Compression of ECG data by vector quantization.
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Algorithms↗
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Reversible 3D compression of CT data using HINT.
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Image Enhancement↗
Compression of EEG data.
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Electroencephalography↗
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↗
[The application of lossless compression algorithm for ECG data in HOLTER].
Recently, HOLTER product is developing to long time recording. In order to decrease the cost, compression of ECG data is needed. It is done first by some kind of DPCM to decrease the range of the data Value, then by using suitable arithmetic of HUFFMAN coding's and Arithmetic coding's. All the methods can be realized in microprocessor and get compression ratio of 2-4.
Algorithms↗
Ellipsoidal fitting of corneal topography data after arcuate keratotomies with compression sutures.
BACKGROUND AND OBJECTIVE: After paired arcuate keratotomies and compression sutures (AK) for treatment of high postkeratoplasty astigmatism, corneal topography tends to be irregular. The purpose of this study was to demonstrate a mathematical method for approximation of discrete corneal topography power data with an ellipsoid for better appreciation of the clinical outcome after AK. PATIENTS AND METHODS: Thirty-one eyes of 28 consecutive patient who underwent AK for excessive postkeratoplasty astigmatism were studied. Regular keratometry, corneal topography (TMS-1), subjective refraction, and best-corrected visual acuity (VA) were assessed preoperatively and at 1 week and 1 year postoperatively. A simplex algorithm was applied for fitting an ellipsoidal surface to raw corneal topography power data. A set of parameters (meridional power, axis, and asphericity) were calculated. The cylinder of subjective refraction was correlated with the keratometric readings, the simulated keratometry (SimK) of the topography system, and the respective parameters of the model surface. RESULTS: Keratometric astigmatism and the cylinder of the model surface decreased from 8.1 +/- 3.2 and 7.9 +/- 2.9 D preoperatively to 4.5 +/- 2.1 and 5.3 +/- 2.0 D after 1 year, respectively. The asphericity in both meridional cross sections changed from a prolate ellipse preoperatively to an ablate ellipse at the early postoperative follow-up stage. Regarding the cylinder axis, there was a significant correlation of the model surface with the refractive cylinder at all examinations (P < .05), whereas there was no significant correlation of the SimK axis and the refractive cylinder axis. CONCLUSION: The approximation of corneal topography power data with an ellipsoidal model surface renders reconstruction of clinically relevant corneal topography parameters, including corneal asphericity with a marked data compression. Even in markedly irregular corneal surfaces, such as after AK, the correlation of amount/axis of refractive cylinder with the model surface parameters is more accurate than it is with respective SimK values of corneal topography analysis.
Adult↗
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↗
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↗
Lossy compression should not be used in certain imaging applications such as chest radiography. For the proposition.
Computational techniques are frequently used to compress image data so that transmission and storage requirements are reduced. If the computational techniques result in no loss in image resolution, the technique is referred to as lossless compression. Greater compression of data may yield some loss in spatial or temporal resolution, and is referred to as lossy compression. In some radiologic examinations [e.g., gastrointestinal (GI) studies], some resolution loss may be tolerable, whereas in others (chest examinations and mammography) it conceivably could result in missed pathology. Without lossy compression, however, data requirements can be overwhelming for transmission, storage and retrieval of images such as chest films. The unanswered question, addressed in this Point/Counterpoint issue, is whether some degree of lossy compression can be tolerated in chest radiography.
Humans↗
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↗
DICOM extensions for narrow-band networks.
DICOM is today's de-facto standard for exchanging medical images. Since new image acquisition devices produce more and more image and non-image data, image compression has become an important part of the standard. However, the compression of non-pixel data also stored in DICOM data sets has been disregarded up to now. In the scope of an EU research project we have examined a large amount of real-world DICOM images to test whether or not there is a potential for compressing the non-pixel attributes. Especially for use with narrow-band networks extensions as proposed in this paper could be a solution to save valuable bandwidth.
Computer Communication Networks↗
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↗
Effect of implant design and endplate preparation on the compressive strength of interbody fusion constructs.
STUDY DESIGN: A human cadaveric study on the compressive strength of different lumbar interbody fusion implants and endplate preparation techniques was performed. OBJECTIVES: To assess the axial compressive strength of an implant with peripheral endplate contact as opposed to full surface contact, and to assess whether removal of the central bony endplate affects the axial compressive strength. SUMMARY OF BACKGROUND DATA: The compressive strength of interbody fusion constructs has been compared between implants and bone grafts. Neither implant design nor endplate preparation has been shown to affect strength. Removal of the central bony endplate for bone grafts was noted to improve graft incorporation but also to facilitate subsidence. METHODS: A total of 44 vertebrae were tested in four experimental groups by combining two interbody implants (full-surface vs peripheral surface support) with two endplate preparation techniques (intact bony endplate vs removal of the central bony endplate). Specimens were tested to ultimate compressive failure using a 50 N/second ramped load. Yield strength and ultimate compressive strength were compared between groups using two-factor analysis of covariance. A P value less than 0.05 was considered significant. Stepwise linear regressions assessed the predictive power of age, bone mineral content, and the implant's normalized endplate coverage on yield strength and ultimate compressive strength. RESULTS: Neither implant design nor endplate preparation technique affected yield strength or ultimate compressive strength. Age, bone mineral content, and the normalized endplate coverage were strong predictors of yield strength (P < 0. 0001; r2 = 0.459) and ultimate compressive strength (P < 0.0001; r2 = 0.510). CONCLUSIONS: An implant with only peripheral support resting on the apophyseal ring offers axial mechanical strength similar to that of an implant with full support. Neither supplementary struts nor a solid implant face has any additional mechanical advantage, but reduces graft-host contact area. Removal of the central bony endplate is recommended because it does not affect the compressive strength and promotes graft incorporation.
Adolescent↗
Intervertebral disc cell death is dependent on the magnitude and duration of spinal loading.
STUDY DESIGN: An in vivo study of the toxic consequences of static compressive stress on the intervertebral disc. OBJECTIVES: To determine whether disc cell death is correlated with the magnitude and duration of spinal compressive loading. SUMMARY OF BACKGROUND DATA: Static compression in vivo has been demonstrated to induce cell death. Cell death, in turn, has been associated with disc degeneration in humans. There are currently no tolerance criteria for the intervertebral disc that combine both biomechanical and biologic factors, although both have been implicated in cases of accelerated degeneration. METHODS: Mouse tail discs were loaded in vivo with an external compression device. Compressive stress was applied at one of two magnitudes (0.4 and 0.8 MPa) for 7 days, and at one additional magnitude (1.3 MPa) for 1, 3, and 7 days. Midsagittal sections of the discs were stained for apoptosis using the TdT-dUTP terminal nick-end labeling (TUNEL) reaction. Quantal analysis was used to correlate the extent of cell death to the magnitude and duration of loading. RESULTS: The probit transformation of the percentage of dying cells was proportional to the sum of the logarithmic transformations of the compressive stress and the time of loading. CONCLUSIONS: The results of this study demonstrate the feasibility of developing a quantitative correlation between spinal loading and disc degeneration. Such a correlation may be coupled in the future to existing engineering models that predict spinal loading in response to physical exposures and lead to improved definition of the bounds of healthy and unhealthy spinal loading, and ultimately, refined guidelines for low back safety.
Animals↗
Quantitative analysis of edema in the dorsal nerve roots induced by acute mechanical compression.
STUDY DESIGN: Edema in the dorsal nerve roots caused by acute compression was assessed quantitatively in the lumbar spine of the adult dog. OBJECTIVE: To establish quantitative evaluation of edema in the dorsal nerve roots and to observe changes after acute compression with time. SUMMARY OF BACKGROUND DATA: Mechanical compression induces an increase in microvascular permeability of the endoneurial capillaries and results in intraneural edema. However, there are no quantitative studies on edema in the nerve roots. METHODS: The seventh lumbar nerve root was compressed with a 60-g force clip for 10 minutes. The nerve roots were removed immediately and at 24 hours, 1 week, and 3 weeks after compression. Nerve roots from the control and the sham groups were also obtained. Before removing the nerve roots, Evans blue albumin was injected intravenously. Changes in edema were examined using fluorescence microscopy. Evans blue albumin emits a bright red fluorescence. The relative red fluorescent area was calculated using computer image analysis, and the data were used to indicate the degree of edema. RESULTS: In the compressed segment, edema was most pronounced just after decompression and reduced in nerves removed at 24 hours. In nerves removed at 1 week, edema was pronounced but was reduced at 3 weeks. In the segments closest to the spinal cord, edema was seen after 1 week and was significant after 3 weeks. In the segments closest to the dorsal root ganglion, edema was not detected at any time. CONCLUSION: In the dorsal nerve roots the degree and the area of edema changed with time elapsed after acute compression. The degree of edema 24 hours after decompression was one third the degree immediately after decompression. These results show that edema induced by mechanical compression can recover after decompression.
Animals↗
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↗
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↗
Clinical and electrophysiologic characteristics of compressed lumbar nerve roots.
STUDY DESIGN: Clinical and electrophysiologic data of compressed nerve roots were evaluated in patients with lumbar disc herniation. OBJECTIVES: To elucidate the characteristics of the nerve root with respect to preoperative neural deficit and to analyze the predictive factors for recovery of leg paralysis after posterior discectomy. SUMMARY OF BACKGROUND DATA: Prolonged paralysis due to disc herniation is reported to be a poor prognostic factor for motor recovery. In addition, an intraoperative somatosensory evoked potential change has been reported to be correlated with clinical outcome. METHODS: Among 64 patients with a lumbar disc herniation, a variety of clinical data, such as age, gender, duration of leg paralysis or leg pain, the angle of the positive straight leg raising test, and time for recovery from paralysis, were investigated. In addition, threshold, amplitude of compound muscle action potentials, and latency for 85 nerve roots were monitored before and after discectomy. Data were analyzed according to the grade of preoperative neural deficits: Grade 1, severe motor and sensory loss; Grade 2, mild motor and sensory loss; Grade 3, sensory loss only; Grade 4, no deficit (leg pain only); and Grade 5, asymptomatic control. RESULTS: The nerve root threshold before discectomy showed an increase in accordance with the severity of neural deficit. Thresholds of Grade 1 and 2 nerve roots were significantly higher than those of normal control subjects. The average amplitudes of compound muscle action potentials before discectomy in Grade 1 and 2 nerve roots were significantly lower than those of asymptomatic control nerve roots. Elongation of latency also showed a correlation with preoperative neurologic abnormality. Patients who complained of leg pain only were significantly younger, and those who showed severe motor disturbance tended to be older and to show a straight leg raising test angle similar to that of control nerve roots. Severe motor weakness for more than 6 months, a negative straight leg raising test, and age were considered to be poor prognostic factors for motor recovery. CONCLUSIONS: Findings of increased threshold, low amplitude of compound muscle action potentials, and elongated latency correlated with degree of motor weakness. Early decompression for compressed nerve root is recommended, especially in older patients with severe motor weakness presenting a negative straight leg raising test.
Action Potentials↗