Sean C L Deoni

Bill & Melinda Gates Foundation · Discovery & Tools

Human voices play a fundamental role in social communication, and areas of the adult "social brain" show specialization for processing voices and their emotional content (superior temporal sulcus, inferior prefrontal cortex, premotor cortical regions, amygdala, and insula). However, it is unclear when this specialization develops. Functional magnet...

Multicomponent-driven equilibrium single-component observation of T(1) and T(2) offers a new approach to multiple component relaxation time and myelin water analysis. The method derives two-component relaxation information from spoiled and fully balanced steady-state (SPGR and bSSFP) imaging data acquired over multiple flip angles. Although these s...

Myelination, the elaboration of myelin surrounding neuronal axons, is essential for normal brain function. The development of the myelin sheath enables rapid synchronized communication across the neural systems responsible for higher order cognitive functioning. Despite this critical role, quantitative visualization of myelination in vivo is not po...

Underlying the exquisite soft tissue contrast provided by magnetic resonance imaging are the inherent biophysical processes of relaxation. Through the intricate relationships between tissue microstructure and biochemistry and the longitudinal and transverse relaxation rates, quantitative measurement of these relaxation parameters is informative of...

The exquisite soft tissue contrast provided by magnetic resonance imaging arises principally from differences in the intrinsic relaxation properties, T1 and T2. Although the intricate relationships that link tissue microstructure and the longitudinal and transverse relaxation times remain to be firmly established, quantitative measurement of these...

To investigate a new approach for more completely accounting for off-resonance affects in the DESPOT2 (driven equilibrium single pulse observation of T(2)) mapping technique. The DESPOT2 method derives T(2) information from fully balanced steady-state free precession (bSSFP) images acquired over multiple flip angles. Off-resonance affects, which pr...

The substantia nigra contains dopaminergic cells that project to the striatum and are affected by the neurodegenerative process that appears in Parkinson's disease (PD). For accurate differential diagnosis and for disease monitoring the availability of a sensitive and non-invasive biomarker for Parkinson's disease would be essential. Although there...

Background: Autism is a pervasive developmental disorder characterized by social, communicative and behavior impairments. A hypothesized substrate of the disorder is aberrant white matter maturation and abnormal myelination, evidence of which has been suggested by volumetric, spectroscopic and diffusion tensor magnetic resonance imaging studies. Ho...

High resolution diffusion tensor imaging and tractography of ex vivo brain specimens has the potential to reveal detailed fibre architecture not visible on in vivo images. Previous ex vivo diffusion imaging experiments have focused on animal brains or small sections of human tissue since the unfavourable properties of fixed tissue (including short...

The driven-equilibrium single-pulse observation of T(1) (DESPOT1) and T(2) (DESPOT2) are rapid, accurate, and precise methods for voxelwise determination of the longitudinal and transverse relaxation times. A limitation of the methods, however, is the inherent assumption of single-component relaxation. In a variety of biological tissues, in particu...

To investigate the effect of chemical exchange and multicomponent relaxation on the rapid T(2) mapping method, DESPOT2 (driven equilibrium single pulse observation of T(2)) and the steady-state free precession (SSFP) sequence upon which it is based. Although capable of rapid T(2) determination, an assumption implicit of the method is single-compone...

The ability to acquire MRI data with consistent tissue contrast at multiple time points, and/or across different imaging centres has become increasingly important as the number of large longitudinal and multicentre studies has grown. Here, the use of quantitative magnetic resonance relaxation times measurement, or, voxel-wise determination of the i...

The cerebellum coordinates movement, thought and emotion through its feedback projections from the deep cerebellar nuclei. Despite recent advancement in our understanding of the functions of the cerebellar cortex, little is known about the functional correlates of the deep cerebellar nuclei in humans. This is mainly due to the inability of current...

To investigate an alternative approach to correct for flip angle inaccuracies in the driven equilibrium single pulse observation of T1 (DESPOT1) T1 mapping method. While DESPOT1 is a robust method for rapid whole-brain voxelwise mapping of the longitudinal relaxation time, the approach is inherently sensitive to inaccuracies in the transmitted flip...

To examine the spoiled steady-state (spoiled gradient-recalled echo sequence [SPGR]) signal arising from two-compartment systems and the role of experimental parameters, in particular TR for resolving signal from each compartment. Using Bloch-McConnell simulations, we examined the SPGR signal from two-component systems in which T(1) is much greater...

Patient outcome in minimally invasive stereotactic neurosurgical procedures depends on the ability to accurately locate the desired functional region within the deep brain while avoiding the surrounding anatomy. Due to the lack of sufficient contrast within this region in pre-operatively acquired MR images, electrophysiological exploration and hist...

The increased use of phased-array and surface coils in magnetic resonance imaging, the push toward increased field strength and the need for standardized imaging across multiple sites during clinical trials have resulted in the need for methods that can ensure consistency of intensity both within the image and across multiple subjects/sites. Here,...

The subthalamic nucleus (STN) has been adopted as a commonly used surgical target in deep brain stimulation (DBS) procedures for the treatment of Parkinson's disease. Many techniques have been developed to facilitate STN DBS targeting, and consequently to improve the surgical outcome. In this work, we conducted a retrospective study on 10 patients...

The ability to differentiate noninvasively between the primary nuclear divisions of the thalamus has immediate clinical applicability for surgical planning and guidance of functional stereotactic procedures. Comparison of prior qualitative magnetic resonance imaging (MRI) studies carried out at field strengths of 1.5 and 4 Tesla have revealed contr...

Variations in the intrinsic T(1) and T(2) relaxation times have been implicated in numerous neurologic conditions. Unfortunately, the low resolution and long imaging time associated with conventional methods have prevented T(1) and T(2) mapping from becoming part of routine clinical evaluation. In this study, the clinical applicability of the DESPO...

Variable nutation SSFP (DESPOT2) permits rapid, high-resolution determination of the transverse (T2) relaxation constant. A limitation of DESPOT2, however, is the presence of T2 voids due to off-resonance banding artifacts associated with SSFP images. These artifacts typically occur in images acquired with long repetition times (TR) in the presence...

The addition of a single, unbalanced diffusion gradient to the steady-state free precession (SSFP) imaging sequence sensitizes the resulting signal to free diffusion. Unfortunately, the confounding influence of both longitudinal (T1) and transverse (T2) relaxation on the diffusion-weighted SSFP (dwSSFP) signal has made it difficult to quantitativel...

Introduction Recent work [1] has demonstrated the use of positive contrast labeling in tracking catheter-based paramagnetic markers, such as those used during endovascular interventions. This "white-marker" technique exploits the natural dipolar field surrounding paramagnetic markers by introducing a dephasing gradient on the slice-select axis to s...

T1 and T2 can be rapidly determined with a combination of multiangle spoiled gradient recalled echo (SPGR) and steady-state free precession (SSFP) imaging. Previously, we demonstrated a simple method for determining the set of SPGR and SSFP angles that provided greater T1 and T2 precision than a set of uniformly spaced angles. In this article a mor...

Diffusion Tensor Imaging (DTI) provides voxel-wise information related to the local diffusion anisotropy. Recent research efforts have centered around the use of this information to infer the direction of local fiber bundles. Calculation of the diffusion tensor and corresponding principle diffusion direction voxel-wise throughout the imaged volume...

A novel, fully 3D, high-resolution T(1) and T(2) relaxation time mapping method is presented. The method is based on steady-state imaging with T(1) and T(2) information derived from either spoiling or fully refocusing the transverse magnetization following each excitation pulse. T(1) is extracted from a pair of spoiled gradient recalled echo (SPGR)...