| 1. |
- Eriksson, Thomas, et al.
(författare)
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Are low-dose CT scans a satisfactory substitute for stereoradiographs for migration studies? A preclinical test of low-dose CT scanning protocols and their application in a pilot patient.
- 2019
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Ingår i: Acta Radiologica. - : Sage Publications. - 0284-1851 .- 1600-0455.
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Computed tomography (CT) has the potential to acquire the data needed for migration studies of orthopedic joint implants of patients who have had tantalum beads implanted at the time of joint replacement surgery. This can be accomplished with the same precision as radiostereometric analysis (RSA). Switching to CT would increase availability without the need for the specific facilities required for RSA. However, higher effective dose is a concern.PURPOSE: To investigate if migration measurements can be done with CT with an accuracy and effective dose comparable to that of conventional RSA.MATERIAL AND METHODS: Fourteen scanning protocols were tested in a hip phantom that incorporated tantalum beads and an uncemented femoral stem. The protocols were graded for clinical practice according to the three parameters of image quality, effective dose, and robustness of numerical data. After grading, the two protocols that graded best overall were applied to a pilot patient.RESULTS: All protocols produced scans in which the numerical data were sufficient for a migration analysis at least as precise as would be expected using RSA. A protocol with an effective dose of 0.70 mSv was shown to be applicable in a pilot patient.CONCLUSION: Low-dose CT scans with an effective dose comparable to a set of routine plain radiographs can be used for precise migration measurements.
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| 2. |
- Försth, Peter, 1966-, et al.
(författare)
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Motion Analysis in Lumbar Spinal Stenosis With Degenerative Spondylolisthesis : A Feasibility Study of the 3DCT Technique Comparing Laminectomy Versus Bilateral Laminotomy.
- 2018
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Ingår i: Clinical spine surgery. - : Wolters Kluwer. - 2380-0186 .- 2380-0194. ; 31:8, s. E397-E402
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Tidskriftsartikel (refereegranskat)abstract
- Study Design: This was a randomized radiologic biomechanical pilot study in vivo. Objective: The objectives of this study was to evaluate if 3-dimensional computed tomography is a feasible tool in motion analyses of the lumbar spine and to study if preservation of segmental midline structures offers less postoperative instability compared with central decompression in patients with lumbar spinal stenosis with degenerative spondylolisthesis. Summary of Background Data: The role of segmental instability after decompression is controversial. Validated techniques for biomechanical evaluation of segmental motion in human live subjects are lacking. Methods: In total, 23 patients (mean age, 68 y) with typical symptoms and magnetic resonance imaging findings of spinal stenosis with degenerative spondylolisthesis (>3 mm) in 1 or 2 adjacent lumbar levels from L3 to L5 were included. They were randomized to either laminectomy (LE) or bilateral laminotomy (LT) (preservation of the midline structures). Documentation of segmental motion was made preoperatively and 6 months postoperatively with CT in provoked flexion and extension. Analyses of movements were performed with validated software. The accuracy for this method is 0.6 mm in translation and 1 degree in rotation. Patient-reported outcome measures were collected from the Swespine register preoperatively and 2-year postoperatively. Results: The mean preoperative values for 3D rotation and translation were 6.2 degrees and 1.8 mm. The mean increase in 3D rotation 6 months after surgery was 0.25 degrees after LT and 0.7 degrees after LE (P=0.79) while the mean increase in 3D translation was 0.15 mm after LT and 1.1 mm after LE (P=0.42). Both surgeries demonstrated significant improvement in patient-reported outcome measures 2 years postoperatively. Conclusions: The 3D computed tomography technique proved to be a feasible tool in the evaluation of segmental motion in this group of older patients. There was negligible increase in segmental motion after decompressive surgery. LE with removal of the midline structures did not create a greater instability compared with when these structures were preserved.
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| 3. |
- Weidenhielm, Lars, et al.
(författare)
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Prosthetic liner wear in total hip replacement : a longitudinal 13-year study with computed tomography.
- 2018
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Ingår i: Skeletal Radiology. - : Springer. - 0364-2348 .- 1432-2161. ; 47:6, s. 883-887
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Tidskriftsartikel (refereegranskat)abstract
- This case report follows a woman who had a total hip replacement in 1992 when she was 45 years old. Six serial computed tomography (CT) examinations over a period of 13 years provided information that allowed her revision surgery to be limited to liner replacement as opposed to replacement of the entire prosthesis. Additionally, they provided data that ruled out the presence of osteolysis and indeed none was found at surgery. In 2004, when the first CT was performed, the 3D distance the femoral head had penetrated into the cup was determined to be 2.6 mm. By 2017, femoral head penetration had progressed to 5.0 mm. The extracted liner showed wear at the thinnest part to be 5.5 mm, as measured with a micrometer. The use of modern CT techniques can identify problems, while still correctable without major surgery. Furthermore, the ability of CT to assess the direction of wear revealed that the liner wear changed from the cranial to dorsal direction.
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| 4. |
- Barbette, Tom, 1990-, et al.
(författare)
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RSS++: load and state-aware receive side scaling
- 2019
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Ingår i: Proceedings of the 15th International Conference on emerging Networking EXperiments and Technologies. - Orlando, FL, USA : Association for Computing Machinery (ACM). - 9781450369985
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Konferensbidrag (refereegranskat)abstract
- While the current literature typically focuses on load-balancing among multiple servers, in this paper, we demonstrate the importance of load-balancing within a single machine (potentially with hundreds of CPU cores). In this context, we propose a new load-balancing technique (RSS++) that dynamically modifies the receive side scaling (RSS) indirection table to spread the load across the CPU cores in a more optimal way. RSS++ incurs up to 14x lower 95th percentile tail latency and orders of magnitude fewer packet drops compared to RSS under high CPU utilization. RSS++ allows higher CPU utilization and dynamic scaling of the number of allocated CPU cores to accommodate the input load, while avoiding the typical 25% over-provisioning. RSS++ has been implemented for both (i) DPDK and (ii) the Linux kernel. Additionally, we implement a new state migration technique, which facilitates sharding and reduces contention between CPU cores accessing per-flow data. RSS++ keeps the flow-state by groups that can be migrated at once, leading to a 20% higher efficiency than a state of the art shared flow table.
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| 5. |
- Bogdanov, Kirill, 1987-
(författare)
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Enabling Fast and Accurate Run-Time Decisions in Geo-Distributed Systems : Better Achieving Service Level Objectives
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Computing services are highly integrated into modern society and used by millions of people daily. To meet these high demands, many popular services are implemented and deployed as geo-distributed applications on top of third-party virtualized cloud providers. However, the nature of such a deployment leads to variable performance. To deliver high quality of service, these systems strive to adapt to ever-changing conditions by monitoring changes in state and making informed run-time decisions, such as choosing server peering, replica placement, and redirection of requests. In this dissertation, we seek to improve the quality of run-time decisions made by geo-distributed systems. We attempt to achieve this through: (1) a better understanding of the underlying deployment conditions, (2) systematic and thorough testing of the decision logic implemented in these systems, and (3) by providing a clear view of the network and system states allowing services to make better-informed decisions. First, we validate an application’s decision logic used in popular storage systems by examining replica selection algorithms. We do this by introducing GeoPerf, a tool that uses symbolic execution and modeling to perform systematic testing of replica selection algorithms. GeoPerf was used to test two popular storage systems and found one bug in each. Then, using measurements across EC2, we observed persistent correlation between network paths and network latency. Based on these observations, we introduce EdgeVar, a tool that decouples routing and congestion based changes in network latency. This additional information improves estimation of latency, as well as increases the stability of network path selection. Next, we introduce Tectonic, a tool that tracks an application’s requests and responses both at the user and kernel levels. In combination with EdgeVar, it decouples end-to-end request completion time into three components of network routing, network congestion, and service time. Finally, we demonstrate how this decoupling of request completion time components can be leveraged in practice by developing Kurma, a fast and accurate load balancer for geo-distributed storage systems. At runtime, Kurma integrates network latency and service time distributions to accurately estimate the rate of Service Level Objective (SLO) violations, for requests redirected between geo-distributed datacenters. Using real-world data, we demonstrate Kurma’s ability to effectively share load among datacenters while reducing SLO violations by a factor of up to 3 in high load settings or reducing the cost of running the service by up to 17%. The techniques described in this dissertation are important for current and future geo-distributed services that strive to provide the best quality of service to customers while minimizing the cost of operating the service.
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| 6. |
- Bogdanov, Kirill, et al.
(författare)
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Fast and accurate load balancing for geo-distributed storage systems
- 2018
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Ingår i: SoCC 2018 - Proceedings of the 2018 ACM Symposium on Cloud Computing. - New York, NY, USA : Association for Computing Machinery (ACM). - 9781450360111 ; , s. 386-400
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Konferensbidrag (refereegranskat)abstract
- The increasing density of globally distributed datacenters reduces the network latency between neighboring datacenters and allows replicated services deployed across neighboring locations to share workload when necessary, without violating strict Service Level Objectives (SLOs). We present Kurma, a practical implementation of a fast and accurate load balancer for geo-distributed storage systems. At run-time, Kurma integrates network latency and service time distributions to accurately estimate the rate of SLO violations for requests redirected across geo-distributed datacenters. Using these estimates, Kurma solves a decentralized rate-based performance model enabling fast load balancing (in the order of seconds) while taming global SLO violations. We integrate Kurma with Cassandra, a popular storage system. Using real-world traces along with a geo-distributed deployment across Amazon EC2, we demonstrate Kurma’s ability to effectively share load among datacenters while reducing SLO violations by up to a factor of 3 in high load settings or reducing the cost of running the service by up to 17%.
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| 7. |
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| 8. |
- Bogdanov, Kirill, 1987-
(författare)
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Reducing Long Tail Latencies in Geo-Distributed Systems
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Computing services are highly integrated into modern society. Millions of people rely on these services daily for communication, coordination, trading, and accessing to information. To meet high demands, many popular services are implemented and deployed as geo-distributed applications on top of third party virtualized cloud providers. However, the nature of such deployment provides variable performance characteristics. To deliver high quality of service, such systems strive to adapt to ever-changing conditions by monitoring changes in state and making run-time decisions, such as choosing server peering, replica placement, and quorum selection.In this thesis, we seek to improve the quality of run-time decisions made by geo-distributed systems. We attempt to achieve this through: (1) a better understanding of the underlying deployment conditions, (2) systematic and thorough testing of the decision logic implemented in these systems, and (3) by providing a clear view into the network and system states which allows these services to perform better-informed decisions.We performed a long-term cross datacenter latency measurement of the Amazon EC2 cloud provider. We used this data to quantify the variability of network conditions and demonstrated its impact on the performance of the systems deployed on top of this cloud provider.Next, we validate an application’s decision logic used in popular storage systems by examining replica selection algorithms. We introduce GeoPerf, a tool that uses symbolic execution and lightweight modeling to perform systematic testing of replica selection algorithms. We applied GeoPerf to test two popular storage systems and we found one bug in each.Then, using traceroute and one-way delay measurements across EC2, we demonstrated persistent correlation between network paths and network latency. We introduce EdgeVar, a tool that decouples routing and congestion based changes in network latency. By providing this additional information, we improved the quality of latency estimation, as well as increased the stability of network path selection.Finally, we introduce Tectonic, a tool that tracks an application’s requests and responses both at the user and kernel levels. In combination with EdgeVar, it provides a complete view of the delays associated with each processing stage of a request and response. Using Tectonic, we analyzed the impact of sharing CPUs in a virtualized environment and can infer the hypervisor’s scheduling policies. We argue for the importance of knowing these policies and propose to use them in applications’ decision making process.
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| 9. |
- Bogdanov, Kirill, et al.
(författare)
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The Nearest Replica Can Be Farther Than You Think
- 2015
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Ingår i: Proceedings of the ACM Symposium on Cloud Computing 2015. - New York, NY, USA : Association for Computing Machinery (ACM). ; , s. 16-29
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Konferensbidrag (refereegranskat)abstract
- Modern distributed systems are geo-distributed for reasons of increased performance, reliability, and survivability. At the heart of many such systems, e.g., the widely used Cassandra and MongoDB data stores, is an algorithm for choosing a closest set of replicas to service a client request. Suboptimal replica choices due to dynamically changing network conditions result in reduced performance as a result of increased response latency. We present GeoPerf, a tool that tries to automate the process of systematically testing the performance of replica selection algorithms for geodistributed storage systems. Our key idea is to combine symbolic execution and lightweight modeling to generate a set of inputs that can expose weaknesses in replica selection. As part of our evaluation, we analyzed network round trip times between geographically distributed Amazon EC2 regions, and showed a significant number of daily changes in nearestK replica orders. We tested Cassandra and MongoDB using our tool, and found bugs in each of these systems. Finally, we use our collected Amazon EC2 latency traces to quantify the time lost due to these bugs. For example due to the bug in Cassandra, the median wasted time for 10% of all requests is above 50 ms.
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| 10. |
- Bogdanov, Kirill, et al.
(författare)
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Toward Automated Testing of Geo-Distributed Replica Selection Algorithms
- 2015
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Ingår i: Proceedings of the 2015 ACM Conference on Special Interest Group on Data Communication. - New York, NY, USA : Association for Computing Machinery (ACM). ; , s. 89-90
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Konferensbidrag (refereegranskat)abstract
- Many geo-distributed systems rely on a replica selection algorithms to communicate with the closest set of replicas. Unfortunately, the bursty nature of the Internet traffic and ever changing network conditions present a problem in identifying the best choices of replicas. Suboptimal replica choices result in increased response latency and reduced system performance. In this work we present GeoPerf, a tool that tries to automate testing of geo-distributed replica selection algorithms. We used GeoPerf to test Cassandra and MongoDB, two popular data stores, and found bugs in each of these systems.
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