Journal articles

1. Synthesis and Characterization of scVEGF-PEG-[Ga]NOTA and scVEGF-PEG-[Ga]DOTA PET Tracers
   Authors: Elisabeth Blom (1), Irina Velikyan (2,3), Azita Monazzam (2), Pasha Razifar, Manoj Nair (2), Payam Razifar (4), Jean-Luc Vanderheyden (5), Arcadius V. Krivoshein (6), Marina Backer (6), Joseph Backer (6), and Bengt Långström (1)
   (1) Dept. of Biochemistry and Organic Chemistry, UU
   (2) Uppsala Applied Science Lab, UU
   (3) Dept. of Radiology, Oncology and Radiation Science, UU
   (4) Dept. of Pharmaceutical Biosciences, UU
   (5) GE Healthcare Systems, Molecular Imaging, Waukesha, WI, USA
   (6) SibTech, Inc., Brookfield, USA
   Journal: Journal of Labelled Compounds and Radiopharmaceuticals, volume 54, number 11, pp 685-692
   Abstract: Vascular endothelial growth factor (VEGF) signaling via vascular endothelial growth factor receptor 2 (VEGFR-2) on tumor endothelial cells is a critical driver of tumor angiogenesis. Novel anti-angiogenic drugs target VEGF/VEGFR-2 signaling and induce changes in VEGFR-2 prevalence. To monitor VEGFR-2 prevalence in the course of treatment, we are evaluating Ga positron emission tomography imaging agents based on macrocyclic chelators, site-specifically conjugated via polyethylene glycol (PEG) linkers to engineered VEGFR-2 ligand, single-chain (sc) VEGF. The Ga-labeling was performed at room temperature with NOTA (2,2, 2-(1,4,7-triazonane-1,4,7-triyl) triacetic acid) conjugates or at 90 degrees C by using either conventional or microwave heating with NOTA and DOTA (2,2, 2, 2-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl) tetraacetic acid) conjugates. The fastest (similar to 2min) and the highest incorporation (90%) of Ga into conjugate that resulted in the highest specific radioactivity (similar to 400MBq/nmol) was obtained with microwave heating of the conjugates. The bioactivity of the NOTA-and DOTA-containing tracers was validated in 3-D tissue culture model of 293/KDR cells engineered to express high levels of VEGFR-2. The NOTA-containing tracer also displayed a rapid accumulation (similar to 20s after intravenous injection) to steady-state level in xenograft tumor models. A combination of high specific radioactivity and maintenance of functional activity suggests that scVEGF-PEG-[Ga] NOTA and scVEGF-PEG-[Ga] DOTA might be promising tracers for monitoring VEGFR-2 prevalence and should be further explored.
2. Increasing the Dynamic Range of in situ PLA
   Authors: Carl-Magnus Clausson (1,2), Amin Allalou, Irene Weibrecht (1,2), Salah Mahmoudi (3), Marianne Farnebo (4), Ulf Landegren (1,2), Carolina Wählby, and Ola Söderberg (1,2)
   (1) Dept. of Immunology, Genetics and Pathology, UU
   (2) Science for Life Laboratory, UU
   (3) Dept. of Oncology-Pathology, Karolinska Institute, Stockholm
   Journal: Nature Methods, volume 8, number 11, pp 892-893
   Abstract: Molecular detection methods based on proximity ligation and padlock probes result in a localized signal with very high intensity, when imaged by fluorescence microscopy. The number of detection events is typically quantified by automated image analysis aimed at identifying each fluorescing signal. However, if the the number of signals is large they tend to form clusters that can not be resolved, limiting the dynamic range of the concentration of target molecules that can be quantified. To allow quantification of both abundant and scarce target molecules in the same reaction, we devised reagents that give rise to three variants of the reporter signal for any targeted molecule added in a concentration ratio of 1:10:100. It is therefore possible to visualize either 100, 10 or 1 out of 111 detected target molecules, enabling quantification at a concentration level without clustering. The ability to increase the dynamic range is of particular value for heterogeneous samples such as tissue sections, in which the amount of a specific protein may vary greatly between neighboring cells.

3. A Conserved Developmental Patterning Network Produces Quantitatively Different Output in Multiple Species of Drosophila
   Authors: Charless C. Fowlkes (1), Kelly B. Eckenrode (2), Meghan D. Bragdon (2), Miriah Meyer (3), Zeba Wunderlich (2), Lisa Simirenko (4), Cris L. Luengo Hendriks, Soile V. E. Keränen (5), Clara Henriquez (5), David W. Knowles (5), Mark D. Biggin (5), Michael B. Eisen (4), and Angela H. DePace (2)
   (1) Dept. of Computer Science, University of California Irvine, CA, USA
   (2) Dept. of Systems Biology, Harvard Medical School, Boston, MA, USA
   (3) School of Engineering and Applied Sciences, Harvard University, Boston, MA, USA
   (4) California Institute for Quantitative Biosciences, University of California Berkeley, CA, USA
   (5) Genomics and Life Sciences Division, Lawrence Berkeley National Laboratory, CA, USA
   Journal: PLoS Genetics, volume 7, number 10, pp e1002346- (electronic publication)
   Abstract: Differences in the level, timing, or location of gene expression can contribute to alternative phenotypes at the molecular and organismal level. Understanding the origins of expression differences is complicated by the fact that organismal morphology and gene regulatory networks could potentially vary even between closely related species. To assess the scope of such changes, we used high-resolution imaging methods to measure mRNA expression in blastoderm embryos of Drosophila yakuba and Drosophila pseudoobscura and assembled these data into cellular resolution atlases, where expression levels for 13 genes in the segmentation network are averaged into species-specific, cellular resolution morphological frameworks. We demonstrate that the blastoderm embryos of these species differ in their morphology in terms of size, shape, and number of nuclei. We present an approach to compare cellular gene expression patterns between species, while accounting for varying embryo morphology, and apply it to our data and an equivalent dataset for Drosophila melanogaster. Our analysis reveals that all individual genes differ quantitatively in their spatio-temporal expression patterns between these species, primarily in terms of their relative position and dynamics. Despite many small quantitative differences, cellular gene expression profiles for the whole set of genes examined are largely similar. This suggests that cell types at this stage of development are conserved, though they can differ in their relative position by up to 3-4 cell widths and in their relative proportion between species by as much as 5-fold. Quantitative differences in the dynamics and relative level of a subset of genes between corresponding cell types may reflect altered regulatory functions between species. Our results emphasize that transcriptional networks can diverge over short evolutionary timescales and that even small changes can lead to distinct output in terms of the placement and number of equivalent cells.

4. Automated Classification of Multicolored Rolling Circle Products in Dual-Channel Wide-Field Fluorescence Microscopy
   Authors: Milan Gavrilovic, Irene Weibrecht (1), Tim Conze (1), Ola Söderberg (1), and Carolina Wählby
   (1) Dept. of Immunology, Genetics and Pathology, UU
   Journal: Cytometry Part A, volume 79A, number 7, pp 518-527
   Abstract: Specific single-molecule detection opens new possibilities in genomics and proteomics, and automated image analysis is needed for accurate quantification. This work presents image analysis methods for the detection and classification of single molecules and single-molecule interactions detected using padlock probes or proximity ligation. We use simple, widespread, and cost-efficient wide-field microscopy and increase detection multiplexity by labeling detection events with combinations of fluorescence dyes. The mathematical model presented herein can classify the resulting point-like signals in dual-channel images by spectral angles without discriminating between low and high intensity. We evaluate the methods on experiments with known signal classes and compare to classical classification algorithms based on intensity thresholding. We also demonstrate how the methods can be used as tools to evaluate biochemical protocols by measuring detection probe quality and accuracy. Finally, the method is used to evaluate single-molecule detection events in situ.

5. Anti-Aliased Euclidean Distance Transform
   Authors: Stefan Gustavson (1) and Robin Strand
   (1) Dept. of Science and Technology, Linköping University
   Journal: Pattern Recognition Letters, volume 32, number 2, pp 252-257
   Abstract: We present a modified distance measure for use with distance transforms of anti-aliased, area sampled grayscale images of arbitrary binary contours. The modified measure can be used in any vector-propagation Euclidean distance transform. Our test implementation in the traditional SSED8 algorithm shows a considerable improvement in accuracy and homogeneity of the distance field compared to a traditional binary image transform. At the expense of a 10 slowdown for a particular image resolution, we achieve an accuracy comparable to a binary transform on a supersampled image with 16 16 higher resolution, which would require 256 times more computations and memory.

6. Regularized Image Denoising Based on Spectral Gradient Optimization
   Authors: Tibor Lukic (1), Joakim Lindblad, and Natasa Sladoje (1)
   (1) Faculty of Technical Sciences, University of Novi Sad, Serbia
   Journal: Inverse Problems, volume 27, number 8, pp 085010:1-17 (electronic publication)
   Abstract: Image restoration methods, such as denoising, deblurring, inpainting, etc, are often based on the minimization of an appropriately defined energy function. We consider energy functions for image denoising which combine a quadratic data-fidelity term and a regularization term, where the properties of the latter are determined by a used potential function. Many potential functions are suggested for different purposes in the literature. We compare the denoising performance achieved by ten different potential functions. Several methods for efficient minimization of regularized energy functions exist. Most are only applicable to particular choices of potential functions, however. To enable a comparison of all the observed potential functions, we propose to minimize the objective function using a spectral gradient approach; spectral gradient methods put very weak restrictions on the used potential function. We present and evaluate the performance of one spectral conjugate gradient and one cyclic spectral gradient algorithm, and conclude from experiments that both are well suited for the task. We compare the performance with three total variation-based state-of-the-art methods for image denoising. From the empirical evaluation, we conclude that denoising using the Huber potential (for images degraded by higher levels of noise; signal-to-noise ratio below 10 dB) and the Geman and McClure potential (for less noisy images), in combination with the spectral conjugate gradient minimization algorithm, shows the overall best performance.

7. Interrogating Health-Related Public Databases from a Food Toxicology Perspective: Computational Analysis of Scoring Data
   Authors: Farzaneh Maddah (1), Daniel Soeria-Atmadja (1), Patrik Malm, Mats G. Gustafsson (2), and Ulf Hammerling (1)
   (1) Dept. of Risk-Benefit Assessment, National Food Administration, Uppsala
   (2) Dept. of Medical Sciences, Cancer Pharmacology and Computational Medicine, UU
   Journal: Food and Chemical Toxicology, volume 49, number 11, pp 2830-2840
   Abstract: Over the last 15 years, an expanding number of databases with information on noxious effects of substances on mammalian organisms and the environment have been made available on the Internet. This set of databases is a key source of information for risk assessment within several areas of toxicology. Here we present features and relationships across a relatively wide set of publicly accessible databases broadly within toxicology, in part by clustering multi-score representations of such repositories, to support risk assessment within food toxicology. For this purpose 36 databases were each scrutinized, using 18 test substances from six different categories as probes. Results have been analyzed by means of various uni- and multi-variate statistical operations. The former included a special index devised to afford context-specific rating of databases across a highly heterogeneous data matrix, whereas the latter involved cluster analysis, enabling the identification of database assemblies with overall shared characteristics. One database - HSDB - was outstanding due to rich and qualified information for most test substances, but an appreciable fraction of the interrogated repositories showed good to decent scoring. Among the six chosen substance groups, Food contact materials had the most comprehensive toxicological information, followed by the Pesticides category.

8. A Graph-based Framework for Sub-pixel Image Segmentation
   Authors: Filip Malmberg, Joakim Lindblad, Natasa Sladoje (1), and Ingela Nyström
   (1) Faculty of Technical Sciences, University of Novi Sad, Serbia
   Journal: Theoretical Computer Science, volume 412, number 15, pp 1338-1349
   Abstract: Many image segmentation methods utilize graph structures for representing images, where the flexibility and generality of the abstract structure is beneficial. By using a fuzzy object representation, i.e., allowing partial belongingness of elements to image objects, the unavoidable loss of information when representing continuous structures by finite sets is significantly reduced, enabling feature estimates with sub-pixel precision. This work presents a framework for object representation based on fuzzy segmented graphs. Interpreting the edges as one-dimensional paths between the vertices of a graph, we extend the notion of a graph cut to that of a located cut, i.e., a cut with sub-edge precision. We describe a method for computing a located cut from a fuzzy segmentation of graph vertices. Further, the notion of vertex coverage segmentation is proposed as a graph theoretic equivalent to pixel coverage segmentations and a method for computing such a segmentation from a located cut is given. Utilizing the proposed framework, we demonstrate improved precision of area measurements of synthetic two-dimensional objects. We emphasize that although the experiments presented here are performed on two-dimensional images, the proposed framework is defined for general graphs and thus applicable to images of any dimension.

9. Measurement of Fibre-Fibre Contact in Three-Dimensional Images of Fibrous Materials Obtained from X-ray Synchrotron Microtomography
   Authors: Filip Malmberg, Joakim Lindblad, Catherine Östlund, Karin Almgren (1), and Kristofer Gamstedt (1)
   (1) Dept. of Solid Mechanics, Royal Institute of Technology (KTH), Stockholm
   Journal: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, volume 637, number 1, pp 143-148
   Abstract: A series of wood-fibre mats was investigated using high-resolution phase-contrast microtomography at the beamline ID 19 of the European Synchrotron Radiation Facility in Grenoble, France. A method fordata reduction to quantify the degree of fibre-fibre contact has been derived. The degree of fibre-fibre contact and bonding plays a fundamental role in the mechanical properties of cellulose-fibre mats, paper materials and cellulose-fibre composites. The proposed computerised automated method consists of two parts. First, fibre lumens are segmented using a watershed based method. This information is then used to identify fibre-fibre contacts in projections along the z-axis of the materia. The method is tested on microtomographic images of mats made of wood pulp fibres, and is shown to successfully detect differences in the amount of fibre-fibre contact between samples. The degree of fibre-fibre contact correlates well with measured out-of-plane strength of the fibrous material.

10. Artificial Selection on Egg Size Perturbs Early Pattern Formation in Drosophila Melanogaster
    Authors: Cecelia M. Miles (1), Susan E. Lott (2), Cris L. Luengo Hendriks, Michael Z. Ludwig (1), Manu (1), Calvin L. Williams (3), and Martin Kreitman (1)
    (1) Dept. of Ecology and Evolution, The University of Chicago, IL, USA
    (2) Dept. of Molecular and Cell Biology, University of California at Berkeley, MA, USA
    (3) Harvard Medical School, Boston, MA, USA
    Journal: Evolution, volume 65, number 1, pp 33-42
    Abstract: Pattern formation in Drosophila embryogenesis has been widely investigated as a developmental and evolutionary model of robustness. To ask whether genetic variation for pattern formation is suppressed in this system, artificial selection for divergent egg size was used to challenge the scaling of even-skipped (eve) pattern formation in mitotic cycle 14 (stage 5) embryos of Drosophila melanogaster. Three-dimensional confocal imaging revealed shifts in the allometry of eve pair-rule stripes along both anterior-posterior (A-P) and dorsoventral (D-V) axes as a correlated response to egg size selection, indicating the availability of genetic variation for this buffered trait. Environmental perturbation was not required for the manifestation of this variation. The number of nuclei at the cellular blastoderm stage also changed in response to selection, with large-egg selected lines having more than 1000 additional nuclei relative to small-egg lines. This increase in nuclear number in larger eggs does not scale with egg size, however, as nuclear density is inversely correlated with egg length. Nuclear density varies along the A-P axis but does not correlate with the shift in eve stripe allometry between the selection treatments. Despite its macroevolutionary conservation, both eve stripe patterning and blastoderm cell number vary genetically both within and between closely related species.

11. Approximating Euclidean Circles by Neighbourhood Sequences in a Hexagonal Grid
    Authors: Benedek Nagy (1) and Robin Strand
    (1) Dept. of Computer Science, Faculty of Informatics, University of Debrecen, Hungary
    Journal: Theoretical Computer Science, volume 412, number 15, pp 1364-1377
    Abstract: In this paper the nodes of the hexagonal grid are used as points. There are three types of neighbours on this grid, therefore neighbourhood sequences contain values 1, 2, 3. The grid is coordinatized by three coordinates in a symmetric way. Digital circles are classified based on digital distances using neighbourhood sequences. They can be triangle, hexagon, enneagon and dodecagon. Their corners and side-lengths are computed, such as their perimeters and areas. The radius of a digital disk is usually not well-defined, i.e., the same disk can have various radii according to the neighbourhood sequence used. Therefore the non-compactness ratio is used to measure the quality of approximation of the Euclidean circles. The best approximating neighbourhood sequence is presented. It is shown that the approximation can be improved using two neighbourhood sequences in parallel. Comparisons to other approximations are also shown.

12. Finite-Element Based Sparse Approximate Inverses for Block-Factorized Preconditioners
    Authors: Maya Neytcheva (1), Erik Bängtsson (1) and Elisabeth Linnér
    (1) Dept. of Information Technology, UU
    Journal: Advances in Computational Mathematics, volume 35, number 2-4, pp 323-355
    Abstract: In this work we analyse a method to construct numerically efficient and computationally cheap sparse approximations of some of the matrix blocks arising in the block-factorized preconditioners for matrices with a two-by-two block structure. The matrices arise from finite element discretizations of partial differential equations. We consider scalar elliptic problems, however the approach is appropriate also for other types of problems such as parabolic problems or systems of equations. The technique is applicable for both selfadjoint and non-selfadjoint problems, in two as well as in three space dimensions. We analyse in detail the two-dimensional case and provide extensive numerical evidence for the efficiency of the proposed matrix approximations, both serial and parallel. Two- and three-dimensional tests are included.

13. Automatic Counting of Annual Rings on Pinus Sylvestris End Faces in Sawmill Industry
    Author: Kristin Norell
    Journal: Computers and Electronics in Agriculture, volume 75, number 2, pp 231-237
    Abstract: The quality of wood can be analyzed using annual ring width. At Swedish sawmills, this is performed using manual inspection for grading purpose. Here a completely automatic method for counting the number of annual rings on log end faces is described and evaluated. The method is applied and tested using images from Pinus sylvestris end faces acquired in online sawmill production with a camera mounted above a conveyor belt. Completely untreated end faces were captured, as well as newly sawn ones. The proposed method includes preprocessing, pith detection and counting the number of rings in two regions of the end face. A new method to remove marks from uneven sawing is presented as a part of the preprocessing steps. The evaluation shows that the suggested automatic method performs as well as the manual measurements that are the method used for measuring today.

14. Efficient Computation of Enclosed Volume and Surface Area from the Same Triangulated Surface Representation
    Authors: Ingela Nyström, George J. Grevera (1), Bruce E. Hirsch (2), and Jayaram K. Udupa (3)
    (1) Computer Science Department, St. Joseph's University, PA, USA
    (2) Dept. of Neurobiology and Anatomy, Drexel University, PA, USA
    (3) Dept. of Radiology, University of Pennsylvania, PA, USA
    Journal: Computerized Medical Imaging and Graphics, volume 35, number 6, pp 460-471
    Abstract: We demonstrate that the volume enclosed by triangulated surfaces can be computed efficiently in the same elegant way the volume enclosed by digital surfaces can be computed by digital surface integration. Although digital surfaces are effective and efficient for visualization and volume measurement, their drawback is that surface area measurements derived from them are inaccurate. On the other hand, triangulated surfaces give more accurate surface area measurements, but volume measurements and visualization are less efficient. Our data structure (called t-shell) for representing triangulated digital surfaces retains advantages and overcomes difficulties of both the digital and the triangulated surfaces. We create a lookup table with area and volume contributions for each of the 256 Marching Cubes configurations. When scanning the shell (e.g., while creating it), the surface area and volume are incrementally computed by using the lookup table and the current x co-ordinate, where the sign of the x component of the triangle normal indicates the sign of the volume contribution. We have computed surface area and volume for digitized mathematical phantoms, physical phantoms, and real objects. The experiments show that triangulated surface area is more accurate, triangulated volume follows digital volume closely, and that the values get closer to the true value with decreasing voxel size.

15. Extracting 3D Information on Bone Remodeling in the Proximity of Titanium Implants in SRCT Image Volumes
    Authors: Hamid Sarve, Joakim Lindblad, Gunilla Borgefors, and Carina B. Johansson (1)
    (1) School of Health and Medical Sciences, Örebro University, Örebro
    Journal: Computer Methods and Programs in Biomedicine, volume 102, number 1, pp 25-34
    Abstract: Bone-implant integration is measured in several ways. Traditionally and routinely, 2D histological sections of samples, containing bone and the biomaterial, are stained and analyzed using a light microscope. Such histological section provides detailed cellular information about the bone regeneration in the proximity of the implant. However, this information reflects the integration in only a very small fraction, a 10 Î14m thick slice, of the sample. In this study, we show that feature values quantified on 2D sections are highly dependent on the orientation and the placement of the section, suggesting that a 3D analysis of the whole sample is of importance for a more complete judgment of the bone structure in the proximity of the implant. We propose features describing the 3D data by extending the features traditionally used for 2D-analysis. We present a method for extracting these features from 3D image data and we measure them on five 3D SRCT image volumes.

    We also simulate cuts through the image volume positioned at all possible section positions. These simulations show that the measurement variations due to the orientation of the section around the center line of the implant are about 30%.

16. Defuzzification of Spatial Fuzzy Sets by Feature Distance Minimization
    Authors: Natasa Sladoje (1), Joakim Lindblad, and Ingela Nyström
    (1) Faculty of Technical Sciences, University of Novi Sad, Novi Sad, Serbia
    Journal: Image and Vision Computing, volume 29, pp 127-141
    Abstract: We present a novel defuzzification method, i.e., a mapping from the set of fuzzy sets to the set of crisp sets, and we suggest its application to image processing. Spatial fuzzy sets are, e.g., useful as information preserving representations of objects in images. Defuzzification of such a spatial fuzzy set can be seen as a crisp segmentation procedure. With the aim to provide preservation of selected quantitative features of the fuzzy set, we define the defuzzification of a fuzzy set to be a crisp set which is as close as possible to the fuzzy set, where the distance measure on the set of fuzzy sets, that we propose for defuzzification, incorporates selected local and global features of the fuzzy sets. The distance measure is based on the Minkowski distance between feature representations of the sets. The distance minimization, performed in the suggested defuzzification method, provides preservation of the selected quantitative features of the fuzzy set. The method utilizes the information contained in the fuzzy representation for defining a mapping from the set of fuzzy sets to the set of crisp sets. If the fuzzy set is a representation of an unknown crisp original set, such that the selected features of the original set are preserved in the fuzzy representation, then the defuzzified set may be seen as an approximate reconstruction of the crisp original. We present four optimization algorithms, exhibiting different properties, for finding the crisp set closest to a given discrete fuzzy set. A number of examples, using both synthetic and real images, illustrate the main properties of the proposed method. An evaluation of both theoretical aspects of the method, and its results, is given.

17. Digital Distance Functions on Three-Dimensional Grids
    Authors: Robin Strand, Benedek Nagy (1), and Gunilla Borgefors
    (1) Dept. of Computer Science, Faculty of Informatics, University of Debrecen, Hungary
    Journal: Theoretical Computer Science, volume 412, number 15, pp 1350-1363
    Abstract: In this paper, we examine five different three-dimensional grids suited for image processing. Digital distance functions are defined on the cubic, face-centered cubic, body-centered cubic, honeycomb, and diamond grids. We give the parameters that minimize an error function that favors distance functions with low rotational dependency. We also give an algorithm for computing the distance transform - the tool by which these distance functions can be applied in image processing applications.