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Biomedical subjects

L Bergqvist

Publications and source records attributed to L Bergqvist.

At least 19 recordsLinked to original sources

Vanishing magnetic interactions in ferromagnetic thin films.

We have used element-specific hysteresis measurements, based on the x-ray magnetic circular dichroism technique, to investigate magnetic trilayer structures composed of Fe and Ni layers. Within a critical regime we have discovered a class of structures in which the exchange interaction, the mechanism responsible for the macroscopic magnetism, can become vanishingly small. The experimental observations are supported by first principles theory and are explained as arising from a cancellation of several competing magnetic interactions. Hence, we have discovered a system with a novel exchange interaction between magnetic layers in direct contact that replaces the conventional exchange interaction in ferromagnets.

Journal Article↗

Magnetic percolation in diluted magnetic semiconductors.

We demonstrate that the magnetic properties of diluted magnetic semiconductors are dominated by short ranged interatomic exchange interactions that have a strong directional dependence. By combining first principles calculations of interatomic exchange interactions with a classical Heisenberg model and Monte Carlo simulations, we reproduce the observed critical temperatures of a broad range of diluted magnetic semiconductors. We also show that agreement between theory and experiment is obtained only when the magnetic atoms are randomly positioned. This suggests that the ordering of diluted magnetic semiconductors is heavily influenced by magnetic percolation, and that the measured critical temperatures should be very sensitive to details in the sample preparation, in agreement with observations.

Journal Article↗

On the sharpness of the interfaces in metallic multilayers.

We show that the three most relevant magnetic properties (magnetic moment, critical temperature, and interlayer exchange coupling) of metallic multilayers can be reproduced with good accuracy by first principles theory, provided that the picture of atomically sharp interfaces is abandoned and one allows instead for both interface alloying and interface roughness. The interface of a metallic multilayer (exemplified by the Fe/V system) is demonstrated to, at best, have interdiffusion essentially over two to three atomic layers on each side of the interface. Our conclusions are the result of combining experimental work with theoretical modeling, and we argue that this approach is the best avenue to obtain accurate information about the interface quality of metallic multilayers.

Journal Article↗

Defect-induced magnetic structure in (Ga(1)-(x)Mn(x))As.

We show that magnetic structures involving partial disorder of local magnetic moments on the Mn atoms in (Ga(1)-(x)Mn(x))As lower the total energy, compared to the case of perfect ferromagnetic ordering, when As defects on the Ga sublattice are present. Such magnetic structures are found to be stable for a range of concentrations of As antisites, and this result accounts for the observed magnetic moments and critical temperatures in (Ga(1)-(x)Mn(x))As. We propose an explanation for the stabilization of the partially disordered magnetic structures and conclude that the magnetization and critical temperatures should increase substantially by reducing the number of As antisite defects.

Journal Article↗

Sentinel node in breast cancer--a Swedish pilot study of 75 patients.

OBJECTIVE: To find out if the sentinel node can be detected in sufficient numbers of women with breast cancer to be useful as a prognostic sign, whether it reflects that state of the entire axilla, and whether it detects micrometastases that would otherwise be missed. DESIGN: Prospective study. SETTING: 3 teaching hospitals, Sweden. SUBJECTS: 75 patients with breast cancer who were listed to have axillary dissection as well as resection of their tumour. INTERVENTIONS: Injection of 99Tc nanocolloid 0.4 ml and patent blue dye 1 ml around the tumour or under the skin above the tumour, followed by preoperative lymphoscintigraphy and then identification of the sentinel node during operation either because it had turned blue or with a gamma probe. Removal of the sentinel node and complete axillary dissection. MAIN OUTCOME MEASURES: Identification of the sentinel node and presence of metastatic nodes in the axilla. RESULTS: The sentinel node was identified in 69/75 (92%). It correctly predicted the state of the axilla in 66/69 (96%), and detected metastases in 24 of the 27 with invaded nodes in the axilla (89%). The false negative rate was 11%. In 14/27 with axillary metastases (52%) the sentinel node was the only involved node. In 3/24, metastases were detected by immunohistochemistry alone. CONCLUSION: Biopsy of the sentinel node predicted the presence or absence of axillary metastases with acceptable accuracy. However, before axillary node dissection is rejected in favour of sentinel node biopsy alone, large multicentre studies are needed to establish the true false negative rate.

Adult↗

Homeopathic Resistant Malaria.

Multiresistant Plasmodium falciparum malaria is a major threat to travelers to subSaharan Africa. However, even if chemoprophylaxis does not prevent clinical malaria in some individuals, it does lead to a reduction in the severity of the disease.1 In Sweden, we have recently seen five patients with malaria (three due to P. ovale and two due to P. falciparum) who have used homeopathic drugs for prophylaxis during visits to West Africa. We are concerned about this incidence and afraid that reduced confidence in modern medical malaria prophylaxis will encourage some individuals to try totally ineffective alternatives. Three women (57, 40, and 39 years old) visited Guinea Conacry in January 1995 as members of a group of 24 persons learning about African dances. The 57-year-old woman took mefloquine irregularly but vomited each time after intake. She also used Spenglersan M, which is a homeopathic drug that is administered (one drop daily in the bend of the arm) as malaria prophylaxis. The two other women used Spenglersan M only. They all fell ill with P. ovale malaria despite ongoing intake. Spenglersan M is said to contain both antigen from P. falciparum and antibodies against the parasite diluted to 1:1,000,000,000 concentration. The fourth case was a 26-year-old man who visited Ghana and Burkina Faso in October and November 1994. He used China D-6 for prophylaxis. This is a homeopathic preparation of the bark from the cinchona tree. Not even trace amounts of quinine were found in the tablets with a very sensitive high-performance liquid chromatographic method.2 Four days after returning from Africa he fell ill with P. falciparum malaria and received sulphadoxine-pyrimethamine treatment. After clinical relapse (RI), mefloquine was given and the patient was eventually cured. The fifth case was a 34-year-old woman admitted to hospital because of P. falciparum malaria after a visit to Guinea Conacry in January 1995. She had taken a homeopathic drug, Charaka comp 118, as prophylaxis. The drug is said to contain different extracts from herbs diluted 30 times. At first she refused to stay in hospital, but 2 days later she was readmitted and treated in the intensive care unit because of severe malaria with hypotonia and anemia. She had hyperparasitemia with 23% infected erythrocytes. Exchange transfusion was done, quinine was given, and the patient recovered without sequelae. The mortality is about 1% in people with P. falciparum infection.3 We therefore urge the readers to stand up against the dangerous use of homeopathic drugs and instead motivate travelers to use protective malaria prophylaxis.

Journal Article↗

Influence of dearterialization on distribution of absolute tumor blood flow between hepatic artery and portal vein.

BACKGROUND: Conflicting results have been obtained regarding blood flow distribution to liver tumors. The emphasis on portal vein perfusion has had a great impact on the design of treatment protocols. METHODS: Double microsphere technique with reference organ sampling was used for the measurement of hepatic artery and portal vein blood flow of an implanted liver tumor in 42 rats after permanent dearterialization and repeated dearterialization (2 hours/day) compared with untreated sham-operated controls. RESULTS: Portal venous blood flow constituted 16% of total tumor blood flow and slightly increased after permanent and repeat dearterializations, though the elevation was not statistically significant as compared with sham-treatment (P > 0.05). In another 3 groups, the treatment was extended to 10 days, and tumor blood flow was measured in central and peripheral parts separately. Arterial blood flow further decreased in tumor periphery and was still lower in the tumor center (P < 0.01 versus tumor periphery), and portal blood flow declined concomitantly to 4% of total tumor blood perfusion. However, no difference in portal blood flow between the tumor center and periphery could be demonstrated (P > 0.05). Furthermore, portal supply increased neither in tumor periphery nor in tumor center after both permanent and repeated dearterialization (P > 0.05). CONCLUSION: The authors' results showed that portal blood flow did contribute to tumor circulation, but made up only 16% of blood flow when tumors were small and declined to 4% of entire tumor blood supply when tumors became large. Portal perfusion also declined as tumors grew larger and did not compensate for the withdrawal of tumor arterial blood supply after dearterialization.

Animals↗

Rearterialization of liver tumors after various dearterialization procedures.

Repeat dearterializations seem to be a means to prevent collateral formation, which is partly responsible for the failure of hepatic artery ligation (HAL) or permanent dearterialization when used to treat liver tumors. In this study restoration of tumor blood flow was evaluated after various procedures: HAL (n = 12), permanent dearterialization (n = 18), repeated dearterializations for 2 hr/day (n = 12), and sham dearterialization (n = 12). Tumor blood flow was measured 10 days after sham dearterialization, permanent dearterialization, and repeated dearterializations for 2 hr in order to further illustrate the effect of prolonged dearterialization on tumor rearterialization. Hepatic and tumor arterial blood flow was measured using the reference organ method (NEN, 141Ce microspheres with diameter 15 microns). Our results showed that during a transient dearterialization blood flow decreased to 1% (0.01 +/- 0.01 ml/min/g) of the flow in the controls (0.82 +/- 0.10 ml/min/g) (P < 0.01). After HAL tumor blood flow recovered to initial levels after 48 hr (0.73 +/- 0.17 ml/min/g). Even in rats subjected to a permanent dearterialization blood flow was reestablished at Day 6 (0.59 +/- 0.21 ml/min/g). In contrast, after repeat daily 2-hr dearteralizations blood flow remained significantly very low during the 6th transient dearterialization (0.11 +/- 0.03 ml/min/g) compared with both sham-operation and HAL as well as permanent dearterialization (P < 0.01). During the 10th daily dearterialization tumor blood flow was still significantly low compared with both controls (P < 0.001) and permanent dearterialization (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Autocorrelation spectroscopy for particle sizing and stability tests of radiolabelled colloids.

In many nuclear medicine applications a well defined particle size and stability of administered colloids is of great importance. A fast and reliable sizing technique for routine quality control is therefore essential. This paper evaluates autocorrelation spectroscopy with an instrument capable of analysing several peaks simultaneously. A total of nine 99mTc-labelled colloids and one 99Y-labelled colloid were studied. The autocorrelation spectroscopy measurements were compared with the standard sizing technique of microfiltration. A good agreement between the sizing techniques was found for most of the colloids. The reproducibility of successive measurements was within +/- 12% and +/- 40% when using unimodal analysis and SDP analysis, respectively. Autocorrelation spectroscopy was found to be well suited for particle sizing and stability tests of radiolabelled colloids.

Colloids↗

Radiolabeled colloids and macromolecules in the lymphatic system.

The scintigraphic technique to investigate the lymphatic system is based on a good knowledge of basic criteria in order to correctly interpret the findings. This article penetrates these criteria, updates the present knowledge, and covers basic science work and clinical applications. The anatomy, physiology, and pathology of the lymphatic system are covered. Basic criteria for the radiopharmaceuticals to be used are described as well as their quality control. The principles for lymphoscintigraphy are described. The dosimetry in lymphoscintigraphy as well as radiation risk is estimated for different procedures. Experimental animal studies are summarized. Clinical applications cover staging procedures for breast cancer, malignant melanoma, pelvic neoplasms, and lymphoma. Lymphadenoectomy follow-up studies are also included. The use of lymphoscintigraphy in radiotherapy dose planning is described as well as lymphatic function studies in, e.g., edema and lymph transplantations.

Colloids↗

Hepatic reticuloendothelial function in rats with various portasystemic shunts and total liver arterialization.

Hepatic reticuloendothelial function was measured in 6 experimental groups of rats with various portasystemic shunts or total liver arterialization by computer calculation of the hepatic uptake rate of intravenously injected 99mTc-sulphur colloid. Marked reduction of the hepatic reticuloendothelial system (RES) function was found both 1 and 3 weeks after the construction of a mesentericocaval or conventional end-to-side portacaval shunt. Hepatic RES function was also lowered both 1 and 3 weeks after a modified portacaval shunt, but the reduction was much less pronounced. Total liver arterialization produced a similar mild reduction of hepatic RES function after 1 week; however, there was no longer any significant reduction after 3 weeks. This study concludes that total liver arterialization ameliorates the negative effect that portasystemic shunting has on hepatic RES function.

Animals↗

The "critical colloid dose" in studies of reticuloendothelial function.

The [99mTc]sulfur colloid distribution in rat organs was investigated after the administration of different amounts of colloid particles. Saturation of the liver and spleen was not observed. Blood clearance was significantly reduced 15 min after injection above approximately 3 X 10(9) particles per kg body weight. With an increasing number of injected particles, lung uptake increased and bone marrow uptake decreased. Microfiltration studies showed that the colloid is unaffected by dilution with saline but may be affected after incubation in normal rat plasma. We conclude that the distribution of [99Tc]sulfur colloid in organs varies with the number of injected particles and therefore, is not dependent upon the blood flow to the reticuloendothelial organs alone. The "critical colloid dose" may differ among the reticuloendothelial organs and cannot, therefore, be evaluated by blood clearance measurements alone. The considerable influence of the number of injected colloid particles on bone marrow uptake should also be recognized when carrying out dosimetric calculations.

Animals↗

Radiolabelled colloid uptake distribution and pulmonary contents and localization of lysosomal enzymes in cholestatic rats.

Studies of the activity uptake of radiolabelled 99mTc2S7 colloid in different tissues showed a moderately increased uptake in the lung 1 week and a greatly increased uptake 3 weeks after permanent bile duct occlusion. Three weeks after bile duct occlusion the activity uptake was also slightly increased in the spleen and moderately reduced in the liver. In pulmonary tissue of cholestatic rats, the levels of alkaline and acid phosphatase, beta-glucuronidase, and beta-hexosaminidase were determined after 6 weeks. The pulmonary contents of beta-glucuronidase was increased tenfold, and that of beta-hexosaminidase was increased fourfold in cholestasis. Histochemical investigation showed that the lysosomal enzymes were located in the macrophages, which in cholestasis were abundant in alveolar walls and inside alveoli. Macrophages were also frequently seen to engorge pulmonary veins.

Animals↗

Reticulo-endothelial function in rats with obstructive jaundice.

Reticulo-endothelial function was evaluated by measuring the biokinetics of a standardized 99mTc-sulphur colloid using scintillation camera technique in rats with biliary obstruction. There was no difference in the uptake of the colloid in the liver (K1) between sham operation and biliary obstruction at 1 week and 3 weeks. However, when corrected for changes in liver volume, the corrected colloidal uptake rate (cK1) of the liver was significantly decreased in 1 week's biliary obstruction (P less than 0.005 compared with sham operation) and 3 weeks' biliary obstruction (P less than 0.025 compared with 1 week obstruction). Colloidal uptake rate of the extrahepatic reticulo-endothelial system (K2) was significantly increased (P less than 0.005) in rats with 3 weeks' biliary obstruction. Activity distribution of 99mTc-sulphur colloid in 3 weeks' biliary obstruction was significantly decreased in both total organ basis and per gram basis (P less than 0.005). The results demonstrated a depression of RE activity of the liver in biliary obstruction.

Animals↗

Influence of a reticuloendothelial-suppressing agent on liver tumor growth in the rat.

Reticuloendothelial (RE) function was evaluated by measuring the biokinetics of a standardized 99Tcm-sulphur colloid. Methyl palmitate was administered intravenously on two consecutive days. A statistically significant reduction in the colloid uptake rate of the liver was registered after methyl palmitate administration. Histological examination revealed no signs of destruction of RE cells or microembolization. Inoculation of an experimental nitrosoguanidine-induced transplantable adenocarcinoma to the liver was performed in 16 rats one day after methyl palmitate administration and in 16 controls. Tumor size was significantly larger in methyl-palmitate-treated animals at 7 and 14 days after inoculation. Survival was significantly decreased in methyl-palmitate-treated rats. These rats showed signs of fatty vacuolization and necrosis of liver parenchyma earlier than controls. Analyses of beta-hexosaminidase and lactate dehydrogenase revealed no deviation of enzyme levels either before or after tumor inoculation. The results indicate that a temporary suppression of RE function at the time of tumor inoculation may influence subsequent tumor growth.

Adenocarcinoma↗

Lymphoscintigraphy in patients with malignant melanoma: a quantitative and qualitative evaluation of its usefulness.

Lymphoscintigraphy using 99mTcSb2S3 colloid was performed in 32 patients with malignant melanoma. Subcutaneous injections were made peritumorally in 20 patients and dorsopedally in 12 patients. Regional lymph node dissections were carried out on the following day in 16 patients and the resected lymph nodes were weighted, measured for radioactivity, and examined by light microscopy. Lymph flow to regional lymph nodes was shown in all but 2 patients. Twenty-nine of 239 lymph nodes contained metastases. Radioactivity was demonstrated in 17 of these nodes. In 5 of 11 patients with metastatic disease, the highest uptake was found in cancerous lymph nodes. The specific activity-uptake distribution in isolated ilio-inguinal lymph nodes after a dorsopedal injection was log-normal with a mean of 0.05%/g indicating a good saturation of colloid particles. This investigation concludes that the observed lymph flow directions in patients injected peritumorally are of value for the follow-up. Quantitative lymphoscintigraphy in patients with melanoma of the lower extremities is, however, of no value for excluding ilio-inguinal lymph node metastases.

Animals↗

Release of beta-hexosaminidase after administration of different agents affecting the reticuloendothelial system. An experimental study in rats.

Plasma levels of a lysosomal enzyme, beta-hexosaminidase (beta-N-acetylglucosaminidase, EC 3.2.1.30) were studied in Wistar rats after administration of 99mTc -sulfur colloid, 198Au colloid, gelatine (Haemaccel), alcohol, methylpalmitate and zymosan. The activity of beta-hexosaminidase was increased 10, 30 and 60 min after the zymosan injection. After 24 and 48 h, enzyme levels had returned to those at outset. The transient release of beta-hexosaminidase probably occurred only during the phagocytosis of zymosan which was evaluated by histological examination of lung, liver and spleen. After the injection of all other agents tested, no significant aberration of beta-hexosaminidase levels was seen. Activity distribution of the radio-labeled colloids revealed differences in organ uptake which were attributed to a difference in colloid particle size. Although the colloids tested have been used extensively for determination of reticuloendothelial function and histological studies suggest phagocytosis of the particles, their administration did not affect plasma beta-hexosaminidase levels. Since lysosomal enzymes are cleared from the blood predominantly by liver macrophages, the primary location of particle phagocytosis may explain the present findings.

Animals↗