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PubMed1997

Iterative function system and genetic algorithm-based EEG compression.

A method for EEG compression is proposed, using Iterative Function System (IFS) and Genetic Algorithms (GAs) with elitist model, keeping the quality sufficiently good for clinical purposes. Compression using IFS is usually called fractal compression. The self transformability property of the EEG signals is assumed and is exploited in the fractal compression technique. To ascertain the self transformability of the EEG signal, some isometric transformations have been applied. The technique described here utilizes Genetic Algorithm that decreases the search space for finding the self similarities in the given signal. This article presents theory and implementation of the proposed method. The fidelity of the reconstructed signal obtained by the present compression algorithm has been assessed both qualitatively and quantitatively. The compression ratios, for the EEG signals in various states, are found to be comparable to the other available techniques for EEG compression. In our method at least 85% data reduction has been achieved.

Algorithms↗

PubMed2001

Multivariate curve resolution of wavelet and Fourier compressed spectra.

The multivariate curve resolution method SIMPLe to use Interactive Self-Modeling Mixture Analysis (SIMPLISMA) was applied to Fourier and wavelet compressed ion-mobility spectra. The spectra obtained from the SIMPLISMA model were transformed back to their original representation, that is, uncompressed format. SIMPULSMA was able to model the same pure variables for the partial wavelet transform, although for the Fourier and complete wavelet transforms, satisfactory pure variables and models were not obtained. Data were acquired from two samples and two different ion mobility spectrometry (IMS) sensors. The first sample was thermally desorbed sodium gamma-hydroxybutyrate (GHB), and the second sample was a liquid mixture of dicyclohexylamine (DCHA) and diethylmethylphosphonate (DEMP). The spectra were compressed to 6.3% of their original size. SIMPLISMA was applied to the compressed data in the Fourier and wavelet domains. An alternative method of normalizing SIMPLISMA spectra was devised that removes variation in scale between SIMPLISMA results obtained from uncompressed and compressed data. SIMPLISMA was able to accurately extract the spectral features and concentration profiles directly from daublet compressed IMS data at a compression ratio of 93.7% with root-mean-square errors of reconstruction < 3%. The daublet wavelet filters were selected, because they worked well when compared to coiflet and symmlet. The effects of the daublet filter width and compression ratio were evaluated with respect to reconstruction errors of the data sets and SIMPLISMA spectra. For these experiments, the daublet 14 filter performed well for the two data sets.

Journal Article↗

PubMed2004

Nonlinear wavelet compression of ion mobility spectra from ion mobility spectrometers mounted in an unmanned aerial vehicle.

Linear and nonlinear wavelet compression of ion mobility spectrometry (IMS) data are compared and evaluated. IMS provides low detection limits and rapid response for many compounds. Nonlinear wavelet compression of ion mobility spectra reduced the data to 4-5% of its original size, while eliminating artifacts in the reconstructed spectra that occur with linear compression, and the root-mean-square reconstruction error was 0.17-0.20% of the maximum intensity of the uncompressed spectra. Furthermore, nonlinear wavelet compression precisely preserves the peak location (i.e., drift time). Small variations in peak location may occur in the reconstructed spectra that were linearly compressed. A method was developed and evaluated for optimizing the compression. The compression method was evaluated with in-flight data recorded from ion mobility spectrometers mounted in an unmanned aerial vehicle (UAV). Plumes of dimethyl methylphosphonate were disseminated for interrogation by the UAV-mounted IMS system. The daublet 8 wavelet filter exhibited the best performance for these evaluations.

Journal Article↗

PubMed2004

Two-dimensional nonlinear wavelet compression of ion mobility spectra of chemical warfare agent simulants.

Ion mobility spectrometry (IMS) affords miniaturized hand-held devices that can be used for monitoring and remote measurement. Because such instruments have limits on storage capacity or bandwidth for wireless transmission, data compression is important. Furthermore, all instruments should be operated with the fastest possible sampling rates because a signal-to-noise gain can be achieved by wavelet compression. Linear wavelet compression (LWC) applied to IMS data may cause peak distortion when the spectra are reconstructed. Nonlinear wavelet compression (NLWC) precisely preserves the peak location (i.e., drift time), height, and shape. IMS data of three chemical warfare simulants, dimethyl methylphosphonate, triethyl phosphate, and dipropyleneglycol monomethyl ether, were collected from an Ion Track ITEMISER and a Graseby Ionics detector CAM. Two-dimensional NLWC was used to compress the IMS data in the drift time and data acquisition dimensions on IMS data of chemical warfare simulants. NLWC was applied to achieve a compression factor of 1/128 with relative error of root-mean-square of <0.25% in the reconstructed spectra. A method was also developed and evaluated for optimizing compression.

Journal Article↗

PubMed2000

Principles and application of ultrasound in pharmaceutical powder compression.

The use of ultrasound during the tableting of pharmaceutical powders is a new concept. However, in the metallurgy, plastic, and ceramic industries, ultrasound-assisted compression of materials has been known for some years. Ultrasound improves the characteristics of the compression process leading to optimized mechanical strength of the compacts without applying excessive compression force. Therefore, problems associated with high-pressure compression in tableting can be overcome and tablets may be manufactured more economically and consistently with the aid of ultrasound compared to conventional pressure processes. Although great progress in the theoretical understanding of the ultrasound-assisted powder compression process has been made since the late 1960s, the need for further research in the area of ultrasound application during pharmaceutical powder compression is essential. Further investigations on a wide range of drugs and excipients, to expand the usefulness and scope of the ultrasound-assisted technique, and to understand the complex phenomena involved in the process, are needed. In this article the principles, advantages, and limitations of the application of ultrasonic vibrations during pharmaceutical powder compression is reviewed with the hope that this article can contribute to, and stimulate research in the area.

Drug Industry↗

PubMed2000

Analysis of the compression mechanics of pharmaceutical agglomerates of different porosity and composition using the Adams and Kawakita equations.

PURPOSE: To analyze the mechanics of some pharmaceutical agglomerates during uniaxial confined compression by using compression parameters derived from the Heckel, Kawakita and Adams equations, and to study the influence of these compression parameters on the tablet-forming ability of agglomerates. METHODS: Force and displacement data sampled during in-die compression of agglomerates was used to calculate compression parameters according to the Heckel (sigmay), Kawakita (1/b and a), and Adams (tau0') equations. Mechanical strength of single agglomerates as well as the air permeability and tensile strength of tablets prepared from them were also determined. RESULTS: Sigmay- from the Heckel equation did not differ between agglomerates of different porosity. Both 1/b and tau0' varied with agglomerate porosity and composition. These two compression parameters were linearly related to each other. No general correlation was found between 1/b and tau0' and the strength of single agglomerates. The two parameters were related to the intergranular pore structure and tensile strength of tablets formed from the agglomerates. CONCLUSIONS: 1/b and tau0' may be interpreted as measures of the agglomerate shear strength during uniaxial confined compression, and as such they may be used as indicators of the tabletting performance of the agglomerates.

Algorithms↗

PubMed2000

Rapid intermittent compression increases skin circulation in chronically ischemic legs with infra-popliteal arterial obstruction.

BACKGROUND: Intermittent pneumatic compression (IPC) has been shown, by duplex, to increase popliteal artery flow in normal legs and in legs with superficial femoral artery occlusion. The objective of this study was to see if IPC improves distal circulation in legs with severe infra-popliteal disease. PATIENTS AND METHODS: Sixteen chronically ischemic legs with arteriographically demonstrated crural or pedal disease were studied during compression with an ArtAssist compression-device. This device delivers rapid compression of the foot and calf. Cutaneous laser-Doppler flux was measured continuously at the dorsal aspect of the distal forefoot. The findings were compared to those in thirteen normal controls of similar age. RESULTS: In ischemic legs, the spontaneous changes in skin-flux are minimal: mean resting flux in sitting position was 0.87 +/- 0.46 AU (Arbitrary Units). Upon activation of the compression device the maximum flux increased to 4.55 +/- 1.35 AU. The difference was statistically significant (p < 0.001). This response was similar to that in normal controls. CONCLUSION: Arterial flow augmentation upon compression is associated with increased skin-flux. This response remains present in severe disease of the crural outflow-arteries. Further investigation to define the role of intermittent compression for management of chronic arterial disease is warranted.

Aged↗

PubMed2003

A randomized comparison of a percutaneous suture device versus manual compression for femoral artery hemostasis after PTCA.

BACKGROUND: The prolonged bed rest following femoral sheath removal after PTCA is a source of discomfort for the patient. We designed a randomized study to evaluate the efficacy and safety of an arterial suture device developed to percutaneously close the vascular access site after PTCA, allowing immediate sheath removal and early ambulation, compared to manual compression. METHODS: After successful PTCA, patients were randomized to manual compression or immediate femoral percutaneous closure. Exclusion criteria were arteritis, age > 80 years and > 3 previous femoral punctures on the same side. The two-needle device was used for the 6F sheath removal and the four-needle device for the 8F sheath. Ambulation was allowed 4 hours after the arterial suture. RESULTS: One hundred and sixty-seven patients (59 +/- 10 years, 81% males) were randomized to suture device (n = 91) or to manual compression (n = 76). The two groups were similar in terms of age, sex, size of sheath, number of patients with stent implantation (62 vs 61%), procedural anticoagulation. Procedural duration was 8 +/- 6 minutes with percutaneous suture versus 25 +/- 11 minutes with manual compression (P < 0.0001). Procedural success with percutaneous suture was 93% whereas six technical failures were treated with prolonged manual compression. Nonsurgical hematoma occurred in five patients (5%) with the suture device and in two (3%) with manual compression with no need for blood transfusion (P = NS). Uneventful blood oozing occurred in 11 patients (12%) with percutaneous suture and in only 2 (3%) with manual compression (P < 0.06). The tolerance of the hemostasis procedure and the length of post-procedure hospital stay (40 +/- 32 hours) were similar in the two groups. CONCLUSION: Percutaneous suture of the femoral artery, allows immediate closure of femoral puncture sites after PTCA, without increasing the incidence of vascular complications. The use of this device should allow earlier discharge and subsequent cost savings.

Aged↗

PubMed1997

Perceptual adjustment to highly compressed speech: effects of talker and rate changes.

This study investigated the perceptual adjustments that occur when listeners recognize highly compressed speech. In Experiment 1, adjustment was examined as a function of the amount of exposure to compressed speech by use of 2 different speakers and compression rates. The results demonstrated that adjustment takes place over a number of sentences, depending on the compression rate. Lower compression rates required less experience before full adjustment occurred. In Experiment 2, the impact of an abrupt change in talker characteristics was investigated; in Experiment 3, the impact of an abrupt change in compression rate was studied. The results of these 2 experiments indicated that sudden changes in talker characteristics or compression rate had little impact on the adjustment process. The findings are discussed with respect to the level of speech processing at which such adjustment might occur.

Female↗

PubMed2000

Pressor response to pulsatile compression of the rostral ventrolateral medulla mediated by nitric oxide and c-fos expression.

It has been reported that neurovascular compression of the rostral ventrolateral medulla might be causally related to essential hypertension. Recently, we found that pulsatile compression of the rostral ventrolateral medulla increases sympathetic nerve activity and elevates arterial pressure via activation of glutamate receptors in rats. We also found that increases in sympathetic and cardiovascular activities by microinjection of L-glutamate into the rostral ventrolateral medulla are mediated by c-fos expression-related substance(s) following activation of the nitric oxide-cyclic GMP pathway. Herein, we investigated whether responses to pulsatile compression are mediated by local activation of the nitric oxide-cyclic GMP pathway and/or c-fos expression-related substance(s) in rats. Increases in arterial pressure (15+/-1 mmHg), heart rate (9+/-1 b.p.m.), and sympathetic nerve activity (% change: 8.5+/-1.1%) induced by pulsatile compression were partially but significantly inhibited after local microinjection of a nitric oxide synthase inhibitor, L-N(G)-nitroarginine methyl ester (8+/-2 mmHg, 1+/-1 b.p.m., 4.0+/-1.3%; P<0.05 vs compression without pretreatment) or 7-nitroindazole (7+/-2 mmHg, 2+/-1 b.p.m., 4.0+/-1. 5%; P<0.05), or a soluble guanylate cyclase inhibitor, methylene blue (9+/-1 mmHg, 4+/-1 b.p.m., 4.1+/-1.4%; P<0.05). In addition, increases in arterial pressure, heart rate, and sympathetic nerve activity by pulsatile compression were significantly reduced 6 h after microinjection of antisense oligodeoxynucleotide to c-fos mRNA (2+/-2 mmHg, 2+/-1 b.p.m., 1.0+/-1.0%; P<0.05 vs sense oligodeoxynucleotide). These results suggest that increases in sympathetic and cardiovascular activities induced by pulsatile compression of the rostral ventrolateral medulla are mediated, at least in part, by local activation of the nitric oxide-cyclic GMP pathway and c-fos expression-related substance(s) in rats.

Animals↗

PubMed1988

Amplitude compression and profound hearing loss.

Nine subjects with prelingually acquired, sensorineural, hearing loss were given a three-interval, forced-choice, test of speech pattern contrast perception under two amplification conditions. The first involved adjustment of the low and high frequency outputs of a two-channel Master Hearing Aid to each subject's highest comfortable level, but without compression of the short-term dynamic range of the signal. The second involved the additional compression of a 30 dB input range into the subject's dynamic range of hearing, as measured by the difference between speech awareness threshold and highest comfortable level, in each of the two channels. One of the subjects performed much better with compression than without. Among the other eight, however, there was a small but significant reduction of performance when compression was introduced. It is proposed that the one positive result is due to the increased audibility of speech cues made possible by amplitude compression. It is further proposed that the negative results are due mainly to the distortions of time-intensity cues introduced by amplitude compression. The results suggest that, in terms of potential access to meaningful speech cues, the addition of amplitude compression, to an otherwise optimized signal, is unnecessary, or even detrimental, for most profoundly deaf subjects, but could be beneficial for some.

Adolescent↗

PubMed2000

Multi-channel compression and speech intelligibility in industrial noise.

This study examined how various forms of compression affect speech intelligibility in moderately high levels of industrial noise. Thirteen listeners with high-frequency sensorineural hearing loss were fit with a digital hearing aid programmed to operate in three modes of compression: compression limiting, compression of low frequencies only (BILL), and compression of high frequencies only (TILL). For each of these conditions, listeners attempted to recognize CID W-22 monosyllabic words delivered in a background of recorded industrial noise. Word recognition was also measured in quiet for the compression-limiting condition. The highest word identification scores were obtained in quiet (80.9%). Of the three conditions in which background noise was present, the mean score was highest for TILL compression (52.4%), and lowest for BILL (39.7%). Representative time-weighted average (TWA) exposures for each of the aided noise conditions were determined by means of a procedure outlined previously by the first author. The projected 8-hour amplified TWA with the hearing aid programmed to the TILL configuration was 94 dBA, whereas TWAs for the linear and BILL configurations were each 104 dBA. Thus, the highest intelligibility and lowest noise exposures were obtained with the aid in the TILL mode.

Adult↗

PubMed2002

Indirect digital images: limit of image compression for diagnosis in endodontics.

AIM: To analyse the impact of the loss of information that results from the compression of a file containing a radiographic image. METHODOLOGY: Fourteen intraoral radiographs were digitized employing an AGFA ARCUS II scanner at an optical resolution of 300 ppi and with a grey scale of 8 bytes. The images were stored in Tagged Image File Format (TIFF). The files were compressed with no information loss with the WinZip 8.0 program. Compression with information loss was performed using the Photoshop 5.0 program (Adobe Systems Inc., San José, CA. USA) and the Joint Photograph Expert (Group (JPEG) format. Each of the images was compressed to one of the 11 qualities available (10-0). An expert performed the qualitative analysis. The quantitative analysis involved digital subtraction with each of the JPEG images to yield a new image using Photoshop 5.). The histograms of grey values were submitted to statistical analysis. The mean and standard deviation were calculated for each image. RESULTS: The data revealed that a JPEG lossy compression, six times smaller than the original TIFF, is compatible with diagnostic applications. CONCLUSIONS: The compression ratio calculated as the quotient between the file sizes and the standard deviation of the values corresponding to the image that resulted from digital subtraction may be employed to assess the outcome of the compression process and guarantee adequate quality.

Artifacts↗

PubMed2000

Acceptable levels of digital image compression in chest radiology.

The introduction of picture archival and communications systems (PACS) and teleradiology has prompted an examination of techniques that optimize the storage capacity and speed of digital storage and distribution networks. The general acceptance of the move to replace conventional screen-film capture with computed radiography (CR) is an indication that clinicians within the radiology community are willing to accept images that have been 'compressed'. The question to be answered, therefore, is what level of compression is acceptable. The purpose of the present study is to provide an assessment of the ability of a group of imaging professionals to determine whether an image has been compressed. To undertake this study a single mobile chest image, selected for the presence of some subtle pathology in the form of a number of septal lines in both costphrenic angles, was compressed to levels of 10:1, 20:1 and 30:1. These images were randomly ordered and shown to the observers for interpretation. Analysis of the responses indicates that in general it was not possible to distinguish the original image from its compressed counterparts. Furthermore, a preference appeared to be shown for images that have undergone low levels of compression. This preference can most likely be attributed to the 'de-noising' effect of the compression algorithm at low levels.

Humans↗

PubMed1999

Movement-related variation in forces under compression stockings.

OBJECTIVES: Compression therapy is widely used in the treatment of venous leg ulcers, but the efficacy of this treatment is variable. Assessment of variation in compression forces associated with movement may help to elucidate the mechanism of action of compression therapy. The aim of this study was to develop and apply a system to investigate forces under compression stockings during movement. METHOD: Three sensors were placed on the medial aspect of the left leg on six healthy volunteers to monitor forces under class 2 (Continental European classification) compression stockings. Data were recorded during dorsiflexion and plantar flexion of the left foot and also during short periods of walking. RESULTS: Changes in pressure were observed, associated with dorsiflexion and plantar flexion of the foot. These changes were dependent on sensor position. Changes in pressure during walking were also position-dependent and of variable duration. CONCLUSIONS: The system enables forces associated with compression therapy to be examined during movement and may thus be of value in further understanding its mechanism of action. Foot movement can be associated with clear changes in pressure under compression stockings and rapid changes in pressure may occur during walking.

Adult↗

PubMed1994

Endoscopic ultrasonography in the diagnosis of extraluminal compressions mimicking gastric submucosal tumors.

We evaluated the diagnostic usefulness of endoscopic ultrasonography (EUS) in 19 patients with extragastric compression. In these 19 cases, the causes of the compression were normal organs or structures in 16 cases (splenic artery 7, spleen 5, normal pancreas two, gall-bladder one, colon one) and extraluminal tumors in three cases (two hepatic hemangiomas, one neurogenic tumor of the omentum minor). In 12 of these 19 cases, the site of the submucosal compression was located in the upper part of the stomach. All three tumors were confirmed by other procedures, and in the remaining 16 patients with compression by normal organs or structures, negative follow-up results (mean: 14 months) supported the absence of a true submucosal tumor. EUS was 100% accurate in the differentiation of an extragastric compression from a submucosal tumor, and in the identification of the compressing organ. EUS was also far superior to other procedures, such as ultrasonography and CT. It significantly shortens the diagnostic procedure, especially in patients with compressions by normal extraluminal structures, making other diagnostic modalities unnecessary.

Adult↗

PubMed1995

[Color Doppler-guided compression of pseudoaneurysms after arterial puncture. Early and late results].

Sixteen pseudoaneurysms occurred after 1796 femoral arterial punctures for diagnostic coronary angiography and/or angioplasty, performed between 1. 1. 1993 and 25. 3. 1994. One additional patient with pseudoaneurysm had undergone a femoral arterial puncture at another hospital. Primary colour Doppler-directed compression of the pseudoaneurysm (15-minute compression followed by 10-minute compressions, as needed) was successful in 16 patients. There was one recurrence, after five days, which was successfully and lastingly treated by another compression. Primary thrombosing by compression of the pseudoaneurysm failed in only one patient, but after spontaneous thrombosis achieved by a compression bandage no flow was demonstrable on the following day. Clinical examination and/or colour Doppler sonography was performed on all patients a mean of 84 days (5 days to 6 months) after successful treatment: no recurrence was recorded. There were no significant early or late complications. These data indicate that colour Doppler-monitored compression of femoral-artery pseudoaneurysm can be considered the treatment of choice, with few exceptions, for this not rare complication of arterial catheterization.

Aneurysm, False↗

PubMed1982

[New method of preventing thrombosis: Intermittent sequential high-pressure leg compression (author's transl)].

The effect of sequential pneumatic leg compression on venous flow velocity was studied in 25 patients. At the usual pressures of 35-55 mm Hg, venous flow velocity was only 175% of control value, but 366% when pressures were between 90 and 100 mm Hg. The incidence of postoperative thrombosis was studied on three groups of patients. In 24 patients, receiving sequential compression prophylaxis with 90-100 mm Hg, there was one case of thrombosis, while there were three cases among the 25 patients with 35 mm Hg compression and three in the 25 receiving 5000 unit of heparin three times daily, Sequential intermittent compression with high pressures, ten compression cycles three times daily, is recommended for all patients unable to undertake active prophylactic measures. An absolute indication exists in those patients which can no be mobilised and those in whom there are additional contraindications to the use of anticoagulants. Sequential compression is no alternative to antithrombosis stockings. These must be worn from the day of hospitalisation until discharge, also during the period of pneumatic compression.

Bandages↗