General time-encoding description and improved RASER imaging
نویسندگان
چکیده
Rapid acquisition by sequential excitation and refocusing (RASER) is a new ultrafast MRI technique (1). It provides single-shot images that are purely T2-weighted, so there are no artifacts due to T2 * effects that plague EPI. RASER shows promise for fMRI studies in areas of the brain that are difficult to image with EPI (2, 3). The basis of RASER is time-encoding, which uses a frequency-swept excitation pulse to encode one dimension of the image (1, 4, 5). All previously reported versions of time-encoding use a chirp pulse, which has a poor slab-selection profile. In this work, we provide a general description of time-encoding for any excitation pulse with frequency and gradient modulation, along with an analysis of the SNR possible with time-encoding, and a comparison of the time-encoded signal produced by chirp, HS20, and HS40 pulses.
منابع مشابه
Parallel Imaging with RASER using Multiband Frequency-modulated Excitation Pulses
Introduction: The recently described RASER sequence is a conceptual novelty in MR imaging [1]. Based on frequency-swept excitation, and timeencoding, RASER is a rapid, pure T2-weighted scheme without signal voids, ghosting and distortion artifacts present in conventional echo-planar imaging (EPI). These properties render it attractive for functional imaging (fMRI). However, in the previous impl...
متن کاملA Method to Reduce Effects of Packet Loss in Video Streaming Using Multiple Description Coding
Multiple description (MD) coding has evolved as a promising technique for promoting error resiliency of multimedia system in real-time application programs over error-prone communicational channels. Although multiple description lattice vector quantization (MDCLVQ) is an efficient method for transmitting reliable data in the context of potential error channels, this method doesn’t consider disc...
متن کاملFunctional MRI using super-resolved spatiotemporal encoding.
Recently, new ultrafast imaging sequences such as rapid acquisition by sequential excitation and refocusing (RASER) and hybrid spatiotemporal encoding (SPEN) magnetic resonance imaging (MRI) have been proposed, in which the phase encoding of conventional echo planar imaging (EPI) is replaced with a SPEN. In contrast to EPI, SPEN provides significantly higher immunity to frequency heterogeneitie...
متن کاملEffect of Phase-Encoding Reduction on Geometric Distortion and BOLD Signal Changes in fMRI
Introduction Echo-planar imaging (EPI) is a group of fast data acquisition methods commonly used in fMRI studies. It acquires multiple image lines in k-space after a single excitation, which leads to a very short scan time. A well-known problem with EPI is that it is more sensitive to distortions due to the used encoding scheme. Source of distortion is inhomogeneity in the static B0 field that ...
متن کاملAn Improved Time-Reversal-Based Target Localization for Through-Wall Microwave Imaging
Recently, time reversal (TR) method, due to its high functionality in heterogeneous media has been widely employed in microwave imaging (MI) applications. One of the applications turning into a great interest is through-wall microwave imaging (TWMI). In this paper, TR method is applied to detect and localize a target obscured by a brick wall using a numerically generated data. Regarding this, i...
متن کامل