Dental MRI for identification and quantification of initial caries lesions
The clinical application of MRI in the field of dentistry is up to now limited to tumors and displacement of the TMJ because of the restricted delineation of the mineralized tissues of the teeth. Due to their fast signal decay and related limited SNR conventional MRI techniques are not able to assess those tissues. In this thesis dedicated imaging sequences using ultra-short echo times (UTE) were applied to detect the signal of mineralised tissues and enable the direct visualization of dental tissues and initial caries lesions. In UTE imaging the FID signal is sampled from central to outer part of the k-space during gradient ramp up. To ensure sufficient image quality, accurate knowledge of the system performance is mandatory to rebuild the waveform and timing of the gradient amplifier output. The system response of the gradient amplifier could be obtained by applying a commonly used trajectory mapping approach and was used to correct for waveform distortions. To automatically correct for timing inconsistencies a dedicated sequence was developed which enables k-space center-acquisition at partial ramp imaging (CAPRI). UTE/CAPRI have the potential for an earlier diagnosis of initial caries lesions and provide a more accurate assessment of the lesion dimension compared to x-ray imaging and enable new applications such as monitoring of re-mineralization therapy. The process of caries lesion can be assessed using MRI as a quantitative tool to observe tissue specific signal behaviour over time. The ability of UTE/CAPRI to visualize the anatomy in three dimensions facilitates the localization of the lesion and the detection of caries lesions located under fillings and crowns (secondary/hidden caries) which are often superimposed in conventional radiography projection images. Therefore the introduced imaging sequences can serve as an alternative technique to the used ionizing radiation based imaging techniques, which are the gold standard in nowadays dental investigations.
Subject HeadingsKaries [GND]
Medical physics [LCSH]
Dental caries; Radiography [MeSH]
Magnetic resonance imaging; Methods [MeSH]
Radiography, dental [MeSH]
Tooth; Radiography [MeSH]