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Biomedical subjects

J L Hamilton

Publications and source records attributed to J L Hamilton.

15 recordsLinked to original sources
PubMed2000

Comparison of 3-D stereoscopic MR imaging with pre and post lesion recording in pallidotomy.

OBJECTIVES: A quantitative on-line analysis of electrical activity in the pallidum of Parkinsonian patients has been developed to determine the focal point of lesioning. Additional recordings are made after the lesioning, to assess residual neural activity. A 3-D volume stereoscopic image system is proposed to display the complex anatomy and to superimpose the electrophysiological data into this system. The purpose of this study is to understand the complex pathophysiology in real-time anatomic/image space and determine the location and effect of lesioning residual energy sites. MATERIAL AND METHODS: Thirty patients undergoing 41 pallidotomies are presented. Neuronal activity from the pallidum is recorded using a semi-microelectrode. Based on this activity, lesioning is performed. Post-lesion recordings are made to determine the necessity of additional lesioning. 3-D volume MR images are acquired pre and postoperatively and compared for accuracy of lesion sites. A 3-D stereoscopic image system has been developed to depict basal ganglia geometry in the last 5 patients. Electrophysiological data are superimposed on this image system to show the surgeon the virtual position of the electrode tip. RESULTS: A stereoscopic 3-D volume MR image system has been developed. This system more efficiently and accurately visualizes and records the coordinates of high neural activity in the pallidum and post lesion residual activity. Post-lesion power analysis was carried out in 30 patients. Additional lesions were indicated in 8 and different trajectories in 6. CONCLUSION: Real-time visualization of neural recording, both pre and post-lesioning during pallidotomy, facilitates the surgeon's understanding of the spatiotemporal relationships of pathophysiological properties within the globus pallidus.

Adult↗
PubMed2000

Quantitative on-line analysis of physiological data for lesion placement in pallidotomy.

A computerized method of determining the focal point of electrical activity in the pallidum of parkinsonian patients was developed using on-line quantitative physiological data analysis. Thirty patients in a series of 70 were studied in depth. Neuronal activity was recorded from the pallidum using a semi-microelectrode. The signal is inspected visually while its average power, characteristic frequency and complexity are computed. The target locus was indicated by the highest level of global activity in the vicinity of the electrode (signal power maximum), maximal signal complexity and minimal characteristic frequency. Most often, the vertical coordinate required correction. The postoperative clinical and imaging results have indicated the effectiveness of this method.

Adult↗
PubMed1999

Electrophysiological recordings in pallidotomy localized to 3D stereoscopic imaging.

A quantitative on-line analysis of electrical activity in the pallidum of Parkinsonian patients has been developed to determine the focal point of lesioning. A 3D volume image system has been developed to display basal ganglia anatomy and coregister the electrophysiological data within the globus pallidus. Thirty patients undergoing 41 pallidotomies are presented. Neuronal activity from the pallidum is recorded using a semi-microelectrode. Based on this activity, lesioning is performed. Postlesion recordings are made to determine the necessity of additional lesioning. A stereoscopic 3D volume MR image system has been developed that along with on-line signal processing allows visualization of high neural activity in the pallidum and postlesion residual activity.

Action Potentials↗
PubMed1995

Evaluation of a semi-automated reticulocyte counting method using the Coulter STKS-2A blood cell counter.

Reticulocyte counting was assessed on the Coulter STKS-2A automated blood cell counter. Using a two step procedure, blood samples were first incubated with the supravital stain new methylene blue. An acidic reagent was then added to clear the haemoglobin and any stained RNA was preserved within the cell. The cells were then analysed by measurement of volume, conductivity and light scatter (VCS). The results of 123 samples analysed on the STKS-2A were compared with those from a Toa Sysmex R-1000 reticulocyte counter. One hundred and seven samples gave no review flags and reticulocyte counts ranging from 0.5% to 22.8%, resulting in a correlation coefficient of 0.93 for the methods. Between run imprecision studies gave CVs ranging from 5.3% for a reticulocyte count of 8.7% to a CV of 16.3% for a 0.34% count. Stability studies showed insignificant changes over 72 h storage. These findings confirm that VCS technology can be adapted to provide precise and accurate routine reticulocyte analysis.

Automation↗
PubMed1994

Inaccuracy of the 'derived' fibrinogen measurement.

The 'derived' fibrinogen method is commonly used for the measurement of plasma fibrinogen. This method is not a direct quantitation of plasma fibrinogen, but an estimation of the fibrinogen concentration from the clotting curve of the prothrombin time on automated photo-optical coagulometers. An increasing number of laboratories are now routinely using this method to cope with increasing demands for fibrinogen testing. To study the suitability of this method for routine laboratory use a total of 58 samples, 20 healthy normals and 38 from other patient groups were tested by the 'derived' and Clauss fibrinogen methods on the ACL 300R. The results clearly demonstrated that 'derived' fibrinogen assay values were significantly higher than the Clauss measurements. The discrepancy between 'derived' and Clauss fibrinogen levels was greater in certain patient groups, e.g. patients receiving oral anticoagulants, than in normal controls. Some patients with documented hypodysfibrinogenaemia with low fibrinogen levels by Clauss assay gave normal 'derived' fibrinogen values. Although the 'derived' fibrinogen assay is rapid, economical and easily available to laboratories with suitable instruments, this study shows that it lacks standardization and is inaccurate compared with the Clauss assay.

Autoanalysis↗
PubMed1984

Chloroplast Structure and Starch Grain Accumulation in Leaves That Received Different Red and Far-Red Levels during Development.

An important step in understanding influence of growth environment on carbon metabolism in plants is to gain a better understanding of effects of light quality on the photosynthetic system. Electron microscopy was used to study chloroplast ultrastructure in developing and fully expanded leaves of tobacco (Nicotiana tabacum L. cv Burley 21). Brief exposures to red or far-red light at the end of each day during growth under controlled environments influenced granum size, granum number and starch grain accumulation in chloroplasts, and the concentration of sugars in leaf lamina. Far-red-treated leaves had chloroplasts with more but smaller grana than did red-treated leaves. Red light at the end of the photosynthetic period resulted in more and larger starch grains in the chloroplasts and a lower concentration of sugars in leaves. Chloroplast ultrastructure and starch grain accumulation patterns that were initiated in the expanding leaves were also evident in the fully expanded leaves that received the treatment during development. It appears that the phytochrome system in the developing leaves sensed the light environment and initiated events which influenced chloroplast development and partitioning of photosynthate to adapt the plant for better survival under those environmental conditions.

Journal Article↗
PubMed1977

Arteriovenous malformation in chronic gastrointestinal bleeding.

Arteriovenous malformations of the gastrointestinal tract are uncommon and treatment is problematic because routine barium contrast studies and endoscopy fail to demonstrate the lesion. Diagnosis is by selective mesenteric arteriography, demonstrating a characteristic vascular tuft and very early venous phase. Two cases of arteriovenous malformation are presented and 47 other reported cases are reviewed. Forty-five per cent were found in the cecum; 37, or 80%, involved the distal ileum, cecum ascending colon, or hepatic flexure. Seventy-five per cent of all patients fall into the 50--80 year age range. The literature reveals a recurring pattern of chronic gastrointestinal blood loss, anemia, and delay (even negative abdominal explorations) before the diagnosis is finally made. A more aggressive approach to chronic gastrointestinal bleeding is suggested through the use of selective mesenteric arteriography.

Adolescent↗
PubMed1976

Optimizing test performance of moderately and severely mentally retarded adolescents and adults.

This study provided further evidence for the validity of a learning potential assessment procedure with institutionalized moderately and severely retarded adolescents and adults. Significant positive correlations were obtained between psychometric and learning scores, attendants' and teachers' ratings of ability, and the posttraining scores on the modified Kohs Extended Learning Potential procedure. In addition, performance on this test-train-test procedure was compared with a train-within-test format for two different tasks: training embedded within the administration of the Leiter International Performance Scale and a formboard version of Raven's Coloured Progressive Matrices. The students responded equally to the two formats. Stanford-Binet IQs were least predictive of performance on the three learning potential measures and were unrelated to teachers' and attendants' ratings of ability. The implications of these data were discussed with particular attention to the potential advantages of the train-within-test model.

Adolescent↗
PubMed1972

False broomrape: a physiological disorder caused by growth-regulator imbalance.

False broomrape on tobacco (Nicotiana tabacum) can be induced by applying cytokinins to the roots, by causing an increase in the cytokinin-auxin ratio in the roots, by removing the apical and auxillary buds, or by applying extracts from tobacco with false broomrape to the roots of healthy plants. It can be prevented by treating debudded plants with auxin.

Journal Article↗