Showing papers by "Jin Hyung Lee published in 2008"

DWI of the spinal cord with reduced FOV single-shot EPI

Abstract: Single-shot echo-planar imaging (ss-EPI) has not been used widely for diffusion-weighted imaging (DWI) of the spinal cord, because of the magnetic field inhomogeneities around the spine, the small cross-sectional size of the spinal cord, and the increased motion in that area due to breathing, swallowing, and cerebrospinal fluid (CSF) pulsation. These result in artifacts with the usually long readout duration of the ss-EPI method. Reduced field-of-view (FOV) methods decrease the required readout duration for ss-EPI, thereby enabling its practical application to imaging of the spine. In this work, a reduced FOV single-shot diffusion-weighted echo-planar imaging (ss-DWEPI) method is proposed, in which a 2D spatially selective echo-planar RF excitation pulse and a 180 degrees refocusing pulse reduce the FOV in the phase-encode (PE) direction, while suppressing the signal from fat simultaneously. With this method, multi slice images with higher in-plane resolutions (0.94 x 0.94 mm(2) for sagittal and 0.62 x 0.62 mm(2) for axial images) are achieved at 1.5 T, without the need for a longer readout.

Synthesis and characterization of PVP-coated large core iron oxide nanoparticles as an MRI contrast agent

Abstract: The purpose of this study was to synthesize biocompatible polyvinylpyrrolidone (PVP)-coated iron oxide (PVP-IO) nanoparticles and to evaluate their efficacy as a magnetic resonance imaging (MRI) contrast agent. The PVP-IO nanoparticles were synthesized by a thermal decomposition method and characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), and a superconducting quantum interface device (SQUID). The core size of the particles is about 8-10 nm and the overall size is around 20-30 nm. The measured r(2) (reciprocal of T(2) relaxation time) and r2∗ (reciprocal of T2∗ relaxation time) are 141.2 and 338.1 (s mM)(-1), respectively. The particles are highly soluble and stable in various buffers and in serum. The macrophage uptake of PVP-IO is comparable to that of Feridex as measured by a Prussian blue iron stain and phantom study. The signal intensity of a rabbit liver was effectively reduced after intravenous administration of PVP-IO. Therefore PVP-IO nanoparticles are potentially useful for T(2)-weighted MR imaging.

Full-brain coverage and high-resolution imaging capabilities of passband b-SSFP fMRI at 3T

Abstract: Passband balanced-steady-state free precession (b-SSFP) fMRI is a recently developed method that utilizes the passband (flat portion) of the b-SSFP off-resonance response to measure MR signal changes elicited by changes in tissue oxygenation following increases in neuronal activity. Rapid refocusing and short readout durations of b-SSFP, combined with the relatively large flat portion of the b-SSFP off-resonance spectrum allows distortion-free full-brain coverage with only two acquisitions. This allows for high-resolution functional imaging, without the spatial distortion frequently encountered in conventional high-resolution functional images. Finally, the 3D imaging compatibility of the b-SSFP acquisitions permits isotropic-voxel-size high-resolution acquisitions. In this study we address some of the major technical issues involved in obtaining passband b-SSFP-based functional brain images with practical imaging parameters and demonstrate the advantages through breath-holding and visual field mapping experiments. Magn Reson Med, 2008. © 2008 Wiley-Liss, Inc.

MRI using a concentric rings trajectory.

Abstract: The concentric rings two-dimensional (2D) k-space trajectory provides an alternative way to sample polar data. By collecting 2D k-space data in a series of rings, many unique properties are observed. The concentric rings are inherently centric-ordered, provide a smooth weighting in k-space, and enable shorter total scan times. Due to these properties, the concentric rings are well-suited as a readout trajectory for magnetization-prepared studies. When non-Cartesian trajectories are used for MRI, off-resonance effects can cause blurring and degrade the image quality. For the concentric rings, off-resonance blur can be corrected by retracing rings near the center of k-space to obtain a field map with no extra excitations, and then employing multifrequency reconstruction. Simulations show that the concentric rings exhibit minimal effects due to T modulation, enable shorter scan times for a Nyquist-sampled dataset than projection-reconstruction imaging or Cartesian 2D Fourier transform (2DFT) imaging, and have more spatially distributed flow and motion properties than Cartesian sampling. Experimental results show that off-resonance blurring can be successfully corrected to obtain high-resolution images. Results also show that concentric rings effectively capture the intended contrast in a magnetization-prepared sequence. Magn Reson Med, 2007. © 2007 Wiley-Liss, Inc.

2105 Graphite/metal core-shell nanocrystals as MRI contrast agents to detect vascular inflammation

Abstract: In Vitro Uptake/Imaging Mouse macrophage cells (RAW264) were incubated with ferumoxytol (Feridex), ferumoxtran-10 (Combidex), or graphite/metal core-shell nanocrystals (CN) for 24 hours, each at a concentration of 100 ugFe/ml. After incubation, 5 × 106 cells from each group were scanned by MRI at 1.5 T (GE Healthcare, Milwaukee, WI) to examine cellular uptake of contrast using a standard gradient echo sequence (TR/TE = 100/10, FA = 30, Matrix = 256 × 256, slice thickness = 2.0, FOV = 12 cm). In Vivo Uptake/Imaging FVB mice (N = 5) underwent a carotid-ligation procedure previously shown to produce a macrophage-rich atherosclerotic lesion. Briefly, they were given high fat diet for 4 weeks and then had diabetes induced by 5 daily intraperitoneal injections of streptozotocin. After 2 weeks of diabetes, carotid ligation of the left carotid artery was performed. Two weeks post carotid ligation, mice were given CN-Cy5.5 (8 nmol of Cy5.5) via tail vein and scanned serially over 12–48 hours using the Maestro invivo fluorescent imaging system (CRI, Woburn, MA). After final in vivo imaging, carotid arteries were exposed and both in situ and ex vivo imaging were performed.

2119 Visualization of micro-vasculature using FeCo-core/graphitic-carbon-shell nanocrystals and high-resolution 3D spiral imaging

Abstract: Methods Normal and stenosis induced white rabbits with body weight of ~4 kg were first catheterized in the ear vein. Through the catheter, 9.6 cc of 5 mM concentration FeCo nanocrystal contrast agent was injected followed by 1 cc of saline injection. Immediately before and after the injection, a small volume covered by a 1 inch custom made surface coil was imaged using spectral-spatial excitation and 3D spiral readout. The spatial resolution was 78 × 78 × 500 um3 with volume coverage of 4 × 4 × 1 cm3. The scan time was 2 min 40 sec for a single volume and the scan was repeated 9 times over 24 min to improve SNR. A whole body volume scan using a fat-saturated 3D SPGR sequence was also performed using a standard GE head coil 1 hour before and after the injection. All the experiments were conducted using a GE 1.5 T EXCITE whole body system with a maximum gradient of 40 mT/m and maximum slew rate of 150 T/m/s.