Worst-case Position Research Articles

Spot-scanning proton therapy for targets with adjacent cardiac implantable electronic devices - Strategies for breast and head & neck cancer.

Cardiac implantable electronic device (CIED) malfunctions can be induced by secondary neutron dose from spot-scanning proton therapy. A recent in-vitro study investigating secondary neutron dose to CIEDs up to 7mSv per fraction found that exposure of secondary neutrons in this range was clinically manageable. This study presents decision algorithms proposed by a national expert group for selection of patients with breast and head & neck (H&N) cancer with CIEDs adjacent to target for proton therapy based on the 7mSv threshold. Ten patients with breast cancer and five with H&N cancer were included in the study. Five patients with breast cancer received photon therapy with CIED and proton plans were retrospectively created. The remaining patients received proton therapy without CIED and a worst-case position of a virtual CIED was retrospectively delineated. Secondary neutron dose was estimated as ambient dose equivalent H*(10) using Monte Carlo simulations. For patients with breast cancer and with contralateral CIED, the secondary neutron dose to the CIED was below 7mSv per fraction for CTV<1500cm3 in 2Gy fractions and CTV<1000cm3 in 2.67Gy fractions. The secondary neutron dose to the CIED was below 7mSv per fraction for all patients with H&N cancer. Simulations of neutron exposure suggest that proton therapy is feasible for most patients with CIED adjacent to target. This forms the basis for decision algorithms for selection of patients with CIED for proton therapy.

Robust Localization Using Time Difference of Arrivals

We investigate a localization problem using time-difference-of-arrival measurements with unknown and bounded measurement errors. Different from most existing algorithms, we consider the minimization of the worst-case position estimation error to improve the robustness of the algorithm. The localization problem is formulated as a nonconvex optimization problem. We adopt semidefinite relaxation to relax the original problem into a convex optimization problem, which can be solved using existing semidefinite program solvers. Simulation results show that our proposed algorithm has lower worst-case position estimation error than other existing algorithms.

Cardiac fibrillation risk of Taser weapons.

The debate on potential health hazards associated with delivering electric discharges to incapacitated subjects, in particular on whether electric discharge weapons are lethal, less lethal or non-lethal, is still controversial. The cardiac fibrillation risks of Taser weapons X26 and X3 have been investigated by measuring the delivered high-tension pulses in dependence on load impedance. Excitation thresholds and sinus-to-Taser conversion factors have been determined by numerical modeling of endocardial, myocardial, and epicardial cells. Detailed quantitative assessment of cardiac electric exposure has been performed by numerical simulation at the normal-weighted anatomical model NORMAN. The impact of anatomical variation has been quantified at an overweight model (Visible Man), both with a spatial resolution of 2 × 2 × 2 mm voxels. Spacing and location of dart electrodes were systematically varied and the worst-case position determined. Based on volume-weighted cardiac exposure assessment, the fibrillation probability of the worst-case hit was determined to 30% (Taser X26) and 9% (Taser X3). The overall risk assessment of Taser application accounting for realistic spatial hit distributions was derived from training sessions of police officers under realistic scenarios and by accounting for the influence of body (over-)weight as well as gender. The analysis of the results showed that the overall fibrillation risk of Taser use is not negligible. It is higher at Taser X26 than at Taser X3 and amounts to about 1% for Europeans with an about 20% higher risk for Asians. Results demonstrate that enhancement as well as further reduction of fibrillation risk depends on responsible use or abuse of Taser weapons.

Lagrangian Point State Estimation with Optimized, Redundant Induction Coil Gauges

This research effort studies the use of redundant induction coil gauges to reduce state estimation uncertainties for moving Lagrangian points (LPs); e.g. discrete points, moving interfaces, projectiles, etc. The technique embeds a small, high-strength magnet at the LP and simultaneously tracks the magnet continuously with five (5) or more induction coils along a single axis of motion. A calibrated coil gauge model is presented as a function of LP position and velocity. The optimized LP state (position and velocity) estimate based upon redundant LP observations allows direct solution for LP velocity; requiring only one differentiation step to obtain acceleration. A specific experimental implementation (Particulate Materials Meso-scale Diagnostics system) is simulated to evaluate and minimize the expected state estimation errors. Induction coil signals with various levels of noise are simulated based upon a prescribed LP state variation with time. The state optimization algorithm attempts to recover the truth state values. Worst-case position estimation errors of ±0.3 mm and velocity estimation errors of ±0.46 m/s are determined for LPs travelling 0–1,000 m/s at realistic in-lab data noise levels.

Regarding the Value Reported for the Term “Spatial Gradient Magnetic Field” and How This Information Is Applied to Labeling of Medical Implants and Devices

translational attraction for a medical device that is conducted according to the proce-dure described by the American Society for Testing and Materials (ASTM) Internation-al Designation F 2052–06e1, “Standard Test Method for Measurement of Magnetically Induced Displacement Force on Passive Im-plants in the MR Environment.” Using this technique, a test apparatus with a protractor (also called the fixture) is placed in an MR system with a horizontal magnetic field at the point of the highest accessible spatial gradi-ent magnetic field [6]. In general, the highest spatial gradient magnetic field used to assess translational attraction for a medical device is located off-axis, at a side wall, and near the opening of the bore of the scanner [1, 3]. Alternatively, the medical device is assessed for translational attraction at the point where the highest deflection angle occurs in associ-ation with the particular MR system used for the assessment. The angular deflection of the device from the vertical is measured and the translational attraction is calculated [6].Notably, the placement of the test fixture (apparatus with the protractor) in the MR system is at a position where it can be used properly (i.e., securely positioned) for the test procedure. This is almost always a worst-case position of greatest attractive force that the patient with the device will pass through when entering the bore of the MR system for an examination.For example, Figure 1 shows the measure -ment of translational attraction using the de -flection angle test as it was applied to evaluate an endoscope adapter. Note the positioning of the test fixture (the apparatus with the pro-tractor). It was placed off-axis near the mouth of the bore of the scanner at the point of the highest accessible spatial gradient magnetic field (i.e., 720 gauss/cm for the 3-T MR sys-tem used for this test). The deflection angle was 36° for the endoscope adapter.

Statistical characterization of composite protection levels for GPS

A statistical characterization is presented of Global Positioning System (GPS) user range error as a normally distributed random variable with non-zero mean over the length of the aircraft precision approach operation, correlated from one GPS measurement epoch to another and from one satellite to another. This leads directly to modeling GPS error in the position domain as multivariate normal with non-zero mean. Based on this model, a vertical composite protection level VPLc and a horizontal composite protection level HPLc are each calculated as scalar values from a univariate normal distribution displaced from the origin by the worst-case position domain bias combination possible, given the maximum possible individual satellite bias magnitudes and the satellite geometry. A method is then presented by which exact values--that is, values accurate to a user-defined error tolerance and consistent with statistical assumptions--of VPLc and HPLc are obtained, and by which computationally efficient approximations may be evaluated. A statistical quadratic form under the multivariate normal distribution is used to derive a new class of protection levels based on the probability enclosed within a radius defined in two or more dimensions. A central Chi-square representation of this quadratic form is also presented and is incorporated into a six-step computational procedure for the two-dimensional composite radial protection level RPLc. This procedure is extended to the spherical protection level (SPLc) and the ellipsoidal protection level (EPLc).

Comparison of fast three-dimensional simulation and actinic inspection for extreme ultraviolet masks with buried defects and absorber features

The printability of buried extreme ultraviolet (EUV) defects near absorber features is studied using aerial images from the actinic inspection tool (AIT) and the fast EUV mask simulation program RADICAL. This work begins by comparing the printability of isolated defects through focus predicted by RADICAL and measured by the AIT. Then, images of defects near features from both simulation and experiment are investigated for different defect sizes and positions through focus. Finally, RADICAL is used to assess the expected defect printability levels in the less in coherent conditions which are expected to be used for production. Defect printability will be investigated as a function of defect size, position, and focus for the small absorber lines critical to 22nm imaging using a top-hat illumination condition of sigma=0.75. Here, defects as small as 0.8nm surface height cause a critical dimension (CD) change greater than 10% at best focus when located in the worst case position. Defects as small as 2.2nm cause a CD change greater than 10% even when located under the center of the absorber.

Small female head and neck interaction with a deploying side airbag

Objective: This paper presents dummy and cadaver experiments designed to investigate the injury potential of an out-of-position small female head and neck from a deploying side airbag. Methods: Seat-mounted, thoracic-type, side airbags were selected for this study to represent those currently available on selected luxury automobiles. A computer simulation program was used to identify the worst case loading position for the small female head and neck. Once the initial position was identified, experiments were performed with the Hybrid III 5th percentile dummy and three small female cadavers, using three different inflators. Results: Peak head center of gravity (CG) accelerations for the dummy ranged from 71× g to 154× g, and were greater than cadaver values, which ranged from 68× g to 103× g. Peak neck tension as measured at the upper load cell of the dummy increased with inflator aggressivity from 992 to 1670 N. A conservative modification of the US National Highway Traffic Safety Administration’s (NHTSA’s) N ij proposed neck injury criteria, which combines neck tension and bending, was used. All values were well below the 1.0 injury threshold for the dummy and suggested a very low possibility of neck injury. In agreement with this prediction, no injuries were observed. Conclusions: Even in a worst case position, small females are at low risk of head or neck injuries under loading from these thoracic-type airbags; however, injury risk increases with increasing inflator aggressivity.

The effects of electronic article surveillance systems on permanent cardiac pacemakers: an in vitro study.

Five Siemens Pacesetter cardiac pacemakers (PM) were subjected to in vitro testing with six different electronic article surveillance (EAS) devices. The PMs consisted of polarity programmable, dedicated bipolar, and dedicated unipolar types. EAS equipment included UHF, RF, Magnetic, and Magnetoacoustic (MA) devices from two manufacturers. Prior to testing, each PM was interrogated and normal operation confirmed. Each PM was attached to a heart simulator via an eight foot cable and then subjected to testing within the EAS field. The PMs were passed through the field in two axes, positioned stationary within the field, and, worst case (WC), placed directly against the transmitter. During testing the ECG was observed and PM behavior recorded. In one PM (Synchrony III), Event Records, and Event Histograms were utilized. At the conclusion of testing with each EAS device the PM was evaluated for normal operation. No PM was reprogrammed by the EAS devices. UHF produced no effect on the PMs. RF produced noise response in one unipolar PM while in the WC position. High frequency and multifrequency magnetic units produced positive results only in the WC position. Unipolar PMs were affected more often than bipolar. MA and older magnetic EAS units produced more positive responses than newer lower power devices. One incident of close coupled (400 msec) ventricular pacing was seen with the MA EAS unit. UHF, RF, high frequency, and dual frequency magnetic EAS produced few effects during in vitro testing. Except with the MA and low frequency magnetic devices, positive results occurred only in WC conditions.(ABSTRACT TRUNCATED AT 250 WORDS)