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PubMed1993

The effect of a distal site of compression on neural regeneration.

The effect of a distal site of nerve compression on neural regeneration after a nerve repair was investigated in the rat model. After chronic compression had been established by placement of a Silastic band about a distal site of the posterior tibial nerve, the proximal posterior tibial nerve was divided, and then immediately repaired. Beginning 6 months after nerve repair, neural regeneration, assayed by walking track analysis, demonstrated significantly impaired function in the group of rats with a distal site of compression, compared with the repair group without a distal site of compression (p < .05). Followed for 3 additional months, neural function further significantly (p < .001) deteriorated in the group with distal compression. Morphometric analysis demonstrated that both the nerve repair alone and repair-plus-compression groups had 1) significantly decreased axon and nerve-fiber diameters (p < .001), and 2) significantly increased myelinated nerve-fiber density (p < .001), compared with normal; these findings are consistent with neural regeneration. However, the repair-plus-compression group had significantly (p < .03) fewer regenerating fibers than did the repair-without-distal-compression group. This experimental study suggests that consideration be given to release of sites of known anatomic narrowing in close proximity to a nerve reconstruction.

Animals↗

PubMed2002

Impact of lossy compression on diagnostic accuracy of radiographs for periapical lesions.

OBJECTIVES: The purpose of this study was to evaluate the lossy Joint Photographic Experts Group compression for endodontic pretreatment digital radiographs. STUDY DESIGN: Fifty clinical charge-coupled device-based, digital radiographs depicting periapical areas were selected. Each image was compressed at 2, 4, 8, 16, 32, 48, and 64 compression ratios. One root per image was marked for examination. Images were randomized and viewed by four clinical observers under standardized viewing conditions. Each observer read the image set three times, with at least two weeks between each reading. Three pre-selected sites per image (mesial, distal, apical) were scored on a five-scale score confidence scale. A panel of three examiners scored the uncompressed images, with a consensus score for each site. The consensus score was used as the baseline for assessing the impact of lossy compression on the diagnostic values of images. The mean absolute error between consensus and observer scores was computed for each observer, site, and reading session. RESULTS: Balanced one-way analysis of variance for all observers indicated that for compression ratios 48 and 64, there was significant difference between mean absolute error of uncompressed and compressed images (P <.05). After converting the five-scale score to two-level diagnostic values, the diagnostic accuracy was strongly correlated (R (2) = 0.91) with the compression ratio. CONCLUSION: The results of this study suggest that high compression ratios can have a severe impact on the diagnostic quality of the digital radiographs for detection of periapical lesions.

Analysis of Variance↗

PubMed2000

Maximizing hemodynamic effectiveness of biventricular assistance by direct cardiac compression studied in ex vivo and in vivo canine models of acute heart failure.

OBJECTIVE: Direct cardiac compression improves effective ventricular contractility. However, associated reductions in filling volumes and increases in arterial pressure occurring at the onset of direct cardiac compression limit the degree to which cardiac output is augmented. We tested the hypothesis that active preload and afterload control maximizes the hemodynamic effectiveness of direct cardiac compression. METHODS AND RESULTS: Studies in isolated canine hearts loaded with a computer-controlled volume servo system that mimicked heart failure were used to clearly define the hemodynamic effects of direct cardiac compression. Immediately on initiation of direct cardiac compression, ventricular end-diastolic pressure and volume decreased substantially, arterial pressure increased, but stroke volume did not change significantly. When end-diastolic pressure was restored to about 20 mm Hg, stroke volume doubled; decreasing afterload resistance further increased stroke volume by about 30%. Such load adjustments were then tested in vivo in a canine model of acute heart failure induced by coronary artery microembolizations titrated to decrease cardiac output to 33% +/- 9% of control as end-diastolic pressure rose to 20.6 +/- 2.2 mm Hg. Direct cardiac compression decreased end-diastolic pressure to 11.4 +/- 2.6 mm Hg while increasing cardiac output from 0.8 +/- 0.2 to 1. 4 +/- 0.5 L/min (to only approximately 55% of normal). Restoring end-diastolic pressure to 19.6 +/- 2.2 mm Hg by infusions of saline solution increased cardiac output to 1.9 +/- 0.5 L/min. Afterload reduction (nitroprusside), while maintaining end-diastolic pressure at 19.8 +/- 1.3 mm Hg, increased cardiac output to its baseline, 2.8 +/- 1.1 L/min. CONCLUSIONS: Direct cardiac compression significantly improves ventricular pumping capacity and can restore cardiac output to about 60% of normal in the setting of acute heart failure. When combined with active preload and afterload manipulations, direct cardiac compression can restore cardiac output to normal.

Analysis of Variance↗

PubMed2003

Hemodynamic effect of intermittent pneumatic compression and the position of the body.

PURPOSE: The purpose of this study was to investigate the three likely mechanisms of intermittent pneumatic compression (IPC) in deep vein thrombosis prophylaxis (increased volume flow, increased flow velocity, and acceleration of flow) and to do this in a variety of positions, in different venous segments, and with the stimulus of three different compression garments. METHODS: In 12 healthy volunteers, three types of compression cuffs were used: foot, calf, and calf + thigh. The foot was compressed with 80 mm Hg, and the calf and thigh with 40 mm Hg. Duplex ultrasound scan was performed before and during the compression in the horizontal, 15-degree head-down, and 15-degree head-up positions. The common femoral, greater saphenous, profunda femoral, superficial femoral, and popliteal veins were examined. RESULTS: In comparison with the horizontal position, the 15-degree head-down position was associated with an increase of volume flow and velocities and the head-up position was associated with decreased flow and velocities in the deep veins. The application of IPC caused significant increases in velocities and volume flow in all venous segments. The lowest increase in velocities and volume flow in the deep veins was observed with the subjects in the head-down position, and in the two other positions, the increases were greater and similar to each other. IPC caused a much more prominent increase in flow velocities and volume flow in deep veins compared with simple elevation of the legs. CONCLUSION: IPC produces significant increases of venous flow volume and flow velocity and acceleration of flow. This is true whether the limbs are elevated, horizontal, or dependent. Segmental flow changes vary with the position of the patient and the compression garment used. Foot compression increases volume flow and velocity primarily in the popliteal vein. Calf compression provides maximal increases of volume flow and flow velocity through the deep veins.

Adult↗

PubMed2000

Effect of CT digital image compression on detection of coronary artery calcification.

PURPOSE: To test the effect of digital compression of CT images on the detection of small linear or spotted high attenuation lesions such as coronary artery calcification (CAC). MATERIAL AND METHODS: Fifty cases with and 50 without CAC were randomly selected from a population that had undergone spiral CT of the thorax for screening lung cancer. CT image data were compressed using JPEG (Joint Photographic Experts Group) or wavelet algorithms at ratios of 10:1, 20:1 or 40:1. Five radiologists reviewed the uncompressed and compressed images on a cathode-ray-tube. Observer performance was evaluated with receiver operating characteristic analysis. RESULTS: CT images compressed at a ratio as high as 20:1 were acceptable for primary diagnosis of CAC. There was no significant difference in the detection accuracy for CAC between JPEG and wavelet algorithms at the compression ratios up to 20:1. CT images were more vulnerable to image blurring on the wavelet compression at relatively lower ratios, and "blocking" artifacts occurred on the JPEG compression at relatively higher ratios. CONCLUSION: JPEG and wavelet algorithms allow compression of CT images without compromising their diagnostic value at ratios up to 20:1 in detecting small linear or spotted high attenuation lesions such as CAC, and there was no difference between the two algorithms in diagnostic accuracy.

Adult↗

PubMed2001

The effect of MPEG audio compression on multidimensional set of voice parameters.

The MPEG-1 Layer 3 compression schema of audio signal, or commonly known as mp3, has caused a great impact in recent years as it has reached high compression rates while also conserving a high sound quality. Previous listening tests have shown that music and speech samples compressed at high bitrates are virtually indistinguishable from the original samples, but very little is known about how compression acoustically affects the voice signal. In Experiment 1 the spectral composition of original and compressed speech signals were analyzed by means of the Long-Term Average Spectrum using the Computerized Speech Laboratory (Kay Elemetrics Corp. (Pine Brook, NJ, USA)). In Experiment 2 a set of 29 voice parameters extracted by using the Multidimensional Voice Program of Kay are compared between original and compressed voices at different bitrates. Results show a high fidelity at high-bitrate compressions (128 and 160 kbit per second (kbps)) both in voice parameters and the amplitude-frequency spectrum. Compressions at 64 kbps or lower bitrates introduces substantial modifications in the voice signal, seriously altering parameters related with tremor, amplitude perturbation, noise, subharmonics and voice irregularities, likewise the signal spectrum is altered in its high frequency region.

Adult↗

PubMed1999

Effects of crystalline form on the tableting compression mechanism of phenobarbital polymorphs.

The effects of the polymorphic form on the compression mechanism of forms A, B, and F of phenobarbital were investigated using a compression simulator, mercury porosimetry, X-ray diffraction analysis, BET gas absorption method, and scanning electron microscopic (SEM) photography. The order of tablet hardness obtained from all phenobarbital polymorphs was form A > form B > form F in accordance with that of the specific surface area. The Cooper and Eaton method was applied to evaluate two individual compression processes: particle rearrangement (phase I) and fragmentation and/or deformation (phase II). The parameters for compression processes were calculated using a nonlinear regression analyses program, and the compression energies of phases I and II were calculated from these parameters. The relationship between specific surface area after compression and compression energy at phase I showed a good linear correlation, but their ratio did not. In contrast, the specific surface area ratio showed a linear relationship with the compression energy on phase II, but again the ratio of these two parameters did not. The tablet hardness showed a linear relationship with the specific surface area ratio, but not with the specific surface area. Again, the ratio of these two parameters did not show a linear relationship.

Anticonvulsants↗

PubMed1995

The effect of multichannel compression on vowel and stop-consonant discrimination in normal-hearing and hearing-impaired subjects.

OBJECTIVE: Multichannel compression (MCC) processing can alter the speech spectrum, perhaps reducing spectral contrasts that are important for the discrimination of certain speech sounds. The effect of MCC processing on the discrimination of vowels and voiced stop consonants was studied. DESIGN: Vowels and voiced stop consonants were MCC-processed in two ways: 1) FLAT MCC having the same compression ratio in each channel, and 2)SHAPED MCC having compression ratios in each channel adjusted to the auditory area of the particular subject. The stimuli were processed both ways using 2, 4, 8, 16, and 31 independent compression channels. Unprocessed and linearly amplified stimuli were used as control conditions. Normal-hearing and hearing-impaired subjects were tested for changes in discrimination performance as a function of the MCC processing parameters. RESULTS: When the MCC processing was adjusted specifically for an individual hearing impared subject, no negative effect of increasing numbers of channels (2 to 31)was found. In the case of FLAT MCC processing, increasingly degraded discrimination performance was found for both subject groups as the compression ratio increased and as the number of channels increased. There was also a strong interaction between the effects of the number of channels and the compression ratio, with the negative effects of increasing numbers of channels being much greater at the highest compression ratio. CONCLUSIONS: Negative effects of MCC were found only for very extreme MCC conditions. MCC processing with compression ratios adjusted in each channel for the individual subject, and having as many as 31 channels, revealed no negative effects on vowel or voiced stop-consonant discrimination. These results do not support the prevalent view that MCC with more than two or three channels will be detrimental and should encourage further research on MCC processing with larger numbers of channels.

Auditory Threshold↗

PubMed1998

Compression-induced degeneration of the intervertebral disc: an in vivo mouse model and finite-element study.

STUDY DESIGN: An in vivo study of the biologic and biomechanical consequences of static compressive loading on the mouse tail intervertebral disc. OBJECTIVES: To determine whether static compression in vivo alters the biologic activity of the disc and leads to diminished biomechanical performance. SUMMARY OF BACKGROUND DATA: Static compressive stress that exceeds the disc's swelling pressure is known to change hydration and the intradiscal stress distribution. Alterations in hydration and stress have been associated with changes in disc cell activity in vitro and in other collagenous tissues in vivo. METHODS: Mouse tail discs were loaded in vivo with an external compression device. After 1 week at one of three different stress levels, the discs were analyzed for their biomechanical performance, morphology, cell activity, and cell viability. A second group of mice were allowed to recuperate for 1 month after the 1-week loading protocol to assess the disc's ability to recover. As an aid to interpreting the histologic and biologic data, finite-element analysis was used to predict region-specific changes in tissue stress caused by the static loading regimen. RESULTS: With increasing compressive stress, the inner and middle anulus became progressively more disorganized, and the percentage of cells undergoing apoptosis increased. The expression of Type II collagen was suppressed at all levels of stress, whereas the expression of aggrecan decreased at the highest stress levels in apparent proportion to the decreased nuclear cellularity. Compression for 1 week did not affect the disc bending stiffness or strength but did increase the neutral zone by 33%. As suggested by the finite-element model, during sustained compression, tension is maintained in the outer anulus and lost in the inner and middle regions where the hydrostatic stress was predicted to increased nearly 10-fold. Discs loaded at the lowest stress recovered anular architecture but not cellularity after 1 month of recuperation. Discs loaded at the highest stress did not recover anular architecture, displaying islands of cartilage cells in the middle anulus at sites previously populated by fibroblasts. CONCLUSIONS: The results of the current project demonstrate that static compressive loading initiates a number of harmful responses in a dose-dependent way: disorganization of the anulus fibrosus; an increase in apoptosis and associated loss of cellularity; and down regulation of collagen II and aggrecan gene expression. The finite element model used in this study predicts loss of collagen fiber tension and increased matrix hydrostatic stress in those anular regions observed to undergo programmed cell death after 1 week of loading and ultimately become populated by chondrocytes after one month of recuperation. This correspondence conforms with the suggestions of others that the cellular phenotype in collagenous tissues is sensitive to the dominant type of tissue stress. Although the specific mechanisms by which alterations in tissue stress lead to apoptosis and variation in cell phenotype remain to be identified, our results suggest that maintenance of appropriate stress within the disc may be an important basis for strategies to mitigate disc degeneration and initiate disc repair.

Aggrecans↗

PubMed1999

A follower load increases the load-carrying capacity of the lumbar spine in compression.

STUDY DESIGN: An experimental approach was used to test human cadaveric spine specimens. OBJECTIVE: To assess the response of the whole lumbar spine to a compressive follower load whose path approximates the tangent to the curve of the lumbar spine. SUMMARY OF BACKGROUND DATA: Compression on the lumbar spine is 1000 N for standing and walking and is higher during lifting. Ex vivo experiments show it buckles at 80-100 N. Differences between maximum ex vivo and in vivo loads have not been satisfactorily explained. METHODS: A new experimental technique was developed for applying a compressive follower load of physiologic magnitudes up to 1200 N. The experimental technique applied loads that minimized the internal shear forces and bending moments, made the resultant internal force compressive, and caused the load path to approximate the tangent to the curve of the lumbar spine. RESULTS: A compressive vertical load applied in the neutral lordotic and forward-flexed postures caused large changes in lumbar lordosis at small load magnitudes. The specimen approached its extension or flexion limits at a vertical load of 100 N. In sharp contrast, the lumbar spine supported a load of up to 1200 N without damage or instability when the load path was tangent to the spinal curve. CONCLUSIONS: Until this study, an experimental technique for applying compressive loads of in vivo magnitudes to the whole lumbar spine was unavailable. The load-carrying capacity of the lumbar spine sharply increased under a compressive follower load, as long as the load path remained within a small range around the centers of rotation of the lumbar segments. The follower load path provides an explanation of how the whole lumbar spine can be lordotic and yet resist large compressive loads. This study may have implications for determining the role of trunk muscles in stabilizing the lumbar spine.

Adult↗

PubMed2001

Lumbar spine disc height and curvature responses to an axial load generated by a compression device compatible with magnetic resonance imaging.

STUDY DESIGN: Axial load-dependent changes in the lumbar spine of supine healthy volunteers were examined using a compression device compatible with magnetic resonance imaging. OBJECTIVE: To test two hypotheses: Axial loading of 50% body weight from shoulder to feet in supine posture 1) simulates the upright lumbar spine alignment and 2) decreases disc height significantly. SUMMARY OF BACKGROUND DATA: Axial compression on the lumbar spine has significantly narrowed the lumbar dural sac in patients with sciatica, neurogenic claudication or both. METHODS: Using a device compatible with magnetic resonance imaging, the lumbar spine of eight young volunteers, ages 22 to 36 years, was axially compressed with a force equivalent to 50% of body weight, approximating the normal load on the lumbar spine in upright posture. Sagittal lumbar magnetic resonance imaging was performed to measure intervertebral angle and disc height before and during compression. RESULTS: Each intervertebral angle before and during compression was as follows: T12-L1 (-0.8 degrees +/- 2.5 degrees and -1.5 degrees +/- 2.6 degrees ), L1-L2 (0.7 degrees +/- 1.4 degrees and 3.3 degrees +/- 2.9 degrees ), L2-L3 (4.7 degrees +/- 3.5 degrees and 7.3 degrees +/- 6 degrees ), L3-L4 (7.9 degrees +/- 2.4 degrees and 11.1 degrees +/- 4.6 degrees ), L4-L5 (14.3 degrees +/- 3.3 degrees and 14.9 degrees +/- 1.7 degrees ), L5-S1 (25.8 degrees +/- 5.2 degrees and 20.8 degrees +/- 6 degrees ), and L1-S1 (53.4 degrees +/- 11.9 degrees and 57.3 degrees +/- 16.7 degrees ). Negative values reflect kyphosis, and positive values reflect lordosis. A significant difference between values before and during compression was obtained at L3-L4 and L5-S1. There was a significant decrease in disc height only at L4-L5 during compression. CONCLUSIONS: The axial force of 50% body weight in supine posture simulates the upright lumbar spine morphologically. No change in intervertebral angle occurred at L4-L5. However, disc height at L4-L5 decreased significantly during compression.

Adult↗

PubMed2001

A randomized trial of the long-term effects of digital ocular compression in the late postoperative period.

PURPOSE: To determine whether digital ocular compression is a viable technique to lower intraocular pressure in patients at least 3 months after trabeculectomy. PATIENTS AND METHODS: A 6-month prospective, randomized, controlled, single-masked trial of 29 patients who underwent a trabeculectomy at the Glaucoma Service of Wills Eye Hospital. Patients were assigned to two groups: ocular compression or cheekbone compression (control group). The ocular compression group performed compression to the operated eye three times a day in the pattern of 10 seconds of pressure, 5 seconds of rest, and 10 seconds of pressure. Pressure was applied with the index finger through the closed lid to the center of the cornea. Pressure was steady and firm, but not painful. No massaging was performed. The cheekbone compression group applied pressure to the zygomatic arch with an identical style and frequency. RESULTS: At 6 months, the change in mean intraocular pressure for the ocular compression group was 0.25 mm Hg compared with -0.44 mm Hg for the control group (P = 0.7). A few patients in both groups experienced large swings in intraocular pressure and mild to moderate discomfort. CONCLUSION: Ocular compression had little to no success in the long-term management of increased intraocular pressure in the late postoperative period in this study.

Aged↗

PubMed2002

Therapy with mud compresses for knee osteoarthritis: comparison of natural mud preparations with mineral-depleted mud.

Mud pack therapy is an alternative mode of treatment for rheumatic diseases. It is based on the application of heated mud packs to the entire body or to specific areas, such as over joints. The aim of the current study was to evaluate the efficacy of treatment with mud compresses at patients' homes for osteoarthritis of the knee. Fifty-eight patients with osteoarthritis of the knee were enrolled in a prospective, double-blinded, controlled study. Forty patients were treated with natural mineral-rich mud compresses and 18 patients were treated with mineral-depleted mud compresses. Mud compresses were applied 5 times each week during 3 weeks for a total of 15 treatments. Patients were assessed at baseline, at completion of the 3-week treatment period, and twice after the conclusion of the treatment period-after 1 month and after 3 months. The main outcome measures were the Lequesne Index of severity of knee osteoarthritis, patient self-assessment of pain, and severity of knee pain on a visual analog scale. A reduction of 20% or more in the pain scores was considered clinically significant. In the group treated with natural mud compresses, a significant reduction in knee pain was observed at all assessments. Similarly, improvement in the Lequesne Index was seen at the end of therapy and a month after treatment. In the control group, given mineral-depleted mud compresses, no significant change in knee pain was seen at any assessment. Improvement in the Lequesne Index was seen 1 and 3 months after completion of the therapy, but not at the end of therapy. Seventy-two percent of the patients in the treatment group had an improvement of >20% in self-assessment of knee pain, compared with 33% in the control group (p = 0.005). The data suggest that treatment with mud compresses, but only in their natural form, temporarily relieves pain in patients with osteoarthritis of the knees. We believe that treatment with mud compresses might augment conventional medical therapy in these patients.

Journal Article↗

PubMed2005

Osteogenic protein-1 (osteogenic protein-1/bone morphogenetic protein-7) inhibits degeneration and pain-related behavior induced by chronically compressed nucleus pulposus in the rat.

STUDY DESIGN: To study the therapeutic efficacy of intradiscal injection of osteogenic protein-1 (OP-1) to reduce degeneration and associated discogenic pain. OBJECTIVE: To evaluate if intradiscal injection of OP-1 can reverse disc degeneration and reduce hyperalgesia, a pain-related behavior. SUMMARY OF BACKGROUND DATA: We showed that induction of hyperalgesia was higher in rats exposed to compressed nucleus pulposus (NP). It has been reported that intradiscal injection of OP-1 stimulates synthesis of proteoglycans and collagen in normal intervertebral discs. METHODS: Rats were divided into several groups. In the sham group, the rings of an Ilizarov-type apparatus were only applied to the tail without compression. In the compressed NP group, the apparatus was used to apply chronically compression to the tail. Four weeks after surgery, the NP group was subdivided into 3 groups: saline-treated and OP-1-treated, which was divided into 2 groups (i.e., the continuous compression OP-1 [COP-1] group, in which compression was continuously applied to the tail for 4 weeks after OP-1 treatment and the release compression OP-1 [ROP-1] group, in which compression was released at treatment. Either physiologic saline or OP-1 was injected into the instrumented NP. The treated NP was harvested and applied to the left lumbar nerve roots 4 weeks after injection. Hyperalgesia was measured up to 3 weeks after surgery. The degree of disc degeneration and the appearance of the extracellular matrix in the intervertebral discs were evaluated by histology. RESULTS: Mechanical hyperalgesia was observed in the sham and saline groups, but not in the OP-1 treated group. In the saline group, NP cells became spindle-shaped. In the OP-1 group, the NP cells became swollen with vacuolated cytoplasm, and the content of the extracellular matrix was markedly increased. CONCLUSION: OP-1 injection into degenerative intervertebral disc resulted in the enhancement of the extracellular matrix and the inhibition of pain-related behavior.

Animals↗

PubMed2002

An efficient coding algorithm for the compression of ECG signals using the wavelet transform.

A wavelet-based electrocardiogram (ECG) data compression algorithm is proposed in this paper. The ECG signal is first preprocessed, the discrete wavelet transform (DWT) is then applied to the preprocessed signal. Preprocessing guarantees that the magnitudes of the wavelet coefficients be less than one, and reduces the reconstruction errors near both ends of the compressed signal. The DWT coefficients are divided into three groups, each group is thresholded using a threshold based on a desired energy packing efficiency. A binary significance map is then generated by scanning the wavelet decomposition coefficients and outputting a binary one if the scanned coefficient is significant, and a binary zero if it is insignificant. Compression is achieved by 1) using a variable length code based on run length encoding to compress the significance map and 2) using direct binary representation for representing the significant coefficients. The ability of the coding algorithm to compress ECG signals is investigated, the results were obtained by compressing and decompressing the test signals. The proposed algorithm is compared with direct-based and wavelet-based compression algorithms and showed superior performance. A compression ratio of 24:1 was achieved for MIT-BIH record 117 with a percent root mean square difference as low as 1.08%.

Algorithms↗

PubMed2002

Cascaded differential and wavelet compression of chromosome images.

This paper proposes a new method for chromosome image compression based on an important characteristic of these images: the regions of interest (ROIs) to cytogeneticists for evaluation and diagnosis are well determined and segmented. Such information is utilized to advantage in our compression algorithm, which combines lossless compression of chromosome ROIs with lossy-to-lossless coding of the remaining image parts. This is accomplished by first performing a differential operation on chromosome ROIs for decorrelation, followed by critically sampled integer wavelet transforms on these regions and the remaining image parts. The well-known set partitioning in hierarchical trees (SPIHT) (Said and Perlman, 1996) algorithm is modified to generate separate embedded bit streams for both chromosome ROIs and the rest of the image that allow continuous lossy-to-lossless compression of both (although lossless compression of the former is commonly used in practice). Experiments on two sets of sample chromosome spread and karyotype images indicate that the proposed approach significantly outperforms current compression techniques used in commercial karyotyping systems and JPEG-2000 compression, which does not provide the desirable support for lossless compression of arbitrary ROIs.

Algorithms↗

PubMed1998

Clinical Validation of Digital Image Compression Levels for Fetal Echocardiograms for Telemedicine.

BACKGROUND: Digital telephone transmission of dynamic fetal echocardiographic sequences requires wide bandwidths. To reduce the transmission of nonessential information present in echocardiographic images, compression algorithms have been used and validated for adult echocardiography. The level of compression that retains all diagnostic clinical information must be determined and validated for fetal echocardiographic studies. The purpose of this study was to validate levels of image compression that are diagnostic for fetal echocardiography. METHODS: Twenty previously recorded fetal echocardiograms representing two normal and 18 congenitally abnormal hearts were looped, digitized, and compressed at differing ratios. Images were reviewed in a blinded manner by four experts. Images were scored for diagnosis, diagnostic quality, and technical quality. RESULTS: Forty-four images were viewed. Experts correctly diagnosed 87% of images. There were no images of unacceptable diagnostic quality at a compression ratio of 300 (0%) and 2% at compression ratio of 600:1. CONCLUSIONS: Digital image compression of 300:1 was diagnostic for fetal congenital heart diseases with a variety of defects using cine-looped images. These data support the use of compressed fetal images for telephone transmission with a low bandwidth.

Journal Article↗

PubMed1982

An investigation of the relationship between particle size and compression during capsule filling with an instrumented mG2 simulator.

An instrumented mG2 capsule filling machine simulator has been employed to study the effects of the amount of compression (compression ratio) on the capsule fill weight uniformity and measured compression and ejection stresses. Four size fractions of lactose were studied (mean particle sizes 15.6, 17.8, 37.5 and 155.2 micron). The range of compression over which satisfactory filling could be achieved was large for fine, cohesive powders but decreased with increasing particle size. The lower limit of filling ability was the ability to retain the powder and the amount of compression needed to achieve retention increased with increasing particle size. The upper limit on compression, was the compaction of the powder which prevented the piston acting to cause retention. Large particle sizes were able to undergo only a small change in volume before compaction occurred whilst fine, cohesive powders were considerably more compressible and hence could be filled satisfactorily at higher compression settings.

Capsules↗