Diagnostic compatibility of various fixed orthodontic retainers for head/neck MRI and dental MRI.

OBJECTIVES: To evaluate the diagnostic MRI compatibility of different fixed orthodontic retainers using a high-resolution 3D-sequence optimized for artifact reduction. MATERIALS AND METHODS: Maxillary and mandibular retainers made of five different materials were scanned in vitro and in vivo at 3 T MRI using an MSVAT-SPACE sequence. In vitro, artifact volumes were determined for all maxillary and mandibular retainers (AVmax; AVmand). In vivo, two independent observers quantified the extent of artifacts based on the visibility of 124 dental and non-dental landmarks using a five-point rating scale (1 = excellent, 2 = good, 3 = acceptable, 4 = poor, 5 = not visible). RESULTS: Rectangular-steel retainers caused the largest artifacts (AVmax/AVmand: 18,060/15,879 mm3) and considerable diagnostic impairment in vivo (mean landmark visibility score ± SD inside/outside the retainer areas: 4.8 ± 0.8/2.9 ± 1.6). Smaller, but diagnostically relevant artifacts were observed for twistflex steel retainers (437/6317 mm3, 3.1 ± 1.7/1.3 ± 0.7). All retainers made of precious-alloy materials produced only very small artifact volumes (titanium grade 1: 70/46 mm3, titanium grade 5: 47/35 mm3, gold: 23/21 mm3) without any impact on image quality in vivo (each retainer: visibility scores of 1.0 ± 0.0 for all landmarks inside and outside the retainer areas). CONCLUSIONS: In contrast to steel retainers, titanium and gold retainers are fully compatible for both head/neck and dental MRI when using MSVAT-SPACE. CLINICAL RELEVANCE: This study demonstrates that titanium and gold retainers do not impair the diagnostic quality of head/neck and dental MRI when applying an appropriate artifact-reduction technique. Steel retainers, however, are not suitable for dental MRI and can severely impair image quality in head/neck MRI of the oral cavity.

Quantitative assessment of contrast-enhancement patterns of the healthy dental pulp by magnetic resonance imaging: A prospective in vivo study.

AIM: This prospective in vivo study aimed to optimize the assessment of pulpal contrast-enhancement (PCE) on dental magnetic resonance imaging (dMRI) and investigate physiological PCE patterns. METHODOLOGY: In 70 study participants, 1585 healthy teeth were examined using 3-Tesla dMRI before and after contrast agent administration. For all teeth, the quotient of post- and pre-contrast pulp signal intensity (Q-PSI) was calculated to quantify PCE. First, pulp chambers were analysed in 10 participants to compare the coefficient of variation of mean versus maximum Q-PSI values (Q-PSImean versus Q-PSImax ). Second, dynamic PCE was evaluated in 10 subjects to optimize the time interval between contrast agent application and image acquisition. Finally, 50 participants (age groups: 20-29, 30-39, 40-49, 50-59 and 60-69 years) were examined to analyse age, gender, tooth types and maxilla versus mandible as independent factors of PCE. Statistical analysis was performed using Wilcoxon signed rank test and linear mixed models. RESULTS: PCE assessment based on Q-PSImax was associated with a significantly smaller coefficient of variation compared with Q-PSImean , with median values of 0.17 versus 0.21 (p = .002). Analysis of dynamic PCE revealed an optimal timing interval for image acquisition 4 min after contrast media application. No significant differences in PCE were observed by comparing age groups, female versus male participants and maxillary versus mandibular teeth (p > .05). Differences between tooth types were small (median Q-PSImax values of 2.52/2.32/2.30/2.20 for molars/premolars/canines/incisors) but significant (p < .05), except for the comparison of canines versus premolars (p = .80). CONCLUSIONS: PCE in dMRI was a stable intra-individual marker with only minor differences between different tooth types, thus forming an important basis for intra-individual controls when assessing teeth with suspected endodontic pathosis. Furthermore, it was demonstrated that PCE is independent of age, gender and jaw type. These findings indicate that dMRI-based PCE analysis could be a valuable diagnostic tool for the identification of various pulp diseases in future patient studies.

Endodontic working length measurements of premolars and molars in high-resolution dental MRI: a clinical pilot study for assessment of reliability and accuracy.

OBJECTIVES: To prospectively assess the reliability and accuracy of high-resolution, dental MRI (dMRI) for endodontic working length (WL) measurements of premolars and molars under clinical conditions. MATERIALS AND METHODS: Three-Tesla dMRI was performed in 9 subjects who also had undergone cone-beam computed tomography (CBCT) (mean age: 47 ± 13.5 years). A total of 34 root canals from 12 molars (4/8, upper/lower jaw; 22 root canals) and 11 premolars (2/9 upper/lower jaw; 12 root canals) were included. CBCT and dMRI datasets were reconstructed to visualize the root canal in one single slice. Subsequently, two radiologists measured the root canal lengths in both modalities twice in blinded fashion. Reliability and accuracy for both modalities were assessed using intraclass correlation coefficients (ICCs) and Bland-Altman analysis, respectively. RESULTS: Reliability (intra-rater I/II; inter-rater) of dental MRI measurements was excellent and comparable to CBCT for premolars (0.993/0.900; 0.958 vs. 0.993/0.956; 0.951) and for molars (0.978/0.995; 0.986 vs. 0.992/0.996; 0.989). Bland-Altman analysis revealed a mean underestimation/bias (95% confidence interval) of dMRI measurements of 0.8 (- 1.44/3.05) mm for premolars and 0.4 (- 1.55/2.39) mm for molars. In up to 59% of the cases, the accuracy of dMRI for WL measurements was within the underestimation margin of 0 to 2 mm short of the apical foramen AF. CONCLUSIONS: In vivo demonstration and measurement of WL are feasible using dMRI. The reliability of measurements is high and equivalent to CBCT. Nonetheless, due to lower spatial resolution and longer acquisition time, the accuracy of dMRI is inferior to CBCT, impeding its current use for clinical treatment planning. CLINICAL RELEVANCE: dMRI is a promising radiation-free imaging technique. Its reliability for endodontic working length measurements is high, but its accuracy is not satisfactory enough yet.

Three-dimensional accuracy of partially guided implant surgery based on dental magnetic resonance imaging.

OBJECTIVES: To measure in vivo 3D accuracy of backward-planned partially guided implant surgery (PGIS) based on dental magnetic resonance imaging (dMRI). MATERIAL AND METHODS: Thirty-four patients underwent dMRI examinations. Tooth-supported templates were backward planned using standard dental software, 3D-printed, and placed intraorally during a cone beam computed tomography (CBCT) scan. Treatment plans were verified for surgical viability in CBCT, and implants were placed with guiding of the pilot drill. High-precision impressions were taken after healing. The 3D accuracy of 41 implants was evaluated by comparing the virtually planned and definitive implant positions with respect to implant entry point, apex, and axis. Deviations from the dMRI-based implant plans were compared with the maximum deviations calculated for a typical single implant. RESULTS: Twenty-eight implants were placed as planned in dMRI. Evaluation of 3D accuracy revealed mean deviations (99% confidence intervals) of 1.7 ± 0.9mm (1.2-2.1mm) / 2.3 ± 1.1mm (1.8-2.9 mm) / 7.1 ± 4.8° (4.6-9.6°) for entry point / apex / axis. The maximum deviations calculated for the typical single implant surpassed the upper bounds of the 99% CIs for the apex and axis, but not for the entry point. In the 13 other implants, dMRI-based implant plans were optimized after CBCT. Here, deviations between the initial dMRI plan and definitive implant position were only in part higher than in the unaltered group (1.9 ± 1.7 mm [0.5-3.4 mm] / 2.5 ± 1.5 mm [1.2-3.8 mm] / 6.8 ± 3.8° [3.6-10.1°] for entry point / apex / axis). CONCLUSIONS: The 3D accuracy of dMRI-based PGIS was lower than that previously reported for CBCT-based PGIS. Nonetheless, the values seem promising to facilitate backward planning without ionizing radiation.

Evaluation of magnetic resonance imaging artifacts caused by fixed orthodontic CAD/CAM retainers-an in vitro study.

OBJECTIVES: Magnetic resonance imaging (MRI) image quality can be severely impaired by artifacts caused by fixed orthodontic retainers. In clinical practice, there is a trend towards using computer-aided design/computer-aided manufacturing (CAD/CAM) retainers. This study aimed to quantify MRI artifacts produced by these novel CAD/CAM retainers. MATERIAL AND METHODS: Three CAD/CAM retainers and a stainless-steel retainer ("Twistflex"; clinical reference standard) were scanned in vitro at 3-T MRI using a high-resolution 3D sequence. The artifact diameters and three-dimensional artifact volumes (AV) were determined for all mandibular (AVmand) and maxillary (AVmax) retainers. Moreover, the corresponding ratio of artifact volume to retainer volume (AV/RVmand, AV/RVmax) was calculated. RESULTS: Twistflex caused large artifact volumes (AVmand: 13530 mm3; AVmax: 15642 mm3; AV/RVmand: 2602; AV/RVmax: 2235). By contrast, artifact volumes for CAD/CAM retainers were substantially smaller: whereas artifact volumes for cobalt-chromium retainers were moderate (381 mm3; 394 mm3; 39; 31), grade-5 titanium (110 mm3; 126 mm3; 12; 12) and nickel-titanium (54 mm3; 78 mm3; 12; 14) both produced very small artifact volumes. CONCLUSION: All CAD/CAM retainers caused substantially smaller volumes of MRI artifacts compared to Twistflex. Grade-5 titanium and nickel-titanium CAD/CAM retainers showed the smallest artifact volumes. CLINICAL RELEVANCE: CAD/CAM retainers made from titanium or nickel-titanium may not relevantly impair image quality in head/neck and dental MRI. Artifacts caused by cobalt-chromium CAD/CAM retainers may mask nearby dental/periodontal structures. In contrast, the large artifacts caused by Twistflex are likely to severely impair diagnosis of oral and adjacent pathologies.

Structural Nerve Remodeling at 3-T MR Neurography Differs between Painful and Painless Diabetic Polyneuropathy in Type 1 or 2 Diabetes.

Background The pathophysiologic mechanisms underlying painful symptoms in diabetic polyneuropathy (DPN) are poorly understood. They may be associated with MRI characteristics, which have not yet been investigated. Purpose To investigate correlations between nerve structure, load and spatial distribution of nerve lesions, and pain in patients with DPN. Materials and Methods In this prospective single-center cross-sectional study, participants with type 1 or 2 diabetes volunteered between June 2015 and March 2018. Participants underwent 3-T MR neurography of the sciatic nerve with a T2-weighed fat-suppressed sequence, which was preceded by clinical and electrophysiologic tests. For group comparisons, analysis of variance or the Kruskal-Wallis test was performed depending on Gaussian or non-Gaussian distribution of data. Spearman correlation coefficients were calculated for correlation analysis. Results A total of 131 participants (mean age, 62 years ± 11 [standard deviation]; 82 men) with either type 1 (n = 45) or type 2 (n = 86) diabetes were evaluated with painful (n = 64), painless (n = 37), or no (n = 30) DPN. Participants who had painful diabetic neuropathy had a higher percentage of nerve lesions in the full nerve volume (15.2% ± 1.6) than did participants with nonpainful DPN (10.4% ± 1.7, P = .03) or no DPN (8.3% ± 1.7; P < .001). The amount and extension of T2-weighted hyperintense nerve lesions correlated positively with the neuropathy disability score (r = 0.37; 95% confidence interval [CI]: 0.21, 0.52; r = 0.37; 95% CI: 0.20, 0.52, respectively) and the neuropathy symptom score (r = 0.41; 95% CI: 0.25, 0.55; r = 0.34; 95% CI: 0.17, 0.49, respectively). Negative correlations were found for the tibial nerve conduction velocity (r = -0.23; 95% CI: -0.44, -0.01; r = -0.37; 95% CI: -0.55, -0.15, respectively). The cross-sectional area of the nerve was positively correlated with the neuropathy disability score (r = 0.23; 95% CI: 0.03, 0.36). Negative correlations were found for the tibial nerve conduction velocity (r = -0.24; 95% CI: -0.45, -0.01). Conclusion The amount and extension of T2-weighted hyperintense fascicular nerve lesions were greater in patients with painful diabetic neuropathy than in those with painless diabetic neuropathy. These results suggest that proximal fascicular damage is associated with the evolution of painful sensory symptoms in diabetic polyneuropathy. © RSNA, 2019 Online supplemental material is available for this article.

Use of dental MRI for radiation-free guided dental implant planning: a prospective, in vivo study of accuracy and reliability.

OBJECTIVES: To evaluate the accuracy and reliability of dental MRI for static guided implant surgery planning. MATERIALS AND METHODS: In this prospective study, a 0.4-mm isotropic, artifact-suppressed, 3T MRI protocol was used for implant planning and surgical guide production in participants in need of dental implants. Two dentists decided on treatment plan. Surgical guides were placed intraorally during a subsequent reference cone beam computed tomography (CBCT) scan. Inter-rater and inter-modality agreement were assessed by Cohen's kappa. For each participant, dental MRI and CBCT datasets were co-registered to determine three-dimensional and angular deviations between planned and surgically guided implant positions. RESULTS: Forty-five implants among 30 study participants were planned and evaluated (17 women, 13 men, mean age 56.9 ± 13.1 years). Inter-rater agreement (mean κ 0.814; range 0.704-0.927) and inter-modality agreement (mean κ 0.879; range 0.782-0.901) were both excellent for the dental MRI-based treatment plans. Mean three-dimensional deviations were 1.1 ± 0.7 (entry point) and 1.3 ± 0.7 mm (apex). Mean angular deviation was 2.4 ± 1.5°. CBCT-based adjustments of MRI plans were necessary for implant position in 29.5% and for implant axis in 6.8% of all implant sites. Changes were larger in the group with shortened dental arches compared with those for tooth gaps. Except for one implant site, all guides were suitable for clinical use. CONCLUSION: This feasibility study indicates that dental MRI is reliable and sufficiently accurate for surgical guide production. Nevertheless, more studies are needed to increase its accuracy before it can be used for implant planning outside clinical trials. KEY POINTS: • An excellent reliability for the dental MRI-based treatment plans as well as agreement between dental MRI-based and CBCT-based (reference standard) decisions were noted. • Ideal implant position was not reached in all cases by dental MRI plans. • For all but one implant site surgical guides derived from dental MRI were sufficiently accurate to perform implant placement (mean three-dimensional deviations were 1.1 ± 0.7 (entry point) and 1.3 ± 0.7 mm (apex); mean angular deviation was 2.4 ± 1.5°).

In vivo comparison of MRI- and CBCT-based 3D cephalometric analysis: beginning of a non-ionizing diagnostic era in craniomaxillofacial imaging?

OBJECTIVES: To evaluate whether magnetic resonance imaging (MRI) can serve as an alternative diagnostic tool to the "gold standard" cone-beam computed tomography (CBCT) in 3D cephalometric analysis. METHODS: In this prospective feasibility study, 12 patients (8 males, 4 females; mean age ± SD, 26.1 years ± 6.6) underwent 3D MRI and CBCT before orthognathic surgery. 3D cephalometric analysis was performed twice by two independent observers on both modalities. For each dataset, 27 cephalometric landmarks were defined from which 35 measurements (17 angles, 18 distances) were calculated. Statistical analyses included the calculation of Euclidean distances, intraclass correlation coefficients (ICCs), Bland-Altman analysis, and equivalence testing (linear mixed effects model) with a predefined equivalence margin of ± 1°/1 mm. RESULTS: Analysis of reliability for CBCT vs. MRI (intra-rater I/intra-rater II/inter-rater) revealed Euclidean distances of 0.86/0.86/0.98 mm vs. 0.93/0.99/1.10 mm for landmarks, ICCs of 0.990/0.980/0.986 vs. 0.982/0.978/0.980 for angles, and ICCs of 0.992/0.988/0.989 vs. 0.991/0.985/0.988 for distances. Bland-Altman analysis showed high levels of agreement between CBCT and MRI with bias values (95% levels of agreement) of 0.03° (- 1.49; 1.54) for angles and 0.02 mm (- 1.44; 1.47) for distances. In the linear mixed effects model, the mean values of CBCT and MRI measurements were equivalent. CONCLUSION: This feasibility study indicates that MRI enables reliable 3D cephalometric analysis with excellent agreement to corresponding measurements on CBCT. Thus, MRI could serve as a non-ionizing alternative to CBCT for treatment planning and monitoring in orthodontics as well as oral and maxillofacial surgery. KEY POINTS: • Clinically established 3D cephalometric measurements performed on MRI are highly reliable and show an excellent agreement with CBCT (gold standard). • The MRI technique applied in this study could be used as a non-ionizing diagnostic tool in orthodontics as well as oral and maxillofacial surgery. • Since most patients benefiting from 3D cephalometry are young in age, the use of MRI could substantially contribute to radiation protection and open up new possibilities for treatment monitoring.

Comparison of non-contrast-enhanced dental magnetic resonance imaging and cone-beam computed tomography in assessing the horizontal and vertical components of furcation defects in maxillary molars: An in vivo feasibility study.

AIM: To compare non-contrast-enhanced dental magnetic resonance imaging (NCE-dMRI) and cone-beam computed tomography (CBCT) in assessing horizontal and vertical furcation defects in maxillary molars in vivo. MATERIALS AND METHODS: (NCE-dMRI) and CBCT were performed in 23 patients with severe periodontitis. Sixty-five first/second maxillary molars (195 furcation entrances) were analysed by two independent observers on both modalities to assess the horizontal and vertical components of furcation defects. Reliability of defect classification was evaluated using weighted kappa (κ) statistics. Agreement between NCE-dMRI and CBCT was determined by the Bland-Altman analysis. Sensitivity and specificity of NCE-dMRI were calculated using CBCT as the reference. RESULTS: Inter-radicular bone loss was observed in 94 furcation entrances. Intra- and inter-rater κ-values were ≥0.9 for both NCE-dMRI and CBCT. The Bland-Altman analysis showed mean differences (95% limits of agreement) of 0.12 mm (-0.67 to 0.90) for horizontal and 0.12 mm (-1.27 to 1.50) for vertical measurements. For the detection of furcation defects, sensitivity/specificity of NCE-dMRI was 98%/100% for horizontal and 99%/99% for vertical components. For defect classification, sensitivity values of NCE-dMRI were 88%/89%/100% (horizontal degree I/II/III) and 95%/91%/80% (vertical subclass A/B/C), respectively. CONCLUSIONS: Non-contrast-enhanced dental magnetic resonance imaging demonstrated high reliability and high agreement with CBCT for the assessment of furcation defects in maxillary molars.

In vivo accuracy of dental magnetic resonance imaging in assessing maxillary molar furcation involvement: A feasibility study in humans.

AIM: To investigate the accuracy and reliability of dental magnetic resonance imaging (dMRI) in assessing maxillary molar furcation involvement (FI). MATERIAL AND METHODS: In this prospective study, 22 patients with severe periodontitis underwent cone-beam computed tomography (CBCT) and dMRI. For 192 furcation entrances, the degree of horizontal FI was assessed by two independent observers on both modalities. Results of dMRI were compared with CBCT (reference modality) to assess the accuracy of dMRI. Cohen's kappa (κ), sensitivity and specificity were calculated for FI classification. Bland-Altman analysis and the Kruskal-Wallis test were used to evaluate measurement accuracy of dMRI. RESULTS: Based on CBCT findings, 93 furcation entrances revealed FI (degree I/II/III: 35/19/39). Intra- and inter-reader agreement was excellent for both modalities (κ-range: 0.884 to 0.933). dMRI measurements showed high agreement with CBCT (bias: 0.17 mm; 95% limits of agreement: -1.05 to 1.38 mm), and measurement accuracy did not differ among different degrees of FI (p = .67). For FI detection, sensitivity and specificity of dMRI were 98% and 99%. For FI classification, sensitivity values of dMRI were 89%/84%/100% for degree I/II/III. CONCLUSIONS: Compared to CBCT (non-invasive gold standard), dMRI demonstrates high accuracy and reliability in evaluating the degree of FI in maxillary molars.

In vivo reliability of 3D cephalometric landmark determination on magnetic resonance imaging: a feasibility study.

OBJECTIVE: 3D cephalometric analysis performed on cone-beam or multi-slice computed tomography (CBCT, MSCT) has superior diagnostic value compared to 2D cephalometry based on radiographs. However, this comes at the expense of increased radiation risks for the predominantly young patients. Magnetic resonance imaging (MRI) has the potential to overcome this diagnostic dilemma but has not been established for 3D cephalometry so far. Since landmark reliability forms the basis for 3D cephalometry, we evaluated the in vivo reliability of established 3D landmarks using MRI. MATERIALS AND METHODS: Sixteen orthodontic patients underwent MRI at 3 Tesla using a 0.5 mm 3D sequence. On each MRI scan, 44 cephalometric landmarks were determined. Image analysis was performed twice by two independent observers. Intra- and inter-rater agreement was assessed by mean measurement errors and intraclass correlation coefficients (ICCs). Measurement errors were calculated as Euclidean distances and distances for x-, y-, and z-coordinates. RESULTS: Overall, MRI-based 3D cephalometric landmarks revealed a high reliability comparable to prior in vivo studies using CBCT/MSCT. Intra- and inter-rater ICCs were consistently higher than 0.9. Intra-rater comparisons showed mean measurement differences (ranges) of 0.87 mm (0.41-1.63) for rater I and 0.94 mm (0.49-1.28) for rater II. Average inter-rater difference was 1.10 mm (0.52-2.29). Distinct differences in reliability between the various landmarks were observed, corresponding well with the landmarks' specific shapes. CONCLUSIONS: The present study demonstrates that MRI enables reliable determination of 3D cephalometric landmarks in vivo. CLINICAL RELEVANCE: This study emphasizes the potential of MRI to perform treatment planning and monitoring in orthodontics as well as oral and maxillofacial surgery without radiation exposure.

In vitro diagnostic accuracy of low-dose CBCT for evaluation of peri-implant bone lesions.

OBJECTIVES: To investigate the in vitro diagnostic accuracy of low-dose cone-beam computed tomography (LD-CBCT) for the detection, classification, and measurement of peri-implant bone lesions. MATERIAL AND METHODS: Titanium dental implants with all-ceramic single crowns (n = 24) were inserted into bovine bone. At twelve implants, four types of peri-implant bone lesions were created. Radiographic imaging was performed using three techniques: LD-CBCT, high-definition CBCT (HD-CBCT), and intraoral radiography (IR). The datasets were presented twice to four observers in a random order. Diagnostic accuracy was measured by calculating sensitivity and specificity, and analyzed using the McNemar's test at a significance level of 0.05. Absolute agreement between the defect sizes was assessed by means of intraclass correlation coefficients (ICC). RESULTS: For all three techniques, diagnostic accuracy and reliability for the detection of defects were almost perfect. The following order was found for classification of the different defect types (sensitivity/specificity): HD-CBCT (0.96/0.99) > LD-CBCT (0.93/0.98) > IR (0.71/0.95). No significant difference was found between the two CBCT techniques. Their performance was superior to that of IR. With regard to absolute agreement of defect size, LD-CBCT agreement with HD-CBCT (ICC, 95% confidence interval) was slight for defect depth (0.342, 0.181-0.625) and substantial for defect width (0.911, 0.775-0.963). CONCLUSION: Intraoral radiography is useful for detecting peri-implant bone lesions. LD-CBCT provides additional information regarding the geometry of defects. The even higher diagnostic accuracy of the HD-CBCT protocol tested needs to be carefully weighed against its radiation dose, which is 14 times higher than that of LD-CBCT.

In vivo accuracy of tooth surface reconstruction based on CBCT and dental MRI-A clinical pilot study.

OBJECTIVES: Guided implant surgery (GIS) requires alignment of virtual models to reconstructions of three-dimensional imaging. Accurate visualization of the tooth surfaces in the imaging datasets is mandatory. In this prospective clinical study, in vivo tooth surface accuracy was determined for GIS using cone-beam computed tomography (CBCT) and dental magnetic resonance imaging (dMRI). MATERIALS AND METHODS: CBCT and 3-Tesla dMRI were performed in 22 consecutive patients (mean age: 54.4 ± 15.2 years; mean number of restorations per jaw: 6.7 ± 2.7). Altogether, 92 teeth were included (31 incisor, 29 canines, 20 premolars, and 12 molars). Surfaces were reconstructed semi-automatically and registered to a reference standard (3D scans of stone models made from full-arch polyether impressions). Reliability of both methods was assessed using intraclass correlation coefficients. Accuracy was evaluated using the two one-sided tests procedure with a predefined equivalence margin of ±0.2 mm root mean square (RMS). RESULTS: Inter- and intrarater reliability of tooth surface reconstruction were comparable for CBCT and dMRI. Geometric deviations were 0.102 ± 0.042 mm RMS for CBCT and 0.261 ± 0.08 mm RMS for dMRI. For a predefined equivalence margin, CBCT and dMRI were statistically equivalent. CBCT, however, was significantly more accurate (p ≤ .0001). For both imaging techniques, accuracy did not differ substantially between different tooth types. CONCLUSION: Cone-beam computed tomography is an accurate and reliable imaging technique for tooth surfaces in vivo, even in the presence of metal artifacts. In comparison, dMRI in vivo accuracy is lower. Still, it allows for tooth surface reconstruction in satisfactory detail and within acceptable acquisition times.

High-resolution dental magnetic resonance imaging for planning palatal graft surgery-a clinical pilot study.

AIM: To evaluate whether high-resolution, non-contrast-enhanced dental magnetic resonance imaging (MRI) can be used for accurate determination of palatal masticatory mucosa thickness (PMMT) and to locate the greater palatal artery (GPA). MATERIALS AND METHODS: In five volunteers (four males, one female; mean age 30.2 ± 0.4 years), two independent raters measured PMMT by use of dental MRI in 180 positions. For comparison, clinical bone sounding was performed. The GPA was identified in time-of-flight (TOF) angiography and MSVAT-SPACE-prototype sequence. Intra- and inter-observer agreement for MRI measurements, agreement between MRI and bone sounding were analysed by intra-class correlation coefficient (ICC) and Cohen's kappa (κ). RESULTS: Reliability of dental MRI measurements was high (intra-observer-ICC 0.962; inter-observer ICC 0.959). Agreement of MRI measurements with bone sounding was moderate (ICC 0.744), and the GPA could be identified in 60% of measurement points using the TOF-angiography alone and in 85% with additional information of the MSVAT-SPACE. Good intra-observer agreement was observed for GPA identification (κ: 0.778). CONCLUSION: Palatal masticatory mucosa thickness measured by high-resolution, non-contrast enhanced dental MRI is comparable with that obtained by bone sounding. Dental MRI enables reliable, non-invasive and radiation-free planning of palatal tissue harvesting and can also be used for location of the GPA at 85% of measurement points, which might help reduce complications during surgery.

Accuracy of cone-beam computed tomography, dental magnetic resonance imaging, and intraoral radiography for detecting peri-implant bone defects at single zirconia implants-An in vitro study.

OBJECTIVES: To evaluate the diagnostic value of cone-beam computed tomography (CBCT), intraoral radiography (IR), and dental magnetic resonance imaging (dMRI) for detecting and classifying peri-implant bone defects at zirconia implants. MATERIALS AND METHODS: Forty-eight zirconia implants were inserted in bovine ribs, 24 of which had standardized defects (1-wall, 2-wall, 3-wall, 4-wall) in two sizes (1 and 3 mm). CBCT, IR, and dMRI were performed and analyzed twice by four readers unaware of the nature of the defects. Cohen's and Fleiss' kappa (κ), sensitivity, and specificity were calculated for the presence/absence of bone defects, defect size, and defect type. Cochran's Q-test with post hoc McNemar was used to test for statistical differences. RESULTS: A high intra- and inter-reader reliability (κ range: 0.832-1) and sensitivity/specificity (IR: 0.97/0.96; CBCT: 0.99/1; dMRI: 1/0.99) for bone defect detection were observed for all three imaging methods. For defect type classification, intra- (κ range: 0.505-0.778) and inter-reader (κ: 0.411) reliability of IR were lower compared to CBCT (κ range intrareader: 0.667-0.889; κ inter-reader: 0.629) and dMRI (κ range intrareader: 0.61-0.832; κ inter-reader: 0.712). The sensitivity for correct defect type classification was not significantly different for CBCT (0.81) and dMRI (0.83; p = 1), but was significantly lower for IR (0.68; vs. CBCT p = 0.003; vs. dMRI p = 0.004). The sensitivity advantage of CBCT and dMRI for defect classification was smaller for 1-mm defects (CBCT/dMRI/IR: 0.68/0.72/0.63, no significant difference) than for 3-mm defects (CBCT/dMRI/IR: 0.95/0.94/0.74; CBCT vs. IR p = 0.0001; dMRI vs. IR p = 0.003). CONCLUSION: Within the limitations of an in vitro study, IR can be recommended as the initial imaging method for evaluating peri-implant bone defects at zirconia implants. CBCT provides higher diagnostic accuracy of defect classification at the expense of higher cost and radiation dose. Dental MRI may be a promising imaging method for evaluating peri-implant bone defects at zirconia implants in the future.

PETRA, MSVAT-SPACE and SEMAC sequences for metal artefact reduction in dental MR imaging.

OBJECTIVES: Dental MRI is often impaired by artefacts due to metallic dental materials. Several sequences were developed to reduce susceptibility artefacts. Here, we evaluated a set of sequences for artefact reduction for dental MRI for the first time. METHODS: Artefact volume, signal-to-noise ratio (SNR) and image quality were assessed on a 3-T MRI for pointwise encoding time reduction with radial acquisition (PETRA), multiple-slab acquisition with view angle tilting gradient, based on a sampling perfection with application-optimised contrasts using different flip angle evolution (SPACE) sequence (MSVAT-SPACE), slice-encoding for metal-artefact correction (SEMAC) and compared to a standard SPACE and a standard turbo-spin-echo (TSE) sequence. Field-of-view and acquisition times were chosen to enable in vivo application. Two implant-supported prostheses were tested (porcelain fused to metal non-precious alloy and monolithic zirconia). RESULTS: Smallest artefact was measured for TSE sequences with no difference between the standard TSE and the SEMAC. MSVAT-SPACE reduced artefacts about 56% compared to the standard SPACE. Effect of the PETRA was dependent on sample used. Image quality and SNR were comparable for all sequences except PETRA, which yielded poor results. CONCLUSION: There is no benefit in terms of artefact reduction for SEMAC compared to standard TSE. Usage of MSVAT-SPACE is advantageous since artefacts are reduced and higher resolution is achieved. KEY POINTS: • SEMAC is not superior to TSE in terms of artefact reduction. • MSVAT-SPACE reduces susceptibility artefacts while maintaining comparable image quality. • PETRA reduces susceptibility artefacts depending on material but offers poor image quality.

Long-term Follow-up After Aneurysm Treatment with the Flow Redirection Endoluminal Device (FRED) Flow Diverter.

INTRODUCTION: This study focuses on long-term outcomes after aneurysm treatment with either the Flow Re-Direction Endoluminal Device (FRED) or the FRED Jr. to investigate the durability of treatment effect and long-term complications. METHODS: This study is based on a retrospective analysis of a prospectively maintained patient data base. Patients treated with either FRED or FRED Jr. between 2013 and 2017 at our institution, and thus a possibility for ≥ 5 years of follow-up, were included. Aneurysm occlusion rates, recurrence rates, modified Rankin scale score shifts to baseline, and delayed complications were assessed. RESULTS: In this study 68 patients with 84 aneurysms had long-term follow-up with a mean duration of 57.3 months and 44 patients harboring 52 aneurysms had a follow-up ≥ 5 years with a mean follow-up period of 69.2 months. Complete occlusion was reached in 77.4% at 2 years and increased to 84.9% when the latest available imaging result was considered. Younger age and the absence of branch involvement were predictors for aneurysm occlusion in linear regression analysis. After the 2­year threshold, there were 3 reported symptomatic non-serious adverse events. Of these, one patient had a minor stroke, one a transitory ischemic attack and one had persistent mass effect symptoms due to a giant aneurysm, none of these resulted in subsequent neurological disability. CONCLUSION: This long-term follow-up study demonstrates that the FRED and FRED Jr. are safe and effective for the treatment of cerebral aneurysms in the long term, with high rates of complete occlusion and low rates of delayed adverse events.

Multiscale and multimodal imaging for three-dimensional vascular and histomorphological organ structure analysis of the pancreas.

Exocrine and endocrine pancreas are interconnected anatomically and functionally, with vasculature facilitating bidirectional communication. Our understanding of this network remains limited, largely due to two-dimensional histology and missing combination with three-dimensional imaging. In this study, a multiscale 3D-imaging process was used to analyze a porcine pancreas. Clinical computed tomography, digital volume tomography, micro-computed tomography and Synchrotron-based propagation-based imaging were applied consecutively. Fields of view correlated inversely with attainable resolution from a whole organism level down to capillary structures with a voxel edge length of 2.0 µm. Segmented vascular networks from 3D-imaging data were correlated with tissue sections stained by immunohistochemistry and revealed highly vascularized regions to be intra-islet capillaries of islets of Langerhans. Generated 3D-datasets allowed for three-dimensional qualitative and quantitative organ and vessel structure analysis. Beyond this study, the method shows potential for application across a wide range of patho-morphology analyses and might possibly provide microstructural blueprints for biotissue engineering.

Reliability and accuracy of intraoral radiography, cone beam CT, and dental MRI for evaluation of peri-implant bone lesions at zirconia implants - an ex vivo feasibility study.

OBJECTIVES: To determine the reliability and accuracy of intraoral radiography (IR), cone-beam-computed tomography (CBCT), and dental magnetic resonance imaging (dMRI) in measuring peri­implant bone defects around single zirconia implants. METHODS: Twenty-four zirconia implants were inserted in bovine ribs with various peri­implant defect sizes and morphologies. True defect extent was measured without implant in CBCT. Defects were measured twice in IR, CBCT, and dMRI with the inserted implant by three experienced readers. Reliability was assessed by ICC, accuracy by the Friedman test, and post-hoc-Tukey's test. RESULTS: A comparable good to excellent intra- and inter-reader reliability was observed for all modalities (intra-/inter-rater-CC range for IR; CBCT; dMRI: 0.81-0.91/0.79;0.87-0.97/0.96;0.87-0.95/0.94). Accuracy was generally high, with mean errors below 1 mm in all directions. However, measuring defect depth in the mesiodistal direction was significantly more accurate in dMRI (0.65 ± 0.38 mm) compared to IR (2.71 ± 1.91 mm), and CBCT (1.98 ± 1.97 mm), p-values ≤ 0.0001 respectively ≤ 0.01. CONCLUSIONS: Osseous defects around zirconia implants can be reliably measured in IR/CBCT/dMRI in the mesiodistal directions. In addition, CBCT and dMRI allow assessment of the buccolingual directions. dMRI provides a comparable accuracy in all directions, except for the mesiodistal defect depth, where it outperforms IR and CBCT.

In vivo assessment of artefacts in MRI images caused by conventional twistflex and various fixed orthodontic CAD/CAM retainers.

PURPOSE: To assess magnetic resonance imaging (MRI) artefacts caused by different computer-aided design/computer-aided manufacturing (CAD/CAM) retainers in comparison with conventional hand bent stainless steel twistflex retainers in vivo. MATERIALS AND METHODS: MRI scans (3 Tesla) were performed on a male volunteer with different CAD/CAM retainers (cobalt-chromium, CoCr; nickel-titanium, NiTi; grade 5 titanium, Ti5) and twistflex retainers inserted. A total of 126 landmarks inside and outside the retainer area (RA; from canine to canine) were evaluated by two blinded radiologists using an established five-point visibility scoring (1: excellent, 2: good, 3: moderate, 4: poor, 5: not visible). Friedman and two-tailed Wilcoxon tests were used for statistical analysis (significance level: p < 0.05). RESULTS: Twistflex retainers had the strongest impact on the visibility of all landmarks inside (4.0 ± 1.5) and outside the RA (1.7 ± 1.2). In contrast, artefacts caused by CAD/CAM retainers were limited to the dental area inside the RA (CoCr: 2.2 ± 1.2) or did not impair MRI-based diagnostics in a clinically relevant way (NiTi: 1.0 ± 0.1; Ti5: 1.4 ± 0.6). CONCLUSION: The present study on a single test person demonstrates that conventional stainless steel twistflex retainers can severely impair the diagnostic value in head/neck and dental MRI. By contrast, CoCr CAD/CAM retainers can cause artefacts which only slightly impair dental MRI but not head/neck MRI, whereas NiTi and Ti5 CAD/CAM might be fully compatible with both head/neck and dental MRI.