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PubMed1998

[Four year's experience with quality assurance in anesthesiology in Hamburg].

PURPOSE: Since 1992 421,851 anaesthesias were documented by 39 institutes with a standard dataset issued by the German Society of Anaesthesiology and Intensive Care (DGAI). The project was run by the Association for Quality Assurance (EQS) in Hamburg. Some results of the evaluation of this datapool are presented questioning the feasibility of the project to support improvement processes within the participating institutions and which adjustments should be done considering these experiences. METHODS: Data from machine-readable protocols and documentation software representing all anaesthesia cases were recorded since 1992 in a pilot project and since 1994 compulsory with a standard dataset issued by the DGAI. Comparing statistics of these data was produced at the EQS project office. In the steering committee and in meetings of the project participants the contents, policy and results of the project office. In the steering committee and in meetings of the project were critically analysed and adjustments initiated whenever necessary. Validity of data and feasibility of the method used was also questioned on the background of comparable studies. RESULTS: With an incidence of 14.1% of all anaesthesias with special occurrences (AVB) the results are in the same range if compared with most other studies. However, documentation of data is not complete. This is assumed to be due to the large size of the dataset with 112 items and the additional workload associated with it. Nevertheless the participants mostly consider the project to be a very useful support for internal improvement projects. CONCLUSION: The project method used so far is not mature yet. The data set must be streamlined and rendered more concise, quality indicators should be defined and tested, and the availability of statistically proven limits of tolerance should be the immediate aims in the further development of the project.

Adult↗
PubMed2003

PROTEOME-3D: an interactive bioinformatics tool for large-scale data exploration and knowledge discovery.

Comprehensive understanding of biological systems requires efficient and systematic assimilation of high-throughput datasets in the context of the existing knowledge base. A major limitation in the field of proteomics is the lack of an appropriate software platform that can synthesize a large number of experimental datasets in the context of the existing knowledge base. Here, we describe a software platform, termed PROTEOME-3D, that utilizes three essential features for systematic analysis of proteomics data: creation of a scalable, queryable, customized database for identified proteins from published literature; graphical tools for displaying proteome landscapes and trends from multiple large-scale experiments; and interactive data analysis that facilitates identification of crucial networks and pathways. Thus, PROTEOME-3D offers a standardized platform to analyze high-throughput experimental datasets for the identification of crucial players in co-regulated pathways and cellular processes.

Computational Biology↗
PubMed2006

Standardized volume rendering for magnetic resonance angiography measurements in the abdominal aorta.

PURPOSE: To compare three methods for standardizing volume rendering technique (VRT) protocols by studying aortic diameter measurements in magnetic resonance angiography (MRA) datasets. MATERIAL AND METHODS: Datasets from 20 patients previously examined with gadolinium-enhanced MRA and with digital subtraction angiography (DSA) for abdominal aortic aneurysm were retrospectively evaluated by three independent readers. The MRA datasets were viewed using VRT with three different standardized transfer functions: the percentile method (Pc-VRT), the maximum-likelihood method (ML-VRT), and the partial range histogram method (PRH-VRT). The aortic diameters obtained with these three methods were compared with freely chosen VRT parameters (F-VRT) and with maximum intensity projection (MIP) concerning inter-reader variability and agreement with the reference method DSA. RESULTS: F-VRT parameters and PRH-VRT gave significantly higher diameter values than DSA, whereas Pc-VRT gave significantly lower values than DSA. The highest interobserver variability was found for F-VRT parameters and MIP, and the lowest for Pc-VRT and PRH-VRT. All standardized VRT methods were significantly superior to both MIP and F-VRT in this respect. The agreement with DSA was best for PRH-VRT, which was the only method with a mean error below 1 mm and which also had the narrowest limits of agreement (95% of cases between 2.1 mm below and 3.1 mm above DSA). CONCLUSION: All the standardized VRT methods compare favorably with MIP and VRT with freely selected parameters as regards interobserver variability. The partial range histogram method, although systematically overestimating vessel diameters, gives results closest to those of DSA.

Analysis of Variance↗
PubMed2006

Misrepresentation of surface rendering of pediatric brain malformations performed following spatial normalization.

PURPOSE: To evaluate the effects of spatial normalization on volume rendering in cases of pediatric brain malformation. MATERIAL AND METHODS: Three-dimensional (3D) T1-weighted volume datasets were acquired in three children, one with pachygyria, one with a Dandy-Walker malformation associated with polymicrogyria, and one with dysgenesis of the corpus callosum. On the non-normalized datasets, the skull margins were cropped and the remainder stripped with the brain extraction technique (BET). The data were also normalized into standard anatomic reference space using pediatric templates prior to the BET script. The surface constructions obtained by both techniques were then compared for geometric distortions. RESULTS: Normalization of 3D datasets resulted in significant distortions in the shape of the brain, with increased anterior-posterior dimensions and narrower transverse diameter in all three cases. In two cases, there were alterations in the appearance of the gyri and sulci, leading to a potential misinterpretation of the volume-rendered surface when the gyri and sulci were in fact normal. CONCLUSION: In pediatric brain, particularly those with congenital brain anomalies, normalization as a post-processing step should be avoided as this may lead to misrepresentation of brain morphometry.

Diagnostic Errors↗
PubMed2006

Respiration correlated cone-beam computed tomography and 4DCT for evaluating target motion in Stereotactic Lung Radiation Therapy.

An image-guidance process for using cone-beam computed tomography (CBCT) for stereotactic body radiation therapy (SBRT) of peripheral lung lesions is presented. Respiration correlated CBCT on the treatment unit and four dimensional computed tomography (4DCT) from planning are evaluated for assessing respiration-induced target motion during planning and treatment fractions. Image-guided SBRT was performed for 12 patients (13 lesions) with inoperable early stage non-small cell lung carcinoma. Kilovoltage (kV) projections were acquired over a 360 degree gantry rotation and sorted based on the pixel value of an image-based aperture located at the air-tissue interface of the diaphragm. The sorted projections were reconstructed to provide volumetric respiration correlated CBCT image datasets at different phases of the respiratory cycle. The 4D volumetric datasets were directly compared with 4DCT datasets acquired at the time of planning. For ten of 12 patients treated, the lung tumour motion, as measured by respiration correlated CBCT on the treatment unit, was consistent with the tumour motion measured by 4DCT at the time of planning. However, in two patients, maximum discrepancies observed were 6 and 10 mm in the anterior-posterior and superior-inferior directions, respectively. Respiration correlated CBCT acquired on the treatment unit allows target motion to be assessed for each treatment fraction, allows target localization based on different phases on the breathing cycle, and provides the facility for adaptive margin design in radiation therapy of lung malignancies. The current study has shown that the relative motion and position of the tumour at the time of treatment may not match that of the planning 4DCT scan. Therefore, application of breathing motion data acquired at simulation for tracking or gating radiation therapy may not be suitable for all patients - even those receiving short course treatment techniques such as SBRT.

Carcinoma, Non-Small-Cell Lung↗
PubMed2002

Comparisons of lung tumour mortality risk in the Japanese A-bomb survivors and in the Colorado Plateau uranium miners: support for the ICRP lung model.

PURPOSES: To estimate the ratio of risks for exposure to radon progeny relative to low-LET radiation based on human lung cancer data, taking account of possible time and age variations in radiation-induced lung cancer risk. MATERIALS AND METHODS: Fitting two sorts of time- and age-adjusted relative risk models to a case-control dataset nested within the Colorado Plateau uranium miner cohort and to the Japanese atomic (A)-bomb survivor mortality data. RESULTS: If all A-bomb survivors are compared with the Colorado data, there are statistically significant (two-sided p < 0.05) differences between the two datasets in the pattern of the variation of relative risk with time after exposure, age at exposure and attained age. The excess relative risk decreases much faster with time, age at exposure and attained age in the Colorado uranium miners than in the Japanese A-bomb survivors. If only male A-bomb survivors are compared with the Colorado data, there are no longer statistically significant differences between the two datasets in the pattern of variation of relative risk with time after exposure, age at exposure or attained age. There are no statistically significant differences between the male and female A-bomb survivors in the speed of reduction of relative risk with time after exposure, age at exposure or attained age, although there are indications of rather faster reduction of relative risk with time and age among male survivors than among female survivors. The implicit risk conversion factor for exposure to radon progeny relative to the A-bomb radiation in the male survivors is 1.8 x 10(-2) Sv WLM(-1) (95% CI 6.1 x10(-3), 1.1 x 10(-1)) using a model with exponential adjustments for the effects of radiation for time since exposure and age at exposure, and 1.9 x 10(-2) Sv WLM(-1) (95% CI 6.2 x 10(-3), 1.6 x 10(-1)) using a model with adjustments for the effects of radiation proportional to powers of time since exposure and attained age. Estimates of the risk conversion factor calculated using variant assumptions as to the definition of lung cancer in the Colorado data, or by excluding miners for whom exposure estimates may be less reliable, are very similar. The absence of information on cigarette smoking in the Japanese A-bomb survivors, and the possibility that this may confound the time trends in radiation-induced lung cancer risk in that cohort, imply that these findings should be interpreted with caution. CONCLUSIONS: There are no statistically significant differences between the male A-bomb survivors data and the Colorado miner data in the pattern of variation of relative risk with time after exposure and age at exposure. The risk conversion factor is very close to the value suggested by the latest ICRP lung model, albeit with substantial uncertainties.

Adult↗
PubMed1998

A non-parametric method of reconstructing single-dose survival curves from multi-fraction experiments.

PURPOSE: A method of estimating the single-dose curve from designed multifraction experiments is described and applied to three datasets. MATERIALS AND METHODS: The method, which is non-parametric and based on standard statistical regression techniques, can be used for functional endpoints which are either continuous or binary. The datasets are concerned with wound healing on mice, myelopathy in guinea pigs and spermatogenesis in mice. The results are compared with the results from fitting the linear quadratic model. The statistical methods of Bootstrapping and residual plots are illustrated. RESULTS: The method is based in part on an assumed statistical model, however, exact knowledge of the correct statistical model is not necessary to obtain an estimate of the shape of the single-dose survival curve. We find no good evidence from the reconstructed single-dose survival curve of an "induced repair" phenomena at low doses for the wound healing and spermatogenesis experiments. For the myelopathy experiment the data are consistent with the LQ model with a low alpha-beta ratio down to doses of at least 1.5 Gy per fraction. CONCLUSIONS: A robust statistical method of estimating the shape of the single-dose survival curve is demonstrated using standard statistical software on three datasets.

Animals↗
PubMed2000

Is daily mortality associated specifically with fine particles? Data reconstruction and replication of analyses.

In 1996, Schwartz, Dockery, and Neas reported that daily mortality was more strongly associated with concentrations of PM2.5 than with concentrations of larger particles (coarse mass [CM]) in six U.S. cities ("original paper"/"original analyses"). Because of the public policy implications of the findings and the uniqueness of the concentration data, we undertook a reanalysis of these results. This paper presents results of the reconstruction of these data and replication of the original analyses using the reconstructed data. The original investigators provided particulate air pollution data for this paper. Daily weather and daily counts of total and cause-specific deaths were reconstructed from original public records. The reconstructed particulate air pollution and weather data were consistent with the summaries presented in the original paper. Daily counts of deaths in the reconstructed data set were lower than in the original paper because of restrictions on residence and place of death. The reconstruction process identified an administrative change in county codes that led to higher numbers of deaths in St. Louis. Despite these differences in daily counts of deaths, the estimated effects of particulate air pollution from the reconstructed dataset, using analytic methods as described in the original paper, produced combined effect estimates essentially equivalent to the originally published results. For example, the estimated association of a 10 micrograms/m3 increase in 2-day mean particulate air pollution on total mortality was 1.3% (95% confidence interval [CI] 0.9-1.7%, t = 6.53) for PM2.5 based on the reconstructed dataset, compared to the originally reported association of 1.5% (95% CI 1.1-1.9%, t = 7.41). For coarse particles, the estimated association from the reconstructed dataset was 0.4% (95% CI -0.2-0.9%, t = 1.43) compared to the originally reported association of 0.4% (95% CI -0.1-1.0%, t = 1.48). These results from the reconstructed data suggest that the original results reported by Schwartz, Dockery, and Neas were essentially replicated.

Adolescent↗
PubMed2002

Molecular systematics of the Eastern Fence Lizard (Sceloporus undulatus): a comparison of Parsimony, Likelihood, and Bayesian approaches.

Phylogenetic analysis of large datasets using complex nucleotide substitution models under a maximum likelihood framework can be computationally infeasible, especially when attempting to infer confidence values by way of nonparametric bootstrapping. Recent developments in phylogenetics suggest the computational burden can be reduced by using Bayesian methods of phylogenetic inference. However, few empirical phylogenetic studies exist that explore the efficiency of Bayesian analysis of large datasets. To this end, we conducted an extensive phylogenetic analysis of the wide-ranging and geographically variable Eastern Fence Lizard (Sceloporus undulatus). Maximum parsimony, maximum likelihood, and Bayesian phylogenetic analyses were performed on a combined mitochondrial DNA dataset (12S and 16S rRNA, ND1 protein-coding gene, and associated tRNA; 3,688 bp total) for 56 populations of S. undulatus (78 total terminals including other S. undulatus group species and outgroups). Maximum parsimony analysis resulted in numerous equally parsimonious trees (82,646 from equally weighted parsimony and 335 from weighted parsimony). The majority rule consensus tree derived from the Bayesian analysis was topologically identical to the single best phylogeny inferred from the maximum likelihood analysis, but required approximately 80% less computational time. The mtDNA data provide strong support for the monophyly of the S. undulatus group and the paraphyly of "S. undulatus" with respect to S. belli, S. cautus, and S. woodi. Parallel evolution of ecomorphs within "S. undulatus" has masked the actual number of species within this group. This evidence, along with convincing patterns of phylogeographic differentiation suggests "S. undulatus" represents at least four lineages that should be recognized as evolutionary species.

Animals↗
PubMedDate not supplied

National Emergency Medical Services Information System (NEMSIS).

The absence of emergency medical services (EMS) patient care data has hindered development and evaluation of EMS systems. The National Highway Traffic Safety Administration (NHTSA), in cooperation with the Health Resources and Services Administration (HRSA), has provided funding to the National Association of State EMS Directors to develop a National EMS Information System (NEMSIS). NEMSIS is being designed to provide a uniform national EMS dataset, with standard terms, definitions, and values, as well as a national EMS database, with aggregated data from all states on a limited number of data elements. Forty-eight of the states, the District of Columbia, and three territories signed a memorandum of agreement documenting support for the NEMSIS project and expressing a desire for full implementation of the NEMSIS dataset. NHTSA has agreed to house the National EMS Database at its National Center for Statistics and Analysis. NHTSA, in cooperation with HRSA and the Centers for Disease Control and Prevention, recently entered into a cooperative agreement with the University of Utah School of Medicine to operate a NEMSIS Technical Assistance Center that will provide related assistance to official EMS agencies and to commercial software vendors. The Technical Assistance Center will also biannually assess state and territorial capabilities to provide data to the national EMS database. NEMSIS will provide a uniform national EMS dataset, with standard terms, definitions, and values, as well as a national EMS database, with aggregated data from all states on a limited number of data elements. Many of the potential benefits of implementation of NEMSIS are enumerated in this report.

Databases as Topic↗
PubMed2005

A novel approach for incremental uncertainty rule generation from databases with missing values handling: application to dynamic medical databases.

Current approaches for mining association rules usually assume that the mining is performed in a static database, where the problem of missing attribute values does not practically exist. However, these assumptions are not preserved in some medical databases, like in a home care system. In this paper, a novel uncertainty rule algorithm is illustrated, namely URG-2 (Uncertainty Rule Generator), which addresses the problem of mining dynamic databases containing missing values. This algorithm requires only one pass from the initial dataset in order to generate the item set, while new metrics corresponding to the notion of Support and Confidence are used. URG-2 was evaluated over two medical databases, introducing randomly multiple missing values for each record's attribute (rate: 5-20% by 5% increments) in the initial dataset. Compared with the classical approach (records with missing values are ignored), the proposed algorithm was more robust in mining rules from datasets containing missing values. In all cases, the difference in preserving the initial rules ranged between 30% and 60% in favour of URG-2. Moreover, due to its incremental nature, URG-2 saved over 90% of the time required for thorough re-mining. Thus, the proposed algorithm can offer a preferable solution for mining in dynamic relational databases.

Algorithms↗
PubMed2002

Rapid generation of preview images for real-time 3D MR angiography.

In 3D real-time MR angiography the reconstruction of images from large raw datasets via Fourier transforms with minimal delays is problematic. In this study strategies for reconstructing time-resolved three-dimensional (3D) datasets at a rate substantially faster than conventional 3D MR image reconstruction were investigated on general-purpose computer hardware. Moderate quality 'preview images' were generated from k-space subsets to reduce image reconstruction times from more than 50 s to 0.3 s per image volume. A blinded review of 3D TRICKS patient examinations showed that these moderate-quality images were sufficient for providing immediate feedback and guiding the subsequent reconstruction of selected time frames (p < 0.05). Fourier projection (reconstruction from a central k-space slice) was the most efficient reconstruction technique. However, the reduction of the reconstructed volume in all three dimensions resulted in higher contrast and better image quality while allowing reconstruction in near-to-real-time (less than 1 s per image volume). The use of such preview images in a real-time system allows for fast feedback from dynamic 3D datasets, enables scanner interaction with minimal latencies and can substantially reduce the postprocessing times.

Angiography↗
PubMed2002

Inversion of the 3D exponential x-ray transform for a half equatorial band and other semi-circular geometries.

This work presents new mathematical results on the inversion of the exponential x-ray transform. It is shown that a reconstruction formula can be obtained for any dataset whose projection directions consist of a union of half great circles on the unit sphere. A basic example of such a dataset is the semi-equatorial band. The discussion in the paper is mostly focused on this example. The reconstruction formula takes the form of a Neumann (geometric) series and is both exact and stable. The exponential x-ray transform has been mainly studied in SPECT imaging. In this context, our results demonstrate mathematically that fully 3D image reconstruction in SPECT with non-zero attenuation does not always require symmetric datasets (opposing views).

Algorithms↗
PubMed2003

A methodology for generating normal and pathological brain perfusion SPECT images for evaluation of MRI/SPECT fusion methods: application in epilepsy.

Quantitative evaluation of brain MRI/SPECT fusion methods for normal and in particular pathological datasets is difficult, due to the frequent lack of relevant ground truth. We propose a methodology to generate MRI and SPECT datasets dedicated to the evaluation of MRI/SPECT fusion methods and illustrate the method when dealing with ictal SPECT. The method consists in generating normal or pathological SPECT data perfectly aligned with a high-resolution 3D T1-weighted MRI using realistic Monte Carlo simulations that closely reproduce the response of a SPECT imaging system. Anatomical input data for the SPECT simulations are obtained from this 3D T1-weighted MRI, while functional input data result from an inter-individual analysis of anatomically standardized SPECT data. The method makes it possible to control the 'brain perfusion' function by proposing a theoretical model of brain perfusion from measurements performed on real SPECT images. Our method provides an absolute gold standard for assessing MRI/SPECT registration method accuracy since, by construction, the SPECT data are perfectly registered with the MRI data. The proposed methodology has been applied to create a theoretical model of normal brain perfusion and ictal brain perfusion characteristic of mesial temporal lobe epilepsy. To approach realistic and unbiased perfusion models, real SPECT data were corrected for uniform attenuation, scatter and partial volume effect. An anatomic standardization was used to account for anatomic variability between subjects. Realistic simulations of normal and ictal SPECT deduced from these perfusion models are presented. The comparison of real and simulated SPECT images showed relative differences in regional activity concentration of less than 20% in most anatomical structures, for both normal and ictal data, suggesting realistic models of perfusion distributions for evaluation purposes. Inter-hemispheric asymmetry coefficients measured on simulated data were found within the range of asymmetry coefficients measured on corresponding real data. The features of the proposed approach are compared with those of other methods previously described to obtain datasets appropriate for the assessment of fusion methods.

Adult↗
PubMed2005

Simulation of realistic abnormal SPECT brain perfusion images: application in semi-quantitative analysis.

Simulation is useful in the validation of functional image analysis methods, particularly when considering the number of analysis techniques currently available lacking thorough validation. Problems exist with current simulation methods due to long run times or unrealistic results making it problematic to generate complete datasets. A method is presented for simulating known abnormalities within normal brain SPECT images using a measured point spread function (PSF), and incorporating a stereotactic atlas of the brain for anatomical positioning. This allows for the simulation of realistic images through the use of prior information regarding disease progression. SPECT images of cerebral perfusion have been generated consisting of a control database and a group of simulated abnormal subjects that are to be used in a UK audit of analysis methods. The abnormality is defined in the stereotactic space, then transformed to the individual subject space, convolved with a measured PSF and removed from the normal subject image. The dataset was analysed using SPM99 (Wellcome Department of Imaging Neuroscience, University College, London) and the MarsBaR volume of interest (VOI) analysis toolbox. The results were evaluated by comparison with the known ground truth. The analysis showed improvement when using a smoothing kernel equal to system resolution over the slightly larger kernel used routinely. Significant correlation was found between effective volume of a simulated abnormality and the detected size using SPM99. Improvements in VOI analysis sensitivity were found when using the region median over the region mean. The method and dataset provide an efficient methodology for use in the comparison and cross validation of semi-quantitative analysis methods in brain SPECT, and allow the optimization of analysis parameters.

Adult↗
PubMed2006

Respiratory motion correction for PET oncology applications using affine transformation of list mode data.

Respiratory motion is a source of artefacts and reduced image quality in PET. Proposed methodology for correction of respiratory effects involves the use of gated frames, which are however of low signal-to-noise ratio. Therefore a method accounting for respiratory motion effects without affecting the statistical quality of the reconstructed images is necessary. We have implemented an affine transformation of list mode data for the correction of respiratory motion over the thorax. The study was performed using datasets of the NCAT phantom at different points throughout the respiratory cycle. List mode data based PET simulated frames were produced by combining the NCAT datasets with a Monte Carlo simulation. Transformation parameters accounting for respiratory motion were estimated according to an affine registration and were subsequently applied on the original list mode data. The corrected and uncorrected list mode datasets were subsequently reconstructed using the one-pass list mode EM (OPL-EM) algorithm. Comparison of corrected and uncorrected respiratory motion average frames suggests that an affine transformation in the list mode data prior to reconstruction can produce significant improvements in accounting for respiratory motion artefacts in the lungs and heart. However, the application of a common set of transformation parameters across the imaging field of view does not significantly correct the respiratory effects on organs such as the stomach, liver or spleen.

Algorithms↗
PubMed2000

A real-time volumetric visualization system for electrical impedance tomography.

Three dimensional (3D) electrical impedance tomography (EIT) presents many additional challenges over and above those associated with two dimensional EIT systems. With present two dimensional (2D) systems, tomographs can be reconstructed and displayed on a PC with a standard computer monitor. In addition, using appropriate data acquisition hardware and simple image reconstruction algorithms, it is possible to collect, reconstruct and display volumetric EIT images in real time using parallel processing architectures. The advantages of this 'real-time' capability are many and include the ability to immediately assess the correct functioning of the system and the ability to track patient events and the effect of procedures in real time. Whilst 3D EIT boundary datasets can be collected in real time, their real-time image reconstruction and display presents some computational challenges. This explains why, to date, no real-time solutions have been presented. In addition the use of a standard computer monitor to display 3D volumes is unsatisfactory since not all depth cues are preserved when using this type of 2D display device. We present a system which is capable of displaying 3D EIT datasets in real time and allows interactive modification of the user's viewpoint. This allows the user to fly around (and through) the EIT volumetric dataset.

Algorithms↗
PubMed2001

Tsukuba BB: a branch and bound algorithm for local multiple alignment of DNA and protein sequences.

In this paper we present a branch and bound algorithm for local gapless multiple sequence alignment (motif alignment) and its implementation. The algorithm uses both score-based bounding and a novel bounding technique based on the "consistency" of the alignment. A sequence order independent search tree is used in conjunction with a technique for avoiding redundant calculations inherent in the structure of the tree. This is the first program to exploit the fact that the motif alignment problem is easier for short motifs. Indeed, for a short fixed motif width, the running time of the algorithm is asymptotically linear in the size of the input. We tested the performance of the program on a dataset of 300 E. coli promoter sequences and a dataset of 85 lipocalin protein sequences. For a motif width of 4, the optimal alignment of the entire set of sequences can be found. For the more natural motif width of 6, the program can align 21 sequences of length 100, more than twice the number of sequences which can be aligned by the best previous exact algorithm. The algorithm can relax the constraint of requiring each sequence to be aligned, and align 105 of the 300 promoter sequences with a motif width of 6. For the lipocalin dataset, we introduce a technique for reducing the effective alphabet size with a minimal loss of useful information. With this technique, we show that the program can find meaningful motifs in a reasonable amount of time by optimizing the score over three motif positions.

Algorithms↗