Towards clinical assessment of velopharyngeal closure using MRI: evaluation of real-time MRI sequences at 1.5 and 3 T

Abstract

Objective: The objective of this study was to demonstrate soft palate MRI at 1.5 and 3 T with high temporal resolution on clinical scanners. Methods: Six volunteers were imaged while speaking, using both four real-time steady-state free-precession (SSFP) sequences at 3 T and four balanced SSFP (bSSFP) at 1.5 T. Temporal resolution was 9-20 frames s 21 (fps), spatial resolution 1.661.6610.0-2.762.7610.0 mm 3 . Simultaneous audio was recorded. Signal-to-noise ratio (SNR), palate thickness and image quality score (1-4, non-diagnostic-excellent) were evaluated. Results: SNR was higher at 3 T than 1.5 T in the relaxed palate (nasal breathing position) and reduced in the elevated palate at 3 T, but not 1.5 T. Image quality was not significantly different between field strengths or sequences (p5NS). At 3 T, 40% acquisitions scored 2 and 56% scored 3. Most 1.5 T acquisitions scored 1 (19%) or 4 (46%). Image quality was more dependent on subject or field than sequence. SNR in static images was highest with 1.961.9610.0 mm 3 resolution (10 fps) and measured palate thickness was similar (p5NS)

Recommendations for real-time speech MRI

“…85 Few groups have proposed regional metrics that characterize SNR in upper airway regions of interest at several undersampling factors. 41,60,86 A controlled task-specific based RT-MRI experimentation was proposed to evaluate the temporal finite difference constraint along with median filtering; 87 the spatiotemporal fidelity of the reconstructions were evaluated on a mechanical motion phantom that consisted of water filled tubes rotating at predefined angular velocities. However, such a rotating phantom may not be optimal for other regularizers such as those involving low rank constraints.…”

“…Over the past decade, a number of technical advancements in acquisition strategies, coil geometry design, reconstruction and artifact correction schemes have emerged, thereby providing a wide range of solutions to RT-MRI tradeoffs. 1,6,[39][40][41][42][43][44][45][46][47] This article focuses on the technical considerations relevant to implementing an RT-MRI protocol for upper airway imaging. This article is motivated by an outcome of the Speech MRI Summit meeting (Los Angeles, February 2014, endorsed by the ISMRM), where the speech MRI research community convened and agreed that there was an unmet need for a recommendations document for RT-MRI of speech.…”

Real-time magnetic resonance imaging and electromagnetic articulography database for speech production research (TC)

“…[16][17][18][19] The quest for improving the possible spatial and temporal resolution, and identifying effective trade offs for given application needs, is ongoing. However, with current imaging and audio acquisition capabilities, it is possible to collect large amounts of speech production data than ever before such as demonstrated by the current database.…”

A fast and flexible MRI system for the study of dynamic vocal tract shaping

“…On-thefly schemes are referred to those that allow for immediate visualization of the reconstructed images (with latency less than 500 ms), whereas off-line schemes are referred to those where the reconstructions are implemented off-line. Scott et al (20) utilized on-the-fly imaging with Cartesian trajectories and demonstrated temporal resolutions between 111 and 50 ms at spatial resolution of 1.6-2.7 mm 2 for velopharyngeal closure. Other investigators (1,21,22) utilized short spiral readouts to acquire images at a native time resolution of 54-78 ms, and a spatial resolution of 3.0-2.4 mm 2 , and visualize at 24 frames/sec using view sharing.…”