Spatial and temporal characteristics of physiological noise in fMRI at 3T.

Rationale And Objectives: Physiological noise in blood oxygen level-dependent functional magnetic resonance imaging (BOLD fMRI) has been shown to have characteristics similar to the BOLD signal itself, suggesting that it may have a vascular dependence. In this study, we evaluated the influence of physiological noise in fMRI as revealed by the differences in vasculature sensitivity of gradient-echo echo-planar imaging (GE-EPI) and spin-echo EPI (SE-EPI).

Materials And Methods: The contribution of physiological noise to the fMRI signal during activation of the visual cortex was assessed by comparing its temporal characteristics with respect to echo time (TE), using both GE-EPI and SE-EPI.

Effect of errors in baseline optical properties on accuracy of transabdominal near-infrared spectroscopy in fetal sheep brain during hypoxic stress.

A continuous-wave (cw) near-infrared spectroscopy (NIRS) instrument has been developed to noninvasively quantify fetal cerebral blood oxygen saturation (StO2). A linear Green's function formulism was used to analytically solve the photon diffusion equation and extract the time-varying fetal tissue oxy- and deoxy-hemoglobin concentrations from the NIR measurements. Here we explored the accuracy with which this instrument can be expected to perform over a range of fetal hypoxic states.

T1rho contrast in functional magnetic resonance imaging.

The application of T1 in the rotating frame (T1rho) to functional MRI in humans was studied at 3 T. Increases in neural activity increased parenchymal T1rho. Modeling suggested that cerebral blood volume mediated this increase.

Temporal resolving power of spin echo and gradient echo fMRI at 3T with apparent diffusion coefficient compartmentalization.

The temporal resolving power of blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) at 3T was investigated in the visual and auditory cortices of the human brain. By using controlled temporal delays and selective visual hemifield stimulation, regions with similar (left vs. right occipital cortex) and different (occipital cortex vs.

Indirect detection of lung perfusion using susceptibility-based hyperpolarized gas imaging.

Purpose: To address the problem of inadequate signal-to-noise ratio (SNR) encountered in lung perfusion magnetic resonance imaging (MRI) by developing an indirect detection based on the strong hyperpolarized (HP) gas signal.

Materials And Methods: Our model is based on detecting the effects of gadolinium (Gd) flowing through lung capillaries by recording the phase of the nearby alveolar HP gas. In a HP gas 3He phantom we imaged gas phases before and after removing tubes containing paramagnetic solution away from the phantom.

Spatial sensitivity and temporal response of spin echo and gradient echo bold contrast at 3 T using peak hemodynamic activation time.

Recent theoretical and experimental work has suggested that spin echo (SE) functional MRI (fMRI) has improved localization of neural activity compared to gradient echo (GE) fMRI at high field strengths, albeit with a decrease in blood oxygenation level-dependent (BOLD) contrast. The present study investigated spatial and temporal variations in GE and SE fMRI at 3 T in response to a brief visual stimulus. The results demonstrate that SE BOLD contrast reaches its maximum amplitude more quickly than does GE contrast at long echo times.

Proton MRI of metabolically produced H2 17O using an efficient 17O2 delivery system.

In vivo detection of H(2)(17)O produced via metabolic reduction of inhaled (17)O-enriched gas is demonstrated using proton magnetic resonance imaging (MRI). Specifically, (1)H T(1rho)-weighted MRI, which may be readily implemented on any MRI scanner, is applied as an indirect (17)O imaging method to quantitatively monitor the distribution of metabolically produced (17)O water (mpH(2)(17)O) in the rat brain. The delivery of (17)O(2) to rats is conducted via a specially designed closed respiration circuit that conserves the expensive gas.

Quantifying arbitrary magnetic susceptibility distributions with MR.

Magnetic susceptibility, as a physical property of materials, plays important roles in many physical, chemical, engineering, and medical applications. Its quantification becomes of significant interest when MRI becomes a commonly used technique in biomedical applications. A general method is presented here for quantifying arbitrary magnetic susceptibility distributions in a localized region on the basis of first principles of magnetic induction field distributions in space.

Muscle metabolism with blood flow restriction in chronic fatigue syndrome.

The purpose of this study was to determine whether chronic fatigue syndrome (CFS) is associated with reduced blood flow and muscle oxidative metabolism. Patients with CFS according to Centers for Disease Control criteria (n = 19) were compared with normal sedentary subjects (n = 11). Muscle blood flow was measured in the femoral artery with Doppler ultrasound after exercise.

T1rho MR imaging of the human wrist in vivo.

Rationale And Objectives: The purpose of this study was (a) to demonstrate the feasibility of computing T1rho maps of, and T1rho dispersion in, human wrist cartilage at MR imaging in vivo and (b) to compare T1rho and T2 weighting in terms of magnitude of relaxation times and signal intensity contrast.

Materials And Methods: T2 and T1rho magnetic resonance images of wrist joints in healthy volunteers (n = 5) were obtained with a spin-echo sequence and a fast spin-echo sequence pre-encoded with a spin-lock pulse cluster. A 1.

Artifacts in T(1rho)-weighted imaging: correction with a self-compensating spin-locking pulse.

Significant artifacts arise in T(1rho)-weighted imaging when nutation angles suffer small deviations from their expected values. These artifacts vary with spin-locking time and amplitude, severely limiting attempts to perform quantitative imaging or measurement of T(1rho) relaxation times. A theoretical model explaining the origin of these artifacts is presented in the context of a T(1rho)-prepared fast spin-echo imaging sequence.

Indirect 17(O)-magnetic resonance imaging of cerebral blood flow in the rat.

Proton T(1rho)-dispersion MRI is demonstrated for indirect, in vivo detection of (17)O in the brain. This technique, which may be readily implemented on any clinical MRI scanner, is applied towards high-resolution, quantitative mapping of cerebral blood flow (CBF) in the rat by monitoring the clearance of (17)O-enriched water. Strategies are derived and employed for 1) quantitation of absolute H(2) (17)O tracer concentration from a ratio of high- and low-frequency spin-locked T(1rho) images, and 2) mapping CBF without having to transform the T(1rho) signal to H(2) (17)O tracer concentration.

Blood flow and muscle metabolism in chronic fatigue syndrome.

The purpose of this study was to determine if chronic fatigue syndrome (CFS) is associated with reduced blood flow and oxidative delivery to skeletal muscle. Patients with CFS according to CDC (Center for Disease Control) criteria ( n =19) were compared with normal sedentary subjects ( n =11). Muscle blood flow was measured with Doppler ultrasound after cuff ischaemia and exercise.

High-resolution assessment of blood flow in murine RIF-1 tumors by monitoring uptake of H(2)(17)O with proton T(1rho)-weighted imaging.

Perfusion parameters, such as blood flow, are critical properties of tumors related to angiogenesis, drug delivery, radiosensitivity, bioenergetic status, and steady state levels of metabolites, such as lactate, that have been proposed as indices of tumor response to therapy. The existing MR methods for measuring tumor blood flow (TBF) have limitations related to sensitivity, spatial resolution, or dependence on other physiological properties such as vascular permeability. To address many of these difficulties, this study introduces the use of an (17)O-enriched tracer in conjunction with high-resolution, indirect MRI to measure TBF.

Chemical-shift MR imaging of acetic acid during percutaneous chemical ablation therapy: preliminary work.

The purpose of this study was to test the hypothesis that chemical-shift magnetic resonance (MR) imaging may be used to map the distribution of acetic acid during percutaneous chemical ablation procedures. Chemical-shift MR imaging was performed with use of standard methods on a 1.5-T scanner.

Pulmonary ventilation and perfusion scanning using hyperpolarized helium-3 MRI and arterial spin tagging in healthy normal subjects and in pulmonary embolism and orthotopic lung transplant patients.

Conventional nuclear ventilation/perfusion (V/Q) scanning is limited in spatial resolution and requires exposure to radioactivity. The acquisition of pulmonary V/Q images using MRI overcomes these difficulties. When inhaled, hyperpolarized helium-3 ((3)He) permits MRI of gas distribution.

Fast MRI of RF heating via phase difference mapping.

A method is presented for the rapid acquisition of temperature maps derived from phase difference maps. The temperature-dependent chemical shift coefficients (TDCSCs) of various concentrations of aqueous cobalt and dysprosium-based compounds were measured. The largest TDCSC calculated was for 100 mM DyEDTA, which had a TDCSC of -0.