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Susceptibility Gradients (susceptibility + gradient)
Selected AbstractsSusceptibility gradient mapping (SGM): A new postprocessing method for positive contrast generation applied to superparamagnetic iron oxide particle (SPIO)-labeled cellsMAGNETIC RESONANCE IN MEDICINE, Issue 3 2008Hannes Dahnke Abstract Local susceptibility gradients result in a dephasing of the precessing magnetic moments and thus in a fast decay of the NMR signals. In particular, cells labeled with superparamagnetic iron oxide particles (SPIOs) induce hypointensities, making the in vivo detection of labeled cells from such a negative image contrast difficult. In this work, a new method is proposed to selectively turn this negative contrast into a positive contrast. The proposed method calculates the susceptibility gradient and visualizes it in a parametric map directly from a regular gradient-echo image dataset. The susceptibility gradient map is determined in a postprocessing step, requiring no dedicated pulse sequences or adaptation of the sequence before and during image acquisition. Phantom experiments demonstrated that local susceptibility differences can be quantified. In vivo experiments showed the feasibility of the method for tracking of SPIO-labeled cells. The method bears the potential also for usage in other applications, including the detection of contrast agents and interventional devices as well as metal implants. Magn Reson Med 60:595,603, 2008. © 2007 Wiley-Liss, Inc. [source] In vivo proton spectroscopy without solvent suppressionCONCEPTS IN MAGNETIC RESONANCE, Issue 4 2001David B. Clayton Abstract In 1H MR spectroscopy of the human brain, it is common practice to suppress the solvent signal prior to acquisition. This reduces the large dynamic range which is otherwise required of the MR receiver and digitizer in order to detect the dilute metabolite resonances in the presence of the much larger water signal. However, complete solvent suppression is not always obtainable, particularly over large volumes and in superficial regions containing large susceptibility gradients. In this work, it demonstrated that modern commercial MR scanners possess the dynamic range necessary to adequately resolve the 1H metabolites in unsuppressed spectra. Moreover, a postacquisition method is presented which can completely remove the intact water signal and accurately quantitate the metabolite peaks. Preserving the water signal in in vivo spectroscopy has several useful benefits, such as providing a high signal-to-noise ratio internal concentration, frequency, and line shape reference. Comparison is made between suppressed and unsuppressed spectra from both a phantom and the human brain acquired at 4 T. © 2001 John Wiley & Sons, Inc. Concepts Magn Reson 13: 260,275, 2001 [source] fMRI studies of sensitivity and habituation effects within the auditory cortex at 1.5 T and 3 TJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2006Kerstin Rabe MD Abstract Purpose To assess habituation effects in relation to field strength by fMRI at 1.5 vs. 3.0 T within the auditory cortex of healthy subjects. Materials and Methods fMRI experiments were performed on 19 healthy subjects at 1.5 T (N = 12) and 3 T (N = 12). The auditory cortex was stimulated binaurally by digitally generated pulsed (, = 5 Hz) 800 Hz sine tones with three alternating on and off periods. Results The mean activation after stimulation (4.4% ± 1.2% (1.5 T) and 5.3% ± 2.3% (3 T)) and number of activated pixels (96.7 ± 49.8 (1.5 T) and 139.9 ± 101 (3 T)) were higher at 3 T compared to 1.5 T; however, that difference did not reach statistical significance. A characteristic signal decay with repeated stimuli was revealed at both 1.5 and 3 T, and the response to the second and third stimulation blocks was significantly lower compared to the first. The habituation pattern was the same, independently of field strength and age. Conclusion The mean activation and number of pixels were only modestly higher at 3 T, probably due to higher physiologic noise and higher local macroscopic susceptibility gradients within the temporal lobes at 3 T. Our data reveal that measured auditory habituation is independent of field strength, and data obtained at two different field strengths do not differ fundamentally in this context. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source] Susceptibility gradient mapping (SGM): A new postprocessing method for positive contrast generation applied to superparamagnetic iron oxide particle (SPIO)-labeled cellsMAGNETIC RESONANCE IN MEDICINE, Issue 3 2008Hannes Dahnke Abstract Local susceptibility gradients result in a dephasing of the precessing magnetic moments and thus in a fast decay of the NMR signals. In particular, cells labeled with superparamagnetic iron oxide particles (SPIOs) induce hypointensities, making the in vivo detection of labeled cells from such a negative image contrast difficult. In this work, a new method is proposed to selectively turn this negative contrast into a positive contrast. The proposed method calculates the susceptibility gradient and visualizes it in a parametric map directly from a regular gradient-echo image dataset. The susceptibility gradient map is determined in a postprocessing step, requiring no dedicated pulse sequences or adaptation of the sequence before and during image acquisition. Phantom experiments demonstrated that local susceptibility differences can be quantified. In vivo experiments showed the feasibility of the method for tracking of SPIO-labeled cells. The method bears the potential also for usage in other applications, including the detection of contrast agents and interventional devices as well as metal implants. Magn Reson Med 60:595,603, 2008. © 2007 Wiley-Liss, Inc. [source] 3T MR of the prostate: Reducing susceptibility gradients by inflating the endorectal coil with a barium sulfate suspensionMAGNETIC RESONANCE IN MEDICINE, Issue 5 2007Yael Rosen Abstract Most prostate MRI/MRS examinations are performed with an endorectal coil inflated with air, leading to an air,tissue interface that induces magnetic susceptibility gradients within the gland. Inflation of the coil with a barium sulfate suspension is described and compared to inflation with air or liquid perfluorocarbon (PFC). The B0 field in the prostate gland was mapped for five healthy volunteers when the endorectal coil was inflated with each of the three agents. A marked decrease in the posterior-anterior (P-A) field gradient and a significant improvement in field homogeneity were evident in the presence of a barium suspension and PFC relative to air. MRS data acquired from the prostate gland in the presence of air, PFC, and a barium suspension in the endorectal coil showed similar trends, demonstrating improvement in line-widths and spectral resolution when the barium suspension or the PFC were inflating the endorectal coil. On this basis we conclude that a barium suspension provides an available, cheap, and safe alternative to PFC, and we suggest that inflating the endorectal coil with a barium suspension should be considered for prostate MR studies, especially at high field strengths (such as 3T). Magn Reson Med 57:898,904, 2007. © 2007 Wiley-Liss, Inc. [source] Proton T2 relaxation study of water, N-acetylaspartate, and creatine in human brain using Hahn and Carr-Purcell spin echoes at 4T and 7TMAGNETIC RESONANCE IN MEDICINE, Issue 4 2002Shalom Michaeli Abstract Carr-Purcell and Hahn spin-echo (SE) measurements were used to estimate the apparent transverse relaxation time constant (T) of water and metabolites in human brain at 4T and 7T. A significant reduction in the T values of proton resonances (water, N-acetylaspartate, and creatine/phosphocreatine) was observed with increasing magnetic field strength and was attributed mainly to increased dynamic dephasing due to increased local susceptibility gradients. At high field, signal loss resulting from T decay can be substantially reduced using a Carr-Purcell-type SE sequence. Magn Reson Med 47:629,633, 2002. © 2002 Wiley-Liss, Inc. [source] | ||||||||||