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Selected AbstractsAssessing the influence of scanner background noise on auditory processing.HUMAN BRAIN MAPPING, Issue 8 2007Abstract We compared two experimental designs aimed at minimizing the influence of scanner background noise (SBN) on functional MRI (fMRI) of auditory processes with one conventional fMRI design. Ten subjects listened to a series of four one-syllable words and had to decide whether two of the words were identical. This was contrasted with a no-stimulus control condition. All three experimental designs had a duration of ,17 min: 1) a behavior interleaved gradients (BIG; Eden et al. [1999] J Magn Reson Imaging 41:13,20) design (repetition time, TR, = 6 s), where stimuli were presented during the SBN-free periods between clustered volume acquisitions (CVA); 2) a sparse temporal sampling technique (STsamp; e.g., Gaab et al., [2003] Neuroimage 19:1417,1426) acquiring only one set of slices following each of the stimulations with a 16-s TR and jittered delay times between stimulus offset and image acquisition; and 3) an event-related design with continuous scanning (ERcont) using the stimulation design of STsamp but with a 2-s TR. The results demonstrated increased signal within Heschl's gyrus for the STsamp and BIG-CVA design in comparison to ERcont as well as differences in the overall functional anatomy among the designs. The possibility to obtain a time course of activation as well as the full recovery of the stimulus- and SBN-induced hemodynamic response function signal and lack of signal suppression from SBN during the STsamp design makes this technique a powerful approach for conducting auditory experiments using fMRI. Practical strengths and limitations of the three auditory acquisition paradigms are discussed. Hum Brain Mapp, 2006. © 2006 Wiley-Liss, Inc. [source] Artifact-reduced two-dimensional cine steady state free precession for myocardial blood- oxygen-level-dependent imagingJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2010Xiangzhi Zhou PhD Abstract Purpose: To minimize image artifacts in long TR cardiac phase-resolved steady state free precession (SSFP) based blood-oxygen-level-dependent (BOLD) imaging. Materials and Methods: Nine healthy dogs (four male, five female, 20,25 kg) were studied in a clinical 1.5 Tesla MRI scanner to investigate the effect of temporal resolution, readout bandwidth, and motion compensation on long repetition time (TR) SSFP images. Breath-held 2D SSFP cine sequences with various temporal resolutions (10,204 ms), bandwidths (239,930 Hz/pixel), with and without first-order motion compensation were prescribed in the basal, mid-ventricular, and apical along the short axis. Preliminary myocardial BOLD studies in dogs with controllable coronary stenosis were performed to assess the benefits of artifact-reduction strategies. Results: Shortening the readout time by means of increasing readout bandwidth had no observable reduction in image artifacts. However, increasing the temporal resolution in the presence of first-order motion compensation led to significant reduction in image artifacts. Preliminary studies demonstrated that BOLD signal changes can be reliably detected throughout the cardiac cycle. Conclusion: Artifact-reduction methods used in this study provide significant improvement in image quality compared with conventional long TR SSFP BOLD MRI. It is envisioned that the methods proposed here may enable reliable detection of myocardial oxygenation changes throughout the cardiac cycle with long TR SSFP-based myocardial BOLD MRI. J. Magn. Reson. Imaging 2010;31:863,871. ©2010 Wiley-Liss, Inc. [source] Signal 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] In vivo and in vitro MR spectroscopic profile of central neurocytomasJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 2 2003Rama Jayasundar PhD Abstract This study reports in vivo and in vitro magnetic resonance spectroscopic findings in two cases of central neurocytomas (CNC) confirmed by immunohistochemistry. Volume localized in vivo proton magnetic resonance spectroscopy (MRS) was carried out before surgery using a point resolved spectroscopy (PRESS) sequence with a repetition time of six seconds and an echo time of 135 msec. Normal spectrum was obtained from gray matter from a volunteer for comparison. 1H and 31P in vitro MRS studies were carried out at 9.4 T on the extracts prepared from the surgically excised tumors. The in vivo spectra showed prominent glycine (Gly) and choline (Cho) and low N-acetyl aspartate compared to the normal. The Gly peak was assigned using the in vitro studies. These studies showed that the major contribution to the Cho peak observed in vivo is from phosphocholine. A combination of the presence of NAA and an increased Gly in the proton MR spectrum could be a characteristic feature of CNCs, which are rare intraventricular tumors of neuronal origin. J. Magn. Reson. Imaging 2003;17:256,260. © 2003 Wiley-Liss, Inc. [source] Applications of neural network analyses to in vivo 1H magnetic resonance spectroscopy of Parkinson disease patientsJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2002David Axelson PhD Abstract Purpose To apply neural network analyses to in vivo magnetic resonance spectra of controls and Parkinson disease (PD) patients for the purpose of classification. Materials and Methods Ninety-seven in vivo proton magnetic resonance spectra of the basal ganglia were recorded from 31 patients with (PD) and 14 age-matched healthy volunteers on a 1.5-T imager. The PD patients were grouped as follows: probable PD (N = 15), possible PD (N = 11), and atypical PD (N = 5). Total acquisition times of approximately five minutes were achieved with a TE (echo time) of 135 msec, a TR (repetition time) of 2000 msec, and 128 scan averages. Neural network (back propagation, Kohonen, probabilistic, and radial basis function) and related (generative topographic mapping) data analyses were performed. Results Conventional data analysis showed no statistically significant differences in metabolite ratios based on measuring signal intensities. The trained networks could distinguish control from PD with considerable accuracy (true positive fraction 0.971, true negative fraction 0.933). When four classes were defined, approximately 88% of the predictions were correct. The multivariate analysis indicated metabolic changes in the basal ganglia in PD. Conclusion A variety of neural network and related approaches can be successfully applied to both qualitative visualization and classification of in vivo spectra of PD patients. J. Magn. Reson. Imaging 2002;16:13,20. © 2002 Wiley -Liss, Inc. [source] Synthesis and Evaluation of Water-Soluble Fluorinated Dendritic Block-Copolymer Nanoparticles as a 19F-MRI Contrast AgentMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 14 2010Michihiro Ogawa Abstract Well-defined water-soluble fluorinated polymer nanoparticles (PNPs) with a high fluorine content and biocompatibility were successfully prepared by living radical polymerization (LRP) of 2,2,3,3-tetrafluoropropyl methacrylate (TFPMA) from the polyamidoamine dendrimer macroinitiator (PAMAM-Br), and successive block polymerization of carboxybetaine monomer (CMB). The obtained core,shell type PNPs (PAMAM- g -PTFPMA- b -PCMB) showed high solubility in water and a sphere-like structure with a diameter in the range of 15,80,nm in water. The short 19F-NMR spin,lattice relaxation time (T1) (<250,ms) of PAMAM- g -PTFPMA- b -PCMB allowed the use of fast repetition time. The spin,spin relaxation time (T2) was evaluated to be as low as 10 ms. 19F-MRI in vitro signals can be detectable even at concentrations lower than 1 µM (particle concentration). These results demonstrate that a new type of 19F-MRI contrast agent can be developed by the molecular design using the dendrimer-initiated LRP method. [source] T1 corrected B1 mapping using multi-TR gradient echo sequencesMAGNETIC RESONANCE IN MEDICINE, Issue 3 2010Tobias Voigt Abstract This work presents a new approach toward a fast, simultaneous amplitude of radiofrequency field (B1) and T1 mapping technique. The new method is based on the "actual flip angle imaging" (AFI) sequence. However, the single pulse repetition time (TR) pair used in the standard AFI sequence is replaced by multiple pulse repetition time sets. The resulting method was called "multiple TR B1/T1 mapping" (MTM). In this study, MTM was investigated and compared to standard AFI in simulations and experiments. Feasibility and reliability of MTM were proven in phantom and in vivo experiments. Error propagation theory was applied to identify optimal sequence parameters and to facilitate a systematic noise comparison to standard AFI. In terms of accuracy and signal-to-noise ratio, the presented method outperforms standard AFI B1 mapping over a wide range of T1. Finally, the capability of MTM to determine T1 was analyzed qualitatively and quantitatively, yielding good agreement with reference measurements. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [source] A technique for rapid single-echo spin-echo T2 mappingMAGNETIC RESONANCE IN MEDICINE, Issue 2 2010Marshall S. Sussman Abstract A rapid technique for mapping of T2 relaxation times is presented. The method is based on the conventional single-echo spin echo approach but uses a much shorter pulse repetition time to accelerate data acquisition. The premise of the new method is the use of a constant difference between the echo time and pulse repetition time, which removes the conventional and restrictive requirement of pulse repetition time , T1. Theoretical and simulation investigations were performed to evaluate the criteria for accurate T2 measurements. Measured T2s were shown to be within 1% error as long as the key criterion of pulse repetition time/T2 ,3 is met. Strictly, a second condition of echo time/T1 , 1 is also required. However, violations of this condition were found to have minimal impact in most clinical scenarios. Validation was conducted in phantoms and in vivo T2 mapping of healthy cartilage and brain. The proposed method offers all the advantages of single-echo spin echo imaging (e.g., immunity to stimulated echo effects, robustness to static field inhomogeneity, flexibility in the number and choice of echo times) in a considerably reduced amount of time and is readily implemented on any clinical scanner. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [source] Multiband multislice GE-EPI at 7 tesla, with 16-fold acceleration using partial parallel imaging with application to high spatial and temporal whole-brain fMRI,MAGNETIC RESONANCE IN MEDICINE, Issue 5 2010Steen Moeller Abstract Parallel imaging in the form of multiband radiofrequency excitation, together with reduced k -space coverage in the phase-encode direction, was applied to human gradient echo functional MRI at 7 T for increased volumetric coverage and concurrent high spatial and temporal resolution. Echo planar imaging with simultaneous acquisition of four coronal slices separated by 44mm and simultaneous 4-fold phase-encoding undersampling, resulting in 16-fold acceleration and up to 16-fold maximal aliasing, was investigated. Task/stimulus-induced signal changes and temporal signal behavior under basal conditions were comparable for multiband and standard single-band excitation and longer pulse repetition times. Robust, whole-brain functional mapping at 7 T, with 2 × 2 × 2mm3 (pulse repetition time 1.25 sec) and 1 × 1 × 2mm3 (pulse repetition time 1.5 sec) resolutions, covering fields of view of 256 × 256 × 176mm3 and 192 × 172 × 176mm3, respectively, was demonstrated with current gradient performance. Magn Reson Med 63:1144,1153, 2010. © 2010 Wiley-Liss, Inc. [source] Improved signal spoiling in fast radial gradient-echo imaging: Applied to accurate T1 mapping and flip angle correctionMAGNETIC RESONANCE IN MEDICINE, Issue 5 2009Wei Lin Abstract In conventional spoiled gradient echo imaging utilizing quadratic radio frequency (RF) spoiling, nonideal signal intensities are often generated, particularly when repetition time is short and/or excitation flip angle (FA) becomes larger. This translates to significant errors in various quantitative applications based on T1 -weighted image intensities. In this work, a novel spoiling scheme is proposed, based on random gradient moments and RF phases. This scheme results in a non-steady-state condition, but achieves ideal mean signal intensity. In order to suppress artifacts created by the inter-TR signal variations and at the same time attain the ideal signal intensity, radial data acquisition is utilized. The proposed method achieves ideal spoiling for a wide range of T1, T2, TR, and FAs. Phantom and in vivo experiments demonstrate improved performance for T1 mapping and FA correction when compared with conventional RF spoiling methods. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source] Simultaneous acquisition of MR angiography and venography (MRAV)MAGNETIC RESONANCE IN MEDICINE, Issue 5 2008Yiping P. Du Abstract A dual-echo pulse sequence for simultaneous acquisition of MR angiography and venography (MRAV) is developed. Data acquisition of the second echo for susceptibility-weighted imaging,based MR venography is added to the conventional three-dimensional (3D) time-of-flight (TOF) MRA pulse sequence. Using this dual-echo acquisition approach, the venography data can be acquired without increasing the repetition time, and, therefore, the scan duration of routine TOF MRA scans is maintained. The feasibility of simultaneous acquisition of MRAV is presented in brain scans at different spatial resolutions. The effect of spatial resolution on vein-to-background contrast is also demonstrated. Venous contrast is improved in high-resolution (0.52 × 0.52 × 1.6 mm3) images compared to that in standard-resolution (0.78 × 0.78 × 1.6 mm3) images. This MRAV technique enables the acquisition of MR venography without the need of an extra scan or injection of contrast agent in routine clinical brain exams at 3T. Magn Reson Med 59:954,958, 2008. © 2008 Wiley-Liss, Inc. [source] Optimized balanced steady-state free precession magnetization transfer imagingMAGNETIC RESONANCE IN MEDICINE, Issue 3 2007O. Bieri Abstract Balanced steady-state free precession (bSSFP) suffers from a considerable signal loss in tissues. This apparent signal reduction originates from magnetization transfer (MT) and may be reduced by an increase in repetition time or by a reduction in flip angle. In this work, MT effects in bSSFP are modulated by a modification of the bSSFP sequence scheme. Strong signal attenuations are achieved with short radio frequency (RF) pulses in combination with short repetition times, whereas near full, i.e., MT-free, bSSFP signal is obtained by a considerable prolongation of the RF pulse duration. Similar to standard methods, the MT ratio (MTR) in bSSFP depends on several sequence parameters. Optimized bSSFP protocol settings are derived that can be applied to various tissues yielding maximal sensitivity to MT while minimizing contribution from other impurities, such as off-resonances. Evaluation of MT in human brain using such optimized bSSFP protocols shows high correlation with MTR values from commonly used gradient echo (GRE) sequences. In summary, a novel method to generate MTR maps using bSSFP image acquisitions is presented and factors that optimize and influence this contrast are discussed. Magn Reson Med 58:511,518, 2007. © 2007 Wiley-Liss, Inc. [source] Saturated double-angle method for rapid B1+ mappingMAGNETIC RESONANCE IN MEDICINE, Issue 6 2006Charles H. Cunningham Abstract For in vivo magnetic resonance imaging at high field (,3 T) it is essential to consider the homogeneity of the active B1 field (B1+), particularly if surface coils are used for RF transmission. A new method is presented for highly rapid B1+ magnitude mapping. It combines the double angle method with a B1 -insensitive magnetization-reset sequence such that the choice of repetition time (TR) is independent of T1 and with a multislice segmented (spiral) acquisition to achieve volumetric coverage with adequate spatial resolution in a few seconds. Phantom experiments confirmed the accuracy of this technique even when TR , T1, with the side effect being lowered SNR. The speed of this method enabled B1+ mapping in the chest and abdomen within a single breath-hold. In human cardiac imaging, the method enabled whole-heart coverage within a single 16-s breath-hold. Results from phantoms and healthy volunteers at 1.5 T and 3 T are presented. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc. [source] Fast acquisition-weighted three-dimensional proton MR spectroscopic imaging of the human prostate,MAGNETIC RESONANCE IN MEDICINE, Issue 1 2004Tom W.J. Scheenen Abstract The clinical application of 3D proton spectroscopic imaging (3D SI) of the human prostate requires a robust suppression of periprostatic lipid signal contamination, minimal intervoxel signal contamination, and the shortest possible measurement time. In this work, a weighted elliptical sampling of k -space, combined with k -space filtering and pulse repetition time (TR) reduction minimized lipid signals, intervoxel contamination, and measurement time. At 1.5 T, the MR-visible prostate metabolites citrate, creatine, and choline can now be mapped over the entire human prostate with uncontaminated spherical voxels, with a volume down to 0.37 cm3, in measurement times of 7,15 min. Magn Reson Med 52:80,88, 2004. © 2004 Wiley-Liss, Inc. [source] High-resolution magic angle spinning proton NMR analysis of human prostate tissue with slow spinning ratesMAGNETIC RESONANCE IN MEDICINE, Issue 3 2003Jennifer L. Taylor Abstract The development of high-resolution magic angle spinning (HR-MAS) NMR spectroscopy for intact tissue analysis and the correlations between the measured tissue metabolites and disease pathologies have inspired investigations of slow-spinning methodologies to maximize the protection of tissue pathology structures from HR-MAS centrifuging damage. Spinning sidebands produced by slow-rate spinning must be suppressed to prevent their complicating the spectral region of metabolites. Twenty-two human prostatectomy samples were analyzed on a 14.1T spectrometer, with HR-MAS spinning rates of 600 Hz, 700 Hz, and 3.0 kHz, a repetition time of 5 sec, and employing various rotor-synchronized suppression methods, including DANTE, WATERGATE, TOSS, and PASS pulse sequences. Among them, DANTE, as the simplest scheme, has shown the most potential in suppression of tissue water signals and spinning sidebands, as well as in quantifying metabolic concentrations. Magn Reson Med 50:627,632, 2003. © 2003 Wiley-Liss, Inc. [source] On the transient phase of balanced SSFP sequencesMAGNETIC RESONANCE IN MEDICINE, Issue 4 2003Klaus Scheffler Abstract The signal intensity of balanced steady-state free precession (SSFP) imaging is a function of the proton density, T1, T2, flip angle (,), and repetition time (TR). The steady-state signal intensity that is established after about 5*T1/TR can be described analytically. The transient phase or the approach of the echo amplitudes to the steady state is an exponential decay from the initial amplitude after the first excitation pulse to the steady-state signal. An analytical expression of the decay rate of this transient phase is presented that is based on a simple analysis derived from the Bloch equations. The decay rate is a weighted average of the T1 and T2 relaxation times, where the weighting is determined by the flip angle of the excitation pulses. Thus, balanced SSFP imaging during the transient phase can provide various contrasts depending on the flip angle and the number of excitation pulses applied before the acquisition of the central k -space line. In addition, transient imaging of hyperpolarized nuclei, such as 3He, 129Xe, or 13C, can be optimized according to their T1 and T2 relaxation times. Magn Reson Med 49:781,783, 2003. © 2003 Wiley-Liss, Inc. [source] High-resolution 8 Tesla imaging of the formalin-fixed normal human hippocampusCLINICAL ANATOMY, Issue 2 2005Donald W. Chakeres Abstract The purpose of this study was to evaluate the capacity of high-resolution magnetic resonance imaging (MRI) to visualize the normal anatomic features of the human hippocampus in vitro, using high field imaging equipment, parameters, and acquisition times appropriate for imaging human subjects in vivo. This research compared high field, high-resolution MRI of formalin-fixed normal human hippocampus specimens to histologic sectioning of the same hippocampus samples. Four specimens were evaluated using an 8 Tesla (T), 80 cm bore whole-body MRI scanner equipped with a 12.7 cm single strut transverse electromagnetic resonator (TEM) coil. Hahn spin echo images were acquired with a repetition time (TR) of 800 msec, echo times (TE) of 20, 50, 90, and 134 msec, and an acquisition time (TA) of 3.25 min. The image quality was superb with demonstration of most of the features of the hippocampus. High field, high-resolution MRI can be used to depict multiple layers of the formalin-fixed human hippocampus in vitro using an 8 T whole-body scanner, a TEM coil, and short acquisition times compatible with human imaging in vivo. Clin. Anat. 18:88,91, 2005. © 2005 Wiley-Liss, Inc. [source] A technique for rapid single-echo spin-echo T2 mappingMAGNETIC RESONANCE IN MEDICINE, Issue 2 2010Marshall S. Sussman Abstract A rapid technique for mapping of T2 relaxation times is presented. The method is based on the conventional single-echo spin echo approach but uses a much shorter pulse repetition time to accelerate data acquisition. The premise of the new method is the use of a constant difference between the echo time and pulse repetition time, which removes the conventional and restrictive requirement of pulse repetition time , T1. Theoretical and simulation investigations were performed to evaluate the criteria for accurate T2 measurements. Measured T2s were shown to be within 1% error as long as the key criterion of pulse repetition time/T2 ,3 is met. Strictly, a second condition of echo time/T1 , 1 is also required. However, violations of this condition were found to have minimal impact in most clinical scenarios. Validation was conducted in phantoms and in vivo T2 mapping of healthy cartilage and brain. The proposed method offers all the advantages of single-echo spin echo imaging (e.g., immunity to stimulated echo effects, robustness to static field inhomogeneity, flexibility in the number and choice of echo times) in a considerably reduced amount of time and is readily implemented on any clinical scanner. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [source] Multiband multislice GE-EPI at 7 tesla, with 16-fold acceleration using partial parallel imaging with application to high spatial and temporal whole-brain fMRI,MAGNETIC RESONANCE IN MEDICINE, Issue 5 2010Steen Moeller Abstract Parallel imaging in the form of multiband radiofrequency excitation, together with reduced k -space coverage in the phase-encode direction, was applied to human gradient echo functional MRI at 7 T for increased volumetric coverage and concurrent high spatial and temporal resolution. Echo planar imaging with simultaneous acquisition of four coronal slices separated by 44mm and simultaneous 4-fold phase-encoding undersampling, resulting in 16-fold acceleration and up to 16-fold maximal aliasing, was investigated. Task/stimulus-induced signal changes and temporal signal behavior under basal conditions were comparable for multiband and standard single-band excitation and longer pulse repetition times. Robust, whole-brain functional mapping at 7 T, with 2 × 2 × 2mm3 (pulse repetition time 1.25 sec) and 1 × 1 × 2mm3 (pulse repetition time 1.5 sec) resolutions, covering fields of view of 256 × 256 × 176mm3 and 192 × 172 × 176mm3, respectively, was demonstrated with current gradient performance. Magn Reson Med 63:1144,1153, 2010. © 2010 Wiley-Liss, Inc. [source] Linear least-squares method for unbiased estimation of T1 from SPGR signalsMAGNETIC RESONANCE IN MEDICINE, Issue 2 2008Lin-Ching Chang Abstract The longitudinal relaxation time, T1, can be estimated from two or more spoiled gradient recalled echo images (SPGR) acquired with different flip angles and/or repetition times (TRs). The function relating signal intensity to flip angle and TR is nonlinear; however, a linear form proposed 30 years ago is currently widely used. Here we show that this linear method provides T1 estimates that have similar precision but lower accuracy than those obtained with a nonlinear method. We also show that T1 estimated by the linear method is biased due to improper accounting for noise in the fitting. This bias can be significant for clinical SPGR images; for example, T1 estimated in brain tissue (800 ms < T1 < 1600 ms) can be overestimated by 10% to 20%. We propose a weighting scheme that correctly accounts for the noise contribution in the fitting procedure. Monte Carlo simulations of SPGR experiments are used to evaluate the accuracy of the estimated T1 from the widely-used linear, the proposed weighted-uncertainty linear, and the nonlinear methods. We show that the linear method with weighted uncertainties reduces the bias of the linear method, providing T1 estimates comparable in precision and accuracy to those of the nonlinear method while reducing computation time significantly. Magn Reson Med 60:496,501, 2008. © 2008 Wiley-Liss, Inc. [source] Optimized balanced steady-state free precession magnetization transfer imagingMAGNETIC RESONANCE IN MEDICINE, Issue 3 2007O. Bieri Abstract Balanced steady-state free precession (bSSFP) suffers from a considerable signal loss in tissues. This apparent signal reduction originates from magnetization transfer (MT) and may be reduced by an increase in repetition time or by a reduction in flip angle. In this work, MT effects in bSSFP are modulated by a modification of the bSSFP sequence scheme. Strong signal attenuations are achieved with short radio frequency (RF) pulses in combination with short repetition times, whereas near full, i.e., MT-free, bSSFP signal is obtained by a considerable prolongation of the RF pulse duration. Similar to standard methods, the MT ratio (MTR) in bSSFP depends on several sequence parameters. Optimized bSSFP protocol settings are derived that can be applied to various tissues yielding maximal sensitivity to MT while minimizing contribution from other impurities, such as off-resonances. Evaluation of MT in human brain using such optimized bSSFP protocols shows high correlation with MTR values from commonly used gradient echo (GRE) sequences. In summary, a novel method to generate MTR maps using bSSFP image acquisitions is presented and factors that optimize and influence this contrast are discussed. Magn Reson Med 58:511,518, 2007. © 2007 Wiley-Liss, Inc. [source] | |||||||||||||