  Background and Purpose: Various 'positive-contrast' neurographic methods have
been investigated for imaging the extracranial course of the facial nerve.
However, nerve visibility can be inconsistent with these sequences and may
depend on the composition of the parotid gland, limiting consistent
identification. To address this, we describe and evaluate a 'negative-contrast'
method for imaging of the extracranial facial nerve using three-dimensional
variable flip angle turbo spin echo (VFA-TSE) imaging. We investigate
strategies for further optimization, including parotid-specific VFA-TSE
optimization and the use of gadolinium-based contrast agent (GBCA). Materials
and Methods: 6 healthy volunteers and 10 patients with parotid tumors underwent
VFA-TSE and double echo steady state (DESS) imaging of the extracranial facial
nerve at 3T. The main trunk, divisions and branches of the extracranial facial
nerve were manually segmented by three radiologists, enabling CNR and Hausdorff
distance computation and confidence scoring. CNR, Hausdorff distance and
confidence scores were compared between sequences and between pre- and
post-contrast imaging to evaluate the effect of GBCA. Results: CNR, Hausdorff
distances and confidence scores were superior for VFA-TSE compared to DESS
imaging. GBCA administration produced a further increase in CNR of nerve
against parotid and improved differentiation of nerve from tumor. Conclusion:
Imaging of the extracranial facial nerve with VFA-TSE depicts the nerve as a
low signal structure ('black nerve') against the high signal parotid parenchyma
('white parotid') and outperforms positive-contrast DESS imaging in terms of
CNR, segmentation consistency and confidence. GBCA further increases negative
contrast and improves differentiation of nerve from tumor.
