First-pass myocardial perfusion MR imaging with interleaved notched saturation: feasibility study.

The authors evaluated a magnetization preparation scheme with a "notched" section profile for T1-weighted first-pass myocardial perfusion magnetic resonance (MR) imaging at 1.5 T. The pulse sequence consisted of a preparation sequence followed by an interleaved gradient-echo echo-planar sequence. Image contrast was evaluated in a feasibility study in 12 adult patients. The notched saturation pulse allowed long magnetization recovery times without sacrificing section coverage. Image contrast between normal and ischemic myocardium was excellent.

Two-dimensional multishot echo-planar coronary MR angiography.

This work presents a two-dimensional (2D) multishot echo-planar imaging (EPI) technique for magnetic resonance angiography (MRA) of individual coronary arteries in a 17-heartbeat breath-hold. Conventional 2D and 3D segmented gradient-echo (GRE) coronary MRA requires repetitive excitation of the same slice or slab within each cardiac cycle, which can result in reduced blood signal and in motion artifacts. Two-dimensional multishot EPI can address these limitations by eliminating multiple excitations per cardiac cycle, using large flip-angle excitations, markedly reducing the data acquisition window, and performing oblique multislice 2D imaging. The goal of this study was to assess the feasibility of breath-hold 2D multishot EPI for multislice coronary MRA and to demonstrate its reliability by consistently acquiring high-quality images of the coronary arteries in a series of 16 volunteers.

An orthogonal correlation algorithm for ghost reduction in MRI.

Ghosting in MRI due to modulation of k-space data can be caused by motion of the subject or characteristics of the sequence. A general solution for 2DFT MRI that reduces ghosting without causal modeling is presented. Separate image data sets are acquired in which the phase and frequency directions are swapped. In these two data sets, the image signal is correlated, whereas the ghost signals are not. By taking a correlation of these two data sets, an image with greatly reduced ghosting is obtained. The reduction is shown to depend both on the correct signal intensity of the image, as well as the ghost intensity in the ghosted region. The reduction approaches 100% in regions of low image signal, and is more moderate in regions of higher image signal. The process was applied to conventional spin-echo, fast-spin-echo, and gradient echo imaging of volunteers and a phantom. Results of a reader study of the volunteer images reflected a significant overall reduction of ghosting artifacts in all volunteer experiments.

Gradient moment smoothing: a new flow compensation technique for multi-shot echo-planar imaging.

This work identifies an additional source of phase error across ky in multi-shot echo-planar imaging resulting from flow or motion along the phase-encoding direction. A velocity-independent flow compensation technique, gradient moment smoothing, is presented that corrects this error by forcing the phase to have smooth quadratic behavior. The correction is implemented, without compromising scan time, by changing the first moment of a bipolar prephaser pulse on a shot-by-shot basis. In phantom and in vivo experiments, gradient moment smoothing effectively eliminates ghosting and signal loss due to phase-encoding flow. When used in conjunction with a "flyback" echo-planar readout, which compensates for flow in the frequency-encoding direction, gradient moment smoothing renders multi-shot echo-planar imaging relatively insensitive to in-plane flow. This can make multi-shot echo-planar imaging a viable technique for accurately imaging in-plane flow and may desensitize it to the otherwise serious problem of in-plane motion.

Dual-echo interleaved echo-planar imaging of the brain.

An interleaved echo-planar imaging (EPI) technique is described that provides images from 20 sections of the brain at two echo times (27 and 84 ms) in 1:05. Six echoes per image per repetition are collected in 24 repetitions of the pulse sequence. MR images of the brain obtained from five volunteers using the dual-echo EPI sequence, fast spin-echo (FSE), and conventional dual-echo spin-echo were evaluated qualitatively for diagnostic use and quantitatively for relative signal-to-noise ratio (SNR), contrast, and contrast-to-noise ratios (CNR).

New technical developments in magnetic resonance imaging of epilepsy.

Within the last several years a number of technical developments have been made in magnetic resonance imaging (MRI) that can potentially impact clinical and research MR imaging application in epilepsy. These include developments in instrumentation and in pulse sequences. Advances in instrumentation include higher capacity gradient systems and multiple receiver coils as directed to brain imaging. Advances in pulse sequence include use of fast or turbo-spin-echo techniques, variants of echo-planar imaging, and sequences such as fluid-attenuation inversion recovery (FLAIR) targeted to specific applications of brain imaging. The purpose of this paper is to review several of these developments.