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| 2. |
- Arildsson, Mikael, 1967-, et al.
(författare)
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Higher order moment processing of laser Doppler perfusion signals
- 1997
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Ingår i: Journal of Biomedical Optics. - : SPIE-Intl Soc Optical Eng. - 1083-3668 .- 1560-2281. ; 2:4, s. 358-363
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Tidskriftsartikel (refereegranskat)abstract
- The laser Doppler technique is used to assess tissue perfusion. Traditionally an integrated, ω-weighted (first-order filter) power spectrum is used to estimate perfusion. In order to be able to obtain selective information about the flow in vessels with different blood cell velocities, higher order filters have been implemented, investigated, and evaluated. Theoretical considerations show that the output of the signal processor will depend on the flow speed, for a given concentration of blood cells, according to Sout∞νn where v is the average blood cell speed and n is the spectral filter order. An implementation of filters using zero-, first-, second-, and third-order spectral moments was utilized to experimentally verify the theory by using a laser Doppler perfusion imager. Two different flow models were utilized: A Plexiglas model was used to demonstrate the various signatures of the power spectrum for different flow speeds and filter orders, whereas a Delrin model was used to study the relationship between the flow velocity and the output of the signal processor for the different filters. The results show good agreement with theory and also good reproducibility. Recordings made on the skin of the wrist area demonstrated that the flow in small veins can be visualized by the use of higher spectral orders.
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| 4. |
- Eriksson, Ola, 1967-, et al.
(författare)
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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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Ingår i: Medical and Biological Engineering and Computing. - 0140-0118 .- 1741-0444. ; 37:6, s. 737-741
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Eriksson, Ola, 1967-, et al.
(författare)
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In vitro evaluation of brain lesioning electrodes (Leksell) using a computer-assisted video system
- 1999
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Ingår i: Neurological Research. - 0161-6412 .- 1743-1328. ; 21:1, s. 89-95
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Tidskriftsartikel (refereegranskat)abstract
- Radiofrequency (RF) generated thermal brain lesions are widely used in functional neurosurgery. The size, shape and development of the lesions depends on system parameter settings and the electrode configuration. Difficulties in studying the effect of these factors in vivo stimulated us to develop an in vitro system for standardized comparison between different electrodes and physical parameters. A computer-assisted video system was set-up allowing continuous video recording of RF-generated coagulations in either a standard albumin solution or in the fresh white of a hen's egg as transparent test substrates. Ten lesions were made with each test electrode (two bipolar and three monopolar) in each of the two substrates at 70 degrees, 80 degrees and 90 degrees C (t = 60 sec). Due to the better homogeneity the lesions in the albumin solution were much more regular and reproducible. This made it possible to calculate the size (width 2.2 +/- 0.1 to 5.3 +/- 0.1 mm and length 3.0 +/- 0.1 to 8.7 +/- 0.3 mm) as well as the volume (8.5 +/- 1.4 mm3 to 133.5 +/- 26.8 mm3). It is concluded that this in vitro system offers a reproducible way to study and document the effect of different electrode configurations and RF-generator settings on the formation of a heat lesion. Even if the results are not directly applicable to the living human brain they give an estimate of the form and size of a coagulation lesion and can be of value for standardized comparisons between different electrodes.
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| 7. |
- Eriksson, Ola, 1967-, et al.
(författare)
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In-vitro size estimation of protein clots generated by brain electrodes
- 1998
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Ingår i: Proceedings of the 20th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 1998. - Hong Kong : IEEE. ; , s. 1783-
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Konferensbidrag (refereegranskat)abstract
- A method for in-vitro size estimation of protein clots generated by brain electrodes is presented. Radiofrequency generated thermal brain lesions are widely used in functional neurosurgery and in-vitro tests are used to confirm the electrodes' ability to generate lesions. To be able to estimate the size of protein clots generated in-vitro by brain electrodes, a computer-assisted video system was set up. The size estimation is carried out by software using two captured images of the protein clot. The “true” length and width (9.5 mm) of a sphere as measured with a slide-caliper differed at the most 0.5 mm (5%) and 0.3 mm (3%) respectively, all random errors fall within 2s.d
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| 10. |
- Ilias, Michail A., 1971-, et al.
(författare)
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Single exposure phototesting utilizing a divergent ultraviolet beam
- 1999
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Ingår i: Skin research and technology. - : Wiley. - 0909-752X .- 1600-0846. ; 5:4, s. 255-259
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Tidskriftsartikel (refereegranskat)abstract
- Background/aims: Confident diagnosis of photosensitivity in patients with light dermatoses requires skin exposure to well determined ultraviolet (UV) light doses, most often from a solar simulator. The traditional test procedure results in a rough classification of skin sensitivity based on the minimal erythema dose (MED) found for each patient. The limited number of constant irradiance doses used during phototesting decreases the precision of the MED value. In the present study we aimed at developing the technical system for the determination of MED by using a single, centrifugally attenuating, UVB provocation.Methods: A divergent UV beam was achieved with the help of an optic lens. To investigate the irradiance profile, an irradiance acquisition system was built that produced three-dimensional intensity maps. In addition, a laser Doppler perfusion imaging (LDPI) system was introduced in the evaluation of the skin response along with visual readings of the same exposed areas, in order to add a quantitative aspect to the assessment of erythema. The procedure was used on one test subject.Results: The divergent UV beam showed the desired profile. With the current setup 20 different UV-dose levels could be discriminated. Relevant UV-dose levels were determined and tested on a subject, which in practice gave results in the form of visual assessment as well as LDPI-images. The visual or LDPI diameter gave the MED. Within the skin reaction, irradiance and the laser Doppler values could be compared mm for mm.Conclusions: A more accurate MED determination with a single UV exposure seems to be feasible by using the proposed method. Though further investigation is required, the technique appears to offer new possibilities for the association of dose to response. In addition LDPI is possibly a useful complement to the visual readings of the skin responses, since the method gives a quantification of the grade of erythema, as opposed to visual (+, ++, +++) readings that are subjective and at best semiquantitative.
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