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At least 829 records · Page 46Linked to original sources
PubMed1995

Rapid, Cost-Effective Diagnosis of Spinal Cord Compression Due to Cancer.

Spinal cord compression in patients with cancer is a devastating complication that can be prevented by effective early detection of epidural metastases. Older algorithms for the diagnosis of epidural metastases call for plain spine films and bone scans, followed by magnetic resonance imaging (MRI) in appropriate patients. Data from the only prospective study of back pain in cancer patients demonstrate that immediate MRI of the symptomatic area provides a more rapid diagnosis, is less expensive, and obviates the need for a time-consuming series of studies. A "screening" total-spine MRI using a shortened but comprehensive protocol would lead to further reductions in cost.

Journal Article↗
PubMed2001

[To select and measure the biomechanical properties of bone of rat].

In the experimental studies designed to evaluate the effects of different factors on the biomechanical properties of bone, careful selection of rats and the scientific indices is very important. The aim of this paper is to recommend some essential methods for testing and calculating the biomechanical properties of rat bone such as tension, compression, bending and torsion.

Algorithms↗
PubMed2003

Current strategies in the management of spinal metastatic disease.

The treatment of metastatic spinal cord compression is complex. The three treatment modalities that are currently applied (in a histologically non-specific manner) are surgery, radiotherapy and the administration of steroids. The development of new spinal instrumentations and surgical approaches considerably changed the extent of therapeutic options in this field. These new surgical techniques have made it possible to resect these tumours totally, with subsequent vertebral reconstruction and spinal stabilization. In this respect, it is important to clearly identify those patients who can benefit from such an extensive surgery. We present our management algorithm to help select patients for surgery and at the same time identifying those for whom primary non-surgical therapy would be indicated. The retrospective review of surgically treated patients in our department in the last four years reveals a meagre application of conventional guidelines for the selection of the appropriate operative approach in the surgical management of these patients. The reasons for this discrepancy are discussed.

Algorithms↗
PubMed2006

Corroboration of mechanoregulatory algorithms for tissue differentiation during fracture healing: Comparison with in vivo results.

Several mechanoregulation algorithms proposed to control tissue differentiation during bone healing have been shown to accurately predict temporal and spatial tissue distributions during normal fracture healing. As these algorithms are different in nature and biophysical parameters, it raises the question of which reflects the actual mechanobiological processes the best. The aim of this study was to resolve this issue by corroborating the mechanoregulatory algorithms with more extensive in vivo bone healing data from animal experiments. A poroelastic three-dimensional finite element model of an ovine tibia with a 2.4 mm gap and external callus was used to simulate the course of tissue differentiation during fracture healing in an adaptive model. The mechanical conditions applied were similar to those used experimentally, with axial compression or torsional rotation as two distinct cases. Histological data at 4 and 8 weeks, and weekly radiographs, were used for comparison. By applying new mechanical conditions, torsional rotation, the predictions of the algorithms were distinguished successfully. In torsion, the algorithms regulated by strain and hydrostatic pressure failed to predict healing and bone formation as seen in experimental data. The algorithm regulated by deviatoric strain and fluid velocity predicted bridging and healing in torsion, as observed in vivo. The predictions of the algorithm regulated by deviatoric strain alone did not agree with in vivo data. None of the algorithms predicted patterns of healing entirely similar to those observed experimentally for both loading modes. However, patterns predicted by the algorithm based on deviatoric strain and fluid velocity was closest to experimental results. It was the only algorithm able to predict healing with torsional loading as seen in vivo.

Animals↗
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↗
PubMed2001

Pulmonary embolism diagnosis in hospitalized and intensive care unit patients.

The diagnosis of acute pulmonary embolism (PE) remains difficult, and diagnostic strategies must consider the unique challenges of hospitalized and critically ill patients. Diagnostic algorithms that are effective and safe for outpatients may not be effective and safe for inpatients or patients in intensive care units. For example, serial compression ultrasonography (US) of the lower extremities may allow physicians to avoid pulmonary angiography for stable inpatients or outpatients, but this strategy is not validated for patients who require intensive care for serious underlying cardiopulmonary disease. Helical computed tomography (CT) is particularly suited for the evaluation of suspected PE for inpatients with serious cardiopulmonary disease. However, the safety of withholding treatment when a helical CT pulmonary angiogram is negative remains to be demonstrated. Lung perfusion and ventilation scans combined with an assessment of pretest probability remain important objective tests for the evaluation of many hospitalized patients.

Acute Disease↗
PubMed1999

An intelligent, interactive platform for ophthalmic teaching, telemedicine, and telecollaboration: design considerations and prototype construction.

The development of technologies permitting processing, compression, and transmission of digital images and image sequences enables powerful methodologies for local and remote medical teleconsultation. We are developing a slit-lamp-based ophthalmic augmented reality (image overlay) environment incorporating features to permit real-time, interactive teaching, telemedicine, and telecollaboration. A binocular slit-lamp biomicroscope interfaced to a CCD camera, framegrabber board, and PC permits acquisition and rendering of anterior segment and retinal images. Computer-vision algorithms facilitate robust tracking, registration, and near-video-rate image overlay of previously stored retinal photographic and angiographic images onto the real-time fundus image. Our algorithms facilitate shared control of pointing, drawing, and measuring functions registered with the retinal image video stream and direct audio communication between an examiner (student, generalist) and remote observer (instructor, specialist). Bandwidth and video compression considerations limit the frame rate and latency for video stream transmission. Excellent and acceptable performance are demonstrated in model eyes over a local area network and through a modem connection, respectively. These studies represent the first investigations towards the design and implementation of an intelligent platform for ophthalmic telemedicine and telecollaboration.

Algorithms↗
PubMed2004

Ischemic-preconditioning does not prevent neuromuscular dysfunction after ischemia-reperfusion injury.

The primary purpose of this study was to evaluate ischemic-preconditioning (IPC) as a means of improving tolerance to ischemia-reperfusion (IR) stress on neuromuscular function. A secondary objective was to isolate the area of injury within the neuromuscular unit responsible for contractile dysfunction after IR injury. Twenty-eight male rabbits were randomly assigned to four groups (sham, IPC only, sustained ischemia only, IPC and sustained ischemia). The IPC protocol consisted of three cycles of 10 min of tourniquet-induced ischemia (125 mmHg) followed by 10 min of reperfusion. Sustained ischemia was induced by 350 mmHg external compression for 2 h. Peak tetanic tension of the tibialis anterior (TA) muscle was evaluated 48 h after the tourniquet protocol by both peroneal nerve and direct muscle stimulation, with and without pharmacologic neuromuscular junction blockade. Animals subjected to combined IPC and sustained ischemia had an equivalent loss of contractile force to those undergoing sustained ischemia alone. Two hours of tourniquet-induced ischemia resulted in marked dysfunction of the TA neuromuscular unit when evaluated by peroneal nerve stimulation (p < 0.0001). Isolation of the TA muscle from the peroneal nerve with direct muscle stimulation and neuromuscular junction blockade preserved muscle function after 3 h of ischemia. In our model, these results clearly demonstrate that IPC provides no significant protective effect from IR injury to either nerve or muscle function in our model. In addition, nerve or neuromuscular junction injury, rather than muscle damage, is identified as primarily responsible for IR-related muscle dysfunction.

Algorithms↗
PubMed1995

Identification of elastic properties of homogeneous, orthotropic vascular segments in distension.

Characterization of the constitutive behavior of normal and pathological blood vessel segments could provide the clinician with a means to predict the onset and assess the severity of certain vascular maladies. Many of the constitutive models that have been proposed to date either fail to properly consider certain features of the anatomic structure and function of vascular tissue or are so mathematically complex that their utilization is intractable. We have developed a material identification technique that first required the adaptation and validation of a constitutive law describing the nonlinear, three-dimensional behavior of orthotropic, compressible, hyperelastic vascular segments. By coupling a nonlinear finite element program and experimental data with a robust nonlinear least-squares regression algorithm, a set of elastic parameters (moduli) is obtained. Regressions on data for a canine carotid artery and rabbit infrarenal aorta yielded coefficients of variation of 0.21 and 0.08, respectively. The estimated moduli demonstrated certain trends found by other investigators: both the canine carotid artery and rabbit aorta were found to be stiffer radially than circumferentially, and the former was found to be stiffer circumferentially than longitudinally. Using these material constants and measured arterial pressures, the stress distribution was computed for each specimen. The predicted radial stress was consistent with a transmural variation of approximately--p (applied luminal pressure) to approximately zero in both specimens, while the circumferential stresses ranged from 2.2p to 0.7p for the canine carotid, and from 6.4p to 3.7p for the rabbit aorta. The stress distributions qualitatively agreed with those reported in previous investigations, as well as with certain physiologic observations. Based on the results of our two sample cases, we believe that our technique could be beneficial to the assessment of the three-dimensional, anisotropic behavior of vascular tissue.

Animals↗
PubMed2005

Fuzzy wavelet packet based feature extraction method and its application to biomedical signal classification.

In this paper, we develop an efficient fuzzy wavelet packet (WP) based feature extraction method for the classification of high-dimensional biomedical data such as magnetic resonance spectra. The key design phases involve: 1) a WP transformation mapping the original signals to many WP feature spaces and finding optimal WP decomposition for signal classification; 2) feature extraction based on the optimal WP decomposition; and 3) signal classification realized by a linear classifier. In contrast to the standard method of feature extraction used in WPs, guided by the criteria of signal compression or signal energy, our method is used to extract discriminatory features from the WP coefficients of the optimal decomposition. The extraction algorithm constructs fuzzy sets of features (via fuzzy clustering) to assess their discriminatory effectiveness. This paper includes a number of numerical experiments using magnetic resonance spectra. Classification results are compared with those obtained from common feature extraction methods in the WP domain.

Algorithms↗
PubMed1997

Thickness-equalization processing for mammographic images.

A digital postprocessing technique was used to compensate for the limitations of laser film or cathode-ray-tube devices used to display digital mammograms. An algorithm identified and equalized for the large change in digital signal caused by the reduction in thickness at the margin of the compressed breast. The resulting images reflected only breast composition, and so the number of gray levels needed to display the processed image was greatly reduced, which facilitated presentation and analysis.

Female↗
PubMed2005

Posterior ankle impingement syndrome.

Posterior ankle impingement syndrome is a clinical disorder characterized by posterior ankle pain that occurs in forced plantar flexion. The pain may be acute as a result of trauma or chronic from repetitive stress. Pathology of the os trigonum-talar process is the most common cause of this syndrome, but it also may result from flexor hallucis longus tenosynovitis, ankle osteochondritis, subtalar joint disease, and fracture. Patients usually report chronic or recurrent posterior ankle pain caused or exacerbated by forced plantar flexion or push-off maneuvers, such as may occur during dancing, kicking, or downhill running. Diagnosis of posterior ankle impingement syndrome is based primarily on clinical history and physical examination. Radiography, scintigraphy, computed tomography, and magnetic resonance imaging depict associated bone and soft-tissue abnormalities. Symptoms typically improve with nonsurgical management, but surgery may be required in refractory cases.

Algorithms↗
PubMedDate not supplied

[Choice of surgical approach in cervical spondylogenic myelopathy].

The purpose of this study was to provide a rationale for surgical decompression in degenetative stenosis in terms of differential electrophysiological evaluation of sensory and motor conduction. The study has provided an algorithm for a comprehensive preoperative examination of patients, which makes it possible to perform differentiated decompressive operations for cervical myelopathy with the higher efficiency of postoperative neurological recovery as compared with conventional methods.

Algorithms↗
PubMed2006

High reliability outdoor sonar prototype based on efficient signal coding.

Many mobile robots and autonomous vehicles designed for outdoor operation have incorporated ultrasonic sensors in their navigation systems, whose function is mainly to avoid possible collisions with very close obstacles. The use of these systems in more precise tasks requires signal encoding and the incorporation of pulse compression techniques that have already been used with success in the design of high-performance indoor sonars. However, the transmission of ultrasonic encoded signals outdoors entails a new challenge because of the effects of atmospheric turbulence. This phenomenon causes random fluctuations in the phase and amplitude of traveling acoustic waves, a fact that can make the encoded signal completely unrecognizable by its matched receiver. Atmospheric turbulence is investigated in this work, with the aim of determining the conditions under which it is possible to assure the reliable outdoor operation of an ultrasonic pulse compression system. As a result of this analysis, a novel sonar prototype based on complementary sequences coding is developed and experimentally tested. This encoding scheme provides the system with very useful additional features, namely, high robustness to noise, multi-mode operation capability (simultaneous emissions with minimum cross talk interference), and the possibility of applying an efficient detection algorithm that notably decreases the hardware resource requirements.

Data Compression↗
PubMed2003

A multi-scale probabilistic network model for detection, synthesis and compression in mammographic image analysis.

We develop a probabilistic network model over image spaces and demonstrate its broad utility in mammographic image analysis, particularly with respect to computer-aided diagnosis. The model employs a multi-scale pyramid decomposition to factor images across scale and a network of tree-structured hidden variables to capture long-range spatial dependencies. This factoring makes the computation of the density functions local and tractable. The result is a hierarchical mixture of conditional probabilities, similar to a hidden Markov model on a tree. The model parameters are found with maximum likelihood estimation using the expectation-maximization algorithm. The utility of the model is demonstrated for three applications: (1) detection of mammographic masses for computer-aided diagnosis; (2) qualitative assessment of model structure through mammographic synthesis; and (3) compression of mammographic regions of interest.

Female↗
PubMed1996

Fitting hearing aids to individual loudness-perception measures.

OBJECTIVE: The purpose of this study was to compare the prescribed gain, compression ratios, compression thresholds, and the relative predicted speech intelligibility (Speech Intelligibility Index [SII], American National Standards Institute 3.79, proposed) provided by four strategies proposed for selecting hearing aid parameters for low-threshold compression hearing instruments and by a traditional threshold-based hearing aid fitting procedure. The strategies used were Desired Sensation Level Input/Output (DSLTM[i/o]; Cornelisse, Seewald, & Jamieson, 1994), Visual Input-Output Locator Algorithm (VIOLA; Cox, 1994), FIG6 strategy (Killion, Reference Note 2), Ricketts and Bentler strategy (RAB), and a threshold-based hearing aid fitting procedure (National Acoustics Laboratories-Revised [NAL-R]; Byrne & Dillion, 1986). These new strategies have been suggested as alternatives to threshold-based strategies, which do not provide the varying amounts of target gain, as a function of input level, necessary to fit low-threshold compression hearing aids. DESIGN: The electroacoustic prescriptions and the predicted speech intelligibility were calculated across all five fitting strategies for 20 subjects. The threshold and loudness growth information used for each fitting was reported previously (Ricketts & Bentler, in press). RESULTS: Comparison across prescriptions revealed that the NAL-R strategy (due to the linear gain provided) prescribed the least gain for low-level inputs and the greatest gain for high-level inputs. Gain comparisons across fitting by loudness (FBL) strategies revealed a more shallow frequency response slope for strategies that require individual measures of loudness growth (RAB, VIOLA) in comparison with strategies that assumed average data (FIG6, DSLTM[i/o]). SII results revealed greater predicted speech intelligibility for the FIG6 and the DSLTM[i/o] compared with the NAL-R, RAB, and VIOLA. These differences were most apparent in noise backgrounds and least evident when loudness differences were minimized. CONCLUSIONS: It appears that differences in SII scores across the FBL fitting strategies are due, in part, to differences in the loudness of the output signal. It is assumed that differences in high-frequency shaping may also be a factor. These data do not appear to support the use of additional clinical time to obtain individual loudness growth measures. However, due to the fact that SII results are based on average performance, it is difficult to predict whether differences across these fitting strategies would be realized in actual measures of speech intelligibility or sound quality on an individual basis.

Correction of Hearing Impairment↗
PubMed2001

A hierarchical storage management (HSM) scheme for cost-effective on-line archival using lossy compression.

A hierarchical storage management (HSM) scheme for cost-effective on-line archival of image data using lossy compression is described. This HSM scheme also provides an off-site tape backup mechanism and disaster recovery. The full-resolution image data are viewed originally for primary diagnosis, then losslessly compressed and sent off site to a tape backup archive. In addition, the original data are wavelet lossy compressed (at approximately 25:1 for computed radiography, 10:1 for computed tomography, and 5:1 for magnetic resonance) and stored on a large RAID device for maximum cost-effective, on-line storage and immediate retrieval of images for review and comparison. This HSM scheme provides a solution to 4 problems in image archiving, namely cost-effective on-line storage, disaster recovery of data, off-site tape backup for the legal record, and maximum intermediate storage and retrieval through the use of on-site lossy compression.

Algorithms↗