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Proton MR spectroscopic imaging (MRSI) at higher magnetic fields (B(0)) suffers metabolite localization errors from different chemical-shift displacements (CSDs) if spatially-selective excitation is used. This phenomenon is exacerbated by the decreasing radiofrequency (RF) field strength, B(1), at higher B(0)s, precluding its suppression with stronger(More)
A survey of Galactic gamma-ray sources at a median energy of ∼20 TeV has been performed using the Milagro Gamma Ray Observatory. Eight candidate sources of TeV emission are detected with pre-trials significance > 4.5σ in the region of Galactic longitude l ∈ [30 • , 220 • ] and latitude b ∈ [−10 • , 10 • ]. Four of these sources, including the Crab nebula(More)
Although recent studies indicate that use of a single global transverse relaxation time, T(2), per metabolite is sufficient for better than +/-10% quantification precision at intermediate and short echo-time spectroscopy in young adults, the age-dependence of this finding is unknown. Consequently, the age effect on regional brain choline (Cho), creatine(More)
The transverse relaxation times, T(2), of N-acetylaspartate (NAA), total choline (Cho), and creatine (Cr) obtained at 3T in several human brain regions of eight healthy volunteers are reported. They were obtained simultaneously in 320 voxels with three-dimensional (3D) proton MR spectroscopy ((1)H-MRS) at 1 cm(3) spatial resolution. A two-point protocol,(More)
Fast, high-resolution, longitudinal relaxation time (T1) mapping is invaluable in clinical and research applications. It has been shown that two spoiled gradient recalled echo (SPGR) images acquired in steady state with variable flip angles is an attractive alternative to the multi-image sets previously acquired with inversion or saturation recovery. The(More)
Although Fourier gradient phase-encoding and Hadamard radio-frequency encoding are two established spatial MR localization techniques, the absence of voxel-shift and interpolation postprocessing algorithms for the latter has always placed it at a discouraging disadvantage. This article presents a method for voxel-shift and interpolation of Hadamard-encoded(More)
Quantitative MR metrics (e.g., T1, T2, diffusion coefficients, and magnetization transfer ratios (MTRs etc)) are often derived from two images collected with one acquisition parameter changed between them (the "two-point" method). Since a low signal-to-noise-ratio (SNR) adversely affects the precision of these metrics, averaging is frequently used, although(More)
In this paper we discuss several methods of significance calculation and point out the limits of their applicability. We then introduce a self consistent scheme for source detection and discuss some of its properties. The method allows incorporating background anisotropies by vetoing existing small scale regions on the sky and compensating for known large(More)
Introduction In MRI, one seeks to produce an accurate image of the effective spin density, ρ(r), from a set of measurements {s q } acquired in the Fourier domain. Because the signal equation (1a) is a continuous-to-discrete mapping, image reconstruction is inherently ill-posed, i.e., infinitely many functions give rise to the same data. Complicating(More)
Fast, 3D radio-frequency transmit field (B1) mapping is important for parallel transmission, spatially selective pulse design and quantitative MRI applications. It has been shown that actual flip angle imaging--two interleaved spoiled gradient recalled echo images acquired in steady state with two very short time delays (TR1, TR2)--is an attractive method(More)