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Biomedical subjects

A Hemmingsson

Publications and source records attributed to A Hemmingsson.

At least 55 records · Page 3Linked to original sources
PubMed1991

Superparamagnetic particles as oral contrast medium in MR imaging of malignant lymphoma.

Non-biodegradable superparamagnetic particles, in plain and viscous aqueous suspensions, were used as an oral contrast medium in 34 patients with known or suspected malignant lymphoma. The contrast effect, the occurrence of artifacts, and the distribution were evaluated in the plain and the viscous aqueous suspensions, and the diagnostic information received from abdominal MR examinations performed without bowel contrast medium was compared with that of post-contrast examinations. Magnetic particles in the concentration of 0.5 g/l displayed a good contrast effect at 0.5 T, and helped in differentiating the intestine from adjacent tissues, resulting in increased diagnostic information in abdominal MR imaging. In the patients given the viscous aqueous suspension the occurrence of artifacts caused by the magnetic particles decreased considerably, and the distribution was homogeneous and improved compared with that in patients given the plain aqueous suspension.

Abdomen↗
PubMed1990

Asbestos-related lesions of the pleura: parietal plaques compared to diffuse thickening studied with chest roentgenography, computed tomography, lung function, and gas exchange.

Lung function tests, tests of working capacity with gas exchange, and computed tomography (CT) with density measurements with the patient supine and prone were performed in 23 males with asbestos-related bilateral pleural lesions. Two had pulmonary asbestosis grade 1/0 or more; all the others had normal lung parenchyma. On x-ray, the pleural lesions were divided into plaques involving only the parietal pleura There was a and diffuse pleural fibrosis of various degrees involving the visceral pleura. There was a good correlation between the findings at plain chest roentgenography and CT, but more lesions were seen on the CT scan. However, a few pleural plaques seen on conventional films were not observed at CT. Individuals with plaques had slightly lowered lung function compared to reference subjects. Bilateral diffuse pleural fibrosis was associated with a marked decrease in pulmonary function. The two patients with radiologically evident pulmonary asbestosis were found in this group. Decreased lung function was also observed in subjects with pleural fibrosis of only grade 1 (involving less than one fourth of the hemithorax) and a normal exercise capacity. The study shows the importance of differentiation between various asbestos-related pleural lesions.

Adult↗
PubMed1990

Magnetic resonance imaging of the transplanted kidney. Correlation to function and histopathology.

Interstitial fibrosis is a frequent finding in biopsies from long-term renal allografts, and may be due to chronic cyclosporine nephrotoxicity or chronic rejection. In this study, long-term renal transplants were investigated with magnetic resonance (MR) imaging, and the results were correlated to histopathology and graft function. Seventeen patients were investigated with MR one to 10 years after transplantation and with simultaneous ultrasonographically guided cortical needle biopsy and function tests. Histopathology included semiquantitative grading of degree of fibrosis and quantitation of ratios of tubular structures to interstitial tissue. The correlation between the histopathological assessment of interstitial fibrosis and graft function was good. Poor differentiation between the renal cortex and the renal medulla at MR imaging was correlated to high degree of interstitial fibrosis in the kidney transplants as well as to reduced graft function. MR examination may thus be of value in the evaluation of long-term renal transplants with chronic functional changes.

Adult↗
PubMed1990

Magnetic resonance imaging of acute myocardial infarction in pigs using Gd-DTPA.

Six pigs with coronary artery occlusion were investigated with MR imaging before and subsequently for about 2.5 hours at repeated intervals after the intravenous administration of Gd-DTPA (0.4 mmol/kg). The animals were sacrificed after a total occlusion time of 6 hours and the hearts were excised. The excised hearts were then reexamined in the MR equipment and stained with TTC (triphenyl tetrazolium) in order to define areas of infarction. Four control hearts with 6-hour-old infarctions were only imaged ex vivo without any previous administration of contrast media. In vivo, there was no clear demarcation of infarction with or without Gd-DTPA. Ex vivo, without any contrast media, the infarctions were poorly discriminated with a discretely increased signal intensity relative to normal myocardium in the T2 weighted images. Gd-DTPA was found to accumulate in the infarctions, which caused an elevated signal intensity most pronounced in the T1 weighted images. This considerably improved the delineation of the infarcted area.

Animals↗
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↗
PubMed1990

Oral superparamagnetic particles for magnetic resonance imaging. Effect in plain and viscous aqueous suspensions.

As a potential gastrointestinal MR contrast medium magnetic particles have been evaluated in preclinical studies as well as in healthy volunteers. The main problem was to achieve an even distribution of the aqueous suspension of magnetic particles in the entire intestine. To improve the distribution of the contrast medium, a viscosity-increasing agent was added to the preparation. In the plain aqueous suspension the magnetic particles sedimented rapidly and caused artifacts, whereas no such sedimentation occurred in the viscous preparation. The contrast effect, as well as the presence of artifacts, increased with particle concentration. The general contrast effect was good in all 5 volunteers, and the contrast medium was well distributed in the small intestine, including the duodenum. There were no artifacts observed, and the contrast medium was well tolerated. The viscosity-increasing agent will thus be introduced in further clinical studies.

Adult↗
PubMed1989

A fast method for T1 fitting.

When NMR signal amplitudes achieved from spin-echo sequences with several different repetition times are used to calculate T1, this can be done rapidly by calculating the time coordinate of the center of gravity of the data and determining which T1 should theoretically give this value. In particular, when a large number of similar calculations are made, the time gain may be massive. Simulations suggested that this procedure is only slightly less accurate than least-squares fitting, and far more rapid. The procedure may also be useful in other types of T1 determination.

Humans↗
PubMed1989

Relative proton density and relaxation times in liver metastases during interferon treatment.

Relaxation times and relative proton densities were calculated from magnetic resonance examinations of the liver in eight patients with liver metastases from neuroendocrine tumours. Single, spin-echo sequences with eight different repetition times and a four-echo sequence were used to calculate T1 and T2 in tumour and normal liver, and the proton density tumour-liver quotient, before and during treatment with interferon. Changes over time of these parameters were compared with variations in tumour marker levels and changes in size and number of the metastases. During therapy, six out of eight cases showed a decrease in tumour T1, five responding to therapy and one with stationary disease, while the two patients with progressive disease showed unchanged tumour T1. The proton density quotient also decreased in a corresponding way, indicating a change in water content in tumours responding to interferon therapy. No significant change in liver T1, tumour T2 or liver T2 occurred in any patient. It is thus possible to perform reliable measurements of relaxation parameters over time, which may be valuable in follow-up of tumour treatment.

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↗
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↗
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

Selective properties of trains of real and complex RF micropulses in slice-selective spin-echo MRI.

The spin nutation properties of frequency selective (space selective in combination with a magnetic field gradient) trains of radiofrequency micropulses were studied in a numeric model. Two cases were considered, one simulating the 90 degrees excitation pulse in spin-echo MRI, the other the 180 degrees spin inversion pulse. Image reconstruction according to the 2-D Fourier transform technique requests that the effect of the 180 degree pulse is independent of the initial phase of the spin vector relative to the radiofrequency field. It was found that with a train of phase-stable radiofrequency micropulses with an envelope of the traditional 'sinc' type the result of the spin inversion pulse was depending on the initial phase whereas this was not the case for a train of phase-shifted (complex) micropulses. The complex train of radiofrequency micropulses also had better selective properties both for excitation and spin inversion than the real one.

Electron Spin Resonance Spectroscopy↗
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↗
PubMed1985

Peroperative staging of renal carcinoma. A methodologic comparison.

Angiography, computed tomography and ultrasonography were compared with respect to staging of renal carcinoma in 41 patients with 46 renal tumours. Angiography and ultrasonography gave correct staging in 52% and 48%, respectively, while correct staging was achieved with computed tomography in 80% of the tumours.

Adenocarcinoma↗