1.
2.
Björkman-Burtscher, Isabella
(författare)
Proton Magnetic Resonance Spectroscopy in Brain Tumors - Clinical Applications
1999
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
Aims: · to present a test phantom and test method for evaluation of proton magnetic resonance spectroscopy (1H-MRS) single volume localization techniques regarding signal contamination; · to describe the introduction of 1H-MRS in the daily routine of a standard MR-unit; · to evaluate the possibilities offered by 1H-MRS to improve preoperative diagnostic accuracy in patients scheduled for stereotactic biopsy of intracranial mass lesions; · to evaluate the possibilities offered by 1H-MRS to improve diagnostics and therapy control in patients with brain abscesses; · to test the hypothesis that 1H-MRS might be useful for differentiation of brain tumors, based on metabolic changes in tissue across brain lesions or surrounding tissue. Results and conclusions: · The test phantom and test method allow quality assessment with good reproducibility. Contamination values for the tested sequence types and sizes of volume of interest (VOI) differed between 0.7% and 13.8% in one dimension and between 7% and 19.1% in three dimensions. · Of the first 102 MRS measurements performed 85% were of high spectral quality. Main reasons for poor quality were mal-positioning of the VOI, susceptibility problems due to hemorrhage, and post operative changes. · Metabolite ratios of normal tissue differed from those representing stereotactic target points. No significant difference between metabolite ratios representing different histopathologic tumor types could be seen. MRS could improve diagnostic accuracy in differentiation between infiltrating and circumscribed brain lesions based on different spatial distribution of pathologic spectra across the lesion. · MR spectra from abscesses showed resonances, not found in other intracranial pathologies and vanishing under antibiotic treatment, and can therefore be used to differentiate abscesses from other ring-enhancing lesions and might be used for therapy control. · Metabolite ratios representing different components of brain lesions or adjacent tissue differed significantly for the following differential diagnoses: a) high-grade glioma versus metastasis: NAA/Cho and Cr/Cho in contrast-enhancing tissue, and NAA/Cho in tissue adjacent to and at one voxel distance to the lesion; b) meningeoma versus low-grade glioma and metastasis: NAA/Cho in contrast-enhancing tissue; c) low-grade glioma versus metastasis: NAA/Cr in tissue adjacent to the lesion. Our data support the hypothesis that proton MRS can be useful for the reliable differentiation between brain tumors, tending to infiltrate adjacent tissue, and circumscribed, non-infiltrating brain lesions.
3.
Boegård, Torsten
(författare)
Radiography and bone scintigraphy in osteoarthritis of the knee: comparison with MR imaging
1998
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
The aim was to compare radiography of the tibiofemoral joint (TFJ) and the patellofemoral joint (PFJ), as well as bone scinigraphy with MR imaging in middle-aged individuals with chronic knee pain in the format of a prospective study of knee osteoarthritis. Individuals aged 35-54 years with chronic knee pain were identified. The prevalence of chronic knee pain was 15% (279/2000). Within this group of people, both knees in 61 randomly chosen persons, were examined with plain weight-bearing radiograms of the TFJ, standing axial radiograms of the PFJ and bone scintigraphy. One knee (the most painful at inclusion in the study) in each person was examined with MR imaging on a 1.0 T imager. Assessment of the minimal joint space (MJS) width in the PA view of the TFJ in weight-bearing examinations should be performed with equal weight on both legs and in semiflexion. MJS of 3 mm in the TFJ and MJS of 5 mm in the PFJ are limits in diagnosing joint-space narrowing (JSN) in the TFJ and the PFJ, respectively. There is a high prevalence of meniscal abnormalities within the narrowed compartments of the TFJ in comparison with those that were narrowed. With the presence of marginal osteophytes in the TFJ there is a high prevalence of MR-detected cartilage defects in the same joint whether JSN (MJS < 3 mm) is present or not. No such relationship, independent of MJS, was found between marginal osteophytes and cartilage defects in the PFJ. The agreement between increased bone uptake and MR-detected subchondral lesion was good. The agreement between increased bone uptake and MR-detected osteophytes or cartilage defects was in general poor. With the increased knowledge about interpreting weight-bearing PA radiograms of the TFJ and axial radiograms of the PFJ, these examinations will even in the future be valuable when evaluating knee pain. Further studies have to be done to evaluate if MR imaging has the same ability as bone scintigraphy to predict the progression of the OA process.
4.
Bornmyr, Siv
(författare)
Laser Doppler Flowmetry and Imaging: Methodological Studies
1998
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
Laser Doppler flowmetry (LDF) and laser Doppler imaging (LDI) are modern methods for non-invasive and continuous assessment of skin blood flow. The techniques are based on the phenomenon that monochromatic light transilluminating a perfused tissue is spectrally broadened owing to scattering by moving blood cells. In this study, methodological aspects of the two methods are presented. LDF was used in healthy subjects and in patients with peripheral arterial occlusive disease to determine the skin perfusion pressure by measuring the flow cessation external pressure (FCEP). With a normal ankle index, FCEP is lower than the ankle pressure and with a decreased ankle index, FCEP correlates with the ankle pressure. LDF and LDI were used in healthy subjects to investigate the mechanisms of skin blood flow regulation particularly related to the sympathetic nervous system, and to elucidate the interrelation between skin temperature and skin blood flow. We found that LDF and LDI can be used to monitor sympathetic vasoconstriction. The interrelation between skin temperature and skin blood flow as measured with the laser Doppler techniques is ambiguous. LDI was used to examine the pathophysiological background to cold intolerance experienced by patients with traumatic division of the ulnar artery. Although ligation of the ulnar artery causes reduced finger skin blood flow, cold intolerance cannot be attributed solely to alterations in blood flow. A clinical test based on LDI was developed for routine assessment of the sympathetic vasoconstrictor response (VAC). Healthy subjects as well as patients with sympathectomy due to hand hyperhidrosis underwent the test procedure. A VAC nomogram was constructed in relation to which the patients with sympathectomy showed a clearly attenuated response. Finally, LDI was combined with digital photography to facilitate the interpretation of blood flow profiles in relation to clinical signs, and the device proved to be of clinical value.
5.
Brockstedt, Sara
(författare)
Nuclear Magnetic Resonance for Diffusion Imaging Development and evaluation of spin-echo-based pulse sequences for in vivo studies of water self-diffusion
1998
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
The interest in diffusion imaging with nuclear magnetic resonance techniques has increased during the last few years. The main reason is the possibility of early diagnosis of acute ischaemic stroke, at a time when conventional MR techniques and computerised tomography fail. The purpose of this study was to develop and evaluate methods for the measurement of water self-diffusion in vivo using magnetic resonance imaging (MRI). The main objective was to design pulse sequences that allow quantification of the diffusion coefficient, and provide diffusion-weighted (DW) images of high quality. DW-MRI is highly sensitive to macroscopic motion, which causes severe image artifacts and makes quantification difficult. This problem was addressed through pulse sequence design and image post-processing techniques. The use of first-order motion-compensating diffusion-encoding gradients in combination with DW spin-echo (SE) imaging proved to increase image quality and accuracy in quantitative data. Further more, quantitative diffusion imaging was found to be possible with fast-SEs, a method that does not require any high-performance gradient systems. Using a segmented echo-planar imaging (SEPI) technique high-resolution DW-images and ADC maps were obtained, showing no proof of susceptibility artifacts or geometrical distortions, problems normally associated with EPI. Navigator-echo phase-corrections were found to reduce motion artifacts present in images obtained with SE, FSE and SEPI techniques. The use of electro-cardiographic triggering for DW-EPI was also evaluated, and found to be relevant in quantitative measurements. Assessment of the perfusion fraction in vivo from DW-images might be helpful in diagnosis and characterisation of acute stroke and can be performed whenever enough data are available. Finally, the performance of DW-SE and DW-EPI for diagnosis of ischaemic stroke in the acute phase was evaluated. DW-EPI and DW-SE in combination with ADC maps were compared with respect to diagnostic accuracy. It was found that although DW-SE methods suffer from limited diffusion sensitivity and limited numbers of slices, it can be used for diagnosis of acute stroke, but ADC maps are essential in discriminating between acute and chronic infarcts.
6.
Bäck, Sven
(författare)
Implementation of MRI gel dosimetry in radiation therapy
1998
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
Gel dosimetry was used together with magnetic resonance imaging (MRI) to measure three-dimensional absorbed dose distributions in radiation therapy. Two different dosimeters were studied: ferrous- and monomer gel, based on the principles of radiation-induced oxidation and polymerisation, respectively. Single clinical electron and photon beams were evaluated and gel dose distributions were mainly within 2% of conventional detector results. The ferrous-gel was also used for clinical proton beams. A decrease in signal per absorbed dose was found close to the end of the range of the protons (15-20%). This effect was explained as a linear energy transfer dependence, further supported with Monte Carlo simulations. A method for analysing and comparing data from treatment planning system (TPS) and gel measurements was developed. The method enables a new pixel by pixel evaluation, isodose comparison and dose volume histogram verification. Two standard clinical radiation therapy procedures were examined using the developed TPS verification method. The treatment regimes included several beams of different radiation qualities. The TPS calculated data were in very good agreement with the dose distribution measured by the ferrous-gel. However, in a beam abutment region, larger dose difference was found. Beam adjustment errors and a minor TPS underestimation of the lateral scatter contribution outside the primary electron beam may explain the discrepancy. The overall uncertainty in the ferrous-gel dose determination was considerably reduced using an optimised MRI acquisition protocol and a new MRI scanner. The relative dose uncertainty was found to be better than 3.3% for all dose levels (95% confidence level). Using the method developed for comparing measured gel data with calculated treatment plans, the gel dosimetry method was proven to be a useful tool for radiation treatment planning verification.
7.
Chen, Jianqing
(författare)
Radiolabeling and Biotinylation of Internalizing Monoclonal Antibody Chimeric BR96: Potential Use for Extracorporeal Immunoadsorption.
1997
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
In this thesis, methodology of radiolabeling and simultaneous biotinylation for internalizing monoclonal antibody (MAb) chimeric BR96 (chiBR96) have been investigated by using three element groups of potential therapeutic radionuclides iodine, indium and rhenium, and their different labeling methods. The biodistribution and kinetics of biotinylated and radiolabeled chiBR96 have been studied in colon carcinoma isografted rats. The potential use of ECIA, based on the biotin-avidin concept, has been evaluated and compared with the approach of avidin "chase" in the same animal tumor model with respect to an enhancement of tumor-to-normal tissue (T/N) activity ratio. In vivo stability and tumor targeting capacity of biotinylated 111In-chiBR96 using the chelate SCN-Bz-CHX-A-DTPA, have increased compared with two other chelates used in this study. Conjugate NSTBB has been successfully used for iodination of chiBR96 combined with biotinylation, in contrast to the combination with electrophilic labeling method
8.
Edin, Anders
(författare)
Interplay between soft and hard processes in quantum chromodynamics
1998
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
In QCD, the theory of strong interactions, hard processes with large momentum transfers can be calculated using perturbation theory, while soft processes with small momentum transfers are poorly understood. In this thesis, phenomenological models of soft and hard QCD processes are developed and tested.A new model is presented for the distribution of quarks and gluons in hadrons. They are derived from a spherically symmetric, Gaussian, distribution of the quark and gluon momenta in the hadron rest frame. The proton structure function F2 is calculated from the model and evolved using next-to-leading order QCD, resulting in a successful comparison-with deep inelastic scattering data.A unified description is given of the hadronic final states observed in deep inelastic electron-proton scattering at HERA, regarding both the large forward energy flow and the rapidity gap events with no particles in a large forward angular region. The model is based on perturbative QCD complemented with a new "soft colour interaction" mechanism which affects the hadronic final state, and provides a continuous description of the transition from diffractive to non-diffractive hard scattering.The model for soft colour interactions also describes the surprisingly high production rate of heavy quarkonia observed in proton-antiproton collisions at the Tevatron.
9.
Engström, Per
(författare)
Electropermeabilization in Experimental Tumour Treatment: Dosimetry and Tissue Effects
1999
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
Short, electric high-voltage pulses can be used to transiently increase the permeability of cell membranes without significant loss of cell viability. During this period of time, extracellular and normally non-permeant, molecules are accessed the cytoplasm and the cell nucleus. This technique is called electroporation or electropermeabilization (EP). EP has been employed in vivo to internalise anticancer agents (bleomycin and cisplatin) into solid tumours. A large number of animal studies and several independent clinical trials have proven this technique to be efficient in many cases. It has recently been reported that EP also can be used to achieve high transfection efficiency of genes and proteins into tissues (e.g. muscle, liver and tumours) in vivo. This thesis investigates techniques to determine the efficiency of in vivo electropermeabilization and to investigate and optimise parameters governing the treatment outcome. In Paper II, radiolabelled bleomycin (111In-BLMC) was internalised by EP into s.c. rat brain tumours and traced continuously with a gamma camera. In Paper III gamma camera measurements of radiolabelled DTPA was used to study the influence of various pulse parameters on the drug uptake in muscle tissue after EP. Paper IV describes a technique for instant measurements of the EP efficiency by impedance spectrometry. The conductivity change in skeletal muscle before and after EP was measured and correlated to concomitant 99mTc-DTPA measurements. The thesis also includes two studies of tumour treatment using EP. Paper V describes the antitumour effect of combined radiation and EP treatment, as well as observed detrimental effect on tumour vasculature after repeated EP treatment. In Paper VI, an adenocarcinoma implanted in rat liver was treated with bleomycin, internalised into the tumour by EP. A 92% cure rate with a pronounced anti-metastasising effect was observed for EP-bleomycin treated animals, which suggests a stimulation of the immune defence. Macrophages and CD8 positive lymphocytes were found in viable tumour of EP+bleomycin treated animals.
10.
Gunther Axelsson, Maria
(författare)
Production asymmetry of strange quarks in electron-positron annihilation at LEP
1998
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
The forward-backward asymmetry in the production of strange quarks in electron-positron annihilation has been measured at a centre-of-mass energy corresponding to the mass of the Z0 particle. The asymmetry at this energy is highly sensitive to the ratio between the vector and axial-vector couplings of the quark to the Z0 and to the value of the electroweak mixing angle sin2 θw. Together with the previously measured value of the forward-backward asymmetry of the bottom quark, the measurement provides a test of the important theoretical prediction that the couplings to the Z0 are universal for all down-type quarks.The analysis is based on 1.4 million hadronic Z0 decays recorded in 1994 with the DELPHI detector system at the LEP collider at CERN. The strange quarks are selected using high-momentum charged kaons identified by the Ring Imaging CHerenkov (RICH) detectors. The charged kaon momentum is used to evaluate the probability for an event to belong to one of six possible event classes. Five classes are determined by the flavour of the primary quark (up, down, charm, strange and bottom) and the sixth class contains misidentified particles. The forward-backward asymmetry is determined using a maximum-likelihood method. At the Z0 pole, the asymmetry is found to beAFB0, s = 0.105 ± 0,016(stat.) ± 0.0006(syst.)which is the most precise measurement available for the strange quark asymmetry. The result is consistent with the previously measured value of the asymmetry of, the bottom quark, and thus with the predicted universality of the down-type quark couplings to the Z0. The obtained asymmetry corresponds to an electroweak mixing angle sin2 θw = 0.2229 ± 0.0030.
