121 research outputs found
2D and 3D ultrasound strain imaging. Methods and in vivo applications.
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87192.pdf (Publisher’s version ) (Open Access)Radboud Universiteit Nijmegen, 03 december 2010Promotores : Thijssen, J.M., Groot, R. de Co-promotores : Korte, C.L. de, Kapusta, L.267 p
Identifiability and optimal experiment design of the standard pharmacokinetic models for dynamic contrast-enhanced imaging of large tumour volumes
No full textIdentifiability analysis of the standard pharmacokinetic models in DCE MR imaging of tumours
No full textIdentifiability analysis of the standard pharmacokinetic models in DCE MR imaging of tumours
No full textThe usage of dynamic contrast-enhanced MRI (DCE-MRI) as a clinical tool is still widely assessed. Application of the standard pharmacokinetic models to obtain physiologically relevant parameter values using DCE-MRI in tumours is not trivial, when the temporal resolution is low. Mathematical analysis and analysis by simulation of the identifiability for the generalized and extended Kety models was executed. Parameter estimation was executed using synthetic data sets and maximum likelihood estimation (MLE). The influence of temporal resolution was examined. The generalized and extended Kety model showed a large bias in the parameter estimates (10-120%) for sampling times >4 s, although the estimated variance was relatively low
Design of a fatty plaque phantom for validation of strain imaging
No full textPrior to clinical application of novel techniques such as vascular elastography and photo acoustic imaging, validation studies are of great importance. Gelatin, agar and polyvinyl-alcohol (PVA) phantoms are commonly used. However, more realistic phantoms are needed with complex geometry and different constituents with known properties. For this purpose, a fatty plaque phantom (fPP) was designed
A dedicated guided-search displacement algorithm for cardiovascular strain imaging
No full textTraditionally, an exhaustive search is performed for 2D strain imaging, often using a priori knowledge or an iterative, multi-level (ML) approach to improve strain quality. In this study, a dedicated guided-search algorithm (CGS), using a seeding procedure that was specifically designed for cardiovascular applications, is introduced and applied to simulation data, and data of aortas, both in vitro and in vitro. The method was compared to two existing methods, a multi-level algorithm and a conventional guided-search approach (GS). Results reveal an improvement of SNRe for the simulation data improvement. The (C)GS method showed good strain results, even when no filtering was applied to the displacements. The in vitro data revealed similar results, however, the in vivo data revealed significant improvement when using the CGS approach over the ML algorithm, whereas the GS method was not able to track the vessel wall over time. A next step will be to apply this algorithm to cardiac data and incorporate stretching
Photoacoustic imaging of superficial vasculature : towards skin disease diagnosis
No full textPostergroup: Tissue Perfusio
Carotid plaque assessment using non-invasive shear strain elastography
No full textStroke is a leading cause of death and morbidity worldwide, and a significant proportion of strokes are caused by carotid atherosclerotic plaque rupture. Non-invasive vascular elastography (NIVE) provides maps of carotid plaque strain computed from radiofrequency ultrasound (US) data sequences. The goal of this project was to evaluate the ability of NIVE shear strain analysis to characterize carotid plaque vulnerability in vivo in patients referred for carotid evaluation. A total of 31 patients with a severe stenosis of the internal carotid artery (> 50%) were enrolled in this study. Twodimensional radiofrequency data were obtained to perform NIVE and to calculate the axial, lateral and shear strains. High-resolution magnetic resonance (MR) images were acquired to segment and quantify the plaques and their internal components. The analysis of plaque regions experiencing large shear strains showed a statistically significant difference (p = 0.046) between symptomatic and asymptomatic patient groups. Statistically significant differences were also found between the time average shear elastogram (Mean |SSE|) of vulnerable versus non-vulnerable plaques without inflammation (p = 0.036). The Mean |SSE| of non-vulnerable plaques with and without inflammation were also significantly different (p = 0.008). The proposed shear measures have the potential to help identifying vulnerable plaques and vulnerable patients
Modeling envelope statistics of blood and myocardium for segmentation of echocardiographic images.
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69451.pdf (Publisher’s version ) (Open Access)The objective of this study was to investigate the use of speckle statistics as a preprocessing step for segmentation of the myocardium in echocardiographic images. Three-dimensional (3D) and biplane image sequences of the left ventricle of two healthy children and one dog (beagle) were acquired. Pixel-based speckle statistics of manually segmented blood and myocardial regions were investigated by fitting various probability density functions (pdf). The statistics of heart muscle and blood could both be optimally modeled by a K-pdf or Gamma-pdf (Kolmogorov-Smirnov goodness-of-fit test). Scale and shape parameters of both distributions could differentiate between blood and myocardium. Local estimation of these parameters was used to obtain parametric images, where window size was related to speckle size (5 x 2 speckles). Moment-based and maximum-likelihood estimators were used. Scale parameters were still able to differentiate blood from myocardium; however, smoothing of edges of anatomical structures occurred. Estimation of the shape parameter required a larger window size, leading to unacceptable blurring. Using these parameters as an input for segmentation resulted in unreliable segmentation. Adaptive mean squares filtering was then introduced using the moment-based scale parameter (sigma(2)/mu) of the Gamma-pdf to automatically steer the two-dimensional (2D) local filtering process. This method adequately preserved sharpness of the edges. In conclusion, a trade-off between preservation of sharpness of edges and goodness-of-fit when estimating local shape and scale parameters is evident for parametric images. For this reason, adaptive filtering outperforms parametric imaging for the segmentation of echocardiographic images
Visualization of vasculature using a hand-held photoacoustic probe: phantom and in vivo validation
Get PDFAssessment of microvasculature and tissue perfusion can provide diagnostic information on local or systemic diseases. Photoacoustic (PA) imaging has strong clinical potential because of its sensitivity to hemoglobin. We used a hand-held PA probe with integrated diode lasers and examined its feasibility and validity in the detection of increasing blood volume and (sub) dermal vascularization. Blood volume detection was tested in custom-made perfusion phantoms. Results showed that an increase of blood volume in a physiological range of 1.3% to 5.4% could be detected. The results were validated with power Doppler sonography. Using a motorized scanning setup, areas of the skin were imaged at relatively short scanning times (<10 s/cm2) with PA. Three-dimensional visualization of these structures was achieved by combining the consecutively acquired cross-sectional images. Images revealed the epidermis and submillimeter vasculature up to depth of 5 mm. The geometries of imaged vasculature were validated with segmentation of the vasculature in high-frequency ultrasound imaging. This study proves the feasibility of PA imaging in its current implementation for the detection of perfusion-related parameters in skin and subdermal tissue and underlines its potential as a diagnostic tool in vascular or dermal pathologies
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