Tooth Length Measurements Made on CBCT and 3T MR Images

Objectives: The aim of this study was to compare tooth length measurements made on whole head cone beam computed tomography (CBCT) scans and whole head 3-Tesla (3T) magnetic resonance (MR) scans performed with and without an alginate bite registration surrounding the crowns of the teeth.
Methods: One CBCT scan (NewTom 5G, AFP Imaging, USA), one 3T MR scan (Siemens Medical Solutions, DE) with an alginate bite registration, and one 3T MR scan without an alginate bite registration were performed on 12 subjects. CBCT images were acquired with an 18x16 inch field of view that covered the whole head. Contiguous sagittal MR images of the whole head were created in a 3.0T imaging system with a T1-weighted 3D imaging sequence (Magnetization Prepared Rapid Acquisition by Gradient Echo (MP-RAGE), TR/TE = 1950/2.26ms) and isotropic resolution of 1.0x1.0x1.0mm. The alginate bite registration was used to provide a proton-rich material to surround proton-poor teeth in an attempt to improve visualization of teeth on the MR images. Tooth length measurements were made from 4mm thick slices made through the long axis of all permanent teeth (336 tooth length measurements) using Osirix imaging software (Pixmeo, CH).
Results: The presence of the alginate bite registration during MR scans made it impossible to determine tooth lengths on MR images. Tooth length measurements from CBCT and MR scans without an alginate bite registration were highly correlated. The correlation coefficient was 0.953 (p<0.001).
Conclusions: This study determined that: 1) an alginate bite registration does not improve visualization of teeth on MR scans, and 2) tooth length measurements made on 3T T1-weighted MR scans are highly correlated with tooth length measurements made on CBCT scans.