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PubMed1997

Image Storage Requirements for Treatment Planning and Verification.

Digital imaging techniques are becoming increasingly accepted in radiation therapy, and they bring significant advantages when compared with film, especially the ease of storage and retrieval. A simple model is proposed for the estimation of digital data storage requirements in a typical department of radiation therapy. The model assumes that 100 patients are undergoing treatment at any given time, and their computed tomography (CT) images, treatment plans, digitized simulator films, and portal images are to be available at short notice ("on-line"). Off-line archival image storage is required after the completion of treatment, for 1,000 patients per year. Reasonable assumptions are postulated regarding image sizes and acquisition rates, and on-line storage requirements are estimated to be up to 300 megabytes (MB) for CT data, 170 MB for treatment plans, 200 MB for digitized simulator films, and 500 MB for digitized port films. If electronic portal imaging is used instead of port films, the on-line requirement becomes about 2 gigabytes (GB) for verification images, and 20 GB if portal movies are to be archived. Off-line storage requirements are a factor of ten larger. It is suggested that data compression may reduce these requirements by up to a factor of 20.

Journal Article↗

PubMed2001

[Wavelet representation of corneal topography data after nonmechanical penetrating keratoplasty--a clinical study].

BACKGROUND: Corneal surface irregularities may limit the visual outcome after penetrating keratoplasty (PK). Corneal topographers mainly render empirically derived and system-specific statistical indices for characterization of superficial inhomogeneities which may lack clinical evidence and make inter-system comparisons difficult. The purpose of this study was to detect and quantify focal surface irregularities of the cornea after nonmechanical PK by 2-dimensional wavelet decomposition based on corneal topography data. PATIENTS AND METHODS: Our study included 15 patients with keratoconus and 10 patients with Fuchs' dystrophy with all-sutures-out after penetrating keratoplasty. For trephination we used the excimer laser MEL60 (Aesculap-Meditec, Germany) (7.5/7.6 mm diameter in dystrophies, 8.0/8.1 mm in keratoconus, double-running 10-0 nylon suture). After suture removal a complete ophthalmological examination including OrbScan topography analysis (Orbtec, USA) was performed. The refraction data were extracted via "data recorder" and decomposed using 2-dimensional wavelet analysis methods (Daubechies-4-wavelets on five scales of resolution). Corneal irregularities were quantified (scale 1 = fine details to scale 5 = coarse details). RESULTS: All detail coefficients (horizontal, vertical and diagonal) correlated statistically significant with the "Irregular Astigmatism" provided by the OrbScan-system (p < 0.05). In scale 3 and 4 a relative maximum of the wavelet detail coefficients occurred, whereas the coefficients at scale 2 and 5 were significantly smaller. The horizontal and vertical detail coefficients correlated significantly inversely with the best-corrected visual acuity (p < 0.04). All detail coefficients were significantly lower in the patient group with keratoconus compared to Fuchs' dystrophy. CONCLUSIONS: Wavelet decomposition of corneal topography refraction data allows an analytical isolation and quantification of focal corneal superficial irregularities. This algorithm is independent of the currently used topography system and allows a smoothing of the raw data set adapted to scale of resolution and data compression.

Adult↗

PubMed1992

Image manipulation: digital versus analog.

A conceptual difference between "analog" and "digital" digitizing is reviewed. Analog and digital type image filing systems are discussed from a comparative point of view: The analog type is advantageous in the number of recordable images, the recording and reproducing speed, and the ability to record a moving picture, while the digital type, in which images are digitized when recorded, is capable of reproducing a higher quality image that does not deteriorate when copied repeatedly. It has the advantage that it easily interfaces with computer systems. As technology developed to compensate for the drawbacks of the digital type systems, image data compression was introduced. Finally, the possibility for recording a moving picture in a digital type system is discussed.

Image Processing, Computer-Assisted↗

PubMed1986

High-resolution facial feature saliency mapping.

For recognition of a target there must be some form of comparison process between the image of that target and a stored representation of that target. In the case of faces there must be a very large number of such stored representations, yet human beings seem able to perform comparisons at phenomenal speed. It is possible that faces are memorized by fitting unusual features or combinations of features onto a bland prototypical face, and such a data-compression technique would help to explain our computational speed. If humans do indeed function in this fashion, it is necessary to ask just what are the features that distinguish one face from another, and also, what are the features that form the basic set of the prototypical face. The distributed apertures technique was further developed in an attempt to answer both questions. Four target faces, stored in an image-processing computer, were each divided up into 162 contiguous squares that could be displayed in their correct positions in any combination of 24 or fewer squares. Each observer was required to judge which of the four target faces was displayed during a 1 s presentation, and the proportion of correct responses for each individual square was computed. The resultant response distributions, displayed as brightness maps, give a vivid impression of the relative saliency of each feature square, both for the individual targets and for all of them combined. The results, while broadly confirming previous work, contain some very interesting and surprising details about the differences between the target faces.

Adult↗

PubMed2002

Algorithmic cooling and scalable NMR quantum computers.

We present here algorithmic cooling (via polarization heat bath)-a powerful method for obtaining a large number of highly polarized spins in liquid nuclear-spin systems at finite temperature. Given that spin-half states represent (quantum) bits, algorithmic cooling cleans dirty bits beyond the Shannon's bound on data compression, by using a set of rapidly thermal-relaxing bits. Such auxiliary bits could be implemented by using spins that rapidly get into thermal equilibrium with the environment, e.g., electron spins. Interestingly, the interaction with the environment, usually a most undesired interaction, is used here to our benefit, allowing a cooling mechanism. Cooling spins to a very low temperature without cooling the environment could lead to a breakthrough in NMR experiments, and our "spin-refrigerating" method suggests that this is possible. The scaling of NMR ensemble computers is currently one of the main obstacles to building larger-scale quantum computing devices, and our spin-refrigerating method suggests that this problem can be resolved.

Journal Article↗

PubMed1982

Increase in apparent compressibility of cytochrome c upon oxidation.

The apparent molal adiabatic compressibilities of ferri- and ferrocytochrome c have been determined from measurements of density and sound velocity. The values found were +2.99 X 10(-8) and -2.40 X 10(-8) cm5 mol-1 dyne-1 for the ferri and ferro forms, respectively. Experiments were performed on identical solutions containing either the oxidized or reduced form of protein. Solutions of ferricytochrome c were found to have significantly greater adiabatic compressibility than equivalent solutions of ferrocytochrome c at 25 degrees C and pH 7.15. The remarkable similarity of the three-dimensional structures of the ferri and ferro proteins [Takano, T. & Dickerson, R.E. (1980) Proc. Natl. Acad. Sci. USA 77, 6371-6375] strongly suggests that this difference in compressibility is due to an increase in volume fluctuations within ferricytochrome c relative to the ferro form rather than a change in equilibrium structure or hydration. Such a difference in the dynamic properties of the structures is consistent with both the crystallographic thermal B factors and the observed increase in amide hydrogen exchange kinetics when ferrocytochrome c is oxidized. The relative magnitude of the root mean square volume fluctuations is approximated from an ideal solution treatment of the compressibility data and yields a ratio of delta Vrms (ferri cyt c)/ delta Vrms (ferro cyt c) = 1.3.

Animals↗

PubMedDate not supplied

Telecardiology for effective healthcare services.

Continuous monitoring of the electrocardiogram (ECG) and other signals related to current heart activity are necessary for patients who are suffering from cardiac diseases. This paper deals with the work that has been carried out to transmit ECGs from remote sites. Software has been developed which enables the uploading of ECG data from a patient so that the physician can monitor the state of the patient from a distance and at the same time may consult other experts for a second opinion. Records can only be examined by the authorized physician after proper registration and diagnosis or prescription may be sent back to the referring site. Further consultation with the patient through a 'chat' facility is also possible. The suitability of the system over transport control protocol (TCP), internet protocol (IP), local area network (LAN), wide area network (WAN) and World Wide Web (WWW) has been assessed. The bandwidth, latency, availability, security and ubiquity have also been discussed. A study has also been undertaken in order to make the system compatible with available bandwidths and to find out which one out of a number of available techniques is most efficient for ECG data compression. The results indicate that the scheme is suitable for telecardiology and can form part of an overall telemedicine system in a health care network.

Computer Security↗

PubMedDate not supplied

Performance improvement of the SPIHT coder based on statistics of medical ultrasound images in the wavelet domain.

This paper proposes some modifications to the state-of-the-art Set Partitioning In Hierarchical Trees (SPIHT) image coder based on statistical analysis of the wavelet coefficients across various subbands and scales, in a medical ultrasound (US) image. The original SPIHT algorithm codes all the subbands with same precision irrespective of their significance, whereas the modified algorithm processes significant subbands with more precision and ignores the least significant subbands. The statistical analysis shows that most of the image energy in ultrasound images lies in the coefficients of vertical detail subbands while diagonal subbands contribute negligibly towards total image energy. Based on these statistical observations, this work presents a new modified SPIHT algorithm, which codes the vertical subbands with more precision while neglecting the diagonal subbands. This modification speeds up the coding/decoding process as well as improving the quality of the reconstructed medical image at low bit rates. The experimental results show that the proposed method outperforms the original SPIHT on average by 1.4 dB at the matching bit rates when tested on a series of medical ultrasound images. Further, the proposed algorithm needs 33% less memory as compared to the original SPIHT algorithm.

Algorithms↗

PubMed1999

Experimental comparison of data transformation procedures for analysis of principal components.

Results of principal component analysis depend on data scaling. Recently, based on theoretical considerations, several data transformation procedures have been suggested in order to improve the performance of principal component analysis of image data with respect to the optimum separation of signal and noise. The aim of this study was to test some of those suggestions, and to compare several procedures for data transformation in analysis of principal components experimentally. The experiment was performed with simulated data and the performance of individual procedures was compared using the non-parametric Friedman's test. The optimum scaling found was that which unifies the variance of noise in the observed images. In data with a Poisson distribution, the optimum scaling was the norm used in correspondence analysis. Scaling mainly affected the definition of the signal space. Once the dimension of the signal space was known, the differences in error of data and signal reproduction were small. The choice of data transformation depends on the amount of available prior knowledge (level of noise in individual images, number of components, etc), on the type of noise distribution (Gaussian, uniform, Poisson, other), and on the purpose of analysis (data compression, filtration, feature extraction).

Computer Simulation↗

PubMed2003

Monotony of surprise and large-scale quest for unusual words.

The problem of characterizing and detecting recurrent sequence patterns such as substrings or motifs and related associations or rules is variously pursued in order to compress data, unveil structure, infer succinct descriptions, extract and classify features, etc. In molecular biology, exceptionally frequent or rare words in bio-sequences have been implicated in various facets of biological function and structure. The discovery, particularly on a massive scale, of such patterns poses interesting methodological and algorithmic problems and often exposes scenarios in which tables and synopses grow faster and bigger than the raw sequences they are meant to encapsulate. In previous study, the ability to succinctly compute, store, and display unusual substrings has been linked to a subtle interplay between the combinatorics of the subword of a word and local monotonicities of some scores used to measure the departure from expectation. In this paper, we carry out an extensive analysis of such monotonicities for a broader variety of scores. This supports the construction of data structures and algorithms capable of performing global detection of unusual substrings in time and space linear in the subject sequences, under various probabilistic models.

Algorithms↗

PubMed1995

Short superstrings and the structure of overlapping strings.

Given a collection of strings S = [s1,...,sn] over an alphabet sigma, a superstring alpha of S is a string containing each si as a substring, that is, for each i, 1 < or = i < or = n, alpha contains a block of magnitude of si consecutive characters that match si exactly. The shortest superstring problem is the problem of finding a superstring alpha of minimum length. The shortest superstring problem has applications in both computational biology and data compression. The shortest superstring problem is NP-hard (Gallant et al., 1980); in fact, it was recently shown to be MAX SNP-hard (Blum et al., 1994). Given the importance of the applications, several heuristics and approximation algorithms have been proposed. Constant factor approximation algorithms have been given in Blum et al. (1994) (factor of 3), Teng and Yao (1993) (factor of 2 8/9), Czumaj et al. (1994) (factor of 2 5/6), and Kosaraju et al. (1994) (factor of 2 50/63). Informally, the key to any algorithm for the shortest superstring problem is to identify sets of strings with large amounts of similarity, or overlap. Although the previous algorithms and their analyses have grown increasingly sophisticated, they reveal remarkably little about the structure of strings with large amounts of overlap. In this sense, they are solving a more general problem than the one at hand. In this paper, we study the structure of strings with large amounts of overlap and use our understanding to give an algorithm that finds a superstring whose length is no more than 2 3/4 times that of the optimal superstring. Our algorithm runs in O(magnitude of S + n3) time, which matches that of previous algorithms. We prove several interesting properties about short periodic strings, allowing us to answer questions of the following form: Given a string with some periodic structure, characterize all the possible periodic strings that can have a large amount of overlap with the first string.

Algorithms↗

PubMed1995

Telemammography: implementation issues.

Telemammography has the potential to improve access to centralized expertise for the interpretation of breast imaging studies. Digital mammography has more demanding spatial resolution requirements than other forms of medical imaging because of the need to detect microcalcifications, the fine details of lesion margins, and subtle architectural distortion. The resolution requirements for mammography have important implications for image acquisition and display technologies. The large size of the resulting image data sets places significant demands on local and wide area networks as well as storage media. Image data compression will be particularly important for telemammography to help make systems practical and affordable. This article describes how existing technologies can be adapted to implement telemammography systems in the near future.

Algorithms↗

PubMed1989

Evaluation of routine telephone transmission of nuclear medicine studies.

Rapid and reliable transmission of nuclear medicine studies using conventional telephone lines and commercially available modems and computer systems has been accomplished through use of software developed within the authors' hospital. Original digital images of all-night and weekend studies, acquired on any of the acquisition computers from different manufacturers, are now routinely sent for remote reading at the physician's home. Data, software, and letters are routinely exchanged using modems and standard telephone lines with a sister institution in Haifa, Israel. The software has been designed to achieve no loss data compression and minimal turnaround time loss. Thus, an average lung perfusion image or gallbladder study requires about 1-3 minutes of transmission time. Full analysis and display software is available on the remote computer.

Computer Communication Networks↗

PubMedDate not supplied

Microcomputer-based coronary care unit central station.

A four-bed central station that can be connected to any commercial intensive-care bedside monitor was developed. The system is based on a personal computer (IBM-AT compatible) as a local unit and on a microcontroller Intel 8031 as a remote unit. Four ECG signals are low-pass filtered, multiplexed, sampled at 256-Hz per channel, 8-bit A/D converted, preprocessed, and converted to a serial format RS-232 by the remote unit. The real-time display of the signals is at the standard speed of 25 and 50 mm/sec. Heartrate, alarms, trend plots, and general patient data are shown on an Olivetti M280 and EGA 13'' color monitor as the local unit. The communication speed was set at 57.6 Kbaud full duplex. Additionally, to reach standard monitoring sweep rates using a 13'' screen with 640 x 350 pixels, an ECG data-compression algorithm was implemented in the remote unit. This unit can support up to eight input channels and can work with any personal computer, via RS-232, with the appropriate software. It also allows other signal preprocessing software that could be developed, such as QRS detection or ST segment quantification, to be loaded into its random access memory and to be run under PC command. The development of this system demonstrated the use of a widespread piece of commercial equipment, the PC, in a very specific application, CCU monitoring, assuring low-cost system implementation. This feature is particularly attractive in upgrading existing CCU units in less developed countries.

Biomedical Engineering↗

PubMed2001

Effects of gender and age differences on the distribution of bone content in the third lumbar vertebra.

STUDY DESIGN: A cross-sectional study on the distribution of bone mineral content in the third lumbar vertebrae. OBJECTIVES: To evaluate the effects of age and gender on the distribution of bone mineral content in the third lumbar vertebrae. SUMMARY OF BACKGROUND DATA: Compression fractures occur mainly at the vertebral body. Variations in the distribution of bone mass in a vertebra, if undefined, may bias the ability of the acquired bone mineral density values, which was usually measured posteroanteriorly, to predict the risk of fractures. METHODS: The bone mineral content of the whole L3, including the L3 vertebral body and the posterior segment, was measured using a lateral approach with a dual energy radiograph absorptiometer on 177 healthy Taiwanese adults including 65 men and 55 premenopausal and 57 postmenopausal women. RESULTS: The proportion of bone mineral content in the vertebral body was significantly lower in premenopausal women than in age-matched men (39.1 +/- 0.9% vs. 50.0 +/- 1.7%, P < 0.0001). Furthermore, whereas postmenopausal women showed a decreased proportion of bone mineral content in the vertebral body with increased age (about -0.0022 per year, P = 0.0001), premenopausal women and men showed a sustained proportion. CONCLUSIONS: The proportion of bone mineral content distributed in the body of L3 vertebrae was lower in women than in men. The discrepancy of this parameter between the genders was even larger with increased ages.

Absorptiometry, Photon↗

PubMed2005

Evaluation of outcome after immediate breast reconstruction: prospective comparison of four methods.

BACKGROUND: Little is known about the association among different methods to assess outcome following breast reconstruction. The aim of this study was to comprehensively compare four distinct methods of outcome evaluation following immediate breast reconstruction. METHODS: There were 102 women who were prospectively evaluated: 46 patients had submuscular implants, and 56 patients had implant-assisted latissimus dorsi breast reconstruction. The mean patient age at the time of operation was 46 years (range, 22 to 72 years), with a mean follow-up of 18 months (range, 12 to 24 months). All patients were evaluated using geometric measurements, photographs, linear analogue scores, and a quality-of-life questionnaire. The Wilcoxon signed rank test, Spearman's correlation, and factor analysis statistics were used. RESULTS: Transverse breast width, vertical breast height, sternal notch-nipple, midclavicular line-nipple, nipple-inframammary crease, midline-nipple, internipple, and intermammary measurements were reproducible and reliable. Median differences of absolute vertical and horizontal differences were less than 1 cm and were associated with high levels of patient satisfaction. Assessors asked to score photographs without being specifically requested to consider shape, cleavage, or symmetry would focus mainly on vertical and horizontal differences. There was a high correlation between surgeon and patient linear analogue scores. Quality-of-life questionnaires provide valuable information on body image, physical effects, and continued cancer worry. Factor analyses failed to identify components to compress data fields to obtain equivalent information from fewer questions. CONCLUSIONS: Evaluation of immediate breast reconstruction is complex. Cumbersome data collection has to be balanced against practical variables that individual units can collect to evaluate outcome for audit and research.

Adult↗

PubMed2003

Information content in the Nagel-Schreckenberg cellular automaton traffic model.

We estimate the set dimension and find bounds for the set entropy of a cellular automaton model for single lane traffic. Set dimension and set entropy, which are measures of the information content per cell, are related to the fractal nature of the automaton [S. Wolfram, Physica D 10, 1 (1989); Theory and Application of Cellular Automata, edited by S. Wolfram (World Scientific, Philadelphia, 1986)] and have practical implications for data compression. For models with maximum speed v(max), the set dimension is approximately log((v(max)+2))2.5, which is close to one bit per cell regardless of the maximum speed. For a typical maximum speed of five cells per time step, the dimension is approximately 0.47.

Journal Article↗

PubMed2003

Vortex dynamics in evolutive flows: a weakly chaotic phenomenon.

We make use of a wavelet method to extract, from experimental velocity signals obtained in an evolutive flow, the dominating velocity components generated by vortex dynamics. We characterize the resulting time series complexity by means of a joint use of data compression and of an entropy diffusion method. We assess that the time series emerging from the wavelet analysis of the vortex dynamics is a weakly chaotic process with a vanishing Kolmogorov-Sinai entropy and a power-law growth of the information content. To reproduce the Fourier spectrum of the experimental signal, we adopt a harmonic dependence on time with a fluctuating frequency, ruled by an inverse power-law distribution of random events. The complexity of these fluctuations is determined by studying the corresponding artificial sequences. We reproduce satisfactorily both spectral and complex properties of the experimental signal by locating the complexity of the fluctuating process at the border between the stationary and the nonstationary states.

Journal Article↗