An open access resource for functional brain connectivity from fully awake marmosets.

The common marmoset (Callithrix jacchus) is quickly gaining traction as a premier neuroscientific model. However, considerable progress is still needed in understanding the functional and structural organization of the marmoset brain to rival that documented in longstanding preclinical model species, like mice, rats, and Old World primates. To accelerate such progress, we present the Marmoset Functional Brain Connectivity Resource (marmosetbrainconnectome.

Receiver phase alignment using fitted SVD derived sensitivities from routine prescans.

Magnetic resonance imaging radio frequency arrays are composed of multiple receive coils that have their signals combined to form an image. Combination requires an estimate of the radio frequency coil sensitivities to align signal phases and prevent destructive interference. At lower fields this can be accomplished using a uniform physical reference coil.

Effects of phase regression on high-resolution functional MRI of the primary visual cortex.

High-resolution functional MRI studies have become a powerful tool to non-invasively probe the sub-millimeter functional organization of the human cortex. Advances in MR hardware, imaging techniques and sophisticated post-processing methods have allowed high resolution fMRI to be used in both the clinical and academic neurosciences. However, consensus within the community regarding the use of gradient echo (GE) or spin echo (SE) based acquisition remains largely divided.

Radiofrequency coil for routine ultra-high-field imaging with an unobstructed visual field.

Many neuroscience applications have adopted functional MRI as a tool to investigate the healthy and diseased brain during the completion of a task. While ultra-high-field MRI has allowed for improved contrast and signal-to-noise ratios during functional MRI studies, it remains a challenge to create local radiofrequency coils that can accommodate an unobstructed visual field and be suitable for routine use, while at the same time not compromise performance. Performance (both during transmission and reception) can be improved by using close-fitting coils; however, maintaining sensitivity over the whole brain often requires the introduction of coil elements proximal to the eyes, thereby partially occluding the subject's visual field.

Elimination of low-inversion-efficiency induced artifacts in whole-brain MP2RAGE using multiple RF-shim configurations at 7 T.

The magnetization-prepared two-rapid-gradient-echo (MP2RAGE) sequence is used for structural T -weighted imaging and T mapping of the human brain. In this sequence, adiabatic inversion RF pulses are commonly used, which require the B magnitude to be above a certain threshold. Achieving this threshold in the whole brain may not be possible at ultra-high fields because of the short RF wavelength.

Demonstration and suppression of respiration-related artifacts in Bloch-Siegert shift-based B maps of the human brain.

Respiration-induced movement of the chest wall and internal organs causes temporal B variations extending throughout the brain. This study demonstrates that these variations can cause significant artifacts in maps obtained at 7 T with the Bloch-Siegert shift (BSS) mapping technique. To suppress these artifacts, a navigator correction scheme was proposed.

Open-source hardware designs for MRI of mice, rats, and marmosets: Integrated animal holders and radiofrequency coils.

Background: Small-animal MRI is an important investigative tool for basic and preclinical research. High-resolution anatomical and functional studies of the brain require artifact-free images that are acquired with a highly sensitive radiofrequency (RF) coil.

New Method: The animal holder plays an important role in mitigating image artifacts: motion artifacts are reduced by immobilizing the animal and geometric-distortion artifacts are reduced by accurately positioning the animal to improve static-field shimming.

Prediction of radiation necrosis in a rodent model using magnetic resonance imaging apparent transverse relaxation ([Formula: see text]).

Background And Purpose: Radiation necrosis remains an irreversible long-term side-effect following radiotherapy to the brain. The ability to predict areas that could ultimately develop into necrosis could lead to prevention and management of radiation necrosis.

Materials And Methods: Fischer 344 rats were irradiated using two platforms (micro-CT irradiator and x-Rad 225 IGRT) with radiation up to 30 Gy for the micro-CT and 40 Gy for the xRAD-224 to half the brain.

Apparent transverse relaxation (R2∗) on MRI as a method to differentiate treatment effect (pseudoprogression) versus progressive disease in chemoradiation for malignant glioma.

Introduction: Pseudoprogression (psPD) is a transient post-treatment imaging change that is commonly seen when treating glioma with chemotherapy and radiation. The use of apparent transverse relaxation rate (R2∗), which is calculated from a contrast-free multi-echo gradient echo Magnetic Resonance Imaging (MRI) sequence, may allow for quantitative identification of patients with suspected psPD.

Methods: We acquired a multi-echo gradient echo sequence using a 3T-Siemens Prisma MRI.

A geometrically adjustable receive array for imaging marmoset cohorts.

The common marmoset (Callithrix jacchus) is an increasingly popular animal model for translational neuroscience studies, during which anatomical and functional MRI can be useful investigative tools. To attain the requisite SNR for high-resolution acquisitions, the radiofrequency coil must be optimized for the marmoset; however, relatively few custom coils have been developed that maximize SNR and are compatible with accelerated acquisitions. For the study of large populations of animals, the heterogeneity in animal size reduces the effectiveness of a "one size fits all" approach to coil sizing and makes coils tailored to individual animals cost and time prohibitive.

Increased deep gray matter iron is present in clinically isolated syndromes.

Objective: Abnormal iron accumulation in MS has been known for decades, however it remains to be established whether iron reflects a cause or epiphenomenon of pathology. The objective of the present study is to determine if iron is increased in the brains of patients with clinically isolated syndromes (CIS) suggestive of early MS.

Methods: Twenty-two patients with a CIS and 16 age- and sex-matched controls underwent 3T MRI studies.

Origins of R2* orientation dependence in gray and white matter.

Estimates of the apparent transverse relaxation rate (R2*) can be used to quantify important properties of biological tissue. Surprisingly, the mechanism of R2* dependence on tissue orientation is not well understood. The primary goal of this paper was to characterize orientation dependence of R2* in gray and white matter and relate it to independent measurements of two other susceptibility based parameters: the local Larmor frequency shift (fL) and quantitative volume magnetic susceptibility (Δχ).

A low-cost, mechanically simple apparatus for measuring eddy current-induced magnetic fields in MRI.

The fidelity of gradient waveforms in MRI pulse sequences is essential to the acquisition of images and spectra with minimal distortion artefacts. Gradient waveforms can become nonideal when eddy currents are created in nearby conducting structures; however, the resultant magnetic fields can be characterised and compensated for by measuring the spatial and temporal field response following a gradient impulse. This can be accomplished using a grid of radiofrequency (RF) coils.

Signal displacement in spiral-in acquisitions: simulations and implications for imaging in SFG regions.

Susceptibility field gradients (SFGs) cause problems for functional magnetic resonance imaging (fMRI) in regions like the orbital frontal lobes, leading to signal loss and image artifacts (signal displacement and "pile-up"). Pulse sequences with spiral-in k-space trajectories are often used when acquiring fMRI in SFG regions such as inferior/medial temporal cortex because it is believed that they have improved signal recovery and decreased signal displacement properties. Previously postulated theories explain differing reasons why spiral-in appears to perform better than spiral-out; however it is clear that multiple mechanisms are occurring in parallel.

Slice-by-slice B1+ shimming at 7 T.

Parallel transmission has been used to reduce the inevitable inhomogeneous radiofrequency fields produced in human high-field MRI greater than 3 T. Further improvements in the transmit homogeneity and efficiency are possible by leveraging the additional degree of freedom permitted by multislice acquisitions. Compared to simple scaling of the flip angle to compensate for B1+ falloff along the radiofrequency coil, calculation of B1+ shim solutions on a slice-by-slice basis can markedly improve homogeneity and/or reduce transmitted power and global SAR.

A conformal transceive array for 7 T neuroimaging.

The first 16-channel transceive surface-coil array that conforms to the human head and operates at 298 MHz (7 T) is described. Individual coil elements were decoupled using circumferential shields around each element that extended orthogonally from the former. This decoupling method allowed elements to be constructed with arbitrary shape, size, and location to create a three-dimensional array.

A radiofrequency coil to facilitate B₁⁺ shimming and parallel imaging acceleration in three dimensions at 7 T.

A 15-channel transmit-receive (transceive) radiofrequency (RF) coil was developed to image the human brain at 7 T. A hybrid decoupling scheme was implemented that used both capacitive decoupling and the partial geometric overlapping of adjacent coil elements. The decoupling scheme allowed coil elements to be arrayed along all three Cartesian axes; this facilitated shimming of the transmit field, B₁⁺, and parallel imaging acceleration along the longitudinal direction in addition to the standard transverse directions.

Transmit/receive radiofrequency coil with individually shielded elements.

A novel method for decoupling coil elements of transmit/receive (transceive) arrays is reported. Each element of a coil array is shielded both concentrically and radially to reduce the magnetic flux linkage between neighboring coils; this substantially reduces the mutual inductance between coil elements and allows them to behave independently. A six-channel transceive coil was developed using this decoupling scheme and compared with two conventional decoupling schemes: the partial overlapping of adjacent elements and capacitive decoupling.

Evaluation of preprocessing steps to compensate for magnetic field distortions due to body movements in BOLD fMRI.

Blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) is currently the dominant technique for non-invasive investigation of brain functions. One of the challenges with BOLD fMRI, particularly at high fields, is compensation for the effects of spatiotemporally varying magnetic field inhomogeneities (DeltaB(0)) caused by normal subject respiration and, in some studies, movement of the subject during the scan to perform tasks related to the functional paradigm. The presence of DeltaB(0) during data acquisition distorts reconstructed images and introduces extraneous fluctuations in the fMRI time series that decrease the BOLD contrast-to-noise ratio.

High-field MRSI of the prostate using a transmit/receive endorectal coil and gradient modulated adiabatic localization.

Purpose: To demonstrate in vivo magnetic resonance spectroscopic imaging (MRSI) of the human prostate at 4.0T using a transmit/receive endorectal coil and a pulse sequence designed specifically for this application.

Materials And Methods: A solid, reusable endorectal probe was designed for both radiofrequency transmission and reception.

Hybrid two-dimensional navigator correction: a new technique to suppress respiratory-induced physiological noise in multi-shot echo-planar functional MRI.

A troublesome source of physiological noise in functional magnetic resonance imaging (fMRI) is due to the spatio-temporal modulation of the magnetic field in the brain caused by normal subject respiration. fMRI data acquired using echo-planar imaging are very sensitive to these respiratory-induced frequency offsets, which cause significant geometric distortions in images. Because these effects increase with main magnetic field, they can nullify the gains in statistical power expected by the use of higher magnetic fields.

MR compatibility of EEG scalp electrodes at 4 tesla.

Purpose: To design and apply a method to quantitatively evaluate the MR compatibility of electroencephalographic (EEG) scalp electrodes based on pulse sequence-independent metrics.

Materials And Methods: Three types of electrodes (constructed primarily of brass, silver, and conductive plastic, respectively) were tested. B0 field distortions, B1 shielding, and heat induction was measured in adjacent agarose and oil phantoms at 4 T.

NMR simulation analysis of statistical effects on quantifying cerebrovascular parameters.

Determining tissue structure and composition from the behavior of the NMR transverse relaxation during free induction decay and spin echo formation has seen significant advances in recent years. In particular, the ability to quantify cerebrovascular network parameters such as blood volume and deoxyhemoglobin concentration from the NMR signal dephasing has seen intense focus. Analytical models have been described, based on statistical averaging of randomly oriented cylinders in both the static and slow diffusion regimes.