Nuclear Magnetic Resonance Pulse Sequences Research Articles

5389877 Nuclear magnetic resonance pulse sequences for determining bound fluid volume

An NMR pulse sequence for use in a borehole logging tool includes a series of CPMG pulses according to: T r - 90° ±x - (t cp - 180° y - t cp - echo j ) where j is the index of CPMG echoes gathered, T r is wait time, t cp is the Carr-Purcell spacing. This pulse sequence is used to determine Bound Fluid Volume (BFV) which is subtracted from total porosity to yield Unbound Fluid Volume (UFV) of a formation surrounding the borehole. Measuring the BVF, the amount of rapidly relaxing fluid (less than 50 ms), is more efficient than measuring UFV (up to 2 secs), and is insensitive to motion of the logging tool.

5363041 Determining bound and unbound fluid volumes using nuclear magnetic resonance pulse sequences

5363041 Determining bound and unbound fluid volumes using nuclear magnetic resonance pulse sequences

NMR flow imaging of Newtonian liquids and a concentrated suspension through an axisymmetric sudden contraction

Using nuclear magnetic resonance (NMR) flow imaging to examine fluid motions at constant velocities or flows that change relatively slowly has been well-documented in the literature. Application of this technique to accelerative flows, on the other hand, has been limited. This study reports the use of an NMR flow imaging method, for which acceleration is not explicitly compensated in the NMR pulse sequence, to measure axial and radial fluid motions during flow through an axisymmetric sudden contraction. In this flow geometry, both velocity and acceleration are spatially dependent. The flow contraction ratio was 2:1. The method was first applied to examine Newtonian liquids at low and high Reynolds numbers under laminar flow conditions. The measured axial and radial velocity profiles, without accounting for acceleration effects in the data analysis, across the contraction are in excellent qualitative agreement with previous experimental data and theoretical calculations reported in the literature. Quantitative comparison of the axial and radial velocities with numerical results indicates that the maximum error from acceleration effects is about 10%. The method has also been used to examine the flow of a concentrated suspension (50% by volume of solid particles) through the contraction. The flow kinematics of the suspension at creeping flow conditions appear to mimic those of the Newtonian fluid with some slight differences. NMR images taken immediately following the cessation of flow suggest a slight degree of particle migration toward the center of the pipe downstream of the contraction.

Quantitative Po2Imaging in Vivo with Perfluorocarbon F-19 NMR: Tracking Oxygen from the Airway Through the Blood to Organ Tissues

The physiological redistribution of perfluorocarbon (PFC) compounds to liver, spleen, bone marrow, and lung after intravenous (i.v.) or intraperitoneal (IP) administration of PFC emulsions affords the unique opportunity for non-invasive monitoring of oxygenation status of these organs and tissues utilizing fluorine (F-19) nuclear magnetic resonance (NMR) imaging techniques. PFCs also may be introduced directly into the pulmonary airways by procedures such as liquid ventilation, intratracheal instillation, or aerosol inhalation. Considerations of importance when establishing methodology for accurate quantitation of oxygen partial pressure (pO2) in vivo using F-19 NMR include: 1.) error analysis of the calibration curves which relate pO2 to the measured PFC F-19 relaxation rate, 2.) optimization of the NMR pulse sequence for efficient oxygen sensitive data acquisition and, 3.) fluorine signal independence from emulsion aqueous phase bioconstituents. The porcine model was investigated at 0.14T following i.v. or IP administration of the PFC emulsion containing perfluorotributylamine (FC-43) to demonstrate the capability for tracking oxygen with F-19 NMR from the lung through the blood to selected organ tissues. Quantitative pO2 projection images and isobaric contour graphs were derived for the liver, spleen, and lungs as a function of inspired oxygen. Blood pO2 levels in aorta, pulmonary artery, and hepatic vein were monitored simultaneously with NMR imaging for correlative analysis.

Improving selectivity by using a multipurpose cross polarization magic angle spinning NMR pulse sequence: Characterization of π-conjugated compounds

The use of a multipurpose cross polarization magic angle spinning nuclear magnetic resonance pulse sequence to simplify high resolution solid state 13C NMR spectra is reported. Several kinds of experiments such as cross polarization, cross depolarization, proton dipolar dephasing and combinations of these are demonstrated for the well characterized trans-3,3′-bibenzo[ c]thienylidene-1,1′-dione. The pulse sequence is further applied to the analysis of insoluble poly(isothianaphthene).

13C NMR characterization of actinyl(VI) carbonate complexes in aqueous solution

The ligand exchange reaction between free and coordinated carbonate on 242 Pu VIO 2( 13CO 3) 3 4− and 243 Am VIO 2( 13CO 3) 3 4− systems was examined by variable temperature 13C pulsed nuclear magnetic resonance (NMR) techniques. A modified Carr-Purcell-Meiboom-Gill NMR pulse sequence was used for the experimental determination of ligand exchange parameters for paramagnetic actinide complexes. Eyring analysis provided activation parameters of ΔG 295 ‡ = 53 kJ M −1, ΔH ‡ = 35 kJ M −1 and ΔS 295 ‡ = −61 J M −1 K −1 for the plutonyl triscarbonate system, suggesting an associative transition state for the plutonyl(VI) carbonate self-exchange reaction.

5023551 Nuclear magnetic resonance pulse sequences for use with borehole logging tools

An NMR pulse sequence for use in the borehole environment is provided which combines a modified fast inversion recovery (FIR) pulse sequence with a series of more than ten, and typically hundreds, of CPMG pulses according to [W.sub.i -180-τ.sub.i -90-(t.sub.cp -180-t.sub.cp -echo).sub.j ].sub.i where j is the index of the CPMG echoes gathered, i is the index of the wait times in the pulse sequence, Wi are the wait times, i are the recovery times before the CPMG pulses, and tcp is the Carr-Purcell spacing. Measurements are made of the signals induced in the formation as a result of the magnetic fields. Determinations of Mo and/or T1 are then made from the measurements according to relationships which relate Mpo, T1 and T2 to the signal magnitude. Other relationships which provide stretched exponentials or multiple exponentials can also be used. From the Mo and/or T1 determinations, formation parameters such as porosity and permeability may be derived according to equations known in the art. In obtaining the most accurate determinations of formation parameters in the least amount of time, the various pulse sequence parameters (I, J, Wi, and τi) are optimized prior to logging. Additional accuracy is obtained by integrating a gated portion of the echoes rather than by measuring amplitude, and by utilizing a phase alternated CPMG sequence in repetitive measurements in order to eliminate baseline shift error.

Dynamics of methyl groups in proteins as studied by proton-detected 13C NMR spectroscopy. Application to the leucine residues of staphylococcal nuclease.

This paper describes the application of recently developed nuclear magnetic resonance (NMR) pulse sequences to obtain information about the internal dynamics of isotopically enriched hydrophobic side chains in proteins. The two-dimensional spectra provided by the pulse sequences enable one to make accurate measurements of nuclear Overhauser effects (NOE) and longitudinal (T1) and transverse (T2) relaxation times of enriched methyl carbons in proteins. Herein, these techniques are used to investigate the internal dynamics of the 11 leucine side chains of staphylococcal nuclease (SNase), a small enzyme having Mr = 16.8K, in the absence and presence of ligands thymidine 3',5'-bisphosphate (pdTp) and Ca2+. We report the synthesis of [5,5'-13C2]leucine, the preparation of SNase containing the labeled leucine, the sequential assignment of the leucine methyl carbons and protons in the liganded and unliganded proteins, and the measurement of the 13C T1, T2, and NOE values for the SNase leucine methyl carbons. Analysis of the relaxation parameters using the formalism of Lipari and Szabo shows that the internal motions of the leucine methyl carbons are characterized by effective correlation times tau f (5-80 ps) and tau s (less than 2 ns). The fast motion is identified with the rapid rotation of the methyl group about the C gamma-C delta bond axis, while the slow motion is associated with reorientation of the C gamma-C delta bond axis itself. The mean squared order parameters associated with the latter motion, Ss2, lie in the range 0.34-0.92. The values of Ss2 correlate reasonably well with the temperature factors of the leucine methyl carbons obtained from the crystal structures, but some are smaller than anticipated on the basis of the fact that nearly all leucine methyl carbons are buried and have temperature factors no larger than that of the leucine backbone atoms. Five leucine residues in liganded SNase and eight in unliganded SNase have values of Ss2 less than 0.71. These order parameters correspond to large amplitude motions (angular excursions of 27-67 degrees) of the C gamma-C delta bond axis. These results indicate that, in solution, the internal motions of the leucine side chains of SNase are significantly larger than suggested by the X-ray structures or by qualitative analysis of NOESY spectra. Comparison of Ss2 values obtained from liganded and unliganded SNase reveals a strong correlation between delta Ss2 and distance between the leucine methyl carbon and the ligands.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification and determination of the different types of hydrogen and carbon atoms in the soluble organic matter of the Puertollano oil shale

The soluble organic matter of the Puertollano oil shale has been studied by NMR (nuclear magnetic resonance) techniques. The sample was obtained by extractive sonication with carbon disulfide as solvent. 1H and 13C NMR spectra were recorded, the latter by using inverse gated heteronuclear decoupling pulse sequences and chromium(III)-acetylacetonate as relaxation reagent to avoid the NOE (nuclear Overhauser effect). Furthermore, the DEPT NMR pulse sequence (distortionless enhancement by polarization transfer) was used to assign different types of carbon atoms. The study and quantitative determination of the different kinds of hydrogen and carbon atoms present in the sample show that this bitumen is composed mainly of aliphatic hydrocarbons such as linear, polyisoprenoid and cyclic alkanes. There is a smaller contribution from aromatic hydrocarbons of variable structures.

Proton, nitrogen-15, and carbon-13 NMR signal assignments of IIIGlc a signal-transducing protein of Escherichia coli, using three-dimensional triple-resonance techniques

IIIGlc is an 18.1-kDa signal-transducing phosphocarrier protein of the phosphoenolpyruvate:glycose phosphotransferase system (PTS) of Escherichia coli. Virtually complete (98%) backbone 1H, 15N, and 13C nuclear magnetic resonance (NMR) signal assignments were determined by using a battery of triple-resonance three-dimensional (3D) NMR pulse sequences. In addition, nearly complete (1H, 95%; 13C, 85%) side-chain 1H and 13C signal assignments were obtained from an analysis of 3D 13C HCCH-COSY and HCCH-TOCSY spectra. These experiments rely almost exclusively upon one- and two-bond J couplings to transfer magnetization and to correlate proton and heteronuclear NMR signals. Hence, essentially complete signal assignments of this 168-residue protein were made without any assumptions regarding secondary structure and without the aid of a crystal structure, which is not yet available. Moreover, only three samples, one uniformly 15N-enriched, one uniformly 15N/13C-enriched, and one containing a few types of amino acids labeled with 15N and/or 13C, were needed to make the assignments. The backbone assignments together with the 3D 15N NOESY-HMQC and 13C NOESY-HMQC data have provided extensive information about the secondary structure of this protein [Pelton, J.G., Torchia, D.A., Meadow, N.D., Wong, C.-Y., & Roseman, S (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 3479-3488]. The nearly complete set of backbone and side-chain atom assignments reported herein provide a basis for studies of the three-dimensional structure and dynamics of IIIGlc as well as its interactions with a variety of membrane and cytoplasmic proteins.

Separation of spin populations with gradient echoes as an aid in pulse sequence tuning

Tuning of nuclear magnetic resonance pulse sequences with pulsed “crusher” gradients or phase cycling serves to remove unwanted spin populations from the data acquisition window. Verification that unwanted spin population are not detected is often determined by the absence of obvious artifacts in an image. This approach is unsatisfactory in some instances because signal contamination with unwanted spin populations may not be obvious. This is a particular concern with multiple-spin echo, volume-selective, and other multiple-pulse sequences. A solution to this problem is the separation of spin populations using gradient echoes, allowing the existence of unwanted populations to be easily observed separately. Tuning of a pulse sequence is straightforward when spin populations can be independently observed.

Backbone dynamics of proteins as studied by 15N inverse detected heteronuclear NMR spectroscopy: application to staphylococcal nuclease.

This paper describes the use of novel two-dimensional nuclear magnetic resonance (NMR) pulse sequences to provide insight into protein dynamics. The sequences developed permit the measurement of the relaxation properties of individual nuclei in macromolecules, thereby providing a powerful experimental approach to the study of local protein mobility. For isotopically labeled macromolecules, the sequences enable measurements of heteronuclear nuclear Overhauser effects (NOE) and spin-lattice (T1) and spin-spin (T2) 15N or 13C relaxation times with a sensitivity similar to those of many homonuclear 1H experiments. Because T1 values and heteronuclear NOEs are sensitive to high-frequency motions (10(8)-10(12) s-1) while T2 values are also a function of much slower processes, it is possible to explore dynamic events occurring over a large time scale. We have applied these techniques to investigate the backbone dynamics of the protein staphylococcal nuclease (S. Nase) complexed with thymidine 3',5'-bisphosphate (pdTp) and Ca2+ and labeled uniformly with 15N. T1, T2, and NOE values were obtained for over 100 assigned backbone amide nitrogens in the protein. Values of the order parameter (S), characterizing the extent of rapid 1H-15N bond motions, have been determined. These results suggest that there is no correlation between these rapid small amplitude motions and secondary structure for S. Nase. In contrast, 15N line widths suggest a possible correlation between secondary structure and motions on the millisecond time scale. In particular, the loop region between residues 42 and 56 appears to be considerably more flexible on this slow time scale than the rest of the protein.

4710718 Spatially selective nuclear magnetic resonance pulse sequences

4710718 Spatially selective nuclear magnetic resonance pulse sequences

8504727 Spatially selective nuclear magnetic resonance pulse sequences

8504727 Spatially selective nuclear magnetic resonance pulse sequences

Menstrual variation of normal breast NMR relaxation parameters.

Nuclear magnetic resonance (NMR) offers great promise in noninvasively distinguishing normal, benign, and malignant tissues in the breast. However, well-documented changes that occur in breast tissues during the normal menstrual cycle suggest that lesion detectability will depend on knowledge of the variations in NMR parameters that occur as a consequence of these changes. Correct selection of optimal NMR pulse sequences and interpulse times, based on spin density and T1 and T2 values, to maximize tissue contrast and lesion detectability, will likewise depend on our understanding of variations in NMR parameters of normal breast tissues. The purpose of this study is to determine the range and variability of NMR parameters (spin density, T1 and T2) associated with changes in normal breast tissues during the menstrual cycle, as measured by NMR imaging. Initial findings suggest that there are measurable differences between breast tissues as a function of time in the menstrual cycle.

Structural and mode of action studies on bio-active molecules

The technique of nuclear Overhauser effect difference spectroscopy allows the determination, from1H nuclear magnetic resonance spectra, of those protons in a structure which are near in space to a selected, irradiated proton. The experiment is extremely powerful in the determination of structure in solution, and is sufficiently precise often to give stereochemical detail. The method was used in determination of the structures of the antibiotics of the teicoplanin complex (members of the vancomycin group), and the principles are briefly illustrated. Additionally, nuclear magnetic resonance pulse sequences can be used to edit13C spectra (separate the spectrum into four spectra, containing C, CH, CH2, and CH3 carbons), and this technique also aided the structure elucidation of the teicoplanin complex. Finally, it is emphasised that nuclear Overhauser effect difference spectroscopy can be used to determine the molecular details of drug binding sites, and an example is given.

Nuclear magnetic resonance pulse sequence and discrimination of high- and low-fat tissues

Signal size compared to independently measured T 1 is described for various pulse sequences on the Aberdeen Mk II nuclear magnetic resonance imager. The ability of these sequences to discriminate between certain tissue types, and in particular between adipose tissue and muscle, is discussed. Inversion recovery, with a t interval of 200 ms, gives the best discrimination for this purpose, with a contrast ratio of 6 between fat and muscle. Other image types, and especially T 1, give better contrast for low-lipid soft tissues such as liver and spleen.

Phase detection and contrast loss in magnetic resonance imaging

Several recent articles have assessed the relative efficiency of nuclear magnetic resonance (NMR) pulse sequences. One consideration that has received little attention is the effect on image contrast of displaying images without information on the sign of the reconstructed signals. The radiofrequency receivers currently used on most NMR imaging systems are quadrature detectors that preserve both the magnitude and sign of the NMR signal. Usually, however, sign or phase information is not used in the final image presentation. We point out that in imaging sequences that may have negative signals, such as inversion recovery, this loss of sign information produces a reduction in contrast between some tissues in an NMR image. We discuss the tissue parameters and interpulse delay times that result in contrast loss in inversion recovery and indicate the extent of contrast loss. We point out that for some tissues with unequal hydrogen spin densities, the region of contrast loss coincides with the region where maximum contrast would occur if sign information were preserved.

Nuclear magnetic resonance imaging of the posterior fossa: 50 Cases

Fifty patients with clinical diagnoses of disease within the posterior fossa were examined with a nuclear magnetic resonance (NMR) scanner and the results were compared with X-ray computed tomography (CT). A variety of NMR pulse sequences reflecting proton density, T1, T2 and blood flow were used and imaging was performed in transverse coronal and sagittal planes. In many cases NMR provided diagnostic information unavailable from CT scans. This included recognition of lesions not seen with CT in infarction and multiple sclerosis, as well as more precise definition of mass effects, oedema and anatomical relationships in other diseases. Extrinsic and intrinsic tumours were readily distinguished, as were brain-stem and cerebellar tumours. Arnold-Chiari malformations were demonstrated with sagittal scans and cerebellar atrophy was identified. A patient treated with radiotherapy displayed more extensive changes in the surrounding brain with NMR than with CT. Evidence of occlusion or reduced flow was found in two cases with vertebro-basilar disease. Occlusion of the internal carotid artery was also demonstrated. Computed tomography was superior to NMR in demonstrating calcification and bone erosion. In four of 14 tumours studied, contrast-enhanced CT demonstrated the margin between tumour and surrounding oedema or brain better than NMR. Nuclear magnetic resonance imaging is a versatile, non-invasive technique capable of demonstrating a wide spectrum of disease within the posterior fossa.