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Loyd, Dan
Publications (10 of 99) Show all publications
Diczfalusy, E., Dizdar (Dizdar Segrell), N., Zsigmond, P., Kullman, A., Loyd, D. & Wårdell, K. (2012). Simulations and visualizations for interpretation of brain microdialysis data during deep brain stimulation. In: IEEE Engineering in Medicine and Biology Society (EMBC), 2012: . Paper presented at 34th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC 2012), 28 August - 1 September 2012, San Diego, CA, USA (pp. 6438-6441). IEEE
Open this publication in new window or tab >>Simulations and visualizations for interpretation of brain microdialysis data during deep brain stimulation
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2012 (English)In: IEEE Engineering in Medicine and Biology Society (EMBC), 2012, IEEE , 2012, p. 6438-6441Conference paper, Published paper (Refereed)
Abstract [en]

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.

Place, publisher, year, edition, pages
IEEE, 2012
Series
IEEE Engineering in Medicine and Biology Society Conference Proceedings, ISSN 1557-170X
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-84275 (URN)10.1109/EMBC.2012.6347468 (DOI)000313296506155 ()23367403 (PubMedID)9781424441198 (ISBN)9781424441204 (ISBN)9781457717871 (ISBN)
Conference
34th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC 2012), 28 August - 1 September 2012, San Diego, CA, USA
Available from: 2012-10-03 Created: 2012-10-03 Last updated: 2018-01-12Bibliographically approved
Diczfalusy, E., Zsigmond, P., Dizdar (Dizdar Segrell), N., Kullman, A., Loyd, D. & Wårdell, K. (2011). A model for simulation and patient-specific visualization of the tissue volume of influence during brain microdialysis. Medical and Biological Engineering and Computing, 49(12), 1459-1469
Open this publication in new window or tab >>A model for simulation and patient-specific visualization of the tissue volume of influence during brain microdialysis
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2011 (English)In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 49, no 12, p. 1459-1469Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Springer Publishing Company, 2011
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-72911 (URN)10.1007/s11517-011-0841-0 (DOI)000297550600012 ()22081236 (PubMedID)
Available from: 2011-12-09 Created: 2011-12-09 Last updated: 2018-01-12Bibliographically approved
Nadali Najafabadi, H., Karlsson, M., Utriainen, E., Kinell, M. & Loyd, D. (2011). A Modified Correlation for Film Effectiveness Prediction of Cylindrical Holes at the Suction Side of A turbine Guide Vane. In: Proceedings of the 6th Baltic Heat Transfer Conference. Paper presented at The 6th Baltic Heat Transfer Conference, August 24-26, 2011, Tampere, Finland. Tampere Convention Bureau
Open this publication in new window or tab >>A Modified Correlation for Film Effectiveness Prediction of Cylindrical Holes at the Suction Side of A turbine Guide Vane
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2011 (English)In: Proceedings of the 6th Baltic Heat Transfer Conference, Tampere Convention Bureau , 2011Conference paper, Published paper (Other academic)
Place, publisher, year, edition, pages
Tampere Convention Bureau, 2011
Keywords
Correlation, Film Cooling, Gas Turbine
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-76909 (URN)
Conference
The 6th Baltic Heat Transfer Conference, August 24-26, 2011, Tampere, Finland
Available from: 2012-04-24 Created: 2012-04-24 Last updated: 2016-03-14
Renner, J., Ghavami Nejad, M., Nadali Najafabadi, H., Loyd, D., Skoog, P., Abrahamsson, D. & Karlsson, M. (2011). Conduction and convection heat transfer for aluminum ingot in preheating furnace. In: Reijo Karvinen & Matti Lindstedt (Ed.), Proceedings of 6th Baltic Heat Transfer Conference 2011. Paper presented at Proceedings of 6th Baltic Heat Transfer Conference 2011 – BHTC2011 August 24-26, 2011 in Tampere, Finland ISBN 978-.
Open this publication in new window or tab >>Conduction and convection heat transfer for aluminum ingot in preheating furnace
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2011 (English)In: Proceedings of 6th Baltic Heat Transfer Conference 2011 / [ed] Reijo Karvinen & Matti Lindstedt, 2011Conference paper, Published paper (Refereed)
Abstract [en]

Aluminium is a widely used material, which is found in a number of products e.g. thin aluminium bands that is the base material in many heat exchangers. Rolling processes are used to produce these thin aluminium bands, in order to get the right properties and to get the aluminium easier to roll, heat treatment is needed. This heat treatment of aluminium ingots prior to the rolling is in focus in this work, where computational fluid dynamics and computational heat transfer techniques is used to predict the heating process in a hot air pre-heating furnace. The used approach includes steady state computational fluid dynamics simulations combined with transient computational heat transfer simulations. The simulation results in form of spatial and temporal distributed aluminium ingot temperature was compared with temperature measurement in a thermocouple prepared ingot in the actual pre-heating furnace. Simulation results correspond well with the measurements and there are small differences. Results of the described simulation approach open the possibility to predict spatial and temporal temperature distribution in these kinds of pre-heating processes.

Keywords
CFD, CHT, Heat transfer
National Category
Fluid Mechanics and Acoustics Applied Mechanics
Identifiers
urn:nbn:se:liu:diva-73617 (URN)978-952-15-2639-8 (ISBN)978-952-15-2638-1 (ISBN)978-952-15-2640-4 (ISBN)
Conference
Proceedings of 6th Baltic Heat Transfer Conference 2011 – BHTC2011 August 24-26, 2011 in Tampere, Finland ISBN 978-
Available from: 2012-01-10 Created: 2012-01-10 Last updated: 2016-03-14
Renner, J., Loyd, D., Länne, T. & Karlsson, M. (2009). Is a flat inlet profile sufficient for WSS estimation in the aortic arch?. WSEAS Transactions on Fluid Mechanics, 4(4), 148-160
Open this publication in new window or tab >>Is a flat inlet profile sufficient for WSS estimation in the aortic arch?
2009 (English)In: WSEAS Transactions on Fluid Mechanics, ISSN 1790-5087, Vol. 4, no 4, p. 148-160Article in journal (Refereed) Published
Abstract [en]

Atherosclerosis is one of the main reasons for cardivascular disease which cause many deaths every year especially in the Western world. The development of atherosclerosis is strongly believed to be influenced by hemodynamic forces in the arteries e.g. wall shear stress (WSS). Estimations of WSS are therefore very important. By combining magnetic resonance imaging (MRI), image processing and computational fluid dynamic (CFD) simulations, it is possible to estimate subject specific WSS in the human arteries. The framework for performing such work includes i.e. using inlet boundary conditions which, however, will influence the final result i.e. the WSS distribution. This paper aims to investigate the influence of the inflow boundary condition in the human aorta with comparing two settings for the inflow: 1) subject specific inlet profile measured with MRI and 2) uniform profile with the subject specific mass flow rate. The analysis of WSS will be performed both on spatial location along the artery as well as on the temporal location in the cardiac cycle. Subject specific data have been used for geometry, inflow velocity profile and blood viscosity. The recommendation due to our findings from nine healthy subjects, is that a measured subject specific inlet boundary condition must be used in order to get a subject specific WSS distribution; the difference in WSS is 8-34% compared to using a mass-flow correct uniform profile. Temporal variations were clearly seen in the WSS differences due to the different inflow velocity profiles used. The lowest influence of the inlet boundary condition was found at peak velocity in the cardiac cycle. The aortic geometry does not form the flow in such extent (compared to the influence by inlet boundary condition) to obtain a more correct WSS distribution further away from the inlet at the systolic parts of the cardiac cycle. The shape of the vessel has only a significant influence at low velocities i.e. the diastolic phase of the cardiac cycle.

Keywords
Aorta; CFD; Inlet boundary condition; Subject specific; Uniform velocity profile; Wall shear stress
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-53002 (URN)
Available from: 2010-01-14 Created: 2010-01-14 Last updated: 2017-03-27Bibliographically approved
Johansson, J. D., Loyd, D., Wårdell, K. & Wren, J. (2007). Impact of cysts during radio frequency (RF) lesioning in deep brain structures: a simulation and in-vitro study. Journal of Neural Engineering, 4(2), 87-95
Open this publication in new window or tab >>Impact of cysts during radio frequency (RF) lesioning in deep brain structures: a simulation and in-vitro study
2007 (English)In: Journal of Neural Engineering, ISSN 1741-2560, E-ISSN 1741-2552, Vol. 4, no 2, p. 87-95Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2007
Keywords
Electrosurgery, RF ablation, Brain, Blood perfusion, Finite-element method
National Category
Other Medical Engineering
Identifiers
urn:nbn:se:liu:diva-13997 (URN)10.1088/1741-2560/4/2/009 (DOI)000247947300015 ()17409483 (PubMedID)2-s2.0-34247183212 (Scopus ID)
Note

Original Publication: Johannes D. Johansson, Dan Loyd, Karin Wårdell and Joakim Wren, Impact of cysts during radio frequency (RF) lesioning in deep brain structures: a simulation and in-vitro study, 2006, Journal of Neural Ingeneering, (4), 2, 87-95. http://dx.doi.org/10.1088/1741-2560/4/2/009 Copyright: Institute of Physics Publishing http://www.iop.org/

Available from: 2008-12-16 Created: 2008-12-16 Last updated: 2017-12-13Bibliographically approved
Wren, J., Loyd, D., Andersson, U. & Karlsson, R. (2007). Thermally induced convective movements in a standard experimental model for characterization of lesions prior to radiofrequency functional neurosurgery. Journal of Biomechanical Engineering, 129(1), 26-32
Open this publication in new window or tab >>Thermally induced convective movements in a standard experimental model for characterization of lesions prior to radiofrequency functional neurosurgery
2007 (English)In: Journal of Biomechanical Engineering, ISSN 0148-0731, E-ISSN 1528-8951, Vol. 129, no 1, p. 26-32Article in journal (Refereed) Published
Abstract [en]

Experimental exploration of equipment for stereotactic functional neurosurgery based on heating induced by radio-frequency current is most often carried out prior to surgery in order to secure a correct function of the equipment. The experiments are normally conducted in an experimental model including an albumin solution in which the treatment electrode is submerged, followed by a heating session during which a protein clot is generated around the electrode tip. The clot is believed to reflect the lesion generated in the brain during treatment. It is thereby presupposed that both the thermal and electric properties of the model are similar to brain tissue. This study investigates the presence of convective movements in the albumin solution using laser Doppler velocimetry. The result clearly shows that convective movements that depend on the time dependent heating characteristics of the equipment arise in the solution upon heating. The convective movements detected show a clear discrepancy compared with the in vivo situation that the experimental model tries to mimic, both the velocity (maximum velocity of about 5 mm/s) and mass flux are greater in this experimental setting. Furthermore the flow geometry is completely different since only a small fraction of the tissue surrounding the electrode in vivo consists of moving blood, whereas the entire surrounding given by the albumin solution in the experimental model is moving. Earlier investigations by our group (Eriksson et al., 1999, Med. Biol. Eng. Comput. 37, pp. 737-741, Wren, 2001, Ph.D. thesis, and Wren et al., 2001, Med. Biol. Eng. Comput. 39, pp. 255-262) indicate that the heat flux is an essential parameter for the lesion growth and final size, and that presence of convective movements in the model might substantially increase the heat flux. Thus, convective movements of the magnitude presented here will very likely underestimate the size of the brain lesion, a finding that definitely should be taken into consideration when using the model prior to patient treatment. Copyright © 2007 by ASME.

Keywords
Brain lesion, Convective movements, Experimental model, Functional neurosurgery, Radiofrequency current
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-50001 (URN)10.1115/1.2401180 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Svensson (Renner), J., Gårdhagen, R., Heiberg, E., Ebbers, T., Loyd, D., Länne, T. & Karlsson, M. (2006). Feasibility of Patient Specific Aortic Blood Flow CFD Simulation (1ed.). In: Rasmus Larsen, Mads Nielsen, Jon Sporring (Ed.), Rasmus Larsen, Mads Nielsen and Jon Sporring (Ed.), Medical Image Computing and Computer-Assisted Intervention – MICCAI 2006: 9th International Conference, Copenhagen, Denmark, October 1-6, 2006. Proceedings, Part I. Paper presented at The 9th MICCAI Conference, Copenhagen, Denmark, 1-6 October 2006 (pp. 257-263). Springer Berlin/Heidelberg, 4190
Open this publication in new window or tab >>Feasibility of Patient Specific Aortic Blood Flow CFD Simulation
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2006 (English)In: Medical Image Computing and Computer-Assisted Intervention – MICCAI 2006: 9th International Conference, Copenhagen, Denmark, October 1-6, 2006. Proceedings, Part I / [ed] Rasmus Larsen, Mads Nielsen and Jon Sporring, Springer Berlin/Heidelberg, 2006, 1, Vol. 4190, p. 257-263Conference paper, Published paper (Refereed)
Abstract [en]

Patient specific modelling of the blood flow through the human aorta is performed using computational fluid dynamics (CFD) and magnetic resonance imaging (MRI). Velocity patterns are compared between computer simulations and measurements. The workflow includes several steps: MRI measurement to obtain both geometry and velocity, an automatic levelset segmentation followed by meshing of the geometrical model and CFD setup to perform the simulations follwed by the actual simulations. The computational results agree well with the measured data.

Place, publisher, year, edition, pages
Springer Berlin/Heidelberg, 2006 Edition: 1
Series
Lecture Notes in Computer Science, ISSN 0302-9743, E-ISSN 1611-3349 ; 4190
National Category
Medical Image Processing
Identifiers
urn:nbn:se:liu:diva-36902 (URN)10.1007/11866565_32 (DOI)000241556300032 ()32988 (Local ID)3-5404-4707-5 (ISBN)978-3-540-44727-6 (ISBN)978-3-540-44707-8 (ISBN)32988 (Archive number)32988 (OAI)
Conference
The 9th MICCAI Conference, Copenhagen, Denmark, 1-6 October 2006
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2018-02-20Bibliographically approved
Johansson, J., Wren, J., Loyd, D., Eriksson, O. & Wårdell, K. (2006). Konvektiva flöden och deras termiska inverkan vid Radiofrekvenslesionering i hjärna. In: Medicinteknikdagarna 2006,2006: .
Open this publication in new window or tab >>Konvektiva flöden och deras termiska inverkan vid Radiofrekvenslesionering i hjärna
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2006 (English)In: Medicinteknikdagarna 2006,2006, 2006Conference paper, Published paper (Other academic)
Abstract [en]

   

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-36217 (URN)30572 (Local ID)30572 (Archive number)30572 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-02-17Bibliographically approved
Johansson, J. D., Eriksson, O., Wren, J., Loyd, D. & Wårdell, K. (2006). Radio-frequency lesioning in brain tissue with coagulation-dependent thermal conductivity: modelling, simulation and analysis of parameter influence and interaction. Medical and Biological Engineering and Computing, 44(9), 757-766
Open this publication in new window or tab >>Radio-frequency lesioning in brain tissue with coagulation-dependent thermal conductivity: modelling, simulation and analysis of parameter influence and interaction
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2006 (English)In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 44, no 9, p. 757-766Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Heidleberg: Springer, 2006
Keywords
Electrosurgery, RF ablation, Brain, Blood perfusion, Finite-element method
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-15926 (URN)10.1007/s11517-006-0098-1 (DOI)000240378700003 ()16941099 (PubMedID)2-s2.0-33748485613 (Scopus ID)
Note

The original publication is available at www.springerlink.com: Johannes D Johansson, Ola Eriksson, Joakim Wren, Dan Loyd and Karin Wårdell, Radio-frequency lesioning in brain tissue with coagulation-dependent thermal conductivity: modelling, simulation and analysis of parameter influence and interaction, 2006, Medical and Biological Engineering and Computing, (44), 9, 757-766. http://dx.doi.org/10.1007/s11517-006-0098-1 Copyright: Springer Science Business Media http://www.springerlink.com/

Available from: 2008-12-16 Created: 2008-12-16 Last updated: 2017-12-14Bibliographically approved
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