The paper presents two methods of noise reduction of speech signal recorded in an MRI device during phonation for the human vocal tract modelling. The applied approach of noise speech signal cleaning is based on cepstral speech analysis and synthesis because the noise is mainly produced by gradient coils, has a mechanical character, and can be processed in spectral domain. Our first noise reduction method is using real cepstrum limitation and clipping the "peaks" corresponding to the harmonic frequencies of mechanical noise. The second method is coming out from substation of the short-time spectra of two signals recorded withal: the first includes speech and noise, and the second consists of noise only. The resulting speech quality was compared by spectrogram and mean periodogram methods.
The paper describes measurement and calculation of 2D distribution of the vibration signal originated by the gradient coil system of the magnetic resonance imaging (MRI) equipment. The measurement experiments were performed at the bottom plastic holder of the scanning area of the open-air weak magnetic field MRI device. Selection of a usable type of a vibration sensor for measurement in a magnetic field with low B0 up to 0.2 T is also discussed. Realized calibration of the chosen sensor (sensitivity and frequency response) together with determination of the propagation time delay between the excitation impulses and the subsequently generated vibration signal is mentioned, too. The picked-up vibration signal exhibits harmonic character so it is suitable to describe it by determined spectral properties and features. Obtained statistical results of spectral analysis will be used to improve image sharpening and reduction of the motion effect in the MR pictures of thin layer samples and phantoms scanned by this MRI system.
The paper deals with the photoplethysmographic (PPG) optical sensor usage for noninvasive acquisition of vital information about the cardiovascular system from different parts of the human skin surface. Finger-ring and ear-clip realizations of the transmission-type PPG sensor were tested first. For next PPG signal recording, the reflection PPG sensor was placed on fingers and on a wrist. PPG signal properties were described by energetic and temporal parameters and their statistical parameters together with determined instantaneous heart rate values. Our final aim was to find conditions, limitations, and recommendations for development of a wearable PPG sensor working in a magnetic field environment.
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