Fred E. Vermeulen

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BACKGROUND Although younger patients are supposed to be less susceptible to bleeding complications of mechanical aortic valve replacement (mAVR) than older patients, there is a relative paucity of data on this subject. Therefore, it remains uncertain whether younger patients are really at a lower risk of these complications than older patients. METHODS(More)
A general analytical framework is presented for the design of birdcage radiofrequency resonators on cylindrical formers having arbitrary cross-sectional shape. The primary objective of such shapes would be to improve the sensitivity of the NMR experiment to noncircular regions of the human anatomy while maintaining field homogeneity and quadrature(More)
A theoretical model is described for a magnetic resonance imaging (MRI) radio-frequency resonator (an MRI "coil") that is useful at ultrahigh frequencies. The device is a "TEM resonator," which is based on a concept originally proposed by Röschmann (1988). The coil comprises a circular cavity-like structure containing several coaxial transmission lines(More)
It is demonstrated that birdcage resonators, satisfying conditions of quadrature operation and radiofrequency field homogeneity, can be realized in practice on formers of non-circular cross section described by an equation of the form (x/a)n + (y/b)n = 1 where a and b are constants and n > or = 2 is an integer. Using a ladder network analogous to that of a(More)
Abstruct-A high pressure, high temperature cell has been constructed and used to determine the temperature dependence of the electrical conductivity of various geological materials at a frequency of 60 Hz. Test conditions in the cell approximate an in situ environment by means of a variable uniaxial confining pressure and a separately variable pore(More)
Quantitative determination of local radioactivity concentration in positron emission tomography (PET) requires a good attenuation correction procedure to reconstruct the emission image. Using a similar Maximum Likelihood (ML) algorithm as for the reconstruction of the emission image, a method is proposed to reconstruct a transmission image, i.e. a map of(More)
EEG recordings from 230 carotid endarterectomies performed with an automatic EEG monitoring system were reviewed with the purpose of establishing the exact relation between EEG changes and intraoperative stroke. Patients were selectively shunted, based on the EEG changes occurring after carotid cross-clamping. Transient EEG asymmetry was not associated with(More)
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