Abstract:Vibrations of a string can provide a model for vibrations of MRI coil assemblies. The string model for the vibrations of MRI coils is presented, and compared with experimental results. Gradient coils exhibit resonant modes because of the finite coil length, l, and the elasticity of materials that comprise the assembly. The resonance frequencies depend on l and the Young modulus, as well as on the current distribution. Under longitudinal gradient pulses, anti-symmetrical modes of surface vibration are produced … Show more
“…This noise has a mechanical character, and can be processed in spectral domain [13] -see spectrograms obtained from phonation of the long vowel "a:" during MR scan in Fig.11. For noise reduction, we used the method based on the cepstral speech model [14].…”
Section: Experiments With Phonation During the Mr Scanmentioning
Magnetic resonance imaging (MRI) is nowadays widely used in medicine for diagnostic imaging and in research studies. The modeling of the human vocal tract acoustics has recently attracted considerable interest. This paper describes the design, realization and first MR scan experiments with a new head probe coil for vocal tract imaging in the open-air MRI equipment working in a weak magnetic field up to 0.2 T. The paper also describes an experimental setting for sound recording during the MR imaging.
“…This noise has a mechanical character, and can be processed in spectral domain [13] -see spectrograms obtained from phonation of the long vowel "a:" during MR scan in Fig.11. For noise reduction, we used the method based on the cepstral speech model [14].…”
Section: Experiments With Phonation During the Mr Scanmentioning
Magnetic resonance imaging (MRI) is nowadays widely used in medicine for diagnostic imaging and in research studies. The modeling of the human vocal tract acoustics has recently attracted considerable interest. This paper describes the design, realization and first MR scan experiments with a new head probe coil for vocal tract imaging in the open-air MRI equipment working in a weak magnetic field up to 0.2 T. The paper also describes an experimental setting for sound recording during the MR imaging.
“…The present paper contains the details and elaborates upon a previous preliminary report [13,14]. In fact, a string approximation has been put forth as a useful model for the dominant frequencies of both longitudinal and transverse gradient coils [15]. The gradient vibrational modes yield a rich spectrum of frequencies (leading to a frequency response over a range of several kHz).…”
“…The MRI equipment consists of a gradient coil system producing three orthogonal linear magnetic fields for spatial scanning. The function of these gradient coils is accompanied by an acoustic noise due to rapidly changing Lorentz forces during fast switching inside the weak static field environment [4]. The speech signal recorded under such conditions may be analyzed only if the adequate signal-to-noise ratio is achieved [5].…”
The paper focuses on two methods of evaluation of successfulness of speech signal enhancement recorded in the open-air magnetic resonance imager during phonation for the 3D human vocal tract modeling. The first approach enables to obtain a comparison based on statistical analysis by ANOVA and hypothesis tests. The second method is based on classification by Gaussian mixture models (GMM). The performed experiments have confirmed that the proposed ANOVA and GMM classifiers for automatic evaluation of the speech quality are functional and produce fully comparable results with the standard evaluation based on the listening test method.
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