Showing papers by "Enrico De Vita published in 2004"

High-resolution fast spin echo imaging of the human brain at 4.7 T: implementation and sequence characteristics.

Abstract: In this work, a number of important issues associated with fast spin echo (FSE) imaging of the human brain at 4.7 T are addressed. It is shown that FSE enables the acquisition of images with high resolution and good tissue contrast throughout the brain at high field strength. By employing an echo spacing (ES) of 22 ms, one can use large flip angle refocusing pulses (162 degrees ) and a low acquisition bandwidth (50 kHz) to maximize the signal-to-noise ratio (SNR). A new method of phase encode (PE) ordering (called "feathering") designed to reduce image artifacts is described, and the contributions of RF (B(1)) inhomogeneity, different echo coherence pathways, and magnetization transfer (MT) to FSE signal intensity and contrast are investigated. B(1) inhomogeneity is measured and its effect is shown to be relatively minor for high-field FSE, due to the self-compensating characteristics of the sequence. Thirty-four slice data sets (slice thickness = 2 mm; in-plane resolution = 0.469 mm; acquisition time = 11 min 20 s) from normal volunteers are presented, which allow visualization of brain anatomy in fine detail. This study demonstrates that high-field FSE produces images of the human brain with high spatial resolution, SNR, and tissue contrast, within currently prescribed power deposition guidelines.

B0 dependence of the on-resonance longitudinal relaxation time in the rotating frame (T1rho) in protein phantoms and rat brain in vivo.

Abstract: On-resonance longitudinal relaxation time in the rotating frame (T 1 ρ )has been shown to provide unique information during the early minutes of acute stroke. In the present study, the contributions of the different relaxation mechanisms to on-resonance T 1 ρ relaxation were assessed by determining relaxation rates (R 1 ρ ) in both protein phantoms and in rat brain at 2.35, 4.7, and 9.4 T. Similar to transverse relaxation rate (R 2 ), R 1 ρ increased substantially with increasing magnetic field strength (B 0 ). The B 0 dependence was more pronounced at weak spin-lock fields. In contrast to R 1 ρ , longitudinal relaxation rate (R 1 ) decreased as a function of increasing B 0 field. The present data argue that dipole-dipole interaction forms only one pathway for T 1 p relaxation and the contributions from other physicochemical factors need to be considered. Magn Reson Med 51:4-8, 2004.

Method for spatially interleaving two images to halve EPI readout times: two reduced acquisitions interleaved (TRAIL)

Abstract: A new MRI method is presented that can generate images using half the normal readout time or, more usefully, half the number of phase-encode steps, combining two readouts per excitation. However, the corresponding data are interleaved in image space-not in k-space, as in many other fast techniques. This gives a resilience to the phase-related artifacts that can occur in many other techniques due to subject motion. A modified stimulated-echo experiment is used to create two low-resolution images from a single sequence. The magnetization that contributes to these images is nonuniformly distributed within each pixel, forming two sinusoidal waves in quadrature, with an oscillation period of exactly two pixels. Since only half of each pixel contributes significant signal, the two images can be interleaved to create a full image with twice as many pixels and double the resolution. When the technique is used in the phase-encode direction, the effective imaging time is halved, though with two readouts per TR period. When two half-length echo-planar readouts are used, the method can also reduce blurring and distortion by halving the effective readout time for echo-planar imaging (EPI). For even further improvements, the technique can be combined with partial Fourier or parallel imaging. (C) 2004 Wiley-Liss, Inc.