| 1. |
- Möller, Páll H., et al.
(författare)
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Interstitial laser thermotherapy in pig liver : Effect of inflow occlusion on extent of necrosis and ultrasound image
- 1997
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Ingår i: Hepato-Gastroenterology. - 0172-6390. ; 44:17, s. 1302-1311
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Tidskriftsartikel (refereegranskat)abstract
- Background/Aims: The aim was to investigate the effect of blood inflow occlusion on lesion size and ultrasonographic findings during interstitial laser thermotherapy of normal liver. Methodology: Pigs were treated with or without hepatic inflow occlusion at a laser power of 3 W or without inflow occlusion at 5 W (target temperature 43°C). The thermotherapy system consisted of an Nd:YAG laser and a temperature feedback circuit. Ultrasonography was performed immediately after treatment. Lesion size was determined using light microscopy including immunohistochemistry with bromodeoxyuridine. Results: Hyperechoic ultrasonographic changes were observed after treatment with inflow occlusion or when there was carbonization. If carbonization did not occur, unoccluded blood flow was associated with hypoechoic lesions. Following inflow occlusion, maximum lesion width 2 and 6 days after thermotherapy averaged 21.9 ± 1.3 and 20.2 ± 0.8 (means ± SEM) mm, respectively. This was larger than the corresponding values of 10.8 ± 0.8 and 11.1 ± 2.0 observed after treatment without inflow occlusion at 3 W (p < 0.01). Increase in laser power from 3 to 5 W in experiments without inflow occlusion produced early carbonization and a slight increase in lesion size that did not match that produced by inflow occlusion. Ultrasound gave a correct prediction of necrosis size after treatment with inflow occlusion but overestimated the necrosis when inflow occlusion was not used. Ultrasound was furthermore unable to predict size of necrosis in individual experiments. Conclusion: Blood flow has a major influence on lesion size in interstitial laser thermotherapy of the liver and affects ultrasonographic images. Also, it appears that intraoperative ultrasonography cannot monitor lesion size with an accuracy that is sufficient for clinical use.
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| 2. |
- Olsrud, Johan, et al.
(författare)
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MRI thermometry in phantoms by use of the proton resonance frequency shift method: application to interstitial laser thermotherapy
- 1998
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Ingår i: Physics in Medicine and Biology. - 1361-6560. ; 43:9, s. 2597-2613
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Tidskriftsartikel (refereegranskat)abstract
- In this work the temperature dependence of the proton resonance frequency was assessed in agarose gel with a high melting temperature (95 degrees C) and in porcine liver in vitro at temperatures relevant to thermotherapy (25-80 degrees C). Furthermore, an optically tissue-like agarose gel phantom was developed and evaluated for use in MRI. The phantom was used to visualize temperature distributions from a diffusing laser fibre by means of the proton resonance frequency shift method. An approximately linear relationship (0.0085 ppm degrees C(-1)) between proton resonance frequency shift and temperature change was found for agarose gel, whereas deviations from a linear relationship were observed for porcine liver. The optically tissue-like agarose gel allowed reliable MRI temperature monitoring, and the MR relaxation times (T1 and T2) and the optical properties were found to be independently alterable. Temperature distributions around a diffusing laser fibre, during irradiation and subsequent cooling, were assessed with high spatial resolution (voxel size = 4.3 mm3) and with random uncertainties ranging from 0.3 degrees C to 1.4 degrees C (1 SD) with a 40 s scan time.
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| 3. |
- Olsrud, Johan
(författare)
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Physical Aspects of Thermotherapy - A study of heat transport with a view to treatment optimisation
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Local treatment with the aim to destruct tissue by heating (thermotherapy) may in some cases be an alternative or complement to surgical methods, and has gained increased interest during the last decade. The major advantage of these, often minimally-invasive methods, is that the disease can be controlled with reduced treatment trauma and complications. The extent of thermal damage is a complex function of the physical properties of tissue, which influence the temperature distribution, and of the biological response to heat. In this thesis, methods of obtaining a well-controlled treatment have been studied from a physical point of view, with emphasis on interstitial laser-induced heating of tumours in the liver and intracavitary heating as a treatment for menorrhagia. Hepatic inflow occlusion, in combination with temperature-feedback control of the output power of the laser, resulted in well defined damaged volumes during interstitial laser thermotherapy in normal porcine liver. In addition, phantom experiments showed that the use of multiple diffusing laser fibres allows heating of clinically relevant tissue volumes in a single session. Methods for numerical simulation of heat transport were used to calculate the temperature distribution and the results agreed well with experiments. It was also found from numerical simulation that the influence of light transport on the damaged volume may be negligible in interstitial laser thermotherapy in human liver. Finite element analysis, disregarding light transport, was therefore proposed as a suitable method for 3D treatment planning. Finite element simulation was also used to model intracavitary heating of the uterus, with the purpose of providing an increased understanding of the influence of various treatment parameters on blood flow and on the depth of tissue damage. The thermal conductivity of human uterine tissue, which was used in these simulations, was measured. Furthermore, magnetic resonance imaging (MRI) was investigated as a method of non-invasive temperature monitoring, and an optically tissue-like phantom material, suitable for MRI, was developed. MRI thermometry in this material was shown to be an excellent method for characterisation of laser applicators and for verification of numerical calculations. Finally, a water-cooled laser applicator for the treatment of benign prostatic hyperplasia, allowing anatomically correct heating, was developed and evaluated ex-vivo. An increased understanding of the physical aspects of thermotherapy, aided by the methods and results presented in this thesis, constitutes a significant contribution to the performance of safe and efficacious treatment.
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| 4. |
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| 5. |
- Persson, Bertil R.R., et al.
(författare)
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Numerical calculations of temperature distribution resulting from intracavitary heating of the uterus
- 1998
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Ingår i: Gynaecological Endoscopy. - 0962-1091. ; 7:4, s. 203-209
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Tidskriftsartikel (refereegranskat)abstract
- Objective To estimate, using numerical calculations, the depth of tissue damage in the uterus following balloon thermal endometrial destruction. Design A parameter, therapeutic depth, was defined. This was the maximum depth into the uterine myometrium, from the uterine cavity, at which a predefined temperature was reached after a certain time and with a constant intracavitary temperature. Setting Departments of radiation physics and gynaecology at a university hospital. Results After 30 min of treatment with an intracavitary temperature of 75°C, the maximum depth into the myometrium at which the tissue had been exposed to a temperature of 55°C, when blood flow was neglected, was 8.9 mm. Taking into account blood flow the depth was 3.4 mm, and including the pressure because of the balloon it was 5.6 mm. With the inclusion of a local increase in blood flow because of elevated tissue temperature the depth was 4.4mm. Finally when damage to blood vessels due to coagulation was also accounted for, the depth was 5.2mm. The therapeutic depth decreased only slightly when the treatment time was shortened to 15 min. Conclusions Numerical calculations provide a basis for estimation of the optimal intracavitary temperature and treatment time when performing thermal endometrial destruction by means of a balloon catheter.
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