3D Double Echo Steady State With Water Excitation MR Imaging Of Facial Nerve

Objective To assess the value of 3D double echo steady state (DESS) with water excitation MR sequence in depicting the normal anatomy of facial nerve. Methods To optimize the image contrast, computer simulations of the 3D-DESS sequence were first carried out through the code written in Matlab 7.1 (MathWorks, Natick, MA). The relationship between the flip angle(FA) and signal to noise ratio(SNR) was explored, and the optimum parameters for the best contrast were obtained.3D-DESSwe MR sequence with the optimum parameters was performed in 15 healthy volunteers on a 1.5-T MR unit. The 3D datasets were reconstructed in relation to the course of the facial nerve by using the multi-planar reconstruction (MPR) and thin slice maximum intensity projection (MIP) programs. Two radiologists analyzed the images in collaboration and recorded on an arbitrary scale of 0—2 grades by comparing with anatomical textbook diagrams. (2 grades: homogeneity and facial nerve identified with certainty; 1 grade:mild inhomogeneity and facial nerve probably identified; 0:severe inhomogeneity and facial nerve not identified). Results In all subjects,3D DESS with water excitation images provided reliable definition of the normal facial nerve anatomy bilaterally and high contrast between the facial nerve and adjacent structures were obtained(score=2). The cisternal segment of facial nerve showed high signal intensity while the moving CSF flow surrounding it showed low signal intensity; the internal auditory canal (IAC) segment of facial nerve showed relatively low signal intensity while the stationary CSF surrounding it showed high signal intensity. The labyrinthine, tympanic, mastoid and extracranial segments of facial nerve showed high signal intensity while the bone and soft tissue surrounding it showed low signal intensity, and branches of intraparotid facial nerve can be demonstrated. And the fluid in parotid ducts showed high signal intensity. Conclusion Various sections of the normal facial nerve can be clearly displayed by 3D-DESSwe sequence. Objective:To explore the usefulness of 3D-DESSwe sequence that dipicts the normal anantomy of the intraparotid facial nerve. Methods:3D-DESSwe sequence with the optimum parameters was performed in 18 healthy volunteers on a 1.5-T MR unit. The data sets from the 3D-DESS sequence were reconstructed in multi-oblique planes oriented in relation to the course of intraparotid facial nerve. The reconstructed images were compared with anatomical textbook diagrams by two radiologists. Each radiologist made initial evaluations independently, and any disagreements regarding final conclusions were resolved by consensus. Results:The main trunks and cervicofacial and temporofacial divisions of the facial nerves were identified in 100%, 94.4% and 55.6%, respectively by using the 3D-DESSwe sequence. The signal intensity of the parotid ducts is slightly higher than the facial nerve in the 3D-DESSwe imaging. Conclusions:The anatomy of intraparotid facial nerve and its main branches can be depicted by using the 3D-DESSwe sequence, and the parotid dusts can also be displayed. This technique may be useful for preoperative evaluation of the relationship between the tumour and facial nerve in the parotid gland.