Intravoxel incoherent motion (IVIM) MRI in pediatric patients with synovitis of the knee joint: a prospective pilot study.

BACKGROUND: Diagnosing synovial inflammation by administration of gadolinium-based contrast agents is limited by invasiveness and possible side effects, especially in children and adolescents. PURPOSE: We investigated diagnostic accuracy of diffusion-weighted (DWI) MRI with intravoxel incoherent motion (IVIM) imaging compared to contrast-enhanced MRI for detecting synovitis of the knee in a population of pediatrics and young adults. In addition we compared quantitative measures of synovial diffusion and perfusion to a group of healthy volunteers. METHODS: In this prospective study, 8 pediatric patients with 10 symptomatic knees (6 girls and 2 boys, mean age 13 years) with known or suspected synovitis underwent pre- and post-contrast 3.0 T MRI of the knee joint and additional DWI sequences between October 2016 and July 2019. For comparison we enrolled 5 healthy young adults (2 women and 3 men, median age 27 years) with contrast-free MRI of both knees. Post-contrast T1w images and DWI images at b = 1000s/mm2 with apparent diffusion coefficient (ADC) maps of patients were separately rated by two independent and blinded readers with different levels of experience for the presence or absence and degree of synovitis along with the level of confidence. We measured signal intensity on DWI of synovium, joint effusion and muscle with regions of interests and calculated the IVIM-parameters tissue diffusion coefficient (D) and perfusion fraction (f) for patients and volunteers. RESULTS: All patients showed at least some synovial contrast enhancement, 8 (80%) children knees were diagnosed with synovitis on contrast-enhanced (= ce)-T1w, the diagnostic standard. Ratings by the first and second reader on ce-T1w and DWI showed full agreement (kappa = 1) in diagnosing synovitis and substantial agreement (k = 0,655) for the degree of synovial enhancement. Interobserver agreement on DWI showed fair agreement (k = 0,220) between both readers. Diagnostic confidence was lower on DWI. Mean D- and f-values of muscle was comparable between patients and volunteers. Effusion mean D was higher, mean f was lower, synovial mean D was lower, mean f higher in patients than in volunteers. All differences were statistically significant (p < 0.001). CONCLUSIONS: Diffusion-weighted MRI with IVIM imaging remains a promising, though reader-dependent alternative to i.v. contrast-enhanced imaging in pediatric patients to reliably diagnose, or rule out, synovitis of the knee joint. We detected significantly restricted synovial diffusion and increased perfusion in patients compared to healthy volunteers. TRIAL REGISTRATION: Ethical Comitee University Hospital Ulm, Nr. 320/16.

Accelerated model-based quantitative diffusion MRI: A feasibility study for musculoskeletal application.

PURPOSE: To develop a model-based reconstruction technique for diffusion quantification based on accelerated two-dimensional echo planar data, obtained with multiple b-weightings. In combination with a dedicated undersampling pattern, acceleration factors above three were proven feasible in a clinical setting. METHODS: The proposed model-based method minimizes a cost function considering the l2-norm of the difference between the Fourier transformation of a synthetic diffusion-model-generated k-space and the measured k-space data. Further regularization is performed by introduction of a total variation (TV) constraint to the cost function. Acceleration is achieved by a non-random undersampling pattern using acceleration factors that correspond to the total number of b-values. A rectangular region of variable size, centered in k-space, remains fully sampled for correction of phase variations, introduced by the different diffusion-encoding strengths. RESULTS: Qualitative analysis of the resulting images (S0 and ADC) demonstrates the potential of the suggested undersampling pattern in combination with a model-based iterative reconstruction. An edge analysis highlights the preservation of high-frequency information for all investigated undersampling factors. In comparison to a conventional SENSE-accelerated reconstruction, the quantitative analysis of the ADC maps revealed a significantly (P<0.05) superior performance of the suggested technique, enabling acceleration factors of R=3.65 without compromising diffusion data fidelity. CONCLUSION: The presented work shows the potential of model-based ADC quantification, which, in combination with a suited undersampling pattern for multiple b-values, enables more than three-fold acceleration using two-dimensional EPI without sacrificing ADC fidelity.

Artifact Properties of Dental Ceramic and Titanium Implants in MRI. / Artefakt-Verhalten von dentalen Keramik- und Titanimplantaten im MRT.

AIM: Assessment of the visualization of titanium and ceramic dental implants using various isotropic three-dimensional magnetic resonance imaging (MRI) methods. MATERIALS AND METHODS: 21 dental implants (7 ceramic, 14 titanium) were scanned in vitro with a spatially isotropically resolved three-dimensional gradient echo (FFE), a turbo spin echo (SE) and an ultra-short-echo time (UTE) imaging technique. The resulting absolute volumes of the implants were quantified and the relative error to the theoretical volume was calculated. RESULTS: Ceramic implants and their periphery could be displayed well in all cases. The observed mean relative error results were 5.4 ±â€Š2.3 % (UTE) to 6.5 ±â€Š4.3 % (FFE). No significant difference was observed between the investigated MRI methods. The transition between implant and surrounding agarose could be shown in all cases without artifacts. Titanium implants resulted in mean relative errors between 1314 ±â€Š350 % (FFE) and 2157 ±â€Š810 % (SE). Here, significant differences were observed between the FFE and the SE and between the UTE and the SE sequence. The periphery of the implants could not be displayed in any case. CONCLUSION: Use of the MRI technique for the diagnosis of peri-implantitis, the assessment of anatomical structures and planning of dental implantation is currently very limited but could be used more frequently, provided there are no disturbing or imaging-disturbing materials in the region of interest. MRI technology is not suitable in case of titanium implants. When using ceramic implants, MRI technology is an option. KEY POINTS: · MRI allows the artifact-free depiction of dental ceramic implants.. · Titanium implants cause the greatest relative errors in SE techniques.. · The UTE technique shows no significant improvements with respect to artifact behavior over the FFE technique.. CITATION FORMAT: · Geibel M, Gelißen B, Bracher A et al. Artefakt-Verhalten von dentalen Keramik- und Titanimplantaten im MRT. Fortschr Röntgenstr 2019; 191: 433 - 441.

Characterisation of apical bone lesions: Comparison of MRI and CBCT with histological findings - a case series.

PURPOSE: The aim of this case series was to compare magnetic resonance imaging (MRI) with cone beam computed tomography (CBCT) in the representation of periapical osteolyses. Based on the histological findings, the potential of MRI for further lesion characterisation was investigated. MATERIALS AND METHODS: Thirteen patients (average age: 41 ±â€…27 years) with a total of 15 periapical lesions (five molars, five premolars, and five front teeth) were examined. Lesion characterisation was based on the homogeneity/heterogeneity of the lesions, the signal intensity within the lesion compared to the surrounding tissue and differences in the signal intensities between different MRI contrast weightings. Results were compared with CBCT and histological findings. RESULTS: Although all patients presented with dental restorations, such as fixed partial dentures and filling materials, all periapical lesions could be diagnosed with either imaging modality. Histologically, 13 cysts and two apical granuloma were confirmed. In CBCT, the similar appearance of all lesions did not allow any further characterisation. In MRI, radicular cysts and granuloma could be characterised by their appearance in the MRI images with different contrast weightings. The MRI-derived characterisations were consistent with the histological findings. CONCLUSIONS: The presented study shows that the application of multi-contrast MRI may lead to better characterisation of apical lesions, thus enabling an improved patient-specific selection of the optimal treatment option. Conflict-of-interest statement: MAG, ESS, and LKS do not report any potential conflict-of-interest; EH and JU are employees of Sirona Dental Systems; VR is receiving a research grant by Sirona Dental Systems.

High-resolution ZTE imaging of human teeth.

MRI with zero echo time (ZTE) is achieved by 3D radial centre-out encoding and hard-pulse RF excitation while the projection gradient is already on. Targeting short-T(2) samples, the efficient, robust and silent ZTE approach was implemented for high-bandwidth high-resolution imaging requiring particularly rapid transmit-receive switching and algebraic image reconstruction. The ZTE technique was applied to image extracted human teeth at 11.7T field strength, yielding detailed depictions with very good delineation of the mineralised dentine and enamel layers. ZTE results are compared with UTE (ultra-short echo time) MRI and micro-computed tomography (µCT), revealing significant differences in SNR and CNR yields. Compared to µCT, ZTE MRI appears to be less susceptible to artefacts caused by dental fillings and to offer superior sensitivity for the detection of early demineralisation and caries lesions.

Feasibility of ultra-short echo time (UTE) magnetic resonance imaging for identification of carious lesions.

The objective of this study was to investigate the potential of ultra short echo time imaging for the assessment of caries lesions and early demineralization. 12 patients with suspected caries lesions underwent a dental magnetic resonance imaging investigation comprising ultra short echo time imaging (echo time=50 µs) and spin echo imaging. Before the dental magnetic resonance imaging, all patients underwent a conventional clinical dental investigation including visual assessment of the teeth as well as dental x-ray imaging. All lesions identifiable in the x-ray could be clearly identified in the ultra short echo time images, but only about 19% of the lesions were visible in the spin echo images. In 19% of all lesions, the lesions could be more clearly delineated in the ultra short echo time images than in the x-ray images. This was especially the case for secondary lesions. In direct comparison with the x-ray images, all lesions appeared substantially larger in the dental magnetic resonance imaging data. The presented data provide evidence that caries lesions can be identified in ultra short echo time magnetic resonance imaging with high sensitivity. The apparent larger volume of the lesions in dental magnetic resonance imaging may be attributed to fluid accumulation in demineralized areas without substantial breakdown of mineral structures.