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Patient Model (patient + model)
Selected AbstractsSAR and power implications of different RF shimming strategies in the pelvis for 7T MRIJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2009Bob van den Bergen MSc Abstract Purpose To determine the best radiofrequency (RF) shimming method for 7 T body imaging that provides sufficient B1+ excitation inside the target region while energy deposition (SAR) and power demands are as low as possible and that does not incorporate anatomy specific electric field information inside the patient models, as this information is not available in practice. Materials and Methods Finite difference time domain (FDTD) simulations were used to evaluate five RF shimming strategies for the pelvis inside a body coil. The results were compared to the theoretical best solution that could be achieved if the electric field inside the patient was known. Results Most of the RF shimming strategies were successful. However, between the different strategies a factor of two difference in average SAR reduction, a factor of three difference in local maximum SAR reduction, and a factor of 20 difference in power efficiency was observed. Phase matching was found to be the most promising RF shimming method for the body coil used and patient models. Conclusion RF shimming can reduce the SAR and improve power efficiency in an accurate patient model without knowing the electric field. However, choosing the right method is critical to prevent unexpected behavior in local SAR deposition. J. Magn. Reson. Imaging 2009;30:194,202. © 2009 Wiley-Liss, Inc. [source] Robust H, glucose control in diabetes using a physiological modelAICHE JOURNAL, Issue 12 2000Robert S. Parker A robust H, controller was developed to deliver insulin via a mechanical pump in Type I diabetic patients. A fundamental nonlinear diabetic patient model was linearized and then reduced to a third-order linear form for controller synthesis. Uncertainty in the nonlinear model was characterized by up to ±40% variation in eight physiological parameters. A sensitivity analysis identified the three-parameter set having the most significant effect on glucose and insulin dynamics over the frequency range of interest , = [0.002, 0.2] (rad/min). This uncertainty was represented in the frequency domain and incorporated in the controller design. Controller performance was assessed in terms of its ability to track a normoglycemic set point (81.1 mg/dL) in response to a 50 g meal disturbance. In the nominal continuous-time case, the controller maintained glucose concentrations within ±3.3 mg/dL of set point. A controller tuned to accommodate uncertainty yielded a maximum deviation of 17.6 mg/dL for the worst-case parameter variation. [source] Postural Cephalometric Analysis and Nasal Resistance in Sleep-Disordered Breathing,THE LARYNGOSCOPE, Issue 7 2003Paula Virkkula MD Abstract Objectives The study was designed to compare upright and supine cephalometric measurements in snorers and to evaluate the effects of mandibular position and nasal resistance on pharyngeal dimensions. Anthropometric, rhinomanometric, and cephalometric measurements were used to investigate predictors of apnea-hypopnea index. Study Design Prospective, cross-sectional. Methods Forty consecutive habitually snoring men waiting for nasal surgery (mean age, 44 y; mean body mass index, 28 kg/m2) underwent an overnight polysomnographic, anterior rhinomanometric, and cephalometric analysis in upright and supine positions. Results Nasal resistance correlated positively with minimal pharyngeal airspace at the level of tongue. The opening of jaws after voluntary relaxation of the mandibular position on lying down correlated with decrease in pharyngeal airway measurements at both velopharyngeal and tongue-base levels. In stepwise multiple regression analysis the overall patient model explained 68% of the variation in apnea-hypopnea index with body mass index as the largest predictor. In the nonobese patients, the model explained 86% of variation in apnea-hypopnea index with change in anteroposterior position of the lower jaw in upright and supine measurements and combined nasal resistance after mucosal decongestion as independent determinants. In selected skeletal subtypes the models predicted 83%, 79%, 61%, and 90% of the variation in apnea-hypopnea index. Conclusions In the nonobese patients nasal resistance and change in mandibular position on lying down were found to be independent contributing factors to the apnea-hypopnea index. Further research on supine cephalometry and relaxed mandibular position may improve prediction of sleep-disordered breathing in snorers. [source] The ability of breathing system filters to prevent liquid contamination of breathing systems: a laboratory study*ANAESTHESIA, Issue 1 2002APPARATUS The ability of 29 different breathing system filters (five pleated hydrophobic and 24 electrostatic) to prevent the passage of water was assessed. Five, 10 or 20 ml of water was added on to the patient side of the filter during ventilation of a patient model with the filter layer orientated either horizontally or vertically. Water did not pass through the filter layer during any of the 30 tests on the pleated hydrophobic filters. In contrast, water passed through the filter layer in 39 of the 144 tests on the electrostatic filters (27%; 95% CI for difference between the filter types 14,35%; p = 0.0004). For electrostatic filters, a smaller internal volume, a larger volume of water added, and having the filter layer horizontal rather than vertical all significantly increased the probability of water penetration. Although pleated hydrophobic filters would protect the breathing system against liquid contamination, electrostatic filters can also be used, provided the internal volume is chosen appropriately and the filter layer is vertical. [source] | ||||||||||