11 research outputs found
Volumetric three-dimensional intravascular ultrasound visualization using shape-based nonlinear interpolation
BACKGROUND: Intravascular ultrasound (IVUS) is a standard imaging modality for identification of plaque formation in the coronary and peripheral arteries. Volumetric three-dimensional (3D) IVUS visualization provides a powerful tool to overcome the limited comprehensive information of 2D IVUS in terms of complex spatial distribution of arterial morphology and acoustic backscatter information. Conventional 3D IVUS techniques provide sub-optimal visualization of arterial morphology or lack acoustic information concerning arterial structure due in part to low quality of image data and the use of pixel-based IVUS image reconstruction algorithms. In the present study, we describe a novel volumetric 3D IVUS reconstruction algorithm to utilize IVUS signal data and a shape-based nonlinear interpolation. METHODS: We developed an algorithm to convert a series of IVUS signal data into a fully volumetric 3D visualization. Intermediary slices between original 2D IVUS slices were generated utilizing the natural cubic spline interpolation to consider the nonlinearity of both vascular structure geometry and acoustic backscatter in the arterial wall. We evaluated differences in image quality between the conventional pixel-based interpolation and the shape-based nonlinear interpolation methods using both virtual vascular phantom data and in vivo IVUS data of a porcine femoral artery. Volumetric 3D IVUS images of the arterial segment reconstructed using the two interpolation methods were compared. RESULTS: In vitro validation and in vivo comparative studies with the conventional pixel-based interpolation method demonstrated more robustness of the shape-based nonlinear interpolation algorithm in determining intermediary 2D IVUS slices. Our shape-based nonlinear interpolation demonstrated improved volumetric 3D visualization of the in vivo arterial structure and more realistic acoustic backscatter distribution compared to the conventional pixel-based interpolation method. CONCLUSIONS: This novel 3D IVUS visualization strategy has the potential to improve ultrasound imaging of vascular structure information, particularly atheroma determination. Improved volumetric 3D visualization with accurate acoustic backscatter information can help with ultrasound molecular imaging of atheroma component distribution
CAVASS: A Computer-Assisted Visualization and Analysis Software System
The Medical Image Processing Group at the University of Pennsylvania has been developing (and distributing with source code) medical image analysis and visualization software systems for a long period of time. Our most recent system, 3DVIEWNIX, was first released in 1993. Since that time, a number of significant advancements have taken place with regard to computer platforms and operating systems, networking capability, the rise of parallel processing standards, and the development of open-source toolkits. The development of CAVASS by our group is the next generation of 3DVIEWNIX. CAVASS will be freely available and open source, and it is integrated with toolkits such as Insight Toolkit and Visualization Toolkit. CAVASS runs on Windows, Unix, Linux, and Mac but shares a single code base. Rather than requiring expensive multiprocessor systems, it seamlessly provides for parallel processing via inexpensive clusters of work stations for more time-consuming algorithms. Most importantly, CAVASS is directed at the visualization, processing, and analysis of 3-dimensional and higher-dimensional medical imagery, so support for digital imaging and communication in medicine data and the efficient implementation of algorithms is given paramount importance
Model driven segmentation and the detection of bone fractures
Bibliography: leaves 83-90.The introduction of lower dosage image acquisition devices and the increase in computational power means that there is an increased focus on producing diagnostic aids for the medical trauma environment. The focus of this research is to explore whether geometric criteria can be used to detect bone fractures from Computed Tomography data. Conventional image processing of CT data is aimed at the production of simple iso-surfaces for surgical planning or diagnosis - such methods are not suitable for the automated detection of fractures. Our hypothesis is that through a model-based technique a triangulated surface representing the bone can be speedily and accurately produced. And, that there is sufficient structural information present that by examining the geometric structure of this representation we can accurately detect bone fractures. In this dissertation we describe the algorithms and framework that we built to facilitate the detection of bone fractures and evaluate the validity of our approach
Anthropometric and genetic determinants of cardiac morphology and function
Background
Cardiac structure and function result from complex interactions between genetic and environmental factors. Population-based studies have relied on 2-dimensional cardiovascular magnetic resonance as the gold-standard for phenotyping. However, this technique provides limited global metrics and is insensitive to regional or asymmetric changes in left ventricular (LV) morphology.
High-resolution 3-dimensional cardiac magnetic resonance (3D-CMR) with computational quantitative phenotyping, might improve on traditional CMR by enabling the creation of detailed 3D statistical models of the variation in cardiac phenotypes for use in studies of genetic and/or environmental effects on cardiac form or function.
Purpose
To determine whether 3D-CMR is applicable at scale, and provides methodological and statistical advantages over conventional imaging for large-scale population studies and to apply 3D-CMR to anthropometric and genetic studies of the heart.
Methods
1530 volunteers (54.8% females, 74.7% Caucasian, mean age 41.3±13.0 years) without self-reported cardiovascular disease were recruited prospectively to the Digital Heart Project. Using a cardiac atlas-based software, these images were computationally processed and quantitatively analysed. Parameters such as myocardial shape, curvature, wall thickness, relative wall thickness, end-systolic wall stress, fractional wall thickening and ventricular volumes were extracted at over 46,000 points in the model. The relationships between these parameters and systolic blood pressure (SBP), fat mass, lean mass and genetic variationswere analysed using 3D regression models adjusted for body surface area, gender, race, age and multiple testing.
Targeted resequencing of titin (TTN), the largest human gene and the commonest genetic cause of dilated cardiomyopathy, was performed in 928 subjects while common variants (~700.000) were genotyped in 1346 subjects.
Results
Automatically segmented 3D images were more accurate than 2D images at defining cardiac surfaces, resulting in fewer subjects being required to detect a statistically significant 1 mm difference in wall thickness. 3D-CMR enabled the detection of a strong and distinct regionality of the effects of SBP, body composition and genetic variation on the heart. It shows that the precursors of the hypertensive heart phenotype can be traced to healthy normotensives and that different ratios of body composition are associated with particular gender-specific patterns of cardiac remodelling. In 17 asymptomatic subjects with genetic variations associated with dilated cardiomyopathy, early stages of ventricular impairment and wall thinning were identified, which were not apparent by 2D imaging.
Conclusions
3D-CMR combined with computational modelling provides high-resolution insight into the earliest stages of heart disease. These methods show promise for population-based studies of the anthropometric, environmental and genetic determinants of LV form and function in health and disease.Open Acces
Optical techniques for non-destructive detection of flaws in ceramic components
No abstract availableThis thesis primarily concerns development of a non-destructive inspection method for
3mol% Yttria-Stabilised Zirconia Polycrystal (3Y-TZP) ceramics used for dental
applications and a scoping study on applying the technique to other ceramic materials
applied in thermal barrier coatings and other fields.
Zirconia ceramics are materials of great interest for various engineering applications,
primarily due to their stiffness, hardness and wear resistance. These factors in
combination with the complex manufacturing processes may reduce the material
strength and durability due to induced cracking. Knowledge of the extent of this
cracking must be obtained and often, if each part is unique as in biomedicine, the
assessment must be carried out for every part non-destructively so the part can be
subsequently used.
Only a few techniques are known for inspection of Zirconia ceramics, however these
techniques are not able to detect flaws in thick (above 500 μm) parts. The main
limitation for optical inspection of 3Y-TZP is the highly scattering nature of the
material due to its multicrystalline grain structure (grains size of 500 nm) which,
particularly in the visible region, reduces imaging capabilities. However, a transmission
window in the mid-infrared (between 3 and 8 μm) exists opening up the potential for
inspection at these wavelengths.
Mid-Infrared Transmission Imaging (MIR-TI) and Confocal Mid-Infrared Transmission
Imaging (CMIR-TI) techniques were developed for inspection of 3Y-TZP parts which
allow for detecting sub mm scale cracks. The measured imaging resolution for the
MIR-TI is 42 ± 5 μm, whereas for the CMIR-TI it is below 38.5 ± 5 μm. The maximum
sample thickness inspected with the MIR-TI and CMIR-TI is 6 mm and 3.5 mm
respectively, considerably more than currently available inspection methods. The MIRTI
technique provides fast inspection of the part due to the large field of view (11 by 7
mm), however the high cost and limited imaging resolution make this technique less
attractive. The CMIR-TI technique on the other hand is more cost effective due to
reduced cost of the infrared sensor and it provides an enhanced imaging capabilities.
The promising results achieved with the MIR-TI and CMIR-TI techniques led to the
development of reflection equivalents (Camera-MIRI and Confocal-MIRI) for ceramic
coating measurements, however further in-depth experiments to determine and quantify
the capabilities of both techniques are required
An image segmentation and registration approach to cardiac function analysis using MRI
Cardiovascular diseases (CVDs) are one of the major causes of death in the world. In recent
years, significant progress has been made in the care and treatment of patients with such
diseases. A crucial factor for this progress has been the development of magnetic resonance
(MR) imaging which makes it possible to diagnose and assess the cardiovascular function
of the patient. The ability to obtain high-resolution, cine volume images easily and safely
has made it the preferred method for diagnosis of CVDs. MRI is also unique in its ability
to introduce noninvasive markers directly into the tissue being imaged(MR tagging) during
the image acquisition process. With the development of advanced MR imaging acquisition
technologies, 3D MR imaging is more and more clinically feasible. This recent development has
allowed new potentially 3D image analysis technologies to be deployed. However, quantitative
analysis of cardiovascular system from the images remains a challenging topic.
The work presented in this thesis describes the development of segmentation and motion
analysis techniques for the study of the cardiac anatomy and function in cardiac magnetic
resonance (CMR) images. The first main contribution of the thesis is the development of a fully
automatic cardiac segmentation technique that integrates and combines a series of state-of-the-art
techniques. The proposed segmentation technique is capable of generating an accurate 3D
segmentation from multiple image sequences. The proposed segmentation technique is robust
even in the presence of pathological changes, large anatomical shape variations and locally
varying contrast in the images.
Another main contribution of this thesis is the development of motion tracking techniques that
can integrate motion information from different sources. For example, the radial motion of
the myocardium can be tracked easily in untagged MR imaging since the epi- and endocardial
surfaces are clearly visible. On the other hand, tagged MR imaging allows easy tracking of
both longitudinal and circumferential motion. We propose a novel technique based on non-rigid
image registration for the myocardial motion estimation using both untagged and 3D tagged MR
images. The novel aspect of our technique is its simultaneous use of complementary information
from both untagged and 3D tagged MR imaging. The similarity measure is spatially weighted
to maximise the utility of information from both images.
The thesis also proposes a sparse representation for free-form deformations (FFDs) using the principles of compressed sensing. The sparse free-form deformation (SFFD) model can
capture fine local details such as motion discontinuities without sacrificing robustness. We
demonstrate the capabilities of the proposed framework to accurately estimate smooth as well
as discontinuous deformations in 2D and 3D CMR image sequences. Compared to the standard
FFD approach, a significant increase in registration accuracy can be observed in datasets with
discontinuous motion patterns.
Both the segmentation and motion tracking techniques presented in this thesis have been
applied to clinical studies. We focus on two important clinical applications that can be
addressed by the techniques proposed in this thesis. The first clinical application aims
at measuring longitudinal changes in cardiac morphology and function during the cardiac
remodelling process. The second clinical application aims at selecting patients that positively
respond to cardiac resynchronization therapy (CRT).
The final chapter of this thesis summarises the main conclusions that can be drawn from the
work presented here and also discusses possible avenues for future research