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1. Dynamic off‐resonance correction for spiral real‐time MRI of speech

   https://doi.org/10.1002/mrm.27373  

   Lim, Yongwan ; Lingala, Sajan Goud ; Narayanan, Shrikanth S. ; Nayak, Krishna S. ( July 2018 , Magnetic Resonance in Medicine)

   To improve the depiction and tracking of vocal tract articulators in spiral real‐time MRI (RT‐MRI) of speech production by estimating and correcting for dynamic changes in off‐resonance.

   The proposed method computes a dynamic field map from the phase of single‐TE dynamic images after a coil phase compensation where complex coil sensitivity maps are estimated from the single‐TE dynamic scan itself. This method is tested using simulations and in vivo data. The depiction of air–tissue boundaries is evaluated quantitatively using a sharpness metric and visual inspection.

   Simulations demonstrate that the proposed method provides robust off‐resonance correction for spiral readout durations up to 5 ms at 1.5T. In ‐vivo experiments during human speech production demonstrate that image sharpness is improved in a majority of data sets at air–tissue boundaries including the upper lip, hard palate, soft palate, and tongue boundaries, whereas the lower lip shows little improvement in the edge sharpness after correction.

   Dynamic off‐resonance correction is feasible from single‐TE spiral RT‐MRI data, and provides a practical performance improvement in articulator sharpness when applied to speech production imaging.

    

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2. Intermittently tagged real‐time MRI reveals internal tongue motion during speech production

   https://doi.org/10.1002/mrm.27745  

   Chen, Weiyi ; Byrd, Dani ; Narayanan, Shrikanth ; Nayak, Krishna S. ( March 2019 , Magnetic Resonance in Medicine)

   To demonstrate a tagging method compatible with RT‐MRI for the study of speech production.

   Tagging is applied as a brief interruption to a continuous real‐time spiral acquisition. Tagging can be initiated manually by the operator, cued to the speech stimulus, or be automatically applied with a fixed frequency. We use a standard 2D 1‐3‐3‐1 binomial SPAtial Modulation of Magnetization (SPAMM) sequence with 1 cm spacing in both in‐plane directions. Tag persistence in tongue muscle is simulated and validated in vivo. The ability to capture internal tongue deformations is tested during speech production of American English diphthongs in native speakers.

   We achieved an imaging window of 650‐800 ms at 1.5T, with imaging signal to noise ratio ≥ 17 and tag contrast to noise ratio ≥ 5 in human tongue, providing 36 frames/s temporal resolution and 2 mm in‐plane spatial resolution with real‐time interactive acquisition and view‐sharing reconstruction. The proposed method was able to capture tongue motion patterns and their relative timing with adequate spatiotemporal resolution during the production of American English diphthongs and consonants.

   Intermittent tagging during real‐time MRI of speech production is able to reveal the internal deformations of the tongue. This capability will allow new investigations of valuable spatiotemporal information on the biomechanics of the lingual subsystems during speech without reliance on binning speech utterance repetition.

    

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3. Improved real‐time tagged MRI using REALTAG

   https://doi.org/10.1002/mrm.28144  

   Chen, Weiyi ; Lee, Nam Gyun ; Byrd, Dani ; Narayanan, Shrikanth ; Nayak, Krishna S. ( December 2019 , Magnetic Resonance in Medicine)

   To evaluate a novel method for real‐time tagged MRI with increased tag persistence using phase sensitive tagging (REALTAG), demonstrated for speech imaging.

   Tagging is applied as a brief interruption to a continuous real‐time spiral acquisition. REALTAG is implemented using a total tagging flip angle of 180° and a novel frame‐by‐frame phase sensitive reconstruction to remove smooth background phase while preserving the sign of the tag lines. Tag contrast‐to‐noise ratio of REALTAG and conventional tagging (total flip angle of 90°) is simulated and evaluated in vivo. The ability to extend tag persistence is tested during the production of vowel‐to‐vowel transitions by American English speakers.

   REALTAG resulted in a doubling of contrast‐to‐noise ratio at each time point and increased tag persistence by more than 1.9‐fold. The tag persistence was 1150 ms with contrast‐to‐noise ratio >6 at 1.5T, providing 2 mm in‐plane resolution, 179 frames/s, with 72.6 ms temporal window width, and phase sensitive reconstruction. The new imaging window is able to capture internal tongue deformation over word‐to‐word transitions in natural speech production.

   Tag persistence is substantially increased in intermittently tagged real‐time MRI by using the improved REALTAG method. This makes it possible to capture longer motion patterns in the tongue, such as cross‐word vowel‐to‐vowel transitions, and provides a powerful new window to study tongue biomechanics.

    

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4. Myocardial T 1 and T 2 quantification and water–fat separation using cardiac MR fingerprinting with rosette trajectories at 3T and 1.5T

   https://doi.org/10.1002/mrm.28404  

   Liu, Yuchi ; Hamilton, Jesse ; Eck, Brendan ; Griswold, Mark ; Seiberlich, Nicole ( July 2020 , Magnetic Resonance in Medicine)

   This work aims to develop an approach for simultaneous water–fat separation and myocardial T₁and T₂quantification based on the cardiac MR fingerprinting (cMRF) framework with rosette trajectories at 3T and 1.5T.

   Two 15‐heartbeat cMRF sequences with different rosette trajectories designed for water–fat separation at 3T and 1.5T were implemented. Water T₁and T₂maps, water image, and fat image were generated with B₀inhomogeneity correction using a B₀map derived from the cMRF data themselves. The proposed water–fat separation rosette cMRF approach was validated in the International Society for Magnetic Resonance in Medicine/National Institute of Standards and Technology MRI system phantom and water/oil phantoms. It was also applied for myocardial tissue mapping of healthy subjects at both 3T and 1.5T.

   Water T₁and T₂values measured using rosette cMRF in the International Society for Magnetic Resonance in Medicine/National Institute of Standards and Technology phantom agreed well with the reference values. In the water/oil phantom, oil was well suppressed in the water images and vice versa. Rosette cMRF yielded comparable T₁but 2~3 ms higher T₂values in the myocardium of healthy subjects than the original spiral cMRF method. Epicardial fat deposition was also clearly shown in the fat images.

   Rosette cMRF provides fat images along with myocardial T₁and T₂maps with significant fat suppression. This technique may improve visualization of the anatomical structure of the heart by separating water and fat and could provide value in diagnosing cardiac diseases associated with fibrofatty infiltration or epicardial fat accumulation. It also paves the way toward comprehensive myocardial tissue characterization in a single scan.

    

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5. 3D dynamic MRI of the vocal tract during natural speech

   https://doi.org/10.1002/mrm.27570  

   Lim, Yongwan ; Zhu, Yinghua ; Lingala, Sajan Goud ; Byrd, Dani ; Narayanan, Shrikanth ; Nayak, Krishna Shrinivas ( November 2018 , Magnetic Resonance in Medicine)

   To develop and evaluate a technique for 3D dynamic MRI of the full vocal tract at high temporal resolution during natural speech.

   We demonstrate 2.4 × 2.4 × 5.8 mm³spatial resolution, 61‐ms temporal resolution, and a 200 × 200 × 70 mm³FOV. The proposed method uses 3D gradient‐echo imaging with a custom upper‐airway coil, a minimum‐phase slab excitation, stack‐of‐spirals readout, pseudo golden‐angle view order ink_x‐k_y, linear Cartesian order alongk_z, and spatiotemporal finite difference constrained reconstruction, with 13‐fold acceleration. This technique is evaluated using in vivo vocal tract airway data from 2 healthy subjects acquired at 1.5T scanner, 1 with synchronized audio, with 2 tasks during production of natural speech, and via comparison with interleaved multislice 2D dynamic MRI.

   This technique captured known dynamics of vocal tract articulators during natural speech tasks including tongue gestures during the production of consonants “s” and “l” and of consonant–vowel syllables, and was additionally consistent with 2D dynamic MRI. Coordination of lingual (tongue) movements for consonants is demonstrated via volume‐of‐interest analysis. Vocal tract area function dynamics revealed critical lingual constriction events along the length of the vocal tract for consonants and vowels.

   We demonstrate feasibility of 3D dynamic MRI of the full vocal tract, with spatiotemporal resolution adequate to visualize lingual movements for consonants and vocal tact shaping during natural productions of consonant–vowel syllables, without requiring multiple repetitions.

    

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