HSQC-1,n-ADEQUATE: a new approach to long-range 13C-13C correlation by covariance processing.

Long-range, two-dimensional heteronuclear shift correlation NMR methods play a pivotal role in the assembly of novel molecular structures. The well-established GHMBC method is a high-sensitivity mainstay technique, affording connectivity information via (n)J(CH) coupling pathways. Unfortunately, there is no simple way of determining the value of n and hence no way of differentiating two-bond from three- and occasionally four-bond correlations.

HSQC-ADEQUATE: an investigation of data requirements.

Utilizing (13)C-(13)C connectivity networks for the assembly of carbon skeletons from HSQC-ADEQUATE spectra was recently reported. HSQC-ADEQUATE data retain the resonance multiplicity information of the multiplicity-edited GHSQC spectrum and afford a significant improvement in the signal-to-noise (s/n) ratio relative to the 1,1-ADEQUATE data used in the calculation of the HSQC-ADEQUATE spectrum by unsymmetrical indirect covariance (UIC) processing methods. The initial investigation into the computation of HSQC-ADEQUATE correlation plots utilized overnight acquisition of the 1,1-ADEQUATE data used for the calculation.

Mechanistic studies of a linear trisazoalkane, a new azimine, and a bicyclic triaziridine. Azoalkane homolysis into seven fragments.

An aliphatic azo compound containing three azo groups (1) has been prepared by IF(5) oxidation of beta-azoamine 3. The thermolysis kinetics of this vicinal trisazoalkane were investigated above 155 degrees C, leading to a rate constant only 5.5 times faster than that of the simple model, azo-tert-butane.

Two-dimensional proton chemical-shift imaging of human muscle metabolites.

Large lipid signals and strong susceptibility gradients introduced by muscle-bone interfaces represent major technical challenges for in vivo proton MRS of human muscle. Here, the demonstration of two-dimensional proton chemical-shift imaging of human muscle metabolites is presented. This technique utilizes a chemical-shift-selective method for water and lipid suppression and automatic shimming for optimal homogeneity of the magnetic field.

Brain proton magnetic resonance spectroscopy studies in recently abstinent alcoholics.

Chronic alcohol-dependent patients have reduced brain volumes and concomitant neurobehavioral deficits that may recover during abstinence. In 10 chronic alcoholic patients, using localized proton magnetic resonance spectroscopy, we found reliable increases during the first 3-4 weeks of abstinence in the concentrations within the superior cerebellar vermis of choline (Cho)-containing compounds relative to the neuronal marker, N-acetylaspartate (NAA). Lesser changes were observed following 1 month of abstinence, and in one of the patients studied longitudinally over 3 months, a marked reduction in the Cho/NAA ratio was associated with relapse.

Dissecting and implementing STEAM spectroscopy.

A rapid, simple method for constructing a site-specific STEAM sequence from a basic Hahn three-pulse sequence is presented. The method assures maximum signal available from the hardware.

Removing effects of eddy currents in proton MR spectroscopy.

The use of pulsed gradients to define a volume of interest for localized magnetic resonance spectroscopy produces magnetic field perturbations which distort both the free induction decay and the spectrum after Fourier transformation. A technique is presented that removes the artifacts from eddy currents from a sampled free induction decay. To linearize the phase, the nonlinear phase of a reference free induction decay is subtracted from the phase of a sample free induction decay.

Magnetic field mapping in NMR imaging.

The Hahn spin preparation sequence provides a practical means for rapid and sensitive mapping of magnetic field inhomogeneity in NMR imaging applications. Choice of the rf pulse delay times tau 1 and tau 2 as well as conditions and limitations on the proposed use of this sequence for chemical shift imaging are discussed.

Nuclear magnetic resonance diagnosis of an anaplastic astrocytoma.

A patient presented with an 8-month history of a progressive left homonymous visual field deficit, left hemiparesis, and a left thalamocortical sensory deficit that was not detectable by repeated conventional neurodiagnostic evaluations. Proton nuclear magnetic resonance (NMR) imaging revealed a right parietal lesion characterized by a prolonged T2 (spin-spin relaxation time). At surgery, the mass proved to be an anaplastic astrocytoma.

Nuclear magnetic resonance evaluation of stroke. A preliminary report.

Nine patients who had acute and subacute stroke were examined by nuclear magnetic resonance (NMR) using a 6-MHz Bruker Instruments proton scanner. A modified Carr-Purcell-Meiboom-Gill pulse sequence was used for signal detection. The resultant string of spin-echoes was Fourier transformed into projections that were subsequently back-projected to a series of spin-echo images.

Accurate T2 NMR images.

We present a method for producing accurate calculated T2 nuclear magnetic resonance (NMR) images. A modified Carr-Purcell-Meiboom-Gill pulse sequence is used to obtain a series of images with progressive T2 dependence. This image series is then analyzed pixel by pixel to generate a T2 and initial signal strength image.

NMR evaluation of stroke in the rat.

Cortical stroke was produced in rats by cautery occlusion of the middle cerebral artery distal to the lenticulostriate origins. Brains were removed, and nuclear magnetic resonance (NMR) scans of whole fixed brains and in vitro measurements of small samples were obtained. Brain tissue was then processed for histology.