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PubMed1984

Anatomic features of the eye disclosed with nuclear magnetic resonance imaging.

Nuclear magnetic resonance (NMR) imaging of the eye and paraorbital areas was performed in 35 volunteers and in four patients with ocular pathology. Two- and three-dimensional images were performed with saturation recovery (SR), inversion recovery (IR), and spin echo (SE) pulse sequences. Fat was brighter than surrounding tissue on images obtained with all pulse sequences, while muscle and optic nerve were of decreased intensity. The optic chiasm and vitreous were of decreased intensity compared with orbital fat on SR. The lens had even less signal intensity than the vitreous on SR and IR images and blended into the surroundings on SE images. A melanoma of the ciliary body and a lymphoma of the lacrimal gland were identified. In conclusion, NMR images can be used to identify normal and pathologic orbital and eyeball anatomy. Image contrast is provided by high intensity fat, which is interspersed throughout other orbital structures.

Eye Diseases↗
PubMed1999

Spectroscopic imaging of the uptake kinetics of human brain ethanol.

Previous measurements of the ratio of brain to venous blood alcohol have ranged from 21-100%, depending on the experimental model, pulse sequence, and the concentration reference used. The goal of this study was to evaluate the uptake kinetics and visibility of brain ethanol in comparison to venous blood levels using a pulse sequence that minimizes uncertainties due to differences in J-modulation, T(1), and T(2) between ethanol and the concentration standard. This was achieved using a short TE (24 msec) spin echo sequence with a semiselective refocusing pulse to minimize J-modulation losses of the ethanol. Brain ethanol levels were measured with 10-min time resolution using a 16 x 16 spectroscopic imaging matrix with nominal voxels of 1.44 cc. During the course of the study, the brain/blood alcohol ratio declined from a value of 1.54 +/- 0.74 at 35 min after drinking to a final value of 0.93 +/- 0.16 at 85 min postdrinking. Magn Reson Med 42:1019-1026, 1999.

Adult↗
PubMed1991

Quantitative determination of the partial oxygen pressure in the vitrectomized rabbit eye in vivo using 19F NMR.

We have quantitatively determined the PO2 within the vitreous space of the vitrectomized rabbit eye in vivo using 19F NMR and perfluorotributylamine (FTBA). The results of the present work are in good agreement with previous measurements of PO2 within the nonvitrectimized rabbit eye obtained using oxygen microelectrodes. In this study, good precision and accuracy were achieved by: (1) having minimal flow effects present, (2) optimizing the signal-to-noise through the use of neat FTBA and surface coil transmission and detection, and (3) performing an inversion-recovery pulse sequence, with adiabatic pulses, to optimize the dynamic range of the T1 experiment. Possible deleterious effects on the measured T1 due to the vitreal temperature gradient are discussed. To the best of our knowledge the results of this study demonstrate, for the first time, a quantitative determination of intraocular PO2 in vivo using 19F NMR and FTBA.

Animals↗
PubMed1997

A method to measure arbitrary k-space trajectories for rapid MR imaging.

A method to measure arbitrary k-space trajectories was developed to compensate for nonideal gradient performance during rapid magnetic resonance (MR) imaging with actively or nonactively shielded gradients at a magnetic field strength of 4.1 T. Accurate MR image reconstruction requires knowledge of the k-trajectory produced by the gradient waveforms during k-space sampling. Even with shielded gradients, residual eddy currents and imperfections in gradient amplifier performance can cause the true k-space trajectory to deviate from the ideal trajectory. The k-space determination was used for spiral gradient-echo imaging fo the human brain. While individual calibrations are needed for new pulse sequences, the method of k-space determination can be used for any sequence of preparation pulses and readout gradient waveforms and should prove useful for other trajectories, including the rastered lines of echo-planar imaging.

Artifacts↗
PubMed2000

Clean TROSY: compensation for relaxation-induced artifacts.

TROSY pulse sequences for recording, e.g., (1)H-(15)N chemical shift correlation spectra of proteins are designed to select only one of four two-dimensional multiplet components. However, all of the variants published so far are prone to relaxation-induced artifacts at the positions of two of the other multiplet components. This article introduces modifications to the two spin-state-selective coherence transfer building blocks of the TROSY mixing sequence resulting in a clean TROSY spectrum with the artifacts largely suppressed. It works by having the new mixing sequence generate peaks of opposite phase at the positions of the relaxation artifacts. The clean TROSY pulse sequence is marginally shorter than the original one and contains the same pulses. Experimental demonstration is presented for the (15)N-labeled proteins RAP 17-97 (N-terminal domain of alpha(2)-macroglobulin receptor associated protein) and EQT, equinatoxin II, from the Mediterranean anemone Actinia equina.

Animals↗
PubMed2001

Difftrain: a novel approach to a true spectroscopic single-scan diffusion measurement.

Diffusion-ordered spectroscopy (DOSY) has gained considerable attention over the past decade as a useful tool for calculating diffusion-related parameters or in the analysis of complex (reaction) mixtures. A major drawback of the established methods are the relatively long recording times needed to acquire the spectra, excluding the monitoring of rapidly progressing reactions and (hence) measurements of less stable components. In order to overcome these shortcomings a new pulse sequence, Difftrain, has been developed. The sequence involves stimulated echo attenuation, multilow flip angle excitation, and multiple sampling of the FID during the longitudinal storage. The calculated diffusion parameters obtained by Difftrain were compared with those obtained by the established sequence BPPSTE (bipolar pulse pair stimulated echo) and were in good agreement. For systems with moderate to good signal-to-noise ratios the Difftrain building block yields significant saving in recording time (single-shot acquisition instead of acquiring n-different gradients strengths), thus opening up new applications in nonequilibrium systems and screening of compositions and/or interactions of (larger) compound arrays.

Journal Article↗
PubMed2000

One- and two-dimensional pulse electron paramagnetic resonance spectroscopy: concepts and applications.

During the last two decades, the possibilities of pulse electron paramagnetic resonance (EPR) and pulse electron nuclear double resonance (ENDOR) spectroscopy have increased tremendously. While at the beginning of the 1980s pulse-EPR and ENDOR applications were still a rarity, the techniques are now very frequently applied in chemistry, physics, materials science, biology and mineralogy. This is mainly due to the considerable efforts invested in the last few years on instrument development and pulse-sequence design. Pulse-EPR spectrometers are now commercially available, which enables many research groups to use these techniques. In this work, an overview of state-of-the-art pulse EPR and ENDOR spectroscopy is given. The rapid expansion of the field, however, does not allow us to give an exhaustive record of all the pulse methods introduced so far. After a brief and very qualitative description of the basic principles of pulse EPR, we discuss some of the experiments in more detail and illustrate the potential of the methods with a number of selected applications.

Bacteriochlorophylls↗
PubMed1987

Magnetic resonance imaging of gynecologic masses.

The pelvis of 21 women with various gynecological masses were imaged with magnetic resonance (MR) imagers at 2.0 and 0.5 T. Fifteen normal individuals were used for studying the normal appearance of the female genitalia using spin echo pulse sequences with various pulse repetition (TR) and spin echo (TE) time values. Images were compared with those of the ultrasonic images, intraoperative findings, and the histopathologic examinations. The masses included simple ovarian cyst, cystadenoma, serous cystadenocarcinoma, ovarian teratoma, dysgerminoma, and uterine myoma. MR imaging was useful in demonstrating the anatomy and pathology of the cases examined in this study. It detected the internal structure of some tumors which were sonographically homogeneous. The potential of MR in staging of malignancies was demonstrated.

Adolescent↗
PubMed2003

Heteronuclear spin decoupling in solid-state NMR under magic-angle sample spinning.

Achieving high spectral resolution is an important prerequisite for the application of solid-state NMR to biological molecules. Higher spectral resolution allows to resolve a larger number of resonances and leads to higher sensitivity. Among other things, heteronuclear spin decoupling is one of the important factors which determine the resolution of a spectrum. The process of heteronuclear spin decoupling under magic-angle sample spinning is analyzed in detail. Continuous-wave RF irradiation leads only in a zeroth-order approximation to a full decoupling of heteronuclear spin systems in solids under magic-angle spinning (MAS). In a higher-order approximation, a cross-term between the dipolar-coupling tensor and the chemical-shielding tensor is reintroduced, providing a scaled coupling term between the heteronuclear spins. In strongly coupled spin systems this second-order recoupling term is partially averaged out by the proton spin-diffusion process, which leads to exchange-type narrowing of the line by proton spin flips. This process can be described by a spin-diffusion type superoperator, allowing the efficient simulation of strongly coupled spin systems under heteronuclear spin decoupling. Low-power continuous-wave decoupling at fast MAS frequencies offers an alternative to high-power irradiation by reversing the order of the averaging processes. At fast MAS frequencies low-power continuous-wave decoupling leads to significantly narrower lines than high-power continuous-wave decoupling while at the same time reducing the power dissipated in the sample by several orders of magnitude. The best decoupling is achieved by multiple-pulse sequences at high RF fields and under fast MAS. Two such sequences, two-pulse phase-modulated decoupling (TPPM) and X-inverse-X decoupling (XiX), are discussed and their properties analyzed and compared.

Ammonium Chloride↗
PubMed1991

[The demonstration of calcifications in magnetic resonance tomography (MRT). The effect of different parameters on the MRT imaging of cerebral calcifications].

The effect of various factors on the demonstration of calcified lesions was studied in 131 areas of calcification which had been demonstrated by CT. By means of MRI (SE 400/30 or GE315/14, 90 degrees and SE 1600/30 + 70; 0.5T) 117 of the 131 calcified lesions (89%) produced a signal difference. Of these 117 lesions, 80 (61%) were recognised as calcification by MRI. Large areas of calcification (more than 5 mm) and high density calcification (more than 100 Hu) were recognised significantly more often than small or low density calcifications. T2-weighted images demonstrated calcification more often than other sequences. With conventional pulse sequences, calcified lesions were frequently recognised as abnormalities on MRI, but their recognition as calcified lesions is unreliable.

Brain↗
PubMed1991

Gd-DTPA-enhanced short repetition time and short inversion time inversion recovery magnetic resonance imaging. Experimental and clinical assessment.

To suppress both water and fat signal while retaining the high signal of Gd-DTPA enhancement, magnetic resonance imaging (MRI) of phantoms and 28 patients with mass lesions was done using short repetition time (TR) and short inversion time inversion recovery (STIR) sequences. Optimal STIR pulse sequences of 500 to 1000/80-100/20-30 (TR/TI/TE) were determined by an experimental study. In most instances, a signal bandwidth of +/- 8 kHz was used to increase the signal-to-noise ratio. The authors measured image contrast between lesions and adjacent fatty tissue and compared postcontrast STIR and T1-weighted spin-echo (T1-W SE) images. When the signal intensity of a lesion is 80% of adjacent fatty tissue on postcontrast T1-W SE, short TR STIR images provide better tumor delineation.

Contrast Media↗
PubMedDate not supplied

Detection and characterization of metastatic cervical adenopathy by MR imaging: comparison of different MR techniques.

Thirty-five patients scheduled to undergo a neck dissection for squamous cell carcinoma of the head and neck were evaluated preoperatively by magnetic resonance (MR) imaging. Axial and occasionally sagittal and coronal images were obtained. To define the most reliable technique to detect cervical lymph node metastasis, we compared several MR pulse sequences with and without Gd-DTPA administration to histopathologic findings in the neck dissection specimens. T1-weighted spin echo combined with T2-weighted gradient recalled echo (GE) sequences were found to be more useful than any other combination of pulse sequences in localizing lymph nodes. On T2-weighted GE images, lymph nodes were depicted with intermediate to high signal intensity in contrast to low signal muscular and fatty tissue. Gadolinium DTPA enhanced T1-weighted GE images reliably depict central lymph node necrosis, the most specific criterion for lymph node metastasis.

Adult↗
PubMed2006

Myxoma of the kidney.

A 62-year-old man had a right renal mass incidentally diagnosed by ultrasonography. Magnetic resonance imaging revealed a well-defined right renal mass with homogenous low-signal intensity on the T(1)-weighted pulse sequence and heterogeneous high-signal intensity on the T(2)-weighted pulse sequence. A right nephrectomy was performed. The histological examination showed a myxoma, which is a very uncommon neoplasm in the kidney. Eight cases have been reported previously.

Diagnosis, Differential↗
PubMed1989

Subdural and epidural empyemas: MR imaging.

The MR images of six patients with extraaxial empyemas (five subdural and four epidural) were reviewed and compared with CT scans. MR demonstrated convexity and interhemispheric collections, which were mildly hyperintense relative to CSF and hypointense relative to white matter on short TR pulse sequences and hyperintense relative to CSF and white matter on long TR pulse sequences, allowing distinction from sterile effusions and most chronic hematomas. A hypointense rim, representing displaced dura, was depicted at the interface between the lesion and brain in epidural empyemas, a feature absent in subdural empyemas. Inflammation-induced parenchymal abnormalities, including edema, mass effect, and reversible cortical hyperintensity, were well depicted on MR imaging. MR was superior to CT in demonstrating the presence, nature, and extent of these lesions in all cases. Because early and accurate diagnosis will significantly improve the prognosis of these serious infections, MR is preferred to CT for patients in whom an acute intracranial infection is suspected.

Adolescent↗
PubMed1992

"Chess-board pattern" spatial modulation of magnetization. Assessment of myocardial function.

Heart motion is a complex combination of translation, rotation, and concentric contraction. Evaluation of these complex motions has been difficult using conventional slice-selective methods. Noninvasive tagging of the heart has been obtained by the use of slice-selective radiofrequency pulses. Through spatial modulation of the magnetization the entire image can be labeled in different patterns. Two new pulse sequences are presented, giving a chess-board like spatial modulation. These pulse sequences have several advantages compared with the previously published methods, as the modulation time is half that required to obtain a 2-dimensional grid, the area in the image with high signal intensity was significantly larger, and the radiofrequency power deposition was substantially decreased. By labeling the heart at diastole the chess-board pattern tagging of the heart wall could be followed through systole. Using this method the complex motions of the heart can be mapped.

Computer Simulation↗
PubMed2006

Metabolomic analysis using optimized NMR and statistical methods.

NMR-based metabolomics requires robust automated methodologies, and the accuracy of NMR-based metabolomics data is greatly influenced by the reproducibility of data acquisition and processing methods. Effective water resonance signal suppression and reproducible spectral phasing and baseline traces across series of related samples are crucial for statistical analysis. We assess robustness, repeatability, sensitivity, selectivity, and practicality of commonly used solvent peak suppression methods in the NMR analysis of biofluids with respect to the automated processing of the NMR spectra and the impact of pulse sequence and data processing methods on the sensitivity of pattern recognition and statistical analysis of the metabolite profiles. We introduce two modifications to the excitation sculpting pulse sequence whereby the excitation solvent suppression pulse cascade is preceded by low-power water resonance presaturation pulses during the relaxation delay. Our analysis indicates that combining water presaturation with excitation sculpting water suppression delivers the most reproducible and information-rich NMR spectra of biofluids.

Animals↗
PubMed1996

Circular sampling: perspective of a time-saving scanning procedure.

A time-saving pulse sequence that requires relatively low gradients and slow rise time is suggested herein. With this pulse sequence the entire k domain is sampled along a set of concentric circles using only 50% of the number of pulses required by the standard line sampling technique (2DFT). This can result in saving about half the total scanning time in gated cardiac imaging. The sampling configuration in the k domain is identical to MR projection reconstruction, with the advantage that a considerably smaller number of excitations is required. Furthermore, computer simulations indicate that the proposed method is also advantageous over the "half-Fourier" method, as it provides better SNR for equal acquisition time (0.83 vs. 0.707 of the 2DFT SNR respectively.

Computer Simulation↗