Magnetic resonance imaging of intraoral hard and soft tissues using an intraoral coil and FLASH sequences

Abstract

Objectives: To ascertain the feasibility of MRI as a non-ionizing protocol for routine dentomaxillofacial diagnostic imaging. Wireless coils were used for MRI of intraoral hard and soft tissues.

Methods: FLASH MRI was applied in vivo with a mandible voxel size of 250 × 250 × 500 μm³, FOV of 64 × 64 × 28 mm³ and acquisition time of 3:57 min and with a maxilla voxel size of 350 μm³ and FOV of 34 cm³ in 6:40 min. Ex vivo imaging was performed in 4:38 min, with a resolution of 200 μm³ and FOV of 36.5 cm³. Cone beam (CB) CT of the mandible and subjects were acquired. MRI was compared to CBCT and histological sections. Deviations were calculated with intraclass correlation coefficient (ICC) and coefficient of variation (c_v).

Results: A high congruence between CBCT, MRI and specimens was demonstrated. Hard and soft tissues including dental pulp, periodontium, gingiva, cancellous bone and mandibular canal contents were adequately displayed with MRI.

Conclusions: Imaging of select intraoral tissues was achieved using custom MRI protocols with an easily applicable intraoral coil in a clinically acceptable acquisition time. Comparison with CBCT and histological sections helped demonstrate dimensional accuracy of the MR images. The course of the mandibular canal was accurately displayed with CBCT and MRI.

Key points: • MRI is a clinically available diagnostic tool in dentistry • Intraoral hard and soft tissues can be imaged with a high resolution with MRI • The dimensional accuracy of MRI is comparable to cone beam CT.

Keywords: Accuracy; Cone beam computed tomography; Dental Implantation; Dimensional measurement; Magnetic resonance imaging.

Fig. 1

(A) Histological section through the second premolar in the left mandible of an ex vivo human specimen. (B) Section through the magnetic resonance image of the tooth with identical visible structures. (C) Section through cone beam computed tomography image of the ex vivo human specimen with fewer visible structures

Fig. 2

Section through the magnetic resonance image (left) and CBCT image (right) of the second premolar of the ex vivo lower jaw. The following landmarks are marked in the magnetic resonance image and the cone beam computed tomography image: (a) vestibular alveolar limbus, (b) oral alveolar limbus, (c) tooth apex, (d) cranial border of the mandibular nerve canal and (e) basal border of the mandibular nerve canal

Fig. 3

Sagittal section through the magnetic resonance (MR) images (left) and the cone beam computed tomography (CBCT) images (right) of the ex vivo lower jaw. The dental pulp, gingiva, spongious bone and inferior alveolar nerve are discerned in the MR image, whereas the dental pulp canal, the bony borders of the inferior alveolar nerve and the spongious bone are delineated with the CBCT

Fig. 4

(B) Axial (left), sagittal (middle) and transverse (right) cross-sections of FLASH magnetic resonance imaging of the lower jaw acquired in vivo with an intraoral coil that was inductively coupled to a small loop coil at 3T with the following parameters: 250 μm² × 500 μm resolution, 64 mm × 64 mm × 28 mm field of view, acquisition time 3:57 min. (A) Axial (left), sagittal (middle) and transverse (right) cross-sections of in vivo cone beam computed tomography of the lower jaw (3D Accuitomo 170, Morita, Japan, nominal resolution 250 μm, 90 kV, 201 images)

Fig. 5

Axial (left), sagittal (middle) and transverse (right) cross-sections of in vivo FLASH magnetic resonance imaging of the maxilla acquired with a small loop coil at 3 T and an inductively coupled coil with the following parameters: isotropic resolution of 350 μm, field of view of 34 cm³, acquisition time of 6:40 min (TE/TR = 4.8/12 ms, flip angle α = 15°, five averages)