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Biomedical subjects

A A Maudsley

Publications and source records attributed to A A Maudsley.

At least 19 recordsLinked to original sources
PubMed1995

Spectral lineshape determination by self-deconvolution.

A data-processing method is described for the determination of spectral lineshapes using deconvolution of the data with an initial estimate of the same spectrum, referred to as self-deconvolution. The method is demonstrated using computer-simulation studies and experimental data, and is shown to accurately determine amplitude and phase lineshape distortions which may be caused by field inhomogeneity and gradient eddy-current effects. The results indicate that the method is robust in the presence of noise and errors in the initial spectral estimate. Once the spectral lineshape is determined it can be incorporated into a parametric spectral-analysis procedure, thereby reducing the number of parameters to be determined and improving the accuracy of the fit. A proposed application of the method is for spatially resolved in vivo NMR studies where local susceptibility effects and gradient eddy-current effects cause significant deviation of the spectral lineshape from a Lorentzian lineshape.

Algorithms↗
PubMed1994

Biochemical alterations in multiple sclerosis lesions and normal-appearing white matter detected by in vivo 31P and 1H spectroscopic imaging.

The goals of the current study were threefold: first, to confirm previous single volume proton (1H) magnetic resonance spectroscopy results of reduced N-acetyl aspartate (NAA, a putative marker of neurons) in multiple sclerosis (MS) white matter lesions using multiple volume 1H magnetic resonance spectroscopic imaging (MRSI); second, to measure the phospholipid metabolites phosphomonoesters and phosphodiesters in such lesions using phosphorus (31P) MRSI; and third, to test the hypothesis that biochemical changes occur in the normal-appearing (on spin echo T2-weighted magnetic resonance images) white matter in patients with MS. Thirteen subjects with clinically definite MS were studied with both 1H and 31P MRSI, and 19 controls were studied with either 1H MRSI, 31P MRSI, or both. MS lesion, MS normal-appearing white matter, and region-matched control spectra from the centrum semiovale were analyzed. The major findings of this study were that in both white matter lesions and normal-appearing white matter in patients with MS, the metabolite ratio NAA/creatine and the total 31P peak integrals were significantly reduced compared with controls. In addition, in MS lesions NAA/choline and phosphodiesters/total 31P were significantly reduced compared with controls, and in MS normal-appearing white matter there was a trend for NAA/choline to be reduced compared with controls. In normal-appearing white matter in patients with MS, total creatine and phosphocreatine were significantly increased compared to controls, as detected with both 1H (total creatine peak integrals) and 31P (phosphocreatine/total 31P) MRSI techniques. These results suggest reduced neuronal density and altered phospholipid metabolites in white matter lesions in patients with MS.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

1H spectroscopic imaging of rat brain at 7 tesla.

1H magnetic resonance spectroscopic imaging has been used to obtain metabolite maps of the rat brain. The spin-echo-based technique has been evaluated with respect to water and lipid suppression and sensitivity. Metabolite maps were constructed for choline, creatine + phosphocreatine, amino acids, N-acetyl aspartate, and lactate. A spatial resolution of 3 x 3 mm (in plane) with 7-mm-thick slices was achieved routinely in 60-min (16 x 16 phase encodings) acquisitions. For higher intensity resonances, metabolite maps could be constructed in as little as 10 min. Results from phantoms and from rats under normal and focal ischemia conditions are presented.

Amino Acids↗
PubMed1992

Three-dimensional 1H spectroscopic imaging of cerebral metabolites in the rat using surface coils.

Three dimensional metabolite maps of protonated metabolites were obtained using 1H magnetic resonance spectroscopic imaging at 7 T. Surface coils were used to increase sensitivity and spatial resolution significantly over a volume coil two-dimensional acquisition. Adiabatic pulses were employed to provide homogeneous B1 excitation and frequency selective refocusing over the volume of the rat brain. These techniques were employed to obtain three-dimensional spectroscopic imaging spectra from nominal voxel volumes of 9-30 microliters from rat brain. The improved spatial resolution and sensitivity are also demonstrated with studies of focal ischemia in the rat.

Animals↗
PubMed1992

Phosphorus-31 MR spectroscopic imaging (MRSI) of normal and pathological human brains.

The goals of this study were to evaluate 31P MR spectroscopic imaging (MRSI) for clinical studies and to survey potentially significant spatial variations of 31P metabolite signals in normal and pathological human brains. In normal brains, chemical shifts and metabolite ratios corrected for saturation were similar to previous studies using single-volume localization techniques (n = 10; pH = 7.01 +/- 0.02; PCr/Pi = 2.0 +/- 0.4; PCr/ATP = 1.4 +/- 0.2; ATP/Pi = 1.6 +/- 0.2; PCr/PDE = 0.52 +/- 0.06; PCr/PME = 1.3 +/- 0.2; [Mg2+]free = 0.26 +/- 0.02 mM.) In 17 pathological case studies, ratios of 31P metabolite signals between the pathological regions and normal-appearing (usually homologous contralateral) regions were obtained. First, in subacute and chronic infarctions (n = 9) decreased Pi (65 +/- 12%), PCr (38 +/- 6%), ATP (55 +/- 6%), PDE (47 +/- 9%), and total 31P metabolite signals (50 +/- 8%) were observed. Second, regions of decreased total 31P metabolite signals were observed in normal pressure hydrocephalus (NPH, n = 2), glioblastoma (n = 2), temporal lobe epilepsy (n = 2), and transient ischemic attacks (TIAs, n = 2). Third, alkalosis was detected in the NPH periventricular tissue, glioblastoma, epilepsy ipsilateral ictal foci, and chronic infarction regions; acidosis was detected in subacute infarction regions. Fourth, in TIAs with no MRI-detected infarction, regions consistent with transient neurological deficits were detected with decreased Pi, ATP, and total 31P metabolite signals. These results demonstrate an advantage of 31P MRSI over single-volume 31P MRS techniques in that metabolite information is derived simultaneously from multiple regions of brain, including those outside the primary pathological region of interest. These preliminary findings also suggest that abnormal metabolite distributions may be detected in regions that appear normal on MR images.

Adult↗
PubMed1992

Phosphorus-31 magnetic resonance metabolite imaging in the human body.

This work examines the feasibility of three-dimensional phosphorus-31 magnetic resonance spectroscopic imaging (31P MRSI) of metabolites in the human body using nonselective excitation with a single large circular surface coil for transmitting and receiving. The potential and limitations of this approach to clinical imaging are demonstrated on four selected examples: normal liver and heart, hematoma in the calf, and lymphoma in the groin. The obtained metabolite images showed anatomical detail and allowed differentiation of body organs and pathologic tissue from adjacent tissue. Three-dimensionally localized 31P spectra were reconstructed from nominal volumes of 4 to 15 cm3. These spectra showed characteristic resonances and metabolite intensity ratios for the tissue of origin demonstrating good three-dimensional localization. We conclude that surface coil 31P MRSI of body organs to map metabolite distributions is practically feasible with this approach, but due to experimental limitations, clinical utility requires technical improvements.

Heart↗
PubMed1992

3D phase encoding 1H spectroscopic imaging of human brain.

A three-dimensional (3D) phase-encoding proton spectroscopic imaging method is presented for a whole body MRI/MRS system. Metabolite images at 2 T of choline, creatine, and N-acetyl aspartate (NAA) of normal brain were obtained with a spatial resolution of 1.5 cc. With PRESS volume preselection and outer volume suppression pulses, brain regions close to the skull could be studied without significant contamination by lipid and water signals.

Brain↗
PubMed1992

Spectroscopic imaging display and analysis.

A system for display of magnetic resonance (MR) spectroscopic imaging (SI) data is described which provides for efficient review and analysis of the multidimensional spectroscopic and spatial data format of this technique. Features include the rapid display of spectra from selected image voxels, formation of spectroscopic images, spectral and image data processing operations, methods for correlating spectroscopic image data with high resolution 1H MR images, and hardcopy facilities. Examples are shown for 31P and 1H spectroscopic imaging studies obtained in human and rat brain.

Humans↗
PubMed1992

Elevated lactate and alkalosis in chronic human brain infarction observed by 1H and 31P MR spectroscopic imaging.

The goal of this study was to investigate lactate and pH distributions in subacutely and chronically infarcted human brains. Magnetic resonance spectroscopic imaging (MRSI) was used to map spatial distributions of 1H and 31P metabolites in 11 nonhemorrhagic subacute to chronic cerebral infarction patients and 11 controls. All six infarcts containing lactate were alkalotic (pHi = 7.20 +/- 0.04 vs. 7.05 +/- 0.01 contralateral, p less than 0.01). This finding of elevated lactate and alkalosis in chronic infarctions does not support the presence of chronic ischemia; however, it is consistent with the presence of phagocytic cells, gliosis, altered buffering mechanisms, and/or luxury perfusion. Total 1H and 31P metabolites were markedly reduced (about 50% on average) in subacute and chronic brain infarctions (p less than 0.01), and N-acetyl aspartate (NAA) was reduced more (approximately 75%) than other metabolites (p less than 0.01). Because NAA is localized in neurons, selective NAA reduction is consistent with pathological findings of a greater loss of neurons than glial cells in chronic infarctions.

Adult↗
PubMed1992

Human brain infarction: proton MR spectroscopy.

Two-dimensional proton magnetic resonance (MR) spectroscopic imaging studies were performed of the distributions of the major hydrogen-1 metabolites of choline, creatine, N-acetyl aspartate (NAA) and lactate in normal (n = 6) and subacutely to chronically infarcted (n = 10) human brain. The two dimensions of phase encoding were applied over a 20-mm-thick section of brain tissue that had been selected with a double spin-echo localization method. Normal brain showed bilaterally symmetric metabolite distributions and no detectable lactate. Nine of 10 studies of brain infarction showed substantial decreases in NAA, creatine, and choline in the infarcted area compared with control areas; averaged for all studies, the decreases were 77% +/- 8, 63% +/- 11, and 54% +/- 12, respectively (mean +/- standard error). The decreased metabolite concentrations are probably due primarily to diminished cell density in the infarct. The decrease in NAA was larger than the decreases in choline and creatine. Findings in all of the studies showed lactate in the infarcted tissue and/or ventricles. The continued presence of lactate in the infarct indicates increased anaerobic glycolysis due to ischemia or other factors.

Adult↗
PubMed1992

Lateralization of human focal epilepsy by 31P magnetic resonance spectroscopic imaging.

We attempted to lateralize the epileptogenic focus (seven temporal lobe hippocampal foci, one frontal lobe focus) in medically refractory unilateral complex partial seizures, using noninvasive 31P magnetic resonance spectroscopic imaging (MRSI) blindly and interictally to compare hippocampal or frontal regions. The seizure foci were more alkaline (intracellular pH = 7.17 +/- 0.03) compared with the contralateral region (7.06 +/- 0.02, p < 0.01) in all eight cases; the inorganic phosphate was relatively increased (240 +/- 50% of contralateral, seven of eight cases, p < 0.01); and phosphomonoesters were relatively reduced (68 +/- 9% of contralateral, seven of eight cases, p < 0.01). Other phosphorus metabolites were symmetric (+/- 10%). 31P MRSI correctly lateralized the seizure focus in all eight cases. By comparison, imaging correctly lateralized four cases and SPECT, two cases. In conclusion, 31P MRSI is a useful tool for the noninvasive clinical assessment of focal epilepsy and can accurately lateralize the epileptogenic focus.

Adult↗
PubMed1990

Spin echo 31P spectroscopic imaging in the human brain.

Spectroscopic imaging of phosphorus metabolites in the human brain has been carried out with two data acquisition methods: by observation of the free induction decay (FID) signal and by a short spin echo sequence. The resultant spectral images and spatially resolved spectra are compared. Spin echo observation is found to provide spectra of superior quality, and by suitably selecting the sequence timing, no significant increase in T2 losses, as compared with the FID method, is encountered. 31P images with approximately 3.5 cm spatial resolution are obtained within times of 37 min at 2.0 T field strength.

Brain↗
PubMed1986

Fourier imaging using rf phase encoding.

Fourier imaging methods encode information in the amplitudes and phases of a NMR signal over multiple acquisitions. Several of the techniques that can be used for encoding this information are reviewed and a general theory of phase encoding presented. The discussion is then extended to include encoding as part of the rf excitation sequence. Radiofrequency phase encoding can be obtained using tailored excitation techniques or special-purpose rf field gradient coils, and may be applied prior to excitation or incorporated within the excitation or refocusing pulses. This phase-encoding method may be used for spatial and spectral discrimination, as well as being combined with other methods of image formation. An example of the proposed imaging method is described which enables Fourier imaging of short T2 signals.

Fourier Analysis↗
PubMed1986

Sodium nuclear magnetic resonance imaging of myocardial tissue of dogs after coronary artery occlusion and reperfusion.

Nuclear magnetic resonance (NMR) imaging techniques have been applied to the observation of tissue sodium-23 in normal and ischemic canine myocardium. To produce a region of ischemia and infarction in the myocardium, in six dogs a coronary artery was subjected to 1 hour of surgical occlusion followed by 1 hour of reperfusion. The dogs were then killed and sodium-23 NMR images of the excised hearts were obtained using a high field NMR imaging system. These images were compared with tissue sodium contents measured by flame photometry. The regions of ischemic damage were clearly visible as areas of increased sodium NMR signal on the three-dimensional images. A good correspondence was found between the relative intensity of the sodium signals and the sodium contents of normal myocardium and myocardium subjected to coronary artery occlusion and reperfusion. The data suggest the feasibility of NMR sodium imaging to detect the location and extent of myocardial damage in patients with coronary artery disease.

Animals↗
PubMed1985

Field inhomogeneity correction and data processing for spectroscopic imaging.

To obtain separate NMR images of spatially resolved high-resolution chemical-shift information the effects of magnetic field inhomogeneity must be accounted for. A suitable correction method is described which relies on first generating a plot of the magnetic field distribution. Using these data the spectroscopic imaging data can be processed to display the spatial distributions of separate resonances without distortion from field inhomogeneity. The field plot is obtained by using the same data acquisition sequence while imaging a phantom object or in particular cases the plot may be derived from the spectroscopic imaging data set itself. The correction procedure is illustrated using proton in vivo imaging of a cat. Some additional data processing techniques are presented which offer alternative methods of displaying spectroscopic imaging data.

Animals↗
PubMed1984

Contrast manipulation in NMR imaging.

The past few years have shown rapid growth of NMR imaging in both image quality and diagnostic usefulness. It has become apparent, as the images have been published, that both inter- and intra-group imaging of the same underlying pathology produces images which can have vastly differing appearance. This effect is mainly due to imaging techniques which use different pulse sequence types and timings thus varying the relative contribution of the protpn density, T1, and T2 properties of the tissues. In this paper we investigate the contrast manipulation effects and methods for SNR optimization for the saturation recovery, inversion recovery, spin echo, and inversion recovery spin echo pulse sequences when applied to three clinically relevant imaging tasks.

Cerebral Infarction↗
PubMed1984

Magnetic resonance and ionizing radiation: a comparative evaluation in vitro of oncogenic and genotoxic potential.

This paper describes experiments designed to investigate possible biological hazards associated with magnetic resonance (MR) imaging. Mouse C3H 10T1/2 cells were exposed to a powerful magnetic field (up to 2.7 T) for periods up to 17 hours together with pulsed field gradients and radio-frequency excitation and compared with untreated controls and cells exposed to gamma rays (0.3 to 0.4 Gy). Several biological endpoints were studied. In the case of oncogenic transformation, no significant difference could be demonstrated between controls and either the gamma-irradiated or MR-exposed cells. When mitotic cells were examined for chromosomal alterations, the frequencies of both chromosomal aberrations per cell and sister chromatid exchanges per chromosome were significantly enhanced over control levels after ionizing radiation exposures but were similar to control (or less) after MR exposures. These studies confirm the known deleterious effects of ionizing radiation (even at low doses) for chromosomal damage, if not for oncogenic transformation, yet show that MR exposures even of long duration (up to 17 hours) at high field strengths (up to 2.7 T) do not result in effects greater than 0.3 Gy of gamma rays. Negative results do not conclusively rule out a health risk; however, the data clearly mitigate against an association between exposure to MR imaging modalities and both carcinogenic and genotoxic effects.

Animals↗