Magnetic Resonance Imaging of the Temporomandibular Joint at 7.0 T Using High-Permittivity Dielectric Pads: A Feasibility Study.
OBJECTIVE
The aims of this study were to show feasibility and to quantitatively and qualitatively evaluate the use of high-permittivity dielectric pads for imaging the temporomandibular joint (TMJ) at 7.0 T.


METHODS
This study is an institutional review board-approved study with written informed consent. Ten asymptomatic volunteers (20 TMJs) were magnetic resonance imaged using a 32-channel head coil at 7.0 T (Achieva; Philips Healthcare, the Netherlands) with and without high-permittivity dielectric pads consisting of barium titanate in deuterated suspension. Imaging protocol consisted of an oblique sagittal proton density-weighted turbo-spin echo sequence. For quantitative evaluation, B1 maps and voxelwise signal-to-noise ratio (SNR) maps were calculated. For qualitative evaluation, 2 readers assessed the visibility of anatomical structures of the TMJ and overall image quality on a 5-point Likert scale from 1 (excellent visibility) to 5 (not visible) in consensus. Quantitative and qualitative measurements were compared between images acquired with and without pads.


RESULTS
Imaging the TMJ using dielectric pads was feasible in all volunteers. The quantitative analysis showed locally higher B1+ and higher SNR in the area covering the TMJ for the scans performed with dielectric pads compared with those without pads (SNR: mean [SD] pads, 12.38 [3.18]; mean [SD] no pads, 6.60 [0.72]). The qualitative analysis showed significantly better visibility and delineation of clinically relevant anatomical structures of the TMJ, including temporomandibular disc, bilaminar zone, mandibular fossa, mandibular condyle, and pterygoid muscle. In addition, observers judged overall image quality as better for images taken with pads compared with those taken without pads (mean [SD] pads, 1.40 [0.50]; mean [SD] no pads, 4.25 [0.78]).


CONCLUSIONS
The application of high-permittivity dielectric pads improves the local B1+ field and thus the SNR, optimizing TMJ magnetic resonance imaging at 7.0 T.
From the *Department of Radiology, Institute for Diagnostic and Interventional Radiology, University Hospital Zurich, University of Zurich; †Institute for Biomedical Engineering, University of Zurich and ETH Zurich; and ‡Center of Dental Medicine, University of Zurich, Zurich, Switzerland.
Andrei
A
Manoliu
Georg
G
Spinner
Michael
M
Wyss
Dominik A
DA
Ettlin
Daniel
D
Nanz
Felix P
FP
Kuhn
Luigi M
LM
Gallo
Gustav
G
Andreisek
D000328:Adult; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011446:Prospective Studies; D013704:Temporomandibular Joint / Q000033:anatomy & histology*; D055815:Young Adult