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At least 811 records · Page 45Linked to original sources

PubMed1992

Compressed radiological images and workstation viewing.

The viewing of radiological images on workstations has peculiarities that must be taken into account in the design of a compression technique. The images may be manipulated on a workstation to change the contrast, to change the center of the brightness levels that are viewed, and even to invert the images. Because of the possible consequences of losing information in a medical application, bit-preserving compression is used for the images used for diagnosis. However, for archiving, the images may be compressed to 10% of their original size. A compression technique based on the discrete cosine transform takes the viewing factors into account by compressing the changes in the local brightness levels. The compression technique is a variation of the Consultive Committee on International Telephony and Telegraphy Joint Photograph Experts Group compression that suppresses the blocking of the discrete cosine transform except in areas of very high contrast.

Artifacts↗

PubMed1998

Wavelet-based vector quantization for high-fidelity compression and fast transmission of medical images.

Compression of medical images has always been viewed with skepticism, since the loss of information involved is thought to affect diagnostic information. However, recent research indicates that some wavelet-based compression techniques may not effectively reduce the image quality, even when subjected to compression ratios up to 30:1. The performance of a recently designed wavelet-based adaptive vector quantization is compared with a well-known wavelet-based scalar quantization technique to demonstrate the superiority of the former technique at compression ratios higher than 30:1. The use of higher compression with high fidelity of the reconstructed images allows fast transmission of images over the Internet for prompt inspection by radiologists at remote locations in an emergency situation, while higher quality images follow in a progressive manner if desired. Such fast and progressive transmission can also be used for downloading large data sets such as the Visible Human at a quality desired by the users for research or education. This new adaptive vector quantization uses a neural networks-based clustering technique for efficient quantization of the wavelet-decomposed subimages, yielding minimal distortion in the reconstructed images undergoing high compression. Results of compression up to 100:1 are shown for 24-bit color and 8-bit monochrome medical images.

Computing Methodologies↗

PubMed1998

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

Efficient data compression is essential for practical daily operation of computed radiography (CR) systems. In this study the clinical applicability of type III irreversible high data compression using an FCR 9501 chest unit (Fuji Photo Film, Tokyo, Japan) was evaluated. Sixty-eight normal and 93 various abnormal cases, with an additional 15 cases of lung cancers with solitary lung nodules, were selected from the file. A pair of hard copies of original images and images reconstructed using type III compression was made for each case. Six radiologists evaluated the image quality by visual rating and receiver operating characteristic (ROC) curve analysis. For all five anatomic regions of normal cases, "original equal to compressed" was the most common response, followed by "original significantly better than compressed." When abnormal cases were evaluated for diagnostic information, there was no significant difference between the compressed and original images. ROC curve analysis on lung nodules with lung cancer showed no significant difference between the two. Compressed CR images using the type III irreversible technique are clinically applicable and acceptable despite slight degradation of image quality.

Adenocarcinoma↗

PubMed2006

Effects of a backboard, bed height, and operator position on compression depth during simulated resuscitation.

OBJECTIVE: To investigate the effect of a backboard, cardiopulmonary resuscitation (CPR) provider body position and bed height on the quality of chest compression during simulated in-hospital resuscitation. DESIGN AND SETTING: Randomised controlled cross-over trial in a university hospital. PARTICIPANTS: Second-year medical student basic life support instructors. INTERVENTIONS: Chest compressions performed on a resuscitation manikin placed on a hospital bed with/without a CPR backboard, kneeling on the bed adjacent to the manikin and lowering the height of the bed. MEASUREMENTS AND RESULTS: Sub-optimal chest compressions were performed on all surfaces. There were no differences in compression depth: standard CPR, 29+/-7 mm; backboard CPR, 31+/-10 mm; kneeling on the bed, 30+/-7 mm; lowering bed height, 32+/-10 mm. Compression rate and duty cycle were similar on each surface. Participants failed to recognise their poor quality CPR, and there was no difference in assessment of fatigue or efficacy of CPR between surfaces. CONCLUSIONS: In contrast to current guidelines, the use of a CPR backboard did not improve chest compressions. Furthermore, kneeling on the bed adjacent to the victim or lowering bed height did not impact materially on the quality of chest compression. These findings should be validated in clinical studies.

Analysis of Variance↗

PubMed2001

Tracheal compression by elongated aortic arch in patients with congenitally corrected transposition of the great arteries.

We investigate the tracheal compression by aortic arch in patients with congenitally corrected transposition of the great arteries. Fourteen patients whose ascending aorta was connected to descending aorta on the contralateral side were divided into two groups according to the severity of tracheal compression on lateral angiogram: group 1 (stenosis > or = 50%, eight patients) and group 2 (stenosis < 50%, six patients). We compared the following variables between the groups: aortic size, lateral displacement of ascending aorta, retrosternal space, and contour of aortic arch. Spiral computed tomography (CT) was done in five patients of group 1. The ratio between measured and normal diameters of ascending aorta of group 1 was significantly larger than that of group 2 (1.57 +/- 0.14 compared to 1.19 +/- 0.26, p = 0.014). There was linear correlation between the tracheal compression and aortic size (r = 0.69, p = 0.001). The ascending aorta was positioned more laterally and the aortic arch was located more posteriorly in group 1. In four patients with decreased tracheal compression after surgery, aortic size decreased and the ascending aorta restored its anterior position. Spiral CT showed transversely oriented aortic arch and severe tracheal compression in the anteroposterior direction by aortic arch. The tracheal compression by aortic arch in corrected transposition is common when the descending aorta is located on the contralateral side of the ascending aorta. Aortic size, posterior position, elongation, and end-on appearance of the aortic arch are the useful predictors of tracheal compression.

Adolescent↗

PubMed1999

Effects of "body compression" on parameters related to ascites formation: therapeutic trial in cirrhotic patients.

Decreased effective circulating blood volume is an important factor in ascites formation in liver cirrhosis. We designed a "body compression" apparatus as a means to restore effective blood volume and investigated its effectiveness in reducing ascites formation in cirrhotics in terms of its effect on parameters of ascites formation noted below. The subjects, eight cirrhotics with ascites and eight cirrhotics without ascites were given spironolactone (50-75 mg/day) and furosemide (40-80 mg/day) while they received a diet containing 85 mEq of sodium per day. All four limbs and the lower abdomen were compressed with constant pressure [height (cm) divided by 13.6 mmHg] once, for 3h, using stroke rehabilitation splints, while patients lay supine. In cirrhotics both with and without ascites, urine volume, urinary sodium excretion, and creatinine clearance during the body compression were greater than values during control (non-compression) periods (urine volume, means 285 vs 169 ml/3h; P < 0.001, urinary sodium excretion 15.8 vs 9.5 mEq/3h; p < 0.001, creatinine clearance 74 vs 59 ml/min, P < 0.001, respectively). The increased basal plasma renin activity, angiotensin II, aldosterone, and norepinephrine levels in all cirrhotics were significantly decreased by the body compression. In another group of six cirrhotics who received no diuretics or albumin, repeat body compression alleviated ascites in three with well preserved renal function, but was ineffective in three with markedly impaired renal function. These results suggest that the improvement in renal function brought about by the body compression is attributable to an increase in effective circulating blood volume. This maneuver may be a useful complementary therapy in patients with cirrhotic ascites with well preserved renal function.

Adult↗

PubMed2004

Kinematic response of lumbar functional spinal units to axial torsion with and without superimposed compression and flexion/extension.

Experimental data suggest that lumbar torsion contributes to lumbar disc degenerative changes, such as instability, spondylolisthesis and spinal canal stenosis. However, some basic mechanical characteristics of the lumbar spine under torsional loading have not yet been reported in detail. For example, the function of the facet joints under combined mechanical loads such as torsion with superimposed flexion or extension postures is an area of interest about which little biomechanical data have been reported. In this study, the kinematic response to axial torsion with superimposed axial compression (200 N), compression-flexion (3 and 6 Nm) and compression-extension (3 and 6 Nm) was investigated in 10 cadaveric lumbar functional spinal units. Range of motion (ROM), and helical axes of motion (HAM), were analyzed. There was no difference in ROM between no preload, pure compressive and flexion-compression preload conditions. The ROM was significantly reduced by both extension-compression preload conditions (11% reduction for 3 Nm and 19% reduction for 6 Nm of extension) compared to the pure compressive preload. For no preload, the average HAM position in the transverse plane of the intervertebral disc was near the posteriormost part of the disc and located laterally on the side contralateral to the applied torsional moment. In the transverse plane, the HAM position showed a discrete trend towards the posterior part of the specimens during extension. Kinematic data were visualized using computer animation techniques and CT-based reconstructions of the respective specimens. This information may be used for identifying and characterizing physiologic and pathologic motion and for specifying conservative and surgical treatment concepts and, thus, may find application to identifying indications for spinal fusion or in evaluating the effect of future semi-flexible instrumentation.

Adult↗

PubMed2001

Biomechanical compression tests with a new implant for thoracolumbar vertebral body replacement.

The authors present an investigation into the biomechanical functioning of a new titanium implant for vertebral body replacement (Synex). Possible indications are fractures and/or dislocations with damage of the anterior column, posttraumatic kyphosis and tumors of the thoracolumbar spine. The construction must be supplemented by a stabilizing posterior or anterior implant. For best fit and contact with adjacent end-plates, Synex is distractable in situ. We performed comparative compression tests with Synex and MOSS ("Harms mesh cage") on human cadaveric specimens of intact vertebrae (L1). The aim of the study was to measure the compressive strength of the vertebral body end-plate in uniaxial loading via both implants to exclude collapse of Synex in vivo. Twelve human cadaveric specimens of intact vertebrae (L1) were divided into two identical groups (matched pairs) according to bone mineral density (BMD), determined using dual-energy quantitative computed tomography (DE-QCT). The specimens were loaded with an axial compression force at a constant speed of 5 mm/min to failure, and the displacement was recorded with a continuous load-displacement curve. The mean ultimate compression force (Fmax) showed a tendency towards a higher reading for Synex: 3396 N versus 2719 N (non-significant). The displacement until Fmax was 2.9 mm in the Synex group, which was half as far as in the MOSS group (5.8 mm). The difference was significant (P < 0.001). The compression force was twice as high, and significantly (P < 0.05) higher with Synex at displacements of 1 mm, 1.5 mm and 2 mm. A significant (P < 0.001) correlation (R = 0.89) between Fmax and BMD was found. Synex was found to be at least comparable to MOSS concerning the compressive performance at the vertebral end-plate. A possible consequence of the significantly higher mean compression forces between 1 and 2 mm displacement might be decreased collapse of the implant into the vertebral body in vivo.

Biomechanical Phenomena↗

PubMed1998

The contributions of arterial and venous volumes to increased cutaneous blood flow during leg compression.

Intermittent lower extremity compression increases cutaneous blood flow. The source of this increased perfusion and, the influence of physical activity on stimulated foot skin perfusion has not been elucidated. The purpose of this study is to determine the arterial and venous contributions to augmented cutaneous blood flow during foot and leg compression, and to evaluate whether physical activity influenced the response to compression. Fifty limbs from 29 normal volunteers were studied in the sitting position. Their daily physical activity was categorized as active if they exercised > or =3 days/week or sedentary if they exercised < or =3 days/week. Inflatable foot and calf compression cuffs attached to a timed-pressure pump (Art-assist AA 1000, ACI, Inc., San Marcos, CA) were applied to the subject's leg and set to deliver 120 mmHg pressure with a 10-sec deflation cycle. Skin perfusion of the great toe was recorded by a laser Doppler (Laserflo Model BPM 403, TSI, Inc., St. Paul, MN). Total perfusion with compression (A), retrograde venous perfusion (B), and compression artifact (C) was recorded. Mean values for A, B, and C and the differences between the two groups were analyzed using multivariate multiple comparison statistical method. The mean baseline skin perfusion was 3.96 +/- 0.91, and mean total stimulated skin perfusion (A) was 9.23 +/- 2.13. With arterial inflow obliterated and compression applied, mean skin perfusion (B) was 1.96 +/- 0.44. The sedentary group had a mean resting perfusion of 1.64 +/- 0.28 and mean stimulated value (A) of 2.29 +/- 0.37 ml/min/100 gm tissue. The active group had a mean resting perfusion of 28.26 +/- 0.91, and stimulated value (A) of 32.65 +/- 4.47 ml/min/100 gm tissue. These differences in the mean skin perfusion between the two groups were significant. It is concluded that in normals, the majority of increased perfusion is from increased arterial inflow. There is a larger resting foot skin perfusion in active individuals and they have quantitatively greater stimulated inflow compared to sedentary individuals.

Adult↗

PubMed2004

Use of lower abdominal compression to combat orthostatic hypotension in patients with autonomic dysfunction.

The aim of this study was to investigate in patients with neurogenic orthostatic hypotension the mechanism and usefulness of abdominal compression to increase standing blood pressure. In three protocols, 23 patients underwent abdominal compression. Protocol 1 evaluated in a 40-60 degrees head-up-tilt position, the effect of abdominal compression on caval vein and femoral diameter, arterial blood pressure and hemodynamics. Protocol 2 documented the relationship between the level of compression and the arterial pressure response. Protocol 3 investigated the ability to maintain standing blood pressure by an elastic binder. During head-up-tilt, compression (40 mm Hg) resulted in a reduction in diameter of the caval vein (mean -2.6mm, range -1.4 to 0.6), without a change in femoral vein diameter. Stroke volume increased by 14 % (range -1 to 23) and blood pressure (systolic/diastolic) by 30/14 mmHg (range 7/2 to 69/36), both p < 0.05; 40 mmHg compression was associated with a higher pressure response than 20 mmHg (mean 18/8 mmHg, range 6/2 to 43/20 vs. mean 9/4 mmHg, range -1/0 to 18/8, p < 0.05). Elastic abdominal binding increased standing blood pressure with 15/6 mmHg (range -3/3 to 36/14, p < 0.05). We conclude that in patients with neurogenic orthostatic hypotension, abdominal compression increases standing blood pressure to a varying degree by increasing stroke volume.

Abdomen↗

PubMed1981

Tracheal or esophageal compression due to benign thyroid disease.

Tracheal or esophageal compression was present in 91 (33 percent) of 273 consecutive patients with benign goiter during a 7 year experience. The underlying disease was nodular colloid goiter in 66 percent, adenoma in 21 percent, thyroiditis in 9 percent and Graves' disease in 4 percent. The incidence of tracheoesophageal compression was higher in patients with thyroiditis (67 percent) than in those with colloid goiter (46 percent). Thirty of 91 patients were completely asymptomatic but had marked tracheal deviation on roentgenography. Two thirds presented with significant dyspnea, or dysphagia or both. A long history of goiter preceding the onset of symptoms and progressive worsening of compression symptoms after its onset were common in the latter group. Previous radiographs demonstrating significant tracheal deviation during a previous presymptomatic period were available in 11 of 36 dyspneic patients. Sudden tracheal occlusion developed in 3 percent and required emergency treatment. Tracheal compression occurred more often and when present was a more ominous symptom. Compression manifestations were more frequent in patients with multinodular goiter, were more likely to appear when the underlying disorder was thyroiditis affected the tracheal more often than the esophagus and were generally gradually progressive with time. A clinical spectrum ranging from a presymptomatic tracheal compression stage to one wherein progressive worsening of symptoms occurs is suggested. After symptoms of tracheal compression become clinically manifest, the occurrence of complete airway occlusion may be sudden and unpredictable. Early operation whenever roentgenographic evidence of tracheal deviation becomes manifest is recommended.

Adolescent↗

PubMed1984

Intermittent sequential high-pressure compression of the leg. A new method of preventing deep vein thrombosis.

The effect of sequential pneumatic leg compression on venous flow velocity was studied in 25 patients. At the usual pressures of 35 to 55 mm Hg, venous flow velocity was only 175 percent of the control value, but 366 percent when pressures were between 90 and 100 mm Hg. The incidence of post-operative thrombosis was studied in three groups of patients. In 24 patients receiving sequential compression prophylaxis of 90 to 100 mm Hg, there was one case of thrombosis, whereas there were three cases among the 25 patients with compression of 35 mm Hg and three cases among the 25 patients receiving 5,000 units of heparin three times per day. Sequential intermittent compression with high pressures, 10 compression cycles three times daily, is recommended for all patients unable to undertake physically active prophylactic measures. An absolute indication exists in those patients who cannot be mobilized and those in whom there are additional contraindications to the use of anticoagulants. Sequential compression is no alternative to antithrombosis stockings which must be worn from the day of hospitalization until discharge and also during the period of pneumatic compression.

Aged↗

PubMed1986

Effects of graded experimental compression on slow and fast axonal transport in rabbit vagus nerve.

Effects of compression at low pressures on slow and fast axonal transport was investigated in rabbit vagus nerve. Proteins in the sensory fibres were radiolabelled by injection of [3H]leucine or [35S]methionine into the nodose ganglion. A small compression chamber and/or ligatures were applied around the cervical part of the vagus nerve for 8 h, at an appropriate time for the subsequent analysis of the effects of compression on both slow and fast transport of radiolabelled proteins. In normal nerves there were two waves of slowly transported proteins with rates of about 12-15 and 25-30 mm/day, respectively. SDS-polyacrylamide gel electrophoresis was used and confirmed that the main proteins which accumulated proximal to the ligatures had a molecular weight of 54 000-56 000. Neither compression of the nerve at 20 mm Hg nor sham-compression induced any statistically significant accumulation of slowly transported proteins at the site of compression. A higher pressure, i.e. 30 mm Hg, induced a marked but incomplete accumulation of slowly transported proteins. Fast transport was partially inhibited in some, but not all, nerves, when 20 mm Hg was applied for 8 h, in contrast to the lack of effect found previously with the same pressure applied for only 2 h. Despite these slight differences, the results indicate that both slow and fast transport are impaired by low pressure levels of around 20-30 mm Hg, which are comparable with those found in human compression neuropathies. The impaired provision of cytoskeletal elements to the distal axon may be of significance in the pathophysiology of nerve entrapment syndromes.

Animals↗

PubMed1990

Improvement in the locally optimum run-length compression of CT images.

In the locally optimum run-length compression of X-ray CT images, differential entropy is selected as the criterion for compression. The reported compressed results for 12 bit CT images are 8-9 bits per pixel, which are far from the differential entropies of the boundaries of the compression, from 5.5 to 6 bits per pixel. Our analysis shows that the compression strategy is defective and this is one reason why the compression cannot reach the boundary. Significant improvement has been achieved and the results challenge the selection of differential entropy as a 'theoretical bench mark' for compression.

Image Processing, Computer-Assisted↗

PubMed1992

Behavioral response of altricial and precocial rodent fetuses to acute umbilical cord compression.

Norway rat fetuses (Rattus norvegicus) exhibit a stereotypic behavioral response when the umbilical cord is experimentally compressed with a vascular clamp. In this study, the development of the fetal behavioral response to cord compression was compared in altricial and precocial rodents, which differ markedly in neural and motor maturity at the time of birth. Both altricial and precocial species showed some form of behavioral response to umbilical cord compression. Fetuses of two altricial species, Norway rats and Mongolian gerbils (Meriones unguiculatus), expressed hyperactivity in response to cord compression throughout the last third of gestation. In contrast, precocial cotton rats (Sigmodon hispidus) and spiny mice (Acomys cahirinus) did not respond to cord compression until relatively late in gestation. Thus, altricial and precocial species do not express the cord compression response during comparable periods of neural development: precocial species are much more mature at the earliest expression of this behavior than altricial species. These findings are consistent with the interpretation that the cord compression response is a behavioral adaptation that can promote survival of the fetus in utero.

Animals↗

PubMed1995

Compression characteristics of CPR manikins.

We evaluated the force-depth compression characteristics of 8 different CPR manikins during mechanical cardiopulmonary resuscitation by a thumper. The force required to compress the manikin's thorax of 1, 2, 3, 4 and 5 cm was measured. It ranged between 6.3 and 14 kp at a depth of 1 cm, 11.6-30 kp at 2 cm, 17-38 kp at 3 cm, 22.5-54 kp at 4 cm and 28.5-69 kp at 5 cm. The manikins with a spring in the thorax (Ambu Man, Ambu MultiMan, Dräger CPR-Max, Laerdal Resusci Anne) as well as one without (Ambu CPR Pal) showed a rather linear relationship between depth and force required to compress the chest. Ambu Man, set at 'High', Laerdal Resusci Anne and Dräger CPR-Max revealed a slight increase in resistance, whereas 2 manikins without a spring (Laerdal Little Anne, Laerdal Family Trainer) and 1 manikin with a plastic spring-like construction (Actar 911) exhibited less resistance with increasing depth. According to our results, the manikins are not uniform in their compression characteristics; some become nonlinear when 3 cm of compression is exceeded. For correct CPR it is of utmost importance that the CPR trainee learns to compress in a sufficiently strong manner, but simultaneously to avoid an exceedingly high depth of compression irrespective of the thorax resistance. In order to prepare the CPR student for the varying chest resistances of the human body, we recommend to train CPR on manikins with different chest resistances.

Cardiopulmonary Resuscitation↗

PubMed1994

Active compression-decompression resuscitation: effect on resuscitation success after in-hospital cardiac arrest.

OBJECTIVES: The purpose of this study was to test the hypothesis that active compression-decompression would improve resuscitation success in human subjects after cardiac arrest. BACKGROUND: Active compression-decompression cardiopulmonary resuscitation is a new method that improves cardiopulmonary hemodynamic function in animal models and humans after cardiac arrest. METHODS: We conducted a prospective randomized clinical trial in patients with in-hospital cardiac arrest. Patients were assigned to receive standard manual or active compression-decompression cardiopulmonary resuscitation. The primary study end points were spontaneous return of circulation, 24-h survival and survival to hospital discharge. RESULTS: Fifty-three consecutive patients after cardiac arrest undergoing 64 resuscitation attempts were studied (30 women, 23 men; mean [+/- SD] age 71 +/- 13 years, range 38 to 96). Spontaneous return of circulation was observed in 24 (47%) of 53 patients and was increased in patients receiving active compression-decompression compared with those receiving standard manual cardiopulmonary resuscitation (15 [60%] of 25 vs. 9 [32%] of 28, respectively, p = 0.042); 24-h survival was increased (12 [48%] of 25 vs. 6 [21%] of 28, respectively, p = 0.041); and there was a trend toward improved survival to hospital discharge (6 [24%] of 25 vs. 3 [11%] of 28, respectively, p = 0.198) when active compression-decompression was compared with standard manual cardiopulmonary resuscitation. CONCLUSIONS: Active compression-decompression cardiopulmonary resuscitation improves return of spontaneous circulation and 24-h survival after in-hospital cardiac arrest. Active compression-decompression cardiopulmonary resuscitation appears to be a beneficial adjunct to standard manual cardiopulmonary resuscitation.

Aged↗

PubMed1995

Utilization of a pressure-sensing monitor to improve in-flight chest compressions.

Previous research at the Division of Air Medical Services at East Carolina University School of Medicine has demonstrated impairment of chest compression efficacy in the setting of an airborne BO-105 helicopter. This study was undertaken to determine whether in-flight compression efficacy could be improved with utilization of a pressure-sensing monitor providing real-time feedback during cardiopulmonary resuscitation (CPR). Ten flight nurses each performed two minutes of in-flight chest compressions on a mannequin that electronically assessed compression depth and hand placement. The session was then repeated using the pressure-sensing device. The mean proportion of correct compressions (95.7 +/- 3.2%) achieved with utilization of the pressure-sensing monitor was significantly higher (P < .01) than the corresponding proportion for the control group (33.4 +/- 12.1%). This study demonstrated that the difficulties of performing effective in-flight chest compressions are largely overcome with utilization of a pressure-sensing device providing real-time feedback on compression efficacy.

Aerospace Medicine↗