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PubMed1999

A chaos-based model for low complexity predictive coding scheme for compression and transmission of electroencephalogram data.

A method for low complexity, low bit rate transmission of EEG (electroencephalogram) data, based on chaotic principles, is presented. The EEG data is assumed to be generated by a non-linear dynamical system of E dimensions. The E dynamical variables are reconstructed from the one-dimensional time series by the process of time-delay embedding. A model of the form X[n + 1] = F(X[n], X[n - 1], ... , X[n - p]) is fitted for the data in the E-dimensional space and this model is used as predictor in the predictive coding scheme for transmission. This model is able to give a reduction of nearly 50% of the dynamic range of the error signal to be transmitted, with a reduced complexity, when compared to the conventionally used linear prediction method. This implies that a reduced bit rate of transmission with a reduced complexity can be obtained. The effects of variation of model parameters on the complexity and bit rate are discussed.

Adult↗
PubMed2000

Simulation of disaster recovery of a picture archiving and communications system using off-site hierarchal storage management.

The purpose of this communication is to report on the testing of the disaster recovery capability of our hierarchical storage management (HSM) system. Disaster recovery implementation is a requirement of every mission-critical information technology project. Picture archiving and communications systems (PACS) certainly falls into this category, even though the counterpart, conventional film archive, has no protection against fire, for example. We have implemented a method for hierarchical storage with wavelet technology that maximizes on-site case storage (using lossy compression), retains bit-preserved image data for legal purposes, provides an off-site backup (lossless bit-preserving wavelet transform), and provides for disaster recovery. Recovery from a natural (earthquake and subsequent fire) or technical (system crash and data loss) disaster was simulated by attempting to restore from the off-site image and database backup to clean core PACS components. The only existing loaded software was the operating system. The database application was reloaded locally, and then the database contents and image store were loaded from the off-site component of the HSM system. The following measurements were analyzed: (1) the ability to recover all data; (2) the integrity of the recovered database and image data; (3) the time to recover the database relative to the number of studies and age of the archive, as well as bandwidth between the local and remote site; and (4) the time to recover image data relative to compression ratio, number of studies, number of images, and time depth of the archive. This HSM system, which maximizes on-site storage, maintains a legal record, and provides off-site backup, also facilitates disaster recovery for a PACS.

Computer Storage Devices↗
PubMed1994

Wavelet compression and segmentation of digital mammograms.

An initial evaluation of Haar wavelets is presented in this study for the compression of mammographic images. Fifteen mammograms with 105 microns/pixel resolution and varying dynamic range (10 and 12 bits per pixel) containing clustered microcalcifications were compressed with two different rates. The quality and content of the compressed reconstructed images was evaluated by an expert mammographer. The visualization of the cluster was on the average good but degraded with increasing compression because of the discontinuities introduced by these types of wavelets as the compression rate increases. However, the artifacts in the decoded images were seen as totally artificial and were not misinterpreted by the radiologist as calcifications. The classification of the parenchymal densities did not change significantly but the morphology of the calcifications was increasingly distorted as the compression rate increased leading to lower estimates of the suspiciousness of the cluster and higher uncertainties in the diagnosis. The uncompressed and two sets of compressed images were also processed by a wavelet method to extract the calcifications. Despite the fact that the segmentation algorithm generated several false-positive signals in highly compressed images, all true clusters were successfully segmented indicating that the compression process preserved the features of interest. Our preliminary results indicated that wavelets could be used to achieve high compression rates of mammographic images without losing small details such as microcalcification clusters as well as detect the calcifications from either the uncompressed or compressed reconstructed data. Further research and application of multiresolution analysis to digital mammography is continuing.

Algorithms↗
PubMed2006

Development and evaluation of different methods to assess download and display time of image web systems.

OBJECTIVES: The aim of this study was to develop and verify different methods of measuring time-to-display (TTD) for radiological images with image web systems (IWS). The process should be automatable in order to repeatedly perform a large number of measurements without human interaction. MATERIALS AND METHODS: Three methods were defined and compared with respect to usability, stability, and quality of results. Method 1 was based on Windows 2000 Performance Monitor, whereas method 2 employed phototransistors taped to the screen and connected to a separate PC. A software tool developed for method 3, which used Windows application programming interface (API) function, calls to read the color code assigned to specific pixels on the screen. RESULTS: Method 3 proved to be the most reliable and easy to automate. The accuracy is practically equivalent to method 2, but it proved to be far more automatable. Method 1 produced the largest mean error, was easily disturbed, but was also easy to set up and provided additional insights into the system's architecture especially if combined with method 3. CONCLUSIONS: To measure the performance of image distribution systems, any of these methods can be used, but method 3 proved to be superior.

Data Compression↗
PubMed1996

Infection after open reduction and internal fixation with dynamic compression plates--clinical and experimental data.

Infection rates for open reduction and internal fixation (ORIF) with the DCP in clinical studies are based on heterogeneous data on general risk factors and do not take into account the direct effect of the implant (material, design, surface, technique). The initial degree of bacterial contamination is generally unknown and the applied definition of the term infection is not mentioned. In our own prospective randomized clinical study including 281 cases of ORIF with the DCP (154 steel vs 127 titanium), the influence of the implant material on susceptibility to local infection was examined in relation to initial bacteria contamination (109 non-contaminated / 172 contaminated). Although in the group of contaminated DCPs the difference in the infection rates for stainless steel (sSt) and commercially pure titanium (cpTi) showed no statistical significance, a tendency was apparent. In an animal experiment, the lower rates of infection for c.p.Ti-DCP compared to sSt-DCP in the presence of a local bacterial challenge could be demonstrated with statistical significance. The need for further experimental research in the field of implant related local infection after ORIF will be discussed and strategies for further investigations proposed.

Animals↗
PubMed1977

Evaluation of polymeric materials for maxillofacial prosthetics.

The methods for initial evaluation of a new prospective maxillofacial prosthetic material, MDX-4-4210, have been described and tensile and compressive test data have been obtained. Evaluation of the data indicates that this is a promising material with significant potential for use in maxillofacial prosthetics. Further studies of the material's biologic implant compatibility, its chemical and environmental stabilities, and its clinical performance are being done.

Elasticity↗
PubMed1989

Aortic diameter and pressure-flow sequence identify mechanism of blood flow during external chest compression in dogs.

Aortic flow and pressure relations and aortic diameter were examined during sinus rhythm, internal cardiac massage, vest cardiopulmonary resuscitation, conventional manual cardiopulmonary resuscitation and high impulse manual cardiopulmonary resuscitation in 14 anesthetized large dogs. During sinus rhythm and during internal cardiac massage, ascending aortic flow and pressure increased simultaneously and the rise in ascending aorta pressure preceded the rise in descending aortic pressure by (mean +/- SEM) 28 +/- 4 and 30 +/- 1 ms, respectively. In contrast, during vest, conventional and high impulse cardiopulmonary resuscitation, ascending aortic flow lagged behind the initial rise in aortic pressure by 40 +/- 4 to 46 +/- 4 ms and ascending and descending aortic pressure increased simultaneously (p less than 0.001 for each external compression mode versus sinus rhythm and internal massage). The ratio of pulse pressure to stroke volume increased by an order of magnitude during all modes of external chest compression (p less than 0.001 versus sinus rhythm and internal massage) and aortic diameter decreased during vest and high impulse cardiopulmonary resuscitation (p less than 0.05 versus sinus rhythm and internal massage). The hemodynamics of external chest compression depart from the normal physiologic sequence of stroke volume-induced increase in aortic pressure and diameter. The rise in aortic pressure precedes flow into the aorta, stroke volume does not fully account for pulse pressure, and aortic diameter decreases during chest compression. These data support the hypothesis that blood flow is due to fluctuations in intrathoracic pressure for high impulse as well as vest and conventional cardiopulmonary resuscitation.

Animals↗
PubMed2006

Digitizing and consolidating mammograms and other images for teaching applications.

RATIONALE AND OBJECTIVES: Most mammograms are obtained using screen-film technique and must be digitized for teaching purposes. Digitizing mammograms poses special problems because of high contrast and multiple views. We describe the equipment and process for digitizing and consolidating mammograms for teaching purposes. These techniques can be applied to any type of images where consolidation may be helpful. MATERIALS AND METHODS: Mammograms are digitized using a high optical density scanner. After the window and levels are adjusted, a four-view mammogram may be consolidated into a single image if desired. RESULTS: The high contrast of film screen mammograms is managed by using a high optical density scanner. Consolidation of image sets, such as a four-view mammogram, allows images to be easily inserted into text, slide, or poster documents. CONCLUSIONS: Digitizing mammograms for teaching purposes is facilitated by use of a high optical density scanner and consolidation of image sets into single images. The techniques described are also useful for other areas of radiology in which display of multiple images or modalities is desirable.

Computer-Assisted Instruction↗
PubMed2004

Diagnostic accuracy of chest X-rays acquired using a digital camera for low-cost teleradiology.

Store-and-forward telemedicine, using e-mail to send clinical data and digital images, offers a low-cost alternative for physicians in developing countries to obtain second opinions from specialists. To explore the potential usefulness of this technique, 91 chest X-ray images were photographed using a digital camera and a view box. Four independent readers (three radiologists and one pulmonologist) read two types of digital (JPEG and JPEG2000) and original film images and indicated their confidence in the presence of eight features known to be radiological indicators of tuberculosis (TB). The results were compared to a "gold standard" established by two different radiologists, and assessed using receiver operating characteristic (ROC) curve analysis. There was no statistical difference in the overall performance between the readings from the original films and both types of digital images. The size of JPEG2000 images was approximately 120KB, making this technique feasible for slow internet connections. Our preliminary results show the potential usefulness of this technique particularly for tuberculosis and lung disease, but further studies are required to refine its potential.

Data Compression↗
PubMed2005

Validation of tele-otology to diagnose ear disease in children.

OBJECTIVE: To determine if digitised still eardrum images, with a clinical history, and audiometry and tympanometry data provide sufficient information to an ear specialist to make an assessment of a patient. METHODS: 66 children (9 months to 16 years) from remote communities were assessed by an ear specialist by standard otoscopy, using a clinical history, audiometry and tympanometry. Up to five images of each ear were digitised. At a later date, the ear specialist made observations, diagnoses and recommendations for management from the images and clinical data. RESULTS: There was a significant correlation (p<0.01) between image quality and age of the subject. There were significant agreements for the clinically important observations of otorrhea, perforation, retracted tympanic membrane and atrophy of the tympanic membrane (p<0.05). There were significant agreements for the diagnoses of acute otitis media, chronic suppurative otitis media, otitis media with effusion and Eustachian tube dysfunction. The rate of recommendations for review or referral after a tele-otology assessment were between 4 and 16% higher than those in made in the field. The agreements between the various forms of advice or recommendations made in the field to those made by tele-otology were statistically significant (p<0.01). CONCLUSIONS: A tele-otology system that incorporates good quality digitised images of the tympanic membrane, audiological and tympanometric data, and a comprehensive clinical history provides the ear specialist with sufficient information to make a confident diagnose of existing middle ear disease, and provide management advice to the patients' primary care provider.

Acoustic Impedance Tests↗
PubMed2005

Mechanical differences between lumbar and tail discs in the mouse.

The mouse lumbar and tail discs are both used as models to study disc degeneration; however, the mechanical behavior of these two levels has not been compared. The objective of this study was to compare the elastic and viscoelastic mechanical properties of lumbar and tail discs of the mouse under axial compression-tension loading. We hypothesized that tail discs would have a larger transition zone (e.g., neutral zone) and would be less stiff in compression. To test these hypotheses, lumbar and tail bone-disc-bone motion segments were loaded in axial compression and tension. The nonlinear elastic mechanical behavior was examined using a tri-linear curvefit. Elastic behavior of lumbar and tail discs was most different in the low-stiffness transition region (neutral zone), where lumbar discs were nearly twice as stiff over half the axial displacement. In addition, viscoelastic behavior, which was examined using a stretch-exponential curvefit, also showed large lumbar and tail differences, where lumbar discs compressed by 60% of their original height and tail discs by 98% after static creep compression. These results demonstrate that tail discs undergo far more axial displacement than lumbar discs under the same load. These findings are relevant to rodent tail models where chronic loads are applied in vivo to study mechanical pathways of degeneration. Furthermore, the tri-linear model, used here to curvefit the nonlinear compression-tension data, quantified stiffness in the transition zone for the first time, which may prove useful in future disc mechanical studies.

Animals↗
PubMed2006

High frame rate ultrasonic imaging system based on the angular spectrum principle.

A kind of high frame rate (HFR) 2D and 3D imaging method was developed by Jianyu Lu in 1997. Because only one transmission is required to construct a frame of image, this method can reach an ultra high frame rate (about 3750 volumes or frames per second for biological soft tissues at a depth of 200 mm). In this paper, a new HFR method is presented in the view of angular spectrum. Compared with conventional dynamic focusing method which uses delay-and-sum processing, and Lu's HFR method which uses a kind of special weighting on the received signal, the new method only uses the Fourier transform algorithm to construct image. So the system implementation of the method could be greatly simplified. During constructing image, several array beams with different parameter are used as transmitted signal, and the spectrum of a frame of image is obtained by synthesizing the image spectrums related to different transmit event. The simulation result shows that the solution not only suppresses the sidelobe of system greatly and obtains the high quality image, but also still keeps high frame rate to some extent.

Algorithms↗
PubMed2006

Study on application of complementary Golay code into high frame rate ultrasonic imaging system.

The high frame rate (HFR) ultrasonic imaging system, which is developed with limited diffraction beams, constructs images at a high frame rate. However the rectangular imaging area, to some extent, restricts the far field imaging information. At the same time, by virtue of one transmission event for constructing image, the system suffers from low SNR. In this paper we present a computationally efficient method to construct sector mode image and to increase the SNR in HFR system. The method uses orthogonal complementary Golay coded excitation to realize two transmit and receive events. Each emission simultaneously transmits two plane waves with different transmission angle. Then according to Golay code orthogonality, the received echo signals related to different angles are isolated and used to construct two images of different imaging area by HFR method. Finally the two images are synthesized to one frame of sector mode image.

Algorithms↗
PubMed2006

Monitoring temperatures in the vaccine cold chain in Bolivia.

This study monitored vaccine cold chain temperatures during routine DTP-HB-Hib vaccine shipments from central stores to 11 communities in 3 provinces of Bolivia. In all 11 monitored shipments, vaccines were exposed to freezing temperatures at one or more points. In each of the shipments, temperatures below 0 degrees C were recorded for 2-50% of the monitoring period. Freezing occurred at almost every level of the cold chain distribution system, especially during district and health center storage and during transport to the province and district levels. Seven of the 11 shipments were exposed to temperatures above 8 degrees C, although none were exposed to excessive heat longer than 1.3% of the total monitoring period.

Bolivia↗
PubMed2002

Non-blood contacting biventricular support for severe heart failure.

BACKGROUND: Direct mechanical ventricular actuation (DMVA) is a non-blood contacting method of biventricular support. DMVA employs a vacuum attached, pneumatically regulated, flexible membrane to transfer both systolic and diastolic forces to the ventricular myocardium. The purpose of this study was to determine if DMVA effectively restores pump performance when applied to the severely failing heart. METHODS: Bovines (n = 10) underwent thoracotomy and were instrumented for continuous hemodynamic monitoring. Cardiac failure was induced by beta1-blockade to achieve a cardiac index of < 1.5 l/min/m2 for 1 hour. Heart rate was maintained at 100 bpm by atrioventricular sequential pacing. Synchronous DMVA support was then applied for 3 hours. RESULTS: Eight animals achieved significant reductions in cardiac index and mean arterial pressures (35%* and 43%* control, respectively; *p < 0.05). DMVA restored cardiac index to baseline and significantly increased arterial pressures (p < 0.05; DMVA versus cardiac failure). Pulmonary flow and mean pulmonary artery pressures were similar to baseline during DMVA (p = NS). Pathologic exam did not demonstrate evidence of significant device trauma. CONCLUSIONS: DMVA support can effectively restore pump performance of the acutely failing heart. Synchronization may be inherent to the stimulus of cardiac compression. These data further substantiate DMVA's potential as an adjunct to the field of circulatory support.

Animals↗
PubMed1999

Confined and unconfined stress relaxation of cartilage: appropriateness of a transversely isotropic analysis.

Previous studies have shown that stress relaxation behavior of calf ulnar growth plate and chondroepiphysis cartilage can be described by a linear transverse isotropic biphasic model. The model provides a good fit to the observed unconfined compression transients when the out-of-plane Poisson's ratio is set to zero. This assumption is based on the observation that the equilibrium stress in the axial direction (deltaz) is the same in confined and unconfined compression, which implies that the radial stress deltar = 0 in confined compression. In our study, we further investigated the ability of the transversely isotropic model to describe confined and unconfined stress relaxation behavior of calf cartilage. A series of confined and unconfined stress relaxation tests were performed on calf articular cartilage (4.5 mm diameter, approximately 3.3 mm height) in a displacement-controlled compression apparatus capable of measuring delta(z) and delta(r). In equilibrium, delta(r) > 0 and delta(z) in confined compression was greater than in unconfined compression. Transient data at each strain were fitted by the linear transversely isotropic biphasic model and the material parameters were estimated. Although the model could provide good fits to the unconfined transients, the estimated parameters overpredicted the measured delta(r). Conversely, if the model was constrained to match equilibrium delta(r), the fits were poor. These findings suggest that the linear transversely isotropic biphasic model could not simultaneously describe the observed stress relaxation and equilibrium behavior of calf cartilage.

Animals↗