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PubMed1997

Stability of a Nanometric Zirconia Colloidal Dispersion under Compression: Effect of Surface Complexation by Acetylacetone

The stability of a colloidal dispersion of nanometric zirconia particles has been studied during a compression process. Using the osmotic stress method, cycles of compression and reswelling were applied to the dispersion to test the reversibility of the process. Original dispersions are stable in a very limited pH range (0.5-2). At pH 3, the bare particles aggregate irreversibly under compression as checked by osmotic pressure and light and X-ray scattering measurements. To improve the stability, small organic complexing molecules (acetylacetone) were added to the original dispersion. The adsorbed monolayer on the particle surfaces acts as a steric barrier and prevents the two colloids from contacting. As a consequence, the dispersion becomes more compressible and the compression cycle is totally reversible. The experimental data are quantitatively reproduced with a classical theory of statistical mechanics of liquids based on a DLVO-like colloid-colloid potential.

Journal Article↗

PubMed1995

Relation between adiabatic and pseudoadiabatic compressibility in ultrasonic velocimetry.

A fundamental problem in measurements of the adiabatic compressibility of macromolecules in aqueous solution using sound velocity is the unknown heat exchange between the interior of the molecule and the bulk solvent. Usually only a pseudoadiabatic compressibility is measured, which is between isothermal and adiabatic compressibility. The measured compressibility might even be close to the isothermal compressibility, depending on the experimental conditions. In this paper, a model is proposed that enables the deviation of experimental conditions from the requirement of adiabatic measurements to be estimated. This model treats the macromolecule as a heat conductive sphere. Analytical solutions for the temporal and local heat diffusion are obtained. Proteins less than 100 kDa in molecular weight at a sound frequency of less than 10 MHz are found to be essentially in thermal equilibrium with the bulk solvent. In this case, for the aqueous protein solution at temperatures < or = 25 degrees C and less than 2% protein concentration, the theory predicts that the sound velocity measurement of the interior of protein is close to isothermal conditions.

Macromolecular Substances↗

PubMed1995

A single pair of interneurons controls motor neuron activity during pre-ecdysis compression behavior in larval Manduca sexta.

Manduca sexta molts several times as a larva (caterpillar) before becoming a pupa and then an adult moth. Each molt culminates in ecdysis behavior, during which the old cuticle is shed. Prior to each larval ecdysis, the old cuticle is loosened by pre-ecdysis behavior, which includes rhythmic, synchronous compressions of the abdomen. A previous study indicated that motor neuron activity during pre-ecdysis compression behavior is driven by an ascending neural pathway from the terminal abdominal ganglion. The present study describes a pair of interneurons, designated IN-402, that are located in the terminal ganglion and belong to the ascending pathway. Each IN-402 is synchronously active with pre-ecdysis compression motor bursts, and bilaterally excites compression motor neurons throughout the abdominal nerve cord via apparently monosynaptic connections. The pair of IN-402s appears to be the sole source of rhythmic synaptic drive to the motor neurons during the pre-ecdysis compression motor pattern. These interneurons play a key role in the production of larval pre-ecdysis behavior, and are candidates for contributing to the developmental weakening of pre-ecdysis behavior at pupation.

Animals↗

PubMed1988

X-ray image compression using run length coding.

The recent availability of a special-purpose IC implementing the standard CCITT run length coder/decoder has made it possible for distortion free image compression to be done economically and quickly with a personal computer plug-in circuit card. Although the code table implemented is designed for bit-mapped document images at one bit per pixel, an experiment has been undertaken to investigate its role in compressing multiple bit per pixel images such as radiographs. Representative x-ray images of various body parts are processed; the average compression ratio and standard deviation is 2.37 and 0.28, respectively, for CCITT group 4 compression, and 2.21 and 0.29, for CCITT group 3 compression.

Computer Systems↗

PubMed1976

[Compression of the celiac trunk (author's transl)].

Besides the vascular changes caused by arteriosclerosis the compression stenosis is the most frequent form of the isolated restriction of the arteria coeliaca. The compression of the arteria coeliaca, caused by the ligamentum arcuatum medianum or a fribromatous ganglion tissue, can cause complaints similar to the symptoms of angina abdominalis: pains in the epigastrium, postprandial pains, loss of weight, nausea/vomiting, diarrhea, 93% of the patients with severe vascular compression have an abdominal vascular murmur. Of 31 patients with angiographically proved compression stenosis, 11 patients suffering from occlusion or intense stenosis had to be operated because of heavy complaints. The angiographic and intraoperative findings allow the conclusion that there is a connection between the extent of the stenosis and the clinical appearance. The decompression of the arteria coeliaca, in other words the detachment of the compressing tissue leads to total complaintlessness in 83% of the patients. If the arteria coeliaca is hypoplastic a vessel widening or a bypass operation is necessary to establish normal blood circulation in the epigastric organs.

Adult↗

PubMed1998

Thoracic Outlet Syndrome: Follow-up on 33 Cases with Regard to Vascular Compression

This follow-up study on 33 operations performed for thoracic outlet syndrome (TOS) proves high efficiency in relieving neurological and arterial symptoms, whereas benefit to venous compression is somewhat less. Twenty-six patients (average age was 36 years) were operated on for TOS, seven of them on both sides. There was a higher incidence in females. All patients showed neurological symptoms. In 15, operations on various entrapment syndromes of the upper extremity were performed previously. Six patients presented with an incomplete resection of the first rib. Arterial compression symptoms were evident in 15 cases, symptoms of venous compression in 14 limbs. All patients underwent a resection of the first rib, bilateral in seven cases, using the axillary and supraclavicular approach. In seven patients, a cervical rib and scalenus muscles were resected additionally, in three patients bilaterally. In two cases a neurolysis of the brachial plexus was performed. Using the supraclavicular approach, no complications occurred. In one early patient using the transaxillary approach to a postoperative hemothorax required a revision. Neurological results after surgery showed a total release in 26 limbs (n = 33). In 14 limbs (n = 15) with arterial compression symptoms and in 6 (n = 14) with symptoms of venous compression the operation showed a curative effect.

Journal Article↗

PubMed1990

High compression of nuclear medicine dynamic studies.

As data compression plays now an important role in the development of medical PACS, a technique has been developed for medical image sequences storage and transmission in order to obtain very high compression ratio: in dynamic nuclear medicine studies it can achieve a compression ratio as high as 100:1 without significant degradation. The implemented technique combines two methods which multiply their effects. In a first step, a principal component analysis (PCA) of the image series is performed. It extracts a limited number of principal components and their associated images. For data compression it is not necessary to perform an oblique factor analysis to estimate the so-called 'physiological functions' and their spatial distributions as in factor analysis of dynamic structures (FADS). In a second step, the principal images are compressed by means of a transform coding procedure: an adaptive block-quantization technique using the 2D discrete cosine transform (DCT) is implemented, followed by a statistical quantization method to encode the DCT coefficients. To reconstruct the principal images, an inverse DCT is applied. Then the original series is computed from the reconstructed images combined with the principal components which have been stored without any modification. The reconstructed series is compared to the original series, as well as the time activity curves generated on different regions of interest (ROI) and the factor estimates obtained using FADS performed on the two series. Method and evaluation are illustrated on an example of first pass radionuclide angiocardiography.

Humans↗

PubMed1994

Postarteriographic femoral pseudoaneurysms: treatment with ultrasound-guided compression.

Pseudoaneurysms following femoral arterial catheterization are increasingly common and are related to factors such as catheter size, periprocedural anticoagulation, hypertension, and improper technique. Ultrasound-guided compression as a noninvasive technique for repair of these lesions was prospectively evaluated in 16 patients whose mean age was 61 years. Nine patients were on anticoagulants and six had hypertension. All patients presented with an enlarging groin hematoma, a pulsatile mass, and/or a bruit following femoral catheterization. Seventeen femoral artery pseudoaneurysms, including one with an associated arteriovenous fistula, were detected using color-flow Doppler imaging. Three pseudoaneurysms thrombosed spontaneously. The remaining 14 were managed with compressive therapy lasting from 20 to 100 minutes. No complications were encountered during the compressions and 10 false aneurysms (71%) responded completely (mean time to thrombosis of 38 minutes). Two lesions responded partially to compression and there were two failures, the latter associated with excessive anticoagulation in one patient and a well-established pseudoaneurysm in the second patient. Only one pseudoaneurysm (6%) in the series required surgical correction. Ultrasound-guided compression of acute pseudoaneurysms in the groin is a safe, inexpensive, and effective method of treatment.

Adult↗

PubMed1998

Errors associated with the use of adaptive differential pulse code modulation in the compression of isometric and dynamic myo-electric signals.

Muscle activity produces an electrical signal termed the myo-electric signal (MES). The MES is a useful clinical tool, used in diagnostics and rehabilitation. This signal is typically stored in 2 bytes as 12-bit data, sampled at 3 kHz, resulting in a 6 kbyte s-1 storage requirement. Processing MES data requires large bit manipulations and heavy memory storage requirements. Adaptive differential pulse code modulation (ADPCM) is a popular and successful compression technique for speech. Its application to MES would reduce 12-bit data to a 4-bit representation, providing a 3:1 compression. As, in most practical applications, memory is organised in bytes, the realisable compression is 4:1, as pairs of data can be stored in a single byte. The performance of the ADPCM compression technique, using a real-time system at 1 kHz, 2 kHz and 4 kHz sampling rates, is evaluated. The data used include MES from both isometric and dynamic contractions. The percent residual difference (PRD) between an unprocessed and processed MES is used as a performance measure. Errors in computed parameters, such as median frequency and variance, which are used in clinical diagnostics, and waveform features employed in prosthetic control are also used to evaluate the system. The results of the study demonstrate that the ADPCM compression technique is an excellent solution for relieving the data storage requirements of MES both in isometric and dynamic situations.

Electromyography↗

PubMed1997

Optimisation algorithms for ECG data compression.

The use of exact optimisation algorithms for compressing digital electrocardiograms (ECGs) is demonstrated. As opposed to traditional time-domain methods, which use heuristics to select a small subset of representative signal samples, the problem of selecting the subset is formulated in rigorous mathematical terms. This approach makes it possible to derive algorithms guaranteeing the smallest possible reconstruction error when a bounded selection of signal samples is interpolated. The proposed model resembles well-known network models and is solved by a cubic dynamic programming algorithm. When applied to standard test problems, the algorithm produces a compressed representation for which the distortion is about one-half of that obtained by traditional time-domain compression techniques at reasonable compression ratios. This illustrates that, in terms of the accuracy of decoded signals, existing time-domain heuristics for ECG compression may be far from what is theoretically achievable. The paper is an attempt to bridge this gap.

Algorithms↗

PubMed2006

Compressed air injection technique to standardize block injection pressures.

PURPOSE: Presently, no standardized technique exists to monitor injection pressures during peripheral nerve blocks. Our objective was to determine if a compressed air injection technique, using an in vitro model based on Boyle's law and typical regional anesthesia equipment, could consistently maintain injection pressures below a 1293 mmHg level associated with clinically significant nerve injury. METHODS: Injection pressures for 20 and 30 mL syringes with various needle sizes (18G, 20G, 21G, 22G, and 24G) were measured in a closed system. A set volume of air was aspirated into a saline-filled syringe and then compressed and maintained at various percentages while pressure was measured. The needle was inserted into the injection port of a pressure sensor, which had attached extension tubing with an injection plug clamped "off". Using linear regression with all data points, the pressure value and 99% confidence interval (CI) at 50% air compression was estimated. RESULTS: The linearity of Boyle's law was demonstrated with a high correlation, r = 0.99, and a slope of 0.984 (99% CI: 0.967-1.001). The net pressure generated at 50% compression was estimated as 744.8 mmHg, with the 99% CI between 729.6 and 760.0 mmHg. The various syringe/needle combinations had similar results. CONCLUSION: By creating and maintaining syringe air compression at 50% or less, injection pressures will be substantially below the 1293 mmHg threshold considered to be an associated risk factor for clinically significant nerve injury. This technique may allow simple, real-time and objective monitoring during local anesthetic injections while inherently reducing injection speed.

Air Pressure↗

PubMed2000

Ultrasound grayscale image compression with JPEG and wavelet techniques.

The purpose of the study was to evaluate the effects of lossy compression on grayscale ultrasound images to determine how much compression can be applied while still maintaining images that are acceptable for diagnostic purposes. The study considered how the acquisition technique (video frame-grabber versus directly acquired in digital form) influences how much compression can be applied. For directly acquired digital images, the study considered how text (that is burned into the image) affects the compressibility of the image. The lossy compression techniques that were considered include JPEG and a Wavelet algorithm using set partitioning in hierarchical trees (SPIHT).

Image Processing, Computer-Assisted↗

PubMed1996

Lossless medical image compression by multilevel decomposition.

Lossless image coding is important for medical image compression because any information loss or error caused by the image compression process could affect clinical diagnostic decisions. This paper proposes a lossless compression algorithm for application to medical images that have high spatial correlation. The proposed image compression algorithm uses a multi-level decomposition scheme in conjunction with prediction and classification. In this algorithm, an image is divided into four subimages by subsampling. One subimage is used as a reference to predict the other three subimages. The prediction errors of the three subimages are classified into two or three groups by the characteristics of the reference subimage, and the classified prediction errors are encoded by entropy coding with corresponding code words. These subsampling and classified entropy coding procedures are repeated on the reference subimage in each level, and the reference subimage in the last repetition is encoded by conventional differential pulse code modulation and entropy coding. To verify this proposed algorithm, it was applied to several chest radiographs and computed tomography and magnetic resonance images, and the results were compared with those from well-known lossless compression algorithms.

Algorithms↗

PubMed1997

Image data compression.

The tutorial will expand on all of the topics outlined above and will provide additional information on other compression techniques. The practical implications of data compression and the important considerations in choosing a compression scheme will also be discussed. Development of new compression algorithms remains an active area of investigation and will continue to increase the degree of compression possible.

Algorithms↗

PubMed1998

Radiologist evaluation of a multispectral image compression algorithm for magnetic resonance images.

With the advent of teleradiology and picture archiving and communication systems (PACS), the expense and time required for image transmission and long term image archiving become important. The use of validated image compression algorithms can greatly reduce these costs. A lossy, multispectral image compression scheme at compression ratios (CR) of 25:1 and 32:1 was used for a set of 26 different patient MR exams. The original and compressed/decompressed (CD) images sets were evaluated in a blinded fashion by four radiologists in two phases. The main objective was to determine whether radiologic interpretation would vary between the two types of CD image sets and the corresponding originals. In general, the compression algorithm caused a slight decrease in image quality; however, the interpretation of pathology did not change between the original and CD image sets. In only one case at the maximum CR = 32 did one of four radiologists change the interpretation of pathology after CD. In this study, lossy multispectral image compression of MR images at CR = 25 maintained diagnostic integrity. This could play a significant role in image storage and communications.

Algorithms↗

PubMed1997

[Dynamic in vivo skin pressure measurement in quality control of compression stockings].

The well-documented positive effect of compression stocking therapy on the venous macro- and microhemodynamics of the legs can only be attained if the stockings fit well. In order to determine the effective pressure exerted by compression stockings, we usually deleted in US journals. One can get this out of journal and author's address have developed a new measuring method based on piezoresistant microprobes and a microprocessor unit. With our 2-mm-thick, 5-mm diameter probe, the pressure between the compression stocking and skin can be measured at any location desired. A temporal resolution of 50 Hz makes it possible to carry out dynamic measurements while the patient is walking or performing exercises on tiptoes. Here we present 4 typical cases out of a total of over 80 which we have evaluated. We have decided empirically that the pressure exerted by a class-2 compression stocking on the skin at the height of the ankles (b-position) should not exceed 70 mm Hg while resting and a peak of 110 mm Hg while exercising on tiptoes. At the middle of the calf (c-position) these values should not exceed 60 mm Hg at rest and 80 mm Hg on tiptoes. The pressure should decrease from the distal to proximal direction in order to produce a drainage gradient. We have found empirically that a pressure gradient of 30-40% from the b to the c measurement is favorable. Too high a proximal pressure or too high a pressure on a part of the lower leg causes pain and swelling. Too low a pressure, on the other hand, does not produce the desired vascular effect and alleviation of symptoms. Although dynamic pressure measurements take about 20-30 minutes per leg, they markedly improve patient compliance with compression therapy.

Adult↗

PubMed1997

[The effect of compression therapy on the microcirculation of the skin in patients with chronic venous insufficiency (CVI)].

Compression therapy was employed for 4 weeks 20 patients with chronic venous insufficiency stage CVI I and CVI II according to Widmer's classification. Compression bandaging for 2 weeks was followed by compression stockings for 2 more weeks. The cutaneous microcirculation was evaluated before therapy, after 2 weeks and after finishing compression therapy after 4 weeks. Marked improvement in symptoms such as pain and itching was observed after 4 weeks, along with a significant reduction in lower limb volume. Video capillary microscopy revealed an increase in capillary density associated with a decrease in capillary diameter and pericapillary halo diameter. Compression treatment achieves at least part of its effect by improving the function of the skin microcirculation. The efficacy of bandaging and stockings was similar.

Bandages↗

PubMed2000

[Compression stocking in treatment of ulcus cruris. An efficient alternative to bandages].

BACKGROUND AND OBJECTIVE: The aim of the study was to measure the pressure exerted on the skin with application of the specially designed UlcerCare compression stocking for treatment of chronic venous leg ulcers and simultaneously to objectify the improvement in venous function. PATIENTS/METHODS: Twenty patients with chronic venous insufficiency according to the CEAP Classification C1-4 EP AS, A14, AP, PR were examined. Static exerted pressure was measured while standing and the dynamic equivalent was measured during 10 repetitions of tip-toe exercise. The patients were wearing the standard stocking JOBST Medical LegWear UlcerCare (Beiersdorf AG, Hamburg, Germany). As a control for the effectiveness of the therapy on venous hemodynamics, the lower leg volume, calculated using optoelectronically-measured lower leg circumference and venous reflux, determined by strain gauge plethysmographically-measured venous refill time, were used. RESULTS: Use of the compression stocking system UlcerCare resulted in a decreased lower leg volume. This decrease was on average 5.3%, corresponding to 106 +/- 78 ml (p < 0.001). The calf and forefoot venous function parameters also improved. The venous refill time improved from 27.2 +/- 15.2 s to 45.0 +/- 27.4 s at the forefoot (p < 0.003) and from 10.5 +/- 4.5 s to 19.4 +/- 10.9 s at the calf (p < 0.002). The exerted pressure at the ankle while standing was 46.2 +/- 24.2 mmHg (resting pressure) and 48.5 +/- 27.2 mmHg during repetitive tip-toe exercises (mean exercise pressure). At the calf, the exerted pressure while standing was 40.7 +/- 26.9 mmHg (resting pressure) and during the repetitive tip-toe exercises it was 42.1 +/- 29.5 mmHg (mean exercise pressure). CONCLUSIONS: The exerted pressure of the UlcerCare compression stocking is equivalent to that of a class 3 medical compression stocking. This newly developed stocking diminishes venous reflux and reduces leg edema. These objectified effects suggest that the UlcerCare stocking is effective as compression therapy for venous ulcers.

Bandages↗