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PubMed2005

Mutual information-based analysis of JPEG2000 contexts.

Context-based arithmetic coding has been widely adopted in image and video compression and is a key component of the new JPEG2000 image compression standard. In this paper, the contexts used in JPEG2000 are analyzed using the mutual information, which is closely related to the compression performance. We first show that, when combining the contexts, the mutual information between the contexts and the encoded data will decrease unless the conditional probability distributions of the combined contexts are the same. Given I, the initial number of contexts, and F, the final desired number of contexts, there are S(I, F) possible context classification schemes where S(I, F) is called the Stirling number of the second kind. The optimal classification scheme is the one that gives the maximum mutual information. Instead of using an exhaustive search, the optimal classification scheme can be obtained through a modified generalized Lloyd algorithm with the relative entropy as the distortion metric. For binary arithmetic coding, the search complexity can be reduced by using dynamic programming. Our experimental results show that the JPEG2000 contexts capture the correlations among the wavelet coefficients very well. At the same time, the number of contexts used as part of the standard can be reduced without loss in the coding performance.

Algorithms↗

PubMed1999

Interslice coding for medical three-dimensional images using an adaptive mode selection technique in wavelet transform domain.

In this article the authors propose a novel interslice coding algorithm especially appropriate for medical 3-dimensional (3D) images. The proposed algorithm is based on a video coding algorithm using motion estimation/compensation and transform coding. In the algorithm, warping is adopted for motion compensation. Then, by using adaptive mode selection, an MC residual image and original image are mixed up in the wavelet transform domain for improvement in coding performance. The mixed image is then compressed by the zerotree coding method. It is proven that the adaptive mode selection technique in the wavelet transform domain is very useful for medical 3D image coding. Simulation results show that the proposed scheme provides good performance, regardless of interslice distance, and is prospective for medical 3D image compression.

Algorithms↗

PubMed2004

JPEG2000 and dissemination of cultural heritage over the Internet.

By applying the latest technologies in image compression for managing the storage of massive image data within cultural heritage databases and by exploiting the universality of the Internet we are now able not only to effectively digitize, record and preserve, but also to promote the dissemination of cultural heritage. In this work we present an application of the latest image compression standard JPEG2000 in managing and browsing image databases, focusing on the image transmission aspect rather than database management and indexing. We combine the technologies of JPEG2000 image compression with client-server socket connections and client browser plug-in, as to provide with an all-in-one package for remote browsing of JPEG2000 compressed image databases, suitable for the effective dissemination of cultural heritage.

Abstracting and Indexing↗

PubMed2002

Elastographic imaging using a handheld compressor.

Elastography is an emerging imaging modality that allows noninvasive imaging of tissue stiffness changes and stiffness values associated with pathology or as a result of therapy. However, many currently-used systems for elastography rely on a fixed geometry transducer and compressor system for imaging. This configuration is disadvantageous for imaging difficult-to-reach regions that are currently accessible with conventional ultrasound. In this paper, we describe a handheld, portable stepper motor controlled system for elastography. This system may reduce motion and jitter errors that are prevalent in completely 'freehand elastography' that employs hand-induced compressions using the transducer. The latter also requires collection of large amounts of data and use of strain estimation algorithms that may not be sensitive to phase changes or use additional preprocessing to minimize decorrelation effects. The stepper motor controlled handheld system provides controlled compressions and synchronized data acquisition. Our technique yields elastograms of a low-contrast phantom that have contrast levels and contrast-to-noise ratios that are comparable to those obtained with a fixed geometry system.

Animals↗

PubMed2005

[Study on the measurement of residual stresses around indentations in SiC/Al2O3 nanocomposite using fluorescence].

The residual stresses induced by an indentation were studied in 5% SiC/Al2O3 nanocomposite using fluorescence spectroscopy in this work. It was found that within the indentation and the region of about 10 microm outside the impression, the broadening of the R-lines is obvious, and that the compression shift is a strong function of the distance from the indentation centre. From the observed frequency shifts, the hydrostatic stresses in regions sampled in the indentation, and in the complex stress field surrounding it were measured. The same variation regularity of stresses exists along the diagonal direction and the side vertical bisector direction. The symmetry of the residual stress field around the indentation was also found.

Algorithms↗

PubMed2005

Sensitivity of kinematics-based model predictions to optimization criteria in static lifting tasks.

The effect of eight different cost functions on trunk muscle forces, spinal loads and stability was investigated. Kinematics-based approach combined with nonlinear finite element modeling and optimization were used to model in vivo measurements on isometric forward flexions at approximately 40 degrees and approximately 65 degrees in sagittal plane with or without a load of 180N in hands. Four nonlinear (summation stress(3), summation stress(2), summation force(2) and muscle fatigue) and four linear (summation stress, summation force, axial compression and double-linear) criteria were considered. Predicted muscle activities were compared with measured EMG data. All predictions, irrespective of the cost function used, satisfied required kinetic, kinematics and stability conditions all along the spine. Four criteria (summation stress(3), summation stress(2), fatigue and double-linear) predicted muscle activities that qualitatively matched measured EMG data. The fatigue and double-linear criteria were inadequate in predicting greater forces in larger muscles with no consideration for their moment arms. Nearly the same stability margin was computed under these four cost functions. At the lower lumbar levels, the compression forces differed by <20% and the shear forces by <14% as various cost functions were considered. Smaller axial compression and anterior shear forces (by less than or approximately equal 6%) were computed when only the active components rather than the total muscle forces were taken as unknown in the summation stress(3) cost function. Overall, one single cost function of summation stress(2) or summation stress(3) rather than a multi-criteria one was found sufficient and adequate in yielding plausible results comparable with measured EMG activities and disc pressure.

Algorithms↗

PubMed2001

S-TREE: self-organizing trees for data clustering and online vector quantization.

This paper introduces S-TREE (Self-Organizing Tree), a family of models that use unsupervised learning to construct hierarchical representations of data and online tree-structured vector quantizers. The S-TREE1 model, which features a new tree-building algorithm, can be implemented with various cost functions. An alternative implementation, S-TREE2, which uses a new double-path search procedure, is also developed. The performance of the S-TREE algorithms is illustrated with data clustering and vector quantization examples, including a Gauss-Markov source benchmark and an image compression application. S-TREE performance on these tasks is compared with the standard tree-structured vector quantizer (TSVQ) and the generalized Lloyd algorithm (GLA). The image reconstruction quality with S-TREE2 approaches that of GLA while taking less than 10% of computer time. S-TREE1 and S-TREE2 also compare favorably with the standard TSVQ in both the time needed to create the codebook and the quality of image reconstruction.

Algorithms↗

PubMed2006

High-performance wavelet compression for mammography: localization response operating characteristic evaluation.

PURPOSE: To evaluate the accuracy of a visually lossless, image-adaptive, wavelet-based compression method for achievement of high compression rates at mammography. MATERIALS AND METHODS: The study was approved by the institutional review board of the University of South Florida as a research study with existing medical records and was exempt from individual patient consent requirements. Patient identifiers were obliterated from all images. The study was HIPAA compliant. An algorithm based on scale-specific quantization of biorthogonal wavelet coefficients was developed for the compression of digitized mammograms with high spatial and dynamic resolution. The method was applied to 500 normal and abnormal mammograms from 278 patients who were 32-85 years old, 85 of whom had biopsy-proved cancer. Film images were digitized with a charge-coupled device-based digitizer. The original and compressed reconstructed images were evaluated in a localization response operating characteristic experiment involving three radiologists with 2-10 years of experience in reading mammograms. RESULTS: Compression rates in the range of 14:1 to 2051:1 were achieved, and the rates were dependent on the degree of parenchymal density and the type of breast structure. Ranges of the area under the receiver operating characteristic curve were 0.70-0.83 and 0.72-0.86 for original and compressed reconstructed mammograms, respectively. Ranges of the area under the localization response operating characteristic curve were 0.39-0.65 and 0.43-0.71 for original and compressed reconstructed mammograms, respectively. The localization accuracy increased an average of 6% (0.04 of 0.67) with the compressed mammograms. Localization performance differences were statistically significant with P = .05 and favored interpretation with the wavelet-compressed reconstructed images. CONCLUSION: The tested wavelet-based compression method proved to be an accurate approach for digitized mammography and yielded visually lossless high-rate compression and improved tumor localization.

Adult↗

PubMed1997

Compressed storage of arterial pressure waveforms by selection of significant points.

Continuous records of arterial blood pressure can be obtained non-invasively with Finapres, even for periods of 24 hours. Increasingly, storage of such records is done digitally, requiring large disc capacities. It is therefore necessary to find methods to store blood pressure waveforms in compressed form. The method of selection of significant points known from ECG data compression is adapted. Points are selected as significant wherever the first derivative of the pressure wave changes sign. As a second stage recursive partitioning is used to select additional points such that the difference between the selected points, linearly interpolated, and the original curve remains below a maximum. This method is tested on finger arterial pressure waveform epochs of 60 s duration taken from 32 patients with a wide range of blood pressures and heart rates. An average compression factor of 4.6 (SD 1.0) is obtained when accepting a maximum difference of 3 mmHg. The root mean squared error is 1 mmHg averaged over the group of patient waveforms. Clinically relevant parameters such as systolic, diastolic and mean pressure are reproduced with an offset error of less than 0.5 (0.3) mmHg and scatter less than 0.6 (0.1) mmHg. It is concluded that a substantial compression factor can be achieved with a simple and computationally fast algorithm and little deterioration in waveform quality and pressure level accuracy.

Blood Pressure↗

PubMed1992

[The computer-assisted processing of CT data in planning endosseous implantation interventions].

The success of dental implantologic measures depends considerably on the correct positioning of the endosseous implants. A sufficient amount of bony substance is mandatory to provide overall covering of the implant with at least 1 mm of cortical bone. By the aid of a custom-developed software system, computed tomography image data can be handled on a conventional MS-DOS personal computer. The user is enabled to simulate size and positioning of the implant by interactive graphic animation. Quick and exact presentation is achieved by optimizing the computation algorithms. Storage needs are minimized by a segmentation procedure and additional compression of the image. Integrated patient data management and user friendly self-documenting program surfaces provide easy application.

Computer Graphics↗

PubMed2001

Surveillance for venous thromboembolic disease after total knee arthroplasty.

The value of deep venous thrombosis screening after total knee arthroplasty is controversial. The purpose of the current study was to examine the value of routine surveillance for venous thrombosis after total knee arthroplasty done with modern operative and perioperative treatment. Computerized search engines were used to identify papers published between 1985 and July 2000 relevant to the purpose of the study. Papers that met the inclusion criteria for review were categorized as follows: the frequency of deep venous thrombosis; the natural history of deep venous thrombosis; the accuracy of screening methods for venous thrombosis; and efficacy of screening in reducing morbidity attributable to venous thromboembolism after total knee arthroplasty. Several studies have shown a low complication rate related to venous thromboembolic disease when compression ultrasound is used for screening as part of a clinical algorithm after knee arthroplasty. However, the only large prospective randomized trial evaluating ultrasound screening failed to show a reduction in morbidity with a surveillance protocol. The benefits of surveillance depend on factors specific to each surgeon's practice including the type and duration of venous prophylaxis, the rate of symptomatic and asymptomatic thromboembolic disease associated with that protocol, and the accuracy of screening tests used for surveillance.

Arthroplasty, Replacement, Knee↗

PubMed2003

Accuracy and applicability of the Terumo ES-H55 double-cuff sphygmomanometer for hospital use.

BACKGROUND: We have developed a new blood pressure (BP)-measuring device with a double-cuff, and evaluated its accuracy and applicability for practical use. DESIGN: The double-cuff method features a small cuff placed in the centre of the compression cuff to detect the oscillation of arterial pulsation, by which algorithms for the determination of systolic BP (SBP) and diastolic BP (DBP) were rendered more objective than with the conventional oscillometric method. Algorithms for automatic BP determination were developed from the oscillation data taken with the small cuff from 217 men and 256 women, and then installed in the Terumo ES-H55 device (length: 17 cm, weight: 120 g). This ES-H55 device was tested on 87 subjects (65 hypertensives and 22 normotensives) to compare its accuracy with that of the auscultatory method according to the AAMI SP-10 protocol. RESULTS: Using Bland and Altman scatter plots, the difference in SBP between the ES-H55 device and the auscultatory method was within +/- 5 mmHg in 88% of subjects, and within +/- 10 mmHg in 97% (mean difference +/- SD: 0.2 +/- 3.9 mmHg). The difference in DBP was within +/- 5 mmHg in 80%, and within +/- 10 mmHg in 97% (difference: -0.1 +/- 4.6 mmHg). These results satisfied AAMI guidelines, and this device was easy to use. CONCLUSIONS: The ES-H55 device is compact and light, with clear algorithms for the determination of BP, and satisfies AAMI criteria, so that it is considered a useful BP-measuring device that could be used instead of a mercury sphygmomanometer by nurses and doctors in hospital wards.

Adolescent↗

PubMed1994

MR cisternography: initial experience in 41 cases.

PURPOSE: To present our initial experience with MR cisternography, an application of fast spin-echo MR with fat suppression, and compare it with routine MR cranial studies in the evaluation of the subarachnoid cisterns and their contents. METHODS: MR cisternography is a heavily T2-weighted fast spin-echo technique with high spatial resolution; it uses fat suppression and video reversal of the images. A small number of individual sections (two to four) are compressed into a composite image by a maximum-intensity projection algorithm, providing better depiction of anatomy in three dimensions. MR cisternography enhances the signal intensity of the cerebrospinal fluid (CSF) with suppression and subtraction of the background. A total of 41 patients were examined during a period of 6 months. MR cisternography was performed as an additional one (n = 31) or two (n = 10) sequences after conventional MR study. RESULTS: Twenty-one cases of disease were examined by MR cisternography, including 8 neoplasms, 4 CSF fistulas, and 3 large intracranial aneurysms. MR cisternography provided information unavailable by conventional MR studies in 17 cases. These included visualization of fistulous tracks in patients with CSF rhinorrhea, origin of a large suprasellar aneurysm, an additional loculus of a posterior fossa aneurysm and its relation to surrounding structures, and proper location of three tumors (intraaxial versus extraaxial). Clear depiction of the pituitary gland separate from the cavernous sinus was noted in 60% of the cases, and a new observation of a CSF sleeve around the third nerve in the posterior cavernous sinus was made in 85% of the cases. CONCLUSION: MR cisternography is superior to conventional MR studies in depicting anatomic structures within the subarachnoid spaces. This technique is recommended in the evaluation of cranial CSF fistulas and suprasellar and posterior fossa masses and in diagnosis of intraaxial versus extraaxial location of intracranial tumors.

Adolescent↗

PubMed2004

Applying informed coding and embedding to design a robust high-capacity watermark.

We describe a new watermarking system based on the principles of informed coding and informed embedding. This system is capable of embedding 1380 bits of information in images with dimensions 240 x 368 pixels. Experiments on 2000 images indicate the watermarks are robust to significant valumetric distortions, including additive noise, low-pass filtering, changes in contrast, and lossy compression. Our system encodes watermark messages with a modified trellis code in which a given message may be represented by a variety of different signals, with the embedded signal selected according to the cover image. The signal is embedded by an iterative method that seeks to ensure the message will not be confused with other messages, even after addition of noise. Fidelity is improved by the incorporation of perceptual shaping into the embedding process. We show that each of these three components improves performance substantially.

Algorithms↗

PubMed1995

High-quality compression of echographic images by neural networks and vector quantisation.

A compression method is presented for medical images based on neural networks and vector quantisation (VQ). The neural net is a perceptron and it is followed by some expressly designed VQ algorithms. The method devotes special attention to the quality of the reconstructed images and to the reduction of artefacts. The compression ratio obtained in the long run with echographic images is greater than 50:1 with good quality.

Algorithms↗

PubMed2005

Dynamic contrast-based quantization for lossy wavelet image compression.

This paper presents a contrast-based quantization strategy for use in lossy wavelet image compression that attempts to preserve visual quality at any bit rate. Based on the results of recent psychophysical experiments using near-threshold and suprathreshold wavelet subband quantization distortions presented against natural-image backgrounds, subbands are quantized such that the distortions in the reconstructed image exhibit root-mean-squared contrasts selected based on image, subband, and display characteristics and on a measure of total visual distortion so as to preserve the visual system's ability to integrate edge structure across scale space. Within a single, unified framework, the proposed contrast-based strategy yields images which are competitive in visual quality with results from current visually lossless approaches at high bit rates and which demonstrate improved visual quality over current visually lossy approaches at low bit rates. This strategy operates in the context of both nonembedded and embedded quantization, the latter of which yields a highly scalable codestream which attempts to maintain visual quality at all bit rates; a specific application of the proposed algorithm to JPEG-2000 is presented.

Algorithms↗

PubMed2006

A fast and efficient hybrid fractal-wavelet image coder.

The excellent visual quality and compression rate of fractal image coding have limited applications due to exhaustive inherent encoding time. This paper presents a new fast and efficient image coder that applies the speed of the wavelet transform to the image quality of the fractal compression. Fast fractal encoding using Fisher's domain classification is applied to the lowpass subband of wavelet transformed image and a modified set partitioning in hierarchical trees (SPIHT) coding, on the remaining coefficients. Furthermore, image details and wavelet progressive transmission characteristics are maintained, no blocking effects from fractal techniques are introduced, and the encoding fidelity problem common in fractal-wavelet hybrid coders is solved. The proposed scheme promotes an average of 94% reduction in encoding-decoding time comparing to the pure accelerated Fractal coding results. The simulations also compare the results to the SPIHT wavelet coding. In both cases, the new scheme improves the subjective quality of pictures for high-medium-low bitrates.

Algorithms↗

PubMed2003

Characterization of monoclinic crystals in tablets by pattern-fitting procedure using X-ray powder diffraction data.

The purpose of this study is to characterize the monoclinic crystals in tablets by using X-ray powder diffraction data and to evaluate the deformation feature of crystals during compression. The monoclinic crystals of acetaminophen and benzoic acid were used as the samples. The observed X-ray diffraction intensities were fitted to the analytic expression, and the fitting parameters, such as the lattice parameters, the peak-width parameters, the preferred orientation parameter and peak asymmetric parameter were optimized by a non-linear least-squares procedure. The Gauss and March distribution functions were used to correct the preferred orientation of crystallites in the tablet. The March function performed better in correcting the modification of diffraction intensity by preferred orientation of crystallites, suggesting that the crystallites in the tablets had fiber texture with axial orientation. Although a broadening of diffraction peaks was observed in acetaminophen tablets with an increase of compression pressure, little broadening was observed in the benzoic tablets. These results suggest that "acetaminophen is a material consolidating by fragmentation of crystalline particles and benzoic acid is a material consolidating by plastic deformation then occurred rearrangement of molecules during compression". A pattern-fitting procedure is the superior method for characterizing the crystalline drugs of monoclinic crystals in the tablets, as well as orthorhombic isoniazid and mannitol crystals reported in the previous paper.

Acetaminophen↗