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Biomedical subjects

A Colchester

Publications and source records attributed to A Colchester.

7 recordsLinked to original sources
PubMed2001

Automated segmentation of multiple sclerosis lesions by model outlier detection.

This paper presents a fully automated algorithm for segmentation of multiple sclerosis (MS) lesions from multispectral magnetic resonance (MR) images. The method performs intensity-based tissue classification using a stochastic model for normal brain images and simultaneously detects MS lesions as outliers that are not well explained by the model. It corrects for MR field inhomogeneities, estimates tissue-specific intensity models from the data itself, and incorporates contextual information in the classification using a Markov random field. The results of the automated method are compared with lesion delineations by human experts, showing a high total lesion load correlation. When the degree of spatial correspondence between segmentations is taken into account, considerable disagreement is found, both between expert segmentations, and between expert and automatic measurements.

Algorithms↗
PubMed2001

Structural MRI volumetric analysis in patients with organic amnesia, 1: methods and comparative findings across diagnostic groups.

BACKGROUND: If they are to be replicable, MRI volume measurements require explicit definitions of structures and of criteria for delineating these structures on MRI. Previously published volumes in healthy subjects show considerable differences in measurements across different studies, including a fourfold variation in estimates of hippocampal volume. Previous neuroimaging reports in patients with Korsakoff syndrome have generally found widespread or non-specific change, whereas in patients with herpes encephalitis the extent of pathological involvement reported beyond the temporal lobes has varied. METHOD: In the present study, a clear set of anatomical criteria and detailed MRI segmentation procedures were applied to measure whole brain, frontal and temporal lobe, and anterolateral and medial temporal volumes, as well as thalamic areas in patients with organic amnesia (from Korsakoff's syndrome, herpes encephalitis, and focal frontal lesions) as well as healthy controls. RESULTS: Patients with Korsakoff's syndrome showed decreased thalamic measurements but no significant changes in the medial temporal lobes, whereas patients with herpes encephalitis showed severe medial temporal but not thalamic atrophy. In the patients with known frontal lobe lesions, quantitative analysis on MRI showed reduced frontal lobe volume but no significant temporal lobe or thalamic atrophy. CONCLUSION: Quantified MRI can be a useful technique with which to examine brain-cognitive relations, provided that detailed techniques are explicitly described. In particular, specific patterns of volume change can be found in vivo in patients with Korsakoff's syndrome and those with herpes encephalitis.

Adult↗
PubMed2001

Structural MRI volumetric analysis in patients with organic amnesia, 2: correlations with anterograde memory and executive tests in 40 patients.

BACKGROUND: Cognitive-MRI correlations have often been studied in disorders in which there are multiple cognitive deficits and widespread cortical atrophy, such as Alzheimer's dementia. In such circumstances, the interpretation of any single cognitive-structural correlation is equivocal. Only by measuring differing cognitive functions and a wide range of brain structures in patients with a varying distribution of lesions or atrophy can specific brain-cognitive relations be determined in neurological disorder. METHOD: In the present study, a clear set of anatomical criteria and detailed MRI segmentation procedures were applied to measure whole brain, and left and right frontal, temporal lobe, anterolateral and medial temporal volumes, as well as thalamic cross sectional areas in 40 patients with organic amnesia (from various diseases) and 10 healthy controls. RESULTS: Within the total patient group, anterograde memory measures correlated significantly with medial temporal, hippocampal, and thalamic measurements. A spatial memory measure correlated significantly with hippocampal volume, and temporal context memory with frontal volume. After a factor analysis of the cognitive measures, the association between anterograde memory and hippocampal volume was corroborated. Forgetting rates and subjective memory evaluations did not show any significant MR correlations and, of executive tests employed, only card sorting categories correlated significantly with frontal volume. CONCLUSION: Loss of volume in key brain structures (for example, hippocampus, thalamus) is detectable on quantitative MRI, and this loss of volume correlates significantly with impaired performance on measures of anterograde memory function. Correlations with hippocampal volume did not indicate a specific role in either recall or verbal memory, as opposed to recognition or visual memory.

Alcohol Amnestic Disorder↗
PubMed1996

Craniotomy guidance using a stereo-video-based tracking system.

In open intracranial neurosurgery, it is desirable to minimize exposure and to approach the target in the most accurate way possible. The VISLAN system described here employs a completely passive hand-held locator which is tracked by a video system and does not require a mechanical linkage nor cables. The system also tracks easily recognizable, constant, anatomical landmarks of the patient. By this means the initial registration of pre-operative imaging and the detection of, and correction for, patient movement can be accomplished. High-resolution MRI segmented interactively is used to define external surface and brain anatomy. Thus, a pre-operative patient representation (POPR) is planned. During the surgical procedure the patient's head is illuminated by structured light and stereo-video pictures obtained from two television cameras mounted above the head. The system is calibrated and registered with the POPR using a chamfered matching algorithm. The locator is also tracked in space by the video system, and its tip position shown in relation to the POPR on the video monitor.

Craniotomy↗
PubMed1992

Subacute idiopathic demyelinating polyradiculoneuropathy.

Seven cases of subacute idiopathic demyelinating polyradiculoneuropathy had a monophasic illness characterized by progressive weakness of all four limbs that evolved during 4 to 8 weeks. Neurophysiological investigations implied demyelination in all seven cases. In two patients, sural nerve biopsy specimens that were taken showed macrophage-associated demyelination. All patients made substantial or complete recoveries with oral prednisolone (four cases) or without treatment (three cases). None of the patients required ventilation or had autonomic complications. These cases provide a link between the acute idiopathic demyelinating form of Guillain-Barré syndrome and chronic idiopathic demyelinating polyradiculoneuropathy.

Adult↗
PubMed1986

Volume flow measurement of pulsatile flow by digitised cine angiography.

The validation, by phantom experiments, of a method of measuring volumetric, pulsatile blood flow in vessels of about 4 mm calibre is described. 'Instantaneous' as well as integrated flow is obtained from cine angiograms by digitisation of the images and densitometric analysis in an advanced computer vision analysis system. From 48 frames per second cine, pulsatile flow at any moment between 0 and about 400 ml/min was calculated within about 10 per cent of the electromagnetic flow meter reading. Further improvement is expected. It is proposed to advance to 3D and have the methodology available for clinical use in due course.

Angiography, Digital Subtraction↗