Biomedical subjects

Robert A Wind

Publications and source records attributed to Robert A Wind.

4 recordsLinked to original sources

PubMed2003

Sensitivity-enhanced phase-corrected ultra-slow magic angle turning using multiple-echo data acquisition.

The increase in the sensitivity of the phase-corrected magic angle turning (PHORMAT) experiment at ultra-slow spinning rates by means of multiple-echo data acquisition (ME-PHORMAT) is evaluated. This is achieved by replacing the acquisition dimension in the original experiment with a train of equally spaced pi-pulses. It is shown that the echoes following the odd and even pi-pulses in the CPMG train must be processed differently in order to avoid spectral distortions. The method is illustrated for 13C CP-ME-PHORMAT on solid 1,2,3-trimethoxybenzene and for 1H ME-PHORMAT on excised rat liver tissue, both at a sample-spinning rate of 1.3 Hz. Sensitivity enhancements of a factor 4 for the solid and 2.3 for the liver were obtained. Finally, it is shown that with ME-PHORMAT one of the two RF pulse sequences, in standard PHORMAT used to obtain a pure absorption mode 2D spectrum, can be eliminated, thus reducing the usually long measuring time by a factor 2.

Algorithms↗

PubMed2002

High-resolution 1H NMR spectroscopy in rat liver using magic angle turning at a 1 Hz spinning rate.

It is demonstrated that a high-resolution (1)H NMR spectrum of excised rat liver can be obtained using the technique of magic angle turning (MAT) at a sample spinning rate of 1 Hz. A variant of the phase-corrected MAT (PHORMAT) pulse sequence that includes a water suppression segment was developed for the investigation. The spectral resolution achieved with PHORMAT approaches that obtained from a standard magic angle spinning (MAS) experiment at a spinning rate of several kHz. With such ultra-slow spinning, tissue and cell damage associated with the standard MAS experiment is minimized or eliminated. The technique is potentially useful for obtaining high-resolution (1)H spectra in live animals.

Animals↗

PubMed2002

Picoliter (1)H NMR spectroscopy.

In this study, a 267-microm-diameter solenoid transceiver is used to acquire localized (1)H NMR spectra and the measured signal-to-noise ratio (SNR) at 500 MHz is shown to be within 20--30% of theoretical limits formulated by considering only its resistive losses. This is illustrated using a 100-microm-diameter globule of triacylglycerols (approximately 900mM) that may be an oocyte precursor in young Xenopus laevis frogs and a water sample containing choline at a concentration often found in live mammalian cells (approximately 33 mM). In chemical shift imaging (CSI) experiments performed using a few thousand total scans, the choline methyl line is shown to have an acceptable SNR in resolved volume elements containing only 50 pL of sample, and localized spectra are resolved from just 5 pL in the Xenopus globule. These findings demonstrate the feasibility of performing (1)H NMR on picoliter-scale sample volumes in biological cells and tissues and illustrate how the achieved SNR in spectroscopic images can be predicted with reasonable accuracy at microscopic spatial resolutions.

Animals↗

PubMed2002

The evaluation of different MAS techniques at low spinning rates in aqueous samples and in the presence of magnetic susceptibility gradients.

UNLABELLED: It was recently demonstrated that the nuclear magnetic resonance (NMR) linewidths for stationary biological samples are dictated mainly by magnetic susceptibility gradients, and that phase-altered spinning sideband (PASS) and phase-corrected magic angle turning (PHORMAT) solid-state NMR techniques employing slow and ultra-slow magic angle spinning (MAS) frequencies can be used to overcome the static susceptibility broadening to yield high-resolution, spinning sideband (SSB)-free 1H NMR spectra [Magn. Reson. Med. 46 (2001) 213; 47 (2002) 829]. An additional concern is that molecular diffusion in the presence of the susceptibility gradients may limit the minimum useful MAS frequency by broadening the lines and reducing SSB suppression at low spinning frequencies. In this article the performance of PASS, PHORMAT, total sideband suppression (TOSS), and standard MAS techniques were evaluated as a function of spinning frequency. To this end, 300MHz (7.05T) 1H NMR spectra were acquired via PASS, TOSS, PHORMAT, and standard MAS NMR techniques for a 230-microm-diameter spherical glass bead pack saturated with water. The resulting strong magnetic susceptibility gradients result in a static linewidth of about 3.7kHz that is larger than observed for a natural biological sample, constituting a worst-case scenario for examination of susceptibility broadening effects. RESULTS: (I) TOSS produces a distorted centerband and fails in suppressing the SSBs at a spinning rate below approximately 1kHz. (II) Standard MAS requires spinning speeds above a few hundred Hz to separate the centerband from the SSBs. (III) PASS produces nearly SSB-free spectra at spinning speeds as low as 30Hz, and is only limited by T(2)-induced signal losses. (IV) With PHORMAT, a SSB-free isotropic projection is obtained at any spinning rate, even at an ultra-slow spinning rate as slow as 1Hz. (V) It is found empirically that the width of the isotropic peak is proportional to F(-x), where F is the spinning frequency, and x=2 for MAS, 0.84 for PASS, and 0.5 for PHORMAT.

Magnetic Resonance Spectroscopy↗