Functional MR Imaging of visuo-spatial network in Autism Spectrum Disorder

Individuals with Autism Spectrum Disorder (ASD) are generally thought to have impaired attentional and executive function upon which all their cognitive and behaviour functions are based. Mental Rotation is a recognized visuo-spatial task, involving spatial working memory, known to involve activation in the fronto-parietal networks. To elucidate the functioning of fronto-parietal networks in ASD, the aim of this study was to use fMRI techniques with a mental rotation task, to characterize the underlying functional neural system. Sixteen male participants (seven highfunctioning autism or Asperger's syndrome; nine ageand performance IQ-matched controls) underwent fMRI. Participants were presented with 18 baseline and 18 rotation trials, with stimuli rotated 3- dimensionaUy (45°-180°). Data were acquired on a 3- Tesla scanner. The most widely accepted area reported to be involved in processing of visuo-spatial information. Posterior Parietal Cortex, was found to be activated in both groups, however, the ASD group showed decreased activation in cortical and subcortical frontal structures that are highly interconnected, including lateral and medial Brodmann area 6, frontal eye fields, caudate, dorsolateral prefrontal cortex and anterior cingulate. The suggested connectivity between these regions indicates that one or more circuits are impaired as a result of the disorder. In future it is hoped that we are able to identify the possible point of origin of this dysfunction, or indeed if the entire network is dysfunctional.

Calculating current densities and fields produced by shielded magnetic resonance imaging probes

A method is presented for computing the fields produced by radio frequency probes of the type used in magnetic resonance imaging. The effects of surrounding the probe with a shielding coil, intended to eliminate stray fields produced outside the probe, are included. An essential feature of these devices is the fact that the conducting rungs of the probe are of finite width relative to the coil radius, and it is therefore necessary to find the distribution of current within the conductors as part of the solution process. This is done here using a numerical method based on the inverse finite Hilbert transform, applied iteratively to the entire structure including its shielding coils. It is observed that the fields are influenced substantially by the width of the conducting rungs of the probe, since induced eddy currents within the rungs become more pronounced as their width is increased. The shield is also shown to have a significant effect on both the primary current density and the resultant fields. Quality factors are computed for these probes and compared with values measured experimentally.

Nmr imaging of the diffusion of water into poly(tetrahydrofurfuryl methacrylate-co-hydroxyethyl methacrylate)

0Nuclear magnetic resonance (n.m.r.) imaging was used to study the ingress of water into poly(tetrahydrofurfuryl methacrylate-co-hydroxyethyl methacrylate). The study offers strong evidence that the diffusion is Fickian in nature. The diffusion coefficient, D, obtained by fitting the underlying diffusion profile, attainable from the images, according to the equation for Fickian diffusion, is 1.5 x 10(-11) m(2) s(-1), which is in good correlation with the value of 2.1 x 10(-11) m(2) s(-1), obtained from mass uptake measurements. Additionally, from the T-2-weighted images, Superimposed features observed in addition to the underlying Fickian diffusion profiles were shown to have a longer spin-spin relaxation time, T-2. This Suggests the presence of two types of water within the polymer matrix; a less mobile phase of absorbed water that is interacting strongly with the polymer matrix and a more mobile phase of absorbed water residing within the cracks observed in the environmental scanning electron micrograph. (C) 1997 Elsevier Science Ltd.

NMR imaging of water sorption into poly(hydroxyethyl methacrylate-co-tetrahydrofurfuryl methacrylate)

The diffusion of water into a series of hydroxyethyl methacrylate, HEMA, copolymers with tetrahydrofurfuryl methacrylate, THFMA, has been studied over a range of copolymer compositions using NMR imaging analyses. For polyHEMA the diffusion was found to be consistent with a Fickian model. The mass diffusion coefficient of water in polyHEMA at 37 degreesC was determined from the profiles of the diffusion front to be 1.5 x 10(-11) m(2) s(-1), which is less than the value based upon mass uptake, 2.0 x 10(-11) m(2) s(-1). The profiles of the water diffusion front obtained from the NMR images showed that stress was induced at the interface between the rubbery and glassy regions which led to formation of small cracks in this region of the glassy matrix of polyHEMA and its copolymers with mole fractions of HEMA greater than 0.6. Water was shown to be able to enter these cracks forming water pools. For copolymers of HEMA and THFMA with mole fractions of HEMA less than 0.6 the absence of cracks was attributed to the ability of the THFMA sequences to undergo stress relaxation by creep.

SAR imaging of buried objects from MoM modelled scattered field

Synthetic aperture radar (SAR) images of resonant buried objects are modelled in the presence of ground surface clutter. The method of moments (MoM) is used to model scattered fields from a resonant buried conductor and clutter is modelled as a bivariant Gaussian distribution. A diffraction stack SAR imaging technique is applied to the ultra-wideband waveforms to give a bipolar signal image. A number of examples have been computed to illustrate the combined effects of SAR processing with resonant targets and clutter. SAR images of different targets show differences which may facilitate target identification. To maximise the peak signal-to-clutter ratio, an image correlation technique is applied and the results are shown.

Active site heterogeneity in dimethyl sulfoxide reductase from Rhodobacter capsulatus revealed by raman spectroscopy

Raman spectroscopy has been used to investigate the structure of the molybdenum cofactor in DMSO reductase from Rhodobacter capsulatus. Three oxidized forms of the enzyme, designated 'redox cycled', 'as prepared', and DMSORmodD, have been studied using 752 nm laser excitation. In addition, two reduced forms of DMSO reductase, prepared either anaerobically using DMS or using dithionite, have been characterized. The 'redox cycled' form has a single band in the Mo=O stretching region at 865 cm(-1) consistent with other studies. This oxo ligand is found to be exchangeable directly with (DMSO)-O-18 or by redox cycling. Furthermore, deuteration experiments demonstrate that the oxo ligand in the oxidized enzyme has some hydroxo character, which is ascribed to a hydrogen bonding interaction with Trp 116. There is also evidence from the labeling studies for a modified dithiolene sulfur atom, which could be present as a sulfoxide. In addition to the 865 cm(-1) band, an extra band at 818 cm(-1) is observed in the Mo=O stretching region of the 'as prepared' enzyme which is not present in the 'redox cycled' enzyme. Based on the spectra of unlabeled and labeled DMS reduced enzyme, the band at 818 cm(-1) is assigned to the S=O stretch of a coordinated DMSO molecule. The DMSORmodD form, identified by its characteristic Raman spectrum, is also present in the 'as prepared' enzyme preparation but not after redox cycling. The complex mixture of forms identified in the 'as prepared' enzyme reveals a substantial degree of active site heterogeneity in DMSO reductase.

The influence of posture on perineal ultrasound imaging parameters

A prospective clinical study was carried out to evaluate the influence of posture on perineal ultrasound imaging parameters. One hundred and thirty-two consecutive women presenting with symptoms of lower urinary tract dysfunction were examined by multichannel videourodynamics and perineal ultrasound, both supine and standing. Ultrasound included color Doppler imaging when available, i.e. in a subgroup of 99 patients. The position of the bladder neck at rest was higher in the supine position (P