Publications by authors named "Renat Yakupov"

12 Publications

  • Page 1 of 1

Detection of Cerebral Microbleeds With Venous Connection at 7 Tesla MRI.

Neurology 2021 Mar 2. Epub 2021 Mar 2.

Department of Neurology, Otto-von-Guericke University, Magdeburg, Germany.

Objective: Cerebral microbleeds (MBs) are a common finding in cerebral small vessel disease (CSVD) and Alzheimer's disease patients as well as in healthy elderly people, but their pathophysiology remains unclear. To investigate a possible role of veins in the development of MBs, we performed an exploratory study, assessing in vivo presence of MBs with a direct connection to a vein.

Methods: 7 Tesla (7 T) MRI was conducted and MBs were counted on Quantitative Susceptibility Mapping (QSM). A submillimeter resolution QSM-based venogram allowed identification of MBs with a direct spatial connection to a vein.

Results: 51 subjects (mean age [SD] 70.5[8.6] years, 37% females) participated in the study: 20 were patients with CSVD (cerebral amyloid angiopathy (CAA) with strictly lobar MBs (n=8), hypertensive arteriopathy (HA) with strictly deep MBs (n=5), and mixed lobar and deep MBs (n=7), 72.4 [6.1] years, 30% females) and 31 were healthy controls (69.4 [9.9] years, 42% females). In our cohort, we counted a total of 96 MBs with a venous connection, representing 14% of all detected MBs on 7T QSM. Most venous MBs (86%, n = 83) were observed in lobar locations and all of these were cortical. CAA subjects showed the highest ratio of venous to total MBs (19%) (HA=9%, mixed=18%, controls=5%) CONCLUSIONS: Our findings establish a link between cerebral MBs and the venous vasculature, pointing towards a possible contribution of veins to CSVD in general and to CAA in particular. Pathological studies are needed to confirm our observations.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1212/WNL.0000000000011790DOI Listing
March 2021

Triple visual hemifield maps in a case of optic chiasm hypoplasia.

Neuroimage 2020 07 8;215:116822. Epub 2020 Apr 8.

Department of Ophthalmology, Otto-von-Guericke University, Magdeburg, 39120, Germany; Center for Behavioral Brain Sciences, Magdeburg, 39106, Germany. Electronic address:

In humans, each hemisphere comprises an overlay of two visuotopic maps of the contralateral visual field, one from each eye. Is the capacity of the visual cortex limited to these two maps or are plastic mechanisms available to host more maps? We determined the cortical organization of the visual field maps in a rare individual with chiasma hypoplasia, where visual cortex plasticity is challenged to accommodate three hemifield maps. Using high-resolution fMRI at 7T and diffusion-weighted MRI at 3T, we found three hemiretinal inputs, instead of the normal two, to converge onto the left hemisphere. fMRI-based population receptive field mapping of the left V1-V3 at 3T revealed three superimposed hemifield representations in the left visual cortex, i.e. two representations of opposing visual hemifields from the left eye and one right hemifield representation from the right eye. We conclude that developmental plasticity including the re-wiring of local intra- and cortico-cortical connections is pivotal to support the coexistence and functioning of three hemifield maps within one hemisphere.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.neuroimage.2020.116822DOI Listing
July 2020

Dynamic 2D self-phase-map Nyquist ghost correction for simultaneous multi-slice echo planar imaging.

Magn Reson Med 2018 10 9;80(4):1577-1587. Epub 2018 Feb 9.

Department of Biomedical Magnetic Resonance, Otto-von-Guericke University Magdeburg, Germany.

Purpose: To develop a reconstruction pipeline that intrinsically accounts for both simultaneous multislice echo planar imaging (SMS-EPI) reconstruction and dynamic slice-specific Nyquist ghosting correction in time-series data.

Methods: After 1D slice-group average phase correction, the separate polarity (i.e., even and odd echoes) SMS-EPI data were unaliased by slice GeneRalized Autocalibrating Partial Parallel Acquisition. Both the slice-unaliased even and odd echoes were jointly reconstructed using a model-based framework, extended for SMS-EPI reconstruction that estimates a 2D self-phase map, corrects dynamic slice-specific phase errors, and combines data from all coils and echoes to obtain the final images.

Results: The percentage ghost-to-signal ratios (%GSRs) and its temporal variations for MB3R 2 with a field of view/4 shift in a human brain obtained by the proposed dynamic 2D and standard 1D phase corrections were 1.37 ± 0.11 and 2.66 ± 0.16, respectively. Even with a large regularization parameter λ applied in the proposed reconstruction, the smoothing effect in fMRI activation maps was comparable to a very small Gaussian kernel size 1 × 1 × 1 mm .

Conclusion: The proposed reconstruction pipeline reduced slice-specific phase errors in SMS-EPI, resulting in reduction of GSR. It is applicable for functional MRI studies because the smoothing effect caused by the regularization parameter selection can be minimal in a blood-oxygen-level-dependent activation map.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/mrm.27123DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6085172PMC
October 2018

Ultra high-field (7 T) multi-resolution fMRI data for orientation decoding in visual cortex.

Data Brief 2017 Aug 24;13:219-222. Epub 2017 May 24.

Center for Behavioral Brain Sciences, Universitätsplatz 2, 39016 Magdeburg, Germany.

Multivariate pattern classification methods have been successfully applied to decode orientation of visual grating stimuli from BOLD fMRI activity recorded in human visual cortex (Kamitani and Tong, 2005; Haynes and Rees, 2005) [12], [10]. Though there has been extensive research investigating the true spatial scale of the orientation specific signals (Op de Beeck, 2010; Swisher et al., 2010; Alink et al., 2013; Freeman et al., 2011, 2013) [2], [15], [1], [4], [5], it remained inconclusive what spatial acquisition resolution is required, or is optimal, for decoding analyses. The research article entitled "The effect of acquisition resolution on orientation decoding from V1 BOLD fMRI at 7 T" Sengupta et al. (2017) [14] studied the effect of spatial acquisition resolution and also analyzed the strength and spatial scale of orientation discriminating signals. In this article, for the first time, we present empirical ultra high-field fMRI data, obtained as a part of the aforementioned study, which were recorded at four spatial resolutions (0.8 mm, 1.4 mm, 2 mm, and 3 mm isotropic voxel size) for orientation decoding in visual cortex. The dataset is compliant with the (Brain Imaging Data Structure) format, and freely available from the portal (dataset accession number: http://openfmri.org/dataset/ds000113c ds000113c).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.dib.2017.05.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5459569PMC
August 2017

False fMRI activation after motion correction.

Hum Brain Mapp 2017 09 5;38(9):4497-4510. Epub 2017 Jun 5.

Biomedical Magnetic Resonance, Otto-von-Guericke University, Magdeburg, Germany.

Motion correction of echo-planar imaging (EPI) data used in functional MRI (fMRI) is an essential preprocessing step performed prior to statistical analysis. At ultra-high resolution fMRI, current requirements regarding translational and rotational motion may no longer be acceptable. This prompts the need for a systematic investigation of the effects of motion correction procedures with in vivo fMRI data. Here we systematically evaluated the effect of retrospective motion correction with freely available fMRI analysis software packages (FSL, AFNI, and SPM) on activation maps using fMRI data acquired with prospective motion detection, to identify and quantify confounding effects of retrospective motion correction, and to evaluate its dependence on spatial resolution and motion correction algorithms. Brain activation maps were obtained for two different resolutions, an ultrahigh, that is, 0.65 mm , and a more widely used 2.0 mm isotropic resolutions at 7 T. The EPI data were acquired using simultaneous non-image-based optical moiré phase tracking (MPT) of physical motion. The results showed that image-based motion detection, performed by SPM8 software package, may be erroneous in high-field fMRI data with partial brain coverage and can introduce spurious motion leading to false-positive and false-negative activation. Further analyses demonstrated that limited acquisition field of view has the dominant influence on the effect. Hum Brain Mapp 38:4497-4510, 2017. © 2017 Wiley Periodicals, Inc.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/hbm.23677DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5553448PMC
September 2017

T-weighted in vivo human whole brain MRI dataset with an ultrahigh isotropic resolution of 250 μm.

Sci Data 2017 03 14;4:170032. Epub 2017 Mar 14.

Department of Biomedical Magnetic Resonance, Otto-von-Guericke University, 39120 Magdeburg, Germany.

We present an ultrahigh resolution in vivo human brain magnetic resonance imaging (MRI) dataset. It consists of T-weighted whole brain anatomical data acquired at 7 Tesla with a nominal isotropic resolution of 250 μm of a single young healthy Caucasian subject and was recorded using prospective motion correction. The raw data amounts to approximately 1.2 TB and was acquired in eight hours total scan time. The resolution of this dataset is far beyond any previously published in vivo structural whole brain dataset. Its potential use is to build an in vivo MR brain atlas. Methods for image reconstruction and image restoration can be improved as the raw data is made available. Pre-processing and segmentation procedures can possibly be enhanced for high magnetic field strength and ultrahigh resolution data. Furthermore, potential resolution induced changes in quantitative data analysis can be assessed, e.g., cortical thickness or volumetric measures, as high quality images with an isotropic resolution of 1 and 0.5 mm of the same subject are included in the repository as well.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/sdata.2017.32DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5349250PMC
March 2017

The effect of acquisition resolution on orientation decoding from V1 BOLD fMRI at 7T.

Neuroimage 2017 03 4;148:64-76. Epub 2017 Jan 4.

Center for Behavioral Brain Sciences, Universitätsplatz 2, 39016 Magdeburg, Germany; Psychoinformatics Lab, Institute of Psychology II, Otto-von-Guericke University, Universitätsplatz 2, 39016 Magdeburg, Germany.

A decade after it was shown that the orientation of visual grating stimuli can be decoded from human visual cortex activity by means of multivariate pattern classification of BOLD fMRI data, numerous studies have investigated which aspects of neuronal activity are reflected in BOLD response patterns and are accessible for decoding. However, it remains inconclusive what the effect of acquisition resolution on BOLD fMRI decoding analyses is. The present study is the first to provide empirical ultra high-field fMRI data recorded at four spatial resolutions (0.8mm, 1.4mm, 2mm, and 3mm isotropic voxel size) on this topic - in order to test hypotheses on the strength and spatial scale of orientation discriminating signals. We present detailed analysis, in line with predictions from previous simulation studies, about how the performance of orientation decoding varies with different acquisition resolutions. Moreover, we also examine different spatial filtering procedures and its effects on orientation decoding. Here we show that higher-resolution scans with subsequent down-sampling or low-pass filtering yield no benefit over scans natively recorded in the corresponding lower resolution regarding decoding accuracy. The orientation-related signal in the BOLD fMRI data is spatially broadband in nature, includes both high spatial frequency components, as well as large-scale biases previously proposed in the literature. Moreover, we found above chance-level contribution from large draining veins to orientation decoding. Acquired raw data were publicly released to facilitate further investigation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.neuroimage.2016.12.040DOI Listing
March 2017

Lower cognitive reserve in the aging human immunodeficiency virus-infected brain.

Neurobiol Aging 2013 Apr 15;34(4):1240-53. Epub 2012 Nov 15.

Department of Medicine, Division of Neurology, John A. Burns School of Medicine, University of Hawai'i at Manoa, and the Queen's Medical Center, Honolulu, HI 96813, USA.

More HIV-infected individuals are living longer; however, how their brain function is affected by aging is not well understood. One hundred twenty-two men (56 seronegative control [SN] subjects, 37 HIV subjects with normal cognition [HIV+NC], 29 with HIV-associated neurocognitive disorder [HAND]) performed neuropsychological tests and had acceptable functional magnetic resonance imaging scans at 3 Tesla during tasks with increasing attentional load. With older age, SN and HIV+NC subjects showed increased activation in the left posterior (reserve, "bottom-up") attention network for low attentional-load tasks, and further increased activation in the left posterior and anterior ("top-down") attention network on intermediate (HIV+NC only) and high attentional-load tasks. HAND subjects had only age-dependent decreases in activation. Age-dependent changes in brain activation differed between the 3 groups, primarily in the left frontal regions (despite similar brain atrophy). HIV and aging act synergistically or interactively to exacerbate brain activation abnormalities in different brain regions, suggestive of a neuroadaptive mechanism in the attention network to compensate for declined neural efficiency. While the SN and HIV+NC subjects compensated for their declining attention with age by using reserve and "top-down" attentional networks, older HAND subjects were unable to compensate which resulted in cognitive decline.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.neurobiolaging.2012.10.012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3984923PMC
April 2013

Declined neural efficiency in cognitively stable human immunodeficiency virus patients.

Ann Neurol 2009 Mar;65(3):316-25

Department of Medicine, University of Hawaii at Manoa, and the Queen's Medical Center, Honolulu, HI 96813, USA.

Objective: To determine whether brain activation changes in clinically and neurocognitively normal human immunodeficiency virus (HIV)-infected and in HIV-seronegative control (SN) participants over a 1-year period.

Methods: Functional magnetic resonance imaging (fMRI) was performed in 32 SN and 31 HIV patients (all with stable combination antiretroviral treatment) at baseline and after 1 year. Each participant performed a set of visual attention tasks with increasing attentional load (from tracking two, three, or four balls). All HIV and SN participants had normal neuropsychological function at both examinations.

Results: Over 1 year, HIV patients showed no change in their neurocognitive status or in task performance during fMRI. However, HIV patients showed significant 1-year increases in fMRI signals in the prefrontal and posterior parietal cortices for the more difficult tasks, whereas SN control participants showed only decreases in brain activation in these regions. This resulted in significant interactions between HIV status and time of study in left insula, left parietal, left temporal, and several frontal regions (left and right middle frontal gyrus, and anterior cingulate).

Interpretation: Because fMRI task performance remained unchanged in both groups, the HIV patients appeared to maintain performance by increasing usage of the attention network, whereas the control participants reduced usage of the attention network after 1 year. These findings suggest improved efficiency or a practice effect in the SN participants but declined efficiency of the neural substrate in HIV patients, possibly because of ongoing brain injury associated with the HIV infection, despite their apparent stable clinical course.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/ana.21594DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2734503PMC
March 2009

CT angiography with gadolinium-based contrast media.

Acad Radiol 2006 Aug;13(8):979-85

Department of Radiology, State University of New York at Stony Brook, University Hospital, HSC Level IV Room 120, Stony Brook, NY 11794, USA.

Rationale And Objectives: To evaluate the potential use of gadolinium (Gd)-based contrast media, especially that of Gadovist, a 1-molar Gd medium, in computed tomography (CT) and compare our findings with standard iodinated contrast media.

Material And Methods: Using a live rabbit and an acrylic CT body phantom for comparative CT imaging of Gd- and I-based media. The images were acquired at 80, 100, and 120 kVp, using fixed standard beam filtration. The phantom study used serial dilutions of the Magnevist and Ultravist 300 (2.4-molar I), whereas the animal study used different volumes of Gadovist, Magnevist (0.5 molar Gd), and Ultravist administered intravenously.

Results: At 80 kVp for the same injection volumes of Gadovist and Ultravist, the image contrast enhancement of the aorta with Gadovist was 40% lower than that of Ultravist. In the phantom studies, however, for the same kVp settings the CT image contrast was up to fourfold higher for Gd compared with iodine when comparing the same molar concentrations of the two elements in the solutions.

Conclusion: These results indicate a potential of Gd-based media for clinical CT angiography and provide incentive for further investigation of this subject.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.acra.2006.03.019DOI Listing
August 2006

Adaptation of the attention network in human immunodeficiency virus brain injury.

Ann Neurol 2004 Aug;56(2):259-72

Medical Department, Brookhaven National Laboratory, Upton, NY, USA.

Human immunodeficiency virus (HIV)-positive patients commonly have attention and concentration problems. However, it remains unclear how HIV infection affects the attention network. Therefore, blood oxygenation level dependent functional magnetic resonance imaging (BOLD-fMRI) was performed in 36 subjects (18 HIV and 18 seronegative [SN] controls) during a set of visual attention tasks with increasing levels of attentional load. Compared with SN controls, HIV subjects showed similar task performance (accuracies and reaction times) but decreased activation in the normal visual attention network (dorsal parietal, bilateral prefrontal, and cerebellar regions) and increased activation in adjacent or contralateral brain regions. Cognitive performance (assessed with NPZ-8), CD4, and viral load all correlated with activated BOLD signals in brain regions that activated more in HIV subjects. Furthermore, HIV subjects activated more than SN controls in brain regions that showed load-dependent increase in activation (right prefrontal and right parietal regions) but less in regions that showed a saturation effect with increasing load. These findings suggest that HIV-associated brain injury leads to reduced efficiency in the normal attention network, thus requiring reorganization and increased usage of neural reserves to maintain performance during attention-requiring tasks. Exceeding the brain reserve capacity may lead to attention deficits and cognitive impairment in HIV patients.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/ana.20190DOI Listing
August 2004