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At least 883 records · Page 49Linked to original sources
PubMed2006

T1-weighted cine FLASH is superior to IR imaging of post-infarction myocardial viability at 4.7T.

PURPOSE: Data are unavailable for rational selection of pulse sequences to assess postinfarction myocardial viability in rodents at high field strength. We implemented a widely used clinical inversion recovery (IR) sequence at 4.7T and compared the results to a heavily T1-weighted cine FLASH sequence (T1-CF) for assessment of infarction size. MATERIALS AND METHODS: Eleven infarcted rats were examined within 24 h of infarction after injection of Gadophrin-3 contrast agent. Images were acquired using both pulse sequences and a standard cine (SC) sequence. Estimates of infarct size were compared to TTC. Global LV function was compared between the T1-CF and SC sequences. RESULTS: SNR, relative SNR, and CNR for the infarcted and normal myocardium were significantly greater for the IR sequence. Infarction size was overestimated by both sequences, but correlated highly and showed very close agreement with TTC. Global function revealed no significant differences between T1-CF and SC. CONCLUSION: Both IR and T1-CF produced reliable results for assessment of infarction size at 4.7T. While the IR sequence delivers better overall SNR and CNR, the T1-CF allows concomitant assessment of global cardiac function with a much shorter acquisition time.

Animals↗
PubMed2005

Vibrational dynamics of ions in glass from fifth-order two-dimensional infrared spectroscopy.

The vibrational dynamics of the first four antisymmetric stretch vibrational levels of azide in an ionic glass have been measured and correlated using a heterodyned fifth-order two-dimensional infrared pulse sequence. By rephasing a two-quantum coherence, a process not possible with third-order spectroscopy, solvent effects on the frequencies and anharmonicities of the potential energy surface are measured. Fifth-order pulse sequences are another step towards precisely controlling vibrational coherence in analogy to the manipulation of spins in NMR but with ultrafast time resolution.

Journal Article↗
PubMed1993

[Quantitative assessment of lipiodol delivered intra-arterially into hepatoma: with evaluation of MR signal intensity].

We performed an experimental study using a CT phantom with various concentrations of Lipiodol emulsion. On the basis of these experimental data, we performed a quantitative analysis of Lipiodol delivered intra-arterially into hepatomas in order to evaluate the effect of Lipiodol accumulation on the MR signal intensities of hepatomas. The Lipiodol concentration and CT value showed an excellent linear correlation in the phantom study (r = 0.99). Lipiodol was estimated from 0.08 to 2.92 ml (8 to 77% of the injected dose) in hepatomas treated with Lipiodol-TAE. In the MR phantom study, signal intensities showed no remarkable change in cases of low concentrations of Lipiodol emulsion, while they decreased with increased Lipiodol concentrations both for T 1-and T 2-weighted SE and FLASH sequences in cases of high concentrations of Lipiodol emulsion. In the clinical materials, the signal intensities of tumors after Lipiodol-TAE tended not to show any apparent change in tumors with low estimated Lipiodol concentrations, but tended to decrease on all pulse sequences in tumors with high estimated Lipiodol concentrations. CT was useful for the quantitative analysis of Lipiodol accumulation in the tumor. Experimentally and clinically, a low concentration of Lipiodol had no apparent influence on MR signal intensities, while a high concentration tended to decrease signal intensities on all pulse sequences.

Adult↗
PubMedDate not supplied

Determination of gradient magnetic field-induced acoustic noise associated with the use of echo planar and three-dimensional, fast spin echo techniques.

The purpose of this study was to assess gradient magnetic-field-induced acoustic noise levels associated with the use of echo planar imaging (EPI) and three-dimensional fast spin echo (3D-FSE) pulse sequences. Acoustic noise measurements were obtained from two different high field-strength MR systems (1.5 T, Siemens and General Electric Co.) under ambient noise conditions and the use of EPI and 3D-FSE pulse sequences. Parameters were selected to produce "worst case" acoustic noise levels. Acoustic noise recordings were made at the entrance, the center, and at the exit of the magnet bores with a specially designed microphone that was unperturbed by electromagnetic fields. The highest ambient noise levels (A-weighted scale) were 67 dB (Siemens: the same values were recorded at the center and at the exit) and 78 dB (General Electric Co.; recorded at the exit). The highest acoustic noise levels recorded during activation of the gradient magnetic fields were 114 dB (Siemens) and 115 dB (General Electric Co.) and those occurred at the centers of the MR systems with the use of the EPI technique. Gradient magnetic fields associated with the use of EPI and 3D-FSE techniques produced acoustic noise levels that were within permissible levels recommended by federal guidelines.

Echo-Planar Imaging↗
PubMed1998

An 1H-13C-13C-edited 1H NMR experiment for making resonance assignments in the active site of heme proteins.

In paramagnetic heme proteins, it is often problematic to make proton resonance assignments for heme substituents that do not have large isotropic shifts and consequently lie under the large envelope of polypeptide resonances. Furthermore, assignments that would normally be performed with the aid of HMBC experiments in diamagnetic molecules can prove difficult in the active site of paramagnetic heme proteins if T2(-1) > 2JCH. To circumvent this problem, a new method is presented to selectively detect 1H in 1Hn-13C-13C fragments biosynthetically introduced into the active site of heme proteins. The pulse sequence combines well-known building blocks such as INEPT to transfer 1H spin magnetization to bonded 13C nuclei, followed by INADEQUATE to generate 13C-13C double-quantum coherence that is selected with pulsed field gradients, and finally reverse-INEPT to transfer magnetization back to 1H nuclei for subsequent observation. The new 1Hn-13C-13C edited experiment takes advantage of the relatively large values of 1JCH and 1JCC, avoiding the long interpulse delays in HMBC that compromise the detectability of rapidly relaxing nuclei. The potential applicability of the pulse sequence is demonstrated by its contribution to the unambiguous assignment of the carbonyl carbons in the heme propionates of ferricytochrome b5.

Fourier Analysis↗
PubMed1998

3D NMR experiments for measuring 15N relaxation data of large proteins: application to the 44 kDa ectodomain of SIV gp41.

A suite of 3D NMR experiments for measuring 15N-¿1H¿ NOE, 15N T1, and 15N T1rho values in large proteins, uniformly labeled with 15N and 13C, is presented. These experiments are designed for proteins that exhibit extensive spectral overlap in the 2D 1H-15N HSQC spectrum. The pulse sequences are readily applicable to perdeuterated samples, which increases the spectral resolution and signal-to-noise ratio, thereby permitting the characterization of protein dynamics to be extended to larger protein systems. Application of the pulse sequences is demonstrated on a perdeuterated 13C/15N-labeled sample of the 44 kDa ectodomain of SIV gp41.

Carbon Isotopes↗
PubMed1989

Intracranial hemorrhagic lesions: evaluation with spin-echo and gradient-refocused MR imaging at 0.5 and 1.5 T.

Twenty patients with intracranial hemorrhage were examined with magnetic resonance (MR) imaging at 0.5 and 1.5 T within 2 hours on the two imagers for lesions less than 30 days old and within 24 hours for lesions older than 30 days. MR studies included T1- and T2-weighted spin-echo (SE) and T2*-weighted gradient-refocused (GR) pulse sequences at each field strength. The number of lesions identified and the characteristics (ie, signal intensity of the margin, body, and core) of each hemorrhagic lesion were assessed and compared by means of the three pulse sequences at each field strength. Lesion depiction and characterization were superior (P less than .01) at 1.5 T with T2-weighted SE sequences. Improved depiction and characterization of lesions 300 or more days old (P less than .01) accounted for this result. With the GR sequence, depiction and characterization were similar at both field strengths. The GR sequence did not provide significant additional information about hemorrhage at 1.5 T in this series, but it improved depiction and characterization of hemorrhage at 0.5 T.

Adolescent↗
PubMed2005

Diffusion-weighted imaging of the liver: technical challenges and prospects for the future.

Diffusion-weighted imaging (DWI) has recently been attempted in the abdominal region. We review diffusion-weighted images of the liver, especially from the technical point of view. We discuss selection of pulse sequence parameters, effects of anti-breathing motion technique, tips for measuring apparent diffusion coefficient (ADC), and utility of superparamagnetic iron oxide (SPIO), showing clinical cases, including those at 3T. Our current trial of new pulse sequencing, such as SPIO-mediated breath-holding black-blood fluid-attenuated inversion recovery (BH-BB-FLAIR), imaging is shown. Some prospects for the future in DWI of the liver are also stated.

Adult↗
PubMedDate not supplied

Non-T1-weighted spin-echo MR imaging with contrast material: experimental and preliminary clinical assessment.

To clarify the role of contrast-enhanced non-T1-weighted spin-echo (SE) MR imaging, phantom experiments and 20 clinical examinations were conducted. All of the SE pulse sequences demonstrated enhancement on gadopentetate dimeglumine solution phantoms. Enhancement effect was also observed on proton density-weighted and T2-weighted images in tumors. This property might be better recognized and utilized in selecting pulse sequences in routine MR examinations.

Adipose Tissue↗
PubMed2005

Heterodyned fifth-order two-dimensional IR spectroscopy: third-quantum states and polarization selectivity.

A heterodyned fifth-order two-dimensional (2D) IR spectrum of a model coupled oscillator system, Ir(CO)(2)(C(5)H(7)O(2)), is reported. The spectrum is generated by a pulse sequence that probes the eigenstate energies up to the second overtone and combination bands, providing a more rigorous potential-energy surface of the coupled carbonyl local modes than can be obtained with third-order spectroscopy. Furthermore, the pulse sequence is designed to generate and then rephase a two-quantum coherence so that the spectrum is line narrowed and the resolution improved for inhomogeneously broadened systems. Features arising from coherence transfer processes are identified, which are more pronounced than in third-order 2D IR spectroscopy because the transition dipoles of the second overtone and combination states are not rigorously orthogonal, relaxing the polarization constraints on the signal intensity for these features. The spectrum provides a stringent test of cascading signals caused by third-order emitted fields and no cascading is observed. In the Appendix, formulas for calculating the signal intensities for resonant fifth-order spectroscopies with arbitrarily polarized pulses and transition dipoles are reported. These relationships are useful for interpreting and designing polarization conditions to enhance specific spectral features.

Journal Article↗
PubMed2000

Robust multiresolution alignment of MRI brain volumes.

An algorithm for the automatic alignment of MRI volumes of the human brain was developed, based on techniques adopted from the computer vision literature for image motion estimation. Most image registration techniques rely on the assumption that corresponding voxels in the two volumes have equal intensity, which is not true for MRI volumes acquired with different coils and/or pulse sequences. Intensity normalization and contrast equalization were used to minimize the differences between the intensities of the two volumes. However, these preprocessing steps do not correct perfectly for the image differences when using different coils and/or pulse sequences. Hence, the alignment algorithm relies on robust estimation, which automatically ignores voxels where the intensities are sufficiently different in the two volumes. A multiresolution pyramid implementation enables the algorithm to estimate large displacements. The resulting algorithm is used routinely to align MRI volumes acquired using different protocols (3D SPGR and 2D fast spin echo) and different coils (surface and head) to subvoxel accuracy (better than 1 mm).

Algorithms↗
PubMed2000

Construction of phase cycles of minimum cycle length: MakeCycle

An algorithm for the generation of a phase cycle of minimum length for a pulse sequence is developed from the basic requirement that only specified coherence transfer pathways will be accumulated. The efficacy of the algorithm is shown by determining the phase cycles of minimum length for DQFCOSY, GHMBC, and INEPT pulse sequences. Copyright 2000 Academic Press.

Journal Article↗
PubMed1992

Multiple pulse NMR imaging of polymers and chemistry.

Multiple pulse line narrowing techniques can be used to improve resolution and sensitivity in solid state NMR imaging. For example, pulse sequences which remove homonuclear dipolar broadening have been used to image proton-containing materials. Further enhancements in resolution and sensitivity are obtained by removing inhomogeneous interactions such as chemical shift, susceptibility, and heteronuclear dipolar broadening. Pulse sequences have been designed which provide efficient line narrowing over large spectral widths by taking into account the experimenter's control over the amplitude and time dependence of the gradient-induced resonance offset. These methods have been applied to centimeter sized samples to obtain images of polymers, composite materials, and gas-solid chemical reactions. T1 and T2 contrast allows differentiation between materials.

Magnetic Resonance Spectroscopy↗
PubMed2006

Time-efficient breath-hold abdominal MRI at 3.0 T.

OBJECTIVE: The purpose of this study was to increase the allowed number of acquired slices per unit time (i.e., time efficiency) for high-power deposition breath-hold abdominal acquisitions at 3.0 T. MATERIALS AND METHODS: Abdominal MRI protocols include various T1-weighted, T2-weighted, and contrast-enhanced acquisitions that require extended spatial coverage and resolution. Ideally, each acquisition is completed within one breath-hold. At 3.0 T, power deposition (i.e., specific absorption rate [SAR]) concerns can limit achieving these conflicting needs because conventional sequences are based on 6-minute time-average SAR requirements. We optimized abdominal-specific sequences based on an approved short-term 10-second time-average SAR criterion and added a delay time after breath-holding to fulfill the long-term 6-minute time-average power deposition regulation. RESULTS: Using our strategy, image acquisition time efficiency at 3.0 T was increased approximately twofold compared with conventional abdominal breath-hold pulse sequences for 2D dual-echo gradient-recalled echo, single-shot fast spin-echo, and 3D steady-state free precession sequences. Volunteers experienced a slight sensation of warmth for the single-shot fast spin-echo implementation, the most SAR-intensive sequence. CONCLUSION: Our optimization strategy is not vendor-specific, is easily implemented for all conventional scanners (provided one can access and modify the pulse sequences directly, or the vendors can make the necessary changes), yields a higher slice-per-unit-time imaging efficiency, and still satisfies all the regulatory power deposition requirements.

Abdomen↗
PubMedDate not supplied

Contrast-enhanced 3D MRA with centric ordering in k space: a preliminary clinical experience in imaging the abdominal aorta and renal and peripheral arterial vasculature.

The objective of this study was to determine the clinical utility of a contrast-enhanced, centric reordered, three-dimensional (3D) MR angiography (MRA) pulse sequence in imaging the abdominal aorta and renal and peripheral lower extremity arteries. Twenty-eight MRA studies were performed on 23 patients and four volunteers at 1.5 T using a 3D contrast-enhanced, centric reordered pulse sequence. In 20 patients, the abdominal aorta and renal arteries were imaged, and in seven patients, the lower extremity arteries were imaged. In 19 patients, a total of 51 renal vessels were evaluated (33 renal arteries using .1 mmol/kg of gadopentetate dimeglumine and 18 renal arteries using .2 mmol/kg of gadoteridol). A total of 70 peripheral arterial segments were assessed using .2 mmol/kg of gadoteridol. Correlation with conventional angiography was made for the following 14 cases: renal artery stenosis (four cases), abdominal aortic stenosis (one case), arteriovenous fistula in a transplant kidney (one case), renal arteriovenous malformation (one case), common iliac artery aneurysms (one case), and peripheral lower extremity (six cases). Of the 70 peripheral arterial segments evaluated, in 35, there was correlation with x-ray angiography. The mean percent of aortic signal enhancement was significantly higher in the .2 mmol/kg dose group (370.8 +/- 190.3) than in the .1 mmol/kg dose group (184.5 +/- 128.9) (P = .02). However, there was no apparent difference between the two doses for visualization of the renal and accessory renal arteries. There was concordance between the contrast-enhanced 3D MRA studies and conventional angiography in all cases of renal artery and peripheral arterial stenoses and occlusions, including visualization of reconstituted peripheral arterial segments. There was no evidence of spin dephasing effects at sites of stenoses on the 3D contrast-enhanced MRA studies. Contrast-enhanced, centric reordered, 3D MRA can rapidly image the abdominal aorta and renal and accessory renal arteries, as well as peripheral lower extremity arteries, with high resolution. Accurate depiction of the vascular lumen at sites of stenosis is made because of the lack of spin dephasing effects, even with hemodynamically significant stenoses. Additional larger clinical trials are required with this promising technique.

Adult↗
PubMed2006

Myocardial perfusion.

Noninvasive cardiac magnetic resonance (CMR) imaging has progressed rapidly over the past few years and will most likely become an integral part of the diagnostic workup of patients with known or suspected coronary artery disease (CAD). In this article the rationale for using perfusion-CMR is discussed, followed by a summary of current state-of-the-art perfusion-CMR techniques that addresses pharmacological stress, monitoring, pulse sequences, and doses of contrast media (CM) for first-pass studies. In the second part, unresolved aspects of perfusion-CMR, such as the lack of fully established and validated imaging protocols, are discussed. The optimum pulse sequence parameters, required cardiac coverage, analysis algorithms, criteria for data quality, and other aspects remain to be defined. Furthermore, since expertise in perfusion-CMR is not yet widely available, training of physicians and technicians to perform perfusion-CMR according to recognized standards is an important future requirement. In the last part of the review, some ideas are proposed to improve the management of patients with known or suspected CAD. This involves making a shift from a "reactive" strategy, in which patients are typically approached when they are symptomatic, to an "active" strategy, in which perfusion-CMR is performed for early detection of high-risk patients so that revascularizations can be performed before potentially deadly infarcts occur. An ideal test for such an active strategy would be highly accurate, reliable, safe (and thus repeatable), and affordable. Large multicenter trials have shown that in experienced centers perfusion-CMR is reliable and repeatable, and it is hoped that future studies will demonstrate its cost-effectiveness as well.

Contrast Media↗
PubMed2004

Optimized pathway selection in intraresidual triple-resonance experiments.

An optimized intraresidual pulse sequence element with better sensitivity and suppression of sequential cross peaks is presented. Concatenation of three magnetization transfer delays allows their independent setting, in accordance with the relaxation properties of the individual spins, without concomitantly prolonging the pulse sequence. Additionally, implementations of the scheme to HNCA, HNCACB, and the TROSY based triple-resonance experiments are proposed. The feasibility of the new element was verified by recording HNCA and HNCACB on the small 8.6 kDa protein ubiquitin. The corresponding HNCA-TROSY experiment was tested on a larger protein, the 30.4 kDa Cel6A from the thermophilic soil bacterium Thermobifida fusca at 800 (1)H MHz.

Carbon Isotopes↗
PubMed1997

MR imaging of segmental renal infarction: an experimental study.

An experimental study was performed in 12 rabbits to evaluate the magnetic resonance (MR) imaging findings of segmental renal infarction. Three or four MR examinations were performed at 6 h, 1 day, 3 days, 1 week, 2 weeks, and 4 weeks following the ligation of segmental artery of the left kidney. The signal intensities of the infarcted area on both T1- and T2-weighted (T1W and T2W, respectively) images were lower than those of the non-affected area in the 6 h group, and pathological examination showed mild interstitial oedema and haemorrhage. The signal intensities of the lesion became higher on T1W images and higher or mixed on T2W scans in the 1 day group, in which the pathological findings were intense interstitial haemorrhage, interstitial oedema, and early coagulative necrosis. The signal intensities of the lesion on both pulse sequences were also higher in the 3 day and 1 week groups in which pathological examination showed progressive coagulative necrosis. The signal intensities of the lesions in the 2 and 4 week groups were lower on both pulse sequences, and the pathological finding was organizing fibrosis. Post-contrast T1W images demonstrated well the extent of the infarction in all but two cases, in which the signal intensities of the lesions were higher on pre-contrast T1W scans.

Animals↗