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K A Thuomas

Publications and source records attributed to K A Thuomas.

At least 73 records · Page 4Linked to original sources
PubMed1987

Magnetic resonance images related to clinical outcome after psychosurgical intervention in severe anxiety disorder.

Postoperative verification of radiosurgical lesions in white matter has been difficult to obtain with CT. With magnetic resonance (MR) imaging, however, lesions could be demonstrated in patients undergoing a psychosurgical procedure, gamma capsulotomy, for anxiety disorder. The appearance and location of the lesions were related to the irradiation dose and to the long-term clinical outcome studied prospectively by two independent evaluators who had not been involved in the selection or the treatment of the patients. Seven consecutive cases were examined. CT was also included for comparison reasons. Lesions were clearly visible with MR in patients who improved after surgery. Conversely, lesions were inadequate in cases who did not benefit. MR proved to be more accurate than CT both in detecting the lesions and in defining their configuration. The observations argue for the use of MR for post-operative verification of radiosurgical lesions. MR may facilitate the determination of a clinically effective radiation threshold estimate for radiosurgical lesions, which should be of value for the planning of studies of this type of limbic system surgery.

Adult↗
PubMed1987

Transsphenoidal therapeutic puncture of a cystic pituitary adenoma.

Transsphenoidal diagnostic puncture of skull base tumours has been a routine procedure in Uppsala for a decade. Bromocriptine is the treatment of choice for patients with prolactin secreting pituitary adenomas. Here we report on a patient with a pituitary adenoma who instead developed an increase in tumour size after bromocriptine treatment. Magnetic resonance imaging showed the tumor to be cystic. A transsphenoidal puncture was used therapeutically instead of surgery with excellent result.

Adenoma↗
PubMed1986

Improved formulae for signal amplitudes in repeated NMR sequences: applications in NMR imaging.

An improved formalism describing the dependence of the signal strength on relaxation times and spin densities in pulsed nuclear magnetic resonance experiments is presented. It is especially applicable to repetitive experiments such as occur in imaging applications. Essentially, it includes long-time spin coherence effects not considered in the algorithms usually adopted. Also, some generalizations of classical concepts are made. Validity criteria are studied using numerical simulations. The algorithm assumes a relatively inhomogeneous main magnetic field, but the computer simulations indicate that the inhomogeneity normally present in magnetic resonance imagers is sufficient. The simulations also indicate that the field gradient pulses applied in the spatial encoding procedure do not necessarily interfere seriously with the validity of the formulae, but complicate the choice of optimal formula and may in some circumstances prevent the spin system from reaching a steady state.

Algorithms↗
PubMed1986

T1, T2, and relative proton density at 0.35 T for spleen, liver, adipose tissue, and vertebral body: normal values.

An MRI installation (Magnetom, Siemens, software version B1 of NUMARIS) working at 0.35 T was used to estimate T1, T2, and relative proton density in the spleen, liver, adipose tissue, and vertebral body in 14 healthy volunteers. Two double-echo sequences were applied for all subjects: TR = 500 ms, TE1 = 35 and TE2 = 70 ms; and TR = 1600 ms, TE1 = 35 and TE2 = 70 ms. The images were sampled in regions of interest and appropriate relaxation expressions fitted to the ROI data yielding relaxation parameters and relative proton densities. Relaxation expressions, included in standard software (Siemens), were compared to more elaborate functions, developed in parallel to this study. The latter were found more appropriate, especially for high T1 values, and gave the following mean values for the four tissues (estimated uncertainty of mean in parentheses) T1 (ms) 915(36), 428(5), 261(7), and 501(11); T2 (ms) 79.7(8.8), 51.0(0.2), 59.8(1.0), and 64.7(0.8); and corresponding relative proton density (rho, arbitrary units) 2088(136), 2182(10), 2915(49), and 2136(21). The uncertainty in the values was estimated in the fitting procedure and does not include systematic errors. The relative noise in the ROIs was about 9% and the reproducibility of the ROI mean values about 8%.

Adipose Tissue↗
PubMed1986

Tumour delineation with magnetic resonance imaging in gliomas. A comparison with positron emission tomography and computed tomography.

In ten patients with histopathologically confirmed low-grade (n = 4) and high-grade (n = 6) cerebral gliomas, the ability of magnetic resonance imaging (MRI) to delineate these tumours was examined. Spin echo (SE) technique with dual and multiple echoes and subtraction of images recorded with multiple echo sequences was applied. Computed tomography (CT) and positron emission tomography (PET) with 11C-L-methionine were used as reference methods. In high-grade gliomas multiple echo sequences and subtractions delineated the tumours better than ordinary SE sequences and equally well as CT, but slightly less well than PET. In low-grade tumours, the tumour delineation was better than with CT and comparable to that obtained with the present PET method. Multiple echo sequences and subtraction increase the reliability of MRI in delineating cerebral gliomas as compared with standard SE sequences.

Adolescent↗
PubMed1986

Magnetic resonance imaging of tumours of the sellar region. Evaluation of treatment with bromocriptine retard.

Magnetic resonance imaging (MRI) with a superconductive 0.5 T magnet has been used in 10 patients with pituitary adenomas to evaluate the effect of bromocriptine treatment. Seven patients had prolactinomas, one a growth hormone (GH) producing adenoma and two patients null cell adenomas with slight hyperprolactinaemia. A single dose of 50 mg bromocriptine was given intramuscularly in a slow release preparation, followed after 6 weeks by 5 mg/day orally. Significant reduction of serum prolactin was noticed in all patients. Visual field defects disappeared rapidly. In all prolactinoma patients and in the patient with the GH producing adenoma MRI showed a decrease in tumour size. In 5 of these 8 patients MR signal analysis, aided by the use of a subtraction technique, clearly visualized the development of large intratumour cysts. In one further patient with a null cell adenoma there was also a rapid development of an intratumour cyst and an increase in tumour size. This patient was treated with transsphenoidal needle aspiration. In all tumour cases an increase in intensity quotients based on T1 and T2 relaxation times was calculated.

Adenoma↗
PubMed1986

Magnetic resonance imaging of brain tissue displacement and brain tissue water contents during progressive brain compression. An experimental study in dogs.

Continuous recording of vital physiologic parameters and magnetic resonance imaging (MRI) was performed during continuous expansion of extradural rubber balloons in spontaneously ventilated anesthetized dogs. Initial physiologic changes appeared when the pontine cistern was compressed while respiratory arrest was regularly paralleled by marked tentorial and tonsillar herniation. Local increase in brain tissue water progressed during brain compression and was most marked in white matter of the brain. This was related to the regional decrease in cerebral perfusion pressure. The correlation between the morphologic and physiologic course of events during brain compression has a predictive value.

Animals↗
PubMed1986

Magnetic resonance imaging of water intoxication. An experimental study in dogs.

Sequential magnetic resonance imaging (MRI) was performed to correlate signs of herniation and increase in local brain tissue water content with continuous changes in vital physiologic parameters during progressive water intoxication in anaesthetized dogs. The intracranial pressure increase ultimately resulted in respiratory and cardiac arrest. MRI concomitantly showed an increase in local brain water content starting and dominating in the cerebral cortex but progressing to all parts of the central nervous system. The late appearance of transtentorial pressure gradients and of brain herniation suggests that development of cerebral edema occurs in at least two stages, an intracellular osmotic edema appearing first, being followed by an ischemic edema related to a progressive decrease in local perfusion pressure.

Animals↗
PubMed1986

Magnetic resonance imaging of cerebral compression and local brain tissue water content during continuous extradural bleeding. An experimental study in dogs.

Continuous recording of vital physiologic parameters and magnetic resonance imaging were performed during progressive extradural bleeding in spontaneously ventilated anesthetized dogs. The volume of the bleeding could exceed the intracranial volume by 500 per cent due to the formation of an extradural arteriovenous shunt. The rate of hematoma growth was dependent on the area of stripped dura. Midline shift, herniation and lateral ventricle compression occurred early, corresponding to changes in vital parameters. Local brain water increased non-linearly with white matter preceding gray matter. Water increase started first in the ipsilateral hemisphere followed by the contralateral hemisphere, brain stem and cerebellum. The correlation between local tissue water increase and local perfusion pressure supports the notion of an ischemic brain edema being formed during an extradural bleeding.

Animals↗
PubMed1986

Evaluation of intracranial pressure rebound after evacuation of intracranial expanding lesions. An experimental study in dogs.

Sequential magnetic resonance imaging was used to follow brain displacement, signs of herniation and increase in local brain tissue water content during expansion and after evacuation of an extradural balloon in anesthetized, artificially ventilated dogs. A fatal intracranial pressure (ICP) rebound occurred if the cerebral perfusion pressure (CPP) was critically reduced to 20 mm Hg for more than half an hour. Despite reduction of brain displacement after balloon evacuation brain water content continued to increase. Compression of CSF outflow pathways and signs of herniation remained. CPP continuously fell to zero. ICP rebound is a grave situation significantly influenced by a large increase in brain tissue water.

Animals↗
PubMed1986

Subtraction in magnetic resonance imaging.

Subtraction of images recorded with multiple echo, spin echo (SE) techniques was performed in phantom and clinical studies of patients with pituitary adenomas and gliomas. The tissue differentiation was enhanced in the subtracted images.

Adenoma↗
PubMed1986

Cerebrospinal fluid flow studied with gated magnetic resonance imaging during the various parts of the cardiac cycle.

The pulsatile movement of cerebrospinal fluid (CSF) through the Sylvian aqueduct has been studied in two normal volunteers. A standard magnetic resonance scanner was used as well as a routine spin echo sequence. Series of ECG-gated axial images were obtained perpendicular to the long axis of the Sylvian aqueduct. Previously it has been demonstrated by flow phantom experiments that the phase information can be used to obtain a linear relation between phase and flow velocity. By multiplying the CSF flow velocity by the cross-sectional area of the aqueduct of Sylvius obtained in each image, the CSF flow variation during the cardiac cycle could be demonstrated and measured.

Cerebrospinal Fluid↗
PubMed1986

Magnetic resonance imaging of stereotactic radiosurgical lesions in the internal capsule.

Confirmation of radiosurgical lesions in white matter has earlier been difficult to obtain, which has hampered the evaluation of clinical outcome in relation to the site and the size of the lesions. In this investigation 7 consecutive patients subjected to bilateral stereotactic gamma capsulotomy for intractable anxiety disorders were re-examined several years after treatment. The protocol included both magnetic resonance imaging (MRI) and computed tomography (CT) interpreted under blind conditions and prospective psychiatric evaluations performed by two independent evaluators who had not been involved in the selection and the treatment of the patients. The lesions were clearly visible with MRI in all patients who improved after treatment. MRI proved to be more accurate than CT both in detecting and in defining the size and the configuration of the lesions. The extent of the tissue reaction following the irradiation seemed to be best defined in T2 weighted images. A high correlation (p less than 0.01) was obtained between ratings of clinical outcome and radiosurgical precision as reflected by MRI. It is concluded that MRI may provide the clinician with more information than CT does. In the future MRI may also facilitate the determination of a radiation threshold value for white and grey matter lesions and provide a more detailed knowledge of the time course of the development of such lesions.

Adult↗
PubMedDate not supplied

Cardiac gated MR imaging of cerebrospinal fluid flow.

This is a preliminary investigation of the cerebrospinal fluid (CSF) spaces using cardiac gated magnetic resonance imaging. A variation of intensity of the signal from the cerebral aqueduct is demonstrated during the cardiac cycle. The pattern of this variation suggests pulsatile CSF flow. Calculations that have been verified by phantom measurements show that CSF flow rates less than 1 mm/s may be detectable. Magnetic resonance may therefore offer a new method for the demonstration and measurement of CSF flow.

Cerebral Aqueduct↗
PubMedDate not supplied

CT and MR evaluation of pericardial and retrosternal adhesions after cardiac surgery.

The visibility of the pericardium as well as of the space between the dorsal aspect of the sternal surface and the pericardial surface after cardiac surgery was determined by CT and/or MR with electrocardiographic (ECG)-gated spin-echo (SE) and gradient-echo sequences. Seventeen patients who had undergone cardiac operations and who were admitted for cardiac reoperation were investigated with CT and/or MR prior to sternal reentry. Five patients were investigated with CT alone, ten with both CT and MR, and two with MR only. At reoperation, retrosternal adhesions were classified as present or absent, and intrapericardial adhesions were classified as absent, minimal, moderate, or severe. A similar classification was applied to the CT and MR findings. In 14 of 15 patients, the CT findings were in agreement with those found at operation regarding postoperative retrosternal extrapericardial adhesions in the cranial retrosternal space and in 12 of 15 in the caudal retrosternal space. Computed tomography could not detect intrapericardial adhesions. Magnetic resonance was sensitive to metal artifacts from sternal sutures in both sequences and could therefore not be used to detect postoperative retrosternal extrapericardial adhesions. On the other hand, MR with ECG-gated SE sequences confirmed intrapericardial adhesions in 44 of 57 locations.

Adult↗
PubMedDate not supplied

Structure enhancement by subtraction in magnetic resonance imaging.

Two patients with tumours in the pituitary gland and the liver, respectively, were studied with MRI. Regions of different transverse relaxation times were found in the tumours. Subtraction of images recorded with different echo times demonstrated the tumour regions better than the original images although these were recorded with 2 repetition times and double and multiple echo sequences. Subtraction techniques may thus aid diagnosis in MRI.

Adenoma, Islet Cell↗
PubMedDate not supplied

Technical aspects of magnetic resonance imaging in parathyroid gland lesions.

Two patients with primary hyperparathyroidism were examined before parathyroid surgery with magnetic resonance imaging at 0.35 tesla in order to analyse optimal methods of visualization. Two large parathyroid glands in the neck had long transverse relaxation times which rendered them clearly visible in T2-weighted images as structures of a signal intensity higher than that of the surrounding. Large parathyroid lesions may thus be easily detected by magnetic resonance imaging provided proper examination parameters are employed.

Adult↗