Tim Hilgenfeld

Lateral cephalometric analysis for treatment planning in orthodontics based on MRI compared with radiographs: A feasibility study in children and adolescents

Objective The objective of this prospective study was to evaluate whether magnetic resonance imaging (MRI) is equivalent to lateral cephalometric radiographs (LCR, “gold standard”) in cephalometric analysis. Methods The applied MRI technique was optimized for short scanning time, high resolution, high contrast and geometric accuracy. Prior to orthodontic treatment, 20 patients (mean age ± SD, 13.95 years ± 5.34) received MRI and LCR. MRI datasets were postprocessed into lateral cephalograms. Cephalometric analysis was performed twice by two independent observers for both modalities with an interval of 4 weeks. Eight bilateral and 10 midsagittal landmarks were identified, and 24 widely used measurements (14 angles, 10 distances) were calculated. Statistical analysis was performed by using intraclass correlation coefficient (ICC), Bland-Altman analysis and two one-sided tests (TOST) within the predefined equivalence margin of ± 2°/mm. Results Geometric accuracy of the MRI technique was confirmed by phantom measurements. Mean intraobserver ICC were 0.977/0.975 for MRI and 0.975/0.961 for LCR. Average interobserver ICC were 0.980 for MRI and 0.929 for LCR. Bland-Altman analysis showed high levels of agreement between the two modalities, bias range (mean ± SD) was -0.66 to 0.61 mm (0.06 ± 0.44) for distances and -1.33 to 1.14° (0.06 ± 0.71) for angles. Except for the interincisal angle (p = 0.17) all measurements were statistically equivalent (p < 0.05). Conclusions This study demonstrates feasibility of orthodontic treatment planning without radiation exposure based on MRI. High-resolution isotropic MRI datasets can be transformed into lateral cephalograms allowing reliable measurements as applied in orthodontic routine with high concordance to the corresponding measurements on LCR.

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

ObjectivesDental 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.MethodsArtefact 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).ResultsSmallest 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.ConclusionThere 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

Somatotopic Fascicular Lesions of the Brachial Plexus Demonstrated by High-Resolution Magnetic Resonance Neurography

Objectives The aim of this study was to evaluate whether high-resolution brachial plexus (BP) magnetic resonance neurography (MRN) is capable of (1) distinguishing patients with compressive neuropathy or noncompressive plexopathy from age- and sex-matched controls, (2) discriminating between patients with compressive neuropathy and noncompressive plexopathy, and (3) detecting spatial lesion patterns suggesting somatotopic organization of the BP. Materials and Methods Thirty-six patients (50.9 ± 12.7 years) with clinical symptoms, nerve conduction studies, and needle electromyography findings suggestive of brachial plexopathy and 36 control subjects matched for age and sex (50.8 ± 12.6 years) underwent high-resolution MRN of the BP. Lesion determination and localization was performed by 2 blinded neuroradiologists at the anatomical levels of the plexus trunks and cords. Results By applying defined criteria of structural plexus lesions on high-resolution MRN, all patients were correctly rated as affected, whereas 34 of 36 controls were correctly rated as unaffected by independent and blinded reading from 2 neuroradiologists with overall good to excellent interrater reliability. In all cases, plexopathies with a compressive etiology (n = 12) were correctly distinguished from noncompressive plexopathies with inflammatory origin (n = 24). Pathoanatomical contiguity of lesion from trunk into cord level allowed recognition of distinct somatotopical patterns of fascicular involvement, which correlated closely with the spatial distribution of clinical symptoms and electrophysiological data. Conclusions Brachial plexus MRN is highly accurate for differentiating patients with symptomatic plexopathy from healthy controls and for distinguishing patients with compressive neuropathy and noncompressive plexopathy. Furthermore, BP MRN revealed evidence for somatotopic organization of the BP. Therefore, as an addition to functional information of electrodiagnostic studies, anatomical information gained by BP MRN may help to improve the efficiency and accuracy of patient care.

Diagnostic Value of Magnetic Resonance Neurography in Cervical Radiculopathy: Plexus Patterns and Peripheral Nerve Lesions

Objective The aim of this study was to assess the imaging appearance and diagnostic value of plexus and peripheral nerve magnetic resonance neurography (MRN) in cervical radiculopathy. Materials and Methods This prospective study was approved by our institutional ethics committee and written informed consent was obtained from all participants. A total of 24 patients were included with a diagnosis of cervical radiculopathy based on clinical examination, supporting electrophysiological examinations and spinal imaging consistent with the clinical syndrome. All patients then underwent a high-resolution MRN protocol including the brachial plexus from nerve roots to plexus cords using a 3-dimensional turbo spin echo with variable flip angle short tau inversion recovery and sagittal-oblique T2-weighted spectral adiabatic inversion recovery sequence, and ulnar, median, and radial nerves at the upper arm and elbow in T2-weighted fat saturated sequences. Two readers independently rated plexus elements regarding the presence of lesions at neuroforaminal levels, roots, trunks, and cord segments. Median, ulnar, and radial nerves were likewise rated. Findings were then compared to a referenced standard of cervical radiculopathy that was defined as the combined diagnosis of clinical syndrome including supporting electrophysiological exams and matching positive spinal imaging, and diagnostic performance parameters were calculated. Additional quantitative and qualitative analysis assessed peripheral nerve caliber and normalized T2-signal at arm level in cervical radiculopathy and compared them to 25 inflammatory neuropathy controls. Results Cervical radiculopathy resulted in distinct plexus lesion patterns for each level of neuroforaminal stenosis. Overall, brachial plexus MRN in cervical radiculopathy reached a sensitivity of 81%, a specificity of 96%, a positive predictive value of 87%, and overall diagnostic accuracy of 87%. Initial spinal magnetic resonance imaging showed multiple positive findings for clinically unaffected root levels and resulted in a specificity of 69%, a positive predictive value of 54%, and an overall diagnostic accuracy of 78%. T2-weighted peripheral nerve lesions were detected in 79% of cervical radiculopathy cases and imitated imaging appearance of inflammatory neuropathies both quantitatively and qualitatively. Conclusions Complementing spine imaging in cervical radiculopathy with brachial plexus MRN can improve diagnostic accuracy by increasing specificity and positive predictive value. T2-weighted lesions of peripheral nerves can be caused by cervical radiculopathy, which must be considered a relevant diagnostic pitfall in MRN of peripheral neuropathies.

Determination of the palatal masticatory mucosa thickness by dental MRI: a prospective study analysing age and gender effects

OBJECTIVES The aim of this prospective study was to evaluate age and gender effects on the palatal masticatory mucosa thickness by using non-invasive and non-ionizing MRI. METHODS 40 periodontally healthy participants of five gender-balanced age groups (20-29, 30-39, 40-49, 50-59 and 60-69 years, respectively) underwent dental MRI at 3 Tesla using a contrast-enhanced, high-resolution 3D-sequence. The palatal masticatory mucosa was measured at 40 standard measurement points by two independent observers. Statistical analysis was performed by using intraclass correlation coefficient (ICC), Shapiro-Wilk test, two-way analysis of variance and post-hoc Tukey HSD test. RESULTS Measurements of the palatal masticatory mucosa thickness were highly reliable with a mean intraobserver ICC of 0.989 and a mean interobserver ICC of 0.987. Mean palatal masticatory mucosa thickness increased with the distance from the gingival margin in all tooth regions. Molars showed a considerably lower average palatal masticatory mucosa thickness at intermediate heights in comparison to canines and premolars. Average palatal masticatory mucosa thickness continuously increased with age and significantly differed between age groups (p < 0.01). A significant increase was observed between the age groups of 30-39 years and 40-49 years (p = 0.04). Gender had no significant effect on average palatal mucosa thickness (p = 0.19). However, there was a tendency towards thicker mucosa in males (mean ± SD, 3.36 mm ± 0.47) compared to females (3.23 mm ± 0.44). CONCLUSIONS In the present study, dental MRI allowed for a highly reliable determination of the palatal masticatory mucosa thickness. Considerable intra- and interindividual variations in palatal masticatory mucosa thickness were observed. Average palatal masticatory mucosa thickness was dependent on age but not on gender.

Application of a Dedicated Surface Coil in Dental MRI Provides Superior Image Quality in Comparison with a Standard Coil

PurposePurpose of our research was the evaluation of a dedicated dental surface coil in comparison with a standard head and neck coil for the improvement of dental magnetic resonance imaging (MRI).Materials and MethodsAxial T1-weighted spin echo MRI was performed by using a newly developed dental coil for MRI and a standard head and neck coil on five volunteers. In addition, MRI was implemented with dental coil on five patients. Using the Wilcoxon test, we compared the volunteers’ signal-to-noise ratio (SNR) of a variety of anatomical structures (e.g., hard tooth tissue, pulp tissue, bone, muscle tissue). Also subjective evaluation of image quality was performed on both volunteers and patients.ResultsCompared with the head and neck coil, the mean SNR was 3.5-fold higher on an average with the dental coil (range: from 2.7 [masseter muscle] to  4.6 [pulp tissue]). That difference was statistically significant for all evaluated structures. The higher SNR also resulted in a superior image quality as determined by subjective evaluation.ConclusionDental MRI benefits profoundly from using a dedicated dental coil.

Protocol for the Evaluation of MRI Artifacts Caused by Metal Implants to Assess the Suitability of Implants and the Vulnerability of Pulse Sequences

As the number of magnetic resonance imaging (MRI) scanners and patients with medical implants is constantly growing, radiologists increasingly encounter metallic implant-related artifacts in MRI, resulting in reduced image quality. Therefore, the MRI suitability of implants in terms of artifact volume, as well as the development of pulse sequences to reduce image artifacts, are becoming more and more important. Here, we present a comprehensive protocol which allows for a standardized evaluation of the artifact volume of implants on MRI. Furthermore, this protocol can be used to analyze the vulnerability of different pulse sequences to artifacts. The proposed protocol can be applied to T1- and T2-weighted images with or without fat-suppression and all passive implants. Furthermore, the procedure enables the separate and three-dimensional identification of signal loss and pile-up artifacts. As previous investigations differed greatly in evaluation methods, the comparability of their results was limited. Thus, standardized measurements of MRI artifact volumes are necessary to provide better comparability. This may improve the development of the MRI suitability of implants and better pulse sequences to finally improve patient care.

Differentiation of periapical granulomas and cysts by using dental MRI: a pilot study

The purpose of this pilot study was to evaluate whether periapical granulomas can be differentiated from periapical cysts in vivo by using dental magnetic resonance imaging (MRI). Prior to apicoectomy, 11 patients with radiographically confirmed periapical lesions underwent dental MRI, including fat-saturated T2-weighted (T2wFS) images, non-contrast-enhanced T1-weighted images with and without fat saturation (T1w/T1wFS), and contrast-enhanced fat-saturated T1-weighted (T1wFS+C) images. Two independent observers performed structured image analysis of MRI datasets twice. A total of 15 diagnostic MRI criteria were evaluated, and histopathological results (6 granulomas and 5 cysts) were compared with MRI characteristics. Statistical analysis was performed using intraclass correlation coefficient (ICC), Cohen’s kappa (κ), Mann–Whitney U-test and Fisher’s exact test. Lesion identification and consecutive structured image analysis was possible on T2wFS and T1wFS+C MRI images. A high reproducibility was shown for MRI measurements of the maximum lesion diameter (intraobserver ICC = 0.996/0.998; interobserver ICC = 0.997), for the “peripheral rim” thickness (intraobserver ICC = 0.988/0.984; interobserver ICC = 0.970), and for all non-quantitative MRI criteria (intraobserver-κ = 0.990/0.995; interobserver-κ = 0.988). In accordance with histopathological results, six MRI criteria allowed for a clear differentiation between cysts and granulomas: (1) outer margin of lesion, (2) texture of “peripheral rim” in T1wFS+C, (3) texture of “lesion center” in T2wFS, (4) surrounding tissue involvement in T2wFS, (5) surrounding tissue involvement in T1wFS+C and (6) maximum “peripheral rim” thickness (all: P < 0.05). In conclusion, this pilot study indicates that radiation-free dental MRI enables a reliable differentiation between periapical cysts and granulomas in vivo. Thus, MRI may substantially improve treatment strategies and help to avoid unnecessary surgery in apical periodontitis.Dental imaging: Diagnosing tooth root lesions using magnetic resonance imagingMagnetic resonance imaging (MRI) can differentiate between periapical (apex of a tooth root) cysts and granulomas (inflammations usually caused by infections). MRI is a radiation-free, non-invasive imaging technique, and a team headed by Tim Hilgenfeld at Heidelberg University Hospital in Germany conducted a pilot study to determine whether dental MRI could be used to distinguish periapical cysts from granulomas in 11 patients with confirmed periapical lesions. The authors found that dental MRI allowed for the identification of six characteristics, each of which had the capacity to clearly differentiate between periapical cysts and granulomas. The team’s findings need to be confirmed in future studies with larger numbers of patients. But the results could have a substantial clinical impact in improving diagnoses and avoiding unnecessary surgery in patients with periapical lesions.