Biomedical subjects

P S Morgan

Publications and source records attributed to P S Morgan.

11 recordsLinked to original sources

PubMed2003

Pyramidal tract mapping by diffusion tensor magnetic resonance imaging in multiple sclerosis: improving correlations with disability.

BACKGROUND: Current magnetic resonance imaging (MRI) outcome measures such as T2 lesion load correlate poorly with disability in multiple sclerosis. Diffusion tensor imaging (DTI) of the brain can provide unique information regarding the orientation and integrity of white matter tracts in vivo. OBJECTIVE: To use this information to map the pyramidal tracts of patients with multiple sclerosis, investigate the relation between burden of disease in the tracts and disability, and compare this with more global magnetic resonance estimates of disease burden. METHODS: 25 patients with relapsing-remitting multiple sclerosis and 17 healthy volunteers were studied with DTI. An algorithm was used that automatically produced anatomically plausible maps of white matter tracts. The integrity of the pyramidal tracts was assessed using relative anisotropy and a novel measure (L(t)) derived from the compounded relative anisotropy along the tracts. The methods were compared with both traditional and more recent techniques for measuring disease burden in multiple sclerosis (T2 lesion load and "whole brain" diffusion histograms). RESULTS: Relative anisotropy and L(t) were significantly lower in patients than controls (p < 0.05). Pyramidal tract L(t) in the patients correlated significantly with both expanded disability status scale (r = -0.48, p < 0.05), and to a greater degree, the pyramidal Kurtzke functional system score (KFS-p) (r = -0.75, p < 0.0001). T2 lesion load and diffusion histogram parameters did not correlate with disability. CONCLUSIONS: Tract mapping using DTI is feasible and may increase the specificity of MRI in multiple sclerosis by matching appropriate tracts with specific clinical scoring systems. These techniques may be applicable to a wide range of neurological conditions.

Adult↗

PubMed2003

Differences in the diagnostic accuracy of acute stroke clinical subtypes defined by multimodal magnetic resonance imaging.

BACKGROUND: Despite its importance for acute stroke management, little is known about the underlying pathophysiology when patients with acute stroke are classified using clinical methods. OBJECTIVE: To examine the relation between the magnetic resonance defined stroke subtype and clinical stroke classifications using diffusion weighted imaging (DWI), perfusion weighted imaging (PWI), and angiographic magnetic resonance techniques. METHODS: Consecutive patients with clinical syndromes consistent with acute anterior circulation stroke were assessed clinically within six hours of onset and scanned as soon as possible using multimodal magnetic resonance imaging (MRI). Patients were classified clinically into total or partial anterior circulation syndromes using the Oxford classification, or according the severity of the National Institutes of Health stroke scale (NIHSS) (severe > 15; mild/moderate 15). There were 42 with partial anterior circulation syndromes (PACS) and 42 with total anterior circulation syndromes (TACS). Patients with TACS or severe stroke were more likely to have actually suffered a stroke (Fischer's exact test, p = 0.01), to have a correctly classified stroke (chi(2) 28.2, p < 0.01), to have persisting occlusion (chi(2) 30.6, p < 0.01), and to have a large DWI-PWI mismatch (chi(2) 17.1, p < 0.01). CONCLUSIONS: There is more inaccuracy in patients presenting with acute PACS or clinically mild to moderate anterior circulation stroke than in those with TACS or severe acute stroke syndromes. The latter appear more likely to be the targets for acute stroke interventions, as they include a significantly higher proportion of patients with persisting occlusion and diffusion/perfusion mismatch.

Acute Disease↗

PubMed2002

Quantitative diffusion characteristics of the human brain depend on MRI sequence parameters.

Quantitative diffusion-weighted MRI has been applied to the study of neurological diseases, including multiple sclerosis, where the molecular self-diffusion coefficient D has been measured in both lesions and normal-appearing white matter. Histograms of D have been used as a novel measure of the "lesion load", with potential applications that include the monitoring of efficacy in new treatment trials. However different ways of measuring D may affect its value, making comparison between different centres and research groups impossible. We aimed to assess the effect, if any, of using two different MRI sequences on the value of D. We studied 13 healthy volunteers, using two different quantitative diffusion sequences (including different b(max) values and gradient applications). Maps of D were analysed using both regions of interest (ROI) in white matter and "whole brain" histograms, and compared between the two sequences. In addition, we studied three standardised test liquids (with known values of D) using both sequences. Histograms from the two sequences had different distributions, with a greater spread and higher peak position from the sequence with lower b(max). This greater spread of D was also evident in the white matter and test liquid ROI. "Limits of agreement" analysis demonstrated that the differences could be clinically relevant, despite significant correlations between the sequences obtained using simple rank methods. We conclude that different quantitative diffusion sequences are unlikely to produce directly comparable values of D, particularly if different b(max) values are used. In addition, the use of inappropriate statistical tests may give false impressions of close agreement. Standardisation of methods for the measurement of D are required if these techniques are to become useful tools, for example in monitoring changes in the disease burden of multiple sclerosis.

Adult↗

PubMed2002

White matter mapping using diffusion tensor MRI.

Diffusion tensor MRI is used to define trajectories that reflect the long-range order of in vivo white matter (WM) fiber tracts. Fiber tracking is particularly prone to cumulative error from noise and partial volume along the length of the trajectory paths, but the overall shape of each path is anatomically meaningful. By considering only the long-range similarity of path shapes, a method of constructing 3D maps of specific WM structures has been developed. A trajectory is first computed from an operator-selected seed voxel, located within the anatomical structure of interest (SOI). Voxels from the same structure are then automatically identified based on the similarity of trajectory path shapes, assessed using Pearson's correlation coefficient. The corpus callosum and pyramidal tracts in 14 patients with multiple sclerosis, and in 10 healthy controls were mapped by this method, and the apparent diffusion coefficient (ADC) was measured. The ADC was significantly higher in patients than in controls, and higher in the corpus callosum than in the pyramidal tracts for both groups. Using this method the different functional structures in the WM may be identified and mapped. Within these maps, MRI parameters can be measured for subsequent comparison with relevant clinical data.

Algorithms↗

PubMed2002

Improved white matter fiber tracking using stochastic labeling.

Diffusion tensor imaging (DTI) promises a robust means of visualizing in vivo white matter fibers in individual subjects, and of inferring direct connectivity between distant points in the brain. By following the primary eigenvector of the diffusion tensor, trajectories may be defined that trace the path of the underlying fiber tract. However, fiber tracking is prone to cumulative error from acquisition noise and partial volume, which limits the repeatability of such techniques. An image-processing method based on stochastic labeling, by which the noisy primary eigenvectors may be reconfigured according to anatomically reasonable assumptions, is described. The method's potential to improve fiber tracking is first demonstrated on numerical test data. It is then applied to real data acquired from healthy volunteers. Trajectories defined within the corpus callosum and the pyramidal tracts are rendered using 3D graphic imaging software, and the results are compared before and after processing. Fiber tracking was shown to produce anatomically plausible results, and typical errors were largely resolved by the method. Further, the sensitivity of trajectories to their start point was greatly reduced after processing. The use of stochastic labeling may therefore improve the reliability of experiments using white matter fiber tracking.

Corpus Callosum↗

PubMed2001

Extracting parametric images from dynamic contrast-enhanced MRI studies of the brain using factor analysis.

Factor analysis of dynamic studies (FADS) is a technique that allows structures with different temporal characteristics to be extracted from dynamic contrast enhanced studies without making any a priori assumptions about physiology. These dynamic structures may correspond to different tissue types or different organs or they may simply be a useful way of characterising the data. This paper describes a method of automatically extracting factor images and curves from contrast enhanced MRI studies of the brain. This method has been applied to 107 studies carried out on patients with acute stroke. The results show that FADS is able to extract factor curves correlated to arterial and venous signal intensity curves and that the corresponding factor images allow a distinction to be made between areas of the brain with normal and abnormal perfusion. The method is robust and can be applied routinely to dynamic studies of the brain. The constraints described are sufficiently general to be applicable to other dynamic MRI contrast enhanced studies where an increase in contrast concentration produces an increase in signal intensity.

Cerebrovascular Circulation↗

PubMed2001

Perfusion MRI of infarcted and noninfarcted brain tissue in stroke: a comparison of conventional hemodynamic imaging and factor analysis of dynamic studies.

RATIONALE AND OBJECTIVES: To investigate the hemodynamics of infarcted and noninfarcted regions of the brain in patients with stroke secondary to a complete middle cerebral artery occlusion. Also, to compare factor analysis, a novel method of analyzing perfusion-weighted images, with more conventional techniques. METHODS: Twenty-two patients with complete unilateral occlusion of the middle cerebral artery were examined by T1-weighted, contrast-enhanced, perfusion-weighted imaging, diffusion-weighted imaging, and magnetic resonance angiography. Quantitative cerebral blood volume (CBV), cerebral blood flow (CBF), and time-to-peak-intensity (TTP) images were generated. Factor analysis of dynamic studies (FADS) was used to generate "early" and "late" images. The hemodynamic parameters for the infarcted and noninfarcted regions of the occluded territory were compared with those for the brain territory on the nonoccluded side. RESULTS: Three regions were shown: (1) Normal tissue on the unaffected side; (2) an infarcted region, which was characterized by reduced CBV, CBF, and early FADS values with increased TTP values; and (3) a noninfarcted region with reduced early FADS and increased late FADS and TTP values compared with the normal region. Cerebral blood volume and CBF values were not reduced significantly in the noninfarcted region. CONCLUSIONS: The differences in parameters such as TTP, CBV, and CBF are significant, and it is necessary to use more than one parameter when interpreting magnetic resonance imaging perfusion data. Factor analysis of dynamic studies provides additional information to conventional methods of analyzing perfusion data.

Brain↗

PubMed2001

Quantitative diffusion weighted magnetic resonance imaging, cerebral atrophy, and disability in multiple sclerosis.

OBJECTIVES: To investigate the relations between quantitative diffusion coefficient MRI histograms, clinical variables, and cerebral atrophy. METHODS: Twenty two patients with clinically definite multiple sclerosis and 11 healthy volunteers were studied. Histograms of apparent diffusion coefficient (ADC) from a volume of interest that included multiple slices encompassing the lateral ventricles were processed from diffusion weighted MRI. In addition, total lesion load was measured on T2 weighted dual echo images, and cerebral volume from 3D magnetisation prepared rapid acquisition gradient echo scans. All patients underwent neurological assessment, including disability on the expanded disability status scale (EDSS). RESULTS: Histograms from the patient group showed a reduced peak height and a "right shift" compared with healthy controls. Peak height of the diffusion histogram correlated with both EDSS (r=-0.54, p=0.0101) and disease duration (r=-0.52, p=0.0140), but not with age. Brain volume correlated with peak height of the ADC histogram (r=0.55, p=0.0129), but not with disability. Total lesion load also correlated moderately with EDSS (r=0.46, p=0.03). CONCLUSIONS: This study shows for the first time that quantitative MRI measures of diffusion correlate with clinical variables (disability, disease duration) and cerebral atrophy in multiple sclerosis. Cerebral atrophy and fixed neurological deficit may be attributed to axonal loss, which would be expected to have a significant effect on ADC. Extension of this method to more patients and longitudinal studies will further elucidate its sensitivity, reproducibility, and potential role in clinical practice and treatment trials.

Adult↗

PubMed1999

Limitations of clinical diagnosis in acute stroke.

Trials in acute stroke have recruited on the basis of clinical diagnosis. Using MRI we have shown that clinical diagnosis is more limited than previously appreciated, thus trials may have been underpowered or confounded.

Clinical Trials as Topic↗

PubMed1996

Collection and local use of accident and emergency hospital data in England.

OBJECTIVE: To obtain information on the collection and local use of accident and emergency data. METHODS: A postal questionnaire was sent to 248 English accident and emergency (A&E) departments. Responses were obtained from 217 (88%). RESULTS: Only 87 (40%) of departments were fully computerised, with 109 (50%) using manual systems, and 21 (10%) a mixture of both. Significantly more computerised departments reported that they undertook studies (epidemiological, accident prevention, and resource management) than non-computerised departments. Only limited information on the types of injury studied was provided. The most common topics were childhood accidents, road traffic accidents, and poisonings. Staff in 45 departments (21%) reported membership of safety organisations. Around 90% of departments reported that they notified general practitioners and health visitors of their patients' attendance, usually within 3 d of the event. CONCLUSIONS: Computerisation appears to help the collection of A&E data for public health research. There is scope to increase the involvement of public health and other workers in epidemiological studies using A&E data. A&E departments should themselves become more involved with local safety organisations.

Accident Prevention↗

PubMed1995

General practitioners' attitudes to child injury prevention in the UK: a national postal questionnaire.

OBJECTIVE: To survey the level of interest and involvement in child injury prevention among general practitioners and their practice teams, and to identify factors associated with current interest. DESIGN: Postal survey of a random sample of United Kingdom (UK) medical practitioners. SETTING: Medical practices throughout the UK. SUBJECTS: 957 general practitioners (50% of the total sample) who responded to the survey questionnaire. OUTCOMES: Answer to questions about role in injury prevention. RESULTS: Despite a response rate of only 50%, this study is the largest to examine the role of general practitioners in child injury prevention. Seven hundred and twenty five (77%) of the respondents considered injury prevention to be part of the general practitioner's role, but only 260 (28%) felt that they did enough in this area. Time was cited as the most significant limiting factor. Women doctors, rural practitioners, members of the Royal College of General Practitioners, and doctors with previous personal experience of serious accidents all had more positive attitudes to injury prevention as a routine part of their activities (p < 0.05). Practices providing first aid training for staff were also associated with an interest in injury prevention. The most appropriate times for offering prevention advice were thought to be during child health surveillance clinics and during treatment of an accident. CONCLUSIONS: Awareness about injury prevention opportunities might be improved by emphasising the roles of individual team members and by better addressing the training needs of the whole team.

Adult↗