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  • 1.
    Alrifaiy, Ahmed
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Bitaraf, Nazanin
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Druzin, Michael
    Umeå universitet, Integrativ Medicinsk Biologi, Fysiologi.
    Lindahl, Olof
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Ramser, Kerstin
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Hypoxia on a chip: a novel approach for patch-clamp studies in a microfluidic system with full oxygen control2012In: World Congress on Medical Physics and Biomedical Engineering, May 26-31, 2012, Beijing, China / [ed] Mian Long, Berlin: Encyclopedia of Global Archaeology/Springer Verlag, 2012, p. 313-316Conference paper (Refereed)
    Abstract [en]

    Here a new approach to perform patch-clamp investigations under anoxic and normoxic conditions on nerve cells from Sprague Dawley rats is presented. A patch-clamp micropipette is integrated within a poly-methyl methacrylate (PMMA) based microchip giving optimal control over the oxygen content and the biochemical environment. Nerve cells were trapped by optical tweezers and steered towards the patch-clamp micropipette within the micro-channels. Several experiments were performed to show proof of principle. The oxygen content within the microfluidic chamber was measured to 0.5-1.5 %. The photo-induced effect of the optical tweezers on the nerve cells was investigated in an open Petri dish. The optical trapping did not influence measurements. The microfluidic system was further tested in patch-clamp experiments. This approach showed significant advantages regarding the tuning of the oxygen content and may be used in various electrophysiological investigations of single cells demanding optimal control of the surroundings.

  • 2.
    Alrifaiy, Ahmed
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Bitaraf, Nazanin
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Druzin, Michael
    Umeå universitet, Integrativ Medicinsk Biologi, Fysiologi.
    Lindahl, Olof
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Ramser, Kerstin
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Patch-clamp measurements on a chip with full control over the oxygen content2012In: Journal of Biochips & Tissue Chips, ISSN 2153-0777, Vol. 2, no 1, p. 1-5Article in journal (Refereed)
  • 3.
    Alrifaiy, Ahmed
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Bitaraf, Nazanin
    Lindahl, Olof
    Ramser, Kerstin
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Development of microfluidic system and optical tweezers for electrophysiological investigations of an individual cell2010In: Optical Trapping and Optical Micromanipulation VII: 1 - 5 August 2010, San Diego, California, United States ; [part of SPIE optics + photonics] / [ed] Kishan Dholakia; Gabriel C. Spalding, Bellingham, Wash: SPIE - International Society for Optical Engineering, 2010Conference paper (Refereed)
    Abstract [en]

    We present a new approach of combining Lab-on-a-chip technologies with optical manipulation technique for accurate investigations in the field of cell biology. A general concept was to develop and combine different methods to perform advanced electrophysiological investigations of an individual living cell under optimal control of the surrounding environment. The conventional patch clamp technique was customized by modifying the open system with a gas-tight multifunctional microfluidics system and optical trapping technique (optical tweezers).The system offers possibilities to measure the electrical signaling and activity of the neuron under optimum conditions of hypoxia and anoxia while the oxygenation state is controlled optically by means of a spectroscopic technique. A cellbased microfluidics system with an integrated patch clamp pipette was developed successfully. Selectively, an individual neuron is manipulated within the microchannels of the microfluidic system under a sufficient control of the environment. Experiments were performed to manipulate single yeast cell and red blood cell (RBC) optically through the microfluidics system toward an integrated patch clamp pipette. An absorption spectrum of a single RCB was recorded which showed that laser light did not impinge on the spectroscopic spectrum of light. This is promising for further development of a complete lab-on-a-chip system for patch clamp measurements.

  • 4.
    Alrifaiy, Ahmed
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Bitaraf, Nazanin
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Lindahl, Olof
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Ramser, Kerstin
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Ett mikroflödessystem för multipla undersökningar av enstaka biologiska celler under hypoxiska förhållanden2011Conference paper (Refereed)
    Abstract [sv]

    Introduktion: Syftet med studien är att studera enstaka nervcellers respons vid syrebrist i ett mikroflödessystem för att förstå nervcellens respons vid stroke. Målet med studien var att utveckla ett slutet mikroflödessystem som ger optimal kontroll av den omgivande miljön och samtidigt möjliggöra elektrofysiologiska undersökningar under kontrollerade syreförhållande. Material och metoder: Mikroflödescellen utvecklades för ett inverterat mikroskop, utrustad med en optisk pincett och optisk spektroskopi samt patch-clamp för elektrofysiologiska studier på en enstaka nervcell. Istället för att föra en pipett mot en cell i ett öppet system fångades en enskild cell optiskt i ett slutet mikroflödessystem och fördes mot en fixerad patch-clamp mikropipett. Cellen utsattes för olika syrehalter och övervakades av ett UV-Vis spektroskop medan cellens elektrofysiologiska aktivitet registreras med patch-clamp. Det slutna mikroflödessystemet med integrerad mikropipett, kopplades till ett pumpsystem för införandet av celler och buffert med olika kemiska egenskaper och syrehalter. I ett inverterat mikroskop integrerades optisk pincett, UV-Vis spektrometer och patch-clamp. Resultat och diskussion: För att pröva konceptet fångades och fördes en röd blodcell optiskt mot mikropipetten som befann sig på en fast position i mikroflödescellen. Cellens syrebindningstillstånd varierades genom att tillsätta syrefri eller syresatt buffert och registrerades med UV-Vis spektrometern. I ett vidare experiment manipulerades en nervcell optiskt i ett öppet system mot patch-clamp pipetten och elektrofysiologiska mätningar utfördes. Vi kunde verifiera att den optiska pincetten inte påverkade den elektrofysiologiska mätningen. För närvarandet utförs elektrofysiologiska mätningar i det slutna mikroflödessystemet för att se hur nervcellerna reagerar under varierande syrehalt. Genom mätningarna hoppas vi att få mer kunskap om försvarsmekanismerna som igångsätts av neuroner under syrefattiga förhållanden.

  • 5. Alrifaiy, Ahmed
    et al.
    Borg, Johan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Lindahl, Olof
    Ramser, Kerstin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    A lab-on-a-chip for hypoxic patch clamp measurements combined with optical tweezers and spectroscopy: first investigations of single biological cells2015In: Biomedical engineering online, ISSN 1475-925X, E-ISSN 1475-925X, Vol. 14, article id 36Article in journal (Refereed)
    Abstract [en]

    The response and the reaction of the brain system to hypoxia is a vital research subject that requires special instrumentation. With this research subject in focus, a new multifunctional lab-on-a-chip (LOC) system with control over the oxygen content for studies on biological cells was developed. The chip was designed to incorporate the patch clamp technique, optical tweezers and absorption spectroscopy. The performance of the LOC was tested by a series of experiments. The oxygen content within the channels of the LOC was monitored by an oxygen sensor and verified by simultaneously studying the oxygenation state of chicken red blood cells (RBCs) with absorption spectra. The chicken RBCs were manipulated optically and steered in three dimensions towards a patch-clamp micropipette in a closed microfluidic channel. The oxygen level within the channels could be changed from a normoxic value of 18% O 2 to an anoxic value of 0.0-0.5% O 2. A time series of 3 experiments were performed, showing that the spectral transfer from the oxygenated to the deoxygenated state occurred after about 227 ± 1 s and a fully developed deoxygenated spectrum was observed after 298 ± 1 s, a mean value of 3 experiments. The tightness of the chamber to oxygen diffusion was verified by stopping the flow into the channel system while continuously recording absorption spectra showing an unchanged deoxygenated state during 5400 ± 2 s. A transfer of the oxygenated absorption spectra was achieved after 426 ± 1 s when exposing the cell to normoxic buffer. This showed the long time viability of the investigated cells. Successful patching and sealing were established on a trapped RBC and the whole-cell access (Ra) and membrane (Rm) resistances were measured to be 5.033 ± 0.412 M Ω and 889.7 ± 1.74 M Ω respectively.

  • 6. Alrifaiy, Ahmed
    et al.
    Lindahl, Olof
    Ramser, Kerstin
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Ett mikroflödessystem med optisk pincett och UV- vis för studier på enskilda biologiska celler2010Conference paper (Other academic)
  • 7.
    Alrifaiy, Ahmed
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Lindahl, Olof
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Ramser, Kerstin
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Patch-clamp electrophysiological measurements on single cells under hypoxic conditions in microfluidic systems2012Conference paper (Refereed)
  • 8.
    Alrifaiy, Ahmed
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Lindahl, Olof
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Ramser, Kerstin
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Polymer-based microfluidic devices for pharmacy, biology and tissue engineering2012In: Polymers, ISSN 2073-4360, E-ISSN 2073-4360, Vol. 4, no 3, p. 1349-1398Article in journal (Refereed)
    Abstract [en]

    This paper reviews microfluidic technologies with emphasis on applications in the fields of pharmacy, biology, and tissue engineering. Design and fabrication of microfluidic systems are discussed with respect to specific biological concerns, such as biocompatibility and cell viability. Recent applications and developments on genetic analysis, cell culture, cell manipulation, biosensors, pathogen detection systems, diagnostic devices, high-throughput screening and biomaterial synthesis for tissue engineering are presented. The pros and cons of materials like polydimethylsiloxane (PDMS), polymethylmethacrylate (PMMA), polystyrene (PS), polycarbonate (PC), cyclic olefin copolymer (COC), glass, and silicon are discussed in terms of biocompatibility and fabrication aspects. Microfluidic devices are widely used in life sciences. Here, commercialization and research trends of microfluidics as new, easy to use, and cost-effective measurement tools at the cell/tissue level are critically reviewed.

  • 9. Bitaraf, Nazanin
    et al.
    Druzin, Mikhail
    Umeå University, Integrative Medical Biology, Physiology.
    Lindahl, Olof
    Ramser, Kerstin
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Elektrofysiologiska mätningar på MPN-neuroner under hypoxi: ett steg mot profylaktisk behandling av patienter i riskzonen för stroke2010In: Medicinteknikdagarana 2010, 2010Conference paper (Other academic)
  • 10.
    Candefjord, Stefan
    et al.
    Chalmers University of Technology.
    Murayama, Yoshinobu
    College of Engineering, Nihon University.
    Nyberg, Morgan
    Hallberg, Josef
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Ramser, Kerstin
    Ljungberg, Börje
    Umeå University, Department of Surgical and Perioperative Science, Urology and Andrology.
    Bergh, Anders
    Department of Medical Biosciences Pathology, Umeå University.
    Lindahl, Olof
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Combining scanning haptic microscopy and fibre optic Raman spectroscopy for tissue characterisation2012In: Journal of Medical Engineering & Technology, ISSN 0309-1902, E-ISSN 1464-522X, Vol. 36, no 6, p. 319-327Article in journal (Refereed)
    Abstract [en]

    The tactile resonance method (TRM) and Raman spectroscopy (RS) are promising for tissue characterisation in vivo. Our goal is to combine these techniques into one instrument, to use TRM for swift scanning, and RS for increasing the diagnostic power. The aim of this study was to determine the classification accuracy, using support vector machines, for measurements on porcine tissue and also produce preliminary data on human prostate tissue. This was done by developing a new experimental setup combining micro-scale TRM — scanning haptic microscopy (SHM) — for assessing stiffness on a micro-scale, with fibre optic RS measurements for assessing biochemical content. We compared the accuracy for using SHM alone versus SHM combined with RS, for different degrees of tissue homogeneity. The cross-validation classification accuracy for healthy porcine tissue types using SHM alone was 65–81%, and when RS was added it was increased to 81–87%. The accuracy for healthy and cancerous human tissue was 67–70% when only SHM was used, and increased to 72–77% for the combined measurements. This shows that the potential for swift and accurate classification of healthy and cancerous prostate tissue is high. This is promising for developing a tool for probing the surgical margins during prostate cancer surgery.

  • 11.
    Candefjord, Stefan
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Nyberg, Morgan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Jalkanen, Ville
    Umeå University. Department of Applied Physics and Electronics.
    Ramser, Kerstin
    Lindahl, Olof
    Combining fibre optic Raman spectroscopy and tactile resonance measurement for tissue characterization2010In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 21, no 12Article in journal (Refereed)
    Abstract [en]

    Tissue characterization is fundamental for identification of pathological conditions. Raman spectroscopy (RS) and tactile resonance measurement (TRM) are two promising techniques that measure biochemical content and stiffness, respectively. They have potential to complement the golden standard-–histological analysis. By combining RS and TRM, complementary information about tissue content can be obtained and specific drawbacks can be avoided. The aim of this study was to develop a multivariate approach to compare RS and TRM information. The approach was evaluated on measurements at the same points on porcine abdominal tissue. The measurement points were divided into five groups by multivariate analysis of the RS data. A regression analysis was performed and receiver operating characteristic (ROC) curves were used to compare the RS and TRM data. TRM identified one group efficiently (area under ROC curve 0.99). The RS data showed that the proportion of saturated fat was high in this group. The regression analysis showed that stiffness was mainly determined by the amount of fat and its composition. We concluded that RS provided additional, important information for tissue identification that was not provided by TRM alone. The results are promising for development of a method combining RS and TRM for intraoperative tissue characterization.

  • 12. Candefjord, Stefan
    et al.
    Nyberg, Morgan
    Jalkanen, Ville
    Umeå University. Department of Applied Physics and Electronics.
    Ramser, Kerstin
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Lindahl, Olof
    Evaluating the use of a Raman fiberoptic probe in conjunction with a resonance sensor for measuring porcine tissue in vitro2009In: World Congress on Medical Physics and Biomedical Engineering: September 7 - 12, 2009, Munich, Germany / [ed] Olaf Dössel; Wolfgang C. Schlegel, Berlin: Springer Science+Business Media B.V., 2009, Vol. 7, p. 414-417Conference paper (Refereed)
    Abstract [en]

    Prostate cancer is the most common form of cancer and the third leading cause of cancer-related death in European men. There is a need for new methods that can accurately localize and diagnose prostate cancer. In this study a new approach is presented: a combination of resonance sensor technology and Raman spectroscopy. Both methods have shown promising results for prostate cancer detection in vitro. The aim of this study was to evaluate the combined information from measurements with a Raman fiberoptic probe and a resonance sensor system. Pork belly tissue was used as a model system. A three-dimensional translation table was equipped with an in-house developed software, allowing measurements to be performed at the same point using two separate instruments. The Raman data was analyzed using principal component analysis and hierarchical clustering analysis. The spectra were divided into 5 distinct groups. The mean stiffness of each group was calculated from the resonance sensor measurements. One of the groups differed significantly (p < 0.05) from the others. A regression analysis, with the stiffness parameter as response variable and the principal component scores of the Raman data as the predictor variables, explained 67% of the total variability. The use of a smaller resonance sensor tip would probably increase the degree of correlation. In conclusion, Raman spectroscopy provides additional discriminatory power to the resonance sensor

  • 13. Candefjord, Stefan
    et al.
    Nyberg, Morgan
    Jalkanen, Ville
    Umeå universitet.
    Ramser, Kerstin
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Lindahl, Olof
    Kombinationsinstrument för detektering av prostatacancer: korrelation mellan resonanssensor och fiberoptisk Ramanprobe2009Conference paper (Other academic)
  • 14.
    Candefjord, Stefan
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Ramser, Kerstin
    Lindahl, Olof
    Effects of snap-freezing and laser illumination of tissue on near-infrared Raman spectra of porcine prostate tissue2008Conference paper (Other academic)
  • 15. Candefjord, Stefan
    et al.
    Ramser, Kerstin
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Lindahl, Olof
    Effects of snap-freezing and near-infrared laser illumination on porcine prostate tissue as measured by Raman spectroscopy2009In: The Analyst, ISSN 0003-2654, E-ISSN 1364-5528, Vol. 134, no 9, p. 1815-1821Article in journal (Refereed)
    Abstract [en]

    Most Raman spectroscopic studies on tissue are performed in vitro. To assure that the results are applicable to in vivo examinations, preparation protocols and measurement procedures of tissue for in vitro studies should preserve tissue characteristics close to the native state. This study had two aims. The first was to elucidate if photoinduced effects arise during 5 minutes' continuous illumination of tissue with an 830 nm laser at an irradiance of 3 × 1010 W/m2. The second was to investigate the effects of snap-freezing of porcine prostate tissue in liquid nitrogen and subsequent storage at -80 °C, by means of multivariate analysis. 830 nm laser illumination of the specified irradiance did not affect the Raman spectra. A decrease of the spectral background was observed, likely due to photobleaching of tissue fluorophores. Snap-freezing and subsequent storage at -80 °C gave rise to subtle but significant alterations in Raman spectra, most likely related to changes in the protein conformations

  • 16.
    Candefjord, Stefan
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Ramser, Kerstin
    Lindahl, Olof
    En ny metod för att lokalisera och diagnostisera prostatacancer2007In: Medicinteknikdagarna, 2007, p. 33-34Conference paper (Other academic)
  • 17.
    Candefjord, Stefan
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Ramser, Kerstin
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Lindahl, Olof
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Kombinationsinstrument för detektering av prostatacancer: mätningar på snitt av grisprostata med resonanssensor och fiberoptisk Ramanprobe2010Conference paper (Refereed)
  • 18. Candefjord, Stefan
    et al.
    Ramser, Kerstin
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Lindahl, Olof
    Technologies for localization and diagnosis of prostate cancer2009In: Journal of Medical Engineering & Technology, ISSN 0309-1902, E-ISSN 1464-522X, Vol. 33, no 8, p. 585-603Article in journal (Refereed)
    Abstract [en]

    The gold standard for detecting prostate cancer (PCa), systematic biopsy, lacks sensitivity as well as grading accuracy. PSA screening leads to over-treatment of many men, and it is unclear whether screening reduces PCa mortality. This review provides an understanding of the difficulties of localizing and diagnosing PCa. It summarizes recent developments of ultrasound (including elastography) and MRI, and discusses some alternative experimental techniques, such as resonance sensor technology and vibrational spectroscopy. A comparison between the different methods is presented. It is concluded that new ultrasound techniques are promising for targeted biopsy procedures, in order to detect more clinically significant cancers while reducing the number of cores. MRI advances are very promising, but MRI remains expensive and MR-guided biopsy is complex. Resonance sensor technology and vibrational spectroscopy have shown promising results in vitro. There is a need for large prospective multicentre trials that unambiguously prove the clinical benefits of these new techniques.

  • 19.
    Candefjord, Stefan
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Ramser, Kerstin
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Lindahl, Olof
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Towards new sensors for cancer detection in vivo, a handheld detector combining a bre-optic Raman probe and a resonance sensor2007Conference paper (Refereed)
  • 20.
    Damber, Jan-Erik
    et al.
    Umeå University, Department of Physiology.
    Bergh, Anders
    Umeå University, Department of Physiology.
    Fagrell, Bengt
    Danderyds sjukhus.
    Lindahl, Olof
    Rooth, Pål
    Umeå University, Department of Histology and Cell Biology.
    Testicular microcirculation in the rat studied by videophotometric capillaroscopy, fluorescence microscopy and laser Doppler flowmetry1986In: Acta Physiologica Scandinavica, ISSN 0001-6772, E-ISSN 1365-201X, Vol. 126, no 3, p. 371-6Article in journal (Refereed)
    Abstract [en]

    Testicular capillary blood flow was studied in rats using laser Doppler flowmetry, in vivo fluorescence microscopy and videophotometric capillaroscopy. All the methods revealed rhythmical oscillations in testicular microcirculation with a periodicity of 4-10 c.p.m. In arterioles, capillaries and small post-capillary vessels, periods of continuous blood flow alternated with periods of no or very low flow. No visible leakage of dextran-150 was observed from the testicular blood vessels. Four, 8 and 16 h after an s.c. injection of 200 IU hCG the blood flow was continuous and there was leakage of dextran-150 from the microvessels to the interstitial tissue. Twenty-four and 32 h after hCG the blood flow pattern was again rhythmical, and at 32 h there was no leakage of dextran-150. This suggests that hCG induces changes in blood flow and transvascular fluid exchange in the testis, perhaps by altering smooth muscle activity at the arteriolar-level.

  • 21.
    Damber, Jan-Erik
    et al.
    Umeå University, Department of Physiology.
    Lindahl, Olof
    Selstam, Gunnar
    Umeå University, Department of Physiology.
    Tenland, Torsten
    Umeå University, Department of Physiology.
    Rhythmical oscillations in rat testicular microcirculation as recorded by laser Doppler flowmetry1983In: Acta Physiologica Scandinavica, ISSN 0001-6772, E-ISSN 1365-201X, Vol. 118, no 2, p. 117-23Article in journal (Refereed)
    Abstract [en]

    We have earlier reported that local testicular blood flow, recorded by laser Doppler flowmetry, shows large oscillations with a frequency of 5-10 min-1. In the present study it is proposed that the recorded oscillations represent mainly local microvascular blood flow variations rather than variations in total testicular blood flow or tissue movements. The reasons for this are: (a) Blood flow simultaneously measured at two separate sites showed oscillations with different frequencies. (b) A local subcapsular injection of room-tempered saline under one probe site eradicated oscillations under that probe but not under another adjacent probe. (c) When the testicular capsule was split open, recordings of blood flow continued to show oscillations. (d) The amplitude of the oscillations was rather large (peak to peak value about 50% of mean flow value). No movements of the testicular surface were seen. A 20 min continuous infusion of 0.4 microgram/min noradrenaline did induce a decrease in plasma testosterone concentration, but did not change the mean blood flow. However, the oscillations nearly completely disappeared during the infusion period. The present study also shows that laser Doppler flowmetry is a versatile method and the rat testis provides a suitable organ in the study of the origin and functional importance of these oscillations

  • 22.
    Damber, Jan-Erik
    et al.
    Umeå University, Department of Physiology.
    Lindahl, Olof
    Selstam, Gunnar
    Umeå University, Department of Physiology.
    Tenland, Torsten
    Umeå University, Department of Physiology.
    Testicular blood flow measured with a laser Doppler flowmeter: acute effects of catecholamines.1982In: Acta Physiologica Scandinavica, ISSN 0001-6772, E-ISSN 1365-201X, Vol. 115, no 2, p. 209-15Article in journal (Refereed)
    Abstract [en]

    Laser Doppler flowmetry was used to continuously measure testicular blood flow in rats. The method was found applicable on surgically exposed testes. Regular oscillations in blood flow, with a periodicity of 8.6 +/- 0.7 cycles per minute (mean +/- SD), were observed in recordings from 22 to 23 rats. Clamping of the testicular artery reduced the blood flow signal to background values. Effects of catecholamines administered into the tail artery on testicular blood flow together with systemic effects on mean arterial blood pressure and heart rate were measured. It was found that noradrenaline as well as adrenaline caused a significant decrease in blood flow when 10 micrograms was injected. Only noradrenaline decreased the blood flow when 1 microgram was given. The large oscillations detected in the blood flow recordings disappeared quickly when 10 or 1 micrograms of both hormones was administered. It was concluded that catecholamines can exert rapid effects on testicular blood flow

  • 23.
    Eklund, Abders
    et al.
    Umeå University Hospital, Department of Biomedical Engineering.
    Bäcklund, Tomas
    Umeå University Hospital, Department of Biomedical Engineering.
    Lindahl, Olof
    Resonanssensor för bestämning av intraokulärt tryck1999In: Program & sammanfattningar. [56]: Stockholmsmässan, Älvsjö 30 nov - 2 dec 1999, Stockholm: Svenska läkaresällskapet , 1999, p. 243-Conference paper (Other academic)
  • 24.
    Eklund, Anders
    et al.
    Umeå University Hospital, Department of Biomedical Engineering.
    Bergh, Anders
    Umeå University Hospital, Department of Pathology.
    Lindahl, Olof
    A catheter tactile sensor for measuring hardness of soft tissue: measurement in a silicone model and in an in vitro human prostate model1999In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 37, no 5, p. 618-24Article in journal (Refereed)
    Abstract [en]

    Tissue hardness is related to tissue composition, and this is often changed by disease. It is therefore of interest to measure the hardness in an objective and non-invasive way. A tactile sensor based on a vibrating piezoelectric ceramic element in a feedback loop is described. When the sensor touches an object it produces a frequency shift related to the hardness of the object. The aim of this study was to develop an in vitro hardness measurement method using a catheter type version of the sensor. The method was evaluated in an established silicone tissue model and on human prostate tissue in vitro. A linear relationship was found with a high degree of explanation (R2 = 0.98) between a cone penetration hardness standard (DIN ISO 2137) applied to the silicone model and the corresponding frequency shift. The results from measurements on a human prostate tissue sample, fixed with formalin, showed that the relative hardness measured with the tactile sensor correlated (R = -0.96, p < 0.001, N = 60) with the proposed hardness related to the histological composition of the prostate tissue. The results indicated that hardness of prostate tissue, and maybe hardness of human tissue in general, can be expressed according to the cone penetration standard and that the hardness can be measured with this tactile sensory system. These findings hold the promise of further development of a non-invasive tool for hardness measurement in a clinical situation

  • 25.
    Eklund, Anders
    et al.
    Umeå University Hospital, Department of Biomedical Engineering.
    Bergh, Anders
    Umeå University Hospital, Department of Biomedical Engineering.
    Lindahl, Olof
    A resonator sensor for evaluation of prostate tissue composition and hardness1999In: Proceedings of the 11th Nordic-Baltic conference on biomedical engineering.: 6-10 June 1999, Tallin, Estonia, 1999, p. 181-182Conference paper (Other academic)
  • 26.
    Eklund, Anders
    et al.
    Umeå University Hospital, Department of Biomedical Engineering.
    Bergh, Anders
    Umeå University Hospital, Department of Biomedical Engineering.
    Lindahl, Olof
    Vibrationssensor för värdering av vävnadsmjukhet1998In: Program & sammanfattningar. [55]: 24-26 november 1998 i Göteborg, Stockholm: Svenska läkaresällskapet , 1998, p. 259-Conference paper (Other academic)
  • 27.
    Eklund, Anders
    et al.
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Bäcklund, Tomas
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Lindahl, Olof
    A resonator sensor for measurement of intraocular pressure: evaluation in an in vitro pig-eye model.2000In: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 21, no 3, p. 355-367Article in journal (Refereed)
    Abstract [en]

    Intraocular pressure (IOP) measurement is performed routinely at every eye clinic. High IOP, which can be a sign of glaucoma, can lead to degeneration of the retina and can cause blindness. In this study we developed a resonator sensor for IOP measurement based on an oscillator consisting of a piezoelectric element made of lead zirconate titanate, a flat contact piece of nylon and a feedback circuit. The aim of this study was to evaluate the new sensor's ability to determine lOP in an in vitro pig-eye model. Six eyes from four pigs were removed and fixed in agar. They were then pressurized by a saline column (10-35 cm H2O) through a cannula inserted into the vitreous chamber. The IOP was measured with the resonator sensor applied to cornea. An Alcon applanation pneumatonometer and a standard Viggo-Spectramed pressure sensor connected to the saline column were used as references. The IOP as measured with the resonator sensor correlated well with the pressure elicited by the saline column for individual eyes (r = 0.96-0.99, n = 60) and for all eyes (r = 0.92, n = 360). The correlation between the resonance sensor and the pneumatonometer was r = 0.92 (n = 360). The pneumatonometer also showed a good correlation with the saline column (r = 0.98, n = 360). We conclude that our in vitro pig-eye model made it possible to induce reproducible variation in IOP, and measurement of that pressure with the newly developed resonator sensor gave very promising results for development of a clinically applicable IOP tonometer with unique properties.

  • 28.
    Eklund, Anders
    et al.
    Umeå University Hospital, Department of Biomedical Engineering.
    Bäcklund, Tomas
    Umeå University Hospital, Department of Biomedical Engineering.
    Lindahl, Olof
    Resonator sensor for measurement of intraocular pressure2000In: World Congress on Medical Physics and Biomedical Engineering,: July 23-28, 2000, Chicago, USA, 2000Conference paper (Other academic)
  • 29.
    Eklund, Anders
    et al.
    Umeå University Hospital, Department of Biomedical Engineering.
    Bäcklund, Tomas
    Umeå University Hospital, Department of Biomedical Engineering.
    Lindahl, Olof
    Lindén, Christina
    Umeå University, Centre for Biomedical Engineering and Physics.
    Resonanssensor för bestämning av intraokulärt tryck2000In: Program & sammanfattningar. [57]: Svenska mässan, Göteborg, 29 november-1 december 2000, Stockholm: Svenska läkaresällskapet , 2000, p. 249-Conference paper (Other academic)
  • 30.
    Eklund, Anders
    et al.
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Hallberg, Per
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Lindén, Christina
    Umeå University, Department of Clinical Science, Ophthalmology.
    Bäcklund, Tomas
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Lindahl, Olof
    Evaluation of an applanation resonator sensor for intraocular pressure measurement in a clinical setting2004In: World Congress on Medical Physics and Biomedical Engineering, 2004Conference paper (Other academic)
  • 31.
    Eklund, Anders
    et al.
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Hallberg, Per
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Lindén, Christina
    Umeå University, Center for Biomedical Engineering and Physics.
    Lindahl, Olof
    An applanation resonator sensor for measuring intraocular pressure using combined continuous force and area measurement2003In: Investigative Ophthalmology and Visual Science, ISSN 0146-0404, E-ISSN 1552-5783, Vol. 44, no 7, p. 3017-24Article in journal (Refereed)
    Abstract [en]

    PURPOSE: For diagnostic purposes and for follow-up after treatment, it is important to have simple and reliable methods for measuring intraocular pressure (IOP). The purpose of this study was to develop a new applanation method for IOP measurement that uses combined continuous force and area measurement and to develop and evaluate an applanation resonator sensor (ARS) tonometer based on that method. METHODS: The tonometer was developed and evaluated in an in vitro porcine eye model, in which enucleated eyes were pressurized with a saline column. A model assuming that the applanation principle is valid over a certain interval of contact area was proposed. Continuous contact area was measured with a resonator sensor device, and contact force was measured with a force transducer, both mounted together in one probe. Reference IOP was measured in the vitreous chamber (IOP(VC)) with a standard fluid pressure transducer. RESULTS: An optimization algorithm determined the applanation interval that was optimal for calculating IOP(ARS). The corresponding time interval was 30 +/- 3 to 77 +/- 4 ms (mean +/- SD, n = 418) after initial contact. The proposed model showed a degree of explanation of R(2 [supi]) = 0.991 (n = 410, six eyes), corresponding to a correlation of r = 0.995 (n = 410) between IOP(ARS) and IOP(VC). The within-eyes precision (i.e., 95% confidence interval for the residuals between IOP(ARS) and IOP(VC)) was +/- 1.8 mm Hg (n = 410, six eyes). CONCLUSIONS: In this study, the ARS method for measuring IOP was evaluated in an in vitro porcine eye model and showed high precision. The ARS method is, to the authors' knowledge, the first to combine simultaneous, continuous sampling of both parameters included in the applanation principle: force and area. Consequently, there is a potential for reducing errors in clinical IOP tonometry.

  • 32.
    Eklund, Anders
    et al.
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Lindahl, Olof
    Umeå universitet.
    Method and device for determining the intraocular pressure, by measuring the changing of the frequency characteristicsPatent (Other (popular science, discussion, etc.))
    Abstract [en]

    The present invention relates to a method and a device for measuring the pressure p in an eye, the so-called intraocular pressure. The method includes a contact body with a known geometry being pressed against the eye with a gradually increasing contact force F and that when the area of deformation of the eye A can be determined, the pressure can be obtained from the relation P=F/A, whereby the frequency characteristic of a contact body associated with a sensor system oscillating in resonance is read, the contact body is pressed against the eye to form a new system oscillating in resonance, the contact force and frequency characteristic for the new system is read, and the change in frequency characteristic is calculated. In this way, the pressure of the eye can be determined since the sought deformation area A is a function of the change A(.function..sub.i ch ar!). The device has a contact body (4) for pressing against the eye (1) and a means (3) of determining the force with which the contact body is pressed against the eye, whereby the contact body (4) is part of a system oscillating in resonance, and the resonance system is connected to a means (9) for reading the frequency characteristic of the system.

  • 33.
    Eklund, Anders
    et al.
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Lindahl, Olof
    Umeå universitet.
    Metod och anordning för bestämning av det intraokulära trycket, med hjälp av förändringen av frekvenskarakteristikenPatent (Other (popular science, discussion, etc.))
  • 34.
    Eklund, Anders
    et al.
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Lindahl, Olof
    Umeå universitet.
    Metod och anordning för brestämning av det intraokulära trycket, med hjälp av förändringen av frekvenskaraktäristikenPatent (Other (popular science, discussion, etc.))
  • 35.
    Eklund, Anders
    et al.
    Umeå University Hospital, Department of Biomedical Engineering.
    Lindahl, Olof
    Bäcklund, Tomas
    Umeå University Hospital, Department of Biomedical Engineering.
    Omata, Sadao
    Nihon University.
    Development of catheter tactile sensor for detecting stiffness of inner organ using piezoelectric element1997In: World Congress on Medical Physics and Biomedical Engineering: Nice, France, 14.-19.09.1997, 1997, p. 1281-Conference paper (Other academic)
  • 36.
    Eklund, Anders
    et al.
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Lindén, Christina
    Umeå University, Department of Clinical Science, Ophthalmology.
    Bäcklund, Tomas
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Andersson, Britt M.
    Umeå University. Department of Applied Physics and Electronics.
    Lindahl, Olof
    Evaluation of applanation resonator sensors for intra-ocular pressure measurement: results from clinical and in vitro studies2003In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 41, no 2, p. 190-7Article in journal (Refereed)
    Abstract [en]

    Glaucoma is an eye disease that, in its most common form, is characterised by high intra-ocular pressure (IOP), reduced visual field and optic nerve damage. For diagnostic purposes and for follow-up after treatment, it is important to have simple and reliable methods for measuring IOP. Recently, an applanation resonator sensor (ARS) for measuring IOP was introduced and evaluated using an in vitro pig-eye model. In the present study, the first clinical evaluation of the same probe has been carried out, with experiments in vivo on human eyes. There was a low but significant correlation between IOP(ARS) and the IOP measured with a Goldmann applanation tonometer (r = 0.40, p = 0.001, n = 72). However, off-centre positioning of the sensor against the cornea caused a non-negligible source of error. The sensor probe was redesigned to have a spherical, instead of flat, contact surface against the eye and was evaluated in the in vitro model. The new probe showed reduced sensitivity to off-centre positioning, with a decrease in relative deviation from 89% to 11% (1 mm radius). For normalised data, linear regression between IOP(ARS) and direct IOP measurement in the vitreous chamber showed a correlation of r = 0.97 (p < 0.001, n = 108) and a standard deviation for the residuals of SD < or = 2.18 mm Hg (n = 108). It was concluded that a spherical contact surface should be preferred and that further development towards a clinical instrument should focus on probe design and signal analysis.

  • 37.
    Fröjse, Rolf
    et al.
    Umeå University Hospital, Department of Surgery.
    Amerlöv, Conny
    Umeå University Hospital, Department of Surgery.
    Hedberg, Bengt
    Umeå University Hospital, Department of Surgery.
    Häggström, Mats
    University Hospital of Umeå, Department of Biomedical Engineering.
    Bäcklund, Tomas
    University Hospital of Umeå, Department of Biomedical Engineering.
    Lindahl, Olof
    Ängquist, Karl-Axel
    Umeå University Hospital, Department of Surgery.
    A new method for continuous tonometric pCO2 measurement: in vitro studies1999In: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 20, no 2, p. 129-36Article in journal (Refereed)
    Abstract [en]

    The available methods for tonometric pCO2 measurement only provide the possibility of performing intermittent registrations. A new method allowing continuous tonometric pCO2 measurement has been developed and tested in an in vitro model. A standard tonometer for intestinal pCO2 measurement was modified to allow continuous perfusion of the balloon with physiological saline solution in a closed system. The pCO2 in the system was determined in a specially sructed measurement chamber with a TCM20 percutaneous pCO2 monitor. In this in vitro model the tonometer balloon was placed in a saline bath with a constant pCO2 concentration and the measurements from the closed circulating system were compared with those obtained from a standard tonometer placed in the same bath. In 8 and 24 h experiments the circulating system measured the pCO2 value as accurately and reliably as traditional tonometry. This study indicates that the new method makes continuous monitoring of pCO2 possible

  • 38.
    Fröjse, Rolf
    et al.
    Department of Surgical and Perioperative Science, Umeå University.
    Hedberg, Bengt
    Department of Surgical and Perioperative Science, Umeå University.
    Bäcklund, Tomas
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Lindahl, Olof
    Häggström, Mats
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Ängquist, Karl-Axel
    Department of Surgical and Perioperative Science, Umeå University.
    Amerlöv, Conny
    Department of Surgical and Perioperative Science, Umeå University.
    Validation of a novel method for continuous saline tonometry in a porcine model2001In: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 22, no 3, p. 453-60Article in journal (Refereed)
    Abstract [en]

    Only intermittent and semi-continuous tonometric measurement of gastric and intestinal pHi is possible with the equipment available today. Earlier we developed a system for continuous saline tonometry and tested it in vitro. To assess the in vivo reliability of this method for continuous gastrointestinal saline tonometry, a standard tonometer for measurement of intestinal pCO2 and corresponding pHi was modified to allow continuous perfusion of physiological saline in a closed system and tested in a porcine model. In 11 anaesthetized and haemodynamically stable pigs, two continuous tonometry balloons were inserted into the distal small bowel, and a standard tonometry balloon was used as reference. To test long-term function of the continuous tonometers the research protocol lasted for eight hours. The two continuous saline tonometers performed well, and after an equilibration time of three hours the mean pHi values were stable between 7.35 and 7.43 and between 7.32 and 7.39 respectively. The standard tonometer measured stable pHi values. These preliminary studies indicate that continuous saline tonometry performs well over eight hours with a small bias and a good precision

  • 39.
    Fröjse, Rolf
    et al.
    Umeå University Hospital, Department of Surgery.
    Hedberg, Bengt
    Umeå University. Department of Applied Physics and Electronics.
    Bäcklund, Tomas
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Lindahl, Olof
    Häggström, Mats
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Ängquist, Karl-Axel
    Umeå University Hospital, Department of Surgery.
    Arnerlöv, Conny
    Umeå University Hospital, Department of Surgery.
    Intestinal pHi studied with continuous saline tonometry during ischaemia and reperfusion in the pig2002In: European Journal of Vascular and Endovascular Surgery, ISSN 1078-5884, E-ISSN 1532-2165, Vol. 24, no 2, p. 150-55Article in journal (Refereed)
    Abstract [en]

    OBJECTIVE: To evaluate continuous saline tonometry for detection of progressive intestinal ischaemia and reperfusion in a porcine model. DESIGN: In eight anaesthetised pigs, small bowel mucosal pCO2 was recorded by means of two identical equipments for continuous saline tonometry and a standard tonometry balloon during ischaemia and reperfusion. RESULTS: Both systems of saline tonometry functioned stably during the four hour protocol ischaemia, although not significant until after 45 min for one of the tonometers. CONCLUSION: The equipment for continuous saline tonometry has a good reactivity, an accuracy comparable with standard tonometry

  • 40.
    Hallberg, Per
    et al.
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Bäcklund, Tomas
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Eklund, Anders
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Lindahl, Olof
    Kontinuerlig mätning av kraft och yta för bestämning av intraokulärt tryck2001In: Program & sammanfattningar, [58]: Svenska Läkaresällskapets riksstämma, Svenska läkaresällskapet , 2001, p. 256-Conference paper (Other academic)
  • 41.
    Hallberg, Per
    et al.
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Eklund, Anders
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Bäcklund, Tomas
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Lindahl, Olof
    Lindén, Christina
    Umeå University, Department of Clinical Science, Ophthalmology.
    Applanation resonator sensors: a new technique for measuring intraocular pressure2003In: EVER 2003: European Association for Vision and Eye Research, October 8-11, 2003, Alicante, Spain : abstracts / [ed] J. Jost, S. Karger, 2003Conference paper (Other academic)
  • 42.
    Hallberg, Per
    et al.
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Eklund, Anders
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Santala, Kenneth
    Umeå University, Department of Clinical Science, Ophthalmology.
    Koskela, Timo
    Koskela Eye Clinic, Umeå.
    Lindahl, Olof
    Lindén, Christina
    Umeå University, Department of Clinical Science, Ophthalmology.
    Underestimation of intraocular pressure after photorefractive keratectomy: a biomechanical analysis2006In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 44, no 8, p. 609-18Article in journal (Refereed)
    Abstract [en]

    Excimer laser surgery, to correct corneal refraction, induces changes in corneal thickness and curvature. Both factors can cause measurement errors when determining intraocular pressure (IOP). This study evaluates effects of photorefractive keratectomy (PRK) on IOP measurements, using Goldmann applanation tonometry (GAT) and Applanation resonance tonometry (ART), in an in vitro model. Six porcine eyes was enucleated and pressurised to a constant IOP=30 mmHg. After removal of the epithelium, the eyes were PRK-treated for a total of 25 dioptres. The measured IOP decreased 13.2 mmHg for GAT and 9.0 mmHg for ART. The total underestimation by GAT was larger than for ART, and a part of the ART underestimation (3.5 mmHg) was assigned to sensitivity to the change in corneal surface structure resulting from the removal of epithelium. The flat contact probe of GAT, as compared with the convex tip of ART, provided explanation for the difference in IOP measurement error after PRK.

  • 43.
    Hallberg, Per
    et al.
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Lindén, Christina
    Umeå University, Department of Clinical Science, Ophthalmology.
    Lindahl, Olof
    Bäcklund, Tomas
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Eklund, Anders
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Applanation resonance tonometry for intraocular pressure in humans2004In: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 25, no 4, p. 1053-65Article in journal (Refereed)
    Abstract [en]

    Glaucoma is a group of diseases associated with optic nerve damage and loss of visual field. The aetiology is not completely understood, but one of the major risk factors is elevated intraocular pressure (IOP). Reliable methods for measuring the IOP are therefore important. The aim of the study was to investigate the ability of the applanation resonance tonometry (ART) system, based on continuous force and area recording, to measure IOP in humans. Both the phase of initial indentation (IOPIndentation) and the phase when the sensor was removed (IOPRemoval) from the cornea were analysed. The Goldmann applanation tonometry (GAT) was used as reference method. The study included 24 healthy volunteers with normal IOP and 24 patients with elevated IOP. The correlation and standard deviation (SD) between IOPIndentation and IOPGAT was R = 0.92 (p < 0.001), SD = 3.6 mmHg, n = 104, and between IOPRemoval and IOPGAT R = 0.94 (p < 0.001), SD = 3.1 mmHg, n = 104. In conclusion, resonance sensor technology has made it possible to introduce a new multi-point method for measuring IOP, and the method is relevant for measuring IOP in humans. The study indicates that with further development towards elimination of position dependence, the ART has the potential to become a useful clinical instrument for IOP measurement.

  • 44.
    Hallberg, Per
    et al.
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Santala, Kenneth
    Umeå University, Department of Clinical Science, Ophthalmology.
    Lindén, Christina
    Umeå University, Centre for Biomedical Engineering and Physics.
    Lindahl, Olof
    Eklund, Anders
    Umeå University Hospital, Department of Biomedical Engineering & Informatics.
    Comparison of Goldmann applanation and applanation resonance tonometry in a biomicroscope-based in vitro porcine eye model2006In: Journal of Medical Engineering & Technology, ISSN 0309-1902, E-ISSN 1464-522X, Vol. 30, no 6, p. 345-52Article in journal (Refereed)
    Abstract [en]

    We have developed an in vitro porcine eye model based on a biomicroscope, to simulate a clinical situation for IOP measurement on enucleated eyes. The aims of this study were to evaluate the model and to apply and compare Goldmann applanation tonometry (GAT) and applanation resonance tonometry (ART) measurements in porcine eyes. The GAT measurement (IOPGAT) showed a lower pressure, mean - 14.0 mm Hg (SD = 1.7 mm Hg) as compared with the reference pressure. For in vitro measurement with GAT on porcine eyes the linear calibration was IOP = 1.14 IOPGAT + 12.5 mm Hg (R2 = 0.99, p < 0.001, n = 280, four eyes). ART measurements correlated significantly to reference IOP, R = 0.86 (p < 0.001, n = 252, six eyes), with a mean difference of 5.4 mm Hg (SD = 6.7 mm Hg). GAT could only be used on porcine eyes if the IOP exceeded 13 mm Hg. Evaluation of the ART in this in vitro model showed position dependence for the sensor. To facilitate centre positioning a guiding tool is suggested. Porcine eyes are a possible substitute for human eyes in in vitro models for pre-clinical evaluation of new tonometry methods.

  • 45.
    Håkansson, Sebastian
    et al.
    Umeå universitetssjukhus.
    Bäcklund, Tomas
    Umeå University Hospital, Department of Biomedical Engineering.
    Granström, L.
    Umeå universitetssjukhus.
    Karlsson, S.
    Umeå universitetssjukhus.
    Lindahl, Olof
    A system for separation and selection of variably encapsylated subpopulations of group B streptococci1989In: Fourth European Congress of Clinical Microbiology, Nice, France, 17-20 April 1989, European Society of Clinical Microbiology and Infectious Diseases. , 1989Conference paper (Other academic)
  • 46.
    Jalkanen, V.
    et al.
    Umeå universitet.
    Andersson, Britt M.
    Umeå University. Department of Applied Physics and Electronics, Centre for Biomedical Engineering and Physics, Umeå University.
    Lindahl, Olof
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Stiffness of a small tissue phantom measured by a tactile resonance sensor2010In: XIIth Mediterranean Conference on Medical and Biological Engineering and Computing 2010: [MEDICON 2010] ; May 27 - 30, 2010, Chalkidiki, Greece / [ed] Panagiotis D. Bamidis; Nicolas Pallikarakis, Berlin: Springer Science+Business Media B.V., 2010, p. 395-398Conference paper (Refereed)
    Abstract [en]

    Many pathological conditions, for instance cancer, alter the elastic stiffness of tissues. Therefore, it is of interest to objectively quantify the stiffness of tissue samples. Tactile resonance sensor technology has been proven to measure the stiffness of tissues in a variety of medical applications. The technique is based on a vibrating piezoelectric sensor element that changes its resonance frequency when it is put in contact with a soft object to be measured. The frequency change is related to the mechanical properties of the soft object. This principle is implemented in an indentation setup where also the impression force and impression depth can be measured. The aim of this study was to investigate how the measured parameters of a tactile resonance sensor system depend on the limited size of a small gelatin tissue phantom sample. Indentation measurements were conducted on different locations on a small gelatin sample. Results showed that the force and frequency change were dependent of the measurement location and thus the sample geometry. The estimated stiffness was independent of the measurement location. Further studies must be conducted to determine the full value of the method for measuring the stiffness of small tissue samples.

  • 47.
    Jalkanen, Ville
    et al.
    Umeå University. Department of Applied Physics and Electronics.
    Andersson, B.M.
    Umeå University. Department of Applied Physics and Electronics.
    Lindahl, Olof
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Instrument towards faster diagnosis and treatment of prostate cancer: resonance sensor stiffness measurements on Human prostate tissue in vitro2009In: World Congress on Medical Physics and Biomedical Engineering: September 7 - 12, 2009, Munich, Germany / [ed] Olaf Dössel; Wolfgang C. Schlegel, Berlin: Springer Science+Business Media B.V., 2009, p. 145-148Conference paper (Refereed)
    Abstract [en]

    Prostate cancer is the most common cancer among men and the methods used to detect and diagnose prostate cancer are not sufficiently accurate. Radical prostatectomy is a surgical treatment of prostate cancer where the whole prostate is removed from the patient. Prostate tissue stiffness can be measured with a stiffness sensitive resonance sensor. The aim of this study was to measure the stiffness on the anterior and posterior side of fresh human prostate tissue in vitro and compare these two groups with each other and relate the findings with the prostate tissue histology. In a prostate tissue slice with mostly normal healthy tissue, the anterior side was significantly harder (p-value < 0.05) as expected. In a prostate tissue slice with areas of cancer tumors, no difference was found between the anterior and posterior sides. However, large stiffness variations were found within groups with measurements points on cancer tissue (coefficient of variation, CV = 42 and 85%), as opposed to groups without cancer tissue (CV = 27 and 28%). The large stiffness variations could be used as a sign for the presence of cancer. The results are promising for the development of an instrument and method for faster diagnosis on radical prostatectomy samples

  • 48.
    Jalkanen, Ville
    et al.
    Umeå University. Department of Applied Physics and Electronics.
    Andersson, Britt M.
    Umeå University. Department of Applied Physics and Electronics.
    Bergh, Anders
    Umeå University Hospital, Department of Biomedical Engineering.
    Eklund, Anders
    Umeå University Hospital, Department of Biomedical Engineering.
    Lindahl, Olof
    Detektering av förändringar i prostatavävnad mha resonanssensor2002In: Program & sammanfattningar. [59]: Svenska mässan, Göteborg, 27-29 november 2002, Stockholm: Svenska läkaresällskapet , 2002, p. 231-Conference paper (Other academic)
  • 49.
    Jalkanen, Ville
    et al.
    Umeå University. Department of Applied Physics and Electronics.
    Andersson, Britt M.
    Umeå University. Department of Applied Physics and Electronics.
    Bergh, Anders
    Umeå University Hospital, Department of Biomedical Engineering.
    Lindahl, Olof
    Prostatacancer detekterad med resonssensor och morphometri?2004In: Svenska läkaresällskapets riksstämma 24-26 november 2004, Stockholm: Svenska läkaresällskapet , 2004, p. F10-Conference paper (Other academic)
  • 50.
    Jalkanen, Ville
    et al.
    Umeå University. Department of Applied Physics and Electronics.
    Andersson, Britt M.
    Umeå University. Department of Applied Physics and Electronics.
    Bergh, Anders
    Department of Medical Biosciences Pathology, Umeå University.
    Ljundberg, Börje
    Umeå University, Department of Surgical and Perioperative Science, Urology and Andrology.
    Lindahl, Olof
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Explanatory models for a tactile resonance sensor system: elastic and density-related variations of prostate tissue in vitro2008In: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 29, no 7, p. 729-745Article in journal (Refereed)
    Abstract [en]

    Tactile sensors based on piezoelectric resonance have been adopted for medical applications. The sensor consists of an oscillating piezoelectric sensor-circuit system, and a change in resonance frequency is observed when the sensor tip contacts a measured object such as tissue. The frequency change at a constant applied force or mass load is used as a stiffness-sensitive parameter in many applications. Differential relations between force and frequency have also been used for monitoring intraocular pressure and stiffness variations in prostate tissue in vitro. The aim of this study was to relate the frequency change (Δf), measured force (F) and the material properties, density and elasticity to an explanatory model for the resonance sensor measurement principle and thereby to give explanatory models for the stiffness parameters used previously. Simulations of theoretical equations were performed to investigate the relation between frequency change and contact impedance. Measurements with a resonance sensor system on prostate tissue in vitro were used for experimental validation of the theory. Tissue content was quantified with a microscopic-based morphometrical method. Simulation results showed that the frequency change was dependent upon density (ρ) and contact area (S) according to Δf ∝ ρS3/2. The experiments followed the simulated theory at small impression depths. The measured contact force followed a theoretical model with the dependence of the elastic modulus (E) and contact area, F ∝ ES3/2. Measured density variations related to histological variations were statistically weak or non-significant. Elastic variations were statistically significant with contributions from stroma and cancer relative to normal glandular tissue. The theoretical models of frequency change and force were related through the contact area, and a material-dependent explanatory model was found as Δf ∝ ρE-1F. It explains the measurement principle and the previously established stiffness parameters from the material properties point of view.

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