Value of Visualization of the Intraparotid Facial Nerve and Parotid Duct Using a Micro Surface Coil and Three-Dimensional Reversed Fast Imaging With Steady-State Precession and Diffusion-Weighted Imaging Sequence
Authors: Zhao Yue , Yang Bin 
Published: June 2018

Objective:
To explore the value of micro surface coil combined with three-dimensional reversed fast imaging with steady-state precession and diffusion-weighted imaging (3D-PSIF-DWI) in displaying intraparotid facial nerves and parotid ducts.

Methods:
In total 24 healthy volunteers with no parotid disease underwent scanning of head and neck coil and 4-cm micro surface coil combined with 3D-PSIF-DWI prospectively. The obtained original images were processed through maximum intensity projection, multiplanar reconstruction, and curved planar reconstruction. The magnetic resonance imaging (MRI) signal characteristics of intraparotid structure, the subjective score of image quality, the signal intensity ratio (SIR) of facial nerve/parotid tissues (SIRN), and SIR of parotid duct/parotid tissues (SIRD) were calculated, and the displaying rates of the facial nerves and parotid ducts were observed. The Wilcoxon matched-sample signed rank sum test was used to compare the scores of head and neck coil and micro surface coil 3D-PSIF-DWI sequence images; paired-t test was used to compare SIRN and SIRD of the 2 groups; χ2 test was used to compare the displaying rate of the facial nerves and parotid ducts in the 2 groups.

Results:
In total 24 volunteers successfully underwent MRI scan of parotid glands. On 3D-PSIF-DWI images, the parotid gland showed slightly low signal intensity, muscle tissues showed intermediate intensity, while the vessels showed slightly high or equal intensity; the parotid segment of facial nerves was displayed as a tortuous line-like high intensity, and the parotid duct showed curved high intensity, lymph nodes showed kidney-shaped, oval, or spindle-shaped high intensity. The subjective scores for head and neck coil and small coil images were (2.2 ± 0.7) and (1.5 ± 0.3) respectively, with significant difference (Z = −2.714, P = 0.007), and image quality of micro surface coils was better than that of head and neck coil. The SIRNs of head and neck coil and micro surface coil images were 1.6 ± 0.5 and 2.2 ± 1.1 respectively; the SIRDs were 2.0 ± 0.6 and 2.8 ± 1.4 respectively, which showed significant differences (t = 3.440, 3.639 respectively, P value was 0.001, 0.001 respectively). All facial nerve trunks could be displayed by head and neck coils and micro surface coils. On head and neck coil images, 46 sides of temporofacial division, 47 sides of cervicofacial division, 21 sides of temporal branches, 22 sides of zygomatic branches, 29 sides of buccal branches, 30 sides of marginal mandibular branches, 32 sides of cervical branches, and 28 sides of the parotid duct could be displayed. On micro coil images, 48 sides of temporofacial division, 48 sides of cervicofacial division, 37 sides of temporal branches, 39 sides of zygomatic branches, 42 sides of buccal branches, 35 sides of marginal mandibular branches, 46 sides of cervical branches, and 28 sides of the parotid duct could be displayed. The display number of first branches of the intraparotid facial nerve by these 2 methods had no significant difference, the number of the secondary branches and parotid duct had significant differences.

Conclusion:
Micro surface coil surpassed parotid MRI with 3D-PSIF-DWI sequence than neck coil, which can simultaneously clearly display the trunk and branches of the intraparotid facial nerves and parotid ducts.