Showing papers by "Andrew Simmons published in 1995"
TL;DR: A computerized system for brain tissue classification of dual echo MR data is developed, which uses a polychotomous logistic model for discriminant analysis, combined with a Bayes allocation rule incorporating differential prior probabilities, and spatial connectivity tests, to assign each voxel in the image to one of four possible classes: gray matter, white matter, cerebrospinal fluid, or unclassified.
55 citations
TL;DR: Results suggest that verbal working memory is subserved by a neurocognitive network comprising cortical regions involved in attention, executive function and short term mnemonic processes.
Abstract: Complex mental operations rely on the coordinated activity of widely distributed brain regions constituting neurocognitive networks Using multislice echoplanar functional magnetic resonance imaging (fMRI) we have contrasted regional brain activity during a control and an experimental condition which differed with respect to the demands placed on verbal working memory Subjects were seven right-handed healthy male volunteers Analysis of group and individual data revealed activation in the anterior and posterior parasagittal cortex in all subjects, left parietal cortex (six subjects) and left dorsolateral prefontal cortex (five subjects) These results suggest that verbal working memory is subserved by a neurocognitive network comprising cortical regions involved in attention, executive function and short term mnemonic processes
44 citations
TL;DR: Choice of normal range has a critical effect on the categorization of osteoporotic patients using DEXA, and the wide variety of normal ranges indicates that there are likely to be differences in patient management throughout the country.
Abstract: The number of different normal ranges used on dual energy X-ray absorptiometry (DEXA) machines in the United Kingdom was determined by means of a postal questionnaire. Both femoral neck and posteroanterior spine L2–L4 regions were considered. It was clear from this survey that a variety of normal ranges were in use for all manufacturers of DEXA systems. The effects of four normal ranges supplied by Norland for use within the UK on the stratification of over 1000 consecutive patients into different grades of bone mineral density (BMD) and Z-score were examined. The main outcomes measure the number of patients with BMD less than 80% of mean age-matched BMD and Z-score less than – 1.5 over the femoral neck and spine for each normal range. The percentage of patients for each normal range with BMD less than 80% of mean for the femoral neck were 24.6%, 7.4%, 17.5% and 11.1% and for the spine 12.1%, 7.4%, 16.5% and 14.4%, respectively. For the femoral neck, 21.2%, 5.0%, 12.9% and 12.1% of patients had Z...
24 citations
TL;DR: Cortical activation in visual association areas known to be responsible for the perception of motion was investigated in two volunteers who viewed a projected animated cartoon periodically "run" and "frozen" during collection of echoplanar MR images.
13 citations
TL;DR: The construction of a unified UK normal range applicable to all UK DEXA systems is recommended in order to harmonize patient management and care.
Abstract: Differences between dual-energy X-ray absorptiometry (DEXA) normal ranges can lead to patients being characterized as osteoporotic using one range and normal using another. To investigate the diversity of normal ranges used within the UK, a survey of all DEXA sites was carried out with a 60.6% response rate. The effect of the different ranges was evaluated by translating each range to an equivalent range for a Norland XR-26 system and applying the ranges to stratify a representative sample of over 1000 patients into grades of bone density based on percentages of age-matched mean BMD, Z-scores and T-scores. The effect of femoral neck and P/A spine L2-L4 regions was considered both separately and jointly. Large differences between the normal ranges were apparent, which resulted in the classification of the number of patients with a Z-score of less than -2.0 varying by a factor of more than 20 for the femoral neck and more than 3 for the spine. The number of patients defined as osteoporotic by a T-score less than -2.5 varied from none to over one-third of patients for the hip and by a factor of almost 3 for the spine. The exclusion criteria used for construction of the normal ranges varied markedly with none constructed using population-based sampling. Smoothing of normal ranges was carried out by DEXA manufacturers, while local normal ranges made use of raw unprocessed data. There is reason to question the validity of such processing. We recommend the construction of a unified UK normal range applicable to all UK DEXA systems in order to harmonize patient management and care.
12 citations
TL;DR: The merits of assessing bone density in patients relative to that in young adults rather than relative to those in controls matched for age are emphasised, on the basis of the recommendations of an expert panel of the World Health Organisation.
Abstract: EDITOR,--J E Compston and colleagues emphasise the merits of assessing bone density in patients relative to that in young adults (the T score) rather than relative to that in controls matched for age (the Z score), on the basis of the recommendations of an expert panel of the World Health Organisation.1 Consensus on this issue, however, is still lacking,2 and the T score has not been widely used clinically in Britain, where comparisons with controls matched for age still dominate.
Among the limitations of bone densitometry …
2 citations
Journal Article•
1 citations