Effect of Task-Correlated Physiological Fluctuations and Motion in 2D and 3D Echo-Planar Imaging in a Higher Cognitive Level fMRI Paradigm.

Purpose: To compare 2D and 3D echo-planar imaging (EPI) in a higher cognitive level fMRI paradigm. In particular, to study the link between the presence of task-correlated physiological fluctuations and motion and the fMRI contrast estimates from either 2D EPI or 3D EPI datasets, with and without adding nuisance regressors to the model. A signal model in the presence of partly task-correlated fluctuations is derived, and predictions for contrast estimates with and without nuisance regressors are made.

Three-dimensional functional MRI with parallel acceleration: balanced SSFP versus PRESTO.

Purpose: To compare the sensitivity and specificity of three-dimensional (3D) principles of echo shifting using a train of observations (PRESTO) and passband balanced steady-state free precession (SSFP) functional MRI (fMRI) sequences combined with integrated parallel acquisition techniques (iPAT) at 3 Tesla (T).

Materials And Methods: The 3D fMRI was performed using PRESTO and passband balanced SSFP with 3 mm and 1.9 mm isotropic voxels combined with iPAT, while volunteers underwent visual stimulation.

Optimized quantification of diffusional non-gaussianity in the human brain.

Purpose: To test the performance of three existing models of diffusional non-Gaussianity and introduce a new model.

Materials And Methods: Quantitative measures of diffusional non-Gaussianity provide clinically useful information. Three-parameter mathematical models are particularly relevant, because they assign one parameter to non-Gaussianity, one to diffusivity and one to the signal in the absence of diffusion weighting.

Estimating non-Gaussian diffusion model parameters in the presence of physiological noise and Rician signal bias.

Purpose: To assess the effects of Rician bias and physiological noise on parameter estimation for non-Gaussian diffusion models.

Materials And Methods: At high b-values, there are deviations from monoexponential signal decay known as non-Gaussian diffusion. Magnitude images have a Rician distribution, which introduces a bias that appears as non-Gaussian diffusion.

Cardiac-induced physiological noise in 3D gradient echo brain imaging: effect of k-space sampling scheme.

The physiological noise in 3D image acquisition is shown to depend strongly on the sampling scheme. Five sampling schemes are considered: Linear, Centric, Segmented, Random and Tuned. Tuned acquisition means that data acquisition at k-space positions k and -k are separated with a specific time interval.

Statistical assessment of non-Gaussian diffusion models.

In human brain diffusion measurements, there are deviations from monoexponential signal decay at high values of the diffusion-weighting factor b. This is known as non-Gaussian diffusion and can provide novel kinds of image contrast. We evaluated quantitatively the goodness-of-fit of five popular diffusion models.

Balanced steady-state free precession with parallel imaging gives distortion-free fMRI with high temporal resolution.

Research on the functions of the human brain requires that functional magnetic resonance imaging (MRI) moves towards producing images with less distortion and higher temporal and spatial resolution. This study compares passband balanced steady-state free precession (bSSFP) acquisitions with and without parallel imaging (PI) to investigate whether combining PI with this pulse sequence is a viable option for functional MRI. Such a novel combination has the potential to offer the distortion-free advantages of bSSFP with the reduced acquisition time of PI.

Manganese transport in the rat optic nerve evaluated with spatial- and time-resolved magnetic resonance imaging.

Purpose: 1) To evaluate a novel theoretical model for in vivo axonal Mn(2+) transport with MRI data from the rat optic nerve (ON); and 2) to compare predictions from the new model with previously reported experimental data.

Materials And Methods: Time-resolved in vivo T(1)-weighted magnetic resonance imaging (MRI) of adult female Sprague-Dawley rat (n = 9) ON was obtained at different timepoints after intravitreal MnCl(2) injection. A concentration-dependent and a rate-dependent function for the Mn(2+) retinal ganglion cell (RGC) axon entrance was convolved with three different transport functions and each model system was optimized to fit the ON data.

Diffusion measurements and diffusion tensor imaging with noisy magnitude data.

Purpose: To compare an unbiased method for estimation of the diffusion coefficient to the quick, but biased, log-linear (LL) method in the presence of noisy magnitude data.

Materials And Methods: The magnitude operation changes the signal distribution in magnetic resonance (MR) images from Gaussian to Rician. If not properly taken into account, this will introduce a bias in the estimated diffusion coefficient.

Combination of Mn(2+)-enhanced and diffusion tensor MR imaging gives complementary information about injury and regeneration in the adult rat optic nerve.

Purpose: To evaluate manganese (Mn(2+))-enhanced MRI (MEMRI) and diffusion tensor imaging (DTI) as tools for detection of axonal injury and regeneration after intravitreal peripheral nerve graft (PNG) implantation in the rat optic nerve (ON).

Materials And Methods: In adult Fischer rats, retinal ganglion cell (RGC) survival was evaluated in Flurogold (FG) back-filled retinal whole mounts after ON crush (ONC), intravitreal PNG, and intravitreal MnCl(2) injection (150 nmol) at 0 and 20 days post lesion (dpl). MEMRI and echo-planar DTI (DTI-EPI) was obtained of noninjured ON one day after intravitreal MnCl(2) injection, and at 1 and 21 dpl after ONC, intravitreal PNG, and intravitreal MnCl(2) injections given at 0 and 20 dpl.

Optimal estimation of the diffusion coefficient from non-averaged and averaged noisy magnitude data.

The magnitude operation changes the signal distribution in MRI images from Gaussian to Rician. This introduces a bias that must be taken into account when estimating the apparent diffusion coefficient. Several estimators are known in the literature.

An apparent unidirectional influx constant for manganese as a measure of myocardial calcium channel activity.

Purpose: To develop an in vivo MR method for evaluation of myocardial calcium channel activity through quantification of apparent unidirectional manganese influx constants following manganese dipyridoxyl-diphosphate (MnDPDP) infusions.

Materials And Methods: A total of 10 healthy volunteers were divided in two groups, and received 5 micromol of MnDPDP per kg of body weight intravenously in a 1.5 Tesla scanner over five or 30 minutes, respectively.

Relaxation enhancing properties of MnDPDP in human myocardium.

Purpose: To assess magnitude and duration of changes in myocardial longitudinal relaxation rate (R1) in humans following infusion of the manganese (Mn) releasing contrast agent MnDPDP (Mn-dipyridoxyl-diphosphate).

Materials And Methods: Fifteen healthy volunteers were divided into three groups. After initial myocardial and liver R1 measurements using an inversion recovery (IR) turbo fast low-angle shot (FLASH) sequence at 1.