| 1. |
- Elawa, Sherif, et al.
(författare)
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Skin perfusion and oxygen saturation after mastectomy and radiation therapy in breast cancer patients
- 2024
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Ingår i: Breast. - : Elsevier. - 0960-9776 .- 1532-3080. ; 75
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Tidskriftsartikel (refereegranskat)abstract
- The pathophysiological mechanism behind complications associated with postmastectomy radiotherapy (PMRT) and subsequent implant-based breast reconstruction are not completely understood. The aim of this study was to examine if there is a relationship between PMRT and microvascular perfusion and saturation in the skin after mastectomy and assess if there is impaired responsiveness to a topically applied vasodilator (Methyl nicotinate - MN). Skin microvascular perfusion and oxygenation >2 years after PMRT were measured using white light diffuse reflectance spectroscopy (DRS) and laser Doppler flowmetry (LDF) in the irradiated chest wall of 31 women with the contralateral breast as a control. In the non-irradiated breast, the perfusion after application of MN (median 0.84, 25th-75th centile 0.59-1.02 % RBC × mm/s) was higher compared to the irradiated chest wall (median 0.51, 25th-75th centile 0.21-0.68 % RBC × mm/s, p < 0.001). The same phenomenon was noted for saturation (median 91 %, 25th-75th centile 89-94 % compared to 89 % 25th-75th centile 77-93 %, p = 0.001). Eight of the women (26%) had a ≥10 % difference in skin oxygenation between the non-irradiated breast and the irradiated chest wall. These results indicate that late microvascular changes caused by radiotherapy of the chest wall significantly affect skin perfusion and oxygenation.
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| 4. |
- Fredriksson, Ingemar, 1980-, et al.
(författare)
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Inverse Monte Carlo in a multilayered tissue model: merging diffuse reflectance spectroscopy and laser Doppler flowmetry
- 2013
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Ingår i: Journal of Biomedical Optics. - Bellingham, WA, United States : SPIE - International Society for Optical Engineering. - 1083-3668 .- 1560-2281. ; 18:12, s. 127004-1-127004-14
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Tidskriftsartikel (refereegranskat)abstract
- The tissue fraction of red blood cells (RBCs) and their oxygenation and speed-resolved perfusion areestimated in absolute units by combining diffuse reflectance spectroscopy (DRS) and laser Doppler flowmetry(LDF). The DRS spectra (450 to 850 nm) are assessed at two source–detector separations (0.4 and 1.2 mm), allowingfor a relative calibration routine, whereas LDF spectra are assessed at 1.2mmin the same fiber-optic probe. Data areanalyzed using nonlinear optimization in an inverse Monte Carlo technique by applying an adaptive multilayeredtissue model based on geometrical, scattering, and absorbing properties, as well as RBC flow-speed information.Simulations of 250 tissue-like models including up to 2000 individual blood vessels were used to evaluatethe method. The absolute root mean square (RMS) deviation between estimated and true oxygenation was 4.1percentage units, whereas the relative RMS deviations for the RBC tissue fraction and perfusion were 19% and23%, respectively. Examples of in vivo measurements on forearm and foot during common provocations arepresented. The method offers several advantages such as simultaneous quantification of RBC tissue fractionand oxygenation and perfusion from the same, predictable, sampling volume. The perfusion estimate is speedresolved, absolute (% RBC × mm∕s), and more accurate due to the combination with DRS.
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| 5. |
- Fredriksson, Ingemar, 1980-, et al.
(författare)
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Laser doppler flowmetry
- 2012
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Ingår i: Microcirculation imaging. - Weinheim : Wiley-VCH Verlagsgesellschaft. - 3527328947 - 9783527328949 - 9783527651238 ; , s. 67-86
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Adopting a multidisciplinary approach with input from physicists, researchers and medical professionals, this is the first book to introduce many different technical approaches for the visualization of microcirculation, including laser Doppler and laser speckle, optical coherence tomography and photo-acoustic tomography. It covers everything from basic research to medical applications, providing the technical details while also outlining the respective strengths and weaknesses of each imaging technique. Edited by an international team of top experts, this is the ultimate handbook for every clinician and researcher relying on microcirculation imaging.
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| 6. |
- Fredriksson, Ingemar, 1980-, et al.
(författare)
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Microcirculatory changes in type 2 diabetes assessed with velocity resolved quantitative laser Doppler flowmetry
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The response to local heating (44oC for 20 min) was evaluated in 28 type 2 diabetes patients (DM) and 29 non-diabetes controls (ND). Microcirculatory perfusion was assessed using conventional and quantitative Laser Doppler flowmetry (cLDF and qLDF), respectively. The qLDF estimates perfusion in a physiological relevant unit (g RBC / 100 g tissue × mm/s) in a fixed output volume, separated into three velocity regions, v < 1 mm/s, 1 - 10 mm/s, and v > 10 mm/s. Perfusion in cLDF is given in arbitrary units with unknown velocity distribution and measurement volume. A significantly lower response in DM than in ND was found after heat provocation both for the initial peak and the plateau response, while no significant differences were found at baseline. The qLDF showed increased perfusion for the velocity regions 1-10 mm/s and above 10 mm/s, while no significant increase was found for v < 1 mm/s. In conclusion, we found a lowered LDF response to local heating in DM. The new qLDF method showed that the increased blood flow occurs in vessels with a velocity above 1 mm/s. Baseline qLDF-data indicated that a redistribution of flow to higher velocity regions was associated with longer DM duration and for DM a negative correlation between perfusion and BMI.
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| 7. |
- Fredriksson, Ingemar, 1980-, et al.
(författare)
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Model-based quantification of skin microcirculatory perfusion
- 2015. - 1
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Ingår i: Computational biophysics of the skin. - Boca Raton : CRC Press. - 9789814463843 - 9789814463850 ; , s. 395-418
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- During the last decades new tools, such as magnetic resonance imaging and Doppler ultra sound imaging, have rapidly been taken into clinical practice for studying the flow dynamics of the macrocirculation. M eanw hile, techniques for quantifying the microcirculation have struggled to become clinically accepted. This includes the use of laser Doppler flow metry (LDF), an optical technique that is capable of monitoring either spatial or temporal changes in the microcirculation by analyzing the backscattered Doppler shifted light from a laser illuminated tissue. Until now , LDF has only been capable of producing non-absolute relative measures, w hich has limited its cl inical acceptance. With a model based analysis approach, as presented here, this can be overcome, and objective diagnosis of the microcirculation may finally be a part of everyday clinical praxis. The most important advantages w ith the proposed method are that a quantitative perfusion estimate (% RBC × mm/ s) can be extracted, and that this measure can be resolved into different speed regions.
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| 8. |
- Fredriksson, Ingemar, 1980-, et al.
(författare)
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Model-based quantitative laser Doppler flowmetry in skin
- 2010
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Ingår i: Journal of Biomedical Optics. - : Society of Photo-optical Instrumentation Engineers. - 1083-3668 .- 1560-2281. ; 15:5
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Tidskriftsartikel (refereegranskat)abstract
- Laser Doppler Flowmetry (LDF) can be used for assessing the microcirculatory perfusion. However, conventional LDF (cLDF) gives only a relative perfusion estimate in an unknown measurement volume. To overcome these limitations a model-based analysis method for quantitative LDF (qLDF) is proposed. The method uses an inverse Monte Carlo technique with an adaptive three layer skin model. By analyzing the optimal model where measured and simulated LDF spectra using two different source-detector separations match, the absolute microcirculatory perfusion for a specified velocity region in a predefined volume is determined. The robustness of the qLDF method and how much it is affected by physiologically relevant variations in optical properties were evaluated using additional Monte Carlo simulations. When comparing qLDF to cLDF, a much smaller deviation from the true perfusion was attained. For physiologically relevant variations in the optical properties of static tissue and blood absorption, qLDF displayed errors <12%. Variations in the scattering properties of blood displayed larger errors (<58%). Evaluations on inhomogeneous models containing small blood vessels, hair and sweat glands displayed errors <5%. For extremely inhomogeneous models containing larger blood vessels, the error increased substantially, but this was detected by analyzing the qLDF model residual. The qLDF algorithm was applied to an in vivo local heat provocation. The perfusion increase was higher with qLDF than cLDF, due to non-linear effects in the latter. The qLDF showed that the perfusion increase was due to an increased amount of blood cells with a velocity > 1 mm/s.
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| 9. |
- Fredriksson, Ingemar, 1980-, et al.
(författare)
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On the equivalence and differencesbetween laser Doppler flowmetry andlaser speckle contrast analysis
- 2016
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Ingår i: Journal of Biomedical Optics. - : SPIE - International Society for Optical Engineering. - 1083-3668 .- 1560-2281. ; 21:12
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Tidskriftsartikel (refereegranskat)abstract
- Laser Doppler flowmetry (LDF) and laser speckle contrast analysis (LASCA) both utilize the spatiotemporalproperties of laser speckle patterns to assess microcirculatory blood flow in tissue. Although the techniquesanalyze the speckle pattern differently, there is a close relationship between them. We present atheoretical overview describing how the LDF power spectrum and the LASCA contrast can be calculatedfrom each other, and how both these can be calculated from an optical Doppler spectrum containing variousdegrees of Doppler shifted light. The theoretical relationships are further demonstrated using time-resolvedspeckle simulations. A wide range of Monte Carlo simulated tissue models is then used to show how perfusionestimates for LDF and LASCA are affected by changes in blood concentration and speed distribution, as well asby geometrical and optical properties. We conclude that perfusion estimates from conventional single exposuretime LASCA are in general more sensitive to changes in optical and geometrical properties and are less accuratein the prediction of real perfusion changes, especially speed changes. Since there is a theoretical one-to-onerelationship between Doppler power spectrum and contrast, one can conclude that those drawbacks with theLASCA technique can be overcome using a multiple exposure time setup.
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| 10. |
- Fredriksson, Ingemar, 1980-
(författare)
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Quantitative Laser Doppler Flowmetry
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Laser Doppler flowmetry (LDF) is virtually the only non-invasive technique, except for other laser speckle based techniques, that enables estimation of the microcirculatory blood flow. The technique was introduced into the field of biomedical engineering in the 1970s, and a rapid evolvement followed during the 1980s with fiber based systems and improved signal analysis. The first imaging systems were presented in the beginning of the 1990s.Conventional LDF, although unique in many aspects and elegant as a method, is accompanied by a number of limitations that may have reduced the clinical impact of the technique. The analysis model published by Bonner and Nossal in 1981, which is the basis for conventional LDF, is limited to measurements given in arbitrary and relative units, unknown and non-constant measurement volume, non-linearities at increased blood tissue fractions, and a relative average velocity estimate.In this thesis a new LDF analysis method, quantitative LDF, is presented. The method is based on recent models for light-tissue interaction, comprising the current knowledge of tissue structure and optical properties, making it fundamentally different from the Bonner and Nossal model. Furthermore and most importantly, the method eliminates or highly reduces the limitations mentioned above.Central to quantitative LDF is Monte Carlo (MC) simulations of light transport in tissue models, including multiple Doppler shifts by red blood cells (RBC). MC was used in the first proof-of-concept study where the principles of the quantitative LDF were tested using plastic flow phantoms. An optically and physiologically relevant skin model suitable for MC was then developed. MC simulations of that model as well as of homogeneous tissue relevant models were used to evaluate the measurement depth and volume of conventional LDF systems. Moreover, a variance reduction technique enabling the reduction of simulation times in orders of magnitudes for imaging based MC setups was presented.The principle of the quantitative LDF method is to solve the reverse engineering problem of matching measured and calculated Doppler power spectra at two different source-detector separations. The forward problem of calculating the Doppler power spectra from a model is solved by mixing optical Doppler spectra, based on the scattering phase functions and the velocity distribution of the RBC, from various layers in the model and for various amounts of Doppler shifts. The Doppler shift distribution is calculated based on the scattering coefficient of the RBC:s and the path length distribution of the photons in the model, where the latter is given from a few basal MC simulations.When a proper spectral matching is found, via iterative model parameters updates, the absolute measurement data are given directly from the model. The concentration is given in g RBC/100 g tissue, velocities in mm/s, and perfusion in g RBC/100 g tissue × mm/s. The RBC perfusion is separated into three velocity regions, below 1 mm/s, between 1 and 10 mm/s, and above 10 mm/s. Furthermore, the measures are given for a constant output volume of a 3 mm3 half sphere, i.e. within 1.13 mm from the light emitting fiber of the measurement probe.The quantitative LDF method was used in a study on microcirculatory changes in type 2 diabetes. It was concluded that the perfusion response to a local increase in skin temperature, a response that is reduced in diabetes, is a process involving only intermediate and high flow velocities and thus relatively large vessels in the microcirculation. The increased flow in higher velocities was expected, but could not previously be demonstrated with conventional LDF. The lack of increase in low velocity flow indicates a normal metabolic demand during heating. Furthermore, a correlation between the perfusion at low and intermediate flow velocities and diabetes duration was found. Interestingly, these correlations were opposites (negative for the low velocity region and positive for the mediate velocity region). This finding is well in line with the increased shunt flow and reduced nutritive capillary flow that has previously been observed in diabetes.
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