Geometric accuracy of magnetic resonance imaging of the mandibular nerve

Identifying the Anatomical Variations of the Inferior Alveolar Nerve with Magnetic Resonance Imaging

BACKGROUND

The inferior alveolar nerve (IAN) is located in the mandibular canal (MC). It is critical to evaluate the position of the MC during treatment planning to prevent intra or postoperative complications.

AIMS

This retrospective study aimed to identify the anatomy and anatomical variations of the IAN using soft tissue imaging (pulse sequence magnetic resonance imaging [MRI]).

MATERIALS AND METHODS

This study was designed as a retrospective Consolidated Standards of Reporting Trials (CONSORT) study. In total, 220 MR images were obtained. Nutrient canals (NCs) were classified as intraosseous and dental NCs, while bifid MCs (BMCs) were classified as forward, retromolar, and buccolingual canals. IBM SPSS Statistics 22 was used. Kolmogorov-Smirnov and Shapiro-Wilk tests, descriptive statistical methods (means, standard deviations, and frequencies), and the Chi-square test were used. Statistical significance was set at P < 0.05.

RESULTS

In total, 220 patients (172 females and 48 males) were evaluated. NCs were present in 92.3% of all MCs and were significantly higher in patients aged <25 years. BMCs were observed in 106 patients (24.1%). The most common BMC of MC/IAN was in the forward canal (14.4%), followed by the retromolar canal (7.5%).

CONCLUSION

Although previously, the dental canal was considered as an anatomical variation, this study revisited the classification and suggested that dental canals are anatomical structures.

Is MRI a viable alternative to CT/CBCT to identify the course of the inferior alveolar nerve in relation to the roots of the third molars?

Objectives

To assess the reliability of judging the spatial relation between the inferior alveolar nerve (IAN) and mandibular third molar (MTM) based on MRI or CT/CBCT images.

Methods

Altogether, CT/CBCT and MRI images of 87 MTMs were examined twice by 3 examiners with different degrees of experience. The course of the IAN in relation to the MTM, the presence/absence of a direct contact between IAN and MTM, and the presence of accessory IAN were determined.

Results

The IAN was in > 40% of the cases judged as inferior, while an interradicular position was diagnosed in < 5% of the cases. The overall agreement was good (κ = 0.72) and any disagreement between the imaging modalities was primarily among the adjacent regions, i.e., buccal/lingual/interradicular vs. inferior. CT/CBCT judgements presented a very good agreement for the inter- and intrarater comparison (κ > 0.80), while MRI judgements showed a slightly lower, but good agreement (κ = 0.74). A direct contact between IAN and MTM was diagnosed in about 65%, but in almost 20% a disagreement between the judgements based on MRI and CT/CBCT was present resulting in a moderate overall agreement (κ = 0.60). The agreement between the judgements based on MRI and CT/CBCT appeared independent of the examiner’s experience and accessory IAN were described in 10 cases in MRI compared to 3 cases in CT/CBCT images.

Conclusions

A good inter- and intrarater agreement has been observed for the assessment of the spatial relation between the IAN and MTM based on MRI images. Further, MRI images might provide advantages in the detection of accessory IAN compared to CT/CBCT.

Clinical relevance

MRI appears as viable alternative to CT/CBCT for preoperative assessment of the IAN in relation to the MTM.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00784-020-03716-4.

Utilização da imagem por ressonância magnética na odontologia: revisão de literatura

A Imagem por Ressonância Magnética (IRM) tem sido considerada a modalidade de escolha para o diagnóstico de processos patológicos que acometem a articulação temporomandibular, tecidos moles e outros processos inflamatórios. Devido a sua característica não invasiva e livre de radiação ionizante, novas aplicações para a técnica têm sido propostas e estudadas nas mais diversas áreas da Odontologia, como Endodontia, Dentística, Periodontia e Cirurgia Oral. O objetivo neste trabalho é apresentar uma revisão de literatura acerca da utilização da IRM na Odontologia, destacando as vantagens e limitações da técnica.

3D cephalometric analysis using Magnetic Resonance Imaging: validation of accuracy and reproducibility

The aim of this study was to validate geometric accuracy and in vivo reproducibility of landmark-based cephalometric measurements using high-resolution 3D Magnetic Resonance Imaging (MRI) at 3 Tesla. For accuracy validation, 96 angular and 96 linear measurements were taken on a phantom in 3 different positions. In vivo MRI scans were performed on 3 volunteers in five head positions. For each in vivo scan, 27 landmarks were determined from which 19 angles and 26 distances were calculated. Statistical analysis was performed using Bland-Altman analysis, the two one-sided tests procedure and repeated measures one-way analysis of variance. In comparison to ground truth, all MRI-based phantom measurements showed statistical equivalence (p < 0.001) and an excellent agreement in Bland-Altman analysis (bias ranges: -0.090-0.044°, -0.220-0.241 mm). In vivo cephalometric analysis was highly reproducible among the five different head positions in all study participants, without statistical differences for all angles and distances (p > 0.05). Ranges between maximum and minimum in vivo values were consistently smaller than 2° and 2 mm, respectively (average ranges: 0.88°/0.87 mm). In conclusion, this study demonstrates that accurate and reproducible 3D cephalometric analysis can be performed without exposure to ionizing radiation using MRI.

MRI for Dental Applications

Imaging of hard and soft tissue of the oral cavity is important for dentistry. However, medical computed tomography, cone beam computed tomography (CBCT), nor MRI enables soft and hard tissue imaging simultaneously. Some MRI sequences were shown to provide fast soft and hard tissue imaging of hydrogen, which increased the interest in dental MRI. Recently, MRI allowed direct visualization of cancellous bone, intraoral mucosa, and dental pulp despite that cortical bone and dental roots are indirectly visualized. MRI seems to be adequate for many indications that CBCT is currently used for: implant treatment and inflammatory diseases of the tooth.

Assessment of impacted and partially impacted lower third molars with panoramic radiography compared to MRI-a proof of principle study

OBJECTIVES

Third molars often require surgical removal. Since three-dimensional radiological assessment is often indicated in difficult cases to avoid surgical complications, the radiation burden has to be considered. Here, MRI may offer a dose-free alternative to conventional X-ray techniques. The aim of this retrospective analysis was to evaluate the assessment quality of MRI compared to panoramic radiography in impacted and partially impacted lower third molars.

METHODS

Panoramic radiographs and MRI scans of 28 Caucasian patients were assessed twice by four investigators. Wisdom teeth were classified according to Juodzbalys and Daugela 2013.

RESULTS

When radiological lower third molar assessments with panoramic radiography and MRI were compared, staging concurred in 73% in the first round of assessments and 77% in the second.

CONCLUSIONS

The presented study demonstrates that MRI not only provides much the same information that panoramic radiography usually does, but also has the advantages of a dose-free three-dimensional view. This may facilitate and shorten third molar surgery. Image interpretation, however, can differ depending on training and experience.

Magnetic resonance imaging-a diagnostic tool for postoperative evaluation of dental implants: a case report

OBJECTIVE

Compared with cone beam computed tomography (CBCT), magnetic resonance imaging (MRI) might be superior for the diagnosis of nerve lesions associated with implant placement.

STUDY DESIGN

A patient presented with unilateral pain associated with dysesthesia in the region of the right lower lip and chin after implant placement. Conventional orthopantomography could not identify an association between the position of the inferior alveolar nerve and the implant. For 3-dimensional display of the implant in relation to the surrounding anatomy, CBCT was compared with MRI.

RESULTS

MRI enabled the precise depiction of the implant position and its spatial relation to the inferior alveolar nerve, whereas the nerve position and its exact course within the mandible could not be directly displayed in CBCT.

CONCLUSION

MRI may be a valuable, radiation-free diagnostic tool for the visualization of intraoral hard and soft tissues, offering an objective assessment of nerve injuries by a direct visualization of the inferior alveolar neurovascular bundle.

Mandibular canal visibility using a plain volumetric interpolated breath-hold examination sequence in MRI

OBJECTIVES

To evaluate the validity of plain volumetric interpolated breath-hold examinations (VIBEs) for detecting the course of the mandibular canal, and to compare the results with contrast-enhanced (CE) VIBE images.

METHODS

From our imaging archives, we collected 28 cases taken with a VIBE sequence both before and after intravenous administration of gadolinium hydrate, and then two observers evaluated neurovascular bundle (NVB) visibility in the VIBE images. For the invisible NVB cases, we identified the invisible areas and analysed the causes of invisibility. For cases that also had corresponding CT thin slice images, we obtained a fusion image between MRI and CT, and investigated the relationship between the NVB in VIBE and the mandibular canal in CT images.

RESULTS

The visibility of the NVBs in plain VIBE was 89%, the same as on CE VIBE. There were three invisible cases in each plain and CE VIBE images. The invisible areas were premolar in three cases, and molar in one case, and the causes of the invisibility were a metallic artefact in one case and motion artefacts in the other two cases.

CONCLUSIONS

A plain VIBE can depict the NVB at the same rate as CE VIBE, and is suitable for detecting NVBs.

Utility of fusion volumetric images from computed tomography and magnetic resonance imaging for localizing the mandibular canal

OBJECTIVES

The purpose of this study was to investigate whether CT/MRI fusion volumetric images can improve the detectability of the mandibular canal (MC) compared with CT alone.

METHODS

Images of 31 lesions within or close to the mandible using both multislice CT (MSCT) and MRI were gathered from our imaging archives. All lesions underwent MSCT and three-dimensional volumetric interpolated breath-hold examination (3D-VIBE) MRI. Of the 62 hemimandibles, 13 hemimandibles were excluded because the MC passed through a lesion. The remaining 49 hemimandibles were included in this study. Each hemimandible was divided into 3 areas (premolar, molar and retromolar), and 147 areas were evaluated. First, the visibility of the MC on CT or its neurovascular bundle (NVB) on 3D-VIBE was evaluated. Second, in areas in which both the MC and NVB were visible, the relative locations of the NVB on MRI and the position of the MC on CT were assessed using CT/MRI fusion volumetric images.

RESULTS

The MC and NVB were clearly visible in 100 (68%) and 144 (98%) of 147 areas on CT and MRI, respectively. All NVBs and MCs were in identical locations, and the NVB on MRI was the same size or smaller than the MC on CT in 79 and 21 areas, respectively.

CONCLUSIONS

3D-VIBE MRI can accurately depict the NVB. Compared with CT alone, CT/MRI fusion volumetric imaging improves MC detectability.

High isotropic resolution magnetic resonance imaging of the mandibular canal at 1.5 T: a comparison of gradient and spin echo sequences

OBJECTIVES

The precision of localizing the mandibular canal prior to surgical intervention depends on the achievable resolution, whereas identification of the nerve depends on the image contrast. In our study, we developed new protocols based on gradient and spin echo sequences. The results from both sequences were quantitatively compared for their agreement to identify the most suitable approach.

METHODS

By limiting the field of view to one side of the mandible, three-dimensional acquisitions with T₁ weighted gradient and spin echo sequences were performed with 0.5 × 0.5 × 0.5 mm³ resolution within 6.5 min covering the mandibular canal from the mandibular to the mental foramen. Aliasing artefacts were suppressed by different techniques. A manual segmentation of the mandibular canal from seven healthy volunteers was performed on this section by three different observers. The surface distance of the segmented volumes was computed between both sequences as well as between the different observers as a measure of equality.

RESULTS

The quantitative comparison of the segmentation resulted in an average surface distance of 0.26 ± 0.05 mm between both sequences and an interobserver difference of 0.26 ± 0.08 mm for gradient and 0.29 ± 0.07 mm for spin echo data. By repeated evaluation, a difference of 0.15 ± 0.02 mm for gradient and 0.18 ± 0.03 mm for spin echo data was observed, indicating a slightly higher variability for spin echo images.

CONCLUSIONS

Both sequences can be used to achieve high-resolution images with good contrast and can be used for precise localization of the mandibular canal. Despite a slightly increased difference for the spin echo data, the advantage of an easy and robust setup remains.

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

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

Electronic supplementary material

The online version of this article (doi:10.1007/s00330-016-4254-1) contains supplementary material, which is available to authorized users.

Determination of the location of the mental foramen: a critical review

INTRODUCTION

The mental foramen (MF) is an important landmark to consider during surgical endodontic procedures. The purpose of this review article was to discuss the variety of techniques that have been developed to determine the location of the MF, to make recommendations for the current best technique available, and to discuss upcoming technologies.

METHODS

Articles that have addressed the location of the MF were evaluated for information pertinent to include in this review.

RESULTS

Different technologies have been used to help operators determine the clinical location of the MF. Most of the techniques have shortcomings such as magnification, radiation, and cost. Cone-beam computed tomographic imaging is the best current available imaging technology to determine the accurate location of the MF, but it has shortcomings such as radiation, cost, and not being real time, which means the data must be interpreted at a later time than when the information was computed.

CONCLUSIONS

In the future, magnetic resonance imaging and ultrasound technologies seem to provide promising noninvasive imaging techniques.

Evaluation of the inferior alveolar canal for cysts and tumors of the mandible-comparison of multidetector computed tomography and 3-dimensional volume interpolated breath-hold examination magnetic resonance sequence with curved multiplanar reformatted reconstructions

OBJECTIVE

To evaluate the mandibular canal using volume interpolated breath-hold examination (VIBE) sequencing in patients with cysts and tumors of the mandible.

MATERIALS AND METHODS

Twenty-five patients with mandibular cysts and tumors were recruited for a study in the authors' institution to compare the role of multidetector row computed tomography with magnetic resonance imaging (MRI) in jaw lesions. Of these 25 patients, VIBE was performed in 12 patients (age range, 16 to 52 yrs; 11 male and 1 female patients) and formed the study group. The status (normal/destroyed/attenuated) and position of the inferior alveolar canal (normal/displaced) on panoramic reconstructed computed tomographic (CT) images and curved multiplanar reformatted (MPR) images reconstructed from VIBE images were analyzed. The contralateral normal mandibular canal was used as the control in these patients.

RESULTS

In all 12 patients, the inferior alveolar canal on the normal side was visualized as a hyperintense structure in relation to the hypointense bone on the curved MPR VIBE images. In 9 patients, the inferior alveolar canal was equally well visualized on panoramic CT and curved MPR VIBE images. In 2 patients, the inferior alveolar canal was better visualized on curved MPR VIBE images; in 1 patient, the course of the mandibular canal was better seen on panoramic CT images.

CONCLUSIONS

MR reconstructions with VIBE sequencing as source images provide images comparable to CT reconstructed images for evaluation of the mandibular canal. Three-dimensional (3D) VIBE sequencing can be added to the MR protocol to visualize the inferior alveolar neurovascular bundle. 3D VIBE sequencing increases the diagnostic capabilities of MRI when used to image mandibular cysts and tumors.

Study of inferior dental canal and its contents using high-resolution magnetic resonance imaging

The aim of this study was to evaluate the visualizability, topography, and course of the mandibular canal with particular attention to the incisive canal on 3-T MRI. Particular attention was paid to the incisive canal anastomosis at the symphysis. A total of 64 dentate patients were examined using a modified T2 space sequence using 3-T MRI. The scans were analyzed with respect to the topography of the entire course of the mandibular canal, mental canal, incisive canal, and nutrient canals. The high-field MRI of the lower jaw allowed detailed visualization of the mandibular canal, the incisive canal, and the surrounding connective tissue structures. In the context of the present study, 3-T MRI was found to be a potentially useful imaging method for displaying the course of the entire inferior dental canal for pre-implantation planning, surgical planning, and diagnosis.

Dental magnetic resonance imaging: study of impacted mandibular third molars

OBJECTIVES

To assess the usefulness of MRI in the evaluation of the relationships between the mandibular canal and impacted mandibular third molars.

METHODS

29 young patients from our hospital dental service, all with a unilateral impacted mandibular third molar, were investigated with MR and the anatomical details were evaluated in three dimensions by two MR-experienced radiologists from our radiology division. MR images were obtained by using a 1.0 T Siemens Magnetom Expert unit with a radiofrequency (RF) head coil. T(1) weighted axial oblique images and proton density-weighted sagittal/coronal oblique images were acquired in order to evaluate the anatomical details in the three dimensions.

RESULTS

In all of the cases it was possible to evaluate the depth of the third molar in the alveolar bone, its inclination towards the occlusal plane and the relationships with the mandibular canal, but in 2 of 29 cases it was not possible to distinguish the mandibular canal from the third molar because of magnetic susceptibility artefacts.

CONCLUSIONS

Owing to the possibility of inferior alveolar nerve injury during oral surgery, where dental panoramic radiography is not sufficient to demonstrate the relationships between mandibular third molar teeth and the mandibular canal, a dental CT scan is often needed; however, in young patients, to avoid high levels of radiation dose, MRI of the jaw may be useful.

Implant radiography and radiology

The practitioner placing dental implants has many options with respect to pre-implant radiographic assessment of the jaws. The advantages and disadvantages of the imaging modalities currently available for pre-implant imaging are discussed in some detail. Intra-oral and extra-oral radiographs are generally low dose but the information provided is limited as the images are not three-dimensional. Tomography is three-dimensional, but the image quality is highly variable. Computed tomography (CT) has been the gold standard for many years as the information provided is three-dimensional and generally very accurate. However, CT examinations are expensive and deliver a relatively high radiation dose to the patient. The latest imaging modality introduced is cone beam volumetric tomography (CBVT) and this technology is very promising with regard to pre-implant imaging. CBVT generally delivers a lower dose to the patient than CT and provides reasonably sharp images with three-dimensional information. A comparison between CT and CBVT is provided. Magnetic resonance imaging is showing some promise, but the examinations are not readily available, generally expensive and bone is not well imaged. Magnetic resonance imaging is excellent for demonstrating soft tissues and therefore may be of great use in identifying the inferior dental nerve and vessels. All of the above technology is of little value if the information required is not obtained and so information is also provided on imaging of some of the vital structures. Of particular interest is the inferior dental canal, incisive canals of the mandible, genial foramina and canals, maxillary sinus and the incisive canal and foramen of the maxilla.

The accuracy of 3-dimensional magnetic resonance 3D vibe images of the mandible: an in vitro comparison of magnetic resonance imaging and computed tomography

OBJECTIVE

The purpose of this study was to investigate in vitro the accuracy of three-dimensional (3D) magnetic resonance imaging (MRI) to measure the mandible.

STUDY DESIGN

The optimal MRI sequence for 3D mandible from the data of 2 volunteers was determined to be 3D vibe. MRI and computed tomography (CT) scans of tube, mandible, and hemimandible phantoms were obtained. MRI with 3D vibe and standard parameters used in clinical practice for 3D reconstructions of jawbones on CT were used. Pearson's correlation coefficient, standard deviation (SD), and accuracy in measurement on reconstructed 3D MRI and CT were compared to direct osteometric measurement of the phantoms.

RESULTS

The correlation coefficient between MRI and direct osteometry was high, with r = 0.85 to 0.99 (P < .001). The difference ranged from -1.5 to 0.7 mm (-8.9%-11.1%) on smaller distances, which is important for orthognathic surgery. The accuracy of MRI was similar to that of CT.

CONCLUSION

3D vibe MRI provided adequate dimensional accuracy and image quality during in vitro examination of the mandible.