The Breakfast and Science Seminar #8, held on 29th September, featured two presentations of CIBM research.
The first talk was given by Maria Giulia Preti and the second one by Daniel Wenz.
Decoupling of brain function from structure reveals regional behavioral specialization in humans
Maria Giulia Preti, Research Staff Scientist, CIBM SP EPFL-UNIGE SectionAbstract: How brain activity is shaped by the underlying brain structure is a complex question still lacking a clear answer. Advanced and non-invasive magnetic resonance imaging (MRI) techniques –such as functional and diffusion MRI– provides us with unique information about both functional and structural connectivity, respectively. However, the degree to which brain structure limits brain function is hard to quantify. Here, we introduced a structural-decoupling index, quantifying the structure-function relationship, its spatial distribution and its behavioral relevance in the healthy human brain. This index was defined within the framework of graph signal processing, where the structural connectome, obtained by diffusion MRI-based tractographic reconstruction of white matter fibers, serves as graph, while resting-state functional MRI activity recorded at each brain region represents a time- varying signal. The structural-decoupling index, defined at each area, indicates the degree to which the functional signal detaches from the anatomical backbone underneath. We discovered that the strength of function-structure coupling spatially varies throughout the healthy brain with a specific gradient going from areas related to lower-level functions (sensory, motor) to regions corresponding to higher-level ones (e.g., memory, reward, emotions). In particular, the activity in primary sensory regions (e.g., visual, auditory, motor) was more strongly coupled with brain structure, while higher-level regions, such as the parietal lobe, which is part of the executive control network, the temporal lobe, including the amygdala and language areas, and orbitofrontal lobes showed a functional activity more independent from the structure. The existence of this macroscale gradient of function-structure coupling, showed here for the first time, appears in line with evidence from other modalities, reporting a similar hierarchy for functional connectivity, temporal hierarchy and microstructural properties. The methodology opens new avenues of research to investigate differences of coupling over time or experimental conditions, and alterations due to neurological disease and disorder.
In Vivo Ultrahigh Field Magnetic Resonance Imaging Using Dielectrically-Shortened Dipole Antennas: The Impact of Quasi-Transverse Dielectric Modes on Transmit Field Distribution and Efficiency
Daniel Wenz,
Research Staff Scientist, CIBM MRI EPFL Section
Abstract: Dipole antennas play critical role in ultrahigh field magnetic resonance imaging (UHF-MRI). They provide high transmit field efficiency in deeper-located regions of human body and support curl-free current patterns which contribute to ultimate intrinsic signal-to- noise-ratio. However, straight dipole antennas are too long for most of MR applications (50 cm in free space). Rectangular dielectric blocks are often used to shorten dipole antennas in but their influence on antenna performance has not been thoroughly studied excluding the special case when perfect direct contact between the block and the subject was achieved. Yet, the lack of such contact is typically expected in clinical settings. This study demonstrates for the first time why different types of dielectrically-shortened dipole antennas can produce (in)efficient transmit field in an in vivo UHF-MRI experiment, and how antenna performance depends on rectangular block geometry, dielectric permittivity and subject/antenna physical separation. Two main types of quasi-transverse dielectric modes were found in different rectangular block geometry and interpreted as (MR-efficient) and (MR-inefficient) and their impact on in vivo MRI experiments involving human head, calf and wrist was investigated.
The monthly meet-up seminar series is a great environment to ask questions or to share insights on challenges and solutions. It’s also a good way to broaden and enrich professional networks.
The next Breakfast and Science Seminar #9 will be held on October 27th.