High-resolution MRI of the human parotid gland and duct at 7 Tesla.
OBJECTIVE
MR techniques have been reported as an alternative to conventional sialography. High-field systems (7 T) provide new contrasts coupled with increased signal-to-noise ratio, and hence higher spatial resolution. To our knowledge, no measurements of the parotid gland at 7 T have been reported. Therefore, our study aimed to optimize sequences for high-field MR imaging of the parotid gland and duct, as well as the facial nerve at 7 T and show the potential of high field imaging.


METHODS
A 7 T whole-body scanner was used together with a 10-cm-diameter loop coil. Various GRE (MEDIC, DESS) and TSE (PD/T2, STIR) sequences were optimized and subsequently tested on 4 healthy volunteers and 4 patients. High-resolution images were compared with 1.5 T images both quantitatively (signal-to-noise ratio, contrast-to-noise) and qualitatively (visual rating of 2 independent readers).


RESULTS
The high 0.6 mm isotropic resolution of the 3D DESS sequence was very useful for defining an oblique orientation with most of the duct being in-plane for subsequent imaging. With the MEDIC sequence, very fine branches of the duct were visible; furthermore, MEDIC yielded a very good depiction of lymph nodes. Severe specific absorption rate problems were observed with the STIR sequence at 7 T. Gland tissue in tumor patients can be well characterized with the PD/T2 TSE. Highest contrast-to-noise between duct and gland was achieved with the 7 T DESS. At 1.5 T, only the STIR sequence showed comparable quality to the overall superiority of the 7 T sequences. The facial nerve could only be depicted close to the skull base.


CONCLUSIONS
MR imaging at 7 T provides excellent image contrast and resolution of the parotid gland and duct. The proposed protocol offers a noninvasive examination within about 30 minutes.
Kraff
Oliver
O
Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany. oliver.kraff@uni-due.de
Theysohn
Jens M
JM
Maderwald
Stefan
S
Kokulinsky
Patrick C
PC
Dogan
Zeynel
Z
Kerem
Alexander
A
Kruszona
Stefan
S
Ladd
Mark E
ME
Gizewski
Elke R
ER
Ladd
Susanne C
SC
D000328:Adult; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010306:Parotid Gland / Q000033:anatomy & histology*; D010363:Pattern Recognition, Automated / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity