MR Imaging of the Extracranial Facial Nerve with the CISS Sequence

BACKGROUND AND PURPOSE

MR imaging is not routinely used to image the extracranial facial nerve. The purpose of this study was to determine the extent to which this nerve can be visualized with a CISS sequence and to determine the feasibility of using that sequence for locating the nerve relative to tumor.

MATERIALS AND METHODS

Thirty-two facial nerves in 16 healthy subjects and 4 facial nerves in 4 subjects with parotid gland tumors were imaged with an axial CISS sequence protocol that included 0.8-mm isotropic voxels on a 3T MR imaging system with a 64-channel head/neck coil. Four observers independently segmented the 32 healthy subject nerves. Segmentations were compared by calculating average Hausdorff distance values and Dice similarity coefficients.

RESULTS

The primary bifurcation of the extracranial facial nerve into the superior temporofacial and inferior cervicofacial trunks was visible on all 128 segmentations. The mean of the average Hausdorff distances was 1.2 mm (range, 0.3-4.6 mm). Dice coefficients ranged from 0.40 to 0.82. The relative position of the facial nerve to the tumor could be inferred in all 4 tumor cases.

CONCLUSIONS

The facial nerve can be seen on CISS images from the stylomastoid foramen to the temporofacial and cervicofacial trunks, proximal to the parotid plexus. Use of a CISS protocol is feasible in the clinical setting to determine the location of the facial nerve relative to tumor.

A single nucleotide polymorphism in the Waxy gene explains a significant component of gel consistency

Gel consistency (GC) is a standard assay used in rice improvement programmes to determine whether rice cultivars/breeding lines of high amylose content are soft or firm textured when cooked. In this study, we show that sequence variation in exon 10 of the Waxy (Wx) gene associates with GC using RILs derived from parents with high amylose content that differ in GC. The association was validated using a diverse set of traditional varieties, selected on the basis of amylose content, from the generation challenge programme. Structural investigations to explain how the mutation leads to differences in GC showed a strong association between GC and the proportion of amylose that leaches. It was shown that cooked rices of hard GC do not change in hardness over 24 h, whereas rices of soft GC retrograde significantly over 24 h. This leads to the conclusion that the mutation on exon 10 of the Wx gene affects the proportion of amylose bound to amylopectin and the proportion able to leach, and these structural differences alter the composition of the gel, which affects the amount of time the gel takes to reach a final hardness. The SNP described here completes the set of markers required to genotype for the current traits of cooking quality, but selecting the allele for soft texture has the negative result of also selecting for retrogradation potential.