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Short TE (short + te)
Selected AbstractsMRA of intracranial aneurysms embolized with platinum coils: A vascular phantom study at 1.5T and 3TJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2008Shingo Kakeda Abstract Purpose To analyze the influence of matrix and echo time (TE) of three-dimensional time-of-flight (3D TOF) magnetic resonance angiography (MRA) on the depiction of residual flow in aneurysms embolized with platinum coils at 1.5T and 3T. Materials and Methods A simulated intracranial aneurysm of the vascular phantom was loosely packed to maintain the patency of some residual aneurysmal lumen with platinum coils and connected to an electromagnetic flow pump with pulsatile flow. MRAs were obtained altering the matrix and TE of 3D TOF sequences at 1.5T and 3T. Results The increased spatial resolution and the shorter TE offered better image quality at 3T. For the depiction of an aneurysm remnant, the high-spatial-resolution 3T MRA (matrix size of 384 × 224 and 512 × 256) with a short TE of ,3.3 msec were superior to the 1.5T MRA obtained with any sequences. Conclusion 3T MRA is superior to 1.5T MRA for the assessment of aneurysms embolized with platinum coils; the combination of the 512 × 256 matrix and short TE (3.3 msec or less) seems feasible at 3T. J. Magn. Reson. Imaging 2008;28:13,20. © 2008 Wiley-Liss, Inc. [source] Selective maximization of 31P MR spectroscopic signals of in vivo human brain metabolites at 3TJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2007Rose-Ann M. Blenman PhD Abstract Purpose To develop a short TR, short TE, large flip angle (LFA), in vivo 31P MR spectroscopy (MRS) technique at 3T that selectively maximizes the signal-to-noise ratio (SNR) of long T1 human brain metabolites implicated in bipolar disorder. Materials and Methods Two pulse sequences were evaluated for efficiency. Slice profiles acquired with the scaled, sinc-shaped, radiofrequency (RF) LFA pulses were compared to those acquired with Shinnar-Le Roux (SLR) RF LFA pulses. The SLR-based LFA pulse sequence was used to maximize the inorganic phosphate signal in a phantom, after which volunteer metabolite signals were selectively maximized and compared to their correlates acquired with conventional spin-echo methods. Results The comparison of slice profiles acquired with sinc-shaped RF LFA pulses vs. SLR RF LFA pulses showed that SLR-based pulse sequences, with their improved excitation and slice profiles, yield significantly better results. In vivo LFA spin-echo MRS implemented with SLR pulses selectively increased the 31P MRS signal, by as much as 93%, of human brain metabolites that have T1 times longer than the TR of the acquisition. Conclusion The data show that the LFA technique can be employed in vivo to maximize the signal of long T131P brain metabolites at a given TE and TR. LFAs ranging between 120° and 150° are shown to maximize the 31P signal of human brain metabolites at 3T. J. Magn. Reson. Imaging 2007. © 2007 Wiley-Liss, Inc. [source] Proton spectroscopic metabolite signal relaxation times in preterm infants: A prerequisite for quantitative spectroscopy in infant brainJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2003Harald Kugel PhD Abstract Purpose To determine relaxation times of metabolite signals in proton magnetic resonance (MR) spectra of immature brain, which allow a correction of relaxation that is necessary for a quantitative evaluation of spectra acquired with long TE. Proton MR spectra acquired with long TE allow a better definition of metabolites as N-acetyl aspartate (NAA) and lactate especially in children. Materials and Methods Relaxation times were determined in the basal ganglia of 84 prematurely born infants at a postconceptional age of 37.8 ± 2.2 (mean ± SD) weeks. Metabolite resonances were investigated using the double-spin-echo volume selection method (PRESS) at 1.5 T. T1 was determined from intensity ratios of signals obtained with TRs of 1884 and 6000 msec, measured at 3 TEs (25 msec, 136 msec, 272 msec). T2 was determined from signal intensity ratios obtained with TEs of 136 msec and 272 msec, measured at 2 TR. Taking only long TEs reduced baseline distortions by macromolecules and lipids. For myo-inositol (MI), an apparent T2 for short TE was determined from the ratio of signals obtained with TE = 25 msec and 136 msec. Intensities were determined by fitting a Lorentzian to the resonance, and by integration. Results Relaxation times were as follows: trimethylamine-containing compounds (Cho): T1 = 1217 msec/T2 = 273 msec; total creatine (Cr) at 3.9 ppm: 1010 msec/111 msec; Cr at 3.0 ppm: 1388 msec/224 msec; NAA: 1171 msec/499 msec; Lac: 1820 msec/1022 msec; MI: 1336 msec/173 msec; apparent T2 at short TE: 68 msec. Conclusion T1 and T2 in the basal ganglia of premature infants do not differ much from previously published data from basal ganglia of older children and adults. T2 of Cho was lower than previous values. T2 of Cr at 3.9 ppm and Lac have been measured under different conditions before, and present values differ from these data. J. Magn. Reson. Imaging 2003;17:634,640. © 2003 Wiley-Liss, Inc. [source] Magnetic resonance elastography in the liver at 3 Tesla using a second harmonic approachMAGNETIC RESONANCE IN MEDICINE, Issue 2 2009D.A. Herzka Abstract Magnetic resonance elastography (MRE) using mechanical stimulation has demonstrated diagnostic value and clinical promise in breast, liver, and kidney at 1.5 Tesla (T). However, MRE at 1.5T suffers from long imaging times and would benefit from greater signal-to-noise for more robust postprocessing. We present an MRE sequence modified for liver imaging at 3.0T. To avoid artifacts in the phase images, the sequence maintains a short TE by using a second harmonic approach, including stronger motion encoding gradients, shorter radio frequency pulses and an echo-planar readout. Scan time was decreased by a factor of ,2 relative to 1.5T by using an EPI readout and a higher density sampling of the phase waveform was used to calculate shear stiffness and viscosity. Localized (small region of interest) and global (whole-liver region of interest) measurements in normal healthy subjects compared very favorably with previously published results at 1.5T. There was no significant difference between global and localized measures. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source] Quantitative evaluation of susceptibility and shielding effects of nitinol, platinum, cobalt-alloy, and stainless steel stentsMAGNETIC RESONANCE IN MEDICINE, Issue 5 2003Yi Wang Abstract The purpose of this study is to quantitatively estimate the shielding and susceptibility effects of commonly used metallic stents on MR signal. Two experiments were performed using a 3D gradient echo sequence with short TE to image a stent phantom: 1) short TR and high flip angle (contrast enhanced MRA parameters), and 2) long TR (TR , T1) and low flip angle. The factor characterizing susceptibility effects was estimated from the signal phase of the first experiment, and then the factor characterizing the shielding effects was derived from the second experiment. Susceptibility induced signal loss was negligible (<1%) for nonstainless-steel (nitinol, platinum, and cobalt-alloy) stents and totally destructive (100%) for the stainless steel stent. Signal loss due to RF shielding was 31,62% for nitinol stents, 14,50% for platinum stents, 50,77% for the cobalt-alloy stents (undetermined for the stainless steel stent), varied with stent orientation, diameter, and wall geometry. In summary, stents made of nitinol, platinum, and cobalt-alloy have negligible susceptibility effects but stents made of stainless steel may have complete dephasing. All stents have substantial shielding effects, which vary with composition, geometry, and orientation. Large platinum stents may have the smallest artifacts and are the best suited for postinterventional MR imaging. Magn Reson Med 49:972,976, 2003. © 2003 Wiley-Liss, Inc. [source] | ||||||||||