A new fabrication method for precision antenna reflectors for space flight and ground test

Communications satellites are using increasingly higher frequencies that require increasingly precise antenna reflectors for use in space. Traditional industry fabrication methods for space antenna reflectors employ successive modeling techniques using high- and low-temperature molds for reflector face sheets and then a final fit-up of the completed honeycomb sandwich panel antenna reflector to a master pattern. However, as new missions are planned at much higher frequencies, greater accuracies will be necessary than are achievable using these present methods. A new approach for the fabrication of ground-test solid-surface antenna reflectors is to build a rigid support structure with an easy-to-machine surface. This surface is subsequently machined to the desired reflector contour and coated with a radio-frequency-reflective surface. This method was used to fabricate a 2.7-m-diameter ground-test antenna reflector to an accuracy of better than 0.013 mm (0.0005 in.) rms. A similar reflector for use on spacecraft would be constructed in a similar manner but with space-qualified materials. The design, analysis, and fabrication of the 2.7-m-diameter precision antenna reflector for antenna ground tests and the extension of this technology to precision, space-based antenna reflectors are described

Structural design of a vertical antenna boresight 18.3 by 18.3-m planar near-field antenna measurement system

A large very precise near-field planar scanner was proposed for NASA Lewis Research Center. This scanner would permit near-field measurements over a horizontal scan plane measuring 18.3 m by 18.3 m. Large aperture antennas mounted with antenna boresight vertical could be tested up to 60 GHz. When such a large near field scanner is used for pattern testing, the antenna or antenna system under test does not have to be moved. Hence, such antennas and antenna systems can be positioned and supported to simulate configuration in zero g. Thus, very large and heavy machinery that would be needed to accurately move the antennas are avoided. A preliminary investigation was undertaken to address the mechanical design of such a challenging near-field antenna scanner. The configuration, structural design and results of a parametric NASTRAN structural optimization analysis are contained. Further, the resulting design was dynamically analyzed in order to provide resonant frequency information to the scanner mechanical drive system designers. If other large near field scanners of comparable dimensions are to be constructed, the information can be used for design optimization of these also

Hardware development for the surface tension driven convection experiment aboard the USML-1 spacelab mission

The Surface Tension Driven Convection Experiment is a Space Transportation System flight experiment to study both transient and steady thermocapillary fluid flows aboard the USML-1 Spacelab mission planned for March 1992. Hardware is under development to establish the experimental conditions and perform the specified measurements, for both ground based research and the flight experiment in a Spacelab single rack. Major development areas include an infrared thermal imaging system for surface temperature measurement, a CO2 laser and control system for surface heating, and for flow visualization, a He-Ne laser and optical system in conjunction with an intensified video camera. For ground based work the components of each system were purchased or designed, and tested individually. The three systems will be interfaced with the balance of the experimental hardware and will constitute a working engineering model. A description of the three systems and examples of the component performance is given along with the plans for the development of flight hardware

Frequency and type of interval adverse events during the waiting period to complex aortic endovascular repair

Objective: The aim of the present study was to evaluate the frequency and type of adverse events that can occur during the waiting period to complex aortic endovascular repair. Methods: We performed a retrospective study of all elective patients with complex aortic aneurysms (including pararenal, suprarenal, thoracoabdominal, and aortic arch aneurysms) that had required a custom-made device (CMD) from Cook Medical (Bloomington, Ind) at a tertiary referral vascular center (November 2010 to May 2020). The waiting period was defined as the interval between the date of the stent-graft order and the date of the procedure or cancellation. Interval adverse events were defined as any event that had occurred during the waiting period and led to either mortality, aneurysm rupture, or cancellation of the planned procedure. Results: A total of 235 patients (mean age, 72 years; 25% female) had had a CMD graft ordered (201 planned as a single-stage procedure). The median waiting time until surgery was 106 days (interquartile range [IQR], 77-146 days) in the whole cohort and 101 days (IQR, 77-140 days) for the single-stage cohort. The planned procedure was performed electively in 219 patients (93%), with an overall 30-day elective mortality of 2% (n = 5). A total of 16 interval adverse events occurred during the waiting period. Of these 16 events, 10 were aneurysm ruptures and 6 were cancellations of the procedure owing to non–aneurysm-related deaths (3% of the entire cohort). A total of 10 interval deaths were registered (4.2%), 4 of which were aneurysm related. The risk of rupture during the waiting period (Kaplan-Meier) was 6.1% ± 2.3% at 180 days. The median interval from the stent-graft order to aneurysm rupture was 101 days (IQR, 54-200 days). Of the 10 aneurysm ruptures that had occurred, 6 had undergone emergent repair, with 0% mortality at 30 days (one open repair, one t-Branch, one physician-modified endograft, two cases for which the CMD was already available, one case for which a different CMD was available). Conclusions: The median waiting time from the stent-graft order to implantation was ∼15 weeks. During this waiting period, a substantial proportion of patients could experience adverse events, either related to aneurysm rupture or underlying comorbidities. The risk of rupture during the waiting period exceeded the risk of perioperative mortality. Thus, efforts to decrease this risk could significantly improve the outcomes. A combination of different techniques might play a vital role in reducing the mortality after cases of interval rupture

Screening for Abdominal Aortic Aneurysm among Patients Referred to the Vascular Laboratory is Cost-effective

AbstractScreening for abdominal aortic aneurysm (AAA) in high-risk groups has been recommended based on a high prevalence of disease, while being questioned due to a high frequency of co-morbidities and inferior life-expectancy. We evaluated the long-term outcome and the cost-effectiveness of selective AAA screening among patients referred to the vascular laboratory for arterial examination.MethodsA total of 5924 patients, referred to the vascular laboratory of a university hospital, were screened for AAA with ultrasound (definition: ∅≥30mm), 1993–2005. Outcome data were gathered through hospital records and the national population registry. A Markov model was used for health–economic evaluation.ResultsAn AAA was detected in 181 patients (mean age 72.8 years), of whom 21.5% underwent elective repair (perioperative mortality 5.1%) after 7.5 years of follow-up. Four of six patients diagnosed with AAA rupture were operated upon. Relative 5-year survival compared with the general Swedish population, controlled for age and sex, was 80.4% (95% confidence interval (CI): 70.8–88.8). The cost-effectiveness was robust in base-case (11 084 Euro/life year gained) and in sensitivity analyses of prevalence, cost and survival.ConclusionsPatients in whom AAA was detected at selective screening had inferior long-term survival and were operated on less frequently, compared with AAA patients described in previous studies. Yet, selective screening at the vascular laboratory was cost-effective

Early Experience With a Novel Dissection-Specific Stent-Graft to Prevent Distal Stent-Graft-Induced New Entry Tears After Thoracic Endovascular Repair of Chronic Type B Aortic Dissections

Background: The aim was to report short and mid-term outcomes of a novel, investigational, dissection-specific stent-graft (DSSG), specifically designed to address the features of chronic type B aortic dissection (CTBAD) and reduce the risk of distal stent-graft-induced new entry tears (dSINE). Materials and Methods: A retrospective single center cohort study of all patients undergoing TEVAR with the DSSG for CTBAD from January 1, 2017 to January 31, 2020. The DSSG, which is a modified stent-graft based on the Cook Zenith Alpha Thoracic platform, has no proximal barbs, and a customized longer body length with substantial taper. The second and third distal Z-stents are sited internally to avoid any contact of the metal skeleton with the dissection membrane and have reduced radial force, while the most distal stent was removed creating a distal 30 mm unsupported Dacron graft. Results: Sixteen patients (13 males, 3 females) with a median age of 66 years (range 31–79 years) underwent elective TEVAR of CTBAD using the DSSG. Six patients (38%) had an underlying connective tissue disorder. The median tapering was 10 mm (range 4 mm–21 mm) and median length 270 mm (range 210–380 mm). Technical success was achieved in all but one case (96%). One patient died within 30 days, due to retrograde type A dissection with cardiac tamponade. The 30-day rate of stroke, spinal cord ischemia, and re-interventions was 0%. After median imaging follow-up time of 17 months (range 1–31 months), one patient developed a dSINE 4 months after the index procedure. After median survival follow-up of 23 months (range 2–35 months), one late death occurred due to traumatic brain injury, while no aortic-related death occurred during follow-up. Complete false lumen (FL) thrombosis was achieved in 9 patients while the remaining 6 showed partial FL thrombosis. No instances of diameter increase at the level oftreated aortic segment were noted with serial measurements showing either stable (n = 7) or decreased (n = 8) maximal transverse diameter. Conclusions: Use of a novel DSSG with low radial force for TEVAR in the setting of CTBAD is safe and feasible. This early real-world experience shows promising mid-term effectiveness with low rates of dSINE or unplanned re-interventions and satisfactory aortic remodeling during follow-up. Longer follow-up is needed, however, before any firm conclusions can be drawn

Dynamics of Selected Biomarkers in Cerebrospinal Fluid During Complex Endovascular Aortic Repair – A Pilot Study

INTRODUCTION: Ischemic spinal cord injury (SCI) is a serious complication of complex aortic repair. Prophylactic cerebrospinal fluid (CSF) drainage, used to decrease lumbar cerebrospinal fluid (CSF) pressure, enables monitoring of CSF biomarkers that may aid in detecting impending SCI. We hypothesized that biomarkers, previously evaluated in traumatic SCI and brain injury, would be altered in CSF over time following complex endovascular aortic repair (cEVAR). OBJECTIVES: To examine if a chosen cohort of CSF biomarker correlates to SCI and warrants further research. METHODS: A prospective observational study on patients undergoing cEVAR with extensive aortic coverage. Vital parameters and CSF samples were collected on ten occasions during 72 hours post-surgery. A panel of ten biomarkers were analyzed (Neurofilament Light Polypeptide (NFL), Tau, Glial Fibrillary Acidic Protein (GFAP), Soluble Amyloid Precursos Protein (APP) α and β, Amyloid β 38, 40 and 42 (Aβ38, 40 and 42), Chitinase-3-like protein 1 (CHI3LI or YKL-40), Heart-type fatty acid binding protein (H-FABP).). RESULTS: Nine patients (mean age 69, 7 males) were included. Median total aortic coverage was 68% [33, 98]. One patient died during the 30-day post-operative period. After an initial stable phase for the first few postoperative hours, most biomarkers showed an upward trend compared with baseline in all patients with >50% increase in value for NFL in 5/9 patients, in 7/9 patients for Tau and in 5/9 patients for GFAP. One patient developed spinal cord and supratentorial brain ischemia, confirmed with MRI. In this case, NF-L, GFAP and tau were markedly elevated compared with non-SCI patients (maximum increase compared with baseline in the SCI patient versus mean value of the maximal increase for all other patients: NF-L 367% vs 79%%, GFAP 95608% versus 3433%, tau 1020% vs 192%). CONCLUSION: . This study suggests an increase in all ten studied CSF biomarkers after coverage of spinal arteries during endovascular aortic repair. However, the pilot study was not able to establish a specific correlation between spinal fluid biomarker elevation and clinical symptoms of SCI due to small sample size and event rate

Intravascular Ultrasound in the Detection of Bridging Stent Graft Instability During Fenestrated and Branched Endovascular Aneurysm Repair Procedures: A Multicentre Study on 274 Target Vessels

Objective: The use of intravascular ultrasound (IVUS) reduces contrast medium use and radiation exposure during conventional endovascular aneurysm repair (EVAR). The aim of this study was to evaluate the safety and efficacy of IVUS in detecting bridging stent graft (bSG) instability during fenestrated and branched EVAR (F/B-EVAR). Methods: This was a prospective observational multicentre study. The following outcomes were evaluated: (1) technical success of the IVUS in each bSG, (2) IVUS findings compared with intra-operative angiography, (3) incidence of post-operative computed tomography angiography (CTA) findings not detected with IVUS, and (4) absence of IVUS related adverse events. Target visceral vessel (TVV) instability was defined as any branch or fenestration issues requiring an additional manoeuvre or re-intervention. Any IVUS assessment that detected stenosis, kinking, or any geometric TVV issue was considered to be branch instability. All procedures were performed in ad hoc hybrid rooms. Results: Eighty patients (69% males; median age 72 years; interquartile range 59, 77 years) from four aortic centres treated with F/B-EVAR between January 2019 and September 2021 were included: 70 BEVAR (21 off the shelf; 49 custom made), eight FEVAR (custom made), and two F/B-EVAR (custom made), for a total of 300 potential TVVs. Two TVVs (0.7%) were left unstented and excluded from the analysis. The TVVs could not be accessed with the IVUS catheter in seven cases (2.3%). Furthermore, 17 (5.7%) TVVs could not be examined due to a malfunction of the IVUS catheter. The technical success of the IVUS assessment was 91.9% (274/298), with no IVUS related adverse events. Seven TVVs (2.5%) showed signs of bSG instability by means of IVUS, leading to immediate revisions. The first post-operative CTA at least 30 days after the index procedure was available in 268 of the 274 TVVs originally assessed by IVUS. In seven of the 268 TVVs (2.6%) a re-intervention became necessary due to bSG instability. Conclusion: This study suggests that IVUS is a safe and potentially valuable adjunctive imaging technology for intra-operative detection of TVV instability. Further long term investigations on larger cohorts are required to validate these promising results and to compare IVUS with alternative technologies in terms of efficiency, radiation exposure, procedure time, and costs