Geometric methods on low-rank matrix and tensor manifolds

In this chapter we present numerical methods for low-rank matrix and tensor problems that explicitly make use of the geometry of rank constrained matrix and tensor spaces. We focus on two types of problems: The first are optimization problems, like matrix and tensor completion, solving linear systems and eigenvalue problems. Such problems can be solved by numerical optimization for manifolds, called Riemannian optimization methods. We will explain the basic elements of differential geometry in order to apply such methods efficiently to rank constrained matrix and tensor spaces. The second type of problem is ordinary differential equations, defined on matrix and tensor spaces. We show how their solution can be approximated by the dynamical low-rank principle, and discuss several numerical integrators that rely in an essential way on geometric properties that are characteristic to sets of low rank matrices and tensors

Influence Of Display Characteristics On Clinical Performance In Digital Pathology

INTRODUCTION / BACKGROUND: Digital Pathology adoption is increasing rapidly. Recent technological advances have resulted in a steep increase in the performance and quality of digital pathology systems. Quality assurance mechanisms are being developed to ensure consistent quality of scanned slide images. However one important component that surprisingly is often overlooked is the display system. Pathologists base their diagnosis on the images presented by the display. The quality of these digital images depends on all of the components in the imaging chain, including the display itself. Even a perfectly scanned high quality image will not be useful if it is visualized on a low quality display. AIMS: The goal of this paper is to study important display characteristics and to determine what their effect is on percent correct diagnosis, reading time, diagnostic confidence and inter-pathologist-agreement. Furthermore a recommendation will be provided for minimum requirements of a digital pathology display system. METHODS: This paper combines and analyses results of several experiments that we have performed during the last two years. These studies included actual clinical studies where pathologists diagnose clinical images, reading studies where pathologists subjectively score quality of clinical images, as well as bench testing on both test and clinical images. Separately analyzing the influence of display luminance, color settings, calibration and quality assurance, stability and resolution allows us to determine a relative importance of these characteristics. It also allows recommending minimal display specifications RESULTS: A first clinical study analyzed the impact of luminance and color instability/aging of display systems on reading time, percent correct diagnosis, and inter pathologist agreement. 120 clinical digital pathology images were presented to pathologists. The images were scored and the diagnosis and reading time was recorded. The study shows that both luminance and color instability result into lower percent correct, lower inter pathologist agreement, and higher reading time. The results also suggest that color instability has a larger influence than luminance instability. A second study focused on color settings of a display. Three different calibration settings were compared: “sRGB”, “DICOM GSDF” and a recently proposed new standard “CSDF”. Bench testing and subjective reader preference analysis was performed. Results indicate that perceived contrast of clinically relevant features in digital pathology images is higher when using CSDF compared to sRGB and DICOM GSDF. A final study looked at display size, resolution, contrast and luminance and their influence on subjective quality preference, ease of reading and reading time. Based on the combination of these different results we make clear recommendations for minimum specifications for digital pathology display systems

Comparison Display Resolution On User Impact For Digital Pathology

Introduction/ Background Digital pathology images are very large, up to 100000x100000 pixels which are 30 to 50 times larger than a radiological image for which 12 Mega Pixels (MP) medical displays can be used. Higher resolution displays may have an important influence on digital pathology ergonomics. Three displays with varying resolutions were studied to determine their impact on user interaction. Aims Our hypothesis was that “with higher resolution displays, pathologists need less interaction such as panning and zooming actions and can focus more on image content”. A psycho-physical study has been carried out for validating this hypothesis at the University of Pittsburgh Medical Center. Methods Three experienced pathologists were selected. Seventy pathology including a wide variety of histological and cytological diagnoses were digitized (Aperio Scanscope XT scanner) and used in a previous study [Ava15]. Customized and optimized viewing software was used to display images and record pathologist’s interactions such mouse clicks, zooming and panning. Three medical displays with different different resolutions were used: 2MP (BARCO MDSC-2124), 4MP (BARCO MDPC-4130) and 12MP (BARCO MDCC-12133), all with the same maximum luminance. Scripts were used for statistical analyze and 1D, 2D, 3D plotting results. User interactions with each image were used to recreate videos documenting of their exact navigation with each digital slide. Results The results of number of zooming and panning interactions are given in the Table 1, as well as averages. When display resolution was increased, the number of panning and zooming interactions significantly decreases for all three observers. For panning, there was on average 1172 panning actions for the 2MP and 951 actions for the 12MP display. For zooming actions, there was on average 12315 zoom actions for the 2MP and 2847 actions for the 12MP display. Between the 2MP and 12MP displays, the ratio of the number of zooms was 4:1 in favor of the 12MP monitor. On figure 1, the 3D plots of one case for the three monitors show the navigation through the slide and show lesser points for higher resolution display. With higher resolution the pathologist goes more directly to the Region Of Interest (ROI) for making the decision. Figure 2 shows more analysis of the zoom values across the cases for the three monitors. The pathologists have the tendency to remain close to a value of 1 with the 12 MP display where a value of 1 means that no zoom is applied. This is illustrated by the Figure 2 showing for observer 2 the boxplots of the zoom values for the three displays. It clearly shows that with higher resolution display the trend goes to get closer to one for the zoom value meaning no need to zoom in in the image. We used three different displays instead of one unique display with three different resolutions. Though using just one display would have reduced variability of differing LCD panels, pixel size and structure, it would not have been commercially or clinically realistic. Despite the limited number of pathologists, this study shows that display resolution used for digital pathology is important. Higher resolution monitors significantly help reducing the number of user interactions and thereby can minimize pathologist fatigue when reading digital slides

Status and recent developments at the polarized-electron injector of the superconducting Darmstadt electron linear accelerator S-DALINAC

At the superconducting Darmstadt electron linac a 100 keV source of polarized electrons has been installed. Major components had been tested prior to installation at an offline teststand. Commissioning of the new source at the S-DALINAC will take place early in 2011. We report on the performance of the teststand, simulations, developments on the laser systems, new radio-frequency components for the S-DALINAC injector, and the status of the implementation of the source