Magnetic Resonance Imaging (MRI)

Magnetic resonance imaging with gadolinium-diethylenetriaminepentaacetic acid complex (GdDTPA) as the contrast agent was used to image the aqueous chamber of the eye. This method, in addition to providing spatial information, permits quantitative study of the aqueous flow. GdDTPA solution was applied either topically or intravenously, entering the anterior chamber via different pathways. The wash-in and wash-out of GdDTPA follow a two-compartment model which enables determination of the aqueous flow rate by multiplying the aqueous chamber volume by the wash-out rate constant.

A technique integrating multishot periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) and parallel imaging is presented for diffusion echo-planar imaging (EPI) at high spatial resolution. The method combines the advantages of parallel imaging to achieve accelerated sampling along the phase-encoding direction, and PROPELLER acquisition to further decrease the echo train length (ETL) in EPI.

The efficacy of proton magnetic resonance imaging (MRI) was evaluated and compared with that of B-scan ultrasound in the detection and differentiation of diabetic vitreous hemorrhage. Although conventional spin-echo MRI could not locate vitreous hemorrhages, gradient-recalled-echo (GRE) MRI readily did so. The aberrant signals appeared to originate from the interfacing between hemorrhages and the vitreous, and possibly also from the paramagnetic effect of the ferrous ion.

UNLABELLED: SUBJECT OBJECTIVES: To assess the effect of the wake-promoting drug modafinil on working memory and brain activation in the executive network, following a single night of sleep deprivation.
DESIGN: Randomized, placebo-controlled, 4-arm, double-blind evaluation of a single 200-mg dose of modafinil on working memory (1-, 2-, and 3-back)-related functional brain activation and performance following overnight sleep deprivation.
SETTING: General Clinical Research Center, Biomedical Imaging Center.
SUBJECTS: Eight medication-free men, aged 21 to 35 years.

Functional magnetic resonance imaging (MRI), using monocrystalline iron oxide nanoparticles (MION) as a new intravascular contrast agent, was adapted for a rabbit model of pigmented choroidal melanoma. Three-dimensionally spoiled gradient recalled sequences were used for the quantitative assessment of blood volume and cellular uptake. In all ocular tissues studied, MION reduced the T(2)-weighted signal intensity within 0.5 h and at 24 h (both p

A model for quantification of perfusion in pulsed labelling techniques is described, based on solving the modified Bloch equation including the effects of flow. The model is designed to fit experimental data acquired in two separate measurements (inversion and control, or selective and non-selective inversions) for different inversion times using a biexponential. Although the signal contrast is 50% less than the continuous labelling technique, it seems more appropriate for human studies because of its lower power deposition, shorter transit time and the use of an interleaved acquisition.

The efficacy of proton magnetic resonance imaging in differentiating vitreous from C3F8 gas and silicone oil tamponades, and in detecting fresh hemorrhages and condensed vitreous was tested in rabbits in vivo. The results suggest that this imaging method could provide a useful alternative to ultrasonography, especially in eyes with opaque media.

Using nuclear magnetic resonance (NMR), we have examined the relationship of high-energy phosphate metabolism and perfusion in human soleus and gastrocnemius muscles. With 31P-NMR spectroscopy, we monitored phosphocreatine (PCr) decay and recovery in eight normal volunteers and four heart failure patients performing ischemic plantar flexion. By using echo-planar imaging, perfusion was independently measured by a local [inversion-recovery (T1-flow)] and a regional technique (NMR-plethysmography).

A technique suitable for diffusion tensor imaging (DTI) at high field strengths is presented in this work. The method is based on a periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) k-space trajectory using EPI as the signal readout module, and hence is dubbed PROPELLER EPI. The implementation of PROPELLER EPI included a series of correction schemes to reduce possible errors associated with the intrinsically higher sensitivity of EPI to off-resonance effects.