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As a common software framework, CONRAD enables the medical physics community to share algorithms and develop new ideas. In particular this offers new opportunities for scientific collaboration and quantitative performance comparison between the methods of different groups.

We present a new checkerboard detection algorithm which is able to detect checkerboards at extreme poses, or checkerboards which are highly distorted due to lens distortion even on low-resolution images. On the detected pattern we apply a surface fitting based subpixel refinement specifically tailored for checkerboard X-junctions. Finally, we investigate how the accuracy of a checkerboard detector affects the overall calibration result in multi-camera setups. The proposed method is evaluated on real images captured with different camera models to show its wide applicability. Quantitative comparisons to OpenCV's checkerboard detector show that the proposed method detects up to 80% more checkerboards and detects corner points more accurately, even under strong perspective distortion as often present in wide baseline stereo setups.

The recent growth in energy technologies and the management of subsurface reservoirs has led to increased human interaction with the Earth's crust. One consequence of this is the overall increase of anthropogenic earthquakes. To manage fluid-injection induced seismicity, in this study we propose to use an advanced fluidinjection scheme. First, long-term fluid-injection experiments are separated from short-term fluid-injection experiments. Of the short-term experiments, enhanced geothermal systems stimulations have shown a higher propensity to produce larger seismic events compared to hydraulic fracturing in oil and gas. Among the factors discussed for influencing the likelihood of an induced seismic event to occur are injection rate, cumulative injected volume, wellhead pressure, injection depth, stress state, rock type and proximity to faults. We present and discuss the concept of fatigue hydraulic fracturing at different scales in geothermal applications. In contrast to conventional hydraulic fracturing with monotonic injection of high pressure fluids, in fatigue hydraulic fracturing, the fluid is injected in pressure cycles with increasing target pressure, separated by depressurization phases for relaxing the crack tip stresses. During pressurization phases, the target pressure level is modified by pulse hydraulic fracturing generated with a second pump system. This combination of two pumps with multiple flow rates may allow a more complex fracture pattern to be designed, with arresting and branching fractures, forming a broader fracture process zone. Small scale laboratory fluid-injection tests on granite cores and intermediate-scale fluid-injection experiments in a hard rock underground laboratory are described. At laboratory scale, cyclic fluid injection test with acoustic emission analysis are reported with subsequent X-ray CT fracture pattern analysis. At intermediate-scale, in a controlled underground experiment at constant depth with wellknown stress state in granitic rock, we test advanced fluid injection schemes. The goal is to optimize the fracture network and mitigate larger seismic events. General findings in granitic rock, independent of scale, are summarized. First, the fracture breakdown pressure in fatigue hydraulic testing is lower than that in conventional hydraulic fracturing. Second, compared to continuous injection the magnitude of the largest induced seismic event seems to be systematically reduced by cyclic injection. Third, the fracture pattern in fatigue testing is different from that in conventional injection tests at high pressures. Cyclic fracture pattern seem to result from chiefly generated low energy grain boundary cracks forming a wider process zone. Fourth, cyclic injection increases the permeability of the system. A combination of cyclic progressive and pulse pressurization leads to the best hydraulic performance of all schemes tested. One advantage of fatigue testing is the fact that this soft stimulation method can be applied in circumstances where conventional stimulation m...

Economic production of a variety of geological resources, such as shale gas, tight oil, coal bed methane and geothermal heat using enhanced geothermal systems (EGS), relies on hydraulic stimulation treatments. These are reservoir enhancement methods where fluid is injected into a reservoir to increase its productivity by a combination of developing new tensile and shear fractures, and tensile opening and shearing of pre-existing fractures. Stimulated fractures may stay open naturally through the self-propping effect or they have to be kept open artificially by proppants, such as sands or ceramics that are injected together with the stimulation fluid to achieve a permanent productivity enhancement. Details about hydraulic fracturing and other reservoir stimulation methods can be found in an abundance of textbooks and other publications (e.g., Bunger et al. 2013; Economides and Nolte 2000; Economides and Martin 2007; Huenges and Ledru 2010). While improving the hydraulic reservoir performance, hydraulic stimulation treatments also cause fluid-injection-induced seismicity. On the one hand, induced seismicity

There is a need for objectively comparing backprojection implementations for reconstruction algorithms. RabbitCT aims to provide a solution to this problem by offering an open platform with fair chances for all participants. The authors are looking forward to a growing community and await feedback regarding future evaluations of novel software- and hardware-based acceleration schemes.

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The Common Unified Device Architecture (CUDA) introduced in 2007 by NVIDIA is a recent programming model making use of the unified shader design of the most recent graphics processing units (GPUs). The programming interface allows algorithm implementation using standard C language along with a few extensions without any knowledge about graphics programming using OpenGL, DirectX, and shading languages.We apply this novel technology to the Simultaneous Algebraic Reconstruction Technique (SART), which is an advanced iterative image reconstruction method in cone-beam CT. So far, the computational complexity of this algorithm has prohibited its use in most medical applications. However, since today's GPUs provide a high level of parallelism and are highly cost-efficient processors, they are predestinated for performing the iterative reconstruction according to medical requirements.In this paper we present an efficient implementation of the most time-consuming parts of the iterative reconstruction algorithm: forward-and back-projection. We also explain the required strategy to parallelize the algorithm for the CUDA 1.1 and CUDA 2.0 architecture. Furthermore, our implementation introduces an acceleration technique for the reconstruction compared to a standard SART implementation on the GPU using CUDA. Thus, we present an implementation that can be used in a time-critical clinical environment.Finally, we compare our results to the current applications on multi-core workstations, with respect to both reconstruction speed and (dis-)advantages. Our implementation exhibits a speed-up of more than 64 compared to a state-of-the-art CPU using hardware-accelerated texture interpolation.