4,945 research outputs found
MRI Visualization of Whole Brain Macro- and Microvascular Remodeling in a Rat Model of Ischemic Stroke: A Pilot Study
Using superparamagnetic iron oxide nanoparticles (SPION) as a single contrast agent, we investigated dual contrast cerebrovascular magnetic resonance imaging (MRI) for simultaneously monitoring macro- and microvasculature and their association with ischemic edema status (via apparent diffusion coefficient [ADC]) in transient middle cerebral artery occlusion (tMCAO) rat models. High-resolution T1-contrast based ultra-short echo time MR angiography (UTE-MRA) visualized size remodeling of pial arteries and veins whose mutual association with cortical ischemic edema status is rarely reported. ??R2?????R2*-MRI-derived vessel size index (VSI) and density indices (Q and MVD) mapped morphological changes of microvessels occurring in subcortical ischemic edema lesions. In cortical ischemic edema lesions, significantly dilated pial veins (p???=???0.0051) and thinned pial arteries (p???=???0.0096) of ipsilateral brains compared to those of contralateral brains were observed from UTE-MRAs. In subcortical regions, ischemic edema lesions had a significantly decreased Q and MVD values (p???<???0.001), as well as increased VSI values (p???<???0.001) than normal subcortical tissues in contralateral brains. This pilot study suggests that MR-based morphological vessel changes, including but not limited to venous blood vessels, are directly related to corresponding tissue edema status in ischemic stroke rat models
Automatic 3D bi-ventricular segmentation of cardiac images by a shape-refined multi-task deep learning approach
Deep learning approaches have achieved state-of-the-art performance in
cardiac magnetic resonance (CMR) image segmentation. However, most approaches
have focused on learning image intensity features for segmentation, whereas the
incorporation of anatomical shape priors has received less attention. In this
paper, we combine a multi-task deep learning approach with atlas propagation to
develop a shape-constrained bi-ventricular segmentation pipeline for short-axis
CMR volumetric images. The pipeline first employs a fully convolutional network
(FCN) that learns segmentation and landmark localisation tasks simultaneously.
The architecture of the proposed FCN uses a 2.5D representation, thus combining
the computational advantage of 2D FCNs networks and the capability of
addressing 3D spatial consistency without compromising segmentation accuracy.
Moreover, the refinement step is designed to explicitly enforce a shape
constraint and improve segmentation quality. This step is effective for
overcoming image artefacts (e.g. due to different breath-hold positions and
large slice thickness), which preclude the creation of anatomically meaningful
3D cardiac shapes. The proposed pipeline is fully automated, due to network's
ability to infer landmarks, which are then used downstream in the pipeline to
initialise atlas propagation. We validate the pipeline on 1831 healthy subjects
and 649 subjects with pulmonary hypertension. Extensive numerical experiments
on the two datasets demonstrate that our proposed method is robust and capable
of producing accurate, high-resolution and anatomically smooth bi-ventricular
3D models, despite the artefacts in input CMR volumes
Generative Models for Preprocessing of Hospital Brain Scans
I will in this thesis present novel computational methods for processing routine clinical brain scans. Such scans were originally acquired for qualitative assessment by trained radiologists, and present a number of difficulties for computational models, such as those within common neuroimaging analysis software. The overarching objective of this work is to enable efficient and fully automated analysis of large neuroimaging datasets, of the type currently present in many hospitals worldwide. The methods presented are based on probabilistic, generative models of the observed imaging data, and therefore rely on informative priors and realistic forward models. The first part of the thesis will present a model for image quality improvement, whose key component is a novel prior for multimodal datasets. I will demonstrate its effectiveness for super-resolving thick-sliced clinical MR scans and for denoising CT images and MR-based, multi-parametric mapping acquisitions. I will then show how the same prior can be used for within-subject, intermodal image registration, for more robustly registering large numbers of clinical scans. The second part of the thesis focusses on improved, automatic segmentation and spatial normalisation of routine clinical brain scans. I propose two extensions to a widely used segmentation technique. First, a method for this model to handle missing data, which allows me to predict entirely missing modalities from one, or a few, MR contrasts. Second, a principled way of combining the strengths of probabilistic, generative models with the unprecedented discriminative capability of deep learning. By introducing a convolutional neural network as a Markov random field prior, I can model nonlinear class interactions and learn these using backpropagation. I show that this model is robust to sequence and scanner variability. Finally, I show examples of fitting a population-level, generative model to various neuroimaging data, which can model, e.g., CT scans with haemorrhagic lesions
Magnetic Resonance Imaging of the Brain in Moving Subjects. Application of Fetal, Neonatal and Adult Brain Studies
Imaging in the presence of subject motion has been an ongoing challenge for
magnetic resonance imaging (MRI). Motion makes MRI data inconsistent, causing
artifacts in conventional anatomical imaging as well as invalidating diffusion
tensor imaging (DTI) reconstruction. In this thesis some of the important issues
regarding the acquisition and reconstruction of anatomical and DTI imaging of
moving subjects are addressed; methods to achieve high resolution and high signalto-
noise ratio (SNR) volume data are proposed.
An approach has been developed that uses multiple overlapped dynamic single shot
slice by slice imaging combined with retrospective alignment and data fusion to
produce self consistent 3D volume images under subject motion. We term this
method as snapshot MRI with volume reconstruction or SVR. The SVR method
has been performed successfully for brain studies on subjects that cannot stay still,
and in some cases were moving substantially during scanning. For example, awake
neonates, deliberately moved adults and, especially, on fetuses, for which no
conventional high resolution 3D method is currently available. Fine structure of the
in-utero fetal brain is clearly revealed for the first time with substantially improved
SNR. The SVR method has been extended to correct motion artifacts from
conventional multi-slice sequences when the subject drifts in position during data
acquisition.
Besides anatomical imaging, the SVR method has also been further extended to
DTI reconstruction when there is subject motion. This has been validated
successfully from an adult who was deliberately moving and then applied to inutero
fetal brain imaging, which no conventional high resolution 3D method is
currently available. Excellent fetal brain 3D apparent diffusion coefficient (ADC)
maps in high resolution have been achieved for the first time as well as promising
fractional Anisotropy (FA) maps.
Pilot clinical studies using SVR reconstructed data to study fetal brain development
in-utero have been performed. Growth curves for the normally developing fetal
brain have been devised by the quantification of cerebral and cerebellar volumes as
well as some one dimensional measurements. A Verhulst model is proposed to
describe these growth curves, and this approach has achieved a correlation over
0.99 between the fitted model and actual data
Evaluation of Interpolation and Registration Techniques in Magnetic Resonance Image for Orthogonal Plane Super Resolution Reconstruction
Super resolution reconstruction (SRR) combines several perspectives of an image (typically low resolution) in order to reconstruct a more complete and comprehensive (higher resolution) image. The aim is to use this concept on magnetic resonance imaging (MRI) data, for which the standard is to scan in several-plane orientation in a 2D fashion. As a result, clinical MRI, functional MRI (FMRI), diffusion weighted imaging (DWI)/diffusion tensor imaging (DTI), and MR angiography (MRA) tend to have high in- plane resolution but low resolution in the slice-select direction. By combining the 2 scans of the orthogonal plane, new 3D images can be reconstructed. This thesis addresses the principal problem of image quality and considers a novel SRR technique that uses the original information from 3 MRI plane orientations in order to enhance the resolution based on prior knowledge of scanning protocol as it relates to voxel resolution. The procedure for validating the MRI data algorithm is executed using MRI dataset of a human brain. The mean squared error (MSE) and peak signal-to-noise ratio (PSNR) were computed for quantitative assessment, whereas the qualitative assessment was performed by visually comparing the SR images to the original HR
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