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PubMed2006

Face recognition using IPCA-ICA algorithm.

In this paper, a fast incremental principal non-Gaussian directions analysis algorithm, called IPCA-ICA, is introduced. This algorithm computes the principal components of a sequence of image vectors incrementally without estimating the covariance matrix (so covariance-free) and at the same time transforming these principal components to the independent directions that maximize the non-Gaussianity of the source. Two major techniques are used sequentially in a real-time fashion in order to obtain the most efficient and independent components that describe a whole set of human faces database. This procedure is done by merging the runs of two algorithms based on principal component analysis (PCA) and independent component analysis (ICA) running sequentially. This algorithm is applied to face recognition problem. Simulation results on different databases showed high average success rate of this algorithm compared to others.

Algorithms↗

PubMed2006

Bayesian Gaussian process classification with the EM-EP algorithm.

Gaussian process classifiers (GPCs) are Bayesian probabilistic kernel classifiers. In GPCs, the probability of belonging to a certain class at an input location is monotonically related to the value of some latent function at that location. Starting from a Gaussian process prior over this latent function, data are used to infer both the posterior over the latent function and the values of hyperparameters to determine various aspects of the function. Recently, the expectation propagation (EP) approach has been proposed to infer the posterior over the latent function. Based on this work, we present an approximate EM algorithm, the EM-EP algorithm, to learn both the latent function and the hyperparameters. This algorithm is found to converge in practice and provides an efficient Bayesian framework for learning hyperparameters of the kernel. A multiclass extension of the EM-EP algorithm for GPCs is also derived. In the experimental results, the EM-EP algorithms are as good or better than other methods for GPCs or Support Vector Machines (SVMs) with cross-validation.

Algorithms↗

PubMed2006

Hybridization of evolutionary algorithms and local search by means of a clustering method.

This paper presents a hybrid evolutionary algorithm (EA) to solve nonlinear-regression problems. Although EAs have proven their ability to explore large search spaces, they are comparatively inefficient in fine tuning the solution. This drawback is usually avoided by means of local optimization algorithms that are applied to the individuals of the population. The algorithms that use local optimization procedures are usually called hybrid algorithms. On the other hand, it is well known that the clustering process enables the creation of groups (clusters) with mutually close points that hopefully correspond to relevant regions of attraction. Local-search procedures can then be started once in every such region. This paper proposes the combination of an EA, a clustering process, and a local-search procedure to the evolutionary design of product-units neural networks. In the methodology presented, only a few individuals are subject to local optimization. Moreover, the local optimization algorithm is only applied at specific stages of the evolutionary process. Our results show a favorable performance when the regression method proposed is compared to other standard methods.

Algorithms↗

PubMed2005

A spline-based algorithm for continuous time-delay estimation using sampled data.

Time delay estimation (TDE) lies at the heart of signal processing algorithms in a broad range of application areas, including communications, coherent imaging, speech processing, and acoustics. In medical ultrasound for example, TDE is used in blood flow estimation, tissue motion measurement, tissue elasticity estimation, phase aberration correction, and a number of other algorithms. Because of its central significance, TDE accuracy, precision, and computational cost are of critical importance. Furthermore, because TDE is typically performed on sampled signals-and delay estimates are usually desired over a continuous domain-time delay estimator performance should be considered in conjunction with associated interpolation. In this paper we present a new time-delay estimator that directly determines continuous time-delay estimates from sampled data. The technique forms a spline-based, piecewise continuous representation of the reference signal then solves for the minimum of the sum squared error between the reference and the delayed signals to determine their relative time delay. Computer simulation results clearly show that the proposed algorithm significantly outperforms other algorithms in terms of jitter and bias over a broad range of conditions. We also describe a modified version of the algorithm that includes companding with only a minor increase in computational cost.

Algorithms↗

PubMedDate not supplied

CartoDraw: a fast algorithm for generating contiguous cartograms.

Cartograms are a well-known technique for showing geography-related statistical information, such as population demographics and epidemiological data. The basic idea is to distort a map by resizing its regions according to a statistical parameter, but in a way that keeps the map recognizable. In this study, we formally define a family of cartogram drawing problems. We show that even simple variants are unsolvable in the general case. Because the feasible variants are NP-complete, heuristics are needed to solve the problem. Previously proposed solutions suffer from problems with the quality of the generated drawings. For a cartogram to be recognizable, it is important to preserve the global shape or outline of the input map, a requirement that has been overlooked in the past. To address this, our objective function for cartogram drawing includes both global and local shape preservation. To measure the degree of shape preservation, we propose a shape similarity function, which is based on a Fourier transformation of the polygons' curvatures. Also, our application is visualization of dynamic data, for which we need an algorithm that recalculates a cartogram in a few seconds. None of the previous algorithms provides adequate performance with an acceptable level of quality for this application. In this paper, we therefore propose an efficient iterative scanline algorithm to reposition edges while preserving local and global shapes. Scanlines may be generated automatically or entered interactively to guide the optimization process more closely. We apply our algorithm to several example data sets and provide a detailed comparison of the two variants of our algorithm and previous approaches.

Algorithms↗

PubMed2003

Cyclic coordinate descent: A robotics algorithm for protein loop closure.

In protein structure prediction, it is often the case that a protein segment must be adjusted to connect two fixed segments. This occurs during loop structure prediction in homology modeling as well as in ab initio structure prediction. Several algorithms for this purpose are based on the inverse Jacobian of the distance constraints with respect to dihedral angle degrees of freedom. These algorithms are sometimes unstable and fail to converge. We present an algorithm developed originally for inverse kinematics applications in robotics. In robotics, an end effector in the form of a robot hand must reach for an object in space by altering adjustable joint angles and arm lengths. In loop prediction, dihedral angles must be adjusted to move the C-terminal residue of a segment to superimpose on a fixed anchor residue in the protein structure. The algorithm, referred to as cyclic coordinate descent or CCD, involves adjusting one dihedral angle at a time to minimize the sum of the squared distances between three backbone atoms of the moving C-terminal anchor and the corresponding atoms in the fixed C-terminal anchor. The result is an equation in one variable for the proposed change in each dihedral. The algorithm proceeds iteratively through all of the adjustable dihedral angles from the N-terminal to the C-terminal end of the loop. CCD is suitable as a component of loop prediction methods that generate large numbers of trial structures. It succeeds in closing loops in a large test set 99.79% of the time, and fails occasionally only for short, highly extended loops. It is very fast, closing loops of length 8 in 0.037 sec on average.

Algorithms↗

PubMed2004

Digital image analysis for diagnosis of cutaneous melanoma. Development of a highly effective computer algorithm based on analysis of 837 melanocytic lesions.

BACKGROUND: Digital image analysis has been introduced into the diagnosis of skin lesions based on dermoscopic pictures. OBJECTIVES: To develop a computer algorithm for the diagnosis of melanocytic lesions and to compare its diagnostic accuracy with the results of established dermoscopic classification rules. METHODS: In the Department of Dermatology, University of Tuebingen, Germany, 837 melanocytic skin lesions were prospectively imaged by a dermoscopy video system in consecutive patients. Of these lesions, 269 were excised and examined by histopathology: 84 were classified as cutaneous melanomas and 185 as benign melanocytic naevi. The remaining 568 lesions were diagnosed by dermoscopy as benign. Digital image analysis was performed in all 837 benign and malignant melanocytic lesions using 64 different analytical parameters. RESULTS: For lesions imaged completely (diameter < or = 12 mm), three analytical parameters were found to distinguish clearly between benign and malignant lesions, while in incompletely imaged lesions six parameters enabled differentiation. Based on the respective parameters and logistic regression analysis, a diagnostic computer algorithm for melanocytic lesions was developed. Its diagnostic accuracy was 82% for completely imaged and 84% for partially imaged lesions. All 837 melanocytic lesions were classified by established dermoscopic algorithms and the diagnostic accuracy was found to be in the same range (ABCD rule 78%, Menzies' score 83%, seven-point checklist 88%, and seven features for melanoma 81%). CONCLUSIONS: A diagnostic algorithm for digital image analysis of melanocytic lesions can achieve the same range of diagnostic accuracy as the application of dermoscopic classification rules by experts. The present diagnostic algorithm, however, still requires a medical expert who is qualified to recognize cutaneous lesions as being of melanocytic origin.

Algorithms↗

PubMed2004

Application of hepatitis serology testing algorithms to assess inappropriate laboratory utilization.

RATIONALE, AIMS AND OBJECTIVES: Many studies pointed out inappropriate utilization of laboratory caused by excessive amounts of tests ordered by doctors. To prevent and to eliminate the ordering of unhelpful tests, introducing diagnostic algorithms, which are also a suitable practice for application to hepatitis serology, have been suggested. This study aimed to determine inappropriate test ordering rates with respect to the commonly approved algorithms for serological diagnosis of viral hepatitis. METHODS: To assess the number of inappropriate test orders, laboratory records of samples sent for hepatitis A, B, and D serology were reviewed and evaluated retrospectively with respect to algorithms for serological diagnosis of viral hepatitis. Orders including serological marker groups with inadequate clinical information to determine whether or not the order was inappropriate were excluded from the analysis. RESULTS: Application of diagnostic algorithms showed that 50% of anti-HAV IgM and anti-HAV total; 12.7% of anti-HBs, 12.7% of anti-HBc total, 78.5% of anti-HBc IgM, 87.3% of HBe Ag, 78.8% of anti-HBe, 58.7% of anti-HD total orders were made inappropriately. CONCLUSIONS: Our study provides information for inappropriate laboratory utilization for hepatitis serology testing and we suggest to use diagnostic algorithms applied by the serology laboratory to decrease the rate of unhelpful test orders.

Algorithms↗

PubMed2005

Evaluation of neonatal verbal autopsy using physician review versus algorithm-based cause-of-death assignment in rural Nepal.

Verbal autopsy (VA) is used to ascertain cause-specific neonatal mortality using parental/familial recall. We sought to compare agreement between causes of death obtained from the VA by physician review vs. computer-based algorithms. Data were drawn from a cluster-randomised trial involving 4130 live-born infants and 167 neonatal deaths in the rural Sarlahi District of Nepal. We examined the agreement between causes ascertained by physician review and algorithm assignment by the kappa (kappa) statistic. We also compared responses to identical questions posed posthumously during neonatal VA interviews with those obtained during maternal interviews and clinical examinations regarding condition of newborns soon after birth. Physician reviewers assigned prematurity or acute lower respiratory infection (ALRI) as causes of 48% of neonatal deaths; 41% were assigned as uncertain. The algorithm approach assigned sepsis (52%), ALRI (31%), birth asphyxia (29%), and prematurity (24%) as the most common causes of neonatal death. Physician review and algorithm assignment of causes of death showed high kappa for prematurity (0.73), diarrhoea (0.81) and ALRI (0.68), but was low for congenital malformation (0.44), birth asphyxia (0.17) and sepsis (0.00). Sensitivity and specificity of VA interview questions varied by symptom, with positive predictive values ranging from 50% to 100%, when compared with maternal interviews and examinations of neonates soon after birth. Analysis of the VA data by physician review and computer-based algorithms yielded disparate results for some causes but not for others. We recommend an analysis technique that combines both methods, and further validation studies to improve performance of the VA for assigning causes of neonatal death.

Algorithms↗

PubMed2005

Clinical algorithms for malaria diagnosis lack utility among people of different age groups.

We conducted a study to determine whether clinical algorithms would be useful in malaria diagnosis among people living in an area of moderate malaria transmission within Kilifi District in Kenya. A total of 1602 people of all age groups participated. We took smears and recorded clinical signs and symptoms (prompted or spontaneous) of all those presenting to the study clinic with a history of fever. A malaria case was defined as a person presenting to the clinic with a history of fever and concurrent parasitaemia. A set of clinical signs and symptoms (algorithms) with the highest sensitivity and specificity for diagnosing a malaria case was selected for the age groups </=5 years, 6-14 years and >/=15 years. These age-optimized derived algorithms were able to identify about 66% of the cases among those <15 years of age but only 23% of cases among adults. Were these algorithms to be used as a basis for a decision on treatment among those presenting to the clinic, 16% of children </=5 years, 44% of those 6-14 years of age and 66% of the adults who had a history of fever and parasitaemia >/=5000 parasites/microl of blood would be sent home without treatment. Clinical algorithms therefore appear to have little utility in malaria diagnosis, performing even worse in the older age groups, where avoiding unnecessary use of anti-malarials would make more drugs available to the really needy population of children under 5 years of age.

Adolescent↗

PubMed2006

On-line adaptive algorithm with glucose prediction capacity for subcutaneous closed loop control of glucose: evaluation under fasting conditions in patients with Type 1 diabetes.

AIMS: To evaluate an algorithm with glucose prediction capacity and continuous adaptation of patient parameters-a model predictive control (MPC) algorithm-to control blood glucose concentration during fasting conditions in patients with Type 1 diabetes. In the subcutaneous (sc) route within a closed loop system. METHODS: Paired experiments were performed in six patients. Over 8 h the MPC algorithm was used to control glucose with s.c. insulin administration and two different glucose monitoring protocols: first, the algorithm was provided with intravenous (i.v.) glucose values for insulin dosage calculation directly (i.v.-s.c. route). Then, in the second experiment, i.v. glucose values were fed to the MPC with a delay of 30 min to simulate s.c. glucose measurements ('s.c.'-s.c. route). In both experiments plasma glucose, insulin dosage, and serum insulin levels were analysed. RESULTS: Glucose concentration was brought from hyper- to normoglycaemia and kept in the physiological range (6-7 mmol/l) with both routes in all subjects. Mean glucose concentration reached the threshold of 7 mmol/l approximately 2 (i.v.-s.c. route) and 3 ('s.c.'-s.c. route) hours after the start of glucose control with the MPC. During the last 2 h of automated glucose control, mean glucose concentration was 6.3 +/- 0.2 mmol/l and 6.6 +/- 0.3 mmol/l for i.v.-s.c. and 's.c.'-s.c. route, respectively. Glucose concentration, insulin doses, and serum insulin levels did not differ significantly between routes (P > 0.05). CONCLUSIONS: The MPC algorithm is suitable for glucose control during fasting within an extracorporeal artificial beta-cell in the subcutaneous route Type 1 diabetic patients.

Administration, Cutaneous↗

PubMed2005

Pneumonia versus aspiration pneumonitis in nursing home residents: prospective application of a clinical algorithm.

OBJECTIVES: To prospectively evaluate a clinical algorithm for the diagnosis of pneumonitis and pneumonia in nursing home residents. DESIGN: Prospective cohort study. SETTING: Inpatient geriatrics unit. PARTICIPANTS: Nursing home residents admitted to the hospital with suspected pneumonia. MEASUREMENTS: Identification of pneumonitis and pneumonia using the algorithm; medical record review and abstraction of clinical data; hospital outcome and length of stay. RESULTS: One hundred seventy episodes of suspected pneumonia were screened with the algorithm and classified into four groups: 25% pneumonia, 28% aspiration pneumonitis of 24 hours or less duration, 12% aspiration pneumonitis of more than 24 hours' duration, and 35% an aspiration event without pneumonitis. Presenting symptoms and signs, laboratory tests, severity of illness measures, or serum C-reactive protein levels did not distinguish between the four groups. Those with an aspiration event without pneumonitis tended to be treated less often with antibiotic therapy after admission (P=.004) and after discharge (P=.01). Of those who survived, there was no significant difference in mean hospital length of stay between the four groups. There was no significant difference in the percentage of case fatality between the four groups, but those with aspiration pneumonitis of 24 hours or less duration and with an aspiration event without pneumonitis had a lower mortality than the other two groups. CONCLUSION: Distribution of episodes of suspected pneumonia by clinical category as determined using the algorithm was similar to that of the derivation study, as were case fatality rates in each category. These findings suggest that the algorithm may be useful for making the distinction between pneumonitis and pneumonia in nursing home residents; further studies are warranted.

Aged↗

PubMed2005

A model-based algorithm for the monitoring of long-term anticoagulation therapy.

It has been shown that computerized algorithms for the prescription of coumarin derivates can improve the quality of long-term anticoagulation treatment. These algorithms are usually based on an empiric relationship between dosage and International Normalized Ratio and do not quantify the delaying effect of the drug's pharmacokinetics or the effect of alternating doses that are used to approximate a certain average dosage. Our objective was to develop a mathematical model that takes into account these effects and to develop a new algorithm based on this model that can be used to further optimize the quality of long-term anticoagulation treatment. We simplified a general model structure that was proposed by Holford in 1986 so that the parameters can be estimated using data that are available during long-term anticoagulation treatment. The constant parameters in the model were estimated separately for phenprocoumon and acenocoumarol using data from 1279 treatment courses from three different anticoagulation clinics in the Netherlands. The only variable parameter in the model is the sensitivity of the patient, which is estimated during the course of each treatment. A total of 194 dosage and appointment intervals that were proposed by the new algorithm were scored as 'good', 'acceptable', or 'bad' by two dosing experts. One hundred and seventy-eight (91.8%) proposals were considered good by at least one expert and bad by none. In 39 cases the experts disagreed. We believe that this algorithm will allow further improvement of anticoagulation treatments.

Acenocoumarol↗

PubMed1992

A new pacemaker algorithm for continuous capture verification and automatic threshold determination: elimination of pacemaker afterpotential utilizing a triphasic charge balancing system.

A new pacemaker algorithm designed to automatically verify pacemaker capture and determine pacing threshold by detection of a stimulus evoked potential was studied in 20 patients undergoing permanent pacemaker implantation. To eliminate pacing stimulus afterpotential and detect an evoked response, a hardware feedback circuit and a software template matching algorithm were used to produce a triphasic charge-balanced pacing pulse. After charge balancing the pacing lead, a residual artifact is measured. A capture window is defined as the area integral of the first 24 msec of the evoked depolarization, and a capture threshold as one third the amplitude of the capture window. The maximum allowable residual artifact is one eighth the amplitude of the capture window. Once the stimulus afterpotential is eliminated and the evoked response detected, capture threshold is automatically and continuously determined and the algorithm adds a 0.8-V safety margin to the pacemaker output. This algorithm was run automatically and after simulated loss of capture, produced by manually decreasing pacer output below threshold, in the bipolar (13 patients) and unipolar (20 patients) pacing modes. In each patient loss of capture was immediately detected. The data were consistent (P = NS) between algorithm runs. During unipolar pacing the area integral of the first 24 msec of the evoked response was 412 +/- 137 versus 413 +/- 144 and the residual artifact 5.8 +/- 4.8 versus 8.1 +/- 7.5. The resulting ratio (signal/noise) of the two parameters was 150 +/- 141 versus 145 +/- 181. Automatically determined threshold was 0.69 +/- 0.43 V versus 0.69 +/- 0.42.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed2000

Enhanced rate response algorithm for orthostatic compensation pacing.

Upon orthostatic stress after a period of rest, the heart rate increases rapidly to maintain cardiac output and minimize the fall in arterial pressure. Pacemaker patients are often prone to a deficient response to orthostatic stress. This may cause lightheadedness and, in rare patients with autonomic dysfunction, syncope. To alleviate these undesirable consequences, an enhanced rate response algorithm was developed using an accelerometer. The pacemaker generates two signals from its accelerometer: instantaneous activity level (Act) and long-term change in activity level (ActVar). Low values of both Act and ActVar indicate a resting state. An increase in Act while ActVar remains low indicates the onset of motion after prolonged rest. Upon detecting this transition, the algorithm increases the pacing rate to a programmable orthostatic compensation rate for a programmable duration. A taped-on pacemaker with this algorithm was evaluated in three healthy women and two healthy men, 36 +/- 8 years of age. Electrocardiogram and ventricular pacing pulses were recorded by a 24-hour ambulatory system. Each trigger of the orthostatic compensation rate was verified against a > 10 beats/min increase in heart rate, a response classified as appropriate. The overall specificity of the algorithm among the five subjects was 78%. The nocturnal specificity (10 PM to 7 AM) was 98%, considerably higher than during daytime (72%). In conclusion, a pacing algorithm to alleviate orthostatic stress was developed, which was highly specific during the night hours.

Acceleration↗

PubMed2005

Reduction of right ventricular pacing in patients with sinus node dysfunction using an enhanced search AV algorithm.

BACKGROUND: Dual chamber pacing typically results in a high percentage of ventricular pacing. A number of studies have been conducted suggesting detrimental effects of ventricular desynchronization produced by long-term RV pacing. Pacemaker algorithms that extend the AV interval to uncover intrinsic AV conduction have been utilized to reduce ventricular pacing. These algorithms are often limited to AV intervals below 250 ms limiting the ventricular pacing reduction. We hypothesized that by allowing AV intervals to extend beyond 300 ms, a marked reduction in RV pacing can be achieved. METHODS: A total of 30 patients (17 men, mean age 71 +/- 9) with standard Brady indications, and implanted with a Medtronic Kappa 700 pacemaker, were randomized to 2-week treatments with default Search AV (KSAV) parameters or Enhanced Search AV (ESAV) parameters. The Enhanced Search AV algorithm included the capability for continuous adjustment of AV delays and the ability to auto disable in patients with persistent AV block. RESULTS: Among patients with intact AV conduction, percent VP was greater in KSAV versus ESAV (70 +/- 40% vs 19 +/- 28%, P < 0.001). In patients with persistent AV block, the algorithm suspended appropriately and there was no significant change in the percent VP between both arms of the study. In 18/22 patients, percent VP was reduced below 40%. CONCLUSIONS: Substantial reduction in ventricular pacing can be achieved by allowing the AV interval parameters to extend beyond 300 ms using the ESAV algorithm. In patients with AV block, ESAV suspended and patients were paced at their nominal settings.

Aged↗

PubMed1999

A comparison of two automated external defibrillator algorithms.

OBJECTIVE: To compare the interval to delivery of the first shock by first responders in mannequin-based cardiac arrest scenarios using two automated external defibrillator (AED) algorithms. METHODS: Thirty-six (18 pairs) of Toronto firefighters (FFs) trained in two AED algorithms, algorithm I (A-I) and algorithm II (A-II), were studied. A-II mandates the immediate application of the AED once pulselessness is established. In contrast to A-I, A-II dictates that no CPR be initiated until it is required by the AED voice prompts. Each FF pair alternated roles while performing "shock-indicated," mannequin-based scenarios according to A-I and A-II. The interval from mannequin contact to delivery of the first shock was recorded. Five pairs were videotaped. The intervals to complete predetermined steps were compared between algorithms to determine in which step(s) time saving occurred. RESULTS: The mean (+/-SD) interval to the first shock in A-I was 80.7 seconds (+/-10.5 sec) (95% CI = 77.2 to 84.2 sec) vs 61.1 seconds (+/-8.75 sec) (95% CI = 58.2 to 64.0 sec) in A-II (p < 0.001). A-II shortened the interval to the first shock by 19.6 sec (+/-11.5) (95% CI = 15.8 to 23.4 sec). The time saving was a direct result of delaying CPR in A-II. CONCLUSION: A-II reduced the interval from mannequin contact to the first shock in standard training scenarios.

Algorithms↗

PubMed2001

Implementation of a cone-beam reconstruction algorithm for the single-circle source orbit with embedded misalignment correction using homogeneous coordinates.

We present an efficient implementation of an approximate cone-beam image reconstruction algorithm for application in tomography, which accounts for scanner mechanical misalignment. The implementation is based on the algorithm proposed by Feldkamp et al. and is directed at circular scan paths. The algorithm has been developed for the purpose of reconstructing volume data from projections acquired in an experimental x-ray micro-tomography (microCT) scanner. To mathematically model misalignment we use matrix notation with homogeneous coordinates to describe the scanner geometry, its misalignment, and the acquisition process. For convenience analysis is carried out for x-ray CT scanners, but it is applicable to any tomographic modality, where two-dimensional projection acquisition in cone beam geometry takes place, e.g., single photon emission computerized tomography. We derive an algorithm assuming misalignment errors to be small enough to weight and filter original projections and to embed compensation for misalignment in the backprojection. We verify the algorithm on simulations of virtual phantoms and scans of a physical multidisk (Defrise) phantom.

Algorithms↗