Noncentral forces in crystals of charged colloids.

The elastic properties of fcc crystals consisting of charge stabilized colloidal particles are determined from real space imaging experiments using confocal microscopy. The normal modes and the force constants of the crystal are obtained from the fluctuations of the particles around their lattice sites using the equipartition theorem. We show that the Cauchy relation is not fulfilled and that only noncentral many-body forces can account for the elastic properties.

Temporal updating scheme for probabilistic neural network with application to satellite cloud classification--further results.

A novel temporal updating approach for probabilistic neural network classifiers was developed by Tian et al. (2000) to account for temporal changes of spectral and temperature features of clouds in the visible and infrared GOES 8 (Geostationary Operational Environmental Satellite) imagery data. In this paper, a new method referred to as moving singular value decomposition (MSVD) is introduced to improve the classification rate of the boundary blocks or blocks containing cloud types with non-uniform texture. The MSVD method is then incorporated into the temporal updating scheme and its effectiveness is demonstrated on several sequences of GOES 8 cloud imagery data. These results indicate that the incorporation of the new MSVD improves the overall performance of the temporal updating process by almost 10%

Temporal updating scheme for probabilistic neural network with application to satellite cloud classification.

In cloud classification from satellite imagery, temporal change in the images is one of the main factors that causes degradation in the classifier performance. In this paper, a novel temporal updating approach is developed for probabilistic neural network (PNN) classifiers that can be used to track temporal changes in a sequence of images. This is done by utilizing the temporal contextual information and adjusting the PNN to adapt to such changes. Whenever a new set of images arrives, an initial classification is first performed using the PNN updated up to the last frame while at the same time, a prediction using Markov chain models is also made based on the classification results of the previous frame. The results of both the old PNN and the predictor are then compared. Depending on the outcome, either a supervised or an unsupervised updating scheme is used to update the PNN classifier. Maximum likelihood (ML) criterion is adopted in both the training and updating schemes. The proposed scheme is examined on both a simulated data set and the Geostationary Operational Environmental Satellite (GOES) 8 satellite cloud imagery data. These results indicate the improvements in the classification accuracy when the proposed scheme is used.

A study of cloud classification with neural networks using spectral and textural features.

The problem of cloud data classification from satellite imagery using neural networks is considered in this paper. Several image transformations such as singular value decomposition (SVD) and wavelet packet (WP) were used to extract the salient spectral and textural features attributed to satellite cloud data in both visible and infrared (IR) channels. In addition, the well-known gray-level cooccurrence matrix (GLCM) method and spectral features were examined for the sake of comparison. Two different neural-network paradigms namely probability neural network (PNN) and unsupervised Kohonen self-organized feature map (SOM) were examined and their performance were also benchmarked on the geostationary operational environmental satellite (GOES) 8 data. Additionally, a postprocessing scheme was developed which utilizes the contextual information in the satellite images to improve the final classification accuracy. Overall, the performance of the PNN when used in conjunction with these feature extraction and postprocessing schemes showed the potential of this neural-network-based cloud classification system.

Relationship of age, gender, race, and body size to infrarenal aortic diameter. The Aneurysm Detection and Management (ADAM) Veterans Affairs Cooperative Study Investigators.

PURPOSE: To assess the effects of age, gender, race, and body size on infrarenal aortic diameter (IAD) and to determine expected values for IAD on the basis of these factors. METHODS: Veterans aged 50 to 79 years at 15 Department of Veterans Affairs medical centers were invited to undergo ultrasound measurement of IAD and complete a pre-screening questionnaire. We report here on 69,905 subjects who had no previous history of abdominal aortic aneurysm (AAA) and no ultrasound evidence of AAA (defined as IAD > or = 3.0 cm). RESULTS: Although age, gender, black race, height, weight, body mass index, and body surface area were associated with IAD by multivariate linear regression (all p < 0.001), the effects were small. Female sex was associated with a 0.14 cm reduction in IAD and black race with a 0.01 cm increase in IAD. A 0.1 cm change in IAD was associated with large changes in the independent variables: 29 years in age, 19 cm or 40 cm in height, 35 kg in weight, 11 kg/m2 in body mass index, and 0.35 m2 in body surface area. Nearly all height-weight groups were within 0.1 cm of the gender means, and the unadjusted gender means differed by only 0.23 cm. The variation among medical centers had more influence on IAD than did the combination of age, gender, race, and body size. CONCLUSIONS: Age, gender, race, and body size have statistically significant but small effects on IAD. Use of these parameters to define AAA may not offer sufficient advantage over simpler definitions (such as an IAD > or = 3.0 cm) to be warranted.

Variability in measurement of abdominal aortic aneurysms. Abdominal Aortic Aneurysm Detection and Management Veterans Administration Cooperative Study Group.

PURPOSE: The purpose of this study was to report interobserver and intraobserver variability of computed tomography (CT) measurements of abdominal aortic aneurysm (AAA) diameter and agreement between CT and ultrasonography observed in the course of a large, multicenter, randomized trial on the management of small AAAs. METHODS: CT measurements of AAA diameter from participating centers were compared with measurements made from the same scan by a central laboratory. Blinded central remeasurement of a randomly selected subset of these CT scans was used to assess intraobserver variability. Agreement between AAA measurements by CT and ultrasonography done within 30 days of each other was also assessed. RESULTS: For interobserver pairs of local and central CT measurements of AAA diameter (n = 806), the difference was 0.2 cm or less in 65% of pairs, but 17% differed by at least 0.5 cm. For intraobserver pairs of central CT remeasurements (n = 70), 90% differed by 0.2 cm or less, 70% were within 0.1 cm, and only one differed by 0.5 cm. Of 258 ultrasound-measured and central CT pairs, the difference was 0.2 cm or less in 44% and at least 0.5 cm in 33%. Ultrasound measurements were smaller than central CT measurements by an average of 0.27 cm (p < 0.0001). Local CT and ultrasound measurements showed a marked preference for recording by half centimeter. CONCLUSIONS: A high degree of precision is possible in CT measurement of AAA diameter, but this precision may not be obtained in practice because of differences in measurement techniques. Differences between imaging modalities increase variability further. Variations in AAA measurement of 0.5 cm or more are not uncommon, and this should be taken into account in management decisions. Efforts to reduce variation in measurement are warranted and might include (1) seeking agreement between surgeons and radiologists on a precise definition of AAA diameter, (2) limiting the number of radiologists who measure AAAs, and (3) use of calipers and magnifying glass for CT measurements.

Use of titanium implants in pedicular screw fixation.

Several types of pedicular screw systems have been utilized to augment lumbar spine fusion. All systems are made of stainless steel, which interferes with imaging techniques, especially MRI and CT scans. In search of a solution for this problem, we decided to study the use of titanium systems in the lumbar spine. Because there were no titanium pedicle screw systems available on the market, we decided to use the titanium Alta system currently used for femur fractures. This report details our experience in using this device for lumbar spine fusion. From 1990 to 1992, 25 patients underwent thoracic and lumbar fusion with Alta titanium screws and plates. Spinal fusion was performed for a variety of conditions, including metastatic tumor, fracture, spondylolisthesis, pseudoarthrosis, and postdecompressive instability. All but two patients obtained solid fusion clinically and radiographically and considerable improvement in back pain. There was loosening of the implant in both patients. Both patients had osteoporosis. One of these two patients developed pseudoarthrosis, which required further surgery. The other patient with a metastatic tumor of the spine remained asymptomatic without change in the spine alignment despite progression of the tumor. There were no broken screws encountered during follow-up. Two patients sustained subsequent fracture of the vertebra above the fusion. One of the patients also developed a fracture below the fusion. Fusion with titanium implants allowed postoperative evaluation and subsequent periodic examination of the spinal canal with high-quality MR images as well as significant reduction of artifacts on CT scan.(ABSTRACT TRUNCATED AT 250 WORDS)

Design of the abdominal aortic Aneurysm Detection and Management Study. ADAM VA Cooperative Study Group.

PURPOSE: This study describes the design of an ongoing randomized trial intended to determine which of two strategies is superior for managing small abdominal aortic aneurysms (AAA). METHODS: Patients aged 50 to 79 years with AAA 4.0 to 5.4 cm in diameter as determined by computed tomography (CT) who are not at high surgical risk are randomized to either repair of the AAA, called "immediate surgery," or follow-up of the AAA with ultrasonography or CT every 6 months, reserving surgery for those aneurysms that enlarge to 5.5 cm, enlarge rapidly, or become symptomatic, called "selective surgery." RESULTS: The primary outcome measure is all-cause death, and secondary outcome measures are AAA-related death, morbidity, and general health status. The study design calls for 1350 patients to be randomized and monitored for a mean of 5 years. A second objective of the study is to accurately define the prevalence and risk factors for AAA with use of information from the large screening program established to detect AAA for recruitment into the randomized trial. CONCLUSIONS: By the end of 1993, 38,697 patients had been screened with ultrasonography, accounting for about three fourths of new randomizations, and 330 patients had been enrolled (70% of the target rate).

Selective screening for abdominal aortic aneurysms with physical examination and ultrasound.

Abdominal aortic aneurysm (AAA) is an important cause of preventable death in older persons. Persistently high rupture mortality rates indicate that these deaths can be prevented only by early detection and treatment of AAA. In an effort to develop an effective and efficient program of AAA detection, we selectively screened a high-risk population. Men aged 60 to 75 years with hypertension and/or coronary artery disease were randomly selected from a general medicine clinic and screened with physical examination and ultrasound. Eighteen previously unsuspected aneurysms, 3.6 to 5.9 cm in size (mean, 4.4 cm), were detected in 201 patients, for a prevalence of 9% (95% confidence interval: 4.7% to 13.3%). The specificity and positive predictive value of ultrasound were each 100%. Abdominal palpation detected only half of these aneurysms, but missed none in patients with an abdominal girth less than 100 cm (n = 6). This degree of sensitivity did not occur with "routine" examinations and requires that the examination be directed specifically toward AAA detection. We conclude that undiagnosed AAAs are common in this large subgroup of the clinic population, that ultrasound is an excellent screening test for AAAs, and that physical examination may be adequate for screening thin patients. We recommend that every two or three years persons over the age of 50 years undergo careful abdominal palpation aimed at detecting AAAs, as part of the periodic health examination. We further recommend that obese older men at high risk for AAA have at least one-time screening with abdominal ultrasound, regardless of findings on physical examination.

Hepatobiliary imaging: the diagnostic use of intravenous morphine in fasting patients.

Fasting and parenteral nutrition are associated with a spectrum of gallbladder disorders. We reviewed the use of hepatobiliary imaging in patients (N = 42) with fasting-induced gallbladder dysfunction. Intravenous morphine was administered in patients (N = 20) whose gallbladders did not visualize at 40 minutes after administration of diisopropyl iminodiacetic acid. In those patients whose gallbladders visualized with morphine (N = 8), the diagnosis of acute cholecystitis was excluded. Of those that did not visualize after morphine administration (N = 12), all were clinically diagnosed as acute cholecystitis. Although ultrasound is effective in demonstrating the anatomical features of prolonged gallbladder stasis including sludge, stones, and thickened gallbladder wall, it cannot detect cystic duct patency. Cholescintigraphy is an accurate test of cystic duct patency, but gallbladder stasis interferes with the ability of cholescintigraphy to visualize the gallbladder. From our experience, we propose that cholescintigraphy with intravenous morphine is beneficial in demonstrating cystic duct patency in fasting patients.

Detailed caliceal anatomy for endourology.

A thorough understanding of caliceal anatomy is required to interpret excretory urograms and to perform safely endourological manipulations. Caliceal angles, posterior rotation of the lateral renal margin and caliceal placement in relation to the lateral aspect of the body were studied in 26 right and 24 left kidneys. Differences between kidneys found to be Brödel's types from those of the Hodson type, and the significance of these findings for performing nephrostolithotomy are described.

Pursuit of the renal mass. Is ultrasound enough?

The accuracy of ultrasonography in evaluating renal masses was assessed retrospectively in 260 renal lesions detected by intravenous urography in 242 patients. The ultrasonographic diagnosis was confirmed by cyst puncture, surgery, or autopsy. Of the lesions, 168 were benign cysts, and all were diagnosed correctly by ultrasonography. The remaining 92 lesions were renal carcinomas, and 90 were diagnosed correctly by ultrasonography. In retrospect, it was clear that the two missed cancers did not fulfill all the ultrasonographic criteria for a cyst. An algorithm is presented for the differential diagnosis of renal masses primarily by ultrasonography, and the arguments in favor of operative diagnosis of renal masses are rebutted. With the approach described, invasive studies such as cyst puncture and arteriography will be required for a definitive diagnosis in fewer than 10 percent of patients, and the morbidity and expense of the diagnostic approach will be minimized, with no decrease in accuracy.

Use of CT to reduce understaging in prostatic cancer: comparison with conventional staging techniques.

Thirty prostatic cancer patients were evaluated for staging purposes with both CT (18-sec scan speed) and certain commonly used "conventional" diagnostic tests, namely: radionuclide bone scan with correlative plain films, the prostatic fraction of the serum acid phosphatase, excretory urogram, and chest radiograph. All patients included in the study had histopathologic proof of diagnosis. CT correctly identified extracapsular prostatic cancer spread locally or in pelvic lymph nodes in 14% of patients with completely negative conventional studies. Sensitivity of extracapsular tumor spread detection increased from 41% to 59% by adding CT to the conventional studies. CT confirmed the presence of tumor spread and localized it in 43% of patients with positive conventional studies. Conventional studies were positive when tumor spread was present in 32% of patients with negative CT. CT reduces understaging when conventional tests are negative, localizes and confirms tumor spread when conventional tests are positive, but cannot demonstrate tumor spread in some patients whose conventional tests are positive and who are subsequently shown to have tumor spread histopathologically.