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Biomedical subjects

A Hemmingsson

Publications and source records attributed to A Hemmingsson.

At least 19 recordsLinked to original sources
PubMed1992

MR imaging of acute myocardial infarction in pigs using Gd-DTPA-labeled dextran.

Myocardial infarctions were induced in 12 pigs. In 6 pigs, dextran-(Gd-DTPA)15 (approximately 0.1 mmol Gd/kg b.w.) was injected i.v. 4 to 4.5 hours after coronary artery occlusion. ECG gated MR images were obtained repeatedly before (n = 4) and after (n = 6) contrast medium injection. Relaxation times in blood samples were measured repeatedly. The animals were sacrificed 2 hours after contrast medium administration. The hearts were excised, reexamined in the MR equipment and stained with triphenyltetrazolium chloride (TTC) in order to define areas of infarction. The remaining 6 pigs were sacrificed 6 hours after occlusion without administration of contrast medium. These hearts were only imaged ex vivo. In vivo, the infarctions could not be identified with or without dextran-(Gd-DTPA)15. Ex vivo, without contrast medium, the infarctions had an increased signal intensity, most pronounced in the T2-weighted images. Dextran-(Gd-DTPA)15 caused a prolonged, pronounced shortening of T1 and T2 in blood samples. The infarct demarcation improved in the T1-weighted images after injection of dextran-(Gd-DTPA)15, due to a moderate enhancement in normal myocardium and a stronger enhancement at the periphery of the infarctions, while the central parts of the infarctions were only weakly enhanced.

Animals↗
PubMed1992

Nonresectable adenocarcinoma of the rectum assessed by MR imaging before and after chemotherapy and irradiation.

Thirty-four patients with nonresectable adenocarcinoma of the rectum, defined as tumor fixation at digital examination, were examined with MR. All 34 patients had, according to MR imaging, perirectal tumor growth. In 23 (68%) of the patients, the tumor has reached an adjacent organ. Eight of these patients had disturbances of the MR characteristics in the adjacent organ which proved to be due to overgrowth, i.e., to tumor invasion into these structures. In the remaining 15 patients, without disturbed MR characteristics, 7 had tumor overgrowth at laparotomy. When there was a visible space between the tumor and adjacent organs, there was no sign of tumor overgrowth at laparotomy, except in one case. In 24 patients, examined both before and after combined irradiation and drug therapy, tumor regression was registered after treatment. MR imaging seems to be useful in the assessment of resectability and to evaluate preoperative anticancer treatment in patients with nonresectable rectal carcinoma.

Adenocarcinoma↗
PubMed1992

Motion associated susceptibility artifacts.

A bowel labeling agent is important for improving abdominal MR. Besides providing contrast between the bowel and other organs, the contrast agent itself is a potential source of artifacts. The artifacts created by superparamagnetic particles (SPP) subjected to motion have been studied in vitro at 0.5 T, and compared to artifacts created by a paramagnetic compound. Apart from the expected static effects of the SPP, movement induced additional artifacts were seen as signal displacements in the phase-encoding direction. The artifacts were obvious at an iron concentration of 1 mg Fe/ml, barely visible at 0.2 mg Fe/ml, and completely absent at 0.1 mg Fe/ml. Artifacts were also evident with the SPP outside the imaging slice. This further emphasizes the importance of choosing the lowest effective dose when using SPP contrast agents. For the paramagnetic agent, motion propagated artifacts consisted of high and low signal regions in a mosaic pattern.

Artifacts↗
PubMed1992

MR imaging with histopathological correlation in vertebral metastases of breast cancer.

In 5 patients with advanced breast cancer and spinal metastases MR imaging of the spine was performed before and/or after death. T1-, proton density-, and T2-weighted and "phase contrast" images were obtained in the sagittal plane. Autopsies included histopathologic examination of whole sagittal sections of the vertebral body. The relative signal intensities on the different MR sequences of various tissues identified histologically were evaluated. "Phase contrast" images combined with T1-weighted images were highly sensitive in detecting metastases. All metastatic tumours over 3 mm in size were found with MR imaging. Vertebrae containing connective tissue and reactive bone marrow had an MR appearance similar to that of metastases even though no metastases were found histopathologically.

Adult↗
PubMed1991

Magnetic resonance imaging in idiopathic hemochromatosis.

The therapeutic management of patients with idiopathic hemochromatosis (IH) requires an accurate estimate of hepatic iron overload in order to prevent tissue fibrosis and organ failure. Magnetic resonance imaging (MRI) was used to estimate liver iron overload in 5 patients with IH and in 8 normal controls. Signal intensity ratio between liver and subcutaneous fat in T1-, proton- and T2-weighted images was significantly lower in IH when compared with normal controls, and increased gradually during treatment by phlebotomy. Mean serum ferritin at diagnosis was 755 micrograms/l (range: 648-900) in IH and 85 micrograms/l (range: 19-232) in normal controls. A high correlation (r = -0.93) was present between liver signal intensity ratio and serum ferritin; both changed in parallel during removal of iron by phlebotomy. MRI may provide a safe and accurate method of detecting iron overload in the precirrhotic phase of IH, obviating the need for liver biopsy. It may also be used to monitor treatment.

Adult↗
PubMed1991

Effect of superparamagnetic particles in agarose gels. A magnetic resonance imaging study.

The effect of different preparations of superparamagnetic particles, designed as potential MR contrast media for the gastrointestinal tract (oral magnetic particles, OMP, diameter of 3.5 microns, iron content 20% by weight) and for the reticuloendothelial system (intravenous magnetic particles, IMP, mean diameter of 0.3 micron, iron content 30% by weight), were evaluated in agarose gels in vitro, using a 0.5 T whole body MR system. The iron content ranged from 2.1 x 10(-4) to 2.1 x 10(-1) mg Fe/ml in both preparations. Both preparations reduced the signal intensities substantially over a range of concentrations in spin echo sequences. Generally, the signal intensity decreased monotonously with concentration, except for IMP at low concentrations, at which a minor signal intensity increase was observed on T1 and proton density weighted images. The reduction of the signal intensity was stronger in gradient echo and phase contrast sequences, as compared to corresponding spin echo sequences with similar timing. Both IMP and OMP had a pronounced T2 effect, the effect of IMP being stronger than that of OMP. IMP had a relatively smaller T1 effect, whereas T1 was almost unaffected by OMP. Susceptibility artifacts occurred at higher concentrations of both OMP and IMP, in all sequences used. Thus, OMP reduced the signal intensity, without causing significant artifacts, on both T1 and T2 weighted images over a relatively wide range of concentrations.

Contrast Media↗
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↗