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- Nordenfur, Tim, 1990-
(författare)
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Advancing Cardiovascular Shear Wave Elastography and Image Registration : Method Development and Safety Evaluation
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cardiovascular disease remains the leading cause of death and disability worldwide, with its burden on health and healthcare systems projected to rise. In cardiovascular diagnostics and treatment strategy decisions, medical imaging plays a significant role. This thesis aims to improve diagnostic tools for stable coronary artery disease, assess the safety of techniques for guiding treatment decisions in carotid artery stenosis, and develop a novel technique for the elastic characterisation of anisotropic tissues.Accurate diagnosis of stable coronary artery disease demands both anatomical information, on the location and severity of coronary plaques, and functional information, on their haemodynamic impact. A composite image of these types of information could offer greater diagnostic value than examining them separately.In this context, Study I explored image registration of 3D echocardiography with coronary computed tomography angiography. Three image registration algorithms were implemented and validated using patient data. Findings suggest that integrating images from these imaging modalities is feasible, and that iterative closest-point methods can be improved by incorporating orienting landmarks to avoid ventricular rotation.In assessing carotid artery stenosis, plaque composition is increasingly recognised as an important factor for guiding treatment. Ultrasound-based shear wave elastography is emerging as a promising non-invasive method for plaque characterisation, although its mechanical impact on plaques and arterial walls is not completely understood. Studies II and III evaluated the safety of arterial shear wave elastography ex vivo in porcine models and in vivo in human carotid arteries. Results indicate that this technique exposes the arterial wall to significantly less strain than arterial pulsation, at strain rates comparable to those experienced during strenuous exercise.In addition to arterial applications, shear wave elastography is increasingly used to measure elasticity of anisotropic tissues, such as the myocardium. However, current techniques can only fully characterise the elastic properties of isotropic tissues. In Study IV, a novel dual-probe shear wave elastography system was developed for elastic characterisation of transversely isotropic tissues, which exhibit multiple wave modes. Ex-vivo experiments successfully tracked all wave modes and demonstrated the system's feasibility to measure all elastic parameters.
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- Nordenfur, Tim, 1990-, et al.
(författare)
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Cardiac fusion imaging of 3D echocardiography and coronary computed tomography angiography
- 2014
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Background. The choice of treatment strategy for coronary artery disease is often based on: 1) anatomical information on stenosis locations, and 2) functional information on their haemodynamic relevance, e.g. myocardial deformation or perfusion. Inspecting a single fused image containing both anatomical and functional information, as opposed to viewing separate images side-by-side, facilitates this treatment choice. The aim of this study is to develop a novel cardiac fusion imaging technique to combine 3D+time echocardiography (3DE) (functional information) with coronary computed tomography angiography (CCTA) (anatomical information).Method. 3DE and CCTA data sets were obtained from 20 patients with suspected coronary artery disease. The coronary artery tree was segmented from the CCTA images. A semi-automatic fusion algorithm was developed to perform the following steps: The left ventricle (LV) 3D surfaces were segmented in the CCTA image and 3DE images and used to align the two data sets. The moving 3DE LV was then visualized along with the CCTA coronary arteries. Myocardial strain was estimated and visualized on the LV surface.Results. Preliminary fusion results from images of one patient have been obtained. The figure shows the CCTA coronary artery tree aligned with a) 3DE LV endocardium in end-systole, b) 3DE LV endocardium in end-diastole, and c) 3DE LV with colour-coded instantaneous longitudinal strain.Discussion. Preliminary results show that fusion of CCTA and 3DE images is feasible. However, the algorithm needs to be further developed to increase automation and include other functional parameters, such as myocardial perfusion. Moreover, a validation study to assess algorithm performance and diagnostic value in multiple patients will be performed.
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- Nordenfur, Tim, 1990-, et al.
(författare)
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Safety of arterial shear wave elastography-ex-vivo assessment of induced strain and strain rates
- 2022
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Ingår i: Biomedical Engineering & Physics Express. - : IOP Publishing. - 2057-1976. ; 8:5
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Tidskriftsartikel (refereegranskat)abstract
- Shear wave elastography (SWE) is a promising technique for characterizing carotid plaques and assessing local arterial stiffness. The mechanical stress to which the tissue is subjected during SWE using acoustic radiation force (ARF), leading to strain at a certain strain rate, is still relatively unknown. Because SWEis increasingly used for arterial applications where the mechanical stress could potentially lead to significant consequences, it is important to understand the risks of SWE-induced strain and strain rate. The aim of this study was to investigate the safety of SWE in terms of induced arterial strain and strain rate ex-vivo and in a human carotid artery in-vivo. SWE was performed on six porcine aortae as a model of the human carotid artery using different combinations of ARF push parameters (push voltage: 60/90 V, aperture width: f/1.0/1.5, push length: 100/150/200 mu s) and distance to push position. The largest induced strain and strain rate were 1.46% and 54 s(-1) (90 V, f/ 1.0, 200 mu s), respectively. Moreover, the SWE-induced strains and strain rates increased with increasing push voltage, aperture, push length, and decreasing distance between the region of interest and the push. In the human carotid artery, the SWE-induced maximum strain was 0.06% and the maximum strain rate was 1.58 s(-1), compared with the maximum absolute strain and strain rate of 12.61% and 5.12 s(-1), respectively, induced by blood pressure variations in the cardiac cycle. Our results indicate that ex-vivo arterial SWE does not expose the artery to higher strain rate than normal blood pressure variations, and to strain one order of magnitude higher than normal blood pressure variations, at the push settings and distances from the region of interest used in this study.
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