True Failure Research Articles

Diminished Dose Minimally Invasive Radioguided Parathyroidectomy: A Case for Radioguidance

Minimally invasive radioguided parathyroidectomy (MIRP) has been established as an alternative to bilateral neck exploration (BNE) for primary hyperparathyroidism. We investigate whether a diminished dose of technetium-99m sestamibi gives similar results to the standard dose. One hundred one patients were offered MIRP or diminished-dose MIRP (ddMIRP). Patients received intravenous Tc-99m sestamibi at a dose of either 25 mCi 1.5 hours or 5 mCi 1 hour preoperatively. The procedure was terminated when the 20 per cent rule was satisfied. All tissue was confirmed to be parathyroid tissue by frozen section analysis. In addition, intraoperative parathyroid hormone levels were measured in a majority of patients. Patients who failed IOM underwent BNE. Frozen section analysis and intraoperative parathyroid hormone monitoring were also performed in the BNEs. Postoperatively, serum calcium levels were measured at 1 week and 6 months. Fifteen per cent of patients were male and 85 per cent were female. The median age was 63 years (range, 25-89 years). The first 58 patients had the standard dose of 25 mCi, whereas 43 patients had ddMIRP. Six patients (10%) failed intraoperative mapping in the MIRP group and were found to have single-gland disease. Five patients (12%) failed intraoperative mapping in the ddMIRP group. However, two patients were identified to have multigland disease making the true failure rate of intraoperative mapping 7 per cent (three patients). Median operative times for MIRP, ddMIRP, and BNE were 40 minutes, 46 minutes, and 105 minutes, respectively. The 20 per cent rule was satisfied in 96 per cent of patients undergoing MIRP and 98 per cent of patients undergoing ddMIRP. Frozen section analysis and intraoperative parathyroid hormone monitoring did not result in a change in management. Median follow up was 193 days and serum calcium levels at 6 months were normal. Diminished-dose MIRP is a feasible alternative to standard-dose MIRP without compromising surgical outcomes.

Endogenous reactivation and true treatment failure as causes of recurrent tuberculosis in a high incidence setting with a low HIV infection

To determine the relative frequencies of reinfection vs. reactivation or treatment failure in patients from a high tuberculosis incidence setting with a low prevalence of HIV infection. We performed DNA fingerprinting on serial isolates from one and multiple TB episodes from 97 retreatment patients; 35 patients had been previously cured, whereas 62 had not. DNA fingerprinting patterns of recurrence Mycobacterium tuberculosis isolates of 5 of the 35 previously cured patients did not match with those of the corresponding initial isolates, indicating reinfection. We did not document reinfection during treatment. Isolates from each of the remaining 30 previously cured patients had identical DNA fingerprinting results, indicating reactivation. DNA fingerprinting patterns of isolates from the 62 patients with persistently positive sputum smears were identical, suggesting treatment failure. These findings suggest that reinfection is not a common cause of relapse and treatment failure in this rural predominantly HIV-free population despite the high incidence of TB.

Regression analysis of failure time data with informative interval censoring

Interval censoring arises when a subject misses prescheduled visits at which the failure is to be assessed. Most existing approaches for analysing interval-censored failure time data assume that the censoring mechanism is independent of the true failure time. However, there are situations where this assumption may not hold. In this paper, we consider such a situation in which the dependence structure between the censoring variables and the failure time can be modelled through some latent variables and a method for regression analysis of failure time data is proposed. The method makes use of the proportional hazards frailty model and an EM algorithm is presented for estimation. Finite sample properties of the proposed estimators of regression parameters are examined through simulation studies and we illustrate the method with data from an AIDS study.

Reliability Sampling Methodology Using Simulation and Re-Sampling

This paper develops and validates a reliability sampling methodology using simulation, and re-sampling; and which incorporates unit-to-unit variation in the determination of significant sample sizes for analytically intractable reliability cases. This sample size determination is very important because the reliability of the sampled vehicles should represent the reliability of the entire fleet. Smaller-than-required sample sizes may lead to an incorrect representation of the reliability of the fleet, which may mislead the Army to make poor decisions, such as deploying a fleet that may not be reliable. These type II errors can be minimized by incorporating a more realistic sampling methodology, as developed in this research. Prior to using this methodology, analytical formulas were used to compute reliability sample sizes with unit-to-unit variation assumed to be constant. This new methodology confirms the analytically derived solutions for fixed usage & true failure rate, as well as for fixed usage & varying vehicle true failure rate. Existing reliability data shows that unit-to-unit variation does exist. Vehicle variation in true failure rate is modeled with a Gamma prior distribution. Recent reliability data are used to validate the hypothesis that this is an adequate tool for reliability sampling when unit-to-unit variation exists. Results of this validation accept the hypothesis, validating that the methodology is an adequate tool. The Army is currently using this methodology for fleet assessment

The Association Between Measures of Progression and Survival in Castrate-Metastatic Prostate Cancer

To explore the association between progression-free survival and overall survival time in patients with castration-resistant prostate cancer treated with microtubule-targeted therapies. We retrospectively studied patients treated in three trials evaluating a taxane or an epothilone for progressive castration-resistant prostate cancer. Study subjects were 98 patients with bone metastases; 63 of them also had soft tissue lesions. All scans were reviewed independently. Associations of radiographic progression-free survival and prostate-specific antigen (PSA) progression-free survival with survival time were measured using Kendall's tau, adjusted for right censoring. A smoothing procedure was applied to estimate Kendall's tau within each neighborhood of the follow-up process. The overall associations between progression-free survival time and overall survival time were moderate: 0.4 for radiographic progression-free survival and 0.33 for PSA progression-free survival. The association between radiographic progression-free survival and overall survival was weakest early in the follow-up process, whereas the PSA association was weakest when the progression-free survival-related event (PSA progression, death, or censoring) occurred after 6 months from the start of treatment. Current measures of progression-free survival time for men with castration-resistant prostate cancer are not strongly concordant with survival time. Factors that attenuate the association include interval censoring and the discontinuation of therapy early in the follow-up due to imaging changes that may not reflect true failure of the treatment. For radiographic progression-free survival, the association may be increased by requiring confirmation of progression with a second scan, as is routinely done when assessing response.

Performance of alloy 800H for high-temperature heat exchanger applications

The tensile properties of austenitic Alloy 800H have been evaluated at temperatures ranging from ambient to 1000 °C. The results indicate that the tensile strength was gradually reduced with increasing temperature. Between ambient temperature and 200 °C, the failure strain was reduced possibly due to the occurrence of dynamic strain aging followed by its enhancement at temperatures up to 500 °C. Alloy 800H did not exhibit any failure in an acidic solution at constant-load. However, the true failure stress in this environment was reduced at elevated temperatures under a slow-strain-rate condition. The magnitude of electrochemical potentials became more active with increasing temperature. A detrimental effect of more noble controlled potential on the cracking susceptibility was noted in terms of the true failure stress. A combination of ductile and intergranular brittle failures was seen in the primary fracture surface of the tested cylindrical specimens.

Technique of percutaneous, CT-guided radiofrequency ablation of small renal lesions under conscious sedation

RESULTS: From July 2001 to July 2005 we ablated 27 tumors in 23 patients with a mean follow-up of 24 months. The mean patient age was 74 years with a mode ASA score of 3. The mean renal mass size was 2.71 cm. The mean preoperative serum creatinine was 1.34, and the mean postoperative serum creatinine was 1.46, yielding a change which was not statistically different(p 0.46). Follow-up imaging revealed a 70%(16/23)initial success rate and a 17%(4/23)initial failure rate. Two of these failures underwent successful repeat ablation, 1 is on watchful waiting and 1 patient was a true failure. Our only complication was a large perinephric hematoma which resolved spontaneously.

Early observed transient prostate-specific antigen elevations on a pilot study of external beam radiation therapy and fractionated MRI guided High Dose Rate brachytherapy boost

PurposeTo report early observation of transient PSA elevations on this pilot study of external beam radiation therapy and magnetic resonance imaging (MRI) guided high dose rate (HDR) brachytherapy boost.Materials and methodsEleven patients with intermediate-risk and high-risk localized prostate cancer received MRI guided HDR brachytherapy (10.5 Gy each fraction) before and after a course of external beam radiotherapy (46 Gy). Two patients continued on hormones during follow-up and were censored for this analysis. Four patients discontinued hormone therapy after RT. Five patients did not receive hormones. PSA bounce is defined as a rise in PSA values with a subsequent fall below the nadir value or to below 20% of the maximum PSA level. Six previously published definitions of biochemical failure to distinguish true failure from were tested: definition 1, rise >0.2 ng/mL; definition 2, rise >0.4 ng/mL; definition 3, rise >35% of previous value; definition 4, ASTRO defined guidelines, definition 5 nadir + 2 ng/ml, and definition 6, nadir + 3 ng/ml.ResultsMedian follow-up was 24 months (range 18–36 mo). During follow-up, the incidence of transient PSA elevation was: 55% for definition 1, 44% for definition 2, 55% for definition 3, 33% for definition 4, 11% for definition 5, and 11% for definition 6.ConclusionWe observed a substantial incidence of transient elevations in PSA following combined external beam radiation and HDR brachytherapy for prostate cancer. Such elevations seem to be self-limited and should not trigger initiation of salvage therapies. No definition of failure was completely predictive.

Fatigue damage analysis in asphalt concrete mixtures using the dissipated energy approach

An asphalt concrete damage–energy fatigue approach based on the concept of change in dissipated energy is presented in this paper. The damage–energy based fatigue approach is simple and based on a sound theoretical background. The central concept of the energy approach is the energy fatigue curve, which is based on two key elements, namely the plateau value (PV) and the number of load cycles to true failure (Ntf). The plateau value represents the constant value of the percentage of dissipated energy that produces damage to the material under cyclic loading. Failure is defined as the number of load cycles at which this percentage of dissipated energy begins to increase rapidly, indicating instability. Flexural fatigue testing was used to test hundreds of asphalt concrete beams, mainly under controlled-strain testing conditions. It was found that PV is highly dependent on the initial loading conditions, stress, strain, and dissipated energy. As a result, it can be used conveniently in pavement design. The number of load cycles to 50% reduction in initial stiffness was found to be highly correlated with the new failure point (Ntf). Using the dissipated energy concepts in fatigue analysis makes it possible to account for damage accumulation in a straightforward manner.Key words: fatigue of asphalt concrete, dissipated energy, damage, energy ratio.

Cracking of Martensitic Alloy EP-823 Under Controlled Potential

The susceptibility of martensitic Alloy EP-823 to stress corrosion cracking was evaluated with and without an applied cathodic potential using the slow-strain-rate (SSR) testing technique. The magnitude of the applied potential was based on the corrosion potential determined by cyclic polarization. The cracking susceptibility in an acidic environment at different temperatures was expressed in terms of the true failure stress (σf), time to failure (TTF), and ductility parameters, including percent elongation (%El) and percent reduction in area (%RA). The data indicate that the magnitudes of σf, TTF, %El, and %RA were reduced due to cathodic charging. The scanning electron microscopic evaluations of the primary fracture surface of the specimens used in SSR testing revealed a combination of ductile and brittle failures. Further, the secondary cracks at the gauge section of these specimens were characterized by branching.

Set theoretic formulation of performance reliability of multiple response time‐variant systems due to degradations in system components

AbstractThis paper presents a design stage method for assessing performance reliability of systems with multiple time‐variant responses due to component degradation. Herein the system component degradation profiles over time are assumed to be known and the degradation of the system is related to component degradation using mechanistic models. Selected performance measures (e.g. responses) are related to their critical levels by time‐dependent limit‐state functions. System failure is defined as the non‐conformance of any response and unions of the multiple failure regions are required. For discrete time, set theory establishes the minimum union size needed to identify a true incremental failure region. A cumulative failure distribution function is built by summing incremental failure probabilities. A practical implementation of the theory can be manifest by approximating the probability of the unions by second‐order bounds. Further, for numerical efficiency probabilities are evaluated by first‐order reliability methods (FORM). The presented method is quite different from Monte Carlo sampling methods. The proposed method can be used to assess mean and tolerance design through simultaneous evaluation of quality and performance reliability. The work herein sets the foundation for an optimization method to control both quality and performance reliability and thus, for example, estimate warranty costs and product recall. An example from power engineering shows the details of the proposed method and the potential of the approach. Copyright © 2006 John Wiley & Sons, Ltd.

Connection failure detection mechanism of UMTS charging protocol

In Universal Mobile Telecommunications System (UMTS), the extension of GPRS tunneling protocol called GTP' is utilized to transfer the charging data records (CDRs) from GPRS support nodes (GSNs) to charging gateways (CGs). To ensure that the mobile operator receives the charging information, availability for the GTP' transmission is essential. One important issue on GTP' availability is connection failure detection. It is desirable to select appropriate parameter values to avoid false failure detections (e.g., temporary network congestions) while to detect the true failures quickly. We propose an analytic model to compute the false failure detection probability and the expected true failure detection time. Based on our study, the network operator can select the appropriate parameter values for various traffic conditions to reduce the probability of false failure detection and/or true failure detection time.

The Role of Applied Potential on Environment-Assisted Cracking of Zirconium Alloys

Abstract Zircaloy-2 and Zircaloy-4 have been tested by the slow-strain-rate technique at ambient and elevated temperatures in an acidic environment relevant to the proposed geologic repository at the Yucca Mountain site. Tests were performed with and without cathodic and anodic applied potentials. The results of stress corrosion cracking testing without applied potentials indicate that the ductility of both alloys was enhanced in terms of percent elongation, percent reduction in area, failure strain, and the time-to-failure with increasing temperature indicating improved ductility. However, the magnitude of true failure stress was gradually reduced at higher testing temperatures. The application of anodic and cathodic controlled potentials during slow-strain-rate testing enhanced the cracking susceptibility of both alloys showing more pronounced effect at anodic applied potentials. The corrosion potential for both alloys, became more active at the elevated temperature. The morphology of failure at cathodic potentials was ductile, showing dimpled microstructure. However, transgranular brittle failure was observed with both alloys at anodic controlled potentials.

Degradations of Type 422 stainless steel in aqueous environments

The susceptibility of Type 422 stainless steel (UNS S42200) to stress corrosion cracking (SCC) and localized corrosion was determined in neutral and acidic aqueous solutions at ambient and elevated temperatures. No failures were observed in the neutral solution at constant load. SCC testing by the slow-strain-rate technique revealed reduced ductility, time-to-failure and true failure stress due to the combined effect of elevated temperature and lower pH. These parameters were further reduced due to the cathodic charging. The localized corrosion studies using the cyclic potentiodynamic polarization technique showed pits and crevices in all specimens. Metallographic and fractographic evaluations showed secondary cracks along the gage section, and a combination of ductile and brittle failures at the primary fracture face of the tested specimen, respectively, depending upon the test environment.

Post‐hypoxic hypoperfusion is associated with suppression of cerebral metabolism and increased tissue oxygenation in near‐term fetal sheep

Secondary cerebral hypoperfusion is common following perinatal hypoxia-ischaemia. However, it remains unclear whether this represents a true failure to provide sufficient oxygen and nutrients to tissues, or whether it is simply a consequence of reduced cerebral metabolic demand. We therefore examined the hypothesis that cerebral oxygenation would be reduced during hypoperfusion after severe asphyxia, and further, that the greater neural injury associated with blockade of the adenosine A(1) receptor during the insult would be associated with greater hypoperfusion and deoxygenation. Sixteen near-term fetal sheep received either vehicle or 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) for 1 h, followed by 10 min of severe asphyxia induced by complete occlusion of the umbilical cord. Infusions were discontinued at the end of the occlusion and data were analysed for the following 8 h. A transient, secondary fall in carotid artery blood flow and laser Doppler flow was seen from approximately 1-4 h after occlusion (P < 0.001), with no significant differences between vehicle and DPCPX. Changes in laser Doppler blood flow were highly correlated with carotid blood flow (r(2)= 0.81, P < 0.001). Cortical metabolism was suppressed, reaching a nadir 1 h after occlusion and then resolving. Cortical tissue P(O(2)) was significantly increased at 1, 2 and 3 h after occlusion compared to baseline, and inversely correlated with carotid blood flow (r(2)= 0.69, P < 0.001). In conclusion, contrary to our initial hypothesis, delayed posthypoxic hypoperfusion was associated with suppression of cerebral metabolism and increased tissue P(O(2)), and was not significantly affected by preceding adenosine A1 blockade. These data suggest that posthypoxic hypoperfusion is actively mediated and reflects suppressed cerebral metabolism.

Pediatric Enteral Nutrition

Common to all pediatric patients receiving enteral nutrition is the inability to consume calories orally. This is often secondary to issues of inadequate weight gain, inadequate growth, prolonged feeding times, weight loss, a decrease in weight/age or weight/height ratios, or a persistent triceps skinfold thickness <5% for age. Enteral nutrition requires enteral access. In the neonatal period the nasoenteric route is usually used. In pediatric patients requiring long-term enteral access, surgically, endoscopically, or radiologically placed percutaneous feeding tubes are common. Jejunal feeding tubes are used in pediatric patients with gastric feeding intolerance or persistent gastroesophageal reflux. Low-profile enteral access devices are preferred by most pediatric patients because of their cosmetic appearance. For most children, a standard pediatric polypeptide enteral formula is well tolerated. There are specialized pediatric enteral formulas available for patients with decreased intestinal length, altered intestinal absorptive capacity, or altered pancreatic function. Weaning patients from tube feeding to oral nutrition is the ultimate nutrition goal. A multidisciplinary approach to patients with short bowel syndrome will maximize the use of enteral nutrition while preserving parenteral nutrition for patients with true enteral nutrition therapy failure.

Reply

Sir, We thank Dr. Sjors Coppus for his interest in our article. The sensitivity and specificity of 3D-HyCoSy stated in the article referred to those for detection of tubal patency in our study, as stated in the abstract and results sections of the manuscript. Although the sensitivity and specificity for tubal occlusion are used in most studies, some studies did express their results in terms of tubal patency 1, 2 including the largest study evaluating the diagnostic accuracy of HyCoSy as compared to laparoscopy by Hamilton et al. 1. In fact, the same problem exists when studies comparing the diagnostic accuracy of various modalities of evaluating tubal patency. In the future, it will be ideal to standardize the data presentation method. In our study, we were unable to determine the tubal patency in 8 out of 42 (19%) tubes. In two patients (9.5% of patients), the procedure was abandoned because of excessive pain. They represented true procedure failure. The percentage was compatible with that reported (7.4%) in the literature 1. We failed to trace the remaining 4 tubes in 2 patients to the fimbrial end and hence could not draw a conclusion as to whether the tubes were patent. This represented 10.5% of all tubes that were subjected to 3D-HyCoSy assessment and was again compatible with that reported (7.4%) in the study by Hamilton et al. 1. Two early studies evaluating tubal patency with 3D-HyCoSy reported even higher failure rates (14.9% and 24%) in visualizing the entire tube 2, 3. The interpretation and calculation of the test accuracy of the inconclusive results from 3D-HyCoSy did present a problem. There is no ideal way to solve this problem, which happens in real clinical situations. We have chosen to assume those which were inconclusive as discordant with laparoscopy so as not to over-exaggerate the diagnostic accuracy of this new modality of tubal assessment at the expense of underestimating its performance. Nevertheless, we believe that one should be more stringent in the evaluation of a new diagnostic method. Underestimating is always better than overestimating its usefulness as a new diagnostic tool. Expressing the sensitivity and specificity of the HyCoSy test based on the number of Fallopian tubes studied has been used previously 1, 2, 4. Using the number of Fallopian tubes rather than patients studied as the base for calculation better reflects the usefulness of this new diagnostic tool in the study of tubal status. Even when clinical practice is concerned, unilateral tubal blockage still bears significance in deciding the treatment that should be advised. Patients should be treated with superovulation and intrauterine insemination only when both tubes are patent. Those with tubal disease including unilateral tubal blockage should be offered in vitro fertilization early. There is little controversy in the operator dependency of conventional 2D-HyCoSy as pointed out by Dr. Sjors Coppus. 3D-HyCoSy has the advantage that the images can be captured at the time of scanning and be evaluated later, so that the requirement on the technique of the operator is minimal. Although we did not evaluate the intrapersonal variability in diagnosis of tubal patency, the reproducibility can be indirectly reflected by the relatively lower percentage of tubes that could not be evaluated in our study as compared to that previously reported 2, 3. All images were analyzed by a single investigator and hence any interpersonal variation was eliminated. We admit that this study was a preliminary one and further evaluation on the diagnostic accuracy, patient acceptability, and cost-effectiveness has to be performed before it can be recommended as a standard diagnostic tool in the initial assessment of patients with subfertility.

The Corrosion Behavior of Nickel-base Austenitic Alloys for Nuclear Hydrogen Generation

ABSTRACTThree nickel-base austenitic alloys, namely Alloy C-22, Alloy C-276 and Waspaloy have been tested for evaluation of their corrosion resistance in an acidic solution at ambient and elevated temperatures. The results of stress corrosion cracking studies indicate that none of these materials did exhibit any failure at constant load. The cracking susceptibility determined by the slow strain rate technique was gradually enhanced at higher temperatures showing reduced ductility and true failure stress. The critical potentials determined by the polarization technique, became more active (negative) with increasing temperature. The fractograpic evaluations by scanning electron microscopy (SEM) revealed ductile failure in Alloys C-22 and C-276. However, Waspaloy showed brittle failure at elevated temperature.

Metallurgical and Corrosion Studies of Modified T91 Grade steel

ABSTRACTModified 9Cr-1Mo steels containing different Silicon (Si) content have been tested for evaluation of their metallurgical and corrosion properties. The results of tensile testing indicated reduced failure strain up to 400°C followed by its enhancement at a higher temperature. Stress corrosion cracking tests at constant load did not show any failure in any materials. However, reduced ductility and true failure stress were noted in slow strain rate (SSR) testing, indicating increased cracking susceptibility at elevated temperatures. The corrosion potential became more active with increasing temperature in polarization studies. A combination of intergranular and cleavage failures was observed in specimens tested by the SSR technique.

Defining biochemical failure after radiotherapy with and without androgen deprivation for prostate cancer

To compare several characteristics of alternative definitions of biochemical failure (BF) in men with extended follow-up after radiotherapy (RT) with or with androgen deprivation therapy (ADT) for prostate cancer. From December 1, 1991, to April 30, 1998, 688 men with Stage T1c-T3NX-N0M0 prostate cancer received RT alone (n = 586) or RT plus ADT (n = 102) with a minimal follow-up of 4 years and five or more "ADT-free" posttreatment prostate-specific antigen levels. BF was defined by three methods: (1) the ASTRO definition (three consecutive rises in prostate-specific antigen level); (2) a modified American Society for Therapeutic Radiology Oncology (ASTRO) definition requiring two additional consecutive rises when a decline immediately subsequent to three consecutive rises occurred; and (3) the "Houston" or nadir plus 2-ng/mL definition (a rise of at least 2 ng/mL greater than the nadir). The sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy were determined for each using clinical progression as the endpoint. Furthermore, the misclassification rates for a steadily rising prostate-specific antigen level, ability to satisfy the proportional hazards (RT with or without ADT), effects of short follow-up, and intervals to the diagnosis of BF were compared. The misclassification rate for BF using the nadir plus 2-ng/mL definition was 2% for RT alone and 0% for RT plus ADT compared with 0% and 0% for the modified ASTRO definition, and 5% and 23% for the ASTRO definition, respectively. The hazard rates for RT alone and RT plus ADT were proportional only for the nadir plus 2 ng/mL definition and seemingly unaffected by the length of follow-up. For RT with or without ADT, the nadir plus 2 ng/mL definition was the most specific (RT, 80% vs. RT plus ADT, 75%) with the greatest positive predictive value (RT, 36% vs. RT plus ADT, 25%) and overall accuracy (RT, 81% vs. RT plus ADT, 77%). A greater proportion of BF was diagnosed in the first 2 years of follow-up with the nadir plus 2 ng/mL definition compared with the ASTRO definition (13% vs. 5%, p = 0.0138, chi-square test). The nadir plus 2 ng/mL definition was the best predictor of sustained, true, biochemical, and clinical failure, and was not affected by the use of ADT or follow-up length.