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PubMed2004

Vertebral neoplastic compression fractures: assessment by dual-phase chemical shift imaging.

PURPOSE: To compare normal vertebrae with vertebrae with neoplastic compression fractures by means of opposed-phase (OP) and in-phase (IP) gradient-echo (GRE) imaging. MATERIALS AND METHODS: On OP and IP T1-W GRE images (obtained at 1.5 T with the fast low-angle shot (FLASH) technique) of dual-phase chemical shift sequences, we compared the signal intensity ratios (SIRs) of normal and compression-fractured vertebrae in 108 patients. Dual-phase chemical shift sequences were measured in three groups of vertebral bone marrow in terms of the relative SIR in OP and IP images: group 1: normal vertebrae (N = 30 with 90 vertebrae); group 2: non-neoplastic compression-fractured vertebrae (N = 58 with 73 vertebrae); and group 3: neoplastic compression-fractured vertebrae (N = 20 with 27 vertebrae). The presence of compressed vertebrae was ascertained based on the consensus of two experienced radiologists. The mean SIRs among the three groups were compared by means of the Tukey-Kramer test. RESULTS: The mean SIRs of the three groups (group 1: 0.46 +/- 0.14; group 2: 0.63 +/- 0.21; and group 3: 1.02 +/- 0.11) were significantly different according to the Tukey-Kramer test (P < 0.01). CONCLUSION: OP and IP T1-W GRE MRI of vertebral SI abnormalities can help predict the nature of compression fractures.

Aged↗

PubMed2002

Influence of excipients, drugs, and osmotic agent in the inner core on the time-controlled disintegration of compression-coated ethylcellulose tablets.

The effect of excipient, drug, and osmotic agent loaded in the inner core tablet on the time-controlled disintegration of compression-coated tablet prepared by direct compression with micronized ethylcellulose was investigated. The excipients [spray-dried lactose, hydroxypropyl methyl cellulose, sodium starch glycolate, microcrystalline cellulose, different drugs (sodium diclofenac: model drug, salbutamol sulfate, and theophylline anhydrate) and osmotic agent (sodium chloride)] were used to formulate the composition of the inner core tablet. The result indicates that drug release from all the compression-coated tablets was characterized by a distinctive lag of time followed by a faster drug release, dependent on the types of excipient and drug, and osmotic agent used in the inner core tablet. Respectively, the lag of time was 8.5, 12.4, 14.6, or 15.8 h for spray-dried lactose, hydroxypropyl methyl cellulose, sodium starch glycolate, or microcrystalline cellulose-loaded inner core tablet, as compared with 16.4 h for an inner core made of sodium diclofenac alone. The direct-compressible excipients such as spray-dried lactose, sodium starch glycolate, and microcrystalline cellulose seemed not to illustrate a marked disintegration function to rapidly rapture the outer coating layer. The lag of time was only slightly shortened from 16.4 to 14.6 h, >24 to 17.8 h, or >24 to 21.3 h for sodium diclofenac, theophylline anhydrate, or salbutamol sulfate incorporated with sodium starch glycolate into the inner core tablet, respectively, suggesting that sodium starch glycolate did not perform its superdisintegration. Once an osmotic agent of sodium chloride was incorporated into the inner core tablet, the lag of time for the compression-coated tablet was markedly shortened to <1 h, as compared with 16.4 h for drug alone. The more the amount of sodium chloride added, the less the time of lag obtained. Osmotic pressure did have a key role in controlling the drug dissolution. The present result implies that osmotic function is more suitable than superdisintegration function in designing a compression-coated tablet with time-controlled disintegration.

Albuterol↗

PubMed1977

Application of gluconolactone in direct tablet compression.

Gluconolactone was evaluated as an excipient for tablets prepared by direct compression using various drugs known to be difficult to compress. The physical properties of the tablets were evaluated after compression and after storage and were satisfactory. Comparative studies were conducted between gluconolactone and anhydrous lactose, a common direct compression diluent, for development of static charges during blending, flow, drug distribution, drug stratification, color distribution, compressibility, and preservation against mold growth. Gluconolactone possesses those properties necessary to produce high quality tablets by the direct compression process. Separate powdered mixtures of aspirin USP with gluconolactone, anhydrous lactose, spray-dried lactose, mannitol, and sorbitol were stored at various humidities and temperatures for specified periods and tested for the integrity of aspirin. Gluconolactone contributed least to the degradation of the drug as compared to other excipients studied. A preliminary in vivo study also was conducted on the bioavailability of aspirin from separate and similar mixtures with gluconolactone, anhydrous lactose, and starch. Gluconolactone did not show any inhibitory effect on aspirin absorption.

Animals↗

PubMed1988

Effect of excipients on tablet properties and dissolution behavior of theophylline-tableted microcapsules under different compression forces.

Theophylline ethylcellulose microcapsules were tableted by compression with or without excipients [lactose or hydroxypropyl cellulose (HPC-H)]. Tablets without excipients had a crushing strength that was independent of the applied compression force and the particle size of the microcapsules used, but tablet thickness decreased with an increase in the particle size of the microcapsules. The dissolution characteristics of theophylline from tableted microcapsules without excipients were almost independent of the applied compression force, but showed a sustained-release behavior. However, the thickness, crushing strength, and dissolution properties of tablets containing excipients were found to be affected by the type of excipient. Tableted microcapsules containing lactose showed an increase in tablet crushing strength that correlated with an increase in the applied compression pressure, but the tablet thickness did not change. In contrast, tableted microcapsules containing HPC-H showed a decrease in tablet thickness with an increase in the applied compression pressure, but the tablet crushing strength was initially reduced and then increased with an increase in the compression force. There was a rapid release rate for theophylline from tableted microcapsules containing lactose; a zero-order release rate for theophylline was found in tableted microcapsules containing HPC-H. The insoluble compacted matrix formation, disintegration of tablet, rupture of microcapsules, and gel matrix formation may be responsible for the release behavior of theophylline-tableted microcapsules with or without excipients. The reduced surface area and porosity resulted in a prolongation of the release from tableted microcapsules compared with untableted microcapsules.

Capsules↗

PubMed1999

Best parameters selection for wavelet packet-based compression of magnetic resonance images.

Transmission of compressed medical images is becoming a vital tool in telemedicine. Thus new methods are needed for efficient image compression. This study discovers the best design parameters for a data compression scheme applied to digital magnetic resonance (MR) images. The proposed technique aims at reducing the transmission cost while preserving the diagnostic information. By selecting the wavelet packet's filters, decomposition level, and subbands that are better adapted to the frequency characteristics of the image, one may achieve better image representation in the sense of lower entropy or minimal distortion. Experimental results show that the selection of the best parameters has a dramatic effect on the data compression rate of MR images. In all cases, decomposition at three or four levels with the Coiflet 5 wavelet (Coif 5) results in better compression performance than the other wavelets. Image resolution is found to have a remarkable effect on the compression rate.

Brain↗

PubMed2002

Comparison of interfacial properties of electrodeposited single carbon fiber/epoxy composites using tensile and compressive fragmentation tests and acoustic emission.

Interfacial and microfailure properties of carbon fiber/epoxy composites were evaluated using both tensile fragmentation and compressive Broutman tests with an aid of acoustic emission (AE). A monomeric and two polymeric coupling agents were applied via the electrodeposition (ED) and the dipping applications. A monomeric and a polymeric coupling agent showed significant and comparable improvements in interfacial shear strength (IFSS) compared to the untreated case under both tensile and compressive tests. Typical microfailure modes including cone-shaped fiber break, matrix cracking, and partial interlayer failure were observed under tension, whereas the diagonal slipped failure at both ends of the fractured fiber exhibited under compression. Adsorption and shear displacement mechanisms at the interface were described in terms of electrical attraction and primary and secondary bonding forces. For both the untreated and the treated cases AE distributions were separated well in tension, whereas AE distributions were rather closely overlapped in compression. It might be because of the difference in molecular failure energies and failure mechanisms between tension and compression. The maximum AE voltage for the waveform of either carbon or large-diameter basalt fiber breakages in tension exhibited much larger than that in compression. AE could provide more likely the quantitative information on the interfacial adhesion and microfailure.

Journal Article↗

PubMed2001

Volume, expansivity and isothermal compressibility changes associated with temperature and pressure unfolding of Staphylococcal nuclease.

We have characterized the temperature- and pressure-induced unfolding of staphylococcal nuclease (Snase) using high precision densitometric measurements. The changes in the apparent specific volume, expansion coefficient and isothermal compressibility were determined by these measurements. To our knowledge, these are the first measurements of the volume and isothermal compressibility changes of a protein undergoing pressure-induced unfolding. In order to aid in interpreting the temperature and pressure dependence of the apparent specific volume of Snase, we have also carried out differential scanning calorimetry under the solution conditions which are used for the volumetric studies. We have seen that large compensating volume and compressibility effects accompany the temperature and pressure-induced protein unfolding. Measurements of the apparent specific volume and thermal expansion coefficient of Snase at ambient pressure indicate the formation of a pre-transitional, molten globule type of intermediate structure about 10 degrees C below the actual unfolding temperature of the protein. Compared to the folded state, the apparent specific volume of the unfolded protein is about 0.3-0.5 % smaller. In addition, we investigated the pressure dependence of the apparent specific volume of Snase at a number of different temperatures. At 45 degrees C we calculate a decrease in apparent specific volume due to pressure-induced unfolding of -3.3 10(-3) cm(3) g(-1) or -55 cm(3) mol(-1). The threefold increase in compressibility between 40 and 70 MPa reflects a transition to a partially unfolded state, which is consistent with our results obtained for the radius of gyration of the pressure-denatured state of Snase. At the lower temperature of 35 degrees C, a significant increase in compressibility around 30 MPa is indicative of the formation of a pressure-induced molten globule-like intermediate. Changes in the apparent volume, expansion coefficient and isothermal compressibility are discussed in terms of instrinsic, hydrational and thermal contributions accompanying the unfolding transition.

Calorimetry, Differential Scanning↗

PubMed1984

Force response to width and length perturbations in compressed skinned skeletal muscle fibers.

Previous studies have shown that radial compression of calcium-activated skinned skeletal muscle fibers, with attendant reduction of filament lattice spacing, reduces isometric force generation. In relaxed skinned fibers, radial compression produces a marked increase in axial elastic modulus, and the response to a small amplitude length perturbation resembles that of a muscle in rigor. We interpret these results as indicating that radial compression of the myofilament lattice produces "hindered" cross-bridges which are load bearing but not force generating. The experiments reported here were designed to study the effect(s) of "hindered" cross-bridges on both the time course of isometric force responses following Ca2+ activation and fiber width and length perturbations. The experiments were carried out at room temperature on radially compressed skinned single rabbit soleus fibers. Force development following step-wise Ca2+ activation and step-wise changes of fiber width was "slow" (60-90 sec) compared to that in normal width fibers (approximately 1 sec), and could be approximated by a single exponential curve. Force redevelopment following a length release in compressed fibers was both more rapid and more complicated than force development following activation and width steps, and required a double exponential curve for an adequate description. The results are consistent with the notion that hindered cross-bridges form as a result of lattice compression, and that the hindered bridges affect the force responses following width and length perturbations.

Adenosine Diphosphate↗

PubMed1985

Force response to rapid and slow small amplitude length releases in isometrically contracting normal width and radially compressed trabeculae from rat heart.

The early transient force response to small amplitude ramp length release, applied at the plateau of calcium activated force development, was studied in normal width and radially compressed trabeculae from rat right ventricle. Force recovery immediately following "rapid" (5 ms ramp duration) release was less in compressed than in normal width muscle. Force recovery immediately following "slow" (ramp duration greater than 160 ms) release was virtually absent in both compressed and normal width muscle. The difference in force levels between the beginning and end of slow releases was small in normal width muscle; in compressed muscle a noticeable difference in force levels was seen. The rate of force recovery immediately following "rapid" release, as given by the rate constant obtained by fitting a single exponential equation to the force recovery vs time data, was not altered by compression. These results suggest that radial compression divides crossbridges into two distinct populations: one which cycles normally and another which cycles very slowly, if at all.

Animals↗

PubMed1990

Anastomotic compression button: a new mechanical device for sutureless bowel anastomosis.

The anastomotic compression button is a new mechanical device that uses three interlocking polypropylene buttons to produce a sutureless bowel anastomosis. The device is unique in that it allows application of the buttons via a device similar to the popular intraluminal stapler, but it leaves no staples or foreign body of any kind in the bowel wall. The authors compared the 25-mm anastomotic compression button with the 25-mm intraluminal stapler in the colon of dogs. After 28 days, the mucosal blood flow, burst pressure, and anastomotic indices were found to be identical between the anastomotic compression button and the stapler. The anastomotic compression button was easier to use, and microscopic examination showed less ulceration, fibrosis, and inflammation, and better re-epithelialization at the anastomotic compression button site. The anastomotic compression button appears to have the potential to be a superior method compared with stapled anastomoses in the colon.

Anastomosis, Surgical↗

PubMed1994

Vascular compression of the esophagus: a manometric and radiologic study.

This study was undertaken to determine the prevalence of vascular compression in manometric tracings and to determine whether these findings had any clinical significance. Vascular compression, defined as a localized area of elevated intraesophageal resting pressure > 4 mm Hg with superimposed cyclic pressure spikes with a frequency of 60-100/min, was noted in 55 of 241 consecutive tracings. The groups with and without vascular compression were similar with regard to mean age, sex, and prevalence of dysphagia. Radiographs were available for 29 of the 55 and showed compression in 18, but there was no relationship with the manometric findings, except for a trend towards finding a positive esophagogram with amplitudes > 16 mm Hg. Eleven tracings showed absent "relaxation" of this elevation of pressure in response to swallows, and five of six available esophagograms showed a corresponding area of compression. We conclude that manometric evidence of vascular compression is common and generally has no clear relationship with esophagographic findings or dysphagia. However, the combined findings of marked increases in pressure and absence of relaxation in response to swallows may indicate evidence for a vascular cause of dysphagia.

Deglutition Disorders↗

PubMed1980

[Investigations of stability with the fixateur externe during strain of bending. Vertical and eccentric strain during compression of the fracture line and while the distance of support is changed (author's transl)].

The Fixateur externe was investigated under vertical and eccentric load when the fracture line was compressed and the distance of support was changed. Three kinds of mounting were used: R (Fixateur externe as frame), Z (three dimensional Fixateur externe) and Z2S (three dimensional Fixateur externe with two screws according to Schanz). If the distance of outer support was increased, the stability became greatly reduced. A compression increased the stability around the fracture line and on the free end of the system. A compression force of 10 kp at the fracture line yielded the greatest increase in stability. If in case of the methods R and Z, the compression was increased beyond 70 kp, there resulted even an instability, which depended on the distance of support. The most stable method of mounting was the three-dimensional Fixateur externe with two screws according to Schanz. The stability was compared if there was either a defect or a compression at the line of the fracture: there resulted a strikingly increased instability, if the distance of support was increased. The compression made it possible to compensate partly for the loss of stability.

Biomechanical Phenomena↗

PubMedDate not supplied

Video microscopy to quantitate the inhomogeneous equilibrium strain within articular cartilage during confined compression.

The objectives of this study were to develop a method to quantitate the displacement and strain fields within articular cartilage during equilibrium confined compression, and to use the method to determine the variation of the equilibrium confined compression modulus with depth from the articular surface in bovine cartilage. The method made use of fluorescently labeled chondrocyte nuclei as intrinsic fiducial markers. Articular cartilage was harvested from the patellofemoral groove of adult bovines and trimmed to rectangular blocks 5 mm long, 0.76 mm wide, and 500 microns deep with the articular surface intact. Test specimens were stained with the DNA binding dye Hoechst 33258, placed in a custom confined compression chamber, and viewed with an epifluorescence microscope equipped for video image acquisition. Image processing was used to localize fluorescing chondrocyte nuclei in uncompressed and compressed (approximately 17%) specimens, allowing determination of the intra-tissue displacement profile. Strain was determined as the slope of linear regression fits of the displacement data in four sequential 125-microns-thick layers. Equilibrium strains varied 6.1-fold from the articular surface through 500 microns of cartilage depth, with the greatest compressive strain in the superficial 125-microns layer and the least compressive strain in the two deepest 125-microns layers. Thus, the four successive 125-microns layers have moduli that are 0.44 (superficial), 1.07, 2.39, and 2.67 (deep) times the apparent modulus for a 500-microns thick cartilage sample assumed to be homogeneous.

Animals↗

PubMed1998

Clinical evaluation of irreversible data compression for computed radiography of the hand.

We evaluated the clinical utility of high data compression for computed radiography (CR) of the hand. Paired original and compressed CR images were obtained using an FCR 9000 system in 35 patients with various abnormalities of the hand. For the paired original and compressed images, we compared the depiction of the bone cortex, bone trabeculae, soft-tissue, and the margin of the abnormalities. The overall impressions for detectability of the abnormalities and for diagnostic capability were also evaluated. Poorer image quality of the compressed images was noted for most of the structures, but there was no significant difference between the original and compressed images as for the overall impressions for detectability of the abnormalities or for diagnostic capability. We conclude that a high data compression may be clinically acceptable with caution in radiography of the hand.

Female↗

PubMed1997

The effect of lossy discrete cosine transform compression on subtle bone fractures.

Extensive research efforts have been devoted to the feasibility of picture archiving and communication systems (PACS) in recent years. The advantages of PACS are numerous but mainly include reduced cost and improvement in the operational efficiency of a PACS-based radiology department. In digital radiography, images are viewed either in hard-copy or soft-copy format. Usually, these images are subsequently compressed and archived for future evaluation. There are various methods used in image compression. In this study, computed radiography images showing subtle pediatric bone fractures were compressed with the lossy method of image compression after they had been initially evaluated on workstation monitors. These studies were subsequently evaluated by observers, who were unaware of the interpretations of these images before compression, to determine if they could detect similar abnormalities. Our conclusion is that there is no difference in the interpretation of soft-copy computed radiographic images before or after lossy 10:1 compression in studies of subtle pediatric bone fractures. This is a US government work. There are no restrictions on its use.

Analysis of Variance↗

PubMed1997

Extrinsic airway compression secondary to pulmonary arterial conduits: MR findings.

Abnormal enlargement or malposition of any vascular structure or mass adjacent to the airway can cause extrinsic airway compression. In children with previous surgery for congenital heart disease, mass effect from prosthetic devices or alteration in the anatomic position of normal structures can lead to extrinsic airway compression. Because many children have complex medical problems after cardiac surgery, wheezing may be attributed to cardiac causes and airway compression may not be investigated. Furthermore, the distal airway compression seen in these children often is not visualized on chest radiographs. MR imaging can be useful in evaluating extrinsic airway compression in these patients. We present the MR imaging of two patients with symptomatic extrinsic airway compression secondary to pulmonary arterial conduits.

Airway Obstruction↗

PubMed2002

Compression and expansion wavefront travel in canine ascending aortic flow: wave intensity analysis.

The forces underlying left ventricular ejection were investigated by applying a wavefront analysis to blood pressure (P) and velocity (U) waveforms measured in the ascending aorta of anesthetized dogs (n = 13). Wavefronts travel forward (to the periphery) and/or backward (to the heart) after peripheral reflection. They are characterized by the rate of pressure change they cause, i.e., the time derivative of pressure (dP/dt): compression wavefronts have dP/dt > 0: expansion wavefronts have dP/dt < 0. Wave intensity is defined as (dP/dt)(dU/dt), where dU/dt is the time derivative of U. Forward wavefronts contribute positively to wave intensity and backward wavefronts contribute negatively. Therefore, wave intensity indicates whether the effects of forward wavefronts are predominant or whether those of backward wavefronts predominate in the formation of pressure and velocity waveforms. Under control conditions, wave intensity was positive in early and late systole, indicating that forward compression and expansion wavefronts dominate aortic acceleration and deceleration, respectively. Compression wave intensity was increased during inotropic stimulation by dobutamine (10-15 microg/kg per min i.v. infusion; +161% +/- 31% mean change in peak value +/- SEM (%), P < 0.05), and was reduced during beta-blockade by propranolol (1 mg/kg i.v. injection; -58% +/- 7%, P < 0.05). Expansion wave intensity was unchanged by dobutamine and propranolol (n = 6). In a separate group of animals (n = 7), expansion wave intensity was reduced during vasodilatation by nitroglycerin (0.5mg i.v. injection and 0.02 microg/kg per min infusion; -32% +/- 12%, P < 0.05), but was unchanged during vasoconstriction by methoxamine (2 mg i.v. injection). However, methoxamine reduced compression wave intensity (-46% +/- 14%, P < 0.05). These results indicate that (1) compression and expansion wavefronts generated by the left ventricle dominate acceleration and deceleration in the ascending aorta, (2) compression wave intensity is related to the inotropic state of the left ventricle, but is reduced during vasoconstriction, and (3) expansion wave intensity is reduced during vasodilatation. This time domain analysis of traveling wavefronts readily provides information concerning the dynamics of the ventriculoarterial interaction.

Adrenergic alpha-Agonists↗

PubMed2005

The effect of intermittent pneumatic compression on the bone uptake of (99m)Tc-labelled methylene diphosphonate in the lower limb.

INTRODUCTION: Venous compression of the lower limbs will obstruct outflow through the deep and superficial veins, yet inflow will continue, without continual swelling of the limb. It is hypothesised that venous channels in the long bones act as collateral channels to restore outflow, and therefore general blood flow through bone will increase. Such a hemodynamic change should affect the uptake of radiopharmaceuticals by the bone, though uptake changes in themselves would not definitely indicate flow changes. The purpose of this study, therefore, was to determine whether bone uptake in the lower limb is affected by intermittent venous compression, irrespective of the mechanism involved. MATERIALS AND METHODS: The effect of intermittent pneumatic compression of the thigh and calf on the uptake of (99m)Tc-methylene diphosphonate (MDP) was studied in 24 patients. All were undergoing routine bone imaging for medical conditions that were not focused on their lower limbs, and received 1 h of the therapy at 60 mmHg on one limb only, after injection of the radiopharmaceutical. Three hours after injection the relative difference in uptake (net counts per pixel) between the two limbs was calculated. The standard imaging protocol was otherwise unchanged. RESULTS: The median differences in uptake in the intermittently compressed limb compared with the contralateral limb were +7.6% (interquartile range +3.9% to +16.0%, p<0.0005 [Wilcoxon]) for the anterior aspect of the femur; +11.7% (interquartile range +4.3% to +22.2%, p<0.0005) posterior, femur; +10.5% (interquartile range +6.5% to +13.8%, p<0.0005) anterior, tibia; +10.6% (interquartile range +5.5% to +17.6%, p<0.0005) posterior, tibia. CONCLUSION: Intermittent pneumatic compression clearly and significantly increased the uptake of (99m)Tc-MDP in long bones. These data are consistent with increases in blood flow through bone, though a direct mechanical influence on the bone cannot be excluded. This effect should be given consideration during routine therapeutic and thromboprophylactic use of intermittent compression, and if the mechanism of the uptake changes can be established, their possible clinical uses should be investigated.

Adult↗