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PubMed1997

Compression guidelines for diagnostic telepathology.

As the healthcare community has begun to rely increasingly upon digital technologies for acquisition, storage, and transmission of pictorial data, image compression has become an indispensable tool. We have investigated the feasibility of lossy compression in a well-defined task domain, the clinical assessment of digitized images of chromatic microscopic pathology specimens. The effect of compression was measured under two distinct perceptual criteria, just noticeable difference (j.n.d.) and largest tolerable distortion (l.t.d.), differing in the involvement required from subjects, who were experts in pathology. For standard JPEG compressed images it was found that when the experiment is performed under the l.t.d. criterion, a significantly larger compression ratio is reported as satisfactory. It is concluded that lossy compression holds promise for diagnostic telepathology.

Algorithms↗
PubMed2004

Image quality assessment: from error visibility to structural similarity.

Objective methods for assessing perceptual image quality traditionally attempted to quantify the visibility of errors (differences) between a distorted image and a reference image using a variety of known properties of the human visual system. Under the assumption that human visual perception is highly adapted for extracting structural information from a scene, we introduce an alternative complementary framework for quality assessment based on the degradation of structural information. As a specific example of this concept, we develop a Structural Similarity Index and demonstrate its promise through a set of intuitive examples, as well as comparison to both subjective ratings and state-of-the-art objective methods on a database of images compressed with JPEG and JPEG2000.

Algorithms↗
PubMed2006

A comparison between amplitude sorting and phase-angle sorting using external respiratory measurement for 4D CT.

Respiratory motion can cause significant dose delivery errors in conformal radiation therapy for thoracic and upper abdominal tumors. Four-dimensional computed tomography (4D CT) has been proposed to provide the image data necessary to model tumor motion and consequently reduce these errors. The purpose of this work was to compare 4D CT reconstruction methods using amplitude sorting and phase angle sorting. A 16-slice CT scanner was operated in ciné mode to acquire 25 scans consecutively at each couch position through the thorax. The patient underwent synchronized external respiratory measurements. The scans were sorted into 12 phases based, respectively, on the amplitude and direction (inhalation or exhalation) or on the phase angle (0-360 degrees) of the external respiratory signal. With the assumption that lung motion is largely proportional to the measured respiratory amplitude, the variation in amplitude corresponds to the variation in motion for each phase. A smaller variation in amplitude would associate with an improved reconstructed image. Air content, defined as the amount of air within the lungs, bronchi, and trachea in a 16-slice CT segment and used by our group as a surrogate for internal motion, was correlated to the respiratory amplitude and phase angle throughout the lungs. For the 35 patients who underwent quiet breathing, images (similar to those used for treatment planning) and animations (used to display respiratory motion) generated using amplitude sorting displayed fewer reconstruction artifacts than those generated using phase angle sorting. The variations in respiratory amplitude were significantly smaller (P < 0.001) with amplitude sorting than those with phase angle sorting. The subdivision of the breathing cycle into more (finer) phases improved the consistency in respiratory amplitude for amplitude sorting, but not for phase angle sorting. For 33 of the 35 patients, the air content showed significantly improved (P < 0.001) correlation with the respiratory amplitude than with the phase angle, suggesting a stronger relationship between internal motion and amplitude. Overall, amplitude sorting performed better than phase angle sorting for 33 of the 35 patients and equally well for two patients who were immobilized with a stereotactic body frame and an abdominal compression plate.

Algorithms↗
PubMed2006

Designing Talbot array illuminators with phase-space optics.

The problem of designing Talbot array illuminators is revisited in the context of phase-space optics. It is shown that for Talbot array illuminators with optimum compression ratio the construction of phase-only grating profiles can be simplified significantly by using phase-space representations of optical signals. Based on the Wigner distribution function a graphical procedure is derived for obtaining the complete design of the array generator for a given compression ratio. The application of phase-space optics to other classes of Talbot array illuminators, and its use as part of numerical optimization algorithms, is considered as well.

Journal Article↗
PubMed1998

In vivo measures of cochlear length and insertion depth of nucleus cochlear implant electrode arrays.

Three-dimensional cochlear canal lengths, electrode array intracochlear insertion depths, and characteristic frequency ranges were estimated for 20 Nucleus implant recipients on the basis of in vivo computed tomography (CT) scans. Ultra-high resolution images were reconstructed from spiral CT data with 0.1-mm slicing and expanded attenuation scales. Canal length estimates (mean 33.01 mm; SD 2.31) were consistent with previous findings for normal human temporal bones. Intracochlear array insertion depths estimated by 3-dimensional (3-D) spiral calculations (mean 20.19 mm; SD 2.86) and by a computerized array tracking algorithm (mean 20.36 mm; SD 2.66) were not significantly different. Estimates from surgical observations were significantly longer (mean 21.03 mm; SD 2.31) because array compressions were not detectable. Characteristic frequencies at apical electrodes estimated from Greenwood's equations ranged from 387 Hz to 2,596 Hz. The results show that significant variations in cochlear anatomy and array distribution among implant patients that may impact implant performance can be reliably detected and quantified by using in vivo high-resolution CT and 3-D reconstructions.

Adult↗
PubMed2004

Automatic spinal disease diagnoses assisted by 3D unaligned transverse CT slices.

This paper describes a three-dimensional (3D) reconstruction method and an automatic diagnosis method for spinal diseases using unaligned transverse slices that have arbitrary angles and intervals but do not intersect to each other at regions of interest. The 3D reconstruction method extends the marching cube algorithm to generate triangulated isosurfaces for these unaligned slices. The automatic spinal disease diagnostic method analyses boundaries of discs and vertebral bodies on unaligned transverse slices to estimate the presence and extent of disc herniation and canal compression, and deformities in the spinal curve. The prototype system can be used as a qualitative and quantitative tool for the diagnosis of various spinal diseases using unaligned transverse slices.

Aged↗
PubMed2005

Phototransduction in primate cones and blowfly photoreceptors: different mechanisms, different algorithms, similar response.

Phototransduction in primate cones is compared with phototransduction in blowfly photoreceptor cells. Phototransduction in the two cell types utilizes not only different molecular mechanisms, but also different signal processing steps, producing range compression, contrast constancy, and an intensity-dependent integration time. The dominant processing step in the primate cone is a strongly compressive nonlinearity due to cGMP hydrolysis by phosphodiesterase. In the blowfly photoreceptor a considerable part of the range compression is performed by the nonlinear membrane of the cell. Despite these differences, both photoreceptor cell types are similarly effective in compressing the wide range of naturally occurring intensities, and in converting intensity variations into contrast variations. A direct comparison of the responses to a natural time series of intensities, simulated in the cone and measured in the blowfly photoreceptor, shows that the responses are quite similar.

Adaptation, Ocular↗
PubMed2003

[Indications for the surgical treatment of the funnel chest].

AIM OF THE STUDY: to establish the indications for surgical treatment of the funnel chest. PATIENTS AND METHODS: There was a retrospective and prospective analysis performed of the methods of investigation and treatment of 504 patients operated for the funnel chest during the period of 35 years (1968-2002). In order to make a right diagnosis and to establish the indications for surgical treatment a standard algorithm of investigations was prepared: examination, collecting the detailed life history, establishing a type and a degree of deformation, chest and column radiological examination, ECG, spirography and heart ultrasound examination. RESULTS: On basis of physical examination and anamnestic data the most clinical signs and complaints were established. The heart compression was found in preoperative X-rays in 476 (94.4%) patients, the heart was rotated and dislocated in 441 (87.5%) patients. Postoperatively 96.1% of patients were free of the heart compression symptoms and for 71.8% the heart rotation has disappeared. The pathological ECG findings were recorded for 382 (71.8%) patients and abnormal spirograms were taken for 31 (8.5%) patients. CONCLUSIONS: The following indications for the funnel chest surgical treatment were established: - obvious funnel chest diagnozed by physical examination, - complaints and disturbances clear from anamnestic data, - heart rotation and compression established by radiological examination, - pathological findings in cardiorespiratory system (ECG, echocardiography, and spirography). An optimal age for operation was found out to be between 3 and 7 years.

Age Factors↗
PubMed2002

Multiscale displacement field measurements of compressed mineral-wool samples by digital image correlation.

We propose a multiscale approach to determine the displacement field by digital image correlation. The displacement field is first estimated on a coarse resolution image and progressively finer details are introduced in the analysis as the displacement is more and more securely and accurately determined. Such a scheme has been developed to increase the robustness, accuracy, and reliability of the image-matching algorithm. The procedure is used on two different types of examples. The first one deals with a representative image that is deformed precisely and purposefully to assess the intrinsic performances. In particular, the maximum measurable strain is determined. The second case deals with a series of pictures taken during compression experiments on mineral-wool samples. The different steps ofthe procedure are analyzed and their respective role is assessed. Both reflection and transmission images are tested.

Journal Article↗
PubMed1993

Generalized K-space analysis and correction of motion effects in MR imaging.

A new approach to understanding and reducing motion artifacts in magnetic resonance imaging (MRI) is introduced. This paper presents a novel technique for correcting generalized motion artifacts arising from translation, rotation, dilation, and compression, or any combination thereof. We also describe a new pulse sequence and a specialized postprocessing technique required to suppress these motion artifacts. The correction algorithm corrects for generalized motion. The theoretical basis of the correction scheme is founded upon the (k,t)-space formalism and the concept of pulse sequence contrast mapping functions. The proposed (k,t) formalism is based on the Fourier projection slice theorem and allows us to determine how motion artifacts arise. The correction technique currently suffers from some spatial resolution and signal-to-noise ratio limitations, and works better for small objects than large objects. These problems will be investigated in subsequent studies.

Artifacts↗
PubMed2005

[Clinical appearance and diagnostic tools in suspected deep-vein thrombosis].

Deep-vein thrombosis is a severe systemic disorder with high socio-economic impact. Because the clinical findings are not as typical as the classical diagnostic signs would suggest, different score-systems have been established to assess the pre-test-probability. Among the frequently used screening methods the D-Dimer-test seems to be most successful. Compression-ultrasound seems to replace the x-ray phlebography, used up to now as a "golden standard", to prove a suspected diagnosis. A standardized algorithm may be helpful in increasing the validity and precision of diagnostic tools.

Diagnosis, Differential↗
PubMed2005

Toward atlas-assisted automatic interpretation of MRI morphological brain scans in the presence of tumor.

RATIONALE AND OBJECTIVES: Determination of distorted brain anatomy surrounding a tumor causing a mass effect is much more difficult than interpretation of normal brain scans, particularly because this distortion is not easily predictable a tumor may be located in any place and vary substantially in size, shape, and radiological appearance. The objective of our work is to provide a qualitative means for rapid estimation of brain anatomy distorted by tumor. MATERIALS AND METHODS: Toward achieving this objective, we use an electronic and deformable brain atlas of gross anatomy along with a fast atlas-to-data warping technique. The deformed atlas determines the distorted anatomy surrounding a tumor and can be used for structure labeling (naming). The warping algorithm uses the Talairach transformation followed by three-dimensional nonlinear tumor deformation based on a geometric assumption that the tumor, delineated on radiological images, compresses its surrounding tissues radially. RESULTS: The approach is implemented and a dedicated application is developed. It processes the data automatically in five steps: (1) load data, (2) set the Talairach landmarks and perform the Talairach transformation, (3) segment the tumor, (4) warp the scan nonlinearly in three dimensions, and (5) explore the scan. The approach is very fast, and a magnetic resonance imaging scan is processed in 10-15 seconds on a standard personal computer. It is fully automatic and gives the user control over the entire process. CONCLUSION: Despite its limitations in modeling and validation, this practical solution provides a rapid and potentially useful qualitative assessment of anatomy deformed by a mass effect tumor.

Anatomy, Artistic↗
PubMed1991

Management of persistent or recurrent urinary incontinence after placement of artificial urinary sphincter.

A rational systematic approach is presented in the evaluation of 14 men with persistent or recurrent urinary incontinence after placement of the AMS800 artificial urinary sphincter. Mechanical malfunctions, including device leaks and control assembly malfunctions, may often be discovered with physical examination and radiographic evaluations. Nonmechanical malfunctions, such as cuff erosion, inadequate cuff compression and functional urethral atrophy, can be diagnosed with perfusion sphincterometry, urethroscopy and a filling cystometrogram, all combined in 1 simplified technique. With the presented algorithm the over-all success rate after 1 revision was 82%. Mechanical malfunctions appear to have a better revision rate of success than nonmechanical malfunctions (100% versus 71.5%, respectively).

Humans↗
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↗
PubMed2006

[The treatment of trophic ulcers of venous etiology from the standpoint of evidence-based medicine. Review of literature].

Presented herein is a review of the modern world literature devoted to the pressing problem of phlebology--the treatment of trophic ulcers. In the given review all the available data on the modern treatment methods for trophic ulcers, resting on the criteria of evidence-based medicine (EBM), are systematized. Proceeding from these data we have evaluated the efficacy and safety of different approaches to the treatment of trophic ulcers and created the diagnostic and treatment algorithm for patients suffering from the pathology in question. The literature review, resting on the general criteria of evidence-based medicine, has demonstrated that the main current trends in the management of venous ulcers are moist healing, compression therapy, and surgical treatment. However, despite this fact there is a number of unsolved problems concerned first of all with the creation of the integral diagnostic and treatment program for patients with venous ulcers, based on the significant statistical data.

Algorithms↗
PubMedDate not supplied

Correlation of multimodality imaging in Paget's disease of bone.

PURPOSE: The aim of this study is double: 1. to review the known and less known radiographic patterns of Paget's disease of bone, employing the most recent imaging techniques; 2. to propose a rationale algorithm for the diagnosis and management of the disease. considering its inconsistency and clinical variability. MATERIALS AND METHODS: Forty-eight patients with Paget's disease of bone (30 males and 18 females, aged 45 and 88 years, mean age 71) were examined in the period 1999-2003. The patients were classified into two groups: symptomatic and asymptomatic. The first group, comprising 32 patients with generic ''low back pain'' with or without sciatica, or ''coxarthritis'' underwent conventional radiography. In the second group (16 patients), bone disease was discovered in course of radiological and/or scintigraphic examinations performed for other conditions. Subsequently, all the patients completed the diagnostic algorithm, consisting of radiographs of the remaining skeletal areas and those segments with abnormal scintigraphic uptake. RESULTS: Monostotic Paget's disease was observed in 31 cases (64.6%), of whom 20 males (64.6%) and 11 females (35.4%), whereas polyostotic disease was found in 17 cases (35.4%), of whom 10 males (58.8%) and 7 females (41.2%). The sites most frequently affected in the monostotic form were: pelvis, 13 cases (43.3%); femur, 5 cases (16.7%); lumbar spine, 5 cases (16.7%); humerus, 2 cases (6.7%); tibia, 2 cases (6.7%); dorsal spine, skull, radius, patella, 1 case respectively (3.3%). In the polyostotic disease (17 cases), the affected bones were predominantly the skull, vertebral spine and pelvis (see text for their variable association). Pathologic fractures of the femur were found in two males. Osteogenic sarcoma (histological diagnosis) developed in the proximal femur in a 81 year-old male. CONCLUSIONS: Paget's disease is asymptomatic in the majority of affected individuals, and may be discovered incidentally with diagnosis being made on routine radiographs obtained for other purposes. Sometimes the x-ray features are so typical that the diagnosis is straightforward. Bone scan should be the imaging technique of choice, because tracer uptake is directly related to degree of activity of disease, and it may advance any radiographic evidence. Vertebral involvement is better evaluated by CT. Both CT and MRI are recommended in spine complications (pathological fractures, radicular or cord compression syndromes, malignant degeneration).

Aged↗
PubMed2006

Analytical solutions of the ideal model for gradient liquid chromatography.

The analytical solutions of the ideal model for gradient elution that ignores the influence of the solute concentration on the retention factor (k) were studied by using the method of characteristics for solving partial differential equations. It is found for any gradient profiles and solvent strength models used that the concentration of the solute will be discontinuous where the mobile-phase composition is. On a given characteristic curve, the product of the concentration and the retention factor is kept constant at the point where the concentration is continuous. At the point where the concentration is discontinuous, the product on the left side of this point is equal to that on the right side. We also discussed the basic equations to predict the retention time in gradient elution and introduced the injection time into them. For linear solvent strength stepwise and linear gradient elution, general expressions were proposed for the prediction and they can be used as the basis to derive others for specific gradient modes such as single linear, stepwise, and ladderlike gradients. For these modes, simple expressions to account for the band compression and the concentration change during the elution were also given.

Algorithms↗