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At least 811 records · Page 45Linked to original sources
PubMed2005

Optimal erasure protection for scalably compressed video streams with limited retransmission.

This paper shows how the priority encoding transmission (PET) framework may be leveraged to exploit both unequal error protection and limited retransmission for RD-optimized delivery of streaming media. Previous work on scalable media protection with PET has largely ignored the possibility of retransmission. Conversely, the PET framework has not been harnessed by the substantial body of previous work on RD optimized hybrid forward error correction/automatic repeat request schemes. We limit our attention to sources which can be modeled as independently compressed frames (e.g., video frames), where each element in the scalable representation of each frame can be transmitted in one or both of two transmission slots. An optimization algorithm determines the level of protection which should be assigned to each element in each slot, subject to transmission bandwidth constraints. To balance the protection assigned to elements which are being transmitted for the first time with those which are being retransmitted, the proposed algorithm formulates a collection of hypotheses concerning its own behavior in future transmission slots. We show how the PET framework allows for a decoupled optimization algorithm with only modest complexity. Experimental results obtained with Motion JPEG2000 compressed video demonstrate that substantial performance benefits can be obtained using the proposed framework.

Algorithms↗
PubMed2006

Effective palette indexing for image compression using self-organization of Kohonen feature map.

The process of limited-color image compression usually involves color quantization followed by palette re-indexing. Palette re-indexing could improve the compression of color-indexed images, but it is still complicated and consumes extra time. Making use of the topology-preserving property of self-organizing Kohonen feature map, we can generate a fairly good color index table to achieve both high image quality and high compression, without re-indexing. Promising experiment results will be presented.

Algorithms↗
PubMed2001

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

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

Adult↗
PubMed2004

Assessing diabetic retinopathy using two-field digital photography and the influence of JPEG-compression.

OBJECTIVE: To study the effectiveness of two digital 50 degree photographic fields per eye, stored compressed or integrally, in the grading of diabetic retinopathy, in comparison to 35-mm colour slides. SUBJECTS AND METHODS: Two-field digital non-stereoscopic retinal photographs and two-field 35-mm retinal photographs were made at the same time from patients visiting a diabetic retinopathy outpatient clinic. The digital images were stored integrally (TIFF-file) and in a compressed way (JPEG-file). Two ophthalmologists assessed the photographs in a masked fashion. The results were compared. The sensitivity and specificity for the detection of vision-threatening diabetic retinopathy were calculated, using only the grading of the most affected eye. The differences between the retinopathy gradings of the two kinds of photographs were analysed. RESULTS: The agreement for the grading of DR compared to slides was good, both for the compressed and for the integrally stored images (kappa 0.63-0.68). The sensitivity for the detection of vision-threatening diabetic retinopathy using the JPEG-stored images was 0.72-0.74, specificity 0.93-0.98. The sensitivity for vision-threatening retinopathy detection using the integrally stored images was 0.86-0.92, specificity 0.93. CONCLUSIONS: Two-field digital retinal photography is effective in diabetic retinopathy grading and it can replace 35-mm retinal photography. Vision-threatening retinopathy can be detected on the images with reasonable to good sensitivity and specificity. An experienced grader should assess the images. The compression of the digital images seems to have some adverse effect on the detection of diabetic retinopathy.

Data Compression↗
PubMed2004

Geometric invariance in image watermarking.

Surviving geometric attacks in image watermarking is considered to be of great importance. In this paper, the watermark is used in an authentication context. Two solutions are being proposed for such a problem. Both geometric and invariant moments are used in the proposed techniques. An invariant watermark is designed and tested against attacks performed by StirMark using the invariant moments. On the other hand, an image normalization technique is also proposed which creates a normalized environment for watermark embedding and detection. The proposed algorithms have the advantage of being robust, computationally efficient, and no overhead needs to be transmitted to the decoder side. The proposed techniques have proven to be highly robust to all geometric manipulations, filtering, compression and slight cropping which are performed as part of StirMark attacks as well as noise addition, both Gaussian and salt & pepper.

Algorithms↗
PubMed2005

EM in high-dimensional spaces.

This paper considers fitting a mixture of Gaussians model to high-dimensional data in scenarios where there are fewer data samples than feature dimensions. Issues that arise when using principal component analysis (PCA) to represent Gaussian distributions inside Expectation-Maximization (EM) are addressed, and a practical algorithm results. Unlike other algorithms that have been proposed, this algorithm does not try to compress the data to fit low-dimensional models. Instead, it models Gaussian distributions in the (N - 1)-dimensional space spanned by the N data samples. We are able to show that this algorithm converges on data sets where low-dimensional techniques do not.

Algorithms↗
PubMedDate not supplied

[Normal and pathological compression of the venous system].

A study of 190 female patients was carried out at the level of the solar ring, the crural arch, the left ilio-caval junction and the vena cava ring of the diaphragm, in order to determine whether these represent, per se, critical areas, which may cause compression and hinder the venous return as a result of the narrowing and the poor distention of their structures. Sonotomography alone or associated with the pulsed Doppler were selected for this study. The action of the various components (bone, muscle, tendon, vessels and nodes) on the venous system is each region, was analyzed. The overall results have demonstrated two types of compression: a) intermittent, b) permanent. The former is considered as a hemokinetic mechanism, especially at the level of the solar arch and the vena cava ring of the diaphragm. They represent a major element of the pump and the vis-a front respectively. The permanent compression was considered as pathological, and could be related to a venous displacement occurring as an adaptation mechanism to the extrinsic compression. The data obtained in all four regions, have demonstrated that their various components are in a precarious balance, but they do not constitute a true obstacle to the venous return, even if in some postures or respiratory movements they may cause an intermittent venous compression.

Adult↗
PubMed2001

Ultrasonic characterization of the curing process of hydroxyapatite-modified bone cement.

Ultrasonic parameters such as velocity of sound and broad-band ultrasonic attenuation (BUA) are sensitive to changes in the viscoelastic properties of a material. Bone cement undergoes changes is these properties as it cures. By monitoring the propagation of ultrasonic pulses through a sample of curing bone cement, the curing reaction of polymethylmethacrylate-based (PMMA) bone cement was investigated for hydroxyapatite (HA) concentrations of 0, 10, and 30% (by weight). As the material hardens, the velocity of sound increases by 70%. BUA shows a large peak at the midpoint of the velocity transition. These data are used to compare the cure time and cure duration for PMMA bone cement mixed with hydroxyapatite particles. Measurements of the final sound velocity and BUA were also performed to investigate the mechanical properties of the fully cured cement, and to compare to compression testing data. This is the first time the curing process of bone cement has been investigated as a function of hydroxyapatite concentration. Results indicate that the cure time is not significantly affected by the addition of HA particles, and that both velocity of sound and BUA are sensitive to the curing process.

Bone Cements↗
PubMed2006

Evaluation of the effect of JPEG and JPEG2000 image compression on the detection of diabetic retinopathy.

AIMS: To compare the effect of classic Joint Photographic Experts Group (JPEG) and JPEG2000 compression algorithms on detection of diabetic retinopathy (DR) lesions. METHODS: In total, 45 colour fundus photographs obtained with a digital nonmydriatic fundus camera were saved in uncompressed Tagged Interchanged Files Format (TIFF) format (1.26 MB). They were graded jointly by two retinal specialists at a 1 month interval for soft exudates, hard exudates, macular oedema, newvessels, intraretinal microvascular abnormalities (IRMA), and retinal haemorrhages and/or microaneurysms. They were compressed to 118, 58, 41, and 27 KB by both algorithms and 24 KB by classic JPEG, placed in random order and graded again jointly by the two retina specialists. Subjective image quality was graded, and sensitivity, specificity, positive and negative predictive values, and kappa statistic were calculated for all lesions at all compression ratios. RESULTS: Compression to 118 KB showed no effect on image quality and kappa values were high (0.94-1). Image degradation became important at 27 KB for both algorithms. At high compression levels, IRMA and HMA detection were most affected with JPEG2000 performing slightly better than classic JPEG. CONCLUSION: Performance of classic JPEG and JPEG2000 algorithms is equivalent when compressing digital images of DR lesions from 1.26 MB to 118 KB and 58 KB. Higher compression ratios show slightly better results with JPEG2000 compression, but may be insufficient for screening purposes.

Algorithms↗
PubMed1994

Quality assessment of DSA, ultrasound and CT digital images compressed with the JPEG protocol.

Digital diagnostic images from subtraction angiography, computer tomography and ultrasound grabbed at 640 x 560 pixel and 320 x 280 pixel, eight-bit resolution were compressed at seven different levels with the 'lossy' JPEG algorithm in order to decrease the computer magnetic memory space required for their storage. After reconstruction, the deformations caused by the process were assessed (i) qualitatively: a perception test was performed twice, by five radiologists, on a total of 14 images compressed at various levels and (ii) quantitatively: the average grey level value per pixel was calculated at each compression level from each system's residual images obtained by subtracting the compressed image from the original and taking the absolute value of the result. It was concluded that images compressed at a ratio of about 10:1 were indistinguishable from the originals and hence could be considered acceptable for clinical use.

Algorithms↗
PubMed2005

[Digital watermarking for electroencephalogram compression].

In this paper, digital watermarking and EEG compression are introduced firstly, and then a number of digital watermarking methods are explored to resolve the problem of integrality and authenticity in EEG compression. At last, the current state of this technique inside and outside country is summarized and future endeavors are discussed.

Computer Security↗
PubMed2000

Biomechanical evaluation of a new bone cement for use in vertebroplasty.

STUDY DESIGN: Comparative ex vivobiomechanical study. OBJECTIVES: To determine the strength and stiffness of osteoporotic vertebral bodies subjected to compression fractures and subsequently stabilized via bipedicular injection of one of two bone cements: one is a commercially available polymethylmethacrylate (Simplex P) and one is a proprietary glass-ceramic-reinforced BisGMA/BisEMA/TEGDMA matrix composite that is being developed for use in vertebroplasty (Orthocomp). SUMMARY OF BACKGROUND DATA: Osteoporotic compression fractures present diagnostic and therapeutic challenges for the clinician. Vertebroplasty, a new technique for treating such fractures, stabilizes vertebral bodies by injection of cement. Little is known, however, about the biomechanics of this treatment. METHODS: Five vertebral bodies (L1-L5) from each of four fresh spines were harvested from female cadavers (age, 80 +/- 5 years), screened for bone density using DEXA (t = -3.4 to -6.4), disarticulated, and compressed in a materials testing machine to determine initial strength and stiffness. The fractures then were repaired using a transpedicular injection of either Orthocomp or Simplex P and recrushed. RESULTS: For both cement treatments, vertebral body strength after injection of cement was significantly greater than initial strength values. Vertebral bodies augmented with Orthocomp recovered their initial stiffness; however, vertebral bodies augmented with Simplex P were significantly less stiff than they were in their initial condition. CONCLUSIONS: Augmentation with Orthocomp results in similar or greater mechanical properties compared with Simplex P, but these biomechanical results have yet to be substantiated in clinical studies.

Aged↗
PubMed1997

Focal hepatic lesions: effect of three-dimensional wavelet compression on detection at CT.

PURPOSE: To evaluate the effect of three-dimensional, wavelet-based compression on the detection of focal hepatic lesions at computed tomography (CT). MATERIALS AND METHODS: CT images obtained in 69 patients with focal hepatic lesions were studied (35 consecutive cases and 34 cases selected to be difficult on the basis of lesion size or contrast). Image data were compressed by means of a three-dimensional, wavelet-based algorIthm at ratios of 10:1, 15:1, and 20:1. Normal and abnormal sections (on original and compressed images) were reviewed by using an interactive workstation. Four readers rated the presence or absence of a lesion with a five-point scale. RESULTS: At receiver operating characteristic analysis, no statistically significant difference was detected for all cases considered together. Differences approached but did not reach statistical significance for the diagnostic performance of one reader with compressed images (15:1, P = .054; 20:1, P = .051). For the subset of difficult cases, a significant difference was observed with 20:1 compressed images for one reader (P = .026). Diagnostic performance of readers was less certain in normal than in abnormal cases with both original and compressed images (difference was significant for 15:1 [P = .035] and 20:1 [P < .0001] compressed images). CONCLUSION: Three-dimensional wavelet compression is satisfactory at ratios of at least 10:1. Additional studies with a larger sample would help confirm findings with higher ratios.

Cysts↗
PubMed2006

Real-time processing and compression of DNA microarray images.

In this paper, we present a pipeline architecture specifically designed to process and compress DNA microarray images. Many of the pixilated image generation methods produce one row of the image at a time. This property is fully exploited by the proposed pipeline that takes in one row of the produced image at each clock pulse and performs the necessary image processing steps on it. This will remove the present need for sluggish software routines that are considered a major bottleneck in the microarray technology. Moreover, two different structures are proposed for compressing DNA microarray images. The proposed architecture is proved to be highly modular, scalable, and suited for a standard cell VLSI implementation.

Algorithms↗
PubMed2005

Quality of BLS decreases with increasing resuscitation complexity.

OBJECTIVE: Multiple procedures performed in parallel may cause each procedure to be performed less effectively than if performed in isolation. BLS performed by prehospital providers potentially includes artificial ventilations, chest compressions, and application of an automated external defibrillator (AED). This study examines the effectiveness of artificial ventilation and chest compressions both with and without an AED. METHODS: Thirty-six prehospital providers participated in a prospective observational study. Tested in pairs (n=18), subjects randomly completed three, 6-min scenarios [apneic patient with a pulse (VENT), a pulseless patient (CPR), and a pulseless patient with an AED available (CPR+AED)]. A full-torso manikin capable of generating a carotid pulse was connected to a computer to record number of ventilations, tidal volume, flow rate, number of compressions, and compression depth. Data were analyzed by t-test, ANOVA, and Mann-Whitney U-test. RESULTS: Artificial ventilation performed in isolation provided more correct ventilations than during CPR or CPR+AED (25.7%, 14.2%, 13.7%, p=0.02). Fewer ventilations were delivered during CPR and CPR+AED (p=0.03). More compressions were delivered with CPR alone vs. CPR+AED (51.9, 35.7 min(-1), p=0.00). More correct compressions were delivered during CPR alone vs. CPR+AED (p=0.05). CONCLUSIONS: Both the quality and quantity of BLS decreases as the number of procedures performed simultaneously increases. Further decrements might occur when ALS skills enter into resuscitation. These results suggest a need to automate and/or prompt the performance of BLS to optimize resuscitation.

Adult↗
PubMed2004

Automated optimization of JPEG 2000 encoder options based on model observer performance for detecting variable signals in X-ray coronary angiograms.

Image compression is indispensable in medical applications where inherently large volumes of digitized images are presented. JPEG 2000 has recently been proposed as a new image compression standard. The present recommendations on the choice of JPEG 2000 encoder options were based on nontask-based metrics of image quality applied to nonmedical images. We used the performance of a model observer [non-prewhitening matched filter with an eye filter (NPWE)] in a visual detection task of varying signals [signal known exactly but variable (SKEV)] in X-ray coronary angiograms to optimize JPEG 2000 encoder options through a genetic algorithm procedure. We also obtained the performance of other model observers (Hotelling, Laguerre-Gauss Hotelling, channelized-Hotelling) and human observers to evaluate the validity of the NPWE optimized JPEG 2000 encoder settings. Compared to the default JPEG 2000 encoder settings, the NPWE-optimized encoder settings improved the detection performance of humans and the other three model observers for an SKEV task. In addition, the performance also was improved for a more clinically realistic task where the signal varied from image to image but was not known a priori to observers [signal known statistically (SKS)]. The highest performance improvement for humans was at a high compression ratio (e.g., 30:1) which resulted in approximately a 75% improvement for both the SKEV and SKS tasks.

Algorithms↗