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Friman, Ola
Publications (10 of 23) Show all publications
Ringaby, E., Forssén, P.-E., Friman, O., Olsvik Opsahl, T., Vegard Haavardsholm, T. & Kåsen, I. (2014). Anisotropic Scattered Data Interpolation for Pushbroom Image Rectification. IEEE Transactions on Image Processing, 23(5), 2302-2314
Open this publication in new window or tab >>Anisotropic Scattered Data Interpolation for Pushbroom Image Rectification
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2014 (English)In: IEEE Transactions on Image Processing, ISSN 1057-7149, E-ISSN 1941-0042, Vol. 23, no 5, p. 2302-2314Article in journal (Refereed) Published
Abstract [en]

This article deals with fast and accurate visualization of pushbroom image data from airborne and spaceborne platforms. A pushbroom sensor acquires images in a line-scanning fashion, and this results in scattered input data that needs to be resampled onto a uniform grid for geometrically correct visualization. To this end, we model the anisotropic spatial dependence structure caused by the acquisition process. Several methods for scattered data interpolation are then adapted to handle the induced anisotropic metric and compared for the pushbroom image rectification problem. A trick that exploits the semi-ordered line structure of pushbroom data to improve the computational complexity several orders of magnitude is also presented.

Place, publisher, year, edition, pages
IEEE, 2014
Keywords
pushbroom, rectification, hyperspectral, interpolation, anisotropic, scattered data
National Category
Engineering and Technology Electrical Engineering, Electronic Engineering, Information Engineering Signal Processing
Identifiers
urn:nbn:se:liu:diva-108105 (URN)10.1109/TIP.2014.2316377 (DOI)000350284400001 ()
Available from: 2014-06-25 Created: 2014-06-25 Last updated: 2018-09-25Bibliographically approved
Friman, O., Follo, P., Ahlberg, J. & Sjökvist, S. (2014). Methods for Large-Scale Monitoring of District Heating Systems Using Airborne Thermography. IEEE Transactions on Geoscience and Remote Sensing, 52(8), 5175-5182
Open this publication in new window or tab >>Methods for Large-Scale Monitoring of District Heating Systems Using Airborne Thermography
2014 (English)In: IEEE Transactions on Geoscience and Remote Sensing, ISSN 0196-2892, E-ISSN 1558-0644, Vol. 52, no 8, p. 5175-5182Article in journal (Refereed) Published
Abstract [en]

District heating is a common way of providing heat to buildings in urban areas. The heat is carried by hot water or steam and distributed in a network of pipes from a central powerplant. It is of great interest to minimize energy losses due to bad pipe insulation or leakages in such district heating networks. As the pipes generally are placed underground, it may be difficult to establish the presence and location of losses and leakages. Toward this end, this work presents methods for large-scale monitoring and detection of leakages by means of remote sensing using thermal cameras, so-called airborne thermography. The methods rely on the fact that underground losses in district heating systems lead to increased surface temperatures. The main contribution of this work is methods for automatic analysis of aerial thermal images to localize leaking district heating pipes. Results and experiences from large-scale leakage detection in several cities in Sweden and Norway are presented.

Place, publisher, year, edition, pages
IEEE, 2014
Keywords
image processing, remote sensing, thermal sensors
National Category
Signal Processing Remote Sensing
Identifiers
urn:nbn:se:liu:diva-105285 (URN)10.1109/TGRS.2013.2287238 (DOI)000332598500055 ()
Available from: 2014-03-15 Created: 2014-03-15 Last updated: 2017-12-05Bibliographically approved
Eklund, A., Friman, O., Andersson, M. & Knutsson, H. (2011). Comparing fMRI Activity Maps from GLM and CCA at the Same Significance Level by Fast Random Permutation Tests on the GPU. In: : . Paper presented at SSBA Symposium on Image Analysis, March 17-18, Linköping, Sweden. Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Comparing fMRI Activity Maps from GLM and CCA at the Same Significance Level by Fast Random Permutation Tests on the GPU
2011 (English)Conference paper, Published paper (Other academic)
Abstract [en]

Parametric statistical methods are traditionally employed in functional magnetic resonance imaging (fMRI) for identifying areas in the brain that are active with a certain degree of statistical significance. These parametric methods, however, have two major drawbacks. First, it isassumed that the observed data are Gaussian distributed and independent; assumptions that generally are not valid for fMRI data. Second, the statistical test distribution can be derived theoretically only for very simple linear detection statistics. In this work it is shown how the computational power of the Graphics Processing Unit (GPU) can be used to speedup non-parametric tests, such as random permutation tests. With random permutation tests it is possible to calculate significance thresholds for any test statistics. As an example, fMRI activity maps from the General Linear Model (GLM) and Canonical Correlation Analysis (CCA) are compared at the same significance level.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2011
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-66206 (URN)
Conference
SSBA Symposium on Image Analysis, March 17-18, Linköping, Sweden
Available from: 2011-03-08 Created: 2011-03-08 Last updated: 2013-08-28Bibliographically approved
Friman, O., Tolt, G. & Ahlberg, J. (2011). Illumination and shadow compensation of hyperspectral images using a digital surface model and non-linear least squares estimation. In: Lorenzo Bruzzone (Ed.), Proc. SPIE 8180, Image and Signal Processing for Remote Sensing XVII: . Paper presented at Image and Signal Processing for Remote Sensing XVII, Prague, Czech Republic, 19–21 September 2011 (pp. Art.nr 8180-26). SPIE - International Society for Optical Engineering
Open this publication in new window or tab >>Illumination and shadow compensation of hyperspectral images using a digital surface model and non-linear least squares estimation
2011 (English)In: Proc. SPIE 8180, Image and Signal Processing for Remote Sensing XVII / [ed] Lorenzo Bruzzone, SPIE - International Society for Optical Engineering, 2011, p. Art.nr 8180-26-Conference paper, Published paper (Refereed)
Abstract [en]

Object detection and material classification are two central tasks in electro-optical remote sensing and hyperspectral imaging applications. These are challenging problems as the measured spectra in hyperspectral images from satellite or airborne platforms vary significantly depending on the light conditions at the imaged surface, e.g., shadow versus non-shadow. In this work, a Digital Surface Model (DSM) is used to estimate different components of the incident light. These light components are subsequently used to predict what a measured spectrum would look like under different light conditions. The derived method is evaluated using an urban hyperspectral data set with 24 bands in the wavelength range 381.9 nm to 1040.4 nm and a DSM created from LIDAR 3D data acquired simultaneously with the hyperspectral data

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2011
Series
Proceedings of SPIE, ISSN 0277-786X ; 8180
Keywords
hyperspectral, shadows, illumination model, digital surface model
National Category
Remote Sensing
Identifiers
urn:nbn:se:liu:diva-120507 (URN)10.1117/12.898084 (DOI)9780819488077 (ISBN)
Conference
Image and Signal Processing for Remote Sensing XVII, Prague, Czech Republic, 19–21 September 2011
Available from: 2015-08-12 Created: 2015-08-12 Last updated: 2015-09-22Bibliographically approved
Vikgren, J., Friman, O., Borga, M., Boijsen, M., Gustavsson, S., Jansson, A., . . . Tylen, U. (2005). Detection of mild emphysema by computed tomography density measurements. Acta Radiologica, 46(3), 237-245
Open this publication in new window or tab >>Detection of mild emphysema by computed tomography density measurements
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2005 (English)In: Acta Radiologica, ISSN 0284-1851, E-ISSN 1600-0455, Vol. 46, no 3, p. 237-245Article in journal (Refereed) Published
Abstract [en]

Purpose: To assess the ability of a conventional density mask method to detect mild emphysema by high- resolution computed tomography ( HRCT), to analyze factors influencing quantification of mild emphysema, and to validate a new algorithm for detection of mild emphysema. Material and Methods: Fifty- five healthy male smokers and 34 never- smokers, 61 - 62 years of age, were examined. Emphysema was evaluated visually, by the conventional density mask method, and by a new algorithm compensating for the effects of gravity and artifacts due to motion and the reconstruction algorithm. Effects of the reconstruction algorithm, slice thickness, and various threshold levels on the outcome of the density mask area were evaluated. Results: Forty- nine percent of the smokers had mild emphysema. The density mask area was higher the thinner the slice irrespective of the reconstruction algorithm and threshold level. The sharp algorithm resulted in increased density mask area. The new reconstruction algorithm could discriminate between smokers with and those without mild emphysema, whereas the density mask method could not. The diagnostic ability of the new algorithm was dependent on lung level. At about 90% specificity, sensitivity was 65 - 100% in the apical levels, but low in the rest of the lung. Conclusion: The conventional density mask method is inadequate for detecting mild emphysema, while the new algorithm improves the diagnostic ability but is nevertheless still imperfect.

Keywords
computed tomography, computerized quantification, emphysema, validation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46113 (URN)10.1080/02841850510021012 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Friman, O., Borga, M., Lundberg, P. & Knutsson, H. (2004). Detection and detrending in fMRI data analysis. NeuroImage, 22(2), 645-655
Open this publication in new window or tab >>Detection and detrending in fMRI data analysis
2004 (English)In: NeuroImage, ISSN 1053-8119, E-ISSN 1095-9572, Vol. 22, no 2, p. 645-655Article in journal (Refereed) Published
Abstract [en]

This article addresses the impact that colored noise, temporal filtering, and temporal detrending have on the fMRI analysis situation. Specifically, it is shown why the detection of event-related designs benefit more from pre-whitening than blocked designs in a colored noise structure. Both theoretical and empirical results are provided. Furthermore, a novel exploratory method for producing drift models that efficiently capture trends and drifts in the fMRI data is introduced. A comparison to currently employed detrending approaches is presented. It is shown that the novel exploratory model is able to remove a major part of the slowly varying drifts that are abundant in fMRI data. The value of such a model lies in its ability to remove drift components that otherwise would have contributed to a colored noise structure in the voxel time series.

Keywords
Detrending, fMRI analysis, Voxel
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-45479 (URN)10.1016/j.neuroimage.2004.01.033 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Friman, O., Borga, M., Lundberg, P. & Knutsson, H. (2003). Adaptive analysis of fMRI data. NeuroImage, 19(3), 837-845
Open this publication in new window or tab >>Adaptive analysis of fMRI data
2003 (English)In: NeuroImage, ISSN 1053-8119, E-ISSN 1095-9572, Vol. 19, no 3, p. 837-845Article in journal (Refereed) Published
Abstract [en]

This article introduces novel and fundamental improvements of fMRI data analysis. Central is a technique termed constrained canonical correlation analysis, which can be viewed as a natural extension and generalization of the popular general linear model method. The concept of spatial basis filters is presented and shown to be a very successful way of adaptively filtering the fMRI data. A general method for designing suitable hemodynamic response models is also proposed and incorporated into the constrained canonical correlation approach. Results that demonstrate how each of these parts significantly improves the detection of brain activity, with a computation time well within limits for practical use, are provided.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46573 (URN)10.1016/S1053-8119(03)00077-6 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Friman, O. (2003). Adaptive analysis of functional MRI data. (Doctoral dissertation). Linköping: Linköpings Universitet
Open this publication in new window or tab >>Adaptive analysis of functional MRI data
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Functional Magnetic Resonance Imaging (fMRI) is a recently developed neuroimaging technique with capacity to map neural activity with high spatial precision. To locate active brain areas, the method utilizes local blood oxygenation changes which are reflected as small intensity changes in a special type of MR images. The ability to non-invasively map brain functions provides new opportunities to unravel the mysteries and advance the understanding of the human brain, as well as to perform pre-surgical examinations in order to optimize surgical interventions.

This dissertation introduces new approaches for the analysis of fMRI data. The detection of active brain areas is a challenging problem due to high noise levels and artifacts present in the data. A fundamental tool in the developed methods is Canonical Correlation Analysis (CCA). CCA is used in two novel ways. First as a method with the ability to fully exploit the spatia-temporal nature of fMRI data for detecting active brain areas. Established analysis approaches mainly focus on the temporal dimension of the data and they are for this reason commonly referred to as being mass-univariate. The new CCA detection method encompasses and generalizes the traditional mass-univariate methods and can in this terminology be viewed as a mass-multivariate approach. The concept of spatial basis functions is introduced as a spatial counterpart of the temporal basis functions already in use in fMRI analysis. The spatial basis functions implicitly perform an adaptive spatial filtering of the fMRI images, which significantly improves detection performance. It is also shown how prior information can be incorporated into the analysis by imposing constraints on the temporal and spatial models and a constrained version of CCA is devised to this end. A general Principal Component Analysis technique for generating and constraining temporal and spatial subspace models is proposed to be used in combination with the constrained CCA analysis approach.

The second use of CCA is found in a novel so-called exploratory analysis method which extracts interesting and representative structures in fMRI data. Functional MRI data sets are large, and exploratory analysis methods are useful for probing the data for unexpected components. It is also shown how drift and trend models adapted to the fMRI data set at hand can be constructed with this new exploratory CCA technique. Compared to traditionally employed drift models, such adaptive drift models better account for the temporal autocorrelation in the data.

Place, publisher, year, edition, pages
Linköping: Linköpings Universitet, 2003. p. 75
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 836
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-24501 (URN)6625 (Local ID)91-7373-699-6 (ISBN)6625 (Archive number)6625 (OAI)
Public defence
2003-09-26, Aulan, Administrationshuset, Universitetssjukhuset, Linköping, 10:30 (Swedish)
Opponent
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2013-01-11
Borga, M., Friman, O., Lundberg, P. & Knutsson, H. (2002). A canonical correlation approach to exploratory data analysis in fMRI. In: : . Paper presented at ISMRM 10th Scientific Meeting & Exhibition, 18-24 May 2002, Honolulu, Hawai’i, USA.
Open this publication in new window or tab >>A canonical correlation approach to exploratory data analysis in fMRI
2002 (English)Conference paper, Published paper (Other academic)
Abstract [en]

A computationally efficient data-driven method for exploratory analysis of functional MRI data is presented. The basic idea is to reveal underlying components in the fMRI data that have maximum autocorrelation. The tool for accomplishing this task is Canonical Correlation Analysis. The proposed method is more robust and much more computationally efficient than independent component analysis, which previously has been applied in fMRI.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-24523 (URN)6655 (Local ID)6655 (Archive number)6655 (OAI)
Conference
ISMRM 10th Scientific Meeting & Exhibition, 18-24 May 2002, Honolulu, Hawai’i, USA
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2014-10-08Bibliographically approved
Borga, M., Friman, O., Lundberg, P. & Knutsson, H. (2002). Blind Source Separation of Functional MRI Data. In: : . Paper presented at SSAB 2002 Symposium i bildanalys, Lund 7-8 mars 2002.
Open this publication in new window or tab >>Blind Source Separation of Functional MRI Data
2002 (English)Conference paper, Published paper (Other academic)
National Category
Biomedical Laboratory Science/Technology
Identifiers
urn:nbn:se:liu:diva-61222 (URN)
Conference
SSAB 2002 Symposium i bildanalys, Lund 7-8 mars 2002
Available from: 2010-11-05 Created: 2010-11-05 Last updated: 2014-10-08
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