA and ERA can provide iodine-specific images with SNR equal to that of DSA. However, stochastic x-ray interaction and detection processes will degrade SNR obtained with ERA and ESA to a larger extent than DSA. Energy-resolved angiography will achieve near-ideal performance only with low detector electronic noise levels, high collection efficiency of secondary quanta liberated in the detector, and low Compton cross sections. It is concluded that, when these conditions are satsified, ESA and ERA can provide iodine SNR within 25% of that of DSA for the same patient entrance exposure, and therefore may provide alternatives to DSA in situations where motion artifacts are expected to result in compromised DSA procedures, such as in coronary applications. This could have important applications for subtraction imaging of the coronary arteries in the near future

Using synchrotron imaging techniques to solve problems in neurosurgery

Objective: The purpose of the research presented in this thesis is to explore new biomedical applications of synchrotron imaging in the field of neurosurgery. Methods: Four different studies were performed, all using advanced biomedical synchrotron imaging techniques. In the first two experiments, diffraction enhanced imaging (DEI) and analyzer based imaging (ABI) were utilized to study the anatomy of the rat spine and a novel rat model of spinal fusion. In a third experiment, K-edge digital subtraction angiography (KEDSA) was used to study the cerebral vasculature in a rabbit model. In a fourth experiment, rapid scanning X-ray fluorescence spectroscopy (RS-XRF) was used to study stem cell migration in a rat stroke model. Results: DEI had superior visualization of ligamentous and boney anatomy in a rat model. Analyzer based imaging was able to visualize physiologic amounts of bone graft material and progressive incorporation into the spine. Intravenous KEDSA showed excellent visualization of the cerebral vasculature in a rabbit model. Finally, RS-XRF was used to track iron labeled stem cells implanted in a rat stroke model. The technique was able to visualize the iron that represented the stem cell migration. This was correlated with histology and magnetic resonance imaging information. Conclusions: 1) Diffraction enhanced imaging has excellent contrast for the study of boney and ligamentous anatomy. 2) Analyzer based imaging is an excellent tool to study animal models of boney fusion. 3) Intravenous KEDSA is able to clearly visualize the arterial vasculature in a rabbit model. 4) RS-XRF can be used to study the migration patterns of implanted iron labeled stem cells

Dual- and multi-energy CT: approach to functional imaging

The energy spectrum of X-ray photons after passage through an absorber contains information about its elemental composition. Thus, tissue characterisation becomes feasible provided that absorption characteristics can be measured or differentiated. Dual-energy CT uses two X-ray spectra enabling material differentiation by analysing material-dependent photo-electric and Compton effects. Elemental concentrations can thereby be determined using three-material decomposition algorithms. In comparison to dual-energy CT used in clinical practice, recently developed energy-sensitive photon-counting detectors sample the material-specific attenuation curves at multiple energy levels and within narrow energy bands; the latter allows the detection of element-specific, k-edge discontinuities of the photo-electric cross section. Multi-energy CT imaging therefore is able to concurrently identify multiple materials with increased accuracy. These specific data on material distribution provide information beyond morphological CT, and approach functional imaging. This article reviews the principles of dual- and multi-energy CT imaging, hardware approaches and clinical applications

Feasibility of Coronary Artery Calcium Scoring on Dual-Energy Chest Computed Tomography: A Prospective Comparison with Electrocardiogram-Gated Calcium Score Computed Tomography

Rationale and Objectives: This study aimed to evaluate the feasibility of assessment using the coronary artery calcium score (CACS) in dual-energy chest computed tomography (CT). Materials and Methods: We prospectively enrolled 30 patients (19 male, 11 female; mean age, 63.73 ± 9.40 years) who clinically required contrast-enhanced chest CT. The patients underwent electrocardiogram-gated cardiac calcium-scoring CT with a slice thickness of 2.5 mm followed by a sequentially non-gated contrast-enhanced dual-energy chest CT using 140/80 fast kVp switching technology with slice thicknesses of 1.25 mm and 2.5 mm. Virtual unenhanced (VUE) images were then reconstructed from the dual-energy CT using the material suppressed iodine (MSI) technique. Results: The mean heart rates were 63.33 ± 12.01 beats per minute. The mean CACS on the coronary calcium-scoring CT was 361.1 ± 435.5, and CACSs of the VUE images were 76.8 ± 128.6 (2.5 mm slice) and 108.7 ± 165.1 (1.25 mm slice). The correlation coefficients of CACS between the coronary calcium-scoring CT with the VUE 2.5 mm and 1.25 mm images were 0.888 and 0.904, respectively. The inter-observer agreements for the calcium score measurement between the calcium-scoring CT, VUE 2.5 mm, and VUE 1.25 mm were 1.000, 0.999, and 1.000, respectively. Conclusions: In conclusion, assessment of CACS using dual-energy chest CT might be feasible when using MSI virtual unenhanced dual-energy chest CT images with a slice thickness of 1.25 mm.ope

Diseases of the Chest, Breast, Heart and Vessels 2019-2022

This open access book focuses on diagnostic and interventional imaging of the chest, breast, heart, and vessels. It consists of a remarkable collection of contributions authored by internationally respected experts, featuring the most recent diagnostic developments and technological advances with a highly didactical approach. The chapters are disease-oriented and cover all the relevant imaging modalities, including standard radiography, CT, nuclear medicine with PET, ultrasound and magnetic resonance imaging, as well as imaging-guided interventions. As such, it presents a comprehensive review of current knowledge on imaging of the heart and chest, as well as thoracic interventions and a selection of "hot topics". The book is intended for radiologists, however, it is also of interest to clinicians in oncology, cardiology, and pulmonology

Diseases of the Chest, Breast, Heart and Vessels 2019-2022

This open access book focuses on diagnostic and interventional imaging of the chest, breast, heart, and vessels. It consists of a remarkable collection of contributions authored by internationally respected experts, featuring the most recent diagnostic developments and technological advances with a highly didactical approach. The chapters are disease-oriented and cover all the relevant imaging modalities, including standard radiography, CT, nuclear medicine with PET, ultrasound and magnetic resonance imaging, as well as imaging-guided interventions. As such, it presents a comprehensive review of current knowledge on imaging of the heart and chest, as well as thoracic interventions and a selection of "hot topics". The book is intended for radiologists, however, it is also of interest to clinicians in oncology, cardiology, and pulmonology