5 research outputs found
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
Mri Methods For Imaging The Feto-Placental Vasculature And Blood
Fetal magnetic resonance imaging (MRI) in recent times has become a well-established adjunct to ultrasound (US) in routine clinical prenatal care and diagnostics. The majority of fetal MRI is restricted to T2-weighted scans, where the diagnosis is based on the appearance of normal and abnormal tissue. Although there have been many advancements in MRI and a plethora of sequences, that probe different anatomical and different physiological process, the adaptation of these in fetal imaging has been rather slow. Many of these can extract quantitative parameters that can throw light on the underlying tissue’s normal/patho-physiology. But the use of such quantitative MRI methods has been extremely limited in fetal imaging due to its unique and dynamic physiological milieu that pose several technical challenges including low signal to noise and/or resolution, artifacts associated with abdominal imaging and most importantly fetal motion. These limitations are expected to be overcome by (a) optimizing and (b) developing novel MR imaging sequences, both of which constitute the primary aim of my work.
This work develops a framework that allows for vascular imaging in the fetus and placenta. This includes both qualitative vascular imaging and blood flow quantification. Towards this, three broad directions were explored (a) Moving to higher field imaging, while optimizing parameters for low energy deposition and (b) application of non-gated phase contrast MRI and (c) optimization of conventional time-of-flight angiography for fetal applications
Computerized Analysis of Magnetic Resonance Images to Study Cerebral Anatomy in Developing Neonates
The study of cerebral anatomy in developing neonates is of great importance for
the understanding of brain development during the early period of life. This
dissertation therefore focuses on three challenges in the modelling of cerebral
anatomy in neonates during brain development. The methods that have been
developed all use Magnetic Resonance Images (MRI) as source data.
To facilitate study of vascular development in the neonatal period, a set of image
analysis algorithms are developed to automatically extract and model cerebral
vessel trees. The whole process consists of cerebral vessel tracking from
automatically placed seed points, vessel tree generation, and vasculature
registration and matching. These algorithms have been tested on clinical Time-of-
Flight (TOF) MR angiographic datasets.
To facilitate study of the neonatal cortex a complete cerebral cortex segmentation
and reconstruction pipeline has been developed. Segmentation of the neonatal
cortex is not effectively done by existing algorithms designed for the adult brain
because the contrast between grey and white matter is reversed. This causes pixels
containing tissue mixtures to be incorrectly labelled by conventional methods. The
neonatal cortical segmentation method that has been developed is based on a novel
expectation-maximization (EM) method with explicit correction for mislabelled
partial volume voxels. Based on the resulting cortical segmentation, an implicit
surface evolution technique is adopted for the reconstruction of the cortex in
neonates. The performance of the method is investigated by performing a detailed
landmark study.
To facilitate study of cortical development, a cortical surface registration algorithm
for aligning the cortical surface is developed. The method first inflates extracted
cortical surfaces and then performs a non-rigid surface registration using free-form
deformations (FFDs) to remove residual alignment. Validation experiments using
data labelled by an expert observer demonstrate that the method can capture local
changes and follow the growth of specific sulcus
Diffusion Weighted Imaging of the Neonatal Brain
Although in the last decades advances in fetal and neonatal medicine
have reduced mortality in neonatal intensive care units in the Western
world, the morbidity due to brain injury remains high. Patterns of neonatal
brain injury can be roughly divided in (1) term and (2) preterm patterns.
Table 1 shows the number of infants admitted to the NICU in the
Sophia Children’s Hospital between March 2008 and March 2010 with a
typical ‘neurological’ diagnosis. The table highlights differences in diagnoses
between preterm and term infants in relation to gender. In preterm
infants the most common diagnoses are: persistent flaring (hypersignal
intensity seen in periventricluar white matter using cranial ultrasound),
intraventricular haemorrhage and venous infarction. In term infants perinatal
asphyxia and perinatal stroke are most often reported