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Application of the EM algorithm to radiographic images.

The expectation maximization (EM) algorithm has received considerable attention in the area of positron emitted tomography (PET) as a restoration and reconstruction technique. In this paper, the restoration capabilities of the EM algorithm when applied to radiographic images is investigated. This application does not involve reconstruction. The performance of the EM algorithm is quantitatively evaluated using a "perceived" signal-to-noise ratio (SNR) as the image quality metric. This perceived SNR is based on statistical decision theory and includes both the observer's visual response function and a noise component internal to the eye-brain system. For a variety of processing parameters, the relative SNR (ratio of the processed SNR to the original SNR) is calculated and used as a metric to compare quantitatively the effects of the EM algorithm with two other image enhancement techniques: global contrast enhancement (windowing) and unsharp mask filtering. The results suggest that the EM algorithm's performance is superior when compared to unsharp mask filtering and global contrast enhancement for radiographic images which contain objects smaller than 4 mm.

Algorithms↗

PubMed1989

A medical algorithm for detecting physical disease in psychiatric patients.

An algorithm for screening psychiatric patients for physical disease was empirically derived from a comprehensive assessment of 509 patients in California's mental health system. The first 343 patients were used to develop the algorithm, and the remaining 166 were used as a test group. Calculations were made for several versions of the algorithm, and the data were compared with the diagnoses listed in the patients' admission mental health record. The algorithmic procedure was more accurate and more cost-effective than the medical evaluation procedures used by the state mental health system. When applied to the test group, the algorithm detected up to 90 percent of patients who had an active, important physical disease at a cost of $156 per patient. The mental health system had detected 58 percent of test-group patients with a disease at a cost of $230 per patient.

Algorithms↗

PubMed1987

Algorithmic diagnosis of jaundice.

Extensive clinical and clinical chemical information was collected from 1002 jaundiced patients. By applying Bayes' theorem and logistic discriminant analysis, a diagnostic algorithm was developed based upon 21 of the 107 variables collected. This algorithm permitted a probabilistic classification of jaundiced patients into four diagnostic categories: acute non-obstructive, chronic non-obstructive, benign obstructive and malignant obstructive jaundice. Of the 985 patients with a final diagnosis a correct probabilistic diagnosis (obstruction vs. non-obstruction) was suggested by the algorithm in 867 patients (88%). Adopting a probability limit of 0.80, 683 patients (69%) were correctly classified, 34 patients (3.5%) were wrongly so, and 268 patients (27%) could not be classified with a probability above 0.80 (doubtful cases). The algorithm was also tested in a further series of 110 jaundiced patients and found to perform equally well: 88 patients classified, 22 patients remaining doubtful. Patients with doubtful diagnoses should be referred to a non-invasive test such as ultrasound examination, whereas patients with definite diagnoses can be referred to invasive tests (liver biopsy, direct cholangiography) as appropriate. The diagnostic algorithm seems to be a valuable aid for the preliminary differential diagnosis of the jaundiced patient and can be used in the planning of a diagnostic strategy for the individual patient.

Algorithms↗

PubMed1992

[Calculation algorithm of three-dimensional absorbed dose distribution due to in vivo administration of nuclides for radiotherapy].

In the in vivo administration of radionuclides for radiotherapy including radioimmunotherapy, an algorithm is proposed for the purpose of calculating three-dimensional absorbed dose distributions of tumors and adjacent tissues, and neighboring organs. The absorbed dose distribution due to the algorithm is given by convolution of the three-dimensional dose matrix for a unit cubic voxel containing unit cumulated activity, with the three-dimensional matrix of the cumulated activity distribution given by the same voxel size above. The dose calculation algorithm does not depend upon the source size, the source shape, and the nonuniform and irregular activity distribution. In addition, it can exceedingly decrease computation time compared to other calculation algorithms. Computer simulations were performed using the MIRD thyroid phantom for 32P, 90Y, 131I, 186Re, and 188Re that appear promising for radioimmunotherapy, and their results verified the validity of the proposed calculation algorithm and high accuracy of the calculations.

Algorithms↗

PubMed1992

Computer-assisted analysis of mixtures (C.A.MAM): statistical algorithms.

This paper presents various algorithmic approaches for computing the maximum likelihood estimator of the mixing distribution of a one-parameter family of densities and provides a unifying computer-oriented concept for the statistical analysis of unobserved heterogeneity (i.e., observations stemming from different subpopulations) in a univariate sample. The case with unknown number of population subgroups as well as the case with known number of population subgroups, with emphasis on the first, is considered in the computer package C.A.MAN (Computer Assisted Mixture Analysis). It includes an algorithmic menu with choices of the EM algorithm, the vertex exchange algorithm, a combination of both, as well as the vertex direction method. To ensure reliable convergence, a step-length menu is provided for the three latter methods, each achieving monotonicity for the direction of choice. C.A.MAN has the option to work with restricted support size-that is, the case when the number of components is known a priori. In the latter case, the EM algorithm is used. Applications of mixture modelling in medical problems are discussed.

Algorithms↗

PubMed1991

Clinical evaluation of an algorithm for the interpretation of hyperamylasemia.

Total amylase concentration in serum continues to be widely determined in the diagnosis of acute pancreatic disease. Accumulated experience has made clear, however, that this determination has distinct limitations. Consequently, the knowledge of the origin of hyperamylasemia may have an important influence on treatment, hospitalization, and extent of clinical investigations. We undertook a logical and systematic approach to the interpretation of hyperamylasemia through the use of an algorithm that can be applied in clinical situations without the need for the integration of radiologic procedures or clinical data. The proposed algorithm was tested for effectiveness in 97 consecutive hospitalized patients with hyperamylasemia (amylase level greater than twice the upper reference limit) for a 2-year period. The majority (52.5%) of these patients had acute pancreatitis. The algorithm assigned the correct diagnostic categories in 95.8% of cases, with a disagreement between patient diagnosis and algorithm-generated diagnosis in only four cases. These four patients (two with acute biliary disease, one with bacterial peritonitis, and one with chronic renal failure) had pancreatic lipase values greater than five times the upper reference limit, so that the algorithm classified their condition as acute pancreatitis. The clinical trial indicated that the proposed decision tree, which requires only knowledge of biochemical data that are readily available, is useful in the evaluation of elevated amylase activity and facilitates arrival at a definitive diagnosis.

Acute Disease↗

PubMed1991

A computational model of approximate Bayesian inference for associating clinical algorithms with decision analyses.

The lack of rationale or explanation is a major deficiency of clinical algorithms. To address this issue, the authors present a computational model for associating decision analyses with clinical algorithms. Automata theory is used to model categorical reasoning with approximate Bayesian inference based on probability intervals. This approximation reduces the number of computations to linear-order instead of the exponential-order combinations of clinical findings in exact Bayes. The linkage of decision analyses and clinical algorithms by means of this model exploits a new concept of "regular" clinical algorithms and their equivalency in theory and provides valuable perspectives in practice for developers of clinical algorithms.

Algorithms↗

PubMed1990

[A comparison of two algorithms for determining renal whole body clearance following simultaneous acquisition with a partially shielded whole-body counter and a gamma camera].

The influence of instrumentation, algorithm, and the time of blood sampling on whole-body renal clearance as defined by effective renal plasma flow (ERPF) was investigated. The study involved simultaneous sampling with a partially shielded whole-body counter (WBC) and a gamma camera to assess ERPF. The results obtained using two different analysis algorithms for each modality are compared. Although ERPF as determined by the Oberhausen technique was significantly higher than that obtained using an algorithm developed by the authors, for each algorithm there was no significant difference between the WBC and gamma camera-derived values within the range of 100 to 800 ml/min. Furthermore, positioning of the ROI was not critical for gamma camera-derived ERPF (SD less than 1% for multiple crescentic ROIs and approximately 4% for multiple rectangular ROIs). However, the time of blood sampling did appear more important since the average ERPF derived from the 10- and 20-min samples compared with that from the 15- and 25-min samples differed significantly for both analysis algorithms. The methodology which we have validated provides a more precise tool for further investigations of the influence of medication, posture, and exercise stress on renal function.

Algorithms↗

PubMed1988

Performance of two new algorithms for estimating within- and between-method carryover evaluated statistically.

Accurate and precise algorithms for estimating within-method carryover, based on the minimization of a unique "carryover sum of squares," and between-method carryover, based on a weighted Deming regression of first sample recovery vs carryover-corrected "true" recovery, are described and compared with traditional methods by use of a Monte Carlo study. In addition, I have studied the experimental parameters that influence the accuracy and precision of carryover estimation. The new algorithm for estimating within-method carryover is unbiased under most conditions, whereas the traditional algorithm is biased low under most conditions. The new algorithm is also more precise, owing to more-efficient utilization of information contained in an analytical run performed for carryover estimation. Between-method carryover in a random-access analyzer is estimated quantitatively by the second proposed algorithm and is found to be readily and precisely determinable. Use of these methods in combination to evaluate analytical interaction should allow the prediction of carryover error under most current analytical situations.

Algorithms↗

PubMed1986

Pitfalls in the use of clinical algorithms.

The algorithm is a very useful tool in medical practice. Like any other tool, it has advantages and disadvantages. The wise physician avoids a modality until he has learned how to use it. The same should be true of algorithms. Obtain some computer primers that explain the writing of algorithms. Experiment with algorithms of your own creation. When you reach the level where you can easily write your own algorithms, you are ready to use those written by others, making any modifications necessary to suit your own philosophy and experience.

Algorithms↗

PubMed1986

An algorithm for comparing two-dimensional electrophoretic gels, with particular reference to the study of mutation.

An algorithm dedicated to the detection of presumed mutational events involving the polypeptides displayed with two-dimensional polyacrylamide gel electrophoresis has been described. Because of the large number of gels necessary in most studies of mutation, the algorithm has been designed to minimize operator intervention in its execution. The basic principle involves a comparison of the graph structures of the gels of a father, mother, and one or more children, searching for protein spots in the child not found in either parent. These so-called "orphan" spots are considered a probable manifestation of mutation only after other possible causes of such an isolated event have been excluded as rigorously as possible. At present, the analysis of gels prepared from a platelet or erythrocyte lysate yields about 2% "false-positive" findings, i.e., results in the incorrect designation of a unique spot in a child. These errors can be disposed of by technician intervention. In an experiment designed to simulate the occurrence of mutational events, the algorithm operated with 70% accuracy. Most of the "errors" ("false negatives") occurred when the position of the simulated mutant polypeptide coincided in whole or part with that of a preexisting polypeptide, resulting in a class of mutation not detectable by the eye either. With correction for this fact, the accuracy was 84%. Possible improvements in the algorithm which would substantially increase accuracy have been discussed at some length, as have some ideas as to how to manage the large body of data resulting from the operation of the algorithm. A murine experiment designed to validate the approach has been outlined.

Blood Proteins↗

PubMed1986

Fluid resuscitation of hypotensive emergency patients with and without an algorithm.

Seventy-seven consecutive hypotensive (mean arterial pressure (MAP) less than 80 mmHg) surgical emergency patients were resuscitated according to either physicians' individual orders (38 patients) or an algorithm (39 patients). The shock was mainly caused by accidental injuries or acute gastrointestinal bleeding. The patients of the algorithm group were given more plasma expanders than the patients of the control group, while the total amount of fluids administered was similar in both groups. The primary goal of the resuscitation (MAP greater than 80 mmHg) was reached within 30 min in three cases in the control group and in seven cases in the algorithm group. The treatment times at the emergency department and the intensive care unit were similar for the groups. The number of severe and moderate pulmonary disturbances was the same, but mild disturbances were significantly more common in the control group. Renal failure was somewhat more common in the control group and the renal function disturbances were significantly more severe among the control patients. The results suggest that the physicians in some extent altered their practices in fluid resuscitation when the algorithm was put to use, and that this change, perhaps, produced the somewhat better outcome of the patients. The authors recommend the algorithm to be used as a basis of shock treatment and particularly in those emergency departments where the resuscitation of hypotensive patients is performed by junior or inexperienced physicians.

Adolescent↗

PubMed1986

An efficient string matching algorithm with k differences for nucleotide and amino acid sequences.

There are a few algorithms designed to solve the problem of the optimal alignment of one sequence, the pattern, of length m, with another, longer sequence the text, of length n. These algorithms allow mismatches, deletions and insertions. Algorithms to date run in O(mn) time. Let us define an integer, k, which is the maximal number of differences allowed. We present a simple algorithm showing that sequences can be optimally aligned in O(k2n) time. For long sequences the gain factor over the currently used algorithms is very large.

Amino Acid Sequence↗

PubMed1986

A microcomputer algorithm for solving compartmental models involving radionuclide transformations.

An algorithm for solving first-order non-recycling compartment models is described. Given the initial amounts of a radioactive material in each compartment and the fundamental transfer rate constants between each compartment, the algorithm gives both the amount of material remaining at any time t and the integrated number of transformations that would occur up to time t. The method is analytical, and consequently, is ideally suited for implementation on a microcomputer. For a typical microcomputer with 64 kilobytes of random access memory, a model containing up to 100 compartments, with any number of interconnecting translocation routes, can be solved in a few seconds; providing that no recycling occurs. An example computer program, written in 30 lines of Microsoft BASIC, is included in an appendix to demonstrate the use of the algorithm. A detailed description is included to show how the algorithm is modified to satisfy the requirements commonly encountered in compartment modelling, for example, continuous intake, partitioning of activity, and transformations from radioactive progeny. Although the algorithm does not solve models involving recycling, it is often possible to represent such cases by a non-recycling model which is mathematically equivalent.

Computers↗

PubMed1985

Image reconstruction from coded data: I. Reconstruction algorithms and experimental results.

Two algorithms have been developed for reconstructing objects from their coded images and a priori knowledge of the object class. Reconstructions from both algorithms are presented, but the results appear to be largely independent of the algorithm used. One of the algorithms, a Monte Carlo approach, is used to investigate the quality of the reconstruction of two- and three-dimensional objects from simulated coded-image data with respect to viewing geometry and multiplexing (mixing) of the data. The cases examined include reconstructions from data with and without signal-dependent photon noise. It is found that reconstructing from multiplexed data is not so serious a problem as reconstructing from data obtained with a limited viewing angle. Also, when photon noise is included in the data, reconstructions obtained from multiplexed data are better than those obtained from unmultiplexed data because of the higher photon count made available by multiplexing. It appears that the fidelity of a reconstruction depends much more strongly on the design of the data-taking system (the coded apertures) than on the reconstruction algorithm.

Models, Structural↗

PubMed1991

Comparison of analytic algorithms for detecting glaucomatous visual field loss.

The sensitivity and specificity of alternate analytic strategies for recognizing glaucomatous visual field loss from automated threshold perimetry (C-30-2 test of the Humphrey Field Analyzer) were compared among one eye each of 106 patients with glaucoma and 249 normal subjects. Algorithms included commercially available global indexes and cross-meridional differences (Statpac 1 and Statpac 2), as well as cross-meridional and cluster analyses that were developed independently for natural history studies and clinical trials. The sensitivity of most algorithms was high, except for those that used only diffuse loss as an indicator of abnormality. Specificity was acceptably high for all algorithms. Subjects who failed to meet the manufacturer's standard for reliability had much reduced specificity, but sensitivity was also affected. Algorithms that were based on any of the alternate definitions of localized reduction in retinal sensitivity performed equally well, which suggests that any of these approaches is useful in searching for glaucomatous visual loss as typified by this database. Availability, familiarity, and convenience may govern the selection of any one analytic approach for use in a particular setting.

Algorithms↗

PubMed1987

A comparative study of attenuation correction algorithms in single photon emission computed tomography (SPECT).

A computer based simulation method was developed to assess the relative effectiveness and availability of various attenuation compensation algorithms in single photon emission computed tomography (SPECT). The effect of the nonuniformity of attenuation coefficient distribution in the body, the errors in determining a body contour and the statistical noise on reconstruction accuracy and the computation time in using the algorithms were studied. The algorithms were classified into three groups: precorrection, post correction and iterative correction methods. Furthermore, a hybrid method was devised by combining several methods. This study will be useful for understanding the characteristics, limitations and strengths of the algorithms and searching for a practical correction method for photon attenuation in SPECT.

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↗