| Abstract: | Purpose The use of gated or ECG triggered MR is a well-established technique and developments in coil technology have enabled this
approach to be applied to areas other than the heart. However, the image quality of gated (ECG or cine) versus non-gated or
real-time has not been extensively evaluated in the mouth. We evaluate two image sequences by developing an automatic image
processing technique which compares how well the image represents known anatomy.
Methods Four subjects practised experimental poly-syllabic sentences prior to MR scanning. Using a 1.5 T MR unit, we acquired comparable
gated (using an artificial trigger) and non-gated sagittal images during speech. We then used an image processing algorithm
to model the image grey along lines that cross the airway. Each line involved an eight parameter non-linear equation to model
of proton densities, edges, and dimensions.
Results Gated and non-gated images show similar spatial resolution, with non-gated images being slightly sharper (10% better resolution,
less than 1 pixel). However, the gated sequences generated images of substantially lower inherent noise, and substantially
better discrimination between air and tissue. Additionally, the gated sequences demonstrate a very much greater temporal resolution.
Conclusion Overall, image quality is better with gated imaging techniques, especially given their superior temporal resolution. Gated
techniques are limited by the repeatability of the motions involved, and we have shown that speech to a metronome can be sufficiently
repeatable to allow high-quality gated magnetic resonance imaging images. We suggest that gated sequences may be useful for
evaluating other types of repetitive movement involving the joints and limb motions. |
