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At least 199 records · Page 11Linked to original sources
PubMed1995

Real-time compression of myoelectric data utilising adaptive differential pulse code modulation.

The myoelectric signal, obtained by either surface or needle electrodes, is used in many areas of clinical research and diagnosis. The conventional method of storing such information is in digitised form on a computer. However, the bandwidth of the signal and the required resolution result in large memory requirements. Adaptive differential pulse code modulation is investigated as a method of reducing the memory requirements for myoelectric data storage. In this scheme, a 12-bit sample is reduced to four bits, thus reducing the memory requirements by a factor of three. In reality, this compression ratio is closer to 4:1 owing to the fact that the widths of most memories are organised as multiples of eight bits.

Computer Systems↗
PubMedDate not supplied

Data predictability for compression of digital fluorography images.

Images obtained by digital fluorography were checked for compressability. These images include images of coronary vessels and images of peripheral vessels. These images have a very low signal-to-noise ratio compared to the optical images usually used for developing compression methods. Configurational entropy was used to represent the information content of these images. Reversible prediction algorithms were extensively checked in a search for minimal residual information, enabling more efficient reversible compression. Optimal results were obtained for algorithms based on two or three neighboring pixels and a semiempirical rule, based on the noise level, was found which decides on the best approach. It was found that raw data images are more predictable than subtracted images although the latter are visually preferred.

Algorithms↗
PubMed1993

Chromosome anomalies in mammary carcinoma from transgenic WAPRAS mice: compression with human data.

Transgenic WAPRAS mice, obtained by infection of the construct WAP promoter murine gene and the HRAS human protooncogene, develop mammary adenocarcinoma within 1-3 months after pregnancy. A cytogenetic analysis was performed on 17 tumors from 10 mice. Almost all detected anomalies were chromosome gains. The resulting trisomies affected recurrently chromosomes 1, 15, 19, 17, 7, and 12, in decreasing order of involvement. Although in situ hybridization showed that the transgene was integrated in chromosome 1, the duplication of this chromosome did not depend on the presence or absence of the transgene. Comparison with human data indicates that the 3 most frequently duplicated chromosomes in WAPRAS mice correspond to the human chromosome segments most frequently duplicated or amplified in breast cancer, i.e., 1q, 8q, and 11q13. None of the chromosome segments often deleted in human tumors were found to be duplicated in the mouse tumors.

Adenocarcinoma↗
PubMed1996

Multivariate determination of glucose concentrations from optimally filtered frequency-warped NIR spectra of human blood serum.

Glucose concentrations over the 39-160 mg dl-1 range have been determined from 357 NIR (near-infrared) spectra of human blood serum in the spectral region from 6766 cm-1 to 4003 cm-1. A frequency-warping procedure was applied to the NIR data to compress 511 spectral components into 102 in the 6766-4003 cm-1 spectral region. Before the data compression process was carried out, the NIR spectrum of deionized water was subtracted from each of the blood serum spectra to remove the intrinsic high background absorption due to the water. PLS (partial least-squares) regression was coupled with time-domain digital Butterworth bandpass filtering in an optimization procedure. The optimization procedure was carried out over a range of centre frequencies and bandwidths for first- (two-pole), second- (four-pole) and third- (six-pole) order bandpass filters, and over a range of PLS factors. The optimal PLS model and filter parameters were determined from a sequence of three-dimensional performance response maps for different numbers of PLS factors and filter orders. As a basis for comparison, the same optimization process was carried out for a Gaussian filter design approach (i.e., Fourier filtering). Using the optimally filtered frequency-warped NIR spectral data, an SEP (standard error of prediction) of 13.2 mg dl-1 was achieved fro the test (monitoring) data using 14 PLS factors and a simple first-order (two-pole) digital Butterworth bandpass filter.

Blood Glucose↗
PubMed1993

FASTPAT: a fast and efficient algorithm for string searching in DNA sequences.

A new string searching algorithm is presented aimed at searching for the occurrence of character patterns in longer character texts. The algorithm, specifically designed for nucleic acid sequence data, is essentially derived from the Boyer-Moore method (Comm. ACM, 20, 762-772, 1977). Both pattern and text data are compressed so that the natural 4-letter alphabet of nucleic acid sequences is considerably enlarged. The string search starts from the last character of the pattern and proceeds in large jumps through the text to be searched. The data compression and searching algorithm allows one to avoid searching for patterns not present in the text as well as to inspect, for each pattern, all text characters until the exact match with the text is found. These considerations are supported by empirical evidence and comparisons with other methods.

Algorithms↗
PubMed1993

A new method for computed tomography image compression using adjacent slice data.

RATIONALE AND OBJECTIVES: The authors developed and subjectively evaluated an interslice compression algorithm that explores the redundancy among adjacent slices of an x-ray computed tomography (CT) scan. This algorithm has been compared to an intraslice compression algorithm based on the two-dimensional discrete cosine transform. METHODS: Nine x-ray CT head images from three patients were compressed with this interslice method at compression ratios of 5:1, 10:1, and 15:1. The same images were also compressed with the intraslice method at the same ratios. Six radiologists judged quality of randomly selected compressed and decompressed images compared to that of the originals. The evaluation data were analyzed statistically with the analysis of variance and Tukey's multiple comparison. Kappa-like statistics (Williams index and O'Connell and Dobson indexes) were also calculated to measure the agreement among readers beyond the amount expected by chance. RESULTS: The interslice coding algorithm showed significantly better quality than the intraslice method at significance level 0.05, even though there was no difference in the objective distortion measure (signal-to-noise ratio). Also, the quality of 10:1 compressed images with the interslice coding algorithm was not significantly different from that of the originals at level 0.05. While large variations in agreement occurred among readers, the overall agreement was statistically significant. CONCLUSIONS: By using adjacent slice information in compressing x-ray CT images, significantly better quality in compressed and decompressed images was achieved. While 10:1 compressed images with the interslice algorithm were not significantly different from the originals in quality at level 0.05, effect on diagnostic accuracy remains to be investigated.

Algorithms↗
PubMed1991

Computerised method for acquisition and display of gastrointestinal motility data.

A computerised system is developed for the acquisition and display of gastrointestinal motility data which utilises a purpose developed software program called 'PC-motil', running on an IBM compatible microcomputer. 'PC-motil' displays data during collection, writes data to disk file and compresses all data at the end of a study on to a single monitor screen for convenient overview. Any area of interest, in single or multiple channels, may be selected and expanded for detailed examination. This system is tested by the recording of gastric and jejunal motility patterns of 11 healthy volunteers in fasting and fed states. All antral and jejunal migrating motor complexes (MMCs) in fasting studies, as well as all fed motility patterns were recognisable in both 'compressed' and 'expanded' form. The reproduction of motility patterns by the computer based system was indistinguishable from that of a conventional analogue chart recorder. This computerised system provides a convenient and cost-effective means of acquisition, storage and display of motility data in digital form.

Adult↗
PubMed1981

Progress in computer analysis of the exercise electrocardiogram.

The potential advantages of digital computer processing of exercise electrocardiographic data include reduction of noise, compression of data, improved precision and application of optimal criteria. Most prior approaches to such processing required equipment that was both expensive and inconvenient. With the revolution in instrumentation brought about by the development of microcomputers, powerful dedicated computers can now be afforded by many exercise laboratories. There are many approaches to computerized management of exercise electrocardiographic data and various criteria for ischemia. Studies are necessary to validate computer algorithms so that these devices can be used diagnostically to best advantage. Cardiologists need some understanding of this field so that they can be discriminating users of computer systems. In addition, the results of studies correlating electrocardiographic changes with radionuclide methods of assessing myocardial perfusion and function should enable such assessments to be made from the electrocardiographic signals alone, particularly when aided by computer analysis of spatial shifts.

Angina Pectoris↗
PubMed1991

The effect of mechanical deformation on the movement of water in foods.

This study has shown the importance of relating NMR spectroscopic information on the water in model food structures to the mechanical properties of those structures. Analysis of the NMR relaxation data can be used to examine the distribution of water domain sizes, and this has been related to the mechanical properties of the samples. A novel NMR probe-head has been designed, which allows both the NMR and the mechanical data to be simultaneously measured during compression of the sample. This probe-head allows compressive stress/strain data to be obtained directly from the NMR sample, allowing changes in the distribution of the water to be directly correlated to changes in mechanical properties.

Chemical Phenomena↗
PubMed1989

Recurrent deep venous thrombosis: limitations of US.

Compression ultrasound (US) has become widely used to diagnose acute deep venous thrombosis (DVT). To determine the appearance of veins with previous DVT, 60 legs (58 patients) in which DVT had been diagnosed 6-31 months earlier (mean, 15.1 months) were reexamined with compression US. At reevaluation there was no indication of acute DVT. Thirty-two extremities had an appearance consistent with clot at the time of this study; 28 demonstrated normal findings. Variables that correlated with findings at follow-up US included age, location of clot, number of previous clots, pain, and augmentation of flow at compression. These preliminary data indicate that compression US may not be reliable as a follow-up study in patients in whom postphlebotic syndrome develops after an acute episode of DVT.

Follow-Up Studies↗
PubMed1992

An efficient algorithm for MR image reconstruction and compression.

In magnetic resonance imaging (MRI), the original data are sampled in the spatial frequency domain. The sampled data thus constitute a set of discrete Fourier transform (DFT) coefficients. The image is usually reconstructed by taking inverse DFT. The image data may then be efficiently compressed using the discrete cosine transform (DCT). We present here a method of using DCT to treat the sampled data, which combines two procedures, image reconstruction and data compression. This method may be particularly useful in medical picture archiving and communication systems (PACS) where both image reconstruction and compression are important issues.

Algorithms↗
PubMed1995

A model for acute, chronic, and delayed graded compression of the dog cauda equina. Neurophysiologic and histologic changes induced by acute, graded compression.

STUDY DESIGN: The results of acute compression on nerve function and morphology were analyzed in a recently developed model for graded cauda equina compression in the dog. OBJECTIVES: The model was developed to better mimic the clinical situation of cauda equina compression in association with spinal canal stenosis. SUMMARY OF BACKGROUND DATA: The compression of the cauda equina has been induced by metal clips, plastic bands, constrictors, and inflatable balloons. No model has used the intact spinal canal and induced compression by increasing the pressure per se in the canal. METHODS: An inflatable balloon with a diameter exceeding the diameter of the spinal canal was placed under the lamina of the L7 vertebra in the dog. The balloon was inflated to various pressures, and muscle action potential area and nerve conduction velocity were monitored during 2 hours of compression and 1.5 hours of recovery. Nerve root specimens were processed for light microscopic examination. RESULTS: There was a progressive reduction of muscle action potential area and nerve conduction velocity that was proportional to the applied pressure. Histologic evaluation revealed no nerve fiber damage but a slight intraneural edema after compression at 200 mg Hg. CONCLUSIONS: The presented model may provide reproducible results regarding neurophysiologic and morphologic effects after acute, graded compression of the dog cauda equina. Two additional conclusions can be made from this study. First, the area measurement of the MAP is probably well suited for recordings and analyses of changes in muscle action potentials. Second, the specific onset rate of this study, in relation to previous studies, indicates that there is a threshold for the compression onset rate for inducing additional nerve injury located in the interval 0.1-0.8 seconds. The results from the present study provides important baseline data for the continued studies on chronic and intermittent compression with the compression model.

Action Potentials↗
PubMed1990

Enhancement and compression of digital chest radiographs.

The application of digital technologies to chest radiography holds the promise of routine application of image processing techniques to effect image enhancement. Because of their inherent spatial resolution, however, digital chest images impose severe constraints on data storage devices. Compression of these images will relax such constraints and facilitate image transmission on a digital network. We evaluated an algorithm for enhancing digital chest images that has allowed significant data compression while improving the diagnostic quality of the image. This algorithm is based on the photographic technique of unsharp masking. Image quality was measured with respect to the task of tumor detection and compression ratios as high as 2:1 were achieved. This compression can be supplemented by irreversible methods.

Algorithms↗
PubMed1976

[The nasopharynx in jaw compression--craniometric and rhinologic data].

113 patients-7 to 29 years old-of the orthodontic department of the School of Dentistry, University of Minnesota, were studied. 51 patients had a high SN-MP angle (a long face) and 62 a low SN-MP angle (a broad face). As compared to the broad-faced group the probands with a long face showed, on the average, a narrower palatal arch, a more posteriorly postitioned hard palate, a smaller nasopharynx (measured in the sagittal plane), and more frequent nasopharyngeal problems. According to our statistical evaluation, a narrower maxillary dental arch and clinical apparent adenoid hypertrophy do not appear to be connected to each other in a cause-and-effect relationship. They rather seem to be two independent symptoms found frequently, though not necessarily in combination with each other, in persons with a long face.

Adolescent↗