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PubMed1989

Modified Box-Cox transform for modulating the dynamic range of flow cytometry data.

We describe an algorithm, Vout = Integer ([2(12)-1/2(12 lambda)-1] V lambda in-1) + 1; lambda greater than 0 based upon Box-Cox transformations as an alternative to nonlinear electronic amplifiers to expand or compress high- or low-amplitude flow cytometer-derived signals. If the indexing parameter lambda less than 1, input channels in the high-amplitude input range are compressed in the output range as occurs when an electronic logarithmic amplifier is used. However, if lambda greater than 1, input channels in the low-amplitude input range are compressed in the output range as occurs when an electronic power amplifier is used. Our modified Box-Cox transform can be implemented either during data collection or off-line for the transformation of previously collected raw data. The transform is the equivalent of an infinite class of nonlinear amplifiers. As the transform is implemented in software, it does not suffer from many of the disadvantages of nonlinear electronic amplifiers.

Algorithms↗
PubMed1994

Joint photographic experts group (JPEG) compatible data compression of mammograms.

We have developed a Joint Photographic Experts Group (JPEG) compatible image compression scheme tailored to the compression of digitized mammographic images. This includes a preprocessing step that segments the tissue area from the background, replaces the background pixels with a constant value, and applies a noise-removal filter to the tissue area. The process was tested by performing a just-noticeable difference (JND) study to determine the relationship between compression ratio and a reader's ability to discriminate between compressed and noncompressed versions of digitized mammograms. We found that at compression ratios of 15:1 and below, image-processing experts are unable to detect a difference, whereas at ratios of 60:1 and above they can identify the compressed image nearly 100% of the time. The performance of less specialized viewers was significantly lower because these viewers seemed to have difficulty in differentiating between artifact and real information at the lower and middle compression ratios. This preliminary study suggests that digitized mammograms are very amenable to compression by techniques compatible with the JPEG standard. However, this study was not designed to address the efficacy of image compression process for mammography, but is a necessary first step in optimizing the compression in anticipation of more elaborate reader performance (ROC) studies.

Algorithms↗
PubMed2007

Biomechanical analysis of cervical spine sagittal stiffness characteristics.

The orientation of the loading, along which the minimum and maximum displacements occur, can be described as the principal axis. This work presents a model to determine extremums of the compliance of the cervical spine and corresponding principal axis, given the pose and flexibility of each functional cervical unit. As the cervical model of C(2)-C(7) section is flexed, it becomes tensionally stiffer and as the structure is extended, it becomes compressively stiffer. The opposite is true for the model including the atlanto-occipito-axial complex suggesting a compressively stiffer column as it is flexed and a tensionally stiffer structure as it is extended.

Algorithms↗
PubMed2000

Applying computer-assisted detection schemes to digitized mammograms after JPEG data compression: an assessment.

RATIONALE AND OBJECTIVES: The authors' purpose was to assess the effects of Joint Photographic Experts Group (JPEG) image data compression on the performance of computer-assisted detection (CAD) schemes for the detection of masses and microcalcification clusters on digitized mammograms. MATERIALS AND METHODS: This study included 952 mammograms that were digitized and compressed with a JPEG-compatible image-compression scheme. A CAD scheme, previously developed in the authors' laboratory and optimized for noncompressed images, was applied to reconstructed images after compression at five levels. The performance was compared with that obtained with the original noncompressed digitized images. RESULTS: For mass detection, there were no significant differences in performance between noncompressed and compressed images for true-positive regions (P = .25) or false-positive regions (P = .40). In all six modes the scheme identified 80% of masses with less than one false-positive region per image. For the detection of microcalcification clusters, there was significant performance degradation (P < .001) at all compression levels. Detection sensitivity was reduced by 4%-10% as compression ratios increased from 17:1 to 62:1. At the same time, the false-positive detection rate was increased by 91%-140%. CONCLUSION: The JPEG algorithm did not adversely affect the performance of the CAD scheme for detecting masses, but it did significantly affect the detection of microcalcification clusters.

Algorithms↗
PubMed2002

Measures of intermittency in driven supersonic flows.

Scaling exponents for structure functions of the velocity, density, and entropy are computed for driven supersonic flows for rms Mach numbers of order unity, with numerical simulations using the piecewise parabolic method algorithm on grids of up to 512(3) points. The driving is made up of either one or three orthogonal shear waves. In all cases studied, the compressible component of the velocity in the statistically steady regime is weaker than its solenoidal counterpart by roughly a factor of 6. Exponents for the longitudinal component of the velocity are comparable to what is found in the incompressible case and appear insensitive to the presence of numerous shocks. Scaling exponents of the transverse components of the velocity are comparable to those for the longitudinal component. Density and entropy structure functions display strong departures from linear scaling. Finally, the scaling of structure functions of the energy transfer is also given and compared with the Kolmogorov refined similarity hypothesis.

Journal Article↗
PubMed2004

Spatially adaptive wavelet denoising using the minimum description length principle.

This paper presents a new spatially adaptive wavelet denoising method. Based on a doubly stochastic process model of wavelet coefficients, the method gives a new threshold, which varies spatially according to the variances of the coefficients, using the minimum description length (MDL) principle. The new threshold is not only easier to analyze since it is in a closed form, but also provides more facility for future compression than several other methods, almost without deteriorating mean square error risk.

Algorithms↗
PubMed2006

Diffusion maps and coarse-graining: A unified framework for dimensionality reduction, graph partitioning, and data set parameterization.

We provide evidence that nonlinear dimensionality reduction, clustering, and data set parameterization can be solved within one and the same framework. The main idea is to define a system of coordinates with an explicit metric that reflects the connectivity of a given data set and that is robust to noise. Our construction, which is based on a Markov random walk on the data, offers a general scheme of simultaneously reorganizing and subsampling graphs and arbitrarily shaped data sets in high dimensions using intrinsic geometry. We show that clustering in embedding spaces is equivalent to compressing operators. The objective of data partitioning and clustering is to coarse-grain the random walk on the data while at the same time preserving a diffusion operator for the intrinsic geometry or connectivity of the data set up to some accuracy. We show that the quantization distortion in diffusion space bounds the error of compression of the operator, thus giving a rigorous justification for k-means clustering in diffusion space and a precise measure of the performance of general clustering algorithms.

Algorithms↗
PubMed2003

Irreversible JPEG compression of digital chest radiographs for primary interpretation: assessment of visually lossless threshold.

PURPOSE: To determine if digital chest images could be compressed in a primary interpretation context without perceived loss of fidelity (below the visually lossless threshold) at transilluminated film or cathode ray tube (CRT) display. MATERIALS AND METHODS: One hundred forty-four posteroanterior radiographs were obtained with a digital chest radiography system. At both film and CRT display, an identified original image was presented side by side with a replicate, which was either an unaltered image or an image that had been Joint Photographic Experts Group (JPEG) compressed to 10:1, 20:1, or 50:1 and reconstructed. Each of the 10 readers indicated whether the replicate was "indistinguishable from the original" or "degraded" at clinical reading distance and at close inspection. The readers' ability to detect compressed images was examined for patterns; 95% CIs were used for statistical testing. RESULTS: With transilluminated film at clinical reading distance, readers were as likely to rate originals (48 [20%] of 240 readings) as degraded as they were to rate 20:1 replicates (106 [22%] of 480 readings) as degraded, but they frequently identified 50:1 replicates (283 [59%] of 480 readings) as degraded. At close inspection, 20:1 replicates (163 [34%] of 480 readings) were often identified as degraded, but 10:1 replicates (19 [8%] of 240 readings) were not identified as degraded more often than originals (17 [7%] of 240 readings). With CRT display, the results were nearly identical. CONCLUSION: At reading distance for primary interpretation, full-size digital chest radiographs that have been JPEG compressed to 10:1 or 20:1 and reconstructed are visually lossless at film or CRT display. Images compressed to 10:1 remain visually lossless at close inspection.

Algorithms↗
PubMed2003

Assessment of spatial inhomogeneities in intima media thickness along an arterial segment using its dynamic behavior.

To assess locally deviating structural and mechanical properties of arterial walls, the spatial variance in end-diastolic intima media thickness (IMT) and the change in IMT during the cardiac cycle (DeltaIMT) were determined along a short segment of the common carotid artery (15.86 mm), at 16 positions simultaneously. Intrasubject spatial inhomogeneities along the artery were revealed by a spatial variance significantly larger than the temporal variance over several beats. If differences between positions were confirmed, the extent of the inhomogeneity was obtained by comparison of IMT and DeltaIMT at each position with their spatial medians +/- the least-significant difference. Because no intersubject comparisons were necessary, a single session of several measurements was sufficient to assess inhomogeneities in the arterial wall properties of a subject, making the method independent of biological variability between subjects. The method was evaluated on 47 presumed healthy subjects (age range 21-75 yr). In 22 subjects, spatial inhomogeneities in DeltaIMT occurred (P < 0.05). In young subjects, DeltaIMT was locally decreased, i.e., in systole inhomogeneities were less compressed than their surrounding tissue. In older subjects, DeltaIMT was locally increased, i.e., the inhomogeneity was locally more compressed than its surrounding wall tissue.

Adult↗
PubMedDate not supplied

ECG data compression using Hebbian neural networks.

Principal component analysis has long been used for a variety of signal processing applications, including signal compression. Neural network implementations of principal component analysis provide a means for unsupervised feature discovery and dimension reduction. In this paper, we describe a method for the compression of ECG data using principal component analysis. Hebbian neural networks were used for principal components computation. A variety of examples of normal and pathological ECGs obtained from the MIT ECG database demonstrate that the proposed method can provide compression ratio up to 30 with PRD% less than 5%.

Algorithms↗
PubMed2006

Cardiopulmonary resuscitation algorithms, defibrillation and optimized ventilation during resuscitation.

PURPOSE OF REVIEW: In 2005, the American Heart Association released its Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. This article reviews the treatment algorithms for Advanced Cardiac Life Support, citing the evidence on which the Guidelines are based. Additional focus is placed on defibrillation and optimized ventilation. RECENT FINDINGS: Major changes include a reorganization of the algorithms for cardiac arrest. Emphasis on effective cardiopulmonary resuscitation is placed as the key to improved survival. Single defibrillation shocks are recommended (compared with three 'stacked' shocks) with immediate provision of cardiopulmonary resuscitation and minimal interruptions in chest compressions. The recommended chest compression : ventilation rate for single rescuers has been changed to 30:2. SUMMARY: Despite advances in resuscitation science, basic life support remains the key to improving survival outcomes. Ultimately, as new knowledge is gained, we believe resuscitation therapies will be more individualized, on the basis of pathophysiology and etiology of the initial cardiac arrest.

Algorithms↗
PubMed2000

Practical low-cost visual communication using binary images for deaf sign language.

Deaf sign language transmitted by video requires a temporal resolution of 8 to 10 frames/s for effective communication. Conventional videoconferencing applications, when operated over low bandwidth telephone lines, provide very low temporal resolution of pictures, of the order of less than a frame per second, resulting in jerky movement of objects. This paper presents a practical solution for sign language communication, offering adequate temporal resolution of images using moving binary sketches or cartoons, implemented on standard personal computer hardware with low-cost cameras and communicating over telephone lines. To extract cartoon points an efficient feature extraction algorithm adaptive to the global statistics of the image is proposed. To improve the subjective quality of the binary images, irreversible preprocessing techniques, such as isolated point removal and predictive filtering, are used. A simple, efficient and fast recursive temporal prefiltering scheme, using histograms of successive frames, reduces the additive and multiplicative noise from low-cost cameras. An efficient three-dimensional (3-D) compression scheme codes the binary sketches. Subjective tests performed on the system confirm that it can be used for sign language communication over telephone lines.

Algorithms↗
PubMed1999

Non-invasive diagnosis of venous thromboembolism in outpatients.

BACKGROUND: We designed a simple and integrated diagnostic algorithm for acute venous thromboembolism based on clinical probability assessment of deep-vein thrombosis (DVT) or pulmonary embolism (PE), plasma D-dimer measurement, lower-limb venous compression ultrasonography, and lung scan to reduce the need for phlebography and pulmonary angiography. METHODS: 918 consecutive patients presenting at the emergency ward of the Geneva University Hospital, Geneva, Switzerland, and Hôpital Saint-Luc, Montreal, Canada, with clinically suspected venous thromboembolism were entered into a sequential diagnostic protocol. Patients in whom venous thromboembolism was deemed absent were not given anticoagulants and were followed up for 3 months. FINDINGS: A normal D-dimer concentration (<500 microg/L by a rapid ELISA) ruled out venous thromboembolism in 286 (31%) members of the study cohort, whereas DVT by ultrasonography established the diagnosis in 157 (17%). Lung scan was diagnostic in 80 (9%) of the remaining patients. Venous thromboembolism was also deemed absent in patients with low to intermediate clinical probability of DVT and a normal venous ultrasonography (236 [26%] patients), and in patients with a low clinical probability of PE and a non-diagnostic result on lung scan (107 [12%] patients). Pulmonary angiography and phlebography were done in only 50 (5%) and 2 (<1%) of the patients, respectively. Hence, a non-invasive diagnosis was possible in 866 (94%) members of the entire cohort. The 3-month thromboembolic risk in patients not given anticoagulants, based on the results of the diagnostic protocol, was 1.8% (95% CI 0.9-3.1). INTERPRETATION: A diagnostic strategy combining clinical assessment, D-dimer, ultrasonography, and lung scan gave a non-invasive diagnosis in the vast majority of outpatients with suspected venous thromboembolism, and appeared to be safe.

Acute Disease↗
PubMed2003

Dictionary learning algorithms for sparse representation.

Algorithms for data-driven learning of domain-specific overcomplete dictionaries are developed to obtain maximum likelihood and maximum a posteriori dictionary estimates based on the use of Bayesian models with concave/Schur-concave (CSC) negative log priors. Such priors are appropriate for obtaining sparse representations of environmental signals within an appropriately chosen (environmentally matched) dictionary. The elements of the dictionary can be interpreted as concepts, features, or words capable of succinct expression of events encountered in the environment (the source of the measured signals). This is a generalization of vector quantization in that one is interested in a description involving a few dictionary entries (the proverbial "25 words or less"), but not necessarily as succinct as one entry. To learn an environmentally adapted dictionary capable of concise expression of signals generated by the environment, we develop algorithms that iterate between a representative set of sparse representations found by variants of FOCUSS and an update of the dictionary using these sparse representations. Experiments were performed using synthetic data and natural images. For complete dictionaries, we demonstrate that our algorithms have improved performance over other independent component analysis (ICA) methods, measured in terms of signal-to-noise ratios of separated sources. In the overcomplete case, we show that the true underlying dictionary and sparse sources can be accurately recovered. In tests with natural images, learned overcomplete dictionaries are shown to have higher coding efficiency than complete dictionaries; that is, images encoded with an overcomplete dictionary have both higher compression (fewer bits per pixel) and higher accuracy (lower mean square error).

Algorithms↗
PubMed1994

Neonatal resuscitation: the NRP guidelines.

The Neonatal Resuscitation Programme, sponsored by the Canadian Heart and Stroke Foundation and by the American Heart Association, is a structured learning package and workshop for all individuals who provide resuscitation for newborns. The emphasis is on rapid, decisive action using algorithms based on clearly stated criteria. This CME article serves as an introduction to the NRP and discusses some of the new guidelines regarding concurrent ventilation and chest compressions, tracheal suction for meconium and the use of medications. The author encourages readers who find this article helpful to register in an accredited NRP course to receive the extensive illustrated textbook and to benefit from the "hands-on" nature of the workshop.

Asphyxia Neonatorum↗
PubMed2001

The use of cross-correlation analysis between high-frequency ultrasound images to measure longitudinal median nerve movement.

Impaired nerve movement can lead to nerve injury (e.g., carpal tunnel syndrome). A noninvasive method to measure nerve movement in longitudinal section would enable an extensive analysis of nerve entrapment syndromes. A method has been developed using cross-correlation between successive high-frequency ultrasound (US) images to measure longitudinal movement of nerve and muscle. Control "phantom" experiments demonstrated the accuracy and reliability of this method at velocities of 1-10 mm/s. Increasing the frame interval between the compared frames enabled the accurate calculation of slower velocities. The correlation algorithm successfully measured relative movement when the US transducer was moved 1-3 mm over the surface of the forearm. Median nerve movement was repeatedly measured in the forearm during 30 degrees passive wrist extension in three subjects (range 2.63-4.12 mm) and index finger extension in seven subjects (range 1.59-4.48 mm). Median nerve movement values were consistent with those from cadaver studies.

Adult↗
PubMed2001

Management of emergent conditions in palliative care.

Emergent conditions arising in patients with advanced terminal disease are inevitable and create stressful situations for patients, caregivers, and health care personnel. Discussions regarding appropriate levels of intervention based on parameters such as patient wishes, proper access to documentation of those wishes, location of care, cognitive status and extent of clinical decline are important to have before crisis situations. Common emergencies to be addressed include those that may or may not be associated with advanced malignancies, including compression syndromes, superior vena cava syndrome, hypercalcemia, acute dyspnea, seizures, acute urinary and bowel obstructions, massive hemorrhage, cardiac tamponade, acute embolic phenomenon, and psychiatric emergencies. Although not all clinical scenarios will be addressed in this article, the more common ones will be discussed.

Algorithms↗
PubMed1998

Two- and three-dimensional computer graphic evaluation of the subacute spinal cord injury.

We have evaluated three-week-old compression lesions of the rat spinal cord using two-dimensional and three-dimensional morphometry, reconstruction, and visualization techniques. We offer a new computer assisted method to determine the number and density of macrophages within the spinal lesion using the macrophage specific monoclonal label ED1. We also provide quantitative information on pathological cyst formation and cavitation. This technique does not require: (1) subjective identification of the cell type, (2) human interaction with the data during the phase of quantification, and (3) can be applied to any sampling paradigm based on immunocytochemical labeling. Using novel algorithms based on solutions to 'correspondence' and 'branching' problems inherent in cross-sectional histological data, we provide three-dimensional reconstructions and visualizations of the macrophagic lesions and cysts imbedded within it. Our three-dimensional surface reconstructions can be interrogated to determine volumes and surface areas of structures within the data set. Using these methods we have learned that macrophage numbers approach the maximum density possible for such isodiametric cells (approximately 12 microm diameter) in the central lesion ranging from 4000-7000 cells per mm2 of lesion. At the time point studied, macrophage numbers would have peaked following the initial insult, and would not be expected to decline for several months. While the density of macrophages is highest in the region of most tissue damage, we show that the central regions of cavitated and cystic spinal parenchyma is not. We discuss how this density of cells may effect the secondary pathological responses of the spinal cord to injury.

Algorithms↗