| 1. |
- Andersson, Roger, 1967-, et al.
(author)
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Cross-sectional changes in an asymmetric tube with bearing on non-invasive pressure measurements
- 2003
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In: Technology and Health Care. - 0928-7329 .- 1878-7401. ; 11:1, s. 11-20
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Journal article (peer-reviewed)abstract
- This study aims at investigating the radial dimensional changes, as a result of an applied intraluminal pressure for an elastic tube with non-uniform cross section. The study is related to a method for non-invasive pressure measurement using the extracorporeal tube as part of the sensor. The intended application is for monitoring of pressure in the blood and dialysate tubes during haemodialysis. The intention is to find a tube cross-section geometry that results in an expansion of the tube so that it is suitable to use as a component in a pressure sensor. The tube should have high radial compliance and expand in a well-defined manner to be able to transfer the intraluminal pressure to a transducer element sensing the radial force. Radial expansion was studied experimentally for tubes with different cross-section geometries. For small tube expansions the resolution in the experimental measurements was not sufficient to study the radial expansion. In this case, numerical simulation was performed. We conclude that a tube with essentially elliptic outer surface and circular inner surface, with a relation of 1:2 between the size of the thin and thick wall, results in a radial expansion upon application of pressure indicating that this tube is suitable for use as part of a sensor.
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| 2. |
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| 3. |
- Andersson, R, et al.
(author)
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Pressure sensed non-invasively directly on the extra corporeal bloodline tube
- 2001
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In: PROCEEDINGS OF THE 23RD ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY, VOLS 1-4. - 0780372115 ; , s. 3179-3181
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Conference paper (peer-reviewed)abstract
- To clinically measure blood pressure at extra corporeal bloodlines involves a hazard due to the infection risk and a risk for thrombosis formation. The aim was to design a non-invasive pressure sensor, measuring directly on a tube section. A modified tube cross-section was used to improve sensitivity. Using the developed sensing principle, a consistent relation (r=0.999) was obtained between pressure and output signal. The output was stable and an acceptable drift within the temperature-range. The method shows great promise for applications in monitoring of the dialysis process.
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| 4. |
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| 5. |
- Ask, Per, et al.
(author)
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Bio-acoustic signals from stenotic tube flow : state of the art and perspectives for future methodological development.
- 1995
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In: Medical and Biological Engineering and Computing. - 0140-0118 .- 1741-0444. ; 33:5, s. 669-675
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Journal article (peer-reviewed)abstract
- To study the degree of stenosis from the acoustic signal generated by the turbulent flow in a stenotic vessel, so-called phonoangiography was first suggested over 20 years ago. A reason for the limited use of the technique today may be that, in the early work, the theory of how to relate the spectrum of the acoustic signal to the degree of the stenosis was not clear. However, during the last decade, the theoretical basis for this and other biological tube flow applications has been clarified. Now there is also easy access to computers for frequency analysis. A further explanation for the limited diagnostic use of bio-acoustic techniques for tube flow is the strong competition from ultrasound Doppler techniques. In the future, however, applications may be expected in biological tube flow where the non-invasive, simple and inexpensive bio-acoustic techniques will have a definite role as a diagnostic method.
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| 6. |
- Ask, Per, 1950-, et al.
(author)
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Bioacoustic signals from stenotic tube flow
- 1995
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In: Medical & Biological Engineering & Computing. - : Springer. - 0140-0118 .- 1741-0444. ; 33, s. 669-675
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Journal article (peer-reviewed)
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| 7. |
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| 8. |
- Ask, Per, et al.
(author)
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THEORETICAL AND EXPERIMENTAL-ANALYSIS OF AORTIC COARCTATION
- 1989
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In: IMAGES OF THE TWENTY-FIRST CENTURY, PTS 1-6. ; , s. 103-103
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Conference paper (peer-reviewed)abstract
- Aortic coarctation, which could severely influence the haemodynamic conditions of the body, is discussed. A theory has been developed which relates the pressure drop over the coarctation to the flow. This theory indicates that the pressure drop across the actual coarctation is related to the flow squared. For the collateral flow the expected pressure drop is either linearly or quadratically related to the flow. Model experiments and patient data support the present theoretical model
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| 9. |
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| 10. |
- Barclay, Susan A, et al.
(author)
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The shape of the proximal isovelocity surface area varies with regurgitant orifice size and distance from orifice : computer simulation and model experiments with color M-mode technique.
- 1993
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In: Journal of the American Society of Echocardiography. - 0894-7317 .- 1097-6795. ; 6:4, s. 433-445
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Journal article (peer-reviewed)abstract
- The hemispheric proximal isovelocity surface area method for quantification of mitral regurgitant flow (i.e., Qc = 2 pi r2v), where 2 pi r2 is the surface area and v is the velocity at radius r, was investigated as distance from the orifice was increased. Computer simulations and steady flow model experiments were performed for orifices of 4, 6, and 8 mm. Flow rates derived from the centerline velocity and hemispheric assumption were compared with true flow rates. Proximal isovelocity surface area shape varied as distance from each orifice was increased and could only be approximated from the hemispheric equation when a certain distance was exceeded: > 7, > 10, and > 12 mm for the 4, 6, and 8 mm orifices, respectively. Prediction of relative error showed that the best radial zone at which to make measurements was 5 to 9, 6 to 14 and 7 to 17 mm for the 4, 6, and 8 mm orifices, respectively. Although effects of a nonhemispheric shape could be compensated for by use of a correction factor, a radius of 8 to 9 mm can be recommended without the use of a correction factor over all orifices studied if a deviation in calculated as compared with true flow of 15% is considered acceptable. These measurements therefore have implications for the technique in clinical practice.
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| 11. |
- Bech-Hanssen, O., et al.
(author)
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Net Pressure Gradients in Aortic Prosthetic Valves can be Estimated by Doppler
- 2003
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In: Journal of the American Society of Echocardiography. - 0894-7317 .- 1097-6795. ; 16:8, s. 858-866
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Journal article (peer-reviewed)abstract
- Background: In aortic prosthetic valves, both the Doppler-estimated gradients and orifice areas are misleading in the assessment of hemodynamic performance. The parameter of major interest is the net pressure gradient after pressure recovery (PR). We, therefore, investigated, in vitro, our ability to predict the net pressure gradient and applied the formulas in a representative patient population with 2 different valve designs. Methods: We studied the St Jude Medical (SJM) standard valve (size 19-27) and SJM Biocor (size 21-27) in an in vitro steady-flow model with simultaneous Doppler-estimated pressure and catheter pressure measurements. Using echocardiography, we also studied patients who received the SJM (n = 66) and SJM Biocor (n = 45). Results: In the SJM, we observed PR both within the prosthesis and aorta, whereas in the SJM Biocor, PR was only present in the aorta. We estimated the PR within the valve and within the aorta separately from echocardiographic in vitro data, combining a regression equation (valve) with an equation on the basis of fluid mechanics theory (aorta). The difference between estimated and catheter-obtained net gradients (mean ± SD) was 0.6 ± 1.6 mm Hg in the SJM and - 0.2 ± 1.9 mm Hg in the SJM Biocor. When these equations were applied in vivo, we found that PR had an overall value of 57 ± 7% of the peak Doppler gradient in the SJM and 33 ± 9% in the SJM Biocor. Conclusions: The in vitro results indicate that it is possible to predict the net pressure gradient by Doppler in bileaflet and stented biologic valves. Our data indicate that important PR is also present in stented biologic valves.
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| 12. |
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| 13. |
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| 14. |
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| 15. |
- Bolger, A F, et al.
(author)
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Understanding continuous-wave Doppler signal intensity as a measure of regurgitant severity.
- 1997
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In: Journal of the American Society of Echocardiography. - 0894-7317 .- 1097-6795. ; 10:6, s. 613-622
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Journal article (peer-reviewed)abstract
- Continuous-wave Doppler signal intensity is commonly expected to reflect the severity of mitral regurgitation. Physical principles predict that alignment of the imaging beam, flow velocity, and turbulence can also be important or even dominant determinants of continuous-wave Doppler signal intensity. The reliability of tracking regurgitant severity with continuous-wave Doppler signal intensity was assessed in vitro with varying volume, velocity, turbulence, and beam alignment. The conditions wherein continuous-wave Doppler signal intensity increased with regurgitant volume were specific but poorly predictable combinations of orifice size, flow volume, and perfect beam alignment. Under other conditions flow velocity and turbulence effects dominated, and continuous-wave Doppler signal intensity did not reflect changing regurgitant volume. Continuous-wave Doppler signal intensity-based impressions of regurgitant severity may be unreliable and even misleading under some circumstances.
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| 16. |
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| 17. |
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| 18. |
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| 19. |
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| 20. |
- Brandberg, Joakim, et al.
(author)
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Non-stationary flow through non-planar circular constrictions : application to mitral valve disease
-
Other publication (other academic/artistic)abstract
- Quantification of valvular malfunctions by means of noninvasive methods is presently far from perfect. Since valvular regurgitation is common, a simple and reliable method for quantitative assessment is desired. In this paper the proximal isovelocity surface area method, (PISA) was studied. Numerical simulations for non-stationary flow and non-planar circular geometries were compared with ultrasound measurements in an invitro model with the same geometry and similar flow characteristics. Three different valvular geometries were used: planar, reversed cone and funnel. In the numerical simulation special emphasis was given to the influence from the angle of the valvular leaflets on the proximal surface area. We found both numerically and experimentally that there is support to use the hemispherical velocity profile assumption for the geometries investigated except for the funnel case. Here the actual geometry at the funnel inlet should be considered instead of the half-sphere approximation.
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| 21. |
- Diczfalusy, Elin, et al.
(author)
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A model for simulation and patient-specific visualization of the tissue volume of influence during brain microdialysis
- 2011
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In: Medical and Biological Engineering and Computing. - : Springer Publishing Company. - 0140-0118 .- 1741-0444. ; 49:12, s. 1459-1469
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Journal article (peer-reviewed)abstract
- Microdialysis can be used in parallel to deep brain stimulation (DBS) to relate biochemical changes to the clinical outcome. The aim of the study was to use the finite element method to predict the tissue volume of influence (TVI(max)) and its cross-sectional radius (r (TVImax)) when using brain microdialysis, and visualize the TVI(max) in relation to patient anatomy. An equation based on Fick's law was used to simulate the TVI(max). Factorial design and regression analysis were used to investigate the impact of the diffusion coefficient, tortuosity and loss rate on the r (TVImax). A calf brain tissue experiment was performed to further evaluate these parameters. The model was implemented with pre-(MRI) and post-(CT) operative patient images for simulation of the TVI(max) for four patients undergoing microdialysis in parallel to DBS. Using physiologically relevant parameter values, the r (TVImax) for analytes with a diffusion coefficient D = 7.5 × 10(-6) cm(2)/s was estimated to 0.85 ± 0.25 mm. The simulations showed agreement with experimental data. Due to an implanted gold thread, the catheter positions were visible in the post-operative images. The TVI(max) was visualized for each catheter. The biochemical changes could thereby be related to their anatomical origin, facilitating interpretation of results.
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| 22. |
- Diczfalusy, Elin, et al.
(author)
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Simulations and visualizations for interpretation of brain microdialysis data during deep brain stimulation
- 2012
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In: IEEE Engineering in Medicine and Biology Society (EMBC), 2012. - : IEEE. - 9781424441198 - 9781424441204 - 9781457717871 ; , s. 6438-6441
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Conference paper (peer-reviewed)abstract
- Microdialysis of the basal ganglia was used in parallel to deep brain stimulation (DBS) for patients with Parkinson’s disease. The aim of this study was to patientspecifically simulate and visualize the maximum tissue volume of influence (TVImax) for each microdialysis catheter and the electric field generated around each DBS electrode. The finite element method (FEM) was used for the simulations. The method allowed mapping of the anatomical origin of the microdialysis data and the electric stimulation for each patient. It was seen that the sampling and stimulation targets differed among the patients, and the results will therefore be used in the future interpretation of the biochemical data.
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| 23. |
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| 24. |
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| 25. |
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| 26. |
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| 27. |
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| 28. |
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| 29. |
- Eidenvall, Lars, et al.
(author)
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Two-dimensional color Doppler flow velocity profiles can be time corrected with an external ECG-delay device.
- 1992
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In: Journal of the American Society of Echocardiography. - 0894-7317 .- 1097-6795. ; 5:4, s. 405-413
-
Journal article (peer-reviewed)abstract
- Although two-dimensional ultrasound color flow imaging is often considered to be a real-time technique, the acquisition time for two-dimensional color images may be up to 200 msec. Time correction is therefore necessary to obtain correct flow velocity profiles. We have developed a time-correction method in which a specially designed unit detects the QRS complex from the patient and creates a trig pulse that is delayed incrementally in relation to the QRS complex. This trig pulse controls the acquisition of the ultrasound images. A number of consecutively delayed images, with known incremental delay between the sweeps, can thus be stored in the memory of the echocardiograph and transferred digitally to a computer. The time-corrected flow velocity profile is obtained by interpolation of data from the time-delayed profiles. The system was evaluated in a Doppler string phantom test. With this technique it is possible to study time-corrected flow velocity profiles without the need to alter existing ultrasound Doppler equipment.
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| 30. |
- Engvall, Jan, et al.
(author)
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Coarctation of the aorta--a theoretical and experimental analysis of the effects of a centrally located arterial stenosis.
- 1991
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In: Medical and Biological Engineering and Computing. - 0140-0118 .- 1741-0444. ; 29:3, s. 291-296
-
Journal article (peer-reviewed)abstract
- Aortic coarctation is a local constriction of the aorta that may severely affect haemodynamics. It is therefore important to quantify these effects. Using Bernoulli's equation and the momentum theorem, the pressure drop is described including the pressure recovery distal to the coarctation and the effects of collateral flow; both laminar and turbulent. Assuming the coarctation and collaterals to be stiff, a quadratic relationship between flow and pressure drop is expected for flow through the coarctation and for turbulent collateral flow. For laminar collateral flow, a linear relationship is expected. The coarctation flow was studied in a model consisting of a rigid tube with local constriction, connected to a flooded-level tank, containing a 36 per cent by weight solution of sucrose, with a viscosity equivalent to that of blood at body temperature. The pressure drop across the constriction showed a quadratic relationship to flow in agreement with theoretical expectations. Pressure recovery in this model was very slight (0-4 mm Hg). Nine patients with aortic coarctation were catheterised. Cardiac output and pressure drop across the coarctation were measured at rest and during supine cycle exercise at two different workloads. The relationship between mean pressure drop and cardiac output tended to be either 'parabolic' or, in some cases, approximately linear, suggesting that the flow situation in aortic coarctation can be quantified by expressions that either linearly or quadratically relate pressure and flow.
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| 31. |
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| 32. |
- Eriksson, Ola, 1967-, et al.
(author)
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A comparison between in vitro studies of protein lesions generated by brain electrodes and finite element model simulations
- 1999
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In: Medical and Biological Engineering and Computing. - 0140-0118 .- 1741-0444. ; 37:6, s. 737-741
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Journal article (peer-reviewed)abstract
- The aim of this study was to develop a finite element model for simulation of the thermal characteristics of brain electrodes and to compare its performances with an in vitro experimental albumin model. Ten lesions were created in albumin using a monopolar electrode connected to a Leksell Neuro Generator and a computer-assisted video system was used to determine the size of the generated lesions. A finite element model was set up of the in vitro experiments using the same thermal properties. With a very simple heat source applied to the finite element model in the proximity of the upper part of the tip, a good agreement (no deviations in width and distance from tip but a deviation in length of −1.6 mm) with the in vitro experiments (width 4.6±0.1 mm and length 7.4±0.1 mm) was achieved when comparing the outline of the lesion. In addition, a gelatinous albumin-model was set up and compared to computer simulations resulting in deviations in width of −0.4 mm, length of −2.2 mm and distance from the tip of −0.1 mm. Hence, the utilisation of finite element model simulations may be a useful complement to in-vitro experiments.
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| 33. |
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| 34. |
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| 35. |
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| 36. |
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| 37. |
- Johansson, Johannes D., et al.
(author)
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Comparison between a detailed and a simplified finite element model of radio-frequency lesioning in the brain
- 2004
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In: 26th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, San Fransisco, USA. ; , s. 2510-2513
-
Conference paper (peer-reviewed)abstract
- A detailed and a simplified model of a lesioning electrode was made using the finite element method. 15 simulations of the lesioning procedure were performed for each model and the resulting lesion volumes were compared in order to investigate if the simplified model is adequate. The simplified model resulted in a very slight overestimation of the volume compared to the detailed model. It was thus concluded that the simplified model is adequate for simulations.
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| 38. |
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| 39. |
- Johansson, Johannes D., 1977-, et al.
(author)
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Impact of cysts during radio frequency (RF) lesioning in deep brain structures : a simulation and in-vitro study
- 2007
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In: Journal of Neural Engineering. - : Institute of Physics Publishing (IOPP). - 1741-2560 .- 1741-2552. ; 4:2, s. 87-95
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Journal article (peer-reviewed)abstract
- Radiofrequency lesioning of nuclei in the thalamus or the basal ganglia can be used to reduce symptoms caused by e.g. movement disorders such as Parkinson's disease. Enlarged cavities containing cerebrospinal fluid (CSF) are commonly present in the basal ganglia and tend to increase in size and number with age. Since the cavities have different electrical and thermal properties compared with brain tissue, it is likely that they can affect the lesioning process and thereby the treatment outcome. Computer simulations using the finite element method and in vitro experiments have been used to investigate the impact of cysts on lesions' size and shape. Simulations of the electric current and temperature distributions as well as convective movements have been conducted for various sizes, shapes and locations of the cysts as well as different target temperatures. Circulation of the CSF caused by the heating was found to spread heat effectively and the higher electric conductivity of the CSF increased heating of the cyst. These two effects were together able to greatly alter the resulting lesion size and shape when the cyst was in contact with the electrode tip. Similar results were obtained for the experiments.
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| 40. |
- Johansson, Johannes D, 1977-, et al.
(author)
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Radio-frequency lesioning in brain tissue with coagulation-dependent thermal conductivity : modelling, simulation and analysis of parameter influence and interaction
- 2006
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In: Medical and Biological Engineering and Computing. - Heidleberg : Springer. - 0140-0118 .- 1741-0444. ; 44:9, s. 757-766
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Journal article (peer-reviewed)abstract
- Radio-frequency brain lesioning is a method for reducing e.g. symptoms of movement disorders. A small electrode is used to thermally coagulate malfunctioning tissue. Influence on lesion size from thermal and electric conductivity of the tissue, microvascular perfusion and preset electrode temperature was investigated using a finite-element model. Perfusion was modelled as an increased thermal conductivity in non-coagulated tissue. The parameters were analysed using a 24-factorial design (n = 16) and quadratic regression analysis (n = 47). Increased thermal conductivity of the tissue increased lesion volume, while increased perfusion decreased it since coagulation creates a thermally insulating layer due to the cessation of blood perfusion. These effects were strengthened with increased preset temperature. The electric conductivity had negligible effect. Simulations were found realistic compared to in vivo experimental lesions.
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| 41. |
- Johansson, Johannes D., et al.
(author)
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Simulations of radio-frequency lesions with varying brain electrode dimensions
- 2005
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In: 13th Nordic Baltic conference biomedical engineering and medical physics, Umeå, Sweden. ; , s. 62-63
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Conference paper (peer-reviewed)abstract
- Radio-frequency (RF) lesioning in thebrain was simulated using the finite element method(FEM). Heating for 60 s with temperature control inorder to keep the tip at 80 °C was simulated. Length,L, (2 – 4 mm) and diameter, D, (0.5 – 2.5 mm) of theelectrode tip were varied and the resulting lesionvolumes were used to calculate a regression model:Lesion Volume = – 13.1D + 15.7L⋅D + 13.1D2 mm3.The results can be useful for electrode design andprediction of lesion size.
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| 42. |
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| 43. |
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| 44. |
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| 45. |
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| 46. |
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| 47. |
- Karlsson, M, et al.
(author)
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Computer simulation for improved assessment of mitral regurgitation.
- 1997
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In: COMPUTERS IN CARDIOLOGY 1997, VOL 24. - 0780344464 ; , s. 169-170
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Conference paper (peer-reviewed)abstract
- Since valvular regurgitation is one of the most common malfunctions of the heart the quantification of valvular regurgitation by means of non-invasive methods is desired. However existing methods for quantitative assessment is far from perfect. The aim of this paper is to study the proximal velocity field for non-stationary flow and non-planar geometries by computer simulation, which were performed using the FIDAP package to numerically solve the governing equations. A plexiglass in-vitro model similar to the computer model was used for comparison and the same results were obtained. We have found that it is possible to refine the PISA method and standardize flow calculations. Further improvements will hopefully create a tool for the echocardiographer that will facilitate evaluation and clinical applicability of the PISA approach.
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| 48. |
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| 49. |
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| 50. |
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