No abstract

ABSTRACT:The MRI-based contrast-enhanced method of tooth surface digitization provides an alternative possibility for making a dental impression. It has recently been demonstrated that tooth surface digitization with an accuracy sufficient for production of dental restorations is possible using a clinical whole-body MRI scanner. However, for an in vivo application of the technique, the required high nominal resolution and signal-tonoise ratio have to be achieved within reasonable measurement times. Existing radio frequency (RF) volume and surface coils have not been able to fulfill this requirement. The objective of this work was to develop a dedicated RF receiver coil for contrast-enhanced dental MRI which provides a high sensitivity in the region of the whole dental arch and allows for application of the contrast media into the mouth of the patient. To achieve this goal, an intraoral dental coil design with a built-in contrast medium applicator was developed and implemented. The coil was shown to enable high-resolution contrast-enhanced dental MRI in vivo. This was demonstrated on four teeth prepared for dental restorations. The average accuracy obtained for all four teeth was below 100 lm. For two of the teeth, copings were modeled based on MRI data and produced from zirconium oxide using computer-aided design and manufacturing (CAD/CAM) technology.

The advantages of array coil imaging in human whole-body MR systems are well known and have gained relevance in many applications and MR techniques. In the field of small-animal studies, this concept has become increasingly important. In this work, three different phased-array coils for performing MRI on mice are presented. For imaging at 300 MHz, a four-channel receive-only phased-array coil is introduced. One two-channel and a four-channel transmit/receive setup operating at 750 MHz show the feasibility of array coil imaging at 17.6 T. All of these coils show excellent performance and deliver high-quality MR images of mice.

Objectives: The purpose of this study was to design, build and test a multielement receive coil array and position system, which is optimized for three-dimensional (3D) high-resolution dental and maxillomandibular MRI with high patient comfort. Methods: A 14 1 1 coil array and positioning system, allowing easy handling by the technologists, reproducible positioning of the patients and high patient comfort, was tested with three healthy volunteers using a 3.0-T MRI machine (Siemens Skyra; Siemens Medical Solutions, Erlangen, Germany). High-resolution 3D T 1 weighted, water excitation T 1 weighted and fatsaturated T 2 weighted imaging sequences were scanned, and 3D image data were reformatted in different orientations and curvatures to aid diagnosis. Results: The high number of receiving coils and the comfortable positioning of the coil array close to the patient's face provided a high signal-to-noise ratio and allowed high quality, high resolution, 3D image data to be acquired within reasonable scan times owing to the possibility of parallel image acquisition acceleration. Reformatting the isotropic 3D image data in different views is helpful for diagnosis, e.g. panoramic reconstruction. The visibility of soft tissues such as the mandibular canal, nutritive canals and periodontal ligaments was exquisite. Conclusions: The optimized MRI receive coil array and positioning system for dental and oral-maxillofacial imaging provides a valuable tool for detecting and diagnosing pathologies in dental and oral-maxillofacial structures while avoiding radiation dose. The high patient comfort, as achieved by our design, is very crucial, since image artefacts due to movement or failing to complete the examination jeopardize the diagnostic value of MRI examinations.

Dental MRI benefits profoundly from using a dedicated dental coil.