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At least 1,261 records · Page 70Linked to original sources

PubMed2002

Objective assessment of bladder neck elevation and urethral compression at colposuspension.

OBJECTIVES: 1. To assess whether magnetic resonance imaging and intra-operative measurements are useful in assessing bladder neck elevation and urethral compression at colposuspension; 2. to see if intra-operative measurements could be a substitute for magnetic resonance scan measurements. DESIGN: Prospective, observational study. SETTING: Urogynaecology Unit, NHS Trust hospital. POPULATION: Seventy-seven women undergoing colposuspension. METHODS: Bladder neck elevation was assessed using magnetic resonance imaging and measuring the amount of suture bow-stringing intra-operatively. Urethral compression was assessed using magnetic resonance imaging and by two intra-operative measurements: the distance between the medial sutures (with a ruler) and the distance between the urethra and the pubic bone (using paired Hegar dilators). RESULTS: The assessment of bladder neck elevation and compression against the pubic bone using magnetic resonance imaging was reliable (95% limits of agreement: -7.1mm to +7.1mm and -1.7mm to +3.8mm, correlation coefficient 0.92 and 0.87, respectively). The intra-operative assessment of urethral compression with a ruler was also reproducible at both paravaginal and pectineal sites (95% limits of agreement -2.6mm to +2mm and -2.1mm to +2.4mm, respectively; correlation coefficient 0.99 for both distances). Other intra-operative measurements of bladder neck elevation (suture bow-stringing) and urethral compression (Hegars) did not correlate with equivalent magnetic resonance scan measurements (kappa =-0.046, P = 0.31; kappa = 0.052, P = 0.41, respectively). CONCLUSIONS: Measurements have been found that can reliably assess bladder neck elevation and urethral compression at colposuspension. These measurements should be suitable for investigating morbidity following colposuspension.

Adult↗

PubMed1997

Pressure differences of elastic compression stockings at the ankle region.

BACKGROUND: Elastic compression stockings are widely used medical devices for the prevention of edema and treatment of venous diseases. Many beneficial effects have been described in the past. The exact amount of pressure underneath elastic compression stockings at different areas of the leg remains controversial. OBJECTIVE: To examine the pressure at the skin underneath class II elastic compression stockings at different places around the ankle at the B level. METHODS: Patients with known venous insufficiency and regularly using class II elastic therapeutic compression stockings (25-35 mm Hg) for venous diseases were included. All subjects were wearing completely new stockings at the time of the study. Measurements were performed with an electropneumatic interface pressure measuring device (Oxford Pressure Monitor MK II) with inflatable small sensoring cells. Six sensors were placed around the smallest circumference at the ankle (B-area). The highest and lowest recordings as well as the means were evaluated. RESULTS: The mean pressure of class II elastic stockings measured around the ankle was 24.7 mm Hg (SD, 8.4). The lowest pressures were found at the medial site (18.3 mm Hg; 74% of the mean), and the highest at the pretibial zone (33.9 mm Hg, 137%). CONCLUSIONS: The pressure exerted by pressure class II elastic compression stockings a the medial site just above the ankle (B area) is too low to have influence and improve the venous insufficiency. For phlebology this is the target area. It might be a reason for the high recurrence rate of venous ulcers even if patients wear stockings. Also, the mean pressure of class II stockings was found to be below the normal levels of its pressure class (25-35 mm Hg according to the European CEN classification). The results advocate the use of pressure class III elastic compression stocking more often and the use of pelottes or foam pads.

Ankle↗

PubMed1998

Compression therapy with medical elastic stockings for venous diseases.

BACKGROUND: Compression therapy is the cornerstone in the treatment of venous disease. In many cases, but especially for the maintenance of compression, medical elastic compression stockings (MECS) are being used. Preprescription investigation includes determining the severity of venous insufficiency and the arterial system. An ankle/arm index < 0.6 will be the contraindication for compression therapy. MECS can be divided in flat-knitted and round-knitted MECS. Flat-knitted MECS can be made tailor sized, with a tolerance up to 0.5 cm. Several classes of MECS are characterized by the elasticity coefficient (EC) of the used elastic threads. The stiffer the stocking (high EC), the better a MECS will prevent edema formation during the day, but the more difficult it is to put them on. MECS with a high EC are always flat-knitted. Most round-knitted MECS will last 4-6 months, and flat-knitted MECS, 6-9 months. RESULTS: The physician can prescribe MECS for a wide variety of venous and some other diseases. He can determine the amount of compression as well as the stiffness of the MECS. CONCLUSION: Only a well-motivated patient and an experienced physician together are able to ensure ongoing successful compression therapy with MECS.

Ankle↗

PubMedDate not supplied

An in vitro biomechanical investigation of the mechanical properties of dynamic compression plated osteotomized adult equine tibiae.

OBJECTIVE: To determine the monotonic mechanical properties of osteotomized adult equine tibiae stabilized with two dynamic compression plates (DCP) and to compare the mechanical properties with those of intact tibiae and in vivo loads. STUDY DESIGN: The compressive, bending, and torsional mechanical properties of plated and intact tibiae were assessed in vitro. ANIMALS OR SAMPLE POPULATION: Twelve pairs of adult equine tibiae. METHODS: Tibiae were loaded in axial compression, craniocaudal 3-point bending, or torsion in external rotation in a single cycle to failure. Mechanical properties were determined from load-displacement data. RESULTS: Compared to intact tibiae, the mean yield load, failure load and stiffness of plated tibiae were significantly lower (P < .05) (compression and torsion); and the mean yield and failure bending moments, and bending stiffness, of the plated tibiae were lower (P < .075 for yield), or significantly lower, respectively. The mean compression and bending yield loads for plated tibiae were greater than in vivo loads. The mean torsional yield load for plated tibiae approximated the torsional load determined for the adult horse at a walk. CONCLUSIONS: Simple, anatomically reduced, DCP plated tibiae should have adequate strength to withstand immediate, postoperative in vivo compressive loads and bending moments placed on the tibia in vivo during immediate postoperative activities, however, may not have adequate torsional strength during immediate postoperative weight-bearing at a walk. CLINICAL RELEVANCE: Additional supportive methods, to decrease torsional loads, may be beneficial in maintaining stability of plate repaired tibiae during recovery from anesthesia and postoperative healing.

Animals↗

PubMed1993

Anatomical and morphological evaluation of pacemaker lead compression.

In recent years, pacemaker lead failure due to compressive damage has been reported with increasing frequency. To document the mechanism of this failure, we evaluated explanted mechanically damaged leads with electrical testing, optical microscopy, and in some cases, scanning electron microscopy (SEM). In addition, we performed an autopsy study to measure the compressive loads on catheters placed percutaneously through the costoclavicular angle, as well as by cephalic cutdown. Of the 49 explanted compression damaged leads with enough clinical data for analysis, all had been placed by percutaneous subclavian puncture. Our autopsy data confirmed the significant increase in pressures generated in the costoclavicular angle for medial percutaneous subclavian catheterization (126 +/- 26 mmHg) compared to a more lateral percutaneous subclavian puncture (63 +/- 15 mmHg) or a cephalic cutdown (38 +/- 13 mmHg) (P < 0.01). In vivo coil compression testing documented loads up to 100 pounds per linear inch of coil and a compressive morphology by SEM identical to that seen in the clinical explants. Pacemaker leads appear to be susceptible to compression damage when placed by subclavian venipuncture. When possible, leads should be placed such that they avoid the tight costoclavicular angle.

Bloodletting↗

PubMed2001

Role of manual compression time and bed rest duration on the occurrence of femoral bleeding complications after sheath retrieval following 4Fr left-sided cardiac catheterization.

To shorten hospital stay or to allow ambulatory procedures, 4Fr catheters for left-sided cardiac catheterization can be used. These latter parameters may also be influenced by compression time and bed rest duration. The role of these parameters was assessed by prospectively including 130 consecutive patients who underwent 4Fr femoral diagnostic procedures. The patients were randomized into two groups: group 1 consisted of 70 patients undergoing 5-minute compression and group 2 consisted of 60 patients with 15-minute compression. In each group, a second randomization was applied to determine the bed rest duration (2-4 hours). More group 1 patients experienced immediate bleeding following manual compression than group 2 patients (12 [17%] vs 3 [5%], P < 0.03, respectively). Compared to group 2, a slight but nonsignificant increase in the total number of hematomas was observed in group 1 (31 vs 22%, NS). No difference existed in terms of local large hematomas at 24 hours (7% in each group) or in terms of benign > or = 10 cm diffuse subcutaneous ecchymosis at 7-day follow-up (13 [19%] group 1 patients vs 8 [13%] group 2 patients, NS). However, persistence of diffuse subcutaneous ecchymosis at 7-day follow-up appeared to be related to the history of immediate bleeding following manual compression in both groups (group 1: 5/13 vs 7/57 patients [P < 0.04] and group 2: 3/8 vs 0/52 patients [P < 0.002]). In conclusion, 4Fr femoral left-sided cardiac catheterization is safe and could be performed as an ambulatory procedure. However, it requires 15-minute duration of manual compression associated with 2-hour bed rest to decrease local bleeding complications.

Aged↗

PubMed1983

The effects of polymorphism, particle size and compression pressure on the dissolution rate of phenylbutazone tablets.

The dissolution rate of phenylbutazone from tablets after disintegration has been used to determine whether the drug particles underwent crushing or bonding during compression. Two polymorphic forms of the drug were used and the predominant effect for high drug concentration (60%), during compression was dependent upon the original particle size of the drug and its polymorphic form. With a low drug concentration (10%) in the tablet, the diluent protected the drug particles from bonding together. The particle size change of the drug during compression was affected by the nature of the diluent present. Lactose had an abrasive action on Form A phenylbutazone compared with Avicel but had little effect on the more ductile Form B. When the contact time of compression was decreased from 29 to 0.26 s, the 6 microns particles of drug showed less bonding at the shorter time (faster rate of compression) but the effect observed with the larger particles was independent the compression rate.

Crystallization↗

PubMed1996

Stabilizing role of moments and pelvic rotation on the human spine in compression.

The mechanisms by which the human spinal column in neutral postures can resist relatively large axial compression forces with no abnormal motions or instabilities remain yet unknown. A nonlinear finite element study of the ligamentous thoracolumbar spine was performed to investigate the stabilizing role of two plausible mechanisms of combined moments and pelvic rotation on the human spine in axial compression. The passive system, by itself was able to carry only a negligible fraction of physiological compression loads without exhibiting large motions. The unconstrained spine was most flexible in the sagittal plane (least stiff plane). The existence of combined moments and pelvic rotation significantly increased the load-bearing capacity of the spine so that the free standing passive thoracolumbar spine resisted the axial compression forces of more than 1000 N with minimal displacements. The former mechanism is much more effective in stabilizing the spine in compression than is the latter one. It is postulated that the pelvic rotation and the off-centered anterior placement of the gravity force are exploited to partially stabilize the passive spine in compression and relieve the musculature. Previous and on- going studies support the validity of the proposed mechanisms.

Humans↗

PubMed1981

Effects of nonlinear strain-dependent permeability and rate of compression on the stress behavior of articular cartilage.

The compressive viscoelastic behavior of articular cartilage, a fiber-reinforced, porous, permeable solid matrix filled with water, is predominately governed by the flow of the interstitial water within the tissue and its exudation across the articular surface. The fluid flow is in turn governed by the permeability of the tissue and the loading imposed upon its surface. But for articular cartilage, the permeability depends nonlinearly on the strain; k = ko exp (Me). Here, M is the nonlinear flow-limiting parameter and e is the dilatation. In this investigation, we studied the influence of M and Ro = koHA/Uh (where HA is the elastic equilibrium modulus of the solid matrix, h is the tissue's thickness and U is the rate of compression applied onto the surface via a rigid, porous, free-draining filter) on the stress history of circular plugs of cartilage specimens attached to the bone. It was found that these two parameters have profound effects on the predicted compressive stress history. For very large Ro, the fluid flow effects become negligible. For small Ro and large M, large instantaneous compressive stresses several times larger than those observed at equilibrium are predicted. This amplification of compressive stress is due to the increase of importance of the relative fluid flow effect, i.e., Ro leads to 0, and nonlinear flow-limit effect, i.e., M greater than 0. Also, the theoretical curves predict that the rate of increase of stress initially decreases (convex) and finally becomes a constant. The results of our 5 percent offset compression experiments are in good agreement with the theoretical predictions.

Biomechanical Phenomena↗

PubMed1996

The effects of lossy compression on the detection of subtle pulmonary nodules.

We examined the ability of radiologists to detect pulmonary nodules in computed radiographic (CR) chest images subjected to lossy image compression. Low-contrast 1-cm diameter targets simulating noncalcified pulmonary nodules were introduced into clinical images and presented to ten radiologists in a series of two-alternative forced-choice (2AFC) observer experiments. The percentages of correct observer responses obtained while viewing noncompressed images (1:1) were compared with those obtained for the same images compressed 7:1, 16:1, 44:1, and 127:1. The images were compressed using a standard full-frame discrete cosine transform (DCT) technique. The degree of compression was determined by quantizing Fourier components in various frequency channels and then Huffman encoding the result. The data show a measurable decline in performance for each compression ratio. Through signal-to-noise ratio (SNR) analysis, we found that the reduction in performance was due primarily to the compression algorithm that increased image noise in the frequency channels of the signals to be detected.

Algorithms↗

PubMed1996

Image compression in digital mammography: effects on computerized detection of subtle microcalcifications.

Our previous receiver operating characteristic (ROC) study indicated that the detection accuracy of microcalcifications by radiologists is significantly reduced if mammograms are digitized at 0.1 mm x 0.1 mm. Our recent study also showed that detection accuracy by computer decreases as the pixel size increases from 0.035 mm x 0.035 mm. It is evident that very large matrix sizes have to be used for digitizing mammograms in order to preserve the information in the image. Efficient compression techniques will be needed to facilitate communication and archiving of digital mammograms. In this study, we evaluated two compression techniques: full frame discrete cosine transform (DCT) with entropy coding and Laplacian pyramid hierarchical coding (LPHC). The dependence of their efficiency on the compression parameters was investigated. The techniques were compared in terms of the trade-off between the bit rate and the detection accuracy of subtle microcalcifications by an automated detection algorithm. The mean-square errors in the reconstructed images were determined and the visual quality of the error images was examined. It was found that with the LPHC method, the highest compression ratio achieved without a significant degradation in the detectability was 3.6:1. The full frame DCT method with entropy coding provided a higher compression efficiency of 9.6:1 at comparable detection accuracy. The mean-square errors did not correlate with the detection accuracy of the microcalcifications. This study demonstrated the importance of determining the quality of the decompressed images by the specific requirements of the task for which the decompressed images are to be used. Further investigation is needed for selection of optimal compression technique for digital mammograms.

Breast Diseases↗

PubMed1998

Effects of lossy compression on lesion detection: predictions of the nonprewhitening matched filter.

The nonprewhitening matched filter (NPWMF) was used to study the effect of wavelet-based lossy image compression on lesion detectability. Two classes of images, representing lesion-present and lesion-absent cases, were generated by simulation techniques. The performance index, da, of the NPWMF was calculated from the reconstructed images of the two classes and was used as an objective measure for quantifying signal detectability. The effect of compression on detectability was analyzed by defining signal amplitude, signal size, and noise amplitude at a constant da. Since human observer studies directly correlate with the performance index da, the effect of signal parameters on compression ratios could be evaluated. For example, a signal with 7 pixels in diameter and an amplitude of 10 that was compressed at a ratio of 4.6:1, and a signal of the same size with an amplitude of 15 but compressed at a ratio of 24.3:1, both had a da of 4.1, implying identical detectability. Similar results for other combinations of signal and noise parameters, but at constant da, can be used to analyze the effect of compression on detectability without requiring human observer studies.

Biophysical Phenomena↗

PubMed1981

Study of multichannel amplitude compression and linear amplification for persons with sensorineural hearing loss.

Experiments were conducted on five listeners with sensorineural hearing impairments using two 16-channel, computer-controlled, amplitude compression systems, and four linear systems. One of the compression systems was designed to restore normal equal loudness contours, the other employed reduced high-frequency emphasis and reduced compression ratios. The linear systems differed only in their frequency-gain characteristics (orthotelephonic plus three characteristics with high-frequency emphasis that were expected to produce better results than orthotelephonic). In the main experiment, all systems were compared for each listener using nonsense CVC monosyllables and sentence materials spoken by male and female talkers and presented in quiet/anechoic and noisy/reverberant environments at the most comfortable level for each listener. The linear systems with high-frequency emphasis performed substantially better than the orthotelephonic system. Performance with compression was generally slightly worse than with linear amplification. Compression was superior to linear amplification only when speech materials with significant item-to-item level variation were used in quiet with subjects with more severe losses and when reduced input speech levels were used. To the extent that these two conditions represent real-life communication conditions, these results suggest that compression is preferable to linear amplification in a wearable hearing aid.

Adult↗

PubMed1991

A formula for comparison of selected sport ball compressibility.

The purpose of this study was to develop a formula to determine and compare the compressibility of selected sport balls. Six balls (basketball, volleyball, soccer ball, baseball, handball, golf ball) were dropped ten times from each of four different heights onto a smooth solid surface overlaid with a white sheet of typing paper, overlaid with a sheet of carbon paper. The diameter of the area of contact of each ball imprinted onto the typing paper was measured in millimetres with calipers. From the data, the distance (d) that each ball compressed for each velocity (v) was calculated. It was found that a linear relationship existed between velocity at impact and the distance for each ball studied. The compressibility coefficient (c) for each ball was calculated and a formula was developed to determine the distance each ball would compress at a given velocity. When velocity is measured in metres per second and the distance a ball compresses is measured in millimetres, the formula to determine d for selected balls, in order of compressibility is: basketball d = 3.07v, volleyball d = 2.90v, soccer ball d = 2.80v, baseball d = 0.77v, handball d = 0.53v, and golf ball d = 0.17v.

Equipment and Supplies↗

PubMedDate not supplied

Introduction to wavelet-based compression of medical images.

Medical image compression can significantly enhance the performance of picture archiving and communication systems and may be considered an enabling technology for telemedicine. The wavelet transform is a powerful mathematical tool with many unique qualities that are useful for image compression and processing applications. Although wavelet concepts can be traced back to 1910, the mathematics of wavelets have only recently been formalized. By exploiting spatial and spectral information redundancy in images, wavelet-based methods offer significantly better results for compressing medical images than do compression algorithms based on Fourier methods, such as the discrete cosine transform used by the Joint Photographic Experts Group. Furthermore, wavelet-based compression does not suffer from blocking artifacts, and the restored image quality is generally superior at higher compression rates.

Humans↗

PubMed2003

Acute cerebral infarction: effect of JPEG compression on detection at CT.

PURPOSE: To evaluate the effect of Joint Photographic Experts Group (JPEG) compression ratios of 10:1 and 20:1 on detection of acute cerebral infarction at computed tomography (CT). MATERIALS AND METHODS: CT images obtained in 25 patients with acute cerebral infarction and 25 patients with no lesions were compressed by means of a JPEG algorithm at ratios of 10:1 and 20:1. Normal and abnormal sections (on original and compressed images) were reviewed by using a color soft-copy computed monochrome cathode ray tube monitor. Five observers rated the presence or absence of a lesion with a 50-point scale (0, definitely absent; 25, equivocal; and 50, definitely present). Diagnostic accuracy was evaluated with receiver operating characteristic (ROC) curve analysis. Significant difference was defined as a P value less than.05 for the area tested with a two-tailed paired Student t test. RESULTS: At ROC analysis, no statistically significant difference was detected for all cases considered together (Az [area under the ROC curve] = 0.887 +/- 0.038 [mean +/- SD] on noncompressed images, Az = 0.897 +/- 0.038 on 10:1 compressed images, and Az = 0.842 +/- 0.073 on 20:1 compressed images; P >.05). CONCLUSION: JPEG compression at ratios of 10:1 and 20:1 was tolerated in the detection of acute cerebral infarction at CT.

Acute Disease↗

PubMed1986

Compression of radiological images with 512, 1,024, and 2,048 matrices.

A comprehensive study was performed using the full-frame bit-allocation compression technique on 78 radiological images, including digitized radiographs, computed radiographs, and computed tomography images. Each radiograph was digitized to 2,048 X 2,048 X 10, 1,024 X 1,024 X 10, and 512 X 512 X 10 matrices, respectively, with a laser scanner. Five compression ratios were used to compress each image, and reconstructed images from each compressed data set were obtained. Altogether, the authors studied 842 images, including the original and compressed-reconstructed images and the images obtained from the difference between the original and the reconstructed images. The results indicate that acceptable compression ratios for 2,048, 1,024, and 512 matrices are 25:1, 20:1, and 10:1, respectively, based on a mean-square error of 0.02%.

Angiography↗

PubMed1992

Mammographic unit compression force: acceptance test and quality control protocols.

Firm compression of the breast in screen-film mammography procedures lowers the radiation dose to patients, enhances image contrast and definition, and improves visibility of pathologic conditions. Most mammography unit compression systems have no force-level indicator. Some systems show force variations with time and others, with angle and region of the compression device. Still other systems give poorly reproducible compression-force levels, and in one unit the force release mechanism jammed repeatedly. Detailed procedures for initial acceptance testing and continuing quality control checks are listed. Recommended measurements include levels of manual and automatic applied force, stability, reproducibility, and dependence on angulation and breast size and evaluation of operation of release mechanisms. Also necessary are observations of the condition and operation of the compression system. Test equipment is described and measurement frequency is specified, as well as suggested tolerance limits. Manufacturers of mammographic units are urged to build in compression-force gauges and to provide both a manual mode and a variable-force automatic mode.

Female↗