Improving BOLD sensitivity with real-time multi-echo echo-planar imaging - Towards a cleaner neurofeedback signal

Real-time functional magnetic resonance imaging (rtfMRI) suffers from known issues related to T2*-weighted single-echo echo-planar imaging (EPI). These include image dropout in areas with increased local magnetic susceptibility susceptibility gradients; suboptimal whole-brain blood oxygen level-dependent (BOLD) contrast due to average T2*-weighting; and confounders like subject motion and physiology. During fMRI neurofeedback a metric calculated from real-time brain activity is presented visually to the subject in the scanner. To prevent sham feedback, new methods should focus on improving BOLD signal quality in real-time. In this work, presented as a poster at the 11th annual meeting of the ISMRM Benelux chapter (17 January 2019), we present our work on real-time multi-echo fMRI and its usefulness in increasing the temporal signal-to-noise ratio (tSNR) of rtfMRI

Neu\u3csup\u3e3\u3c/sup\u3eCA-RT:a framework for real-time fMRI analysis

\u3cp\u3eReal-time functional magnetic resonance imaging (rtfMRI) allows visualisation of ongoing brain activity of the subject in the scanner. Denoising algorithms aim to rid acquired data of confounding effects, enhancing the blood oxygenation level-dependent (BOLD) signal. Further image processing and analysis methods, like general linear models (GLM) or multivariate analysis, then present application-specific information to the researcher. These processes are typically applied to regions of interest but, increasingly, rtfMRI techniques extract and classify whole brain functional networks and dynamics as correlates for brain states or behaviour, particularly in neuropsychiatric and neurocognitive disorders. We present Neu\u3csup\u3e3\u3c/sup\u3eCA-RT: a Matlab-based rtfMRI analysis framework aiming to advance scientific knowledge on real-time cognitive brain activity and to promote its translation into clinical practice. Design considerations are listed based on reviewing existing rtfMRI approaches. The toolbox integrates established SPM preprocessing routines, real-time GLM mapping of fMRI data to a basis set of spatial brain networks, correlation of activity with 50 behavioural profiles from the BrainMap database, and an intuitive user interface. The toolbox is demonstrated in a task-based experiment where a subject executes visual, auditory and motor tasks inside a scanner. In three out of four experiments, resulting behavioural profiles agreed with the expected brain state.\u3c/p\u3

\u3csup\u3e89\u3c/sup\u3eZr- and Fe-labeled polymeric micelles for dual modality PET and T\u3csub\u3e1\u3c/sub\u3e-weighted MR imaging

\u3cp\u3eIn this study, a new \u3csup\u3e89\u3c/sup\u3eZr- and Fe\u3csup\u3e3+\u3c/sup\u3e-labeled micelle nanoplatform (\u3csup\u3e89\u3c/sup\u3eZr/Fe-DFO-micelles) for dual modality position emission tomography/magnetic resonance (PET/MR) imaging is investigated. The nanoplatform consists of self-assembling amphiphilic diblock copolymers that are functionalized with \u3csup\u3e89\u3c/sup\u3eZr-deferoxamine (\u3csup\u3e89\u3c/sup\u3eZr-DFO) and Fe\u3csup\u3e3+\u3c/sup\u3e-deferoxamine (Fe-DFO) for PET and MR purposes, respectively. \u3csup\u3e89\u3c/sup\u3eZr displays favorable PET imaging characteristics with a 3.3 d half-life suitable for imaging long circulating nanoparticles. The nanoparticles are modified with Fe-DFO as MR T\u3csub\u3e1\u3c/sub\u3e-contrast label instead of commonly used Gd\u3csup\u3e3+\u3c/sup\u3e-based chelates. As these micelles are cleared by liver and spleen, any long term Gd- related toxicity such as nephrogenic systemic fibrosis is avoided. As a proof of concept, an in vivo PET/MR study in mice is presented showing tumor targeting of \u3csup\u3e89\u3c/sup\u3eZr/Fe-DFO-micelles through the enhanced permeability and retention (EPR) effect of tumors, yielding high tumor-to-blood (10.3 ± 3.6) and tumor-to-muscle (15.3 ± 8.1) ratios at 48 h post injection. In vivo PET images clearly delineate the tumor tissue and show good correspondence with ex vivo biodistribution results. In vivo magnetic resonance imaging (MRI) allows visualization of the intratumoral distribution of the \u3csup\u3e89\u3c/sup\u3eZr/Fe-DFO-micelles at high resolution. In summary, the \u3csup\u3e89\u3c/sup\u3eZr/Fe-DFO-micelle nanoparticulate platform allows EPR-based tumor PET/MRI, and, furthermore, holds great potential for PET/MR image guided drug delivery.\u3c/p\u3

Functional network abnormalities consistent with behavioral profile in autism spectrum disorder

\u3cp\u3eAutism spectrum disorder (ASD) is a neurodevelopmental disorder in which the severity of symptoms varies over subjects. The iCAPs model (innovation-driven co-activation patterns) is a recently developed spatio-temporal model to describe fMRI data. In this study, the iCAPs model was employed to find functional imaging biomarkers for ASD in resting-state fMRI data. MRI data from 125 ASD patients and 243 healthy controls was selected from the online ABIDE data repository. Following standard fMRI preprocessing steps, the iCAP patterns were fitted to the data to obtain network time series. Furthermore, specific combinations of iCAPs were mapped to behavioral domain time series. To quantify to which extent the time series contribute to the fMRI dynamics, their (temporal) standard deviation was calculated and compared between patients and controls. Abnormalities were found in networks involving subcortical and limbic areas and default mode network regions. When mapping the network dynamics to behavioral domain time series, abnormalities were found in emotional and visual behavioral subdomains, and within the ASD spectrum were more pronounced in subjects with autism compared to Asperger's syndrome. Also a trend towards impairment in networks facilitating social cognition was found. The functional imaging abnormalities are consistent with the behavioral impairments typical for ASD.\u3c/p\u3

Relaxometric studies of gadolinium-functionalized perfluorocarbon nanoparticles for MR imaging

Fluorine MRI (19F MRI) is receiving an increasing attention as a viable alternative to proton-based MRI (1H MRI) for dedicated application in molecular imaging. The 19F nucleus has a high gyromagnetic ratio, a 100% natural abundance and is furthermore hardly present in human tissues allowing for hot spot MR imaging. The applicability of 19F MRI as a molecular and cellular imaging technique has been exploited, ranging from cell tracking to detection and imaging of tumors in preclinical studies. In addition to applications, developing new contrast materials with improved relaxation properties has also been a core research topic in the field, since the inherently low longitudinal relaxation rates of perfluorocarbon compounds result in relatively low imaging efficiency. Borrowed from 1H MRI, the incorporation of lanthanides, specifically Gd(III) complexes, as signal modulating ingredients in the nanoparticle formulation has emerged as a promising approach to improvement of the fluorine signal. Three different perfluorocarbon emulsions were investigated at five different magnetic field strengths. Perfluoro-15-crown-5-ether was used as the core material and Gd(III)DOTA-DSPE, Gd(III)DOTA-C6-DSPE and Gd(III)DTPA-BSA as the relaxation altering components. While Gd(III)DOTA-DSPE and Gd(III)DOTA-C6-DSPE were favorable constructs for 1H NMR, Gd(III)DTPA-BSA showed the strongest increase in 19FR1. These results show the potential of the use of paramagnetic lipids to increase 19FR1 at clinical field strengths (1.5-3T). At higher field strengths (6.3-14T), gadolinium does not lead to an increase in 19FR1 compared with emulsions without gadolinium, but leads to an significant increase in 19FR2. Our data therefore suggest that the most favorable situation for fluorine measurements is at high magnetic fields without the inclusion of gadolinium constructs. Copyright © 2014 John Wiley & Sons, Ltd