Pulse Sequence (pulse + sequence)

Distribution by Scientific Domains

Kinds of Pulse Sequence

  • mri pulse sequence
  • nmr pulse sequence

  • Selected Abstracts

    Suppressing One-Bond Correlations in HMBC Spectra: Improved Performance for the BIRD,HMBC Pulse Sequence

    Julien Furrer
    Abstract An improved version of the BIRD,HMBC experiment is proposed. In comparison to the original version, the filtering (suppression of 1JCH signals) is accomplished using a double tuned G-BIRD filter positioned in the middle of the long-range correlations evolution period. Compensation of offset dependence by replacing the rectangular 180 pulses with the broadband inversion pulses (BIPs), with superior inversion performance and improved tolerance to B1 field inhomogeneity, significantly improves the sensitivity of the original BIRD,HMBC experiment. For usual one-bond coupling constants ranges (115,180 Hz), optimal results are easily obtained by adjusting the delays, ,, of the BIRD elements to an average J value. For larger ranges (e.g. 110,260 Hz), the use of a double tuned G-BIRD filter allows excellent suppression degrees for all types of one-bond constants present in a molecule, superior to the original scheme and other purging schemes. These attributes make the improved version of the BIRD,HMBC experiment a valuable and robust tool for rapid spectral analysis and rapid checks of molecular skeletons with a minimum spectrometer time. Copyright 2009 John Wiley & Sons, Ltd. [source]

    Thermal relaxation and coherence dynamics of spin 3/2.


    Abstract The relaxation dynamics of the spin 3/2 density operator in the presence of fluctuating and static quadrupolar interactions is reviewed. The nuclear magnetic resonance (NMR) line shapes are analyzed for any value of the static quadrupolar interaction, ranging from isotropic systems to systems exhibiting large splitting far exceeding the line widths. Pulse sequences optimized for the elimination of line broadening due to an inhomogeneous static quadrupolar interaction and for the detection of nuclei involved in slow molecular motion and/or in anisotropic, liquid crystalline environment are discussed. In Part II, the dynamics of spin 3/2 in the presence of a (pulsed) radio frequency (RF) field is reviewed. 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part A 19A: 97,116, 2003. [source]

    NMR studies of chiral organic compounds in non-isotropic phases

    Marek J. Potrzebowski
    Abstract In this article, new applications and perspectives of one- and two-dimensional NMR spectroscopy for study of chiral organic compounds in the non-isotropic phases (solid state and liquid crystals) are presented. The review is organized into five sections. In the first part, theoretical background and short introduction to solid state NMR are shown. The second part presents how NMR isotropic chemical shift can be used for distinguishing of racemates and enantiomers. In the third section, the power of the ODESSA pulse sequence for investigation of racemates, enantiomers and establishing of enantiomeric excess are discussed. The fourth part shows the application of analysis of principal elements of chemical shift tensors obtained by means of 2D NMR techniques for searching of absolute configuration and conformational changes in the solid state. The final part presents recent achievements of chiral liquid crystals NMR methodology for study of chiral compounds. 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A:201,218, 2008. [source]

    A pulse programmer for nuclear magnetic resonance spectrometers

    C.C. Odebrecht
    Abstract A pulse programmer (PP) designed to control a nuclear magnetic resonance (NMR) spectrometer is reported on. The heart of the PP is a computer programmable logic device (CPDL) that provides flexibility to the design and, at the same time, reduces the number of electronics components needed and the dimensions of the printed circuit board. The PP works as follow: first, a pulse sequence defined by a set of instructions is loaded into the RAM memory of the PP. Then, when the process is started, the instructions are, one by one, read, decoded, and executed. Four types of instructions (functions) were defined: PRINT A, PRINT B, WAIT, and STOP. PRINT A and PRINT B change the status of the output channels A and B, respectively, WAIT generates a time delay, and STOP terminates the sequence. The output ports A and B have 14 channels each, and the shortest pulse and resolution are both 200 ns. The design of the PP is versatile, and new functions can be added through software without modifying the printed circuit board. To control the PP from a personal computer, a program named PulseJr was developed. It contains a graphical user interface (GUI) and pulse sequences can be drawn on the monitor screen with the mouse of the computer. Once the pulse sequence is sketched, clicking a button the program compiles the pulse sequence, generates the set of instructions, loads them into the RAM memory of the PP, and starts the pulse sequence. 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 127,131, 2007. [source]

    MR determination of glomerular filtration rate in subjects with solitary kidneys in comparison to clinical standards of renal function: feasibility and preliminary report,

    Richard W. Katzberg
    Abstract This study was conducted to demonstrate the feasibility of quantifying single kidney glomerular filtration rate (skGFR) by magnetic resonance (MR) by comparison to the clinical estimates of GFR in volunteer subjects with a single kidney. Seven IRB-approved subjects with a solitary kidney, stable serum creatinine (SCr) and a 24,h creatinine clearance (CrCl) volunteered to undergo an MR examination that determined renal extraction fraction (EF) with a breathhold inversion recovery echo planar pulse sequence and renal blood flow with a velocity encoded phase imaging sequence. The product of EF and blood flow determines GFR. These values were compared with the 24,h CrCl, estimated GFR by the modification of diet in renal disease (MDRD) regression analysis and the Cockroft,Gault (CG) determination of CrCl. The mean and standard deviation of differences between the MR GFR, MDRD and CG vs the 24,h CrCl were 12.3,,35.7, ,8.9,,18.5 and 1.2,,19.6, respectively. The Student t -test showed that none of the mean differences were statistically significant between techniques. This clinical investigation shows that MR can be used for skGFR determination in human subjects with comparable values to those derived from clinically used serum-based GFR estimation techniques. Copyright 2009 John Wiley & Sons, Ltd. [source]

    Relative increase in choline in the occipital cortex in chronic fatigue syndrome

    B. K. Puri
    Puri BK, Counsell SJ, Zaman R, Main J, Collins AG, Hajnal JV, Davey NJ. Relative increase in choline in the occipital cortex in chronic fatigue syndrome. Acta Psychiatr Scand 2002: 106: 224,226. Blackwell Munksgaard 2002. Objective:,To test the hypothesis that chronic fatigue syndrome (CFS) is associated with altered cerebral metabolites in the frontal and occipital cortices. Method:,Cerebral proton magnetic resonance spectroscopy (1H MRS) was carried out in eight CFS patients and eight age- and sex-matched healthy control subjects. Spectra were obtained from 20 20 20 mm3 voxels in the dominant motor and occipital cortices using a point-resolved spectroscopy pulse sequence. Results:,The mean ratio of choline (Cho) to creatine (Cr) in the occipital cortex in CFS (0.97) was significantly higher than in the controls (0.76; P=0.008). No other metabolite ratios were significantly different between the two groups in either the frontal or occipital cortex. In addition, there was a loss of the normal spatial variation of Cho in CFS. Conclusion:,Our results suggest that there may be an abnormality of phospholipid metabolism in the brain in CFS. [source]

    Novel technique to improve the fault detection sensitivity in transformer maintenance test

    E. A. Al-Ammar
    Abstract Early detection of incipient faults in transformer windings is important, so that required corrective measures can be taken to help prevent interruption during operation. Low voltage impulse (LVI) and sweep frequency response analysis (SFRA) tests have been widely adopted within the industry to determine a transformer winding's deformation. However, these tests have drawbacks, including limited frequency ranges for the LVI test and time-consuming measurements for the SFRA test. To obtain better signature analysis in the transformer maintenance test, especially detection of minor faults, this paper suggests a new input signal using a pulse sequence (PS) in the transfer function (TF) analysis. The results of the PS test are compared against the LVI and SFRA tests to complete the assessments, which are derived from experimental works on the 25,kVA distribution transformer. It is concluded that the PS method improves fault detection sensitivity significantly. Copyright 2009 John Wiley & Sons, Ltd. [source]

    Isotropic resolution diffusion tensor imaging with whole brain acquisition in a clinically acceptable time

    HUMAN BRAIN MAPPING, Issue 4 2002
    Derek Kenton Jones
    Abstract Our objective was to develop a diffusion tensor MR imaging pulse sequence that allows whole brain coverage with isotropic resolution within a clinically acceptable time. A single-shot, cardiac-gated MR pulse sequence, optimized for measuring the diffusion tensor in human brain, was developed to provide whole-brain coverage with isotropic (2.5 2.5 2.5 mm) spatial resolution, within a total imaging time of approximately 15 min. The diffusion tensor was computed for each voxel in the whole volume and the data processed for visualization in three orthogonal planes. Anisotropy data were further visualized using a maximum-intensity projection algorithm. Finally, reconstruction of fiber-tract trajectories i.e., ,tractography' was performed. Images obtained with this pulse sequence provide clear delineation of individual white matter tracts, from the most superior cortical regions down to the cerebellum and brain stem. Because the data are acquired with isotropic resolution, they can be reformatted in any plane and the sequence can therefore be used, in general, for macroscopic neurological or psychiatric neuroimaging investigations. The 3D visualization afforded by maximum intensity projection imaging and tractography provided easy visualization of individual white matter fasciculi, which may be important sites of neuropathological degeneration or abnormal brain development. This study has shown that it is possible to obtain robust, high quality diffusion tensor MR data at 1.5 Tesla with isotropic resolution (2.5 2.5 2.5 mm) from the whole brain within a sufficiently short imaging time that it may be incorporated into clinical imaging protocols. Hum. Brain Mapping 15:216,230, 2002. 2002 Wiley-Liss, Inc. [source]

    Highly Ordered Interstitial Water Observed in Bone by Nuclear Magnetic Resonance,

    Erin E Wilson
    Abstract NMR was used to study the nanostructure of bone tissue. Distance measurements show that the first water layer at the surface of the mineral in cortical bone is structured. This water may serve to couple the mineral to the organic matrix and may play a role in deformation. Introduction: The unique mechanical characteristics of bone tissue have not yet been satisfactorily connected to the exact molecular architecture of this complex composite material. Recently developed solid-state nuclear magnetic resonance (NMR) techniques are applied here to the mineral component to provide new structural distance constraints at the subnanometer scale. Materials and Methods: NMR dipolar couplings between structural protons (OH, and H2O) and phosphorus (PO4) or carbon (CO3) were measured using the 2D Lee-Goldburg Cross-Polarization under Magic-Angle Spinning (2D LG-CPMAS) pulse sequence, which simultaneously suppresses the much stronger proton-proton dipolar interactions. The NMR dipolar couplings measured provide accurate distances between atoms, e.g., OH and PO4 in apatites. Excised and powdered femoral cortical bone was used for these experiments. Synthetic carbonate (,2-4 wt%)-substituted hydroxyapatite was also studied for structural comparison. Results: In synthetic apatite, the hydroxide ions are strongly hydrogen bonded to adjacent carbonate or phosphate ions, with hydrogen bond (O-H) distances of ,1.96 observed. The bone tissue sample, in contrast, shows little evidence of ordered hydroxide. Instead, a very ordered (structural) layer of water molecules is identified, which hydrates the small bioapatite crystallites through very close arrangements. Water protons are ,2.3-2.55 from surface phosphorus atoms. Conclusions: In synthetic carbonated apatite, strong hydrogen bonds were observed between the hydroxide ions and structural phosphate and carbonate units in the apatite crystal lattice. These hydrogen bonding interactions may contribute to the long-range stability of this mineral structure. The biological apatite in cortical bone tissue shows evidence of hydrogen bonding with an ordered surface water layer at the faces of the mineral particles. This structural water layer has been inferred, but direct spectroscopic evidence of this interstitial water is given here. An ordered structural water layer sandwiched between the mineral and the organic collagen fibers may affect the biomechanical properties of this complex composite material. [source]

    Fast spin-echo triple-echo Dixon: Initial clinical experience with a novel pulse sequence for fat-suppressed T2-weighted abdominal MR imaging

    Russell N. Low MD
    Abstract Purpose To evaluate a prototype fast spin echo (FSE) triple-echo-Dixon (fTED) technique for breath-hold, fat-suppressed, T2-weighted abdominal imaging. Materials and Methods Forty patients underwent breath-hold T2-weighted abdominal imaging with fTED and conventional fast recovery (FR) FSE with chemical shift-selective saturation (CHESS). FRFSE and fTED images were compared for overall image quality, homogeneity of fat suppression, image sharpness, anatomic detail, and phase artifact. Depiction of disease was recorded separately for FRFSE and fTED images. Results FTED successfully reconstructed water-only and fat-only images from source images in all 40 cases. Water and fat separation was perfect in 36 (0.90) patients. Homogeneity of fat suppression was superior on the fTED images in 38 (0.95) of 40 cases. FTED images showed better anatomic detail in 27 (0.68), and less susceptibility artifact in 20 (0.50). FRFSE images showed less vascular pulsation artifact in 30 (0.75) cases, and less phase artifact in 21 (0.53) cases. There was no difference in depiction of disease for FRFSE and fTED images. Conclusion FTED is a robust sequence providing breath-hold T2-weighted images with superior fat suppression, excellent image quality, and at least equal depiction of disease compared to conventional breath-hold T2-weighted FRFSE imaging. J. Magn. Reson. Imaging 2009;30:569,577. 2009 Wiley-Liss, Inc. [source]

    High-field MRSI of the prostate using a transmit/receive endorectal coil and gradient modulated adiabatic localization

    Jamie Near PhD
    Abstract Purpose To demonstrate in vivo magnetic resonance spectroscopic imaging (MRSI) of the human prostate at 4.0T using a transmit/receive endorectal coil and a pulse sequence designed specifically for this application. Materials and Methods A solid, reusable endorectal probe was designed for both radiofrequency transmission and reception. Finite difference time domain (FDTD) simulations were performed to characterize the coil's electric field distribution, and temperature measurements were performed in a beef tissue phantom to determine the coil's safe operating limit. The localization by selective adiabatic refocusing (LASER) pulse sequence was implemented using six gradient modulated offset independent adiabatic (GOIA) pulses for very sharp, B1 -insensitive voxel localization. Results Based on the simulations and temperature measurements, the coil's safe operating limit was conservatively estimated to be 1.0W for 15 minutes. The transition width of the GOIA pulse selection profiles was only 6% of the bandwidth, compared with 22% for a specific absorption rate (SAR)-matched conventional adiabatic pulse. Using the coil and pulse sequence described here, MRSI data were successfully acquired from a patient with biopsy-proven prostate cancer, with a nominal voxel size of 0.34 cc in a scan time of 15 minutes. Conclusion This work demonstrates the safe and effective use of a transmit/receive endorectal coil for in vivo MRSI of the prostate. J. Magn. Reson. Imaging 2009;30:335,343. 2009 Wiley-Liss, Inc. [source]

    Cine cardiac imaging using black-blood steady-state free precession (BB-SSFP) at 3T

    Tamer A. Basha MSE
    Abstract Purpose To propose a new black-blood (BB) pulse sequence that provides BB cine cardiac images with high blood-myocardium contrast. The proposed technique is based on the conventional steady-state free precession (SSFP) sequence. Materials and Methods Numerical simulations of the Bloch equation were conducted to compare the resulting signal-to-noise ratio (SNR) to that of conventional BB imaging, including the effects of changing the imaging flip angle and heart rates. Simulation results were verified using a gel phantom experiment and five normal volunteers were scanned using the proposed technique. Results The new sequence showed higher SNR and contrast-to-noise ratio (CNR) (,100%) compared to the conventional BB imaging. Also, the borders of the left ventricle (LV) and right ventricle (RV) appear more distinguishable than the conventional SSFP. We were also able to cover about 80% of the cardiac cycle with short breath-hold time (,10 cardiac cycles) and with reasonable SNR and CNR. Conclusion Based on an SSFP conventional sequence, the new sequence provides BB cines that cover most of the cardiac cycle and with higher SNR and CNR than the conventional BB sequences. J. Magn. Reson. Imaging 2009;30:94,103. 2009 Wiley-Liss, Inc. [source]

    Improved myelin water quantification using spatially regularized non-negative least squares algorithm

    Dosik Hwang PhD
    Abstract Purpose To improve the myelin water quantification in the brain in the presence of measurement noise and to increase the visibility of small focal lesions in myelin-water-fraction (MWF) maps. Materials and Methods A spatially regularized non-negative least squares (srNNLS) algorithm was developed for robust myelin water quantification in the brain. The regularization for the conventional NNLS algorithm was expanded into the spatial domain in addition to the spectral domain. Synthetic data simulations were performed to study the effectiveness of this new algorithm. Experimental free-induction-decay measurements were obtained using a multi-gradient-echo pulse sequence and MWF maps were estimated using the srNNLS algorithm. The results were compared with other conventional methods. Results A substantial decrease in MWF variability was observed in both simulations and experimental data when the srNNLS algorithm was applied. As a result, false lesions in the MWF maps disappeared and the visibility of small focal lesions improved greatly. On average, the contrast-to-noise ratio for focal lesions was improved by a factor of 2. Conclusion The MWF variability due to the measurement noise can be substantially reduced and the detection of small focal lesions can be improved by using the srNNLS algorithm. J. Magn. Reson. Imaging 2009;30:203,208. 2009 Wiley-Liss, Inc. [source]

    3D diffusion tensor MRI with isotropic resolution using a steady-state radial acquisition

    Youngkyoo Jung PhD
    Abstract Purpose To obtain diffusion tensor images (DTI) over a large image volume rapidly with 3D isotropic spatial resolution, minimal spatial distortions, and reduced motion artifacts, a diffusion-weighted steady-state 3D projection (SS 3DPR) pulse sequence was developed. Materials and Methods A diffusion gradient was inserted in a SS 3DPR pulse sequence. The acquisition was synchronized to the cardiac cycle, linear phase errors were corrected along the readout direction, and each projection was weighted by measures of consistency with other data. A new iterative parallel imaging reconstruction method was also implemented for removing off-resonance and undersampling artifacts simultaneously. Results The contrast and appearance of both the fractional anisotropy and eigenvector color maps were substantially improved after all correction techniques were applied. True 3D DTI datasets were obtained in vivo over the whole brain (240 mm field of view in all directions) with 1.87 mm isotropic spatial resolution, six diffusion encoding directions in under 19 minutes. Conclusion A true 3D DTI pulse sequence with high isotropic spatial resolution was developed for whole brain imaging in under 20 minutes. To minimize the effects of brain motion, a cardiac synchronized, multiecho, DW-SSFP pulse sequence was implemented. Motion artifacts were further reduced by a combination of linear phase correction, corrupt projection detection and rejection, sampling density reweighting, and parallel imaging reconstruction. The combination of these methods greatly improved the quality of 3D DTI in the brain. J. Magn. Reson. Imaging 2009;29:1175,1184. 2009 Wiley-Liss, Inc. [source]

    Comparison of lipid-rich necrotic core size in symptomatic and asymptomatic carotid atherosclerotic plaque: Initial results

    Vincent C. Cappendijk MD
    Abstract Purpose To investigate the potential difference in the size of the lipid-rich necrotic core (LRNC) in carotid plaques of symptomatic patients versus asymptomatic patients. Pathological studies established that a large LRNC is an important feature of vulnerable atherosclerotic plaque. Previously, we have demonstrated a high correlation between semiquantitative analysis of the LRNC size in T1-weighted (w) turbo field echo (TFE) MR images and histology. Materials and Methods Thirty-seven patients with carotid stenosis >70% with (n = 26) or without (n = 11) symptoms were included. Three independent MR readers quantified the amount of LRNC with a T1w TFE pulse sequence. The relative amount of LRNC (LRNC score) was defined as sum of cross-sectional area percentages LRNC per carotid plaque. Results Interreader agreement for the three MR readers was good, with an intraclass correlation coefficient (ICC, 95% confidence interval [CI]) of 0.72 (0.57,0.83). All three MR readers on average found a larger LRNC in the symptomatic group of patients, although this was not statistically significant. The mean LRNC score was 116 129 and 59 62 for symptomatic and asymptomatic patients, respectively (P = 0.13). Symptomatic patients showed wide ranges in LRNC scores (0,424), while the range was much lower in the asymptomatic group (0,170). Conclusion Single-sequence T1w TFE may be a promising technique to study atherosclerotic plaque at risk of stroke. Larger studies are warranted to confirm these promising results. J. Magn. Reson. Imaging 2008;27:1356,1361. 2008 Wiley-Liss, Inc. [source]

    Simultaneous myocardial and fat suppression in magnetic resonance myocardial delayed enhancement imaging,

    Thomas 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]

    Staining methods for magnetic resonance microscopy of the rat fetus

    Alexandra Petiet MS
    Abstract Purpose To develop a magnetic resonance histology (MRH) staining and fixation method by immersion to enhance the signal-to-noise ratio (SNR) with a paramagnetic contrast agent permitting microscopic acquisition within a 3-hour scan time. Materials and Methods Methods were optimized for embryonic day 18.5 (E18.5) rat fetuses and imaging at 9.4T with an RF refocused spin-echo pulse sequence (TR/TE = 75 msec/5.2 msec). Fixation/staining was performed by immersion in Bouin's fixative containing varied concentrations of ProHance (from 10:1 to 500:1 Bouin's:ProHance) and for varied immersion durations (up to 24 hours). Results The results showed a significant change in T1 and T2 relaxation times as a function of concentration of contrast agent and immersion duration. As the contrast agent penetrated the tissues, T1 was reduced as desired (typically by 10), but at the same time T2 was profoundly reduced (typically by 3) due to both protein cross-linking from the fixative and the high concentration of contrast agent. A systematic assessment of this staining protocol showed an increased SNR (by 5) over that in unstained specimens. Conclusion This staining protocol reduced scan time for very-high-resolution images (19.5 ,m) to only 3 hours, making MRH a routine tool for evaluating fetal development. J. Magn. Reson. Imaging 2007;25:1192,1198. 2007 Wiley-Liss, Inc. [source]

    Selective maximization of 31P MR spectroscopic signals of in vivo human brain metabolites at 3T

    Rose-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]

    Controlling diffusion of 3He by buffer gases: A structural contrast agent in lung MRI

    Rodolfo H. Acosta PhD
    Abstract Purpose To study the influence of admixing inert buffer gases to laser-polarized 3He in terms of resulting diffusion coefficients and the consequences for image contrast and resolution. Materials and Methods The diffusion coefficient of 3He was altered by admixing buffer gases of various molecular weights (4He, N2, and SF6). The influence of the pulse sequence and the diffusion coefficient on the appearance of MRI of (laser-polarized) gases was analyzed by comparison of basic theoretical concepts with demonstrative experiments. Results Excellent agreement between theoretical description and observed signal in simple gradient echoes was observed. A maximum signal gain can be predicted and was experimentally validated. Images acquired under such conditions revealed improved resolution. The nature and concentration of the admixed gas defines a structural threshold for the observed apparent diffusion coefficient (ADC) as demonstrated with diffusion-weighted MRI on a pig's lung flooded with suitable gas mixtures. Conclusion A novel procedure is proposed to control the diffusion coefficient of gases in MRI by admixture of inert buffer gases. Their molecular mass and concentration enter as additional parameters into the equations that describe structural contrast. This allows for setting a structural threshold up to which structures contribute to the image. For MRI of the lung this enables images of very small structural elements (alveoli) only, or in the other extreme, all airways can be displayed with minimal signal loss due to diffusion. J. Magn. Reson. Imaging 2006. 2006 Wiley-Liss, Inc. [source]

    A pulse sequence for rapid in vivo spin-locked MRI

    Arijitt Borthakur PhD
    Abstract Purpose To develop a novel pulse sequence called spin-locked echo planar imaging (EPI), or (SLEPI), to perform rapid T1, -weighted MRI. Materials and Methods SLEPI images were used to calculate T1, maps in two healthy volunteers imaged on a 1.5-T Sonata Siemens MRI scanner. The head and extremity coils were used for imaging the brain and blood in the popliteal artery, respectively. Results SLEPI-measured T1, was 83 msec and 103 msec in white (WM) and gray matter (GM), respectively, 584 msec in cerebrospinal fluid (CSF), and was similar to values obtained with the less time-efficient sequence based on a turbo spin-echo readout. T1, was 183 msec in arterial blood at a spin-lock (SL) amplitude of 500 Hz. Conclusion We demonstrate the feasibility of the SLEPI pulse sequence to perform rapid T1, MRI. The sequence produced images of higher quality than a gradient-echo EPI sequence for the same contrast evolution times. We also discuss applications and limitations of the pulse sequence. J. Magn. Reson. Imaging 2006. 2006 Wiley-Liss, Inc. [source]

    EPI distortion correction from a simultaneously acquired distortion map using TRAIL

    Andrew N. Priest D.Phil
    Abstract Purpose To develop a method for shot-by-shot distortion correction of single-shot echo-planar imaging (EPI) that is capable of correcting each image individually using a distortion measurement performed during acquisition of the image itself. Materials and Methods The recently-introduced method known as two reduced acquisitions interleaved (TRAIL) was extended to measure the distribution of the main magnetic field B0 with each shot. This corresponded to a map of distortion, and allowed distortion to be corrected in the acquired images. Results Distortion-corrected images were demonstrated in the human brain. The distortion field could be directly visualized using the "stripe" distribution imposed by the TRAIL pulse sequence. This confirmed the success of the correction. Over a time-course measurement of 10 images, variance was reduced by using shot-by-shot distortion correction compared to correction with a constant field map. Conclusion Shot-by-shot distortion correction may be performed for EPI images acquired using an extension of the TRAIL technique, ensuring that the correction reflects the actual distortion pattern and not merely a previously measured, but possibly no longer valid, distortion field. This avoids errors due to changes in the distortion field or misregistration of a previously measured distortion map resulting from subject motion. J. Magn. Reson. Imaging 2006. 2006 Wiley-Liss, Inc. [source]

    Continuous arterial spin labeling using a train of adiabatic inversion pulses,

    Bradford A. Moffat PhD
    Abstract Purpose To develop a simple and robust magnetic resonance imaging (MRI) pulse sequence for the quantitative measurement of blood flow in the brain and cerebral tumors that has practical implementation advantages over currently used continuous arterial spin labeling (CASL) schemes. Materials and Methods Presented here is a single-coil protocol that uses a train of hyperbolic secant inversion pulses to produce continuous arterial spin inversion for perfusion weighting of fast spin echo images. Flow maps of normal rat brains and those containing a 9L gliosarcoma orthotopic tumor model conditions were acquired with and without carbogen. Results The perfusion-weighted images have reduced magnetization transfer signal degradation as compared to the traditional single-coil CASL while avoiding the use of a more complex two-coil CASL technique. Blood flow measurements in tumor and normal brain tissue were consistent with those previously reported by other CASL techniques. Contralateral and normal brain showed increased blood flow with carbogen breathing, while tumor tissue lacked the same CO2 reactivity. Conclusion This variation of the CASL technique is a quantitative, robust, and practical single-coil method for measuring blood flow. This CASL method does not require specialized radiofrequency coils or amplifiers that are not routinely used for anatomic imaging of the brain, therefore allowing these flow measurements to be easily incorporated into traditional rodent neuroimaging protocols. J. Magn. Reson. Imaging 2005;21:290,296. 2005 Wiley-Liss, Inc. [source]

    In vivo detection of hemorrhage in human atherosclerotic plaques with magnetic resonance imaging,

    Vincent C. Cappendijk MD
    Abstract Purpose To investigate the performance of high-resolution T1-weighted (T1w) turbo field echo (TFE) magnetic resonance imaging (MRI) for the identification of the high-risk component intraplaque hemorrhage, which is described in the literature as a troublesome component to detect. Materials and Methods An MRI scan was performed preoperatively on 11 patients who underwent carotid endarterectomy because of symptomatic carotid disease with a stenosis larger than 70%. A commonly used double inversion recovery (DIR) T1w turbo spin echo (TSE) served as the T1w control for the T1w TFE pulse sequence. The MR images were matched slice by slice with histology, and the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the MR images were calculated. Additionally, two readers, who were blinded for the histological results, independently assessed the MR slices concerning the presence of intraplaque hemorrhage. Results More than 80% of the histological proven intraplaque hemorrhage could be detected using the TFE sequence with a high interobserver agreement (Kappa = 0.73). The TFE sequence proved to be superior to the TSE sequence concerning SNR and CNR, but also in the qualitative detection of intraplaque hemorrhage. The false positive TFE results contained fibrous tissue and were all located outside the main plaque area. Conclusion The present study shows that in vivo high-resolution T1w TFE MRI can identify the high-risk component intraplaque hemorrhage with a high detection rate in patients with symptomatic carotid disease. Larger clinical trials are warranted to investigate whether this technique can identify patients at risk for an ischemic attack. J. Magn. Reson. Imaging 2004;20:105,110. 2004 Wiley-Liss, Inc. [source]

    Dynamic T1 estimation of brain tumors using double-echo dynamic MR imaging

    Yoshiyuki Ishimori RT
    Abstract Purpose To assess the clinical utility of a new method for real-time estimation of T1 during the first pass of contrast agent by using this method to examine brain tumors. Materials and Methods The multi-phase spoiled gradient-echo pulse sequence using the double-echo magnetic resonance (MR) technique was modified. In the first half of the pulse sequence, the flip angle was varied systematically. Then, static T1 values were calculated using differences in MR signal intensities between different flip angles. In the latter half of this sequence, changes in absolute T1 were calculated using differences in signal intensities before and after injection of contrast agent. The double-echo MR data were used to minimize the T2* effect. Five cases of neurinoma and seven cases of meningioma were examined. Changes in T1 during the first pass of contrast agent were compared between neurinoma and meningioma. Results Changes in absolute T1 were clearly demonstrated on the parametric map. Although the changes in absolute T1 during the first pass of contrast agent did not allow differentiation between the two types of tumors, the mean gradient after the first pass was statistically higher for neurinoma than for meningioma (P < 0.05; meningioma, 0.011 0.012 second,1/second; neurinoma, 0.034 0.020 second,1/second). Conclusion The present method appears to be useful for estimation of dynamic T1 changes in brain tumors in clinical settings. J. Magn. Reson. Imaging 2003;18:113,120. 2003 Wiley-Liss, Inc. [source]


    JOURNAL OF PHYCOLOGY, Issue 3 2004
    Matilde S. Chauton
    Lipid composition in extracted samples of Chaetoceros muelleri Lemmermann was studied with 13C-NMR and distortionless enhancement by polarization transfer (DEPT) 13C-NMR, resulting in well-resolved 13C-NMR spectra with characteristic resonance signals from carboxylic, olefinic, glyceryl, methylene, and methyl groups. The application of a DEPT pulse sequence aided in the assignment of methylene and methine groups. Resonance signals were compared with literature references, and signal assignment included important unsaturated fatty acids such as eicosapentaenoic and docosahexaenoic and also phospholipids and glycerols. Results from the extracted samples were used to assign resonance signals in a high-resolution magic angle spinning (HR MAS) DEPT 13C spectrum from whole cells of C. muelleri. The NMR analysis on whole cells yielded equally good information on fatty acids and also revealed signals from carbohydrates and amino acids. Broad resonance signals and peak overlapping can be a problem in whole cell analysis, but we found that application of HR MAS gave a well-resolved spectrum. The chemical shift of metabolites in an NMR spectrum depends on the actual environment of nuclei during analysis, and some differences could therefore be expected between extracted and whole cell samples. The shift differences were small, and assignment from analysis of lipophilic extract could be used to identify peaks in the whole cell spectrum. HR MAS 13C-NMR therefore offers a possibility for broad-range metabolic profiling directly on whole cells, simultaneously detecting metabolites that are otherwise not detected in the same analytical set up and avoiding tedious extraction procedures. [source]

    Natural Abundance 43Ca NMR Spectroscopy of Tobermorite and Jennite: Model Compounds for C,S,H

    Geoffrey M. Bowers
    There are few effective methods for characterizing the molecular scale structural environments of Ca2+ in hydrated cements, which has limited our ability to understand the structure of, for example, Ca,silicate hydrate (C,S,H). 43Ca nuclear magnetic resonance (NMR) spectroscopy has long been considered too insensitive to provide useful data in this regard, but 43Ca magic angle spinning (MAS) NMR spectra reported here for synthetic tobermorite and jennite with naturally abundant levels of 43Ca demonstrate that this is a viable approach. We show that spectra with useful signal/noise ratios can be obtained in a reasonable acquisition period (,2 days) using an H0 field strength of 21.1 T, 5 mm rotors spinning at a frequency of 5 kHz, and a double frequency sweep preparatory pulse sequence. Tobermorite and jennite produce relatively broad resonances due to their complex structures and structural disorder, however, the chemical shift differences between six-coordinate 43Ca in jennite and seven-coordinate 43Ca in 11 tobermorite are large enough that the signals are entirely resolved at this field. These data suggest that signal from ideal tobermorite-like and jennite-like sites in cement C,S,H can most likely be distinguished by 43Ca NMR and that this method will be a powerful approach for studying cement-based ceramic materials in the coming decade. [source]

    Spark Plasma Sintering of Alumina

    Zhijian Shen
    A systematic study of various spark plasma sintering (SPS) parameters, namely temperature, holding time, heating rate, pressure, and pulse sequence, was conducted to investigate their effect on the densification, grain-growth kinetics, hardness, and fracture toughness of a commercially available submicrometer-sized Al2O3 powder. The obtained experimental data clearly show that the SPS process enhances both densification and grain growth. Thus, Al2O3 could be fully densified at a much lower temperature (1150C), within a much shorter time (minutes), than in more conventional sintering processes. It is suggested that the densification is enhanced in the initial part of the sintering cycle by a local spark-discharge process in the vicinity of contacting particles, and that both grain-boundary diffusion and grain-boundary migration are enhanced by the electrical field originating from the pulsed direct current used for heating the sample. Both the diffusion and the migration that promote the grain growth were found to be strongly dependent on temperature, implying that it is possible to retain the original fine-grained structure in fully densified bodies by avoiding a too high sintering temperature. Hardness values in the range 21,22 GPa and fracture toughness values of 3.5 0.5 MPam1/2 were found for the compacts containing submicrometer-sized Al2O3 grains. [source]

    Kinetics of Demixing and Remixing Transitions in Aqueous Solutions of Poly(N -isopropylacrylamide): A Temperature-Jump 1H NMR Study

    Pavel V. Yushmanov
    Abstract Summary: The time course of the coil-to-globule collapse and intermolecular aggregation of poly(N -isopropylacrylamide) in aqueous solution upon exceeding the lower critical solution temperature (LCST) are investigated by temperature-jump 1H NMR spectroscopy. After the temperature jump, we record the time dependences of (i) the mobile fraction of the polymer chain as revealed by the intensity of the liquid-like NMR signal, (ii) the local mobility of those chains as revealed by the transverse relaxation time T2, and (iii) their self-diffusion coefficient D. The same data are also reported at their temperature-dependent long-time limits. The results suggest a sudden, faster than one second, collapse and intermolecular aggregation into globules and a slower reorganization/redistribution of the individual chains among and within the globular and mobile states. We found that all molecular changes are reversible if the temperature remains less than ca. 6,8 K above the LCST for less than a few minutes; under those conditions, experiments upon sudden temperature quench below the LCST show that the aggregates disintegrate and swell into coils in less than a few seconds. 1H NMR signal intensity of the methyl groups of 1 wt.-% PNIPAM dissolved in 0.1 M NaCl solution in D2O in a temperature-jump experiment from 300 to 312 K. The data were recorded by the 90,,,(180,2, -)n -detection of the CPMG pulse sequence. [source]

    High resolution-HMBC (HR-HMBC), a new method for measuring heteronuclear long-range coupling constants

    Kazuo Furihata
    Abstract A useful pulse sequence for measuring long-range CH coupling constants (JCH) named high resolution-HMBC (HR-HMBC) has been developed. In this pulse sequence, the J -scaling pulse [(nt1)/2180 (H/C) , (nt1)/2] is incorporated after the spin evolution period, and then followed by an 1H 180 pulse to reverse the magnetization of JCH couplings. As a result, splittings of the cross peaks due to the long-range JCH are realigned with separations of nJCH along the F1 dimension, and thus even the small long-range JCH values can easily be determined. The efficiency of measuring the long-range JCH using the proposed pulse sequences has been demonstrated in application to the complicated natural product, portmicin. Copyright 2010 John Wiley & Sons, Ltd. [source]

    An efficient use of the WATERGATE W5 sequence for observing a ligand binding with a protein receptor

    Kazuo Furihata
    Abstract An efficient pulse sequence for observing a ligand binding with a receptor has been developed by incorporating the WATERGATE W5 sequence. In the conventional water ligand observed via gradient spectroscopy (WaterLOGSY) techniques, the water resonance is selectively excited using,e.g. the double-pulsed field gradient spin,echo (DPFGSE) sequence at the initial portion of pulse sequence. In the current version, the modified WATERGATE W5 sequence is incorporated at the initial portion of the pulse sequence, and the resonance at the water frequency can be selectively reserved by the modified WATERGATE W5 sequence. The efficiency of ligand-observed NMR screening techniques has been demonstrated using the human serum albumin (HSA),tryptophan complex. Copyright 2008 John Wiley & Sons, Ltd. [source]