A Specialized Multi-Transmit Head Coil for High Resolution fMRI of the Human Visual Cortex at 7T

Sengupta, Shubharthi; Roebroeck, Alard; Kemper, Valentin G.; Poser, Benedikt A.; Zimmermann, Jan; Goebel, Rainer; Adriany, Gregor

doi:10.1371/journal.pone.0165418

Cited by 29 publications

(42 citation statements)

References 26 publications

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“…Data acquisition was performed on a whole-body Magnetom scanner (nominal field strength 7 T, Siemens Medical Systems, Erlangen, Germany) at the Maastricht Brain Imaging Centre, The Netherlands. All images were acquired using a surface coil (4 channel transmit, 16 channel receive) custom-made for high resolution fMRI of the human visual cortex [22]. Images with anatomical contrast were acquired using the 3D MP2RAGE sequence (TR = 5000 ms; TI1/TI2 = 900/2750 ms; TE = 2.55 ms; FA1/FA2 = 5 • /3 • ; FOV = 230 x 230 mm 2 ; matrix size = 384 x 384; slices = 240; voxel resolution = 0.6 mm isotropic; GRAPPA factor = 2, partial Fourier = 6/8; phase encoding direction anteriorposterior) [30].…”

Section: Mri Acquisitionmentioning

confidence: 99%

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Motion Displaces Population Receptive Fields in the Direction Opposite to Motion

Schneider

Marquardt

Sengupta

et al. 2019

Preprint

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Motion signals can bias the perceived position of visual stimuli. While the apparent position of a stimulus is biased in the direction of motion, electro-physiological studies have shown that the receptive field (RF) of neurons is shifted in the direction opposite to motion, at least in cats and macaque monkeys. In humans, it remains unclear how motion signals affect population RF (pRF) estimates. We addressed this question using psychophysical measurements and functional magnetic resonance imaging (fMRI) at 7 Tesla. We systematically varied two factors: the motion direction of the carrier pattern (inward, outward and flicker motion) and the contrast of the mapping stimulus (low and high stimulus contrast). We observed that while physical positions were identical across all conditions, presence of low-contrast motion, but not high-contrast motion, shifted perceived stimulus position in the direction of motion. Correspondingly, we found that pRF estimates in early visual cortex were shifted against the direction of motion for low-contrast stimuli but not for high stimulus contrast. We offer an explanation in form of a model for why apertures are perceptually shifted in the direction of motion even though pRFs shift in the opposite direction.Keywords visual neuroscience · position perception · population receptive fields · visual field projections 1 IntroductionAn important task of the visual system is to infer the location of objects in our environment. A wide range of psychophysical studies shows that motion signals lead to systematic localisation biases [1,2,3,4,5,6,7,8,9]. In illusions called motion-induced position shifts (MIPS), a coherent motion signal shifts the apparent location of a stimulus [1]. For example, when drifting Gabor patches are presented within a stationary aperture, the stimulus appears shifted in the direction of motion [2,6,7]. Such illusions raise the question how our visual system encodes location and how, in the case of MIPS, the apparent position shift can be explained. Furthermore, they offer a dissociation between the physical and the perceived position of a stimulus that can clarify which neuronal processes correspond to the apparent position of the stimulus. MOTION DISPLACES POPULATION RECEPTIVE FIELDSThe magnitude of MIPS is known to depend on spatial and temporal properties of the stimulus. MIPS are larger when the stimulus is shown for longer duration (tested up to 453 ms; [6]), presented at higher speed [6,9] or at higher eccentricities [10,6,9]. The magnitude of MIPS furthermore depends on spatial blurring of the presented stimulus. Blurred stimulus edges lead to larger perceptual displacements than sharp edges [4,9] and increasing the size of the Gaussian envelope of a Gabor stimulus yields larger MIPS [4]. Arnold et al. [7] have suggested that MIPS are driven by modulation of apparent contrast of the stimulus. Supporting this suggestion, they reported perceived position shifts when observers were asked to match the extremities of two contrast envelopes (low-contrast region),...

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Section: Mri Acquisitionmentioning

confidence: 99%

“…Yet advances in ultra-high field MRI [21] now allow for reliable recordings of human subjects at higher field strength which yield an improved signal-to-noise ratio. For the present study, we combined 7 Tesla [T] MRI with a custom-made surface coil optimized for high-resolution imaging of the human visual cortex [22] to obtain state-of-the-art recordings.…”

mentioning

confidence: 99%

Motion Displaces Population Receptive Fields in the Direction Opposite to Motion

Schneider

Marquardt

Sengupta

et al. 2019

Preprint

Self Cite

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“…Often, multiple mirrors and prisms have to be used, at the cost of reducing the participant's visual angle. Half volume multi‐transmit coils that are specialized for the visual cortex do not have this drawback, and have recently been shown as a promising research tool for functional imaging 21. The concept of an open half volume coil design22, 23, 24, 25, 26, 27 is used in this study to construct a setup that enables visual stimulation with a large visual angle.…”

Section: Designmentioning

confidence: 99%

Maximizing sensitivity for fast GABA edited spectroscopy in the visual cortex at 7 T

et al. 2018

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The combination of functional MRI (fMRI) and MRS is a promising approach to relate BOLD imaging to neuronal metabolism, especially at high field strength. However, typical scan times for GABA edited spectroscopy are of the order of 6‐30 min, which is long compared with functional changes observed with fMRI.The aim of this study is to reduce scan time and increase GABA sensitivity for edited spectroscopy in the human visual cortex, by enlarging the volume of activated tissue in the primary visual cortex. A dedicated setup at 7 T for combined fMRI and GABA MRS is developed. This setup consists of a half volume multi‐transmit coil with a large screen for visual cortex activation, two high density receive arrays and an optimized single‐voxel MEGA‐sLASER sequence with macromolecular suppression for signal acquisition.The coil setup performance as well as the GABA measurement speed, SNR, and stability were evaluated. A 2.2‐fold gain of the average SNR for GABA detection was obtained, as compared with a conventional 7 T setup. This was achieved by increasing the viewing angle of the participant with respect to the visual stimulus, thereby activating almost the entire primary visual cortex, allowing larger spectroscopy measurement volumes and resulting in an improved GABA SNR. Fewer than 16 signal averages, lasting 1 min 23 s in total, were needed for the GABA fit method to become stable, as demonstrated in three participants. The stability of the measurement setup was sufficient to detect GABA with an accuracy of 5%, as determined with a GABA phantom. In vivo, larger variations in GABA concentration are found: 14‐25%. Overall, the results bring functional GABA detections at a temporal resolution closer to the physiological time scale of BOLD cortex activation.

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“…Multi-transmit coils offer reduced power requirement to produce RF field and thus, a decreased SAR value [63][64][65][66][73][74][75][76][77][78].…”

Section: Type Of Rf Transmit Coilmentioning

confidence: 99%

Safety of Simultaneous Scalp or Intracranial EEG during MRI: A Review

Hawsawi

Carmichael²,

Lemieux

2017

Front. Phys.

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Understanding the brain and its activity is one of the great challenges of modern science. Normal brain activity (cognitive processes, etc.) has been extensively studied using electroencephalography (EEG) since the 1930's, in the form of spontaneous fluctuations in rhythms, and patterns, and in a more experimentally-driven approach in the form of event-related potentials (ERPs) allowing us to relate scalp voltage waveforms to brain states and behavior. The use of EEG recorded during functional magnetic resonance imaging (EEG-fMRI) is a more recent development that has become an important tool in clinical neuroscience, for example for the study of epileptic activity. The purpose of this review is to explore the magnetic resonance imaging safety aspects specifically associated with the use of scalp EEG and other brain-implanted electrodes such as intracranial EEG electrodes when they are subjected to the MRI environment. We provide a theoretical overview of the mechanisms at play specifically associated with the presence of EEG equipment connected to the subject in the MR environment, and of the resulting health hazards. This is followed by a survey of the literature on the safety of scalp or invasive EEG-fMRI data acquisitions across field strengths, with emphasis on the practical implications for the safe application of the techniques; in particular, we attempt to summarize the findings in terms of acquisition protocols when possible.

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A Specialized Multi-Transmit Head Coil for High Resolution fMRI of the Human Visual Cortex at 7T

Cited by 29 publications

References 26 publications

Motion Displaces Population Receptive Fields in the Direction Opposite to Motion

Motion Displaces Population Receptive Fields in the Direction Opposite to Motion

Maximizing sensitivity for fast GABA edited spectroscopy in the visual cortex at 7 T

Safety of Simultaneous Scalp or Intracranial EEG during MRI: A Review

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