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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The Utility of Manganese for Magnetic Resonance Imaging of Transient Myocardial Ischemia

Eriksson, Rolf January 2005 (has links)
<p>In order to improve the diagnosis of coronary artery disease, better methods for detection of myocardial perfusion defects would be useful. One of the methods used for myocardial perfusion evaluation today is magnetic resonance imaging. </p><p>This method could be improved if a contrast agent that induced long-lasting contrast enhancement in the myocardium could be developed. The paramagnetic manganese(II) ion has promising properties for meeting this need, since it enters cardiomyocytes through voltage-gated calcium channels and remains inside the cells for a long time after an intravenous injection. If these properties can be utilized, manganese-enhanced MRI has potential for detecting transient periods of ischemia in a manner similar to the conventional SPECT stress test.</p><p>To investigate the contrast-enhancing properties of the manganese(II) ion, a series of experiments was performed in pigs, using a manganese salt (MnCl<sub>2</sub>) and two manganese-based chelates (MnDPDP and MnHPTA) and measuring the longitudinal relaxation rates before and after contrast agent administration. This was done in normal pig myocardium at rest and during dobutamine-induced stress with several different doses of contrast agent, and in a model for coronary artery stenosis using MnCl<sub>2</sub> administered during dobutamine stress to determine whether transient ischemia could be detected with this contrast agent.</p><p>The results of these experiments showed that of the three contrast agents, MnCl<sub>2</sub> induces the greatest increase in ΔR1, followed by MnHPTA. Using MnCl<sub>2</sub> it was possible to produce images on which transient myocardial ischemia was visible, but only during the first 30 minutes after contrast agent injection.</p><p>The stenosis model is still far from the clinical situation and several complications, including the potential toxicity of the manganese(II) ion, remain to be overcome. However, the results from this model are promising for the future development of manganese- enhanced magnetic resonance imaging of transient myocardial ischemia.</p>
2

The Utility of Manganese for Magnetic Resonance Imaging of Transient Myocardial Ischemia

Eriksson, Rolf January 2005 (has links)
In order to improve the diagnosis of coronary artery disease, better methods for detection of myocardial perfusion defects would be useful. One of the methods used for myocardial perfusion evaluation today is magnetic resonance imaging. This method could be improved if a contrast agent that induced long-lasting contrast enhancement in the myocardium could be developed. The paramagnetic manganese(II) ion has promising properties for meeting this need, since it enters cardiomyocytes through voltage-gated calcium channels and remains inside the cells for a long time after an intravenous injection. If these properties can be utilized, manganese-enhanced MRI has potential for detecting transient periods of ischemia in a manner similar to the conventional SPECT stress test. To investigate the contrast-enhancing properties of the manganese(II) ion, a series of experiments was performed in pigs, using a manganese salt (MnCl2) and two manganese-based chelates (MnDPDP and MnHPTA) and measuring the longitudinal relaxation rates before and after contrast agent administration. This was done in normal pig myocardium at rest and during dobutamine-induced stress with several different doses of contrast agent, and in a model for coronary artery stenosis using MnCl2 administered during dobutamine stress to determine whether transient ischemia could be detected with this contrast agent. The results of these experiments showed that of the three contrast agents, MnCl2 induces the greatest increase in ΔR1, followed by MnHPTA. Using MnCl2 it was possible to produce images on which transient myocardial ischemia was visible, but only during the first 30 minutes after contrast agent injection. The stenosis model is still far from the clinical situation and several complications, including the potential toxicity of the manganese(II) ion, remain to be overcome. However, the results from this model are promising for the future development of manganese- enhanced magnetic resonance imaging of transient myocardial ischemia.
3

Den korta mötet i vården : Litteraturstudie med tonvikt på mötet med röntgensjuksköterskan

Jovicic, Senka January 2010 (has links)
<p>Bakgrund: Tidigare forskning visar att röntgensjuksköterskor som gör patienterna delaktiga genom att tillhandahålla information gör det möjligt för patienterna att förstå och själv ta aktiv roll i sin undersökning vilket leder till mindre oro. Med kunskaper och erfarenheter kunde röntgensjuksköterskorna stödja patienterna i samband med undersökningen vilket skapade förtroende och säkerställde trygg atmosfär. Dock kunde sjuksköterskorna även visa brist på känslomässigt engagemang samt bristande förmåga att kommunicera när de var upptagen med praktiska arbetsuppgifter.</p><p>Syfte: Syftet med studien var att beskriva patientens upplevelse av det korta mötet inom vården, med tanken att finna överförbarhet till möte med en röntgensjuksköterska.</p><p>Metod: Litteraturstudie med en kvalitativ ansats och med en kvalitativ innehållsanalys. Studien inkluderade tio vetenskapliga artiklar, som beskriver möten med vården på röntgen, akut- och operationsavdelning.</p><p>Resultat: Resultatet speglar patienternas upplevelser av korta möten, med tonvikten lagd på möten med röntgensjuksköterskor. I resultatet kan referens till källmaterial och dess kontext, såsom röntgen-, akut- och operationsavdelning, utläsas. Dataanalysen resulterade tre huvudkategorier: <em>att bli bekräftad</em>, <em>att uppleva</em> <em>trygghet</em> och <em>att känna</em> <em>maktlöshet</em>. I kategorierna finns totalt sju subkategorier inkluderade. Patienterna kände sig respekterade och bekräftade som individer när sjuksköterskan lyssnade på dem samt tog deras klagomål och önskemål på allvar. Patienterna upplevde trygghet när sjuksköterskan uttryckte intresse och gav dem relevant information. Patienterna upplevde däremot maktlöshet när det var svårt att få kontakt med sjuksköterskan samt göra sina åsikter hörda.</p><p>Slutsats: Studiens resultat visar att patienternas upplevelser av korta möten med röntgensjuksköterskor är allmängiltiga i den bemärkelsen att de kan sägas gälla för verksamheter såsom röntgen-, akut- och operationsavdelning. Dock är det viktigt att poängtera att varje möte med en patient är unikt, vilket innebär att varje patient ska bemötas på ett sätt som skapar förutsättningar för ett välbefinnande.</p>
4

Impact of Tissue Characteristics on Radio-Frequency Lesioning and Navigation in the Brain : Simulation, experimental and clinical studies

Johansson, Johannes January 2009 (has links)
Radio-Frequency (RF) lesioning, or RF ablation, is a method that uses high frequency currents for thermal coagulation of pathological tissue or signal pathways. The current is delivered from an electrode, which also contains a temperature sensor permitting control of the current at a desired target temperature. In the brain, RF lesioning can e.g. be used for treatment of severe chronic pain and movement disorders such as Parkinson’s disease. This thesis focuses on modelling and simulation with the aim of gaining better understanding and predictability of the lesioning process in the central brain.   The finite element method (FEM), together with experimental comparisons, was used to study the effects of electric and thermal conductivity, blood perfusion (Paper I), and cerebrospinal fluid (CSF) filled cysts (Paper II) on resulting lesion volume and shape in brain tissue. The influence of blood perfusion was modelled as an increase in thermal conductivity in non-coagulated tissue. This model gave smaller simulated lesions with increasing blood perfusion as heat was more efficiently conducted from the rim of the lesion. If the coagulation was not taken into consideration, the lesion became larger with increasing thermal conductivity instead, as the increase in conducted heat was compensated for through an increased power output in order to maintain the target temperature. Simulated lesions corresponded well to experimental in-vivo lesions. The electric conductivity in a homogeneous surrounding had little impact but this was not true for a heterogeneous surrounding. CSF has a much higher electric conductivity than brain tissue, which focused the current to the cyst if the electrode tip was in contact with both a cyst and brain tissue. Heating of CSF could also cause considerable convective flow and as a result a very efficient heat transfer. This affected both simulated and experimental lesion sizes and shapes. As a result both very large and very small lesions could be obtained depending on whether sufficient power was supplied or if the heating was mitigated over a large volume.   Clinical (Paper IV) and experimental (Paper III) measurements were used for investigation of changes in reflected light intensity from undamaged and coagulating brain tissue respectively. Monte Carlo (MC) simulations for light transport were made for comparison (Paper V). For the optical measurements, an RF electrode with adjacent optical fibres was used and this electrode was also modelled for the optical simulations. According to the MC simulations, coagulation should make grey matter lighter and white matter darker, while thalamic light grey should remain approximately the same. Experiments in ex-vivo porcine tissue gave an increase in reflected light intensity from grey matter at approximately 50 °C but the signal was very variable and the isotherm 60 °C gave better agreement between simulated and experimental lesions. No consistent decrease in reflected light intensity could be seen during coagulation of white matter. Clinical measurements were performed during the creation of 21 trajectories for deep brain stimulation electrodes. In agreement with the simulations, reflected light intensity was found to differentiate well between undamaged grey, light grey and white matter.   In conclusion, blood perfusion and CSF in particular may greatly affect the lesioning process and can be important to consider when planning surgery. Reflected light intensity seems unreliable for the detection of coagulation in light grey brain matter such as the thalamus. However, it seems very promising for navigation in the brain and for detection of coagulation in other tissue types such as muscle.
5

Power Doppler - Principles and Potential Clinical Applications

Nilsson, Anders January 2003 (has links)
<p>The purpose of this work was to: a) Determine whether the amount of colour in a power Doppler image is dependent on the angle between the examined vessel and the soundbeam and/or on the velocity of the flow within the vessel; b) Investigate if a dependency on flow velocity could be used for the detection of volume flow differences and c) Define clinical applications utilising the improved sensitivity to low flow of PD.</p><p>In the experimental studies (study I and II) a silicon tube in a water bath was insonated, the insonation angle and the volume flow changed and the resulting images stored, transferred to a personal computer and analysed with regard to the amount of colour present in the image.</p><p>In study III and IV the ability of power Doppler to depict low flow was used to produce a map of the perfusion in well perfused organs, lack of colour in all or part of an organ taken as a sign of decreased perfusion. 150 patients with a renal transplant (study III) and 15 patients with abdominal trauma (study IV) were examined; the detected areas of decreased perfusion were correlated to other imaging modalities, laboratory and clinical records in order to determine the underlying pathology.</p><p>In study V the power Doppler sensitivity was used to look for and describe small portosystemic shunts in 141 patients with liver cirrhoses and suspected portal hypertension.</p><p>The colour representation in a power Doppler image was found to be dependent both on the insonation angle and the flow velocity. Computer analysis of the images could detect differences in volume flow down to a change of 10 ml/min.</p><p>Of the 150 renal transplants, areas of decreased perfusion were found in 12, all of which could be given a plausible explanation (2 focal infections, 4 AV fistulae, 1 kinked segmental artery and 5 with problems related to an accessory artery).</p><p>Of the 20 organs (7 livers and 13 spleens) examined in the 15 trauma patients, 5 were found to have areas without colour, corresponding to localised haematomas. Using computed tomography as gold standard, ultrasound showed neither false positive nor false negative findings.</p><p>Of the 141 patients with cirrhosis, 40 had Doppler ultrasound findings of a shunt, consistent with a portal hypertension. 7 of these 40 shunts showed a typical “ball ” or “corkscrew ” pattern.</p><p>Conclusion: The colour in a power Doppler image is dependent not only on reflector concentration (as it should be in theory) but also on the insonation angle and the velocity of the flow. This can be used to detect relative changes in volume flow. Clinical applications of power Doppler include mapping of organ perfusion and the detection of small vessels. These applications are based on the high sensitivity of power Doppler.</p>
6

Percutaneous Nephrostomies : Planning for an Optimal Access, Complications, Follow-up and Outcome

Radecka, Eva January 2005 (has links)
<p>Percutaneous nephrostomy (PCN) is a well-established intervention performed to divert urine from the collecting system in ureteric obstruction or as a prelude to interventional procedures such as stent placement or percutaneous nephrolithotripsy (PCNL). The aim of this thesis is to enhance planning for an optimal insertion of PCN, investigate complications, long-term management, follow-up and outcome in patients with PCN treatment and to increase accuracy in CT-guided punctures.</p><p>To enhance planning for an optimal insertion of PCN prior to PCNL, biomodels from CT data were performed. Eight patients with complex urinary calculi were selected. Multislice CT of the kidney was performed and the CT data were transformed into a biomodel. The biomodels visualised unique structures before surgery, which aided the planning of endourological procedures.</p><p>PCNL is an essential procedure for treating complex urinary calculi. A subcostal approach is preferred to avoid laceration to the lung and pleura. However, a supracostal approach is often preferable, as it gives a better passage to the renal pelvis. The nature and frequency of complications after supra- versus subcostal punctures were studied in 85 patients treated with PCNL. In 63 patients, a subcostal track was established. In 22, a supracostal puncture was chosen. The main difference in preoperative complications was the higher number of patients in the supracostal group complaining of respiratory correlated pain (32%). In the subcostal group, this was (5%). </p><p>401 patients were reviewed retrospectively regarding underlying disease, subsequent management and complications of PCN treatment. The number of major complications was 4%. Minor complications were recorded in 38%, urinary tract infection being the most common. 151/401patients suffered from malignancy. 84/151 of the malignant patients died with the catheter. The median survival time of the patients with malignancies was 255 days and the median catheterisation time was 62 days. </p><p>In order to increase accuracy when performing CT guided punctures, a new puncture guide was evaluated. In 15/17 patients the puncture was successful on the first attempt. The benefits of the puncture guide were the artefact from the needle guide pointing at the target indicating the puncture path and the needle support enhancing an accurate puncture.</p>
7

The Utility of Ultrasmall Superparamagnetic Iron Oxide Contrast Agents for Cardiovascular Magnetic Resonance Imaging

Johansson, Lars January 2005 (has links)
<p>The purpose of this thesis was to investigate the utility of the Ultrasmall Superparamagnetic Iron Oxide Particle (USPIO), NC100150 Injection for assessment of macro- and microvascular morphology and function using magnetic resonance imaging. The feasibility of NC100150 Injection was tested for the following applications: Coronary angiography, Thrombus detection, Cardiac function, Myocardial perfusion, Assessment of myocardial blood volume and water exchange and finally assessment of endothelial integrity of the myocardium.</p><p>The test method included computer simulations, in vitro, animal and clinical experiments. The computer simulations included propagation of longitudinal magnetization in non-steady state acquisitions. Animal models used were coronary artery stenosis in pigs, thrombus formation in the jugular vein in pigs, normal pig myocardium and transplanted hearts in rats. A human study of patients with suspected coronary artery disease was also performed.</p><p>The results showed that angiography using an USPIO is less efficient in the coronary arteries than in the peripheral arteries. Direct targeting to thrombus using an USPIO is possible but will be limited by the spatial resolution. An USPIO will enhance gradient echo imaging of cardiac function. T2-weighted myocardial perfusion imaging is feasible as well as assessment of myocardial blood volume and endothelial integrity.</p><p>Due to physiological limitations and technical development the utility of NC100150 Injection for assessment of the macrovascular morphology is limited.However for the assessment of microvascular function, especially perfusion and permeability, NC100150 Injection may contribute to a successful implementation of these methods.</p>
8

Power Doppler - Principles and Potential Clinical Applications

Nilsson, Anders January 2003 (has links)
The purpose of this work was to: a) Determine whether the amount of colour in a power Doppler image is dependent on the angle between the examined vessel and the soundbeam and/or on the velocity of the flow within the vessel; b) Investigate if a dependency on flow velocity could be used for the detection of volume flow differences and c) Define clinical applications utilising the improved sensitivity to low flow of PD. In the experimental studies (study I and II) a silicon tube in a water bath was insonated, the insonation angle and the volume flow changed and the resulting images stored, transferred to a personal computer and analysed with regard to the amount of colour present in the image. In study III and IV the ability of power Doppler to depict low flow was used to produce a map of the perfusion in well perfused organs, lack of colour in all or part of an organ taken as a sign of decreased perfusion. 150 patients with a renal transplant (study III) and 15 patients with abdominal trauma (study IV) were examined; the detected areas of decreased perfusion were correlated to other imaging modalities, laboratory and clinical records in order to determine the underlying pathology. In study V the power Doppler sensitivity was used to look for and describe small portosystemic shunts in 141 patients with liver cirrhoses and suspected portal hypertension. The colour representation in a power Doppler image was found to be dependent both on the insonation angle and the flow velocity. Computer analysis of the images could detect differences in volume flow down to a change of 10 ml/min. Of the 150 renal transplants, areas of decreased perfusion were found in 12, all of which could be given a plausible explanation (2 focal infections, 4 AV fistulae, 1 kinked segmental artery and 5 with problems related to an accessory artery). Of the 20 organs (7 livers and 13 spleens) examined in the 15 trauma patients, 5 were found to have areas without colour, corresponding to localised haematomas. Using computed tomography as gold standard, ultrasound showed neither false positive nor false negative findings. Of the 141 patients with cirrhosis, 40 had Doppler ultrasound findings of a shunt, consistent with a portal hypertension. 7 of these 40 shunts showed a typical “ball ” or “corkscrew ” pattern. Conclusion: The colour in a power Doppler image is dependent not only on reflector concentration (as it should be in theory) but also on the insonation angle and the velocity of the flow. This can be used to detect relative changes in volume flow. Clinical applications of power Doppler include mapping of organ perfusion and the detection of small vessels. These applications are based on the high sensitivity of power Doppler.
9

Percutaneous Nephrostomies : Planning for an Optimal Access, Complications, Follow-up and Outcome

Radecka, Eva January 2005 (has links)
Percutaneous nephrostomy (PCN) is a well-established intervention performed to divert urine from the collecting system in ureteric obstruction or as a prelude to interventional procedures such as stent placement or percutaneous nephrolithotripsy (PCNL). The aim of this thesis is to enhance planning for an optimal insertion of PCN, investigate complications, long-term management, follow-up and outcome in patients with PCN treatment and to increase accuracy in CT-guided punctures. To enhance planning for an optimal insertion of PCN prior to PCNL, biomodels from CT data were performed. Eight patients with complex urinary calculi were selected. Multislice CT of the kidney was performed and the CT data were transformed into a biomodel. The biomodels visualised unique structures before surgery, which aided the planning of endourological procedures. PCNL is an essential procedure for treating complex urinary calculi. A subcostal approach is preferred to avoid laceration to the lung and pleura. However, a supracostal approach is often preferable, as it gives a better passage to the renal pelvis. The nature and frequency of complications after supra- versus subcostal punctures were studied in 85 patients treated with PCNL. In 63 patients, a subcostal track was established. In 22, a supracostal puncture was chosen. The main difference in preoperative complications was the higher number of patients in the supracostal group complaining of respiratory correlated pain (32%). In the subcostal group, this was (5%). 401 patients were reviewed retrospectively regarding underlying disease, subsequent management and complications of PCN treatment. The number of major complications was 4%. Minor complications were recorded in 38%, urinary tract infection being the most common. 151/401patients suffered from malignancy. 84/151 of the malignant patients died with the catheter. The median survival time of the patients with malignancies was 255 days and the median catheterisation time was 62 days. In order to increase accuracy when performing CT guided punctures, a new puncture guide was evaluated. In 15/17 patients the puncture was successful on the first attempt. The benefits of the puncture guide were the artefact from the needle guide pointing at the target indicating the puncture path and the needle support enhancing an accurate puncture.
10

The Utility of Ultrasmall Superparamagnetic Iron Oxide Contrast Agents for Cardiovascular Magnetic Resonance Imaging

Johansson, Lars January 2005 (has links)
The purpose of this thesis was to investigate the utility of the Ultrasmall Superparamagnetic Iron Oxide Particle (USPIO), NC100150 Injection for assessment of macro- and microvascular morphology and function using magnetic resonance imaging. The feasibility of NC100150 Injection was tested for the following applications: Coronary angiography, Thrombus detection, Cardiac function, Myocardial perfusion, Assessment of myocardial blood volume and water exchange and finally assessment of endothelial integrity of the myocardium. The test method included computer simulations, in vitro, animal and clinical experiments. The computer simulations included propagation of longitudinal magnetization in non-steady state acquisitions. Animal models used were coronary artery stenosis in pigs, thrombus formation in the jugular vein in pigs, normal pig myocardium and transplanted hearts in rats. A human study of patients with suspected coronary artery disease was also performed. The results showed that angiography using an USPIO is less efficient in the coronary arteries than in the peripheral arteries. Direct targeting to thrombus using an USPIO is possible but will be limited by the spatial resolution. An USPIO will enhance gradient echo imaging of cardiac function. T2-weighted myocardial perfusion imaging is feasible as well as assessment of myocardial blood volume and endothelial integrity. Due to physiological limitations and technical development the utility of NC100150 Injection for assessment of the macrovascular morphology is limited.However for the assessment of microvascular function, especially perfusion and permeability, NC100150 Injection may contribute to a successful implementation of these methods.

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