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PubMed2001

Automatic segmentation algorithm for the extraction of lumen region and boundary from endoscopic images.

A new segmentation algorithm for lumen region detection and boundary extraction from gastro-intestinal (GI) images is presented. The proposed algorithm consists of two steps. First, a preliminary region of interest (ROI) representing the GI lumen is segmented by an adaptive progressive thresholding (APT) technique. Then, an adaptive filter, the Iris filter, is applied to the ROI to determine the actual region. It has been observed that the combined APT-Iris filter technique can enhance and detect the unclear boundaries in the lumen region of GI images and thus produces a more accurate lumen region, compared with the existing techniques. Experiments are carried out to determine the maximum error on the extracted boundary with respect to an expert-annotated boundary technique. Investigations show that, based on the experimental results obtained from 50 endoscopic images, the maximum error is reduced by up to 72 pixels for a 256 x 256 image representation compared with other existing techniques. In addition, a new boundary extraction algorithm, based on a heuristic search on the neighbourhood pixels, is employed to obtain a connected single pixel width outer boundary using two preferential sequence windows. Experimental results are also presented to justify the effectiveness of the proposed algorithm.

Algorithms↗

PubMed2003

Analytical guide wire motion algorithm for simulation of endovascular interventions.

Performing minimally invasive vascular interventions requires proper training, as a guide wire needs to be manipulated, by the tail, under fluoroscopic guidance. To provide a training environment, the motion of the guide wire inside the human vasculature can be simulated by computer. Such a simulation needs to be based on an algorithm that is both realistic and fast. To meet these two demands, an analytical solution to the problem of guide wire motion has been derived, using a new parametrisation of guide wire shape. The algorithm is highly generic, is entirely based on elementary physics and has good convergence properties (accuracy of 22 micron after two iterations). In an experimental validation of the algorithm in a planar model, the RMS of the spatial discrepancy between the real and simulated catheter positions was about 10% of the lumen size. Comparison of the simulated guide wire motion with 3D rotational angiography data of a real guide wire advanced in a plastic phantom of the cerebral vasculature showed that the new algorithm produced realistic results.

Algorithms↗

PubMed1991

New algorithm for the detection of the ECG fiducial point in the averaging technique.

The use of the coherent averaging technique applied to the electrocardiographic signal implies the location of a fiducial point as a synchronisation reference. An algorithm easily adaptable to a personal computer, operable in real time, insensitive to mains and to ECG-baseline fluctuations, with a low jitter value and the capacity to trigger any ECG signal wave or complex, has been developed. The algorithm detects those waveforms which, within certain confidence intervals, are morphologically equal to a reference wave. This wave is chosen by the user as the repetitive waveform within which the fiducial point is to be located. A two-window template and differential parameters are used. The possibility of building the template permits the user to adapt the algorithm to each patient's ECG. To evaluate its accuracy objectively, a software simulation was built of a generator capable of producing test signals as the sum of the 'useful' signal plus 'noise'. A jitter standard deviation of 1.65 ms was obtained in the worst test (SNR = 10 dB; noiseband = 0-50 Hz), which shows the excellent recognition accuracy of the algorithm.

Algorithms↗

PubMed1992

A local algorithm for DNA sequence alignment with inversions.

A dynamic programming algorithm to find all optimal alignments of DNA subsequences is described. The alignments use not only substitutions, insertions and deletions of nucleotides but also inversions (reversed complements) of substrings of the sequences. The inversion alignments themselves contain substitutions, insertions and deletions of nucleotides. We study the problem of alignment with non-intersecting inversions. To provide a computationally efficient algorithm we restrict candidate inversions to the K highest scoring inversions. An algorithm to find the J best non-intersecting alignments with inversions is also described. The new algorithm is applied to the regions of mitochondrial DNA of Drosophila yakuba and mouse coding for URF6 and cytochrome b and the inversion of the URF6 gene is found. The open problem of intersecting inversions is discussed.

Algorithms↗

PubMed1997

Optimisation algorithms for ECG data compression.

The use of exact optimisation algorithms for compressing digital electrocardiograms (ECGs) is demonstrated. As opposed to traditional time-domain methods, which use heuristics to select a small subset of representative signal samples, the problem of selecting the subset is formulated in rigorous mathematical terms. This approach makes it possible to derive algorithms guaranteeing the smallest possible reconstruction error when a bounded selection of signal samples is interpolated. The proposed model resembles well-known network models and is solved by a cubic dynamic programming algorithm. When applied to standard test problems, the algorithm produces a compressed representation for which the distortion is about one-half of that obtained by traditional time-domain compression techniques at reasonable compression ratios. This illustrates that, in terms of the accuracy of decoded signals, existing time-domain heuristics for ECG compression may be far from what is theoretically achievable. The paper is an attempt to bridge this gap.

Algorithms↗

PubMed1987

A microcomputer implementation of status and alarm algorithms in a cardiac surgical intensive care unit.

Algorithms have been developed for monitoring the cardiovascular status of patients on their return to an intensive care unit after cardiac surgery and also for giving an immediate alarm of a critical deterioration in this status. The two systems for implementing these algorithms were initially developed on Z80 based microprocessor systems and preliminary clinical trials based on the resulting instruments proved encouraging. For further clinical trials of the algorithms the systems have been integrated and implemented on a BBC microcomputer with a 6502 second processor. The development and structure of the programs for implementing the algorithms are described, together with the program input and output facilities and diagnostic techniques used to analyse the information output from the program.

Algorithms↗

PubMed2006

Effects of image reconstruction algorithm on neurotransmission PET studies in humans: comparison between filtered backprojection and ordered subsets expectation maximization.

OBJECTIVES: Both reconstruction algorithms, filtered backprojection (FBP) and ordered subsets expectation maximization (OSEM), are widely used in clinical positron emission tomography (PET) studies. Image reconstruction for most neurotransmission PET scan data is performed by FBP, while image reconstruction for whole-body [18F]FDG scan data is usually performed by OSEM. Although several investigators have compared FBP and OSEM in terms of the quantification of regional radioactivity and physiological parameters calculated from PET data, only a few studies have compared the two reconstruction algorithms in PET studies that estimate neurotransmission, i.e., neuroreceptor and neurotransporter binding. In this study we compared mean regional radioactivity concentration in the late phase and binding potential (BP) between FBP and OSEM algorithms in neurotransmission PET studies for [11C]raclopride and [11C]DASB. METHODS: Dynamic PET scans with [11C]raclopride in 3-dimensional mode were performed on seven healthy subjects. Dynamic PET scans with [11C]DASB in 2-dimensional mode were performed on another seven subjects. OSEM images were post-filtered so that its transverse spatial resolution became similar to that of FBP with the same Hanning filter (Kernel FWHM 6 mm). In both PET studies we calculated the BP of [11C]raclopride and [11C]DASB by a reference tissue model for each ROI (region of interest). RESULTS: There was no significant difference in mean regional radioactivity concentration between FBP and OSEM for [11C]raclopride and [11C]DASB. Only +2.4 - +3.2%, but still a significant difference in BP of [11C]raclopride between FBP and OSEM was observed in the striatum. There was no significant difference in BP between FBP and OSEM in other than the striatum for [11C]raclopride and in all regions for [11C]DASB. In addition, there was no significant difference in root mean square error between FBP and OSEM when BP was calculated. CONCLUSIONS: The BP values were similar between FBP and OSEM algorithms with [11C]raclopride and [11C]DASB. This study indicates that OSEM can be used for human neurotransmission PET studies for calculating BP although OSEM was not necessarily superior to FBP in the present study.

Adult↗

PubMed1999

Contour tracking using a knowledge-based snake algorithm to construct three-dimensional pharyngeal bolus movement.

Videofluorography (VFG) using a barium-mixed bolus is in wide clinical use for assessing patients with swallowing disorders. VFG is usually done with both lateral (LA) and anterior-posterior (AP) views, most commonly in two separate sittings. A real-time, three-dimensional (3-D) representation of the evolution of a pharyngeal bolus and its volumetric information can potentially help clinicians analyze and visualize the kinematics of swallowing, dysphagia, and compensatory therapeutic strategies. Active contour models, also known as "Snakes," have been used to solve various image analysis and computer vision problems. We applied a Snake algorithm to automate in part the contour tracking and reconstruction of VFG images to visualize and quantitatively analyze the 3-D evolution of a pharyngeal bolus. To improve the accuracy of the Snake search, we provided the additional "knowledge" of the pharyngeal image itself, which served as an extra constraint to push the Snake curve toward the desired contour. VFG of pharyngeal bolus transport in a normal subject was recorded by using barium-mixed boluses (viscosity: 185 centipoise, density: 2.84 g/cc) with volumes of 5, 10, and 20 ml. The resulting LA and AP video images were digitally captured and matched frame by frame. The knowledge-based Snake search algorithm was used to generate Snake points to satisfy both internal (i.e., smoothness) and external (i.e., boundary fitting) constraints. Using these Snake points, we traced the 3-D bolus movement at each time instant, assuming elliptic geometry in the cross-section of the pharyngeal bolus. By concentrating the 3-D images for each time instant, we developed a 3-D movie representing pharyngeal bolus movement. The efficiency, reproducibility, and accuracy of this algorithm in tracing pharyngeal bolus boundaries and estimating front/tail velocities were assessed and found satisfactory. We conclude that 3-D pharyngeal bolus movement can be traced both accurately and efficiently by using a knowledge-based Snake search algorithm.

Algorithms↗

PubMed2004

Limitations of score-based daily outcome predictions in the individual intensive care patient. An example of the RIAHDH algorithm.

OBJECTIVE: The nature of score-based predictions is probabilistic, and their accuracy depends on the reliability and validity of the applied system. As an example, the present study investigates the accuracy of the RIP-algorithm (RIP = Riyadh Intensive Care Program) based on daily APACHE II scores, and compares it with published results of that algorithm from other investigators. DESIGN: Prospective observational study and review of the literature. PATIENTS AND METHODS: 1,986 consecutive admissions of 1,808 patients to a surgical intensive care unit were documented. Daily changes of score values were used to derive a risk of death estimation. Sensitivity and the rate of false predictions were calculated for score-based predictions. Health status one year after discharge was assessed in survivors predicted to die. RESULTS: Daily application of the algorithm identified 109 situations leading to death predictions in 56 patients. Five of these patients were discharged alive from the hospital (positive predictive value 91%). One year later 3 of these patients were still alive. The algorithm identified 51 of the non-survivors (sensitivity 19%), 110 died in the ICU without prediction. Altogether 270 patients died during their hospital stay. Among the 6 independent validation studies, similar results were found, but differences occurred due to the problematic assessment of consciousness. CONCLUSIONS: Sequential assessment of scores in intensive care could identify high risk patients, but with some degree of uncertainty. Therefore, the scores should only be used by those familiar with their limitations and risks.

APACHE↗

PubMed2005

[The Würzburg polytrauma algorithm. Concept and first results of a sliding-gantry-based computer tomography diagnostic system].

BACKGROUND: The purpose of this study was to show the practicability of a new algorithm in the management of polytraumatized patients based on Advanced Trauma Live Support (ATLS) and using mobile whole body multislice CT (MMDCT) as the primary imaging system. PATIENTS AND METHODS: A series of 120 trauma patients referred to the Würzburg University Hospital Trauma Emergency Room were categorized into suspected polytrauma and suspected non-polytrauma groups. The polytraumatized patients were investigated using the Würzburg polytrauma-algorithm including whole body multislice CT with a 16-row-scanner. The algorithm is described. The time for the diagnostic procedure was measured and compared with data from the Trauma Registry of the German Society of Trauma Surgery. RESULTS: From 120 patients 78 (66%) underwent whole body CT. The diagnostic procedure was quick with significant advantages especially for cranial and trunk diagnostics. CONCLUSION: The Würzburg polytrauma algorithm worked well. There was excellent cooperation within the interdisciplinary leading team consisting of anaesthesiologists, surgeons, and radiologists. The principles of ATLS could be respected. Mobile whole body multislice CT was an effective tool in the diagnostic evaluation of polytrauma patients.

Algorithms↗

PubMed2002

[Algorithm for prehospital blunt trauma management].

Clinical algorithms can divide sophisticated treatment concepts for blunt trauma care into logical, systematic and easy to follow sequences. The presented algorithm for prehospital management of major and suspected blunt trauma will assure appropriate trauma care within narrow time windows. The risk of over- or undertreatment is reduced for both, the suspected and confirmed diagnosis of polytrauma. Due to the lack of evident data the algorithm was confirmed via consent expert opinion of trauma surgeons, incorporating the ABC priorities and also the concept of the ATLS((R))-programme. The algorithm was validated in simulated scenarios and was by affirmed by the German Trauma Surgeons Task Force on Emergency Care under the regulations of a nominal group process via resolution.

Algorithms↗

PubMed2004

Population-based stepwise screening for unrecognised Type 2 diabetes is ineffective in general practice despite reliable algorithms.

AIMS/HYPOTHESIS: The yield of screening programmes for Type 2 diabetes in the existing healthcare setting might be lower than anticipated from tests of screening algorithms in data from epidemiological surveys. Our aims were to evaluate the reliability of the algorithms and the effectiveness of a proposed stepwise screening programme for Type 2 diabetes in general practice. METHODS: The screening programme had four steps: (i) mail-distributed self-administered risk-chart; (ii) screening tests: random blood glucose (RBG) and HbA(1)c; (iii) diagnostic procedure 1 for fasting blood glucose (FBG) (if RBG >/=5.5 mmol/l or HbA(1)c >/=6.1%); and (iv) OGTT as diagnostic procedure 2 (if 5.6</=FBG<6.1 mmol/l or HbA(1)c >/=6.1%). Abnormalities of glucose metabolism were classified according to the WHO 1999 criteria, based on capillary whole blood. The subjects were all patients between 40 and 69 years of age ( n=60,926) who were registered in 88 general practices and had not been previously diagnosed with diabetes. RESULTS: A total of 11,263 individuals had a high-risk risk-score and attended the screening consultation (step 1 test-positive). Of these, 30.1% needed diagnostic tests (step 2 test-positive) and 27.2% of these needed an OGTT (step 3 test-positive). The test-positive proportions were equal to the proportions obtained in data from a population-based survey from Step 2 onwards, and the algorithms were thus reliable. The identification rate was only 19% of all prevalent undiagnosed diabetes according to a recently published prevalence estimate. This was due to a large dropout rate among high-risk individuals prior to entry into the programme. CONCLUSIONS/INTERPRETATION: Population-based mail-distributed stepwise screening for Type 2 diabetes in general practice is ineffective, despite reliable screening algorithms, primarily because many high-risk individuals fail to participate.

Adult↗

PubMed1997

High survival rate in 122 ARDS patients managed according to a clinical algorithm including extracorporeal membrane oxygenation.

OBJECTIVE: We investigated whether a treatment according to a clinical algorithm could improve the low survival rates in acute respiratory distress syndrome (ARDS). DESIGN: Uncontrolled prospective trial. SETTING: One university hospital intensive care department. PATIENTS AND PARTICIPANTS: 122 patients with ARDS, consecutively admitted to the ICU. INTERVENTIONS: ARDS was treated according to a criteria-defined clinical algorithm. The algorithm distinguished two main treatment groups: The AT-sine-ECMO (advanced treatment without extracorporeal membrane oxygenation) groups (n = 73) received a treatment consisting of a set of advanced non-invasive treatment options, the ECMO treatment group (n = 49) received additional extracorporeal membrane oxygenation (ECMO) using heparin-coated systems. MEASUREMENTS AND RESULTS: The groups differed in both APACHE II (16 +/- 5 vs 18 +/- 5 points, p = 0.01) and Murray scores (3.2 +/- 0.3 vs 3.4 +/- 0.3 points, p = 0.0001), the duration of mechanical ventilation prior to admission (10 +/- 9 vs 13 +/- 9 days, p = 0.0151), and length of ICU stay in Berlin (31 +/- 17 vs 50 +/- 36 days, p = 0.0016). Initial PaO2/FIO2 was 86 +/- 27 mm Hg in AT-sine-ECMO patients that improved to 165 +/- 107 mm Hg on ICU day 1, while ECMO patients showed an initial PaO2/FIO2 of 67 +/- 28 mm Hg and improvement to 160 +/- 102 mm Hg was not reached until ICU day 13. QS/QT was significantly higher in the ECMO-treated group and exceeded 50% during the first 14 ICU days. The overall survival rate in our 122 ARDS patients was 75%. Survival rates were 89% in the AT-sine ECMO group and 55% in the ECMO treatment group (p = 0.0000). CONCLUSIONS: We conclude that patients with ARDS can be successfully treated with the clinical algorithm and high survival rates can be achieved.

Adult↗

PubMed2006

A linear modulation-based stochastic resonance algorithm applied to the detection of weak chromatographic peaks.

A simple stochastic resonance algorithm based on linear modulation was developed to amplify and detect weak chromatographic peaks. The output chromatographic peak is often distorted when using the traditional stochastic resonance algorithm due to the presence of high levels of noise. In the new algorithm, a linear modulated double-well potential is introduced to correct for the distortion of the output peak. Method parameter selection is convenient and intuitive for linear modulation. In order to achieve a better signal-to-noise ratio for the output signal, the performance of two-layer stochastic resonance was evaluated by comparing it with wavelet-based stochastic resonance. The proposed algorithm was applied to the quantitative analysis of dimethyl sulfide and the determination of chloramphenicol residues in milk, and the good linearity of the method demonstrated that it is an effective tool for detecting weak chromatographic peaks.

Algorithms↗

PubMed2005

Comparison of pharmacovigilance algorithms in drug hypersensitivity reactions.

BACKGROUND: A firm diagnosis of drug hypersensitivity, because it may re-induce the reaction, is seldom confirmed. Causality assessment algorithms are therefore of interest. AIMS: The objective of this work was to compare three algorithms in the diagnosis of drug hypersensitivity. METHODS: Evaluation of 120 clinical histories of drug hypersensitivity was carried out: 60 involving beta-lactams (50%) and 60 involving non-steroidal anti-inflammatory drugs (50%). Each of these groups of patients underwent a standardised allergy diagnosis, which included a detailed anamnesis, skin tests and, often, provocation tests under strict hospital surveillance. Unaware of the final allergy diagnosis, scores were established for all of the cases and compared using algorithms suggested by Begaud and coworkers [2, 20], Jones [13] and Naranjo et al. [21]. RESULTS: Although the methods of Jones [13] and Naranjo et al. [21] were perfectly concordant (k=1), no concordance was noted using the Begaud and coworkers [2, 20] method. CONCLUSIONS: All three algorithms are dissimilar regarding the diagnosis of drug hypersensitivity.

Adult↗

PubMed2005

The association between neurological deficit in acute ischemic stroke and mean transit time: comparison of four different perfusion MRI algorithms.

The purpose of our study was to identify the perfusion MRI (pMRI) algorithm which yields a volume of hypoperfused tissue that best correlates with the acute clinical deficit as quantified by the NIH Stroke Scale (NIHSS) and therefore reflects critically hypoperfused tissue. A group of 20 patients with a first acute stroke and stroke MRI within 24 h of symptom onset were retrospectively analyzed. Perfusion maps were derived using four different algorithms to estimate relative mean transit time (rMTT): (1) cerebral blood flow (CBF) arterial input function (AIF)/singular voxel decomposition (SVD); (2) area peak; (3) time to peak (TTP); and (4) first moment method. Lesion volumes based on five different MTT thresholds relative to contralateral brain were compared with each other and correlated with NIHSS score. The first moment method had the highest correlation with NIHSS (r = 0.79, P < 0.001) followed by the AIF/SVD method, both of which did not differ significantly from each other with regard to lesion volumes. TTP and area peak derived both volumes, which correlated poorly or only moderately with NIHSS scores. Data from our pilot study suggest that the first moment and the AIF/SVD method have advantages over the other algorithms in identifying the pMRI lesion volume that best reflects clinical severity. At present there seems to be no need for extensive postprocessing and arbitrarily defined delay thresholds in pMRI as the simple qualitative approach with a first moment algorithm is equally accurate. Larger sample sizes which allow comparison between imaging and clinical outcomes are needed to refine the choice of best perfusion parameter in pMRI.

Aged↗

PubMed1998

An algorithm for correction of distortion in stereotaxic digital subtraction angiography.

An algorithm for correction of the geometrical distortion in digital subtraction angiography (DSA) images was developed. Originally invented for 3D X-ray angiography, the algorithm was implemented in a computer program designed to fulfil the specific needs of stereotaxic DSA. The algorithm is based on transformation of an image of a grid from a distorted image back into its original pattern. The same transformation is then applied pixel-by-pixel to the angiographic images, which are acquired in direct conjunction with the grid image, without moving the gantry. The algorithm was tested in phantom studies and in the clinical situation with seven patients in ten examinations. Comparisons were made between co-ordinate determinations made on conventional full-size cut film and those performed on uncorrected and corrected DSA images, using 30- and 23-cm fields of view. With our method of measurement we could not shown any remaining geometric distortion in the corrected DSA images. This distortion correction can, if properly applied, be used for high-precision stereotaxic DSA.

Algorithms↗

PubMed2001

Precise determination of aortic length in patients with aortic stent grafts: in vivo evaluation of a thinning algorithm applied to CT angiography data.

The aim of this study was to develop a technique for precise determination of the aortic length using volumetric CT data for potential use prior to endovascular stent-graft placement. The study population consisted of 20 patients (38 measurements) with already performed endoluminal grafting. This allowed for in vivo evaluation of our technique. Its length according to the graft specifications served as a gold standard for our own measurements. The implemented graft length varied between 120 and 195 mm. Computed tomography angiography was performed with 3-mm slice collimation, 5-mm table feed and a reconstruction interval of 2 mm. Following semi-automatic segmentation of the aorta and its large side branches, the median centerline (skeleton) of the vessels was determined employing a modified three-dimensional thinning algorithm. The algorithm was validated by comparing the calculated length of the resulting skeleton with the specifications of the grafts. The calculated length was sufficiently precise despite the limiting reconstruction interval of 2 mm of our CT data which only permitted an assessment of stent length in 2-mm steps. The differences in the measured length and graft length were in the range between 0 and 8 mm (< 5%) with a mean fractional error of 2.46 +/- 2.37 mm. The use of an intelligent region growing algorithm capable of coping with variable arterial enhancement significantly reduced operator post-processing time. The average time necessary for segmentation was 7 min (range 3-10 min). Our algorithm provides a non-invasive method for objective and precise measurement of aortic length apparently even in tortuous vessels. It has the potential to replace angiography for aortic and iliac length measurements with calibrated catheters prior to endovascular intervention.

Algorithms↗