Comparison of Cartesian and Non-Cartesian Real-Time MRI Sequences at 1.5T to Assess Velar Motion and Velopharyngeal Closure during Speech

Abstract

Dynamic imaging of the vocal tract using real-time MRI has been an active and growing area of research, having demonstrated great potential to become routinely performed in the clinical evaluation of speech and swallowing disorders. Although many technical advances have been made in regards to acquisition and reconstruction methodologies, there is still no consensus in best practice protocols. This study aims to compare Cartesian and non-Cartesian real-time MRI sequences, regarding image quality and temporal resolution trade-off, for dynamic speech imaging. Five subjects were imaged at 1.5T, while performing normal phonation, in order to assess velar motion and velopharyngeal closure. Data was acquired using both Cartesian and non-Cartesian (spiral and radial) real-time sequences at five different spatial-temporal resolution sets, between 10 fps (1.7×1.7×10 mm3) and 25 fps (1.5×1.5×10 mm3). Only standard scanning resources provided by the MRI scanner manufacturer were used to ensure easy applicability to clinical evaluation and reproducibility. Data sets were evaluated by comparing measurements of the velar structure, dynamic contrast-to-noise ratio and image quality visual scoring. Results showed that for all proposed sequences, FLASH spiral acquisitions provided higher contrast-to-noise ratio, up to a 170.34% increase at 20 fps, than equivalent bSSFP Cartesian acquisitions for the same spatial-temporal resolution. At higher frame rates (22 and 25 fps), spiral protocols were optimal and provided higher CNR and visual scoring than equivalent radial protocols. Comparison of dynamic imaging at 10 and 22 fps for radial and spiral acquisitions revealed no significant difference in CNR performance, thus indicating that temporal resolution can be doubled without compromising spatial resolution (1.9×1.9 mm2) or CNR. In summary, this study suggests that the use of FLASH spiral protocols should be preferred over bSSFP Cartesian for the dynamic imaging of velopharyngeal closure, as it allows for an improvement in CNR and overall image quality without compromising spatial-temporal resolution.

Feasibility of through‐time spiral generalized autocalibrating partial parallel acquisition for low latency accelerated real‐time MRI of speech

“…RT-MRI is challenged by trade-offs between the achievable spatial resolution, temporal resolution, slice coverage, and signal to noise. Several rapid MRI methods based on non-Cartesian imaging, parallel imaging, and compressed sensing (CS) have been applied to improve the above trade-offs (10)(11)(12)(13)(14)(15)(16). The latency time, which is the time between acquisition of a set of raw data and reconstruction of the final image, is a useful criterion to classify the above methods to either on-the-fly or off-line methods.…”

“…Iterative CS methods that exploit spatiotemporal redundancies of dynamic images have demonstrated greater acceleration levels (>6-to 7-fold). These invoke constraints based on low-rank assumptions, transform sparsity, or both (11)(12)(13)(14)(15)(16)22). These have demonstrated improved spatiotemporal resolutions in 2D RT-MRI (up to 1.5-2.4 mm 2 and 10-33 ms/frame) and also more recently in 3D RT-MRI (frame rate of 166 frames/sec) (22).…”

Application of radial GRAPPA techniques to single‐ and multislice dynamic speech MRI using a 16‐channel neurovascular coil

“…Accelerated MRI data acquisition is required to image at the frame rates used in clinical speech assessment (15 fps or higher) while maintaining acceptable spatial resolutions and image quality. Dynamic speech MRI at frame rates of 15 fps or higher has been achieved by using non‐Cartesian k‐space sampling trajectories and/or parallel imaging to accelerate MRI data acquisition . Each non‐Cartesian trajectory has its advantages and disadvantages: while spiral trajectories sample k‐space more efficiently, radial trajectories are less susceptible to off‐resonance effects.…”

Influence of the Human Body Mass in the Open-air MRI on Acoustic Noise Spectrum

“…Due to its harmonic nature and the audio frequency range, the produced acoustic noise of this device can generally be treated as a voiced speech signal, and thus it can be recorded by a microphone and processed in the spectral domain using similar methods as those used for speech signal analysis. The MRI technique enables analysis of the human vocal tract structure and its dynamic shaping during speech production while simultaneous recording of a speech signal [3], [4] is performed. The primary volume models of the human acoustic supra-glottal cavities constructed from the MR images can be transformed into three-dimensional (3D) finite element (FE) models [5].…”