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PubMed1999

An experimental comparison of neural algorithms for independent component analysis and blind separation.

In this paper, we compare the performance of five prominent neural or adaptive algorithms designed for Independent Component Analysis (ICA) and blind source separation (BSS). In the first part of the study, we use artificial data for comparing the accuracy, convergence speed, computational load, and other relevant properties of the algorithms. In the second part, the algorithms are applied to three different real-world data sets. The task is either blind source separation or finding interesting directions in the data for visualisation purposes. We develop criteria for selecting the most meaningful basis vectors of ICA and measuring the quality of the results. The comparison reveals characteristic differences between the studied ICA algorithms. The most important conclusions of our comparison are robustness of the ICA algorithms with respect to modest modeling imperfections, and the superiority of fixed-point algorithms with respect to the computational load.

Algorithms↗

PubMed1999

A self-organizing algorithm for vector quantizer design applied to signal processing.

Vector quantization plays an important role in many signal processing problems, such as speech/speaker recognition and signal compression. This paper presents an unsupervised algorithm for vector quantizer design. Although the proposed method is inspired in Kohonen learning, it does not incorporate the classical definition of topological neighborhood as an array of nodes. Simulations are carried out to compare the performance of the proposed algorithm, named SOA (self-organizing algorithm), to that of the traditional LBG (Linde-Buzo-Gray) algorithm. The authors present an evaluation concerning the codebook design for Gauss-Markov and Gaussian sources, since the theoretic optimal performance bounds for these sources, as described by Shannon's Rate-Distortion Theory, are known. In speech and image compression, SOA codebooks lead to reconstructed (vector-quantized) signals with better quality as compared to the ones obtained by using LBG codebooks. Additionally, the influence of the initial codebook in the algorithm performance is investigated and the algorithm ability to learn representative patterns is evaluated. In a speaker identification system, it is shown that the the codebooks designed by SOA lead to higher identification rates when compared to the ones designed by LBG.

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PubMed1987

Algorithms in radiology and medical imaging.

As a tool in clinical decision making, algorithms deserve careful consideration. The potential use or abuse of algorithms in rationing health care renders such consideration essential. In radiology and medical imaging, algorithms have been applied as teaching tools in the conference room setting. These teaching decision trees, however, may not be applicable in the clinical situation. If an algorithmic approach to clinical radiology is pursued, several issues should be considered. Specifically, the application, design, designer, economics, and universality of the algorithms must be addressed. As an alternative to the wide dissemination of clinical algorithms, the authors propose the development of consensus opinions among specialists and the promulgation of the principle of radiologist-consultant-decision maker. A decision team is preferable to a decision tree.

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PubMed1987

Prospective evaluation of a sequential pacing and high-energy bidirectional shock algorithm for transvenous cardioversion in patients with ventricular tachycardia.

Rapid ventricular pacing alone or in combination with low- or intermediate-energy shocks has limited efficacy in cardioverting rapid ventricular tachycardia (VT) when delivered through two transvenous catheter electrodes. This prospective study determined the efficacy and safety of an algorithm that used a sequence of rapid ventricular pacing (RVP) and intermediate-energy (5 and 15 J) and high-energy (25J) single, bidirectional shocks delivered by two transvenous catheter electrodes in conjunction with a cutaneous electrode in patients with sustained VT. The bidirectional shock was simultaneously delivered over two electrical vectors via a common right ventricular apical cathode and tow anodes consisting of the superior vena caval catheter electrode and cutaneous patch. The electrical therapy delivered was determined by the cycle length of VT. Slow VT (cycle length greater than 300 msec) was sequentially treated by RVP followed by incremental bidirectional shocks of 5, 15, and 25 J. Rapid VT (cycle length less than 300 msec) was treated with no incremental bidirectional shocks of 15 and 25 J. VT was reinduced to determine reproducibility of the algorithm for episodes that were successfully terminated. For patients in whom the primary algorithm failed, a second algorithm was used that excluded 5 and 15 J shocks and went directly to a 25 J shock. VT was reinduced twice and the secondary algorithm was evaluated. Thus, reproducibility of termination of VT with the primary and secondary algorithm was examined. Fifty episodes of slow VT and 40 episodes of rapid VT were induced in 22 patients (mean left ventricular ejection fraction 31 +/- 14%). Six patients had rapid VT, nine patients had slow VT, and seven patients had both.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2001

Theoretical analysis of mutation-adaptive evolutionary algorithms.

Adaptive evolutionary algorithms require a more sophisticated modeling than their static-parameter counterparts. Taking into account the current population is not enough when implementing parameter-adaptation rules based on success rates (evolution strategies) or on premature convergence (genetic algorithms). Instead of Markov chains, we use random systems with complete connections - accounting for a complete, rather than recent, history of the algorithm's evolution. Under the new paradigm, we analyze the convergence of several mutation-adaptive algorithms: a binary genetic algorithm, the 1/5 success rule evolution strategy, a continuous, respectively a dynamic (1+1) evolutionary algorithm.

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PubMed1999

A statistical study of a class of cellular evolutionary algorithms.

Parallel evolutionary algorithms, over the past few years, have proven empirically worthwhile, but there seems to be a lack of understanding of their workings. In this paper we concentrate on cellular (fine-grained) models, our objectives being: (1) to introduce a suite of statistical measures, both at the genotypic and phenotypic levels, which are useful for analyzing the workings of cellular evolutionary algorithms; and (2) to demonstrate the application and utility of these measures on a specific example-the cellular programming evolutionary algorithm. The latter is used to evolve solutions to three distinct (hard) problems in the cellular-automata domain: density, synchronization, and random number generation. Applying our statistical measures, we are able to identify a number of trends common to all three problems (which may represent intrinsic properties of the algorithm itself), as well as a host of problem-specific features. We find that the evolutionary algorithm tends to undergo a number of phases which we are able to quantitatively delimit. The results obtained lead us to believe that the measures presented herein may prove useful in the general case of analyzing fine-grained evolutionary algorithms.

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PubMed1996

A real-time scan conversion algorithm on commercially available microprocessors.

We have developed a new ultrasound scan conversion algorithm that can be executed very efficiently on modern microprocessors. Our algorithm is designed to handle the address calculations and input and output (I/O) data loading concurrently with the interpolation. The processing unit's computing power can be dedicated to performing pixel interpolations while the other operations are handled by an independent direct memory access (DMA) controller. By making intelligent use of the I/O transfer capabilities of the DMA controller, the algorithm avoids spending the processing unit's valuable computing cycles in address calculations and nonactive pixel blanking. Furthermore, the new approach speeds up the computation by utilizing the ability of superscalar and very long instruction word (VLIW) processors to perform multiple operations in parallel. Our scan conversion algorithm was implemented on a multimedia and imaging system based on the Texas Instruments TMS320C80 Multimedia Video Processor (MVP). Computing cycles are spent only on predeterminable nonzero output pixels. For example, an execution time of 11.4 ms was achieved when there are 101,829 nonzero output pixels. This algorithm demonstrates a substantial improvement over previous scan conversion algorithms, and its optimized implementation enables modern commercially available programmable processors to support scan conversion at video rates.

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PubMed1997

EM algorithms without missing data.

Most problems in computational statistics involve optimization of an objective function such as a loglikelihood, a sum of squares, or a log posterior function. The EM algorithm is one of the most effective algorithms for maximization because it iteratively transfers maximization from a complex function to a simple, surrogate function. This theoretical perspective clarifies the operation of the EM algorithm and suggests novel generalizations. Besides simplifying maximization, optimization transfer usually leads to highly stable algorithms with well-understood local and global convergence properties. Although convergence can be excruciatingly slow, various devices exist for accelerating it. Beginning with the EM algorithm, we review in this paper several optimization transfer algorithms of substantial utility in medical statistics.

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PubMed1997

The EM algorithm in medical imaging.

This article outlines the statistical developments that have taken place in the use of the EM algorithm in emission and transmission tomography during the past decade or so. We discuss the statistical aspects of the modelling of the projection data for both the emission and transmission cases and define the relevant probability models. This leads to the use of the method of maximum likelihood as a means of estimating the relevant unknown parameters within a given region of a patient's body and to the use of the EM algorithm to compute the reconstruction. Various different types of EM algorithm are discussed, including the SAGE algorithms of Fessler and Hero. The limitations of the EM algorithm, per se, are covered and the need for regularization is stressed. A number of different methods for penalizing the likelihood are described and a number of algorithms for the computation of the penalized EM reconstruction are discussed.

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PubMed1996

Routine use of a higher order interpolator and bone algorithm in thoracic CT.

OBJECTIVE: This study was designed to evaluate the utility of the routine use of high spatial frequency algorithms and higher order helical interpolators for imaging lung parenchyma during routine thoracic CT. SUBJECTS AND METHODS: We evaluated 50 consecutive patients undergoing clinically indicated thoracic CT using the same imaging parameters and scanner. The helical volume was reconstructed three separate times using standard and higher order (180 degrees linear with double-sided lobes) interpolators and standard and high spatial frequency (bone) algorithms. The images were photographed and given to five separate readers who were kept unaware of the interpolator and algorithm and who were asked to evaluate simultaneously each patient's three sets of images for best, in-between, and worst images of the lung interstitium, pathology, and normal anatomy. RESULTS: All five readers rated the standard interpolator and algorithm images as the worst (p < .01). All five readers consistently rated the double-sided lobe interpolator and bone algorithm images as the best (p < .01). CONCLUSION: A second reconstruction of routine thoracic helical CT data using higher order helical interpolators and a bone algorithm significantly improves interstitial detail of lung parenchyma and overall visualization of normal anatomy and pathologic processes.

Aged↗

PubMed2000

Comparing the performance of mammographic enhancement algorithms: a preference study.

OBJECTIVE: The objective of this study was to compare the performance of four image enhancement algorithms on secondarily digitized (i.e., digitized from film) mammograms containing masses and microcalcifications of known pathology in a clinical soft-copy display setting. MATERIALS AND METHODS: Four different image processing algorithms (adaptive unsharp masking, contrast-limited adaptive histogram equalization, adaptive neighborhood contrast enhancement, and wavelet-based enhancement) were applied to one image of secondarily digitized mammograms of forty cases (10 each of benign and malignant masses and 10 each of benign and malignant microcalcifications). The four enhanced images and the one unenhanced image were displayed randomly across three high-resolution monitors. Four expert mammographers ranked the unenhanced and the four enhanced images from 1 (best) to 5 (worst). RESULTS: For microcalcifications, the adaptive neighborhood contrast enhancement algorithm was the most preferred in 49% of the interpretations, the wavelet-based enhancement in 28%, and the unenhanced image in 13%. For masses, the unenhanced image was the most preferred in 58% of cases, followed by the unsharp masking algorithm (28%). CONCLUSION: Appropriate image enhancement improves the visibility of microcalcifications. Among the different algorithms, the adaptive neighborhood contrast enhancement algorithm was preferred most often. For masses, no significant improvement was observed with any of these image processing approaches compared with the unenhanced image. Different image processing approaches may need to be used, depending on the type of lesion. This study has implications for the practice of digital mammography.

Aged↗

PubMed2001

Quantification of coronary artery calcium using multidetector CT and a retrospective ECG-gating reconstruction algorithm.

OBJECTIVE: The purpose of our study was to evaluate the quality of and motion artifacts on multidetector CT scans and to compare the results with those of and on electron beam CT scans for the assessment of coronary calcium scores. MATERIALS AND METHODS: First, 20 volunteers were scanned using multidetector CT. We compared the signal-to-noise ratio in the heart, motion artifacts at the heart border, and the highest CT values in the regions of the coronary arteries using single-sector and multisector reconstruction algorithms. Next, 60 patients with coronary calcified deposits underwent both multidetector CT and electron beam CT. We compared coronary calcium scores determined with multidetector CT using the two algorithms (thresholds of 90 and 130 H) with those determined using electron beam CT. RESULTS: The signal-to-noise ratio was higher and motion artifacts were reduced when we used the multisector algorithm. The highest CT value in the region of the coronary arteries exceeded 90 H in one of 55 arteries on the multisector algorithm images and 17 of 55 arteries on single-sector algorithm images (chi-square test, p < 0.01). In coronary calcium scoring, correlation coefficients ranged from 0.920 to 0.992 (Pearson's product moment) and from 0.932 to 0.969 (Spearman's rank correlation coefficient). CONCLUSION: Multidetector CT with a retrospective ECG-gating algorithm (multisector reconstruction) produced cardiac images with fewer motion artifacts and showed a high correlation with coronary calcium scores determined using electron beam CT. Therefore, multidetector CT is a potential tool for coronary calcium scoring.

Adult↗

PubMedDate not supplied

Evaluation of shading algorithms for surface display: depth information, surface orientation, colour and transparency.

When interpreting a shaded surface image the observer must infer a three-dimensional shape from a two-dimensional image. The principal monocular cues used in this process are surface orientation and apparent depth. Four shading algorithms were compared, ranging from pure depth to pure surface orientation with two intermediates. Eight observers assessed these algorithms using 40 sets of images showing test objects derived from emission computed axial tomograms, X-ray computed tomograms and simulated data. The results demonstrated a highly significant preference (p less than 0.01) for surface orientation over depth information for all observers and both imaging modalities. The coefficient of concordance showed that the observers were in good agreement as to the rank order of the algorithms, with significant agreement (p less than 0.05) for 37 of the 40 sets of images. The overall preferred algorithm was based on a local polynomial fitting procedure and contained primarily surface information. This shading algorithm was extended to include colour, which was used both as an arbitrary surface property to identify parts of a complex object and as a means of conveying temporal information. Further extension of the algorithm to the display of transparent surfaces was facilitated by an illumination model based on purely isotropic light. This enabled even irregular surfaces to be displayed as transparent objects, and was combined with opaque shading for displaying nested surfaces in nuclear magnetic resonance data.

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PubMed2003

A computer algorithm for calculating the adequacy of antidepressant treatment in unipolar and bipolar depression.

BACKGROUND: Major depression is often treated with medications in doses that are too low or too short in duration. We published an early version of the Antidepressant Treatment History Form (ATHF) that rates the adequacy of antidepressant treatment. The updated ATHF presented here includes newer medications and a computer algorithm to automate the evaluation of the adequacy of pharmacotherapy or electroconvulsive therapy for depression. METHOD: The computer algorithm was written in MS-DOS Q-BASIC and in Visual Basic 5.0. Treatment data from 47 depressed (Structured Clinical Interview for DSM-III-R) patients were scored by the computer algorithm and assigned a number from 0 to 5 for the adequacy of antidepressant treatment. A psychiatrist blinded to the computer ratings manually rated the treatment using the ATHF. RESULTS: The computer algorithm, based on an updated version of the ATHF, estimates the adequacy of treatment of unipolar and bipolar depression. Computer algorithm results agreed with those generated by a clinician completing the form manually (kappa = 0.88 to 1.00). CONCLUSION: The computer algorithm can be used to analyze large databases and may help reduce the morbidity and mortality associated with major depression by improving the assessment of adequacy of pharmacologic treatments for research and quality assurance purposes. The availability of the updated ATHF on the Internet for downloading allows for modifications according to the user's purposes.

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PubMed2003

[A multicenter evaluation of seven commercial ML-EM algorithms for SPECT image reconstruction using simulation data].

The maximum likelihood expectation maximization (ML-EM) algorithm has become available as an alternative to filtered back projection in SPECT. The actual physical performance may be different depending on the manufacturer and model, because of differences in computational details. The purpose of this study was to investigate the characteristics of seven different types of ML-EM algorithms using simple simulation data. Seven ML-EM algorithm programs were used: Genie (GE), esoft (Siemens), HARP-III (Hitachi), GMS-5500UI (Toshiba), Pegasys (ADAC), ODYSSEY-FX (Marconi), and Windows-PC (original software). Projection data of a 2-pixel-wide line source in the center of the field of view were simulated without attenuation or scatter. Images were reconstructed with ML-EM by changing the number of iterations from 1 to 45 for each algorithm. Image quality was evaluated after a reconstruction using full width at half maximum (FWHM), full width at tenth maximum (FWTM), and the total counts of the reconstructed images. In the maximum number of iterations, the difference in the FWHM value was up to 1.5 pixels, and that of FWTM, no less than 2.0 pixels. The total counts of the reconstructed images in the initial few iterations were larger or smaller than the converged value depending on the initial values. Our results for the simplest simulation data suggest that each ML-EM algorithm itself provides a simulation image. We should keep in mind which algorithm is being used and its computational details, when physical and clinical usefulness are compared.

Algorithms↗

PubMed1998

Evaluation of syndromic patient management algorithm for urethral discharge.

OBJECTIVE: To determine feasibility, validity, and cost effectiveness of the syndromic approach to male patients with urethral discharge in Bandung, Indonesia. METHODS: The WHO algorithm on urethral discharge with no microscopy available was evaluated. Patients presented with a complaint of urethral discharge and if discharge was confirmed the algorithm was applied. Treatment covered gonococcal and chlamydial infection (ciprofloxacin 500 mg single oral dose plus doxycycline 100 mg, twice daily orally for 7 days). The gold standard for validation was gonococcal culture and chlamydia antigen detection. RESULTS: 140 male patients with a complaint of urethral discharge were enrolled; 119 had confirmed discharge and entered the decision tree: 107 were followed and 104 (97%) were clinically cured. Of the three patients with persistent discharge, one had a purulent urethral discharge, diagnosed as gonococcal urethritis and he was probably reinfected; two patients had a serous discharge and microbiological tests were negative. Overall, 106 out of 107 patients (99%) were microbiologically cured. Sensitivity of the algorithm is 100% and its positive predictive value (PPV) is 75% or 97% if validated against gold standard microbiological tests or Gram stain, respectively. Cost per patient is rupiah (Rp)5.894 ($US2.56) for the algorithm compared with Rp43.024 ($18.70) for full microbiological diagnosis. The cost estimate for an algorithm of urethral discharge with microscopy available is Rp6.432 ($2.80) CONCLUSION: The "symptom and sign" algorithm is fully adapted to the prevailing situation in primary healthcare settings, is acceptable to healthcare workers and patients (who are effectively treated at their first visit), is highly cost effective, is 100% sensitive (no false negatives, which is not the case with microbiological diagnosis), and has a high PPV, between 75% and 97%. It is an excellent patient management tool and a sound basis for partner notification so that it should have a major impact on STD/HIV control and prevention in both men and women.

Administration, Oral↗

PubMed1999

Do management algorithms improve chest pain triage?

OBJECTIVE: To audit the use of management algorithms for chest pain in an emergency department. DESIGN AND SETTING: Prospective study of all patients with chest pain presenting to the emergency department of an urban teaching hospital between 12 January and 4 May 1997. Staff were asked to complete a standardised admission form that incorporated the risk stratification algorithms for managing patients with suspected acute coronary syndrome. MAIN OUTCOME MEASURES: Compliance with the use of management algorithms; concordance with a cardiologist's review of the triage grouping and admission/discharge decision; and major cardiovascular events over four months. RESULTS: Emergency department staff documented the triage group in 223 of 503 cases (45%). Concordance with the group assigned by a cardiologist was 70% (kappa = 0.73; SE kappa = 0.04). When the management algorithm was applied correctly, 92% of triage decisions were correct (95% confidence interval [CI], 87%-96%). The triage decision was less often correct when risk stratification was not done (78% [73%-83%], P < 0.001), overestimated (77% [66%-88%], P < 0.01), or underestimated (50% [18%-82%], P < 0.001). The proportion of patients free of major cardiovascular events at four-month follow-up was 50% for those with myocardial infarction with ST-segment elevation, 47% for those with a high short-term risk of an adverse cardiac event, 82% for those with intermediate risk, and 99% for those with a low risk or non-coronary chest pain (P < 0.001). CONCLUSIONS: Use of management algorithms by emergency staff was poor. When used, triage decisions were more likely to be correct. Subsequent outcome confirms that the NHMRC risk stratification algorithms are useful for prognostic stratification of patients with suspected acute coronary syndrome.

Adult↗

PubMed2000

Evaluation of the WHO/UNICEF algorithm for integrated management of childhood illness between the ages of one week to two months.

OBJECTIVE: To evaluate the utility of the WHO/UNICEF algoritham for integrated management of childhood illness (IMCI) between the ages of 1 week to 2 months. DESIGN: Prospective observational. SETTING: The Outpatient Department and Emergency Room of a medical college hospital. METHODS: 129 infants presenting to Outpatient Department (n=70) or Emergency Room (n=59) were assessed and classified as per 'IMCI' algorithm and treatment required was identified. A detailed evaluation with all relevant investigations was also done for these subjects. The final diagnoses made and therapies instituted on this basis served as 'gold standard'. The diagnostic and therapeutic agreement between 'gold standard and the 'IMCI' was computed. RESULTS: More than one illness was present in 97(75.2%) of subjects as per 'gold standard' (mean 2.1). Subjects having any referral criteria as per 'IMCI' algorithm had a greater (p=0.002) co-existence of illnesses (mean 2.3 vs. 1.8 illnesses per child, respectively. IMCI algorithm covered majority (81-84%) of the recorded diagnoses either partly (40-41%) or fully (40-44%). The referral criteria proved quite sensitive (86-87%) in predicting hospitalization but had a lower specificity (53-58%). a total agreement with IMCI was found in 60-66% cases. The mismatch (34-40%) was more commonly of overdiagnosis (21-23%) rather than underdiagnosis (15-21%). The sensitivity of the algorithm to identify serious bacterial infection was high (96.1-96.5%) while the specificity was relatively low (51. 8-59.7%). Upper respiratory infection (URI)emerged as an important cause resulting in unnecessary referrals (13 out of 21 cases). Of the 43 cases identified as diarrhea by the algorithm, 6 had breast fed stools, which do not require any therapy. The 'IMCI' algorithm had a provision for preventive services of immunization and breastfeeding counseling (18% possibility of availing missed opportunities in both). CONCLUSION: There is a sound scientific basis for adopting IMCI approach even in young infants as there is a need to improve the specificity of referral criteria. Two important conditions identified for possible refinement are URI and breast fed stools

Algorithms↗