Abstract
This article compares open-air and whole-body magnetic resonance imaging (MRI) equipment working with a weak magnetic field as regards the methods of its generation, spectral properties of mechanical vibration and acoustic noise produced by gradient coils during the scanning process, and the measured noise intensity. These devices are used for non-invasive MRI reconstruction of the human vocal tract during phonation with simultaneous speech recording. In this case, the vibration and noise have negative influence on quality of speech signal. Two basic measurement experiments were performed within the paper: mapping sound pressure levels in the MRI device vicinity and picking up vibration and noise signals in the MRI scanning area. Spectral characteristics of these signals are then analyzed statistically and compared visually and numerically.
Highlights
The magnetic resonance imaging (MRI) tomograph is basically a huge intelligent sensor used for biomedical purposes
Esaote S.p.A., Genoa, Italy [21], and the experimental whole-body experimental MR imager TMR96 device built at the Institute of Measurement Science (IMS) in Bratislava, using the Apollo (Tecmag Inc., Houston, TX, USA) console for control by the NTNMR ver. 1.4 software package [22]
The measurements in the vicinity of the open-air MRI equipment E-scan Esaote Opera have shown that the maximum sound pressure level of about 72 dB(C) was achieved for the SPL meter located in the direction of 30◦, the height of 85 cm, and at the distance of 45 cm, while the background noise SPL0 originating from the temperature stabilizer reached approximately 52 dB(C) measured in the time instant when no scan sequence was executed
Summary
The magnetic resonance imaging (MRI) tomograph is basically a huge intelligent sensor used for biomedical purposes. Sensors 2018, 18, 1112 range, so it can be processed in the spectral domain and analyzed using methods similar to those of audio and speech signal analysis These MRI devices can be successfully used for analysis of the human vocal tract structure and its dynamic shaping during speech production [4]. The main motivation of this study was to measure and compare intensity, distribution, and spectral properties of mechanical vibration and acoustic noise produced by the low magnetic field MR imagers. As both types of investigated tomographs use the same physical principles for modulation of the basic magnetic field, we suppose comparable results of measured vibration and noise signals. The time delay between the vibration signal and the excitation impulse in the gradient coil from simultaneously recorded electrical excitation, vibration, and noise signals was analyzed and evaluated
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