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A Hemmingsson

Publications and source records attributed to A Hemmingsson.

At least 19 recordsLinked to original sources
PubMed1999

Chemical shift artifact-free microscopy: spectroscopic microimaging of the human skin.

A spectroscopic imaging technique with high spatial resolution was used for the study of human skin in vivo. The measurements were performed using a whole-body magnetic resonance system (1.5 T) with standard gradients and a standard 8-cm diameter circular surface coil. A decisive gain in signal-to-noise ratio was achieved by reducing the receiver bandwidth of the imaging system to values less than +/-5 kHz. The chemical shift misregistration was eliminated by post-detection data processing. The method was tested on different kinds of skin, on the foot sole and head. Water, fat, and chemical shift artifact-free images were obtained with resolution 0.107 x 0.143 mm in plane and slice thickness 1 mm. A major advantage of the spectroscopic imaging procedure is that the pulse sequence can be optimized for the maximum signal-to-noise ratio. There is no need for special modification of the sequence to circumvent the chemical shift artifacts (water, fat suppression, etc.).

Adipose Tissue↗
PubMed1999

Characterization of human head vasculature by percolation parameters.

A data reduction procedure, originally proposed for characterization of fractals and random percolation clusters, has been used to evaluate the vascular system of the human head. The motivation behind this study arose from the wish to study empirically transport properties of vascular systems and to find a suitable formalism for their description. MR angiographic data acquired by a standard 3D inflow method were used. The evaluated parameters refer to the backbone fractal dimensionality and the correlation length. The fractal dimensionality of the backbone was found to be 1.71 for the human head vasculature. This value fits the theoretical range of random percolation networks. It is concluded that concepts of percolation theory might have some value for characterizing the structure and transport properties of the vascular system.

Brain↗
PubMed1998

Chemical shift artifact-free imaging: a new option in MRI?

A high-speed proton spectroscopic imaging method with high spatial resolution was used for obtaining water, fat, and chemical shift artifact-free images on a 1.5 T MR scanner. The technique is based on a fast radiofrequency (RF) spoiled gradient-echo sequence. The chemical shift information is encoded by incrementing the echo time in a series of image records. Suppression of water or fat signals is not used. The technique does not require a highly homogeneous magnetic field. Spectroscopic images of a human volunteer were compared with corresponding conventional images obtained using the short inversion time inversion recovery (STIR) and the selective partial inversion recovery (SPIR) methods. The results demonstrate that it is possible to produce images entirely free from chemical shift artifacts using only a few chemical shift encoding steps. The technique also produces pure water and fat images which are significantly better than those produced by using the conventional methods STIR and selective partial inversion recovery. The described method appears to be promising for routine clinical applications because it can be fully automated.

Adipose Tissue↗
PubMed1998

Magnetic resonance spectroscopic imaging for visualization and correction of distortions in MRI: high precision applications in neurosurgery.

We present a method for the quantification and correction of geometrical/intensity distortions of magnetic resonance images predominantly caused by bulk magnetic susceptibility shifts due to susceptibility heterogeneities of measured biologic tissues and shape of the object under investigation. The method includes precise and fast measurements of the static magnetic-field distribution inside the measured object and automated data processing. Magnetic-field deviations in the range (-2.4; 2.6) ppm were found in the human brain at B0 = 1.5 T. For routinely used imaging parameters, with a read gradient strength of about approximately 1 mT/m, the magnetic-field perturbations in the human brain can cause geometrical distortions up to +/-4 mm and intensity changes up to +/-50%. MR images corrected by the described method are suitable for planning high precision applications in neurosurgery.

Artifacts↗
PubMed1997

1H-spectroscopic imaging with read gradient during acquisition in inhomogeneous fields: analysis, measurement strategy, and data processing.

The proton magnetic resonance spectroscopic imaging techniques that use read gradient during acquisition produce proton spectra with high spatial and moderately high spectroscopic resolution in a reasonable time for in vivo applications. These techniques suffer mainly from the spatial and spectral distortions caused by the convolution of spectral/spatial information (chemical-shift artifacts) and from the spectral shifts caused by static magnetic field inhomogeneities. The investigators analyze the chemical-shift artifacts in the presence of nonnegligible static magnetic field inhomogeneities and propose a postdetection processing scheme to correct for such effects. Spectral artifacts caused by chemical shifts, spectral line overlapping, streak broadening, and magnetic field inhomogeneities are discussed. The postdetection data processing scheme is demonstrated on measurements of a phantom as well as a human leg.

Artifacts↗
PubMed1997

Dysprosium-enhanced MR imaging for tumor tissue characterization. An experimental study in a human xenograft model.

PURPOSE: To evaluate dysprosium-enhanced MR imaging for differentiation between morphologically intact and necrotic tumor tissue in a tumor model. MATERIAL AND METHODS: A human colon carcinoma was transplanted subcutaneously into 9 nude (immunodeprived) rats. MR imaging was performed before and after injection of the dysprosium agent Dy-DTPA-BMA. T1-, T2- and T2*-weighted sequences were acquired. The tumors were dissected, histological sections were prepared, and compared with corresponding MR images. RESULTS: In intact tissue, the MR signal intensity in the T2- and T2*-weighted images decreased after Dy injection and the delineation of the intact regions were sharp and corresponded well to the gross histological sections. CONCLUSION: Dy-enhanced MR imaging facilitated the differentiation between intact and necrotic tumor tissue.

Adenocarcinoma↗
PubMed1997

Diagnostic efficacy of MnDPDP in MR imaging of the liver. A phase III multicentre study.

PURPOSE: To assess the diagnostic efficacy, safety and tolerability of mangafodipir trisodium (MnDPDP, Teslascan) in MR imaging of the liver. MATERIAL AND METHODS: Eighty-two patients from 4 centres underwent MR imaging with pre-contrast sequences including T1-weighted SE and GRE, and T2-weighted turbo SE sequences. MnDPDP at a dose of 5 mumol/kg b.w. was administered by slow i.v. infusion, and 20-60 min after infusion the T1-weighted SE and GRE sequences were repeated. Diagnostic efficacy was evaluated by counting the number of lesions and by evaluating whether more information for lesion characterisation was available in post-contrast images. Safety and tolerability were assessed by recording adverse events and infusion-related discomfort. RESULTS: Significantly more lesions were found in MnDPDP-enhanced T1-weighted SE and GRE images than in unenhanced images of the same sequences. More lesions were also found in these images compared with T2-weighted images at a level of marginal significance. More information was obtained from MnDPDP-enhanced images in 40 cases. Mild to moderate adverse events were experienced by 17% of the patients. CONCLUSION: MnDPDP-enhanced images can improve lesion detection in the liver and are helpful for lesion characterisation. To obtain optimal diagnostic information of liver lesions T2-weighted images are also valuable. MnDPDP is a safe contrast agent for MR imaging of liver lesions.

Adult↗
PubMed1997

MR imaging properties and pharmacokinetics of MnDPDP in healthy volunteers.

PURPOSE: Thirteen male volunteers were studied to evaluate the MR imaging properties and pharmacokinetics of 10 mM mangafodipir trisodium infusion (MnDPDP, Teslascan). MATERIAL AND METHODS: Doses of 5 and 10 mumol/kg b.w. were administered by bolus injection (< 1 min) to 5 subjects, and by infusion (20 min) to 8 subjects, with a 3-week wash-out between doses. Infusion subjects underwent MR imaging. RESULTS: At 1 h after infusion, the plasma concentration of Mn was reduced to approximately 15% of the maximum value. Fifteen to 20% of Mn was recovered in the urine, and 50-60% was recovered in the faeces. The rapid initial plasma clearance of Mn is consistent with both rapid tissue uptake and rapid renal elimination. Increases in signal intensity were apparent on T1-weighted images of the liver, pancreas, spleen, renal cortex and the renal medulla, but not in regions of the brain protected by an intact blood-brain barrier. Increases were seen in the choroid plexus and pituitary. Contrast-related adverse events, only flushing of moderate intensity, occurred in bolus injection subjects. CONCLUSION: At 5 and 10 mumol/kg, mangafodipir produces relatively long-lasting enhancement of several abdominal organs, including the liver, pancreas and kidney.

Adult↗
PubMed1996

Myocardial cell death in reperfused and nonreperfused myocardial infarctions. MR imaging with dysprosioum-DTPA-BMA in the pig.

PURPOSE: To investigate whether Dy-DTPA-BMA-enhanced MR imagining would permit identification of myocardial cell death, myocardial infarction was induced in 12 domestic pigs. MATERIAL AND METHODS: In 6 pigs with irreversible cell damage, Dy-DTPA-BMA (1.0 mmol/kg b.w.) was administered i.v. 70 min after coronary occlusion. In 6 other pigs, the infarctions were reperfused 80 min after the occlusion, followed by injection of Dy-DTPA-BMA after 30 min of reperfusion. In 4 additional pigs, the hearts were reperfused after 2 min of occlusion. All 16 pigs were sacrificed 10 min after the injection of Dy-DTPA-BMA. The hearts were excised and imaged with MR. RESULTS: Reversibly injured myocardium could not be distinguished from adjacent nonischaemic myocardium after the administration of Dy-DTPA-BMA. Reperfused, infarcted myocardium demonstrated a high signal intensity in the proton-density- and T2-weighted sequences, despite a 5-fold higher Dy concentration compared with both nonreperfused infarcted and nonischaemic myocardium. CONCLUSION: This lack of susceptibility effect in infarcted myocardium, due to a homogeneous distribution of Dy, indicates the usefulness of Dy as a marker of tissue viability.

Animals↗
PubMed1996

Double-contrast MR imaging of reperfused porcine myocardial infarction. An experimental study using Gd-DTAA and Dy-DTPA-BMA.

PURPOSE: Myocardial infarctions were induced in 12 pigs to investigate whether a double-contrast method, combining a positive and a negative MR contrast agent, could improve the visualization of reperfused myocardial infarctions. MATERIAL AND METHODS: All 12 pigs were subjected to 80 min of occlusion followed by reperfusion. In the double-contrast group (6 pigs), Gd-DTPA-BMA (0.3 mmol/kg b.w.) and Dy-DTPA-BMA (1.0 mmol/kg b.w.) were administered i.v. after 30 min of reperfusion. In the remaining 6 pigs, a single injection of Gd-DTPA-BMA (0.3 mmol/kg b.w.) was given after 30 min of reperfusion. All pigs were sacrificed 10 min post-contrast injection, corresponding to a reperfusion time of 40 min. The hearts were excised and imaged with MR. The concentrations of GD and Dy were measured in infarcted and nonischaemic myocardium using ICP-AES. RESULTS AND CONCLUSION: Contrast media concentrations were more than 4-fold higher in infarcted compared with nonischaemic myocardium. The infarctions were best shown on T1-weighted images, and there were no differences between the double and single contrast groups. In the T2-weighted images, the infarctions were significantly better visualized in the double-contrast group, due to a Dy-induced signal intensity loss in nonischaemic myocardium.

Animals↗
PubMed1995

Measurements of magnetic field variations in the human brain using a 3D-FT multiple gradient echo technique.

A magnetic resonance 3DFT multiple gradient-echo technique was used for measurements of the proton spectrum for each voxel in the measured slice. Water, fat, magnetic field and T2 distributions in the head of a normal volunteer and a patient with intracerebral hematoma were computed. Magnetic field variations caused by the head were calculated after correction for the static magnetic field inhomogeneity. Large local magnetic field variations up to 3 ppm were found in the human brain near interfaces between air or bone and brain tissues and 0.5 ppm between hematoma and brain tissue. Information about magnetic field variations could be useful for shimming procedures in vivo and for correcting artifacts in imaging and spectroscopy.

Aged↗
PubMed1995

Dy-DTPA-BMA as an indicator of tissue viability in MR imaging. An experimental study in the pig.

The aim of this study was to investigate whether dysprosium (Dy) induced signal intensity (SI) loss in infarcted tissue in MR imaging. Myocardial infarction was induced in 12 pigs and Dy-DTPA-BMA (1.0 mmol/kg b.w.) was administered i.v. to 6 pigs 4 hours after occlusion and allowed to accumulate in the infarctions for 2 hours. Dy was analysed by inductively coupled plasma atomic emission spectrometry in infarcted and non-ischaemic tissue samples. The remaining 6 pigs, not administered contrast medium, served as controls. The infarctions demonstrated a high SI in the proton density- and T2-weighted sequences in both groups (ex vivo), although the Dy-DTPA-BMA group demonstrated a 3-fold greater concentration of Dy in infarcted compared with non-ischaemic myocardium. The lack of SI loss after Dy accumulation indicates that susceptibility effects are minor or absent in infarcted myocardium.

Analysis of Variance↗
PubMed1995

MR imaging of double-contrast enhanced porcine myocardial infarction. Correlation with microdialysis.

MR imaging was performed to investigate whether Gd-DTPA-BMA-induced contrast enhancement of myocardial infarction is counteracted by Dy-DTPA-BMA. Myocardial infarction was induced in 5 pigs. Microdialysate probes were inserted in ischemic and nonischemic myocardium. Gd-DTPA-BMA (0.3 mmol/kg b.w.) and Dy-DTPA-BMA (1.0 mmol/kg b.w.) were administered i.v. 4 hours post occlusion. The microdialysate was collected every 10 min and measured for Gd and Dy using inductively coupled plasma atomic emission spectrometry. The pigs were sacrificed 2 hours after administration of contrast media. The concentration of both contrast agents was 3 times higher in infarcted myocardium than in nonischemic myocardium. The infarctions displayed high signal intensity in spin-echo sequences ex vivo. This lack of detectable susceptibility effects from Dy may be caused by loss of cell membrane integrity in infarcted tissue as shown by our microdialysate and biopsy data.

Analysis of Variance↗
PubMed1995

Combination of gadolinium and dysprosium chelates as a cellular integrity marker in MR imaging.

A combination of gadolinium (Gd) and dysprosium (Dy) chelates was investigated as a potential marker of cell-membrane integrity by means of a double-contrast effect in MR imaging. Blood samples with varying hematocrit (Hct) levels containing intact or lysed cells were used as model systems. With intact cells, the agents were assumed to be distributed solely extracellularly and the highest Hct studied (69%) was assumed to mimic the ratio of extracellular to intracellular water in tissue. The combined effect on image intensity of Gd (in a concentration corresponding to 0.2 mmol/kg b.w. in humans) and Dy (0.6 mmol/kg b.w.) applied simultaneously was a marked difference in signal intensity between samples with intact and lysed cells in both the T1- and T2-weighted spin-echo images with a corresponding increase in the contrast-to-noise ratio. This was the result of a T1 reduction caused by Gd with a negligible Dy susceptibility effect in areas with lysed cells. On the other hand, the Dy susceptibility effect (i.e. reduced apparent T2) dominated in areas with intact cells. Thus, the combination of Gd and Dy may serve as a marker of cell-membrane integrity in MR examinations.

Cell Membrane↗
PubMed1995

MR imaging of gadolinium-DTPA-BMA-enhanced reperfused and nonreperfused porcine myocardial infarction.

To investigate whether Gd-DTPA-BMA-enhanced MR imaging permits differentiation between reperfused and nonreperfused myocardial infarction, myocardial infarction was induced in 12 domestic pigs. In 6 pigs, Gd-DTPA-BMA, 0.3 mmol/kg b.w. was administered i.v. 60 min after the occlusion. In 6 other pigs, the infarctions were reperfused 80 min after the occlusion, followed by injection of Gd-DTPA-BMA after 20 min of reperfusion. Radiolabeled microspheres were used to confirm zero-flow during the occlusion period and reperfusion in the infarcted myocardium. All pigs were killed 20 min after injection of contrast medium, and the hearts were excised and imaged with MR. The Gd concentration was measured in infarcted and nonischemic myocardium by ICP-AES. In the reperfused hearts, the infarctions were strongly highlighted, corresponding to a 5-fold higher Gd concentration in infarcted vis-à-vis nonischemic myocardium. In the hearts subjected to occlusion without reperfusion, there was only a rim of enhancement in the peripheral part of the infarctions.

Animals↗
PubMed1994

Measurement of magnetic susceptibility and MR contrast agent concentration.

This paper describes an MR imaging method for determining magnetic susceptibility constants of solutions containing paramagnetic contrast agents. The method's validity is demonstrated on Gd(DTPA) and Dy(DTPA) water solutions. The method can be used for measurement of the volume magnetic susceptibility or concentration of contrast agents in biological tissues.

Animals↗