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Biomedical subjects

K A Thuomas

Publications and source records attributed to K A Thuomas.

At least 55 records · Page 3Linked to original sources
PubMed1992

Manganese induced brain lesions in Macaca fascicularis as revealed by positron emission tomography and magnetic resonance imaging.

A series of positron emission tomography scans was made on two monkeys during a 16-month period when they received manganese(IV)oxide by subcutaneous injection. The distribution of [11C]-nomifensine uptake, indicating dopamine terminals, was followed in both monkey brains. The brain distributions of [11C]-raclopride, demonstrating D2 dopamine receptors, and [11C]-L-dopa, as a marker of dopamine turnover, were followed in one monkey each. The monkeys developed signs of poisoning namely unsteady gait and hypoactivity. The [11C]-nomifensine uptake in the striatum was reduced with time and reached a 60% reduction after 16 months exposure. This supports the suggestion that dopaminergic nerve endings degenerate during manganese intoxication. The [11C]-L-dopa decarboxylation was not significantly altered indicating a sparing of [11C]-L-dopa decarboxylation during manganese poisoning. A transient decrease of [11C]-raclopride binding occurred but at the end of the study D2-receptor binding had returned to starting values. The magnetic resonance imaging (MRI) revealed that the manganese accumulated in the globus pallidus, putamen and caudate nucleus. There were also suggestions of gliosis/edema in the posterior limb of the internal capsule. MRI might be useful to follow manganese intoxication in humans as long as the scan is made within a few months of exposure to manganese, i.e. before a reversal of the manganese accumulation.

Animals↗
PubMed1992

Otoneurologic disturbances caused by solvent pollution.

Subjects exposed to industrial solvents may experience vertigo and nausea. Solvents are usually volatile hydrocarbon compounds, which are important parts of everyday life in a modern society. They may also cause neurastenia, personality changes, and reduced intellectual capacity. The syndrome that may develop was formerly named psycho-organic syndrome (POS), but in modern terminology it is called chronic toxic encephalopathy (CTE). The syndrome develops slowly, and during the first years no pathological findings will be found using various test batteries. Somewhat later, when the syndrome still might be reversible, psychometric, auditory, and otoneurologic testing may well unveil disturbances within the posterior fossa structures. Animal experiments suggest one site of effect for solvents to be within the cerebellum and brainstem regions with close relationship to the gamma-amino-butyric acid (GABA) transmission. In the otoneurologic test battery, visual suppression and smooth pursuit are of extreme value, as are some auditory tests such as discrimination of interrupted speech and cortical response audiometry using frequency glides as stimuli. Dynamic posturography and magnetic resonance imaging (MRI) have recently proved valuable in the diagnosis. Research is needed concerning the most efficient test battery for early detection of solvent-induced lesions. During further research it is important to unveil other toxic agents, like heavy metals and alcohol, and their damage to the central nervous system and to make comparisons between these substances and the lesions caused by hydrocarbon solvents.

Animals↗
PubMed1992

Concomitant changes in MR image and morphology induced by glucose and fructose in B16 mouse melanomas.

The short proton relaxation times in the MR images of malignant melanomas make them different from most other tumors. We have previously shown that the T1 and T2 signals may be significantly influenced when the water distribution of the tumor is changed in vivo and in vitro. In the present work T1 and T2 were estimated and compared with the electron microscopy picture in subcutaneously implanted B16 melanomas in mice. Two hours after the mice were given an i.p. injection of 0.9% NaCl containing 10% glucose and 10% fructose (9 mice) both the T2 components were markedly and the T1 slightly prolonged. At the same time the electron microscopy picture displayed swelling of the melanocytes together with a marked decrease in number and size of their mitochondriae. There were no changes in the MR image or the melanocyte structure in control mice injected with 0.9% NaCl (9 mice) or 0.9% NaCl containing 10% fructose. It is concluded that the changed MR image may be coupled to the metabolism in melanoma.

Animals↗
PubMed1991

Acute peripheral facial palsy simulating Bell's palsy in a case of probable multiple sclerosis with a clinically correlated transient pontine lesion on magnetic resonance imaging.

A transient pontine lesion was demonstrated in a young adult male who had a complete acute peripheral facial nerve palsy due probably to multiple sclerosis. In the acute stage of the palsy. T2-weighted magnetic resonance imaging (MRI) revealed a high signal intensity in the ipsilateral pons in the region of the nucleus and pontine part of the facial nerve. The patient recovered completely 5 weeks after the onset of the palsy, and at this stage, the lesion in the brainstem was no longer demonstrable on MRI. The onset and course of the disease resembled the idiopathic form of facial palsy (Bell's palsy): the present findings along with recent MRI and topodiagnostic studies may indicate that in some cases of Bell's palsy the primary lesion is located centrally. By improved MRI techniques and intravenous contrast agents it may be possible to visualize and follow the disease process and ascertain more of the pathogenesis of Bell's palsy.

Acute Disease↗
PubMed1991

Comparison of MR imaging and CT in pituitary macroadenomas.

The findings on mid-field MR imaging and CT were compared retrospectively in 65 patients with pituitary macroadenomas. The evaluation comprised tumour extension and delineation, invasiveness, relationship to adjacent structures, and internal tumoral changes. MR was superior to CT except in the demonstration of bone changes and tumour calcification. The superiority of MR was most pronounced regarding cavernous sinus invasion, tumour relationship to the carotid arteries and optic chiasm, and tumour haemorrhage. Extensive bone changes were visualized with both methods; erosions were often seen only with CT. It is concluded that MR is the preferable method for evaluation of pituitary macroadenomas. CT is useful as a supplementary modality when detailed information on bone anatomy is required, particularly if a transsphenoidal surgical approach is contemplated.

Adenoma↗
PubMed1991

Changes in MR of malignant melanomas induced by glucose and fructose. A clinical and experimental investigation.

MR imaging has been performed on malignant melanomas in vitro and in vivo. Changes of the water content in an enucleated malignant melanoma in vitro were followed by significant changes of the T1 and T2 values. In mice with implanted subcutaneous melanoma similar changes could be obtained after injection of glucose and fructose intraperitoneally. Malignant melanoma of the eye could be influenced in the same way in 10 consecutive patients after oral intake of glucose and fructose. The present study shows that the MR images may be significantly changed after a few hours by altered metabolism induced by glucose and fructose. It is anticipated that this is due to changes within the tumor leading to different water distribution. The finding may be of importance as a further help for diagnosing malignant melanoma of the eye.

Adult↗
PubMed1990

Rebound of ICP after brain compression. An MRI study in dogs.

The rebound of intracranial pressure (ICP) occurring after decompression of an intracranial mass lesion was studied in an epidural balloon compression model. Intracranial morphology and brain tissue water content were assessed with magnetic resonance imaging (MRI). Fast and slow components of the transverse relaxation time (T2) were used as indicators of brain oedema development. During balloon compression a progressive prolongation of both the fast and the slow T2 components took place. Following deflation of the balloon both components increased rapidly, particularly the slow-T2. The MR scans displayed progressive occlusion of the aqueduct, and obliteration of the ambient and pontine cisterns. The changes in morphology and in water content after decompression had largely the same time course as the development of the rebound of ICP. In contrast, no changes in morphology and tissue water content occurred after hydrostatic brain compression achieved by subarachnoid fluid infusion. The findings suggest that the intracranial pressure rebound is caused by cerebral oedema accumulated during and particularly in the recirculation phase after an ischaemic injury of adequate intensity and adequate duration.

Animals↗
PubMed1990

Evaluation of syringomyelia and Chiari malformations using ultra-low magnetic resonance imaging.

The accuracy of ultra-low field magnetic resonance imaging (MRI) compared to medium-field MRI in detecting syringomyelia and associated Chiari malformations is examined. In all cases the size of the syrinxes and the type and extent of the Chiari malformations was clearly shown at low-field MRI. The present spatial solution and high sensitivity allows for low-field imagers to localize even minor morphological changes of the spinal cord, brainstem, and cerebellum.

Adolescent↗
PubMed1990

Magnetic resonance in Bell's palsy.

The brain and the brain stem were investigated by magnetic resonance (MR) in 19 patients with complete acute peripheral facial palsy, diagnosed as Bell's palsy. Five patients with a median age of 57 years had changes on T2 weighted MR: One patient showed transient signal changes with increased signal intensity in the ipsilateral brain stem. Another patient had persisting abnormal signals both in the brain and the brain stem. Two patients presented regions of high signal intensity in the subcortical cerebral white matter and still another patient had increased signal intensity in the periventricular white matter. MR abnormalities anatomically related to the facial nerve or its nucleus were not demonstrated. The significance of the MR findings is not quite certain but the MR pattern in conjunction with the patient's high median age most likely indicate vascular disease.

Adult↗
PubMed1989

Magnetic resonance imaging in patients with Bell's palsy.

Magnetic resonance imaging of the brain and the brain stem was performed in 18 patients with complete acute peripheral facial palsy and diagnosed as Bell's palsy. In five patients T2 weighted images revealed regions of high signal intensity in the cerebral white matter and/or in the brain stem. The changes indicate that in cases of Bell's palsy the central nervous system may be involved and the disease may be related to microvascular or demyelinating disorder.

Adolescent↗
PubMed1989

The effects of brain edema on intracranial pressure in focal cerebral ischemia. An experimental study in a rat using magnetic resonance imaging.

Intracranial pressure (ICP) changes and the development of cerebral edema during the first 24 hours after middle cerebral artery (MCA) occlusion in a rat were studied. ICP was measured via a catheter implanted into cisterna magna and the dynamics of cerebral edema was observed using serial T2 magnetic resonance (MR) measurements. Two T2 components were separated, fast (30-120 ms) and slow (120-240 ms). The first IPC increase was noted within first 2 hours after MCA occlusion and thereafter ICP started to rise 6 hours after stroke. These findings correlated with the development of edema, especially with the increase in extracellular water seen in T2 images. The highest ICP and the largest edema was noted in rats with largest infarcts. An experiment forms a basis for further studies on ICP and edema in a rat model of focal cerebral ischemia.

Animals↗
PubMed1989

Magnetic resonance studies on the development of ischemic edema in an early period after occlusion of middle cerebral artery in a rat.

The development of ischemic edema after middle cerebral artery occlusion in a rat was studied using T1 and T2-weighted magnetic resonance imaging (MRI). Examinations were performed with Helmholtz coil and multiple echo sequences with TR 1,500 ms and TE 30-240 ms (8 echoes) were used. T2 prolongation was noted already 3 hours after experimental stroke and the values increased during the time of the study. T1-weighted images were much less sensitive for the detection of increased water content. This experiment forms a basis for MR studies on the formation and resolution of cerebral edema and can be useful for studies on efficacy of different medical measures against ischemic edema.

Animals↗
PubMed1988

The congruence of the distal radioulnar joint. A magnetic resonance imaging study.

The functional anatomy of the distal radioulnar joint was studied in 10 healthy volunteers. The joint surface of both the ulnar head and the sigmoid notch of the radius form arcs of circles with small areas of contact because the diameters of the circles are different. The distal radioulnar joint is congruent throughout its range of motion, but the area of contact shifts from dorsal in the sigmoid notch in pronation to volar in supination. The insertion of the distal radioulnar ligaments on the ulnar head explains the congruence of the joint.

Adult↗
PubMed1987

Treatment of hormone-producing adrenocortical cancer with o,p'DDD and streptozocin.

Three patients with advanced adrenocortical carcinoma were treated with a combination of intermittent streptozocin and continuous o,p'DDD. Two patients were treated preoperatively and the primary tumors, initially considered as inoperable, could be resected after 19 and 5.5 months, respectively. In the patient with the longer treatment (35 months), lung and lymph node metastases disappeared and she has no evidence of recurrent disease 6.5 years after start of therapy. One patient was followed by magnetic resonance imaging (MRI) and urinary steroid secretion. The MRI gave a good visualization of the tumor. Measurements of relaxation times showed a significant decrease in T1 values. The urinary steroid profile showed an increased secretion of 3 beta-hydroxy-5-ene steroids and tetrahydro-11-deoxy-cortisol. Treatment with streptozocin and o,p'DDD initially increased 16-oxygenation of dehydroepiandrosterone and androst-5-en-3 beta,17 beta-diol, followed by a decrease in the secretion of all urinary steroids. The third patient received postoperative treatment with no effect on metastatic disease in the lungs, she died 9 months after start of treatment. The therapeutic approach with the combination regimen of streptozocin and o,p'DDD pretreatment plus aggressive surgery has to be further evaluated, as well as MRI and urinary steroid profile as methods to monitor the effect of therapy.

Adrenal Cortex↗