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D M Doddrell

Publications and source records attributed to D M Doddrell.

At least 37 records · Page 2Linked to original sources
PubMed1995

A design methodology for short, whole-body, shielded gradient coils for MRI.

A series of designs is presented for restricted length, whole-body, shielded gradient coils. By using the real space optimization technique, simulated annealing (SA), it is possible to produce viable gradient sets with a length-to-diameter ratio (LDR) of just 1.0. Radially remote return paths for the transverse coils aid in producing such short coils. While the linear regions of such coils cannot be as large as longer coils, they produce homogeneous linear regions suitable for use in whole-body imaging. The coil sets are well shielded even at such small LDRs.

Magnetic Resonance Imaging↗
PubMed1995

MRI demonstration of impairment of the blood-CSF barrier by glucose administration to the thiamin-deficient rat brain.

Contrast-enhanced T1-weighted spin-echo magnetic resonance imaging (MRI) has demonstrated that Gd-diethylenetriaminepentaacetate (Gd-DTPA), which normally does not cross the blood-brain or blood-CSF barriers, does so approximately 40 min after administration of glucose to a vitamin B1 deficient rat. The period of the onset of this blood-CSF or blood-brain barrier dysfunction coincides with our previous observations of accumulation of glutamate or glutamate derivatives following an equivalent glucose load under identical conditions of thiamin deficiency, consistent with a relationship between these two observations. The dysfunction was reversed when a thiamin deficient animal was made thiamin replete.

Animals↗
PubMed1995

A report of accidental ethylene glycol ingestion in 2 siblings.

We describe a case of 2 siblings aged 2 1/2 and 3 1/2 yrs accidentally poisoned by ethylene glycol ingestion. We found estimating the level of ethylene glycol in plasma by calculation of osmolar gap too insensitive to be of value and advocate the availability of a specific method. In our study only one of the 2 children had a toxic level of ethylene glycol but assay by conventional assay and by proton magnetic resonance spectroscopy (1HMRS) of toxic metabolites viz glycolate, glyoxylate and oxalate showed both to be excreting grossly elevated levels. This indicates the desirability of assaying the toxic metabolites of the glycol as well as the parent compound in assessing ingestions.

Accidents, Home↗
PubMed1994

Localized two-dimensional shift correlated spectroscopy in humans at 2 Tesla.

A method for the acquisition of localized 2D shift-correlated spectra, based on the combination of the stimulated-echo volume-selection and gradient-enhanced COSY experiments, is described. The sequence can be modified to perform a number of localized experiments including HOHAHA and DQF-COSY. The method is demonstrated in vivo by presentation of localized COSY and HOHAHA spectra of human tibia marrow, and a localized COSY spectrum of human brain acquired at a field strength of 2 Tesla. Cross peaks corresponding to correlations between coupled groups along the acyl chains of triglycerides are observed in the spectra of marrow. The major cerebral metabolites are represented in the in vivo COSY brain spectrum, including N-acetylaspartate, glutamate/glutamine, total creatine, aspartate, and myo-inositol. Difficulties in the implementation of localized shift-correlation spectroscopy, including water suppression and T2 relaxation, are discussed.

Bone Marrow↗
PubMed1994

High resolution high field rodent cardiac imaging with flow enhancement suppression.

A method that incorporates cardiorespiratory-gated 2DFT spin-echo imaging with blood flow enhancement suppression is described which enables high resolution microimaging of the rodent heart. This methodology was applied to obtain in vivo cardiac mouse and rat images with in-plane resolutions of 100-200 microns using high field vertical bore magnet systems. Suppression of intraventricular blood flow enhancement was achieved using a combined spin-echo/gradient-refocussed sequence to dephase magnetization from flowing spins prior to imaging.

Animals↗
PubMed1994

Practical aspects of shielded gradient-coil design for localised in vivo NMR spectroscopy and small-scale imaging.

For a number of NMR applications the availability of screened gradients is crucial to minimize the effect of eddy currents on the NMR signal. In this paper we review two types of shielded gradient design: the target field and minimum inductance methods. The two designs are compared and construction details are presented. A novel coil design constructed with a double-sided primary and a single layered screen is outlined. Experimental results for both target field and minimum inductance coils are presented and compared.

Magnetic Resonance Spectroscopy↗
PubMed1993

Respiratory triggered imaging with an optical displacement sensor.

Motion of abdominal organs with respiration is a major problem in NMR spectroscopy and imaging thereof. Triggering each phase-encoding step with respiration or gating a number of phase-encoding steps is one approach to the problem. The design of a sensor for small animal experiments has not been as simple. An optical device, implemented with polymer optical fibres is described, along with associated hardware and electronics which can act as a trigger for small animal NMR experiments. A brief description of a similar device for human application is also given. 2DFT spin-echo and B0 susceptibility images, both triggered and untriggered, are presented to validate the technique.

Abdomen↗
PubMed1992

Measurement of the T2 relaxation time of ethanol and cerebral metabolites, in vivo.

The SPACE volume selection technique was combined with a spin-echo sequence to measure the transverse relaxation time of the resonances of ethanol and cerebral metabolites in the dog brain, in vivo. The method was extended to measure brain metabolite T2 values in the rat using 1H NMR microspectroscopy. The T2 decays for the resonances of the metabolites N-acetylaspartate, creatine/phosphocreatine, and choline/phosphorylcholine were found to be biexponential with long T2 components of 490, 260, and 350 ms for the dog and 490, 220, and 355 ms for the rat brain, respectively. The existence of a second T2 component may originate from J-coupled nonresolved metabolite resonances. The relaxation decay for the ethanol triplet could be fitted to a single exponential giving a T2 relaxation time of 335 ms. However, given the large errors in the measurement of ethanol peak intensities at short echo times because of overlapping lipid signal and the effects of J-modulation, a biexponential decay with a long T2 component of 335 ms cannot be ruled out. Ambiguities regarding the reported partial detection of the 1H NMR signal of ethanol in the brain are discussed.

Animals↗
PubMed1992

Application of self-refocusing band selective RF pulses for spectroscopic localization.

A new self-refocusing slice selection 90 degrees pulse is presented and its incorporation in the SPACE localization sequence described. Experimental comparisons are made with the self-refocusing pulse reported by Geen (H. Geen, S. Wimperis and R. Freeman, J. Magn. Reson. 85, 620 (1990)). The main source of localization error in the SPACE sequence is traced to the hard pi/2 pulse and the development of a shaped-pulse version of the sequence is described. This required the calculation of a slice-selective pulse capable of rotating coherent transverse magnetization to the z-axis. The RF power requirements for these experiments are also discussed.

Magnetic Resonance Spectroscopy↗
PubMed1991

The visibility of the 1H NMR signal of ethanol in the dog brain.

In vivo, high-resolution, volume-selected 1H NMR spectroscopy was used to monitor the concentration of ethanol in the dog brain following intravenous injection of ethanol. Equilibration of ethanol in the body water should result in approximately equivalent concentrations of ethanol in the blood and brain. However, the mean equilibrium brain ethanol concentration determined using N-acetylaspartate as an internal standard was only 23 +/- 5% of the blood ethanol concentration. The disparity between blood and brain ethanol concentrations was attributed to underestimation of the ethanol concentration due to overlapping resonances with NAA and to T2 attenuation or possible nondetection of the 1H signal from ethanol bound at the surface of cell membranes and partitioned into the hydrophobic core of membrane lipids.

Animals↗
PubMed1990

High-field localized in vivo proton spectroscopy on micro volumes.

A water-suppressed volume-selected in vivo 1H spectrum of 0.2 ml of a rat brain has been obtained at 200 MHz using the SPACE localization method. Good signal-to-noise and spectral resolution were obtained by averaging 256 acquisitions. The spectrum shows little T2 weighting effect.

Animals↗
PubMed1990

Application of reverse-DEPT polarization transfer pulse sequence to study the metabolism of carbon-13-labeled substrates in perfused organs by 1H NMR spectroscopy.

Metabolism of 13C-enriched metabolites can be advantageously studied by reverse-polarization transfer methods. In this work an improved reverse-DEPT sequence has been applied for the first time on perfused organs in a 20-mm probe. The metabolic fate of 99% enriched [2-13C]acetate perfused in excised rat liver and heart has been documented.

Acetates↗
PubMed1990

In vivo volume-selective metabolite editing via correlated z-order.

Volume-selected 1H NMR spectroscopy was combined with spectral editing to selectively detect brain metabolites. The SPACE localization sequence was used to create a voxel of zeta-magnetization which could then be edited for any scalar coupled metabolite by the use of selective excitation in the ECZOTIC sequence to generate longitudinal spin order. The sequence returns an edited signal with no intrinsic loss of magnetization. The method was applied to observe approximately 10 mM ethanol and 17 mM lactate in the brain of a dog.

Animals↗
PubMed1990

Application of volume-selected, two-dimensional multiple-quantum editing in vivo to observe cerebral metabolites.

The volume selection technique SPACE has been combined with a two-dimensional multiple-quantum editing sequence to uniquely detect certain J-coupled cerebral metabolites. In vivo results demonstrating edited glutamate/glutamine and lactate from 0.4 ml of a rat's brain at 4.7 T are presented. The sequence was optimized to balance multiple-quantum generation and signal loss due to T2 relaxation. Without due regard to T2 relaxation little signal is observed.

Animals↗
PubMed1990

Signal-to-noise ratio improvements in in vivo high resolution micro-volume selected spectroscopy.

A system capable of in vivo volume selected 1H NMR spectroscopy of voxels as small as 0.2 cm3 is described. Signal-to-noise ratio improvements with probe design and a novel signal steering device are detailed. A high-resolution, image-directed proton spectrum from 0.2 cm3 of a rat's brain at 200 MHz obtained using the SUBMERGE/SPACE pulse sequence is presented. Single-scan voxel shimming was implemented to improve spectral resolution.

Animals↗