Home About us Contact
|
Home About us Contact | ||
|
|
||
Longitudinal Magnetization (longitudinal + magnetization)
Selected AbstractsSignal fluctuations induced by non-T1 -related confounds in variable TR fMRI experimentsJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2009Shuowen Hu BS Abstract Purpose To assess and model signal fluctuations induced by non-T1 -related confounds in variable repetition time (TR) functional magnetic resonance imaging (fMRI) and to develop a compensation procedure to correct for the non-T1 -related artifacts. Materials and Methods Radiofrequency disabled volume gradient sequences were effected at variable offsets between actual image acquisitions, enabling perturbation of the measurement system without perturbing longitudinal magnetization, allowing the study of non-T1 -related confounds that may arise in variable TR experiments. Three imaging sessions utilizing a daily quality assurance (DQA) phantom were conducted to assess the signal fluctuations, which were then modeled as a second-order system. A modified projection procedure was implemented to correct for signal fluctuations arising from non-T1 -related confounds, and statistical analysis was performed to assess the significance of the artifacts with and without compensation. Results Assessment using phantom data reveals that the signal fluctuations induced by non-T1 -related confounds was consistent in shape across the phantom and well-modeled by a second-order system. The phantom exhibited significant spurious detections (at P < 0.01) almost uniformly across the central slices of the phantom. Conclusion Second-order system modeling and compensation of non-T1 -related confounds achieves significant reduction of spurious detection of fMRI activity in a phantom. J. Magn. Reson. Imaging 2009;29:1234,1239. © 2009 Wiley-Liss, Inc. [source] Simultaneous myocardial and fat suppression in magnetic resonance myocardial delayed enhancement imaging,JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2007Thomas K.F. Foo PhD Abstract Purpose To develop a method for fat suppression in myocardial delayed enhancement (MDE) studies that achieves effective signal intensity reduction in fat but does not perturb myocardial signal suppression. Materials and Methods A new approach to fat suppression that uses a spectrally-selective inversion-recovery (SPEC-IR) tip-up radio frequency (RF) pulse following the conventional nonselective IR RF pulse together with a second SPEC-IR RF pulse is proposed. The tip-up pulse restores the fat longitudinal magnetization after the nonselective IR pulse and allows the fat magnetization to recover more fully toward its equilibrium value, providing for better fat suppression by the second SPEC-IR RF pulse. This new approach was validated in phantom studies and in five patients. Results Effective fat suppression was achieved using the proposed technique with minimal impact on normal myocardial signal suppression. Mean fat suppression achieved using this approach was 67% ± 8%, as measured in the chest wall immediately opposite the heart. Conclusion The results indicate this modular-type approach optimizes fat suppression in myocardial delayed enhancement studies but does not perturb the basic IR pulse sequence or change basic acquisition parameters. J. Magn. Reson. Imaging 2007;26:927,933. © 2007 Wiley-Liss, Inc. [source] Fast multidimensional NMR by polarization sharingMAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2007Eriks Kup Abstract The speed of multidimensional NMR spectroscopy can be significantly increased by drastically shortening the customary relaxation delay between scans. The consequent loss of longitudinal magnetization can be retrieved if ,new' polarization is transferred from nearby spins. For correlation spectroscopy involving heteronuclei (X = 13C or 15N), protons not directly bound to X can repeatedly transfer polarization to the directly bound protons through Hartmann,Hahn mixing. An order of magnitude increase in speed has been observed for the 600 MHz two-dimensional HMQC spectra of amikacin and strychnine using this technique, and it also reduces the noisy F1 ridges that degrade many heteronuclear correlation spectra recorded with short recovery times. Copyright © 2007 John Wiley & Sons, Ltd. [source] T1 quantification with inversion recovery TrueFISPMAGNETIC RESONANCE IN MEDICINE, Issue 4 2001Klaus Scheffler Abstract A snapshot FLASH sequence can be used to acquire the time course of longitudinal magnetization during its recovery after a single inversion pulse. However, excitation pulses disturb the exponential recovery of longitudinal magnetization and may produce systematic errors in T1 estimations. In this context the possibility of using the TrueFISP sequence to detect the recovery of longitudinal magnetization for quantitative T1 measurements was examined. Experiments were performed on different Gd-doped water phantoms and on humans. T1 values derived from inversion recovery TrueFISP were in excellent agreement with the single-point method even for flip angles up to 50°. In terms of T1 accuracy and SNR, the proposed method seems to be superior to the conventional inversion recovery snapshot FLASH technique. Magn Reson Med 45:720,723, 2001. © 2001 Wiley-Liss, Inc. [source] Saturation transfer in human red blood cells with normal and unstable hemoglobin,NMR IN BIOMEDICINE, Issue 1 2003Masaru Sogami Abstract Saturation transfer phenomena from irradiated protein protons to observed water protons in packed human red blood cells (RBCs) with normal or unstable hemoglobin (Hb), i.e. Hb Yokohama and Hb Koeln, were studied using intermolecular cross-relaxation rates [CR; 1/TIS(H2O)], action spectra {[1 ,(I,/I0)] vs f2 (ppm), where I0 and I, are the longitudinal magnetization of observed water protons before and after long-time f2 -irradiation, respectively}, CR spectra [CR vs f2 (ppm)] and CR ratio vs f2 (ppm) with f2 -irradiation from ,100 to 100,ppm at ,H2/2, of 69 or 250,Hz. RBCs (Hb Yokohama) exhibited many large Heinz bodies and strongly impaired filterability, while RBCs (Hb Koeln) showed few microscopically typical Heinz bodies and virtually normal filterability. However, increases in CR values for RBCs (Hb Koeln) and RBCs (Hb Yokohama), monitored by f2 -irradiation below ,,6 and above ,14,ppm, clearly indicated marked increases in association or aggregation of unstable Hb in RBCs compared with those in normal RBCs. CR values, monitored between ,0 and ,10,ppm, were related to not only association or aggregation of unstable Hb but also amounts of water in RBCs. Aggregation or association of unstable Hb exhibited greater effects on CR values compared with those of methemoglobin formation. Copyright © 2003 John Wiley & Sons, Ltd. [source] | ||||||||||