Mapping fine-scale anatomy of gray matter, white matter, and trigeminal-root region applying spherical deconvolution to high-resolution 7-T diffusion MRI.

OBJECTIVES: We assessed the use of high-resolution ultra-high-field diffusion magnetic resonance imaging (dMRI) to determine neuronal fiber orientation density functions (fODFs) throughout the human brain, including gray matter (GM), white matter (WM), and small intertwined structures in the cerebellopontine region. MATERIALS AND METHODS: We acquired 7-T whole-brain dMRI data of 23 volunteers with 1.4-mm isotropic resolution; fODFs were estimated using constrained spherical deconvolution. RESULTS: High-resolution fODFs enabled a detailed view of the intravoxel distributions of fiber populations in the whole brain. In the brainstem region, the fODF of the extra- and intrapontine parts of the trigeminus could be resolved. Intrapontine trigeminal fiber populations were crossed in a network-like fashion by fiber populations of the surrounding cerebellopontine tracts. In cortical GM, additional evidence was found that in parts of primary somatosensory cortex, fODFs seem to be oriented less perpendicular to the cortical surface than in GM of motor, premotor, and secondary somatosensory cortices. CONCLUSION: With 7-T MRI being introduced into clinical routine, high-resolution dMRI and derived measures such as fODFs can serve to characterize fine-scale anatomic structures as a prerequisite to detecting pathologies in GM and small or intertwined WM tracts.

Localizing the human primary auditory cortex in vivo using structural MRI.

Currently there are no routine methods to delineate the primary auditory cortex (PAC) of humans in vivo. Due to the large differences in the location of the PAC between subjects, labels derived from post-mortem brains may be inaccurate when applied to different samples of in vivo brains. Recent magnetic resonance (MR) imaging studies suggested that MR-tissue properties can be used to define the location of the PAC region in vivo. The basis for such an approach is that the PAC region is more strongly myelinated than the secondary areas. We developed a fully automatic method to identify the PAC in conventional anatomical data using a combination of two complementary MR contrasts, i.e., T1 and T2, at 3T with 0.7mm isotropic resolution. Our algorithm maps the anatomical MR data to reconstructed cortical surfaces and uses a classification approach to create an artificial contrast that is highly sensitive to the effects of an increased myelination of the cortex. Consistent with the location of the PAC defined in post-mortem brains, we found a compact region on the medial two thirds of Heschl's gyrus in both hemispheres of all 39 subjects. With further improvements in signal-to-noise ratio of the anatomical data and manual correction of segmentation errors, the results suggest that the primary auditory cortex can be defined in the living brain of single subjects.

High-resolution mechanical imaging of the human brain by three-dimensional multifrequency magnetic resonance elastography at 7T.

Magnetic resonance elastography (MRE) is capable of measuring the viscoelastic properties of brain tissue in vivo. However, MRE is still limited in providing high-resolution maps of mechanical constants. We therefore introduce 3D multifrequency MRE (3DMMRE) at 7T magnetic field strength combined with enhanced multifrequency dual elasto-visco (MDEV) inversion in order to achieve high-resolution elastographic maps of in vivo brain tissue with 1mm(3) resolution. As demonstrated by phantom data, the new MDEV-inversion method provides two high resolution parameter maps of the magnitude (|G*|) and the phase angle (ϕ) of the complex shear modulus. MDEV inversion applied to cerebral 7T-3DMMRE data of five healthy volunteers revealed structures of brain tissue in greater anatomical details than previous work. The viscoelastic properties of cortical gray matter (GM) and white matter (WM) could be differentiated by significantly lower values of |G*| and ϕ in GM (21% [P<0.01]; 8%, [P<0.01], respectively) suggesting that GM is significantly softer and less viscous than WM. In conclusion, 3DMMRE at ultrahigh magnetic fields and MDEV inversion open a new window into characterizing the mechanical structure of in vivo brain tissue and may aid the detection of various neurological disorders based on their effects to mechanical tissue properties.

Effect of age on lateralized auditory processing.

The lateralization of processing in the auditory cortex for different acoustic parameters differs depending on stimuli and tasks. Thus, processing complex auditory stimuli requires an efficient hemispheric interaction. Anatomical connectivity decreases with aging and consequently affects the functional interaction between the left and right auditory cortex and lateralization of auditory processing. Here we studied with magnetic resonance imaging the effect of aging on the lateralization of processing and hemispheric interaction during two tasks utilizing the contralateral noise procedure. Categorization of tones according to their direction of frequency modulations (FM) is known to be processed mainly in the right auditory cortex. Sequential comparison of the same tones according to their FM direction strongly involves additionally the left auditory cortex and therefore a stronger hemispheric interaction than the categorization task. The results showed that older adults more strongly recruit the auditory cortex especially during the comparison task that requires stronger hemispheric interaction. This was the case although the task difficulty was adapted to achieve similar performance as the younger adults. Additionally, functional connectivity from auditory cortex to other brain areas was stronger in older than younger adults especially during the comparison task. Diffusion tensor imaging data showed a reduction in fractional anisotropy and an increase in mean diffusivity in the corpus callosum of older adults compared to younger adults. These changes indicate a reduction of anatomical interhemispheric connections in older adults that makes larger processing capacity necessary when tasks require functional hemispheric interaction.

Effect of Contralateral Noise on Speech Intelligibility.

In patients with strong asymmetric hearing loss, standard clinical practice involves testing speech intelligibility in the ear with the higher hearing threshold by simultaneously presenting noise to the other ear. However, psychoacoustic and functional magnetic resonance imaging (fMRI) studies indicate that this approach may be problematic as contralateral noise has a disruptive effect on task processing. Furthermore, fMRI studies have revealed that the effect of contralateral noise on brain activity depends on the lateralization of task processing. The effect of contralateral noise is stronger when task-relevant stimuli are presented ipsilaterally to the hemisphere that is processing the task. In the present study, we tested the effect of four different levels of contralateral noise on speech intelligibility using the Oldenburg sentence test (OLSA). Cortical lateralization of speech processing was assessed upfront by using a visual speech test with fMRI. Contralateral OLSA noise of 65 or 80 dB SPL significantly reduced word intelligibility irrespective of which ear the speech was presented to. In participants with left-lateralized speech processing, 50 dB SPL contralateral OLSA noise led to a significant reduction in speech intelligibility when speech was presented to the left ear, i.e. when speech was presented ipsilaterally to the hemisphere that is mainly processing speech. Thus, contralateral noise, as used in standard clinical practice, not only prevents listeners from using the information in the better-hearing ear but may also have the unintended effect of hampering central processing of speech.

In vivo magnetic resonance elastography of human brain at 7 T and 1.5 T.

PURPOSE: To investigate the feasibility of quantitative in vivo ultrahigh field magnetic resonance elastography (MRE) of the human brain in a broad range of low-frequency mechanical vibrations. MATERIALS AND METHODS: Mechanical vibrations were coupled into the brain of a healthy volunteer using a coil-driven actuator that either oscillated harmonically at single frequencies between 25 and 62.5 Hz or performed a superimposed motion consisting of multiple harmonics. Using a motion sensitive single-shot spin-echo echo planar imaging sequence shear wave displacements in the brain were measured at 1.5 and 7 T in whole-body MR scanners. Spatially averaged complex shear moduli were calculated applying Helmholtz inversion. RESULTS: Viscoelastic properties of brain tissue could be reliably determined in vivo at 1.5 and 7 T using both single-frequency and multifrequency wave excitation. The deduced dispersion of the complex modulus was consistent within different experimental settings of this study for the measured frequency range and agreed well with literature data. CONCLUSION: MRE of the human brain is feasible at 7 T. Superposition of multiple harmonics yields consistent results as compared to standard single-frequency based MRE. As such, MRE is a system-independent modality for measuring the complex shear modulus of in vivo human brain in a wide dynamic range.

MR imaging of the human hand and wrist at 7 T.

OBJECTIVE: The purpose of this study was to evaluate the feasibility, quality, and possible future implications of magnetic resonance imaging (MRI) of the human hand and wrist at 7 T. MATERIALS AND METHODS: Images of the left hand of a healthy volunteer were acquired with a 7- and a 1.5-T whole body system and comparatively analyzed. Axial and coronal two-dimensional gradient echo (GRE) images with inflow saturation, coronal 3D GRE images, and time-of-flight angiographies were obtained without averaging. Image details were related to the complex hand anatomy. RESULTS: With the 7-T protocols established in this study, high-quality and high-resolution images of the hand and wrist were obtained. In the 2D GRE images at 7 T, small anatomical structures of the hand were depicted in vivo with superior detail and resolution, compared to 1.5 T and published studies at lower field strength. Signal-to-noise ratios (SNRs) were approximately five times higher at 7 T compared to 1.5 T. Additionally, thin 3D GRE images with good quality of the whole hand were obtained in a short acquisition time. Moreover, time-of-flight angiographies of the small hand arteries have been acquired without the application of contrast agents. CONCLUSION: Seven-tesla imaging of the hand can be used in vivo with ultra-high resolution and sufficient SNR. It allows for exact delineation of most anatomical structures including nerves, muscles, tendons, ligaments, cartilage, and blood vessels.

Fast three-dimensional 1H MR spectroscopic imaging at 7 Tesla using "spectroscopic missing pulse--SSFP".

The use of spectroscopic Missing Pulse--SSFP (spMP-SSFP) for fast three-dimensional (3D) proton MR spectroscopic imaging (MRSI) at 7 Tesla (T) is demonstrated. Sequence modifications were required regarding the limits of the specific absorption rate as well as hardware limitations with respect to maximum B(1) field strength and B(0) gradient slew rate, as compared to previous studies performed at 3T. The combination of two spatially selective radiofrequency (RF) pulses (with orthogonal slice orientation) and a dual-band chemical shift selective RF pulse for simultaneous water and lipid suppression proved to enable fast 3D MRSI measurements of the brain of healthy volunteers. Using a total measurement time of approximately 8.5 minutes and a nominal and real voxel size of 0.62 cm(3) and 2.6 cm(3), respectively, signals of N-acetyl aspartate, total creatine, choline containing compounds, myo-inositol, and glutamate+glutamine could be detected.

Susceptibility weighted imaging at ultra high magnetic field strengths: theoretical considerations and experimental results.

We present numerical simulations and experimental results for susceptibility weighted imaging (SWI) at 7 T. Magnitude, phase, and SWI contrast were simulated for different voxel geometries and imaging parameters, resulting in an echo time of 14 msec for optimum contrast between veins and surrounding tissue. Slice thickness of twice the in-plane voxel size or more resulted in optimum vessel visibility. Phantom and in vivo data are in very good agreement with the simulations and the delineation of vessels at 7 T was superior compared to lower field strengths. The phase of the complex data reveals anatomical details that are complementary to the corresponding magnitude images. Susceptibility weighted imaging at very high field strengths is a promising technique because of its high sensitivity to tissue susceptibility, its low specific absorption rate, and the phase's negligible sensitivity to B(1) inhomogeneities.

Metamaterial-based transmit and receive system for whole-body magnetic resonance imaging at ultra-high magnetic fields.

Magnetic resonance imaging (MRI) at ultra-high fields (UHF), such as 7 T, provides an enhanced signal-to-noise ratio and has led to unprecedented high-resolution anatomic images and brain activation maps. Although a variety of radio frequency (RF) coil architectures have been developed for imaging at UHF conditions, they usually are specialized for small volumes of interests (VoI). So far, whole-body coil resonators are not available for commercial UHF human whole-body MRI systems. The goal of the present study was the development and validation of a transmit and receive system for large VoIs that operates at a 7 T human whole-body MRI system. A Metamaterial Ring Antenna System (MRAS) consisting of several ring antennas was developed, since it allows for the imaging of extended VoIs. Furthermore, the MRAS not only requires lower intensities of the irradiated RF energy, but also provides a more confined and focused injection of excitation energy on selected body parts. The MRAS consisted of several antennas with 50 cm inner diameter, 10 cm width and 0.5 cm depth. The position of the rings was freely adjustable. Conformal resonant right-/left-handed metamaterial was used for each ring antenna with two quadrature feeding ports for RF power. The system was successfully implemented and demonstrated with both a silicone oil and a water-NaCl-isopropanol phantom as well as in vivo by acquiring whole-body images of a crab-eating macaque. The potential for future neuroimaging applications was demonstrated by the acquired high-resolution anatomic images of the macaque's head. Phantom and in vivo measurements of crab-eating macaques provided high-resolution images with large VoIs up to 40 cm in xy-direction and 45 cm in z-direction. The results of this work demonstrate the feasibility of the MRAS system for UHF MRI as proof of principle. The MRAS shows a substantial potential for MR imaging of larger volumes at 7 T UHF. This new technique may provide new diagnostic potential in spatially extended pathologies such as searching for spread-out tumor metastases or monitoring systemic inflammatory processes.

Coarsening of axial segregation patterns of slurries in a horizontally rotating drum.

Segregation structures of granular mixtures in rotating drums represent classical examples of pattern formation in granular material. We investigate the coarsening of axial segregation patterns of slurries in a long horizontally rotating cylinder. The dynamics and the three-dimensional geometry of the segregation structures are analyzed with optical methods and nuclear magnetic resonance imaging. Previous studies have mainly considered global statistical features of the pattern dynamics. In order to get insight into driving mechanisms for the coarsening process, we focus on the details of the dissolution of individual bands. We treat the coarsening as a consequence of interactions of adjacent bands in the pattern, which are determined by their geometrical relations. In addition to initially homogeneous mixtures, which evolve to spontaneously formed patterns, we study the evolution of specially prepared simple initial states. The role of the three-dimensional geometry of the axial core in the dissolution process of segregation bands is demonstrated. Relations between geometry and dynamic processes are established, which may help to find the correct microscopic models for the coarsening mechanism.

Auditory intensity processing: Effect of MRI background noise.

Studies on active auditory intensity discrimination in humans showed equivocal results regarding the lateralization of processing. Whereas experiments with a moderate background found evidence for right lateralized processing of intensity, functional magnetic resonance imaging (fMRI) studies with background scanner noise suggest more left lateralized processing. With the present fMRI study, we compared the task dependent lateralization of intensity processing between a conventional continuous echo planar imaging (EPI) sequence with a loud background scanner noise and a fast low-angle shot (FLASH) sequence with a soft background scanner noise. To determine the lateralization of the processing, we employed the contralateral noise procedure. Linearly frequency modulated (FM) tones were presented monaurally with and without contralateral noise. During both the EPI and the FLASH measurement, the left auditory cortex was more strongly involved than the right auditory cortex while participants categorized the intensity of FM tones. This was shown by a strong effect of the additional contralateral noise on the activity in the left auditory cortex. This means a massive reduction in background scanner noise still leads to a significant left lateralized effect. This suggests that the reversed lateralization in fMRI studies with loud background noise in contrast to studies with softer background cannot be fully explained by the MRI background noise.

A studyforrest extension, retinotopic mapping and localization of higher visual areas.

The studyforrest (http://studyforrest.org) dataset is likely the largest neuroimaging dataset on natural language and story processing publicly available today. In this article, along with a companion publication, we present an update of this dataset that extends its scope to vision and multi-sensory research. 15 participants of the original cohort volunteered for a series of additional studies: a clinical examination of visual function, a standard retinotopic mapping procedure, and a localization of higher visual areas-such as the fusiform face area. The combination of this update, the previous data releases for the dataset, and the companion publication, which includes neuroimaging and eye tracking data from natural stimulation with a motion picture, form an extremely versatile and comprehensive resource for brain imaging research-with almost six hours of functional neuroimaging data across five different stimulation paradigms for each participant. Furthermore, we describe employed paradigms and present results that document the quality of the data for the purpose of characterising major properties of participants' visual processing stream.

A studyforrest extension, simultaneous fMRI and eye gaze recordings during prolonged natural stimulation.

Here we present an update of the studyforrest (http://studyforrest.org) dataset that complements the previously released functional magnetic resonance imaging (fMRI) data for natural language processing with a new two-hour 3 Tesla fMRI acquisition while 15 of the original participants were shown an audio-visual version of the stimulus motion picture. We demonstrate with two validation analyses that these new data support modeling specific properties of the complex natural stimulus, as well as a substantial within-subject BOLD response congruency in brain areas related to the processing of auditory inputs, speech, and narrative when compared to the existing fMRI data for audio-only stimulation. In addition, we provide participants' eye gaze location as recorded simultaneously with fMRI, and an additional sample of 15 control participants whose eye gaze trajectories for the entire movie were recorded in a lab setting-to enable studies on attentional processes and comparative investigations on the potential impact of the stimulation setting on these processes.

The Travelling-Wave Primate System: A New Solution for Magnetic Resonance Imaging of Macaque Monkeys at 7 Tesla Ultra-High Field.

INTRODUCTION: Neuroimaging of macaques at ultra-high field (UHF) is usually conducted by combining a volume coil for transmit (Tx) and a phased array coil for receive (Rx) tightly enclosing the monkey's head. Good results have been achieved using vertical or horizontal magnets with implanted or near-surface coils. An alternative and less costly approach, the travelling-wave (TW) excitation concept, may offer more flexible experimental setups on human whole-body UHF magnetic resonance imaging (MRI) systems, which are now more widely available. Goal of the study was developing and validating the TW concept for in vivo primate MRI. METHODS: The TW Primate System (TWPS) uses the radio frequency shield of the gradient system of a human whole-body 7 T MRI system as a waveguide to propagate a circularly polarized B1 field represented by the TE11 mode. This mode is excited by a specifically designed 2-port patch antenna. For receive, a customized neuroimaging monkey head receive-only coil was designed. Field simulation was used for development and evaluation. Signal-to-noise ratio (SNR) was compared with data acquired with a conventional monkey volume head coil consisting of a homogeneous transmit coil and a 12-element receive coil. RESULTS: The TWPS offered good image homogeneity in the volume-of-interest Turbo spin echo images exhibited a high contrast, allowing a clear depiction of the cerebral anatomy. As a prerequisite for functional MRI, whole brain ultrafast echo planar images were successfully acquired. CONCLUSION: The TWPS presents a promising new approach to fMRI of macaques for research groups with access to a horizontal UHF MRI system.

A proof-of-principle study of multi-site real-time functional imaging at 3T and 7T: Implementation and validation.

Real-time functional Magnetic Resonance Imaging (rtfMRI) is used mainly for neurofeedback or for brain-computer interfaces (BCI). But multi-site rtfMRI could in fact help in the application of new interactive paradigms such as the monitoring of mutual information flow or the controlling of objects in shared virtual environments. For that reason, a previously developed framework that provided an integrated control and data analysis of rtfMRI experiments was extended to enable multi-site rtfMRI. Important new components included a data exchange platform for analyzing the data of both MR scanners independently and/or jointly. Information related to brain activation can be displayed separately or in a shared view. However, a signal calibration procedure had to be developed and integrated in order to permit the connecting of sites that had different hardware and to account for different inter-individual brain activation levels. The framework was successfully validated in a proof-of-principle study with twelve volunteers. Thus the overall concept, the calibration of grossly differing signals, and BCI functionality on each site proved to work as required. To model interactions between brains in real-time, more complex rules utilizing mutual activation patterns could easily be implemented to allow for new kinds of social fMRI experiments.

Functional asymmetry and effective connectivity of the auditory system during speech perception is modulated by the place of articulation of the consonant- A 7T fMRI study.

To differentiate between stop-consonants, the auditory system has to detect subtle place of articulation (PoA) and voice-onset time (VOT) differences between stop-consonants. How this differential processing is represented on the cortical level remains unclear. The present functional magnetic resonance (fMRI) study takes advantage of the superior spatial resolution and high sensitivity of ultra-high-field 7 T MRI. Subjects were attentively listening to consonant-vowel (CV) syllables with an alveolar or bilabial stop-consonant and either a short or long VOT. The results showed an overall bilateral activation pattern in the posterior temporal lobe during the processing of the CV syllables. This was however modulated strongest by PoA such that syllables with an alveolar stop-consonant showed stronger left lateralized activation. In addition, analysis of underlying functional and effective connectivity revealed an inhibitory effect of the left planum temporale (PT) onto the right auditory cortex (AC) during the processing of alveolar CV syllables. Furthermore, the connectivity result indicated also a directed information flow from the right to the left AC, and further to the left PT for all syllables. These results indicate that auditory speech perception relies on an interplay between the left and right ACs, with the left PT as modulator. Furthermore, the degree of functional asymmetry is determined by the acoustic properties of the CV syllables.

A high-resolution 7-Tesla fMRI dataset from complex natural stimulation with an audio movie.

Here we present a high-resolution functional magnetic resonance (fMRI) dataset - 20 participants recorded at high field strength (7 Tesla) during prolonged stimulation with an auditory feature film ("Forrest Gump"). In addition, a comprehensive set of auxiliary data (T1w, T2w, DTI, susceptibility-weighted image, angiography) as well as measurements to assess technical and physiological noise components have been acquired. An initial analysis confirms that these data can be used to study common and idiosyncratic brain response patterns to complex auditory stimulation. Among the potential uses of this dataset are the study of auditory attention and cognition, language and music perception, and social perception. The auxiliary measurements enable a large variety of additional analysis strategies that relate functional response patterns to structural properties of the brain. Alongside the acquired data, we provide source code and detailed information on all employed procedures - from stimulus creation to data analysis. In order to facilitate replicative and derived works, only free and open-source software was utilized.

Multicenter study of subjective acceptance during magnetic resonance imaging at 7 and 9.4 T.

OBJECTIVES: The aims of this study were to investigate the subjective discomfort and sensory side effects during ultrahigh field (UHF) magnetic resonance imaging (MRI) examinations in a large-scale study and to evaluate differences between magnetic resonance (MR) sites. MATERIALS AND METHODS: Four MR sites with a 7-T MR system and 2 MR sites with a 9.4-T MR system participated in this multicenter study with a total number of 3457 completed questionnaires on causes of discomfort and sensations during the examination. For a pooled retrospective analysis of the results from the partially different questionnaires, all data were adapted to an answer option with a 4-point scale (0 = no discomfort/side effect, 3 = very unpleasant/very strong sensation). To differentiate effects evoked by the low-frequency time-varying magnetic fields due to movement through the static magnetic field, most questionnaires separated the manifestation of sensory side effects during movement on the patient table from manifestation while lying still in the isocenter. RESULTS: In general, a high acceptance of UHF examinations was found, where in 82% of the completed questionnaires, the subjects stated the examination to be at least tolerable. Although in 7.6% of the questionnaires, subjects felt discomfort during the examination, only 0.9% of the image acquisitions had to be terminated prematurely. No adverse events occurred in any of the examinations. Only 1% of the subjects were unwilling to undergo further UHF MRI examinations. Examination duration was the most complained cause of discomfort, followed by acoustic noise and lying still. All magnetic-field-related sensations were more pronounced when moving the patient table versus the isocenter position (19%/2% of the subjects felt unpleasant vertigo during the moving/stationary state). In general, vertigo was the most often stated sensory side effect and was more pronounced at 9.4 T compared with 7 T. However, the results varied substantially among the different sites. CONCLUSIONS: The high levels of subjective acceptance found in this study lead to the conclusion that UHF MRI would be tolerated as a diagnostic tool in clinical practice. For more consistent data ascertainment, we propose a standardized questionnaire for subjective perception monitoring.

Integration of ultra-high field MRI and histology for connectome based research of brain disorders.

Ultra-high field magnetic resonance imaging (MRI) became increasingly relevant for in vivo neuroscientific research because of improved spatial resolutions. However, this is still the unchallenged domain of histological studies, which long played an important role in the investigation of neuropsychiatric disorders. While the field of biological psychiatry strongly advanced on macroscopic levels, current developments are rediscovering the richness of immunohistological information when attempting a multi-level systematic approach to brain function and dysfunction. For most studies, histology sections lost information on three-dimensional reconstructions. Translating histological sections to 3D-volumes would thus not only allow for multi-stain and multi-subject alignment in post mortem data, but also provide a crucial step in big data initiatives involving the network analyses currently performed with in vivo MRI. We therefore investigated potential pitfalls during integration of MR and histological information where no additional blockface information is available. We demonstrated that strengths and requirements from both methods can be effectively combined at a spatial resolution of 200 µm. However, the success of this approach is heavily dependent on choices of hardware, sequence and reconstruction. We provide a fully automated pipeline that optimizes histological 3D reconstructions, providing a potentially powerful solution not only for primary human post mortem research institutions in neuropsychiatric research, but also to help alleviate the massive workloads in neuroanatomical atlas initiatives. We further demonstrate (for the first time) the feasibility and quality of ultra-high spatial resolution (150 µm isotopic) imaging of the entire human brain MRI at 7T, offering new opportunities for analyses on MR-derived information.