Dr. Aymeric Stamm Profile

Dr. Aymeric Stamm

at Boston Children's Hospital

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Author

Publications (2)

Proceedings Article | 20 March 2015 Paper

Multi-session complex averaging for high resolution high SNR 3T MR visualization of ex vivo hippocampus and insula

Aymeric Stamm, Jolene Singh, Benoit Scherrer, Onur Afacan, Simon Warfield

Proceedings Volume 9413, 941328 (2015) https://doi.org/10.1117/12.2082493

KEYWORDS: Signal to noise ratio, Spatial resolution, Visualization, Magnetic resonance imaging, Brain, Scanners, Image resolution, Phase shifts, Neuroimaging, Image quality

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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, current clinical MR imaging operates at the millimeter scale while these anatomical landmarks are organized into sub-millimeter structures. For instance, the hippocampus contains several layers, including the CA3-dentate network responsible for encoding events and experiences. To investigate whether memory loss is a result of injury or degradation of CA3/dentate, spatial resolution must exceed one hundred micron, isotropic, voxel size. Going from one millimeter voxels to one hundred micron voxels results in a 1000× signal loss, making the measured signal close to or even way below the precision of the receiving coils. Consequently, the signal magnitude that forms the structural images will be biased and noisy, which results in inaccurate contrast and less than optimal signal-to-noise ratio (SNR).

In this paper, we propose a strategy to perform high spatial resolution MR imaging of the hippocampus and insula with 3T scanners that enables accurate contrast (no systematic bias) and arbitrarily high SNR. This requires the collection of additional repeated measurements of the same image and a proper averaging of the k-space data in the complex domain. This comes at the cost of additional scan time, but long single-session scan times are not practical for obvious reasons. Hence, we also develop an approach to combine k-space data from multiple sessions, which enables the total scan time to be split into arbitrarily short sessions, where the patient is allowed to move and rest in-between. For validation, we hereby illustrate our multi-session complex averaging strategy by providing high spatial resolution 3T MR visualization of the hippocampus and insula using an ex-vivo specimen, so that the number of sessions and the duration of each session are not limited by physiological motion or poor subject compliance.

Proceedings Article | 18 March 2015 Paper

Optimized magnetic resonance diffusion protocol for ex-vivo whole human brain imaging with a clinical scanner

Benoit Scherrer, Onur Afacan, Aymeric Stamm, Jolene Singh, Simon Warfield

Proceedings Volume 9412, 94122U (2015) https://doi.org/10.1117/12.2082387

KEYWORDS: Brain, Diffusion, Tissues, Scanners, Neuroimaging, Distortion, Computer programming, Magnetic resonance imaging, Signal to noise ratio, In vivo imaging

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