Aymeric Stamm

Aymeric Stamm
Boston Children's Hospital, Harvard Medical School · Radiology

PhD

About

45
Publications
3,393
Reads
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426
Citations
Additional affiliations
August 2013 - present
Boston Children's Hospital, Harvard Medical School
Position
  • PostDoc Position
April 2013 - June 2013
INRIA Rennes-Bretagne Atlantique
Position
  • PhD Student
November 2012 - March 2013
Centre Hospitalier Universitaire de Rennes
Position
  • Statistician

Publications

Publications (45)
Article
Functional data are smooth, often continuous, random curves, which can be seen as an extreme case of multivariate data with infinite dimensionality. Just as component‐wise inference for multivariate data naturally performs feature selection, subset‐wise inference for functional data performs domain selection. In this paper, we present a unified tes...
Article
Networks are a natural way of representing the human brain for studying its structure and function and, as such, have been extensively used. In this framework, case–control studies for understanding autism pertain to comparing samples of healthy and autistic brain networks. In order to understand the biological mechanisms involved in the pathology,...
Article
Full-text available
In the framework of Object Oriented Data Analysis, a permutation approach to the two-sample testing problem for network-valued data is proposed. In detail, the present framework proceeds in four steps: (i) matrix representation of the networks, (ii) computation of the matrix of pairwise (inter-point) distances, (iii) computation of test statistics...
Chapter
Full-text available
The single diffusion tensor model for mapping the brain white matter microstructure has long been criticized as providing sensitive yet non-specific clinical biomarkers for neurodegenerative diseases because (i) voxels in diffusion images actually contain more than one homogeneous tissue population and (ii) diffusion in a single homogeneous tissue...
Article
This work evaluates the predictive ability of a novel personalized computational tool for simulating the growth of brain tumours using the neuroimaging data collected during one clinical case study. The mathematical model consists of an evolutionary fourth-order partial differential equation with degenerate motility, in which the spreading dynamics...
Article
We address the problem of finite-sample null hypothesis significance testing on the mean element of a random variable that takes value in a generic separable Hilbert space. For this purpose, we propose a (re)definition of Hotelling's T² that naturally expands to any separable Hilbert space that we further embed within a permutation inferential appr...
Article
Introduction: Neurological manifestations in Tuberous Sclerosis Complex (TSC) are highly variable. Diffusion tensor imaging (DTI) may reflect the neurological disease burden. We analyzed the association of autism spectrum disorder (ASD), intellectual disability (ID) and epilepsy with callosal DTI metrics in subjects with and without TSC. Methods:...
Article
Background and purpose: Segmentation of human brain structures is crucial for the volumetric quantification of brain disease. Advances in algorithmic approaches have led to automated techniques that save time compared to interactive methods. Recently, the utility and accuracy of template library fusion algorithms, such as Local MAP PSTAPLE (PSTAPL...
Chapter
While Hotelling’s T² statistic is traditionally defined as the Mahalanobis distance between the sample mean and the true mean induced by the inverse of the sample covariance matrix, we hereby propose an alternative definition which allows a unifying and coherent definition of Hotelling’s T² statistic in any Hilbert space independently from its dime...
Conference Paper
Full-text available
Diffusion MRI is a key in-vivo non invasive imaging capability that can probe the microstructure of the brain. However, its limited resolution requires complex voxelwise generative models of the diffusion. Diffusion Compartment (DC) models divide the voxel into smaller compartments in which diffusion is homogeneous. We present a comprehensive frame...
Article
Full-text available
Background Numerous bone age estimation techniques exist, but little is known about what methods radiologists use in clinical practice. Objective To determine which methods pediatric radiologists use to assess bone age in children, and their confidence in these methods. Materials and methods Society for Pediatric Radiology (SPR) members were invite...
Conference Paper
Full-text available
Multi-compartment diffusion models (MCM) are increasingly used to characterize the brain white matter microstructure from diffusion MRI. We address the problem of interpolation and averaging of MCM images as a simplification problem based on spectral clustering. As a core part of the framework, we propose novel solutions for the averaging of MCM co...
Conference Paper
Magnetic resonance (MR) imaging provides a unique in-vivo capability of visualizing tissue in the human brain non-invasively, which has tremendously improved patient care over the past decades. However, there are still prominent artifacts, such as intensity inhomogeneities due to the use of an array of receiving coils (RC) to measure the MR signal...
Article
Objective: To assess the extent and evolution of tissue abnormality of tubers, perituber tissue, and normal-appearing white matter (NAWM) in patients with tuberous sclerosis complex using serial diffusion tensor imaging. Methods: We applied automatic segmentation based on a combined global-local intensity mixture model of 3T structural and 35 di...
Article
Diffusion tensor imaging (DTI) tractography reconstruction of white matter pathways can help guide brain tumor resection. However, DTI tracts are complex mathematical objects and the validity of tractography-derived information in clinical settings has yet to be fully established. To address this issue, we initiated the DTI Challenge, an internatio...
Article
The hippocampus and the insula are responsible for episodic memory formation and retrieval. Hence, visualization of the cytoarchitecture of such structures is of primary importance to understand the underpinnings of conscious experience. Magnetic Resonance Imaging (MRI) offers an opportunity to non-invasively image these crucial structures. However...
Article
Diffusion-weighted magnetic resonance imaging (DW-MRI) provides a novel insight into the brain to facilitate our understanding of the brain connectivity and microstructure. While in-vivo DW-MRI enables imaging of living patients and longitudinal studies of brain changes, post-mortem ex-vivo DW-MRI has numerous advantages. Ex-vivo imaging benefits f...
Patent
Full-text available
Method to extract a diffusion direction from DW-MR signals, in which a magnetic field gradient qi is applied to a body part, a magnetic resonance signal Si is measured and a diffusion direction μj is determined, wherein for a predetermined positive number m of diffusion direction(s) μj, the signals Si are linked to the probability density function...
Article
Full-text available
We present a pipeline to reconstruct the corticospinal tract (CST) that connects the spinal cord to the motor cortex. The proposed method combines a new white matter microstructure model coined Diffusion Directions Imaging and a new tractography algorithm based on a particle filter adapted for approximating multi-modal distributions. In this paper,...
Conference Paper
Full-text available
Analytic multi-compartment models have gained a tremendous popularity in the recent literature for studying the brain white matter microstructure from diffusion MRI. This class of models require the number of compartments to be known in advance. In the white matter however, several non-collinear bundles of axons, termed fascicles, often coexist in...
Conference Paper
PURPOSE Semantic dementia (SD) is a rare subtype of frontotemporal lobar degeneration. Structural MRI usually shows temporal lobe atrophy predominantly on the left side but it could be insufficiency. Fluorodeoxyglucose-positron emission tomography (FDG-PET) is known to improve the diagnostic accuracy. Nevertheless, Arterial spin labeling magnetic r...
Article
Full-text available
The objective of this thesis is to provide a complete pipeline that achieves an accurate reconstruction of the white matter fascicles using clinical diffusion images characterized by a low angular resolution. This involves (i) a diffusion model inferred in each voxel from the diffusion images and (ii) a tractography algorithm fed with these local m...
Article
Full-text available
In this work, we present a pipeline to reconstruct the corti-cospinal tract (CST) that connects the spinal cord to the motor cortex. The proposed method combines a new geometry-based multi-compartment diffusion model coined Diffusion Directions Imaging and a new adaptive multi-modal particle filter for tractography. The DTI Tractography challenge p...
Article
Full-text available
Children affected by Specific Language Impairment (SLI) fail to develop a normal language capability. To date, the etiology of SLI remains largely unknown. It induces difficulties with oral language which cannot be directly attributed to intellectual deficit or other developmental delay. Whereas previous studies on SLI focused on the psychological...
Article
Full-text available
We provide a generalization of Hotelling’s Theorem that enables inference (i) for the mean vector of a multivariate normal population and (ii) for the comparison of the mean vectors of two multivariate normal populations, when the number $p$ of components is larger than the number $n$ of sample units and the (common) covariance matrix is unknown. I...
Conference Paper
Full-text available
Particle filtering has recently been introduced to perform probabilistic tractography in conjunction with DTI and Q-Ball models to estimate the diffusion information. Particle filters are particularly well adapted to the tractography problem as they offer a way to approximate a probability distribution over all paths originated from a specified vox...
Article
Background and purpose: Endovascular mechanical thrombectomy is emerging as a promising therapeutic approach for acute ischemic stroke. This study was aimed at identifying factors influencing outcomes after thrombectomy with a Solitaire stent device. Materials and methods: Forty-five consecutive patients treated with thrombectomy using Solitaire...
Article
Background: Nontraumatic impaired consciousness is a common issue in emergency departments with a serious but widely variable prognosis. Study objectives: The aim of this prospective study was to evaluate the ability of systematic combined noncontrast computed tomography (NCCT)/computed tomography angiography (CTA) imaging, firstly to provide a...
Article
Purpose: To determine the minimal optimal functional arterial spin labeling (fASL) sequence duration allowing steady and reproducible motor activation mapping. Materials and methods: Three magnetic resonance imaging (MRI) sessions including fASL and blood oxygenation level-dependent (BOLD) functional MRI (fMRI) sequences were performed on 12 hea...
Conference Paper
Diffusion imaging, through the study of water diffusion, allows for the characterization of brain white matter, both at the population and individual level. In recent years, it has been employed to detect brain abnormalities in patients suffering from a disease, e.g., from multiple sclerosis (MS). State-of-the-art methods usually utilize a database...
Article
Diffusion MRI is a tool of choice for the analysis of the brain white matter fiber pathways. When translated to clinics, the short acquisition time leads to low angular resolution diffusion (LARD) images. Fiber pathways are then inferred assuming Gaussian diffusion (a.k.a. DTI) that provides one fiber orientation per voxel. In the past decade, rece...
Conference Paper
Full-text available
In this paper, we build upon a new model, describing the random motion of water molecules in fibrous tissues, to develop a mul-tifiber deterministic tractography algorithm. We apply this algorithm to track the corticospinal tract of the human brain, in both controls and patients with tumors.
Article
Full-text available
In this paper, we propose to compare three diffusion mod-els to track the portion of the corticospinal tract dedicated to the hand motor function (called hand motor fibers hereafter), using diffusion, func-tional and anatomical MRI. The clinical diffusion data have few gradient directions and low b-values. In this context, we show that a newly intr...
Article
Full-text available
Diffusion magnetic resonance imaging (dMRI) is the reference \emph{in vivo} modality to study the connectivity of the brain white matter. Images obtained through dMRI are indeed related to the probability density function (pdf) of displacement of water molecules subject to restricted diffusion in the brain white matter. The knowledge of this diffus...
Article
Functional arterial spin labeling (fASL) is an innovative biomarker of neuronal activation that allows direct and absolute quantification of activation-related CBF and is less sensitive to venous contamination than BOLD fMRI. This study evaluated fASL for motor activation mapping in comparison with BOLD fMRI in terms of involved anatomical area loc...
Article
Full-text available
We present a new result that enables inference for the mean vector of a multivariate normal random variable when the number p of its components is far larger than the number n of sample units and the covariance structure is completely unknown. The result turns out to be a useful tool for the inferential analysis (e.i. confidence region and hypothes...

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