Value of visualization of the intraparotid facial nerve and parotid duct using a micro surface coil and three-dimensional fast imaging with steady state precession with fat-suppression sequence

Abstract

Objective To explore the value of small surface coil combine with three-dimensional fast imaging with steady state precession and fat-suppression (3D-FISP-FS) sequence in displaying intra-parotid facial nerves segment and parotid ducts. Methods The parotid regions of 18 healthy volunteers who were excluded any parotid diseases were scanned by head & neck coil (36 sides) and 4 cm small surface coil (32 sides) combined with 3D-FISP-FS sequence prospectively. The obtained original images were treated through MIP, MPR and CPR, The MRI signal characteristics of parotid region structure, the subjective score of image quality, the signal intensity ratio (SIR) of facial nerve/parotid tissue (SIRN) and parotid duct/parotid tissue (SIRD) was calculated, and the displaying rates of the facial nerves and parotid ducts were observed. Wilcoxon matched-samples signed rank sum test was used to compare the scores of head & neck coil and small coil 3D-FISP-FS sequence images, paired t test was used to compare SIRN, SIRD of the two groups, Chi-square test was used to compare of the displaying rate of the facial nerves and parotid ducts in two groups. Results Eighteen volunteers were successfully performed MRI scan of parotid gland. On 3D-FISP-FS sequence images, the parotid gland was showed slightly low signal intensity, muscle tissue was showed medium signal intensity, the vessels were showed slightly high or high signal, parotid segment of facial nerve was showed tortuous line-like high signal intensity, and parotid duct was showed curve high signal intensity, lymph nodes were showed kidney shaped, oval or spindle shaped high signal intensity structures. The subjective scores for head and neck coil and coil images were (2.0±0.9) and (1.5±0.7) respectively, and the difference was statistically significant (Z=-2.714, P=0.007), image quality of small coil group was better than that of head and neck coil group. The SIRN of the two groups was 1.7±0.8 and 2.1±1.2 respectively, and the SIRD was 1.8±0.7 and 2.5±1.7 respectively, which showed a statistically significant difference between the two groups (t value was 2.978, 2.427 respectively, P value was 0.006, 0.031 respectively).All facial nerve trunks could be displayed by head and neck coil and small coil. On head and neck coil images, 25 sides of temporofacial truck, 15 sides of cervicofacial truck, 17 sides of temporofacial branches, 11 sides of cervicofacial branches, 16 sides of the parotid duct could be displayed. On small coil images, 30 sides of temporofacial truck, 28 sides of cervicofacial truck, 26 sides of temporofacial branches, 23 sides of cervicofacial branches, 27 sides of the parotid duct could be displayed, which showed a statistically significant difference (P<0.05). Conclusion Small surface coil performed better in parotid MR imaging with 3D-FISP-FS sequence than that of head and neck coil, which can simultaneous clearly display the trunk and branches of the intra-parotid facial nerves and parotid ducts. Key words: Parotid gland; Facial nerve; Parotid duct; Magnetic resonance imaging; Small surface coil