Metallic Artifacts in MRI Caused by Dental Alloys and Magnetic Keeper

Shellock F.G., Kanal E.

Magnetic resonance (MR) imaging-related artifacts associated with five different aneurysm clips made of five different metals (commercially pure titanium, titanium alloy, Phynox, Elgiloy, and cobalt alloy) were evaluated. Aneurysm clips made of commercially pure titanium and titanium alloy produced the smallest artifacts, whereas the aneurysm clip made of Elgiloy produced the largest artifacts. These results have implications for the selection of aneurysm clips in patients who may require MR procedures.

Hinshaw D.B., Holshouser B.A., Engstrom H.I., Tjan A.H., Christiansen E.L., Catelli W.F.

Magnetic resonance (MR) imaging of the head and neck is becoming an important aid in evaluating pathologic conditions of the brain, midface, and pharynx. Certain dental materials cause artifacts during MR imaging of the lower midface. These artifacts can obscure the normal anatomy. This study describes the degree of artifact production caused by various materials commonly used in dental restorations. Of the materials tested, those causing artifacts were made of stainless steel, such as orthodontic bands used for braces, and pins or posts that are commonly drilled into teeth to provide structure or stability before filling. Materials used as temporary or permanent fillings or crowns--such as amalgam, gold alloy, aluminum, microfilled resin, and polyvinyl acrylics--did not cause artifacts in the images.

Teitelbaum G.P., Bradley W.G., Klein B.D.

Experiments were conducted in which various intravascular filters, stents, and coils were imaged using magnetic resonance (MR) spin-echo technique at 0.35 T. These devices were also evaluated for ferromagnetism (at 0.35, 1.5, and 4.7 T), magnetic torque (at 0.35 and 1.5 T), and magnetically induced migration within a plastic tube (at 0.35 and 1.5 T for the Greenfield filter [GF]). The stainless-steel GF was evaluated in vitro for its propensity to perforate canine inferior venae cavae (IVC). Magnetic force and torque at 1.5 T did not dislodge the GF or result in perforation of canine IVC by the GF. Beta-3 titanium alloy (used in a new percutaneous version of the GF) is apparently one of the best-suited metals for use with MR imaging because of its lack of ferromagnetism (up to 4.7 T) and absence of MR imaging artifacts (at 0.35 T). Devices composed of Elgiloy (Mobin-Uddin filter), nitinol, and MP32-N (Amplatz filter) alloys all created mild artifacts. Devices fashioned from 304 and 316L (GF and Palmaz stent) stainless-steel alloys created severe "black-hole" artifacts, with the 304 alloy devices also showing marked image distortion. Generally, the greater the ferromagnetism of a device, the greater its magnetic susceptibility artifact.

New P.F., Rosen B.R., Brady T.J., Buonanno F.S., Kistler J.P., Burt C.T., Hinshaw W.S., Newhouse J.H., Pohost G.M., Taveras J.M.

The risks to patients with metal surgical implants who are undergoing nuclear magnetic resonance (NMR) imaging and the artifacts caused by such implants were studied. Twenty-one aneurysm and other hemostatic clips and a variety of other materials (e.g., dental amalgam, 14 karat gold) were used. Longitudinal forces and torques were found to be exerted upon 16 of the 21 clips. With five aneurysm clips, forces and torques sufficient to produce risk of hemorrhage from dislocation of the clip from the vessel or aneurysm, or cerebral injury by clip displacement without dislodgement were identified. The induced ferromagnetism was shown to be related to the composition of the alloys from which the clips were manufactured. Clips with 10-14% nickel are evidently without sufficient induced ferromagnetism to cause hazard. The extent of NMR imaging artifacts was greater for materials with measurable ferromagnetic properties, but metals without measurable ferromagnetism in our tests also resulted in significant artifacts. Dental amalgam and 14 karat gold produced no imaging artifacts, but stainless steels in dentures and orthodontic braces produced extensive artifacts in the facial region.

Shafiei F., Honda E., Takahashi H., Sasaki T.

The potential advantage of magnetic resonance imaging (MRI) has been limited by artifacts due to the presence of metallic materials. For quantitative evaluation of the magnitude of artifacts from dental casting alloys and implant materials in MR imaging, 11 dental casting or implant materials were imaged by means of 1.5 T MRI apparatus with three different sequences. Mean and standard deviation of water signal intensity (SI) around the sample in the region of interest (1200 mm2) were determined, and the coefficient of variation was compared for evaluation of the homogeneity of the SI. A variety of artifacts with different magnitudes was observed. Only one of the samples, composed mainly of Pd, In, and Sb, showed no artifacts in all imaging sequences. We concluded that selection of specific dental casting alloys according to their elemental compositions could minimize the metal artifacts in MRI; however, titanium alloys currently pose a problem with respect to causing MRI artifacts.

Bennett L.H., Wang P.S., Donahue M.J.

Metallic biomedical implants, such as aneurysm clips, endoprostheses, and internal orthopedic devices give rise to artifacts in the magnetic resonance image (MRI) of patients. Such artifacts impair the information contained in the image in precisely the region of most interest, namely near the metallic device. Ferromagnetic materials are contraindicated because of the hazards associated with their movement during the MRI procedure. In less-magnetic metals, it has been suggested that the extent of the artifact is related to the magnetic susceptibility of the metal, but no systematic data appear to be available. When the susceptibility is sufficiently small, an additional artifact due to electrical conductivity is observed. We present an initial systematic study of MRI artifacts produced by two low susceptibility metals, titanium (relative permeability μr≊1.0002) and copper (μr≊0.99998), including experimental, theoretical, and computer simulation results.

Beuf O., Lissac M., Crémillieux Y., Briguet A.

The purpose of this study was to correlate the size and the orientation of image disturbances observed on specific samples of dental materials with their magnetic susceptibility. The measurement of the magnetic susceptibility was performed in the 10(-5) or 10(-6) range using MRI to establish a classification of dental materials.Cylindrical dental alloy samples incorporating gold, silver, and palladium were placed in a Pyrex beaker filled with distilled water. Images were performed at 0.13 Tesla using two-dimensional Fourier transformation and projection reconstruction at 360 degrees imaging methods. The magnetic susceptibilities were obtained by measuring distances between spots having the highest intensity on the image.A very discriminating classification may be established on MRI criteria. This method permits one to determine the dia- or para-magnetic character of the dental materials tested. Only palladium-based alloys have been detected to be paramagnetic with kappa > 0. One of the silver-based alloys did not induce detectable distortion because its susceptibility was very close to that of distilled water. Based on this MRI data, the use of this material may be recommended for applications that may be subjected to MRI evaluation.With the increasing use of MRI as a diagnostic tool, it is useful to establish a classification of prosthetic biomaterials compatible with MRI.

IIMURO F.T.

The use of a rare earth magnetic attachment system as a means of retaining dentures or maxillofacial prostheses results in artifacts, when magnetic resonance imaging (MRI) is used as a diagnostic tool. In such cases, the artifact is not caused by the magnet itself, but by the ferromagnetic stainless steel keeper that is placed in the body. This report evaluates such ferromagnetic stainless steel devices with respect to magnetic resonance imaging artifacts. A grid phantom and a 0.2 Tesla superconducting system were used to assess the imaging artifacts. The magnetic properties, shape, composition and size of ferromagnetic stainless steel devices were analyzed to study the relation MRI artifacts and ferromagnetic materials. The higher the magnetic permeability was, the greater the artifact produced. The size and volume of the material directly influence the artifact produced. The artifact size can be attenuated by the sequence used to obtain the images.

Masumi S., Nagatomi K., Miyake S., Toyoda S.

Magnetic dental attachments cause magnetic resonance image (MRI) degradation. A new magnetic dental attachment that allows removal of magnetic parts to exchange them for nonmagnetic parts was developed and tested. It allows high quality MRI with no change in occlusal vertical dimension. A volunteer test subject with combinations of attachments in place was examined by MRI. The images produced showed no degradation or distortion. Magnetic attachments for overdentures or maxillofacial prostheses should be removable to permit use of MRI.

Shimamoto H., Felemban D., Uchimoto Y., Matsuda N., Takagawa N., Takeshita A., Iwamoto Y., Okahata R., Tsujimoto T., Kreiborg S., Mallya S.M., Yang F.G.

Abstract Objective To assess quantitatively the effect of metallic materials on MR image uniformity using a standardized method. Methods Six types of 1 cm cubic metallic materials (i.e., Au, Ag, Al, Au–Ag–Pd alloy, Ti, and Co–Cr alloy) embedded in a glass phantom filled were examined and compared with no metal condition inserted as a reference. The phantom was scanned five times under each condition using a 1.5-T MR superconducting magnet scanner with an 8-channel phased-array brain coil and head and neck coil. For each examination, the phantom was scanned in three planes: axial, coronal, and sagittal using T1-weighted spin echo (SE) and gradient echo (GRE) sequences in accordance with the American Society for Testing and Materials (ASTM) F2119-07 standard. Image uniformity was assessed using the non-uniformity index (NUI), which was developed by the National Electrical Manufacturers Association (NEMA), as an appropriate standardized measure for investigating magnetic field uniformity. Results T1-GRE images with Co–Cr typically elicited the lowest uniformity, followed by T1-GRE images with Ti, while all other metallic materials did not affect image uniformity. In particular, T1-GRE images with Co–Cr showed significantly higher NUI values as far as 6.6 cm at maximum equivalent to 11 slices centering around it in comparison with the measurement uncertainty from images without metallic materials. Conclusion We found that MR image uniformity was influenced by the scanning sequence and coil type when Co–Cr and Ti were present. It is assumed that the image non-uniformity in Co–Cr and Ti is caused by their high magnetic susceptibility.

Iwamoto Y., Shimamoto H., Felemban D., Terai T., Kreiborg S., Mallya S.M., Yang F.G., Tanikawa C., Murakami S.

Abstract Objectives To evaluate magnetic susceptibility artefacts produced by orthodontic wires on MRI and the influence of wire properties and MRI image sequences on the magnitude of the artefact. Methods Arch form orthodontic wires [four stainless steels (SS), one cobalt chromium (CC) alloy, 13 titanium (Ti) alloys] were embedded in a polyester phantom, and scanned using a 1.5-T superconducting magnet scanner with an eight-channel phased-array coil. All wires were scanned with T1-weighted spin echo (SE) and gradient echo (GRE) sequences according to the American Society for Testing and Materials (ASTM) F2119-07 standard. The phantom also scanned other eight sequences. Artefacts were measured using the ASTM F2119-07 definition and OsiriX software. Artefact volume was analysed according to metal composition, wire length, number of wires, wire thickness, and imaging sequence as factors. Results With SE/GRE, black/white artefacts volumes from all SS wires were significantly larger than those produced by CC and Ti wires (P < .01). With the GRE, the black artefacts volume was the highest with the SS wires. With the SE, the black artefacts volume was small, whereas white artefacts were noticeable. The cranio-caudal extent of the artefacts was significantly longer with SS wires (P < .01). Although a direct relationship of wire length, number of wires, and wire thickness with artefact volume was noted, these factors did not influence artefact extension in the cranio-caudal direction. Conclusions Ferromagnetic/paramagnetic orthodontic wires create artefacts due to local alteration of magnetic field homogeneity. The SS-type wires produced the largest artefacts followed by CC and Ti.

Gao X., Wan Q., Gao Q.

This study aimed to investigate the artifacts induced by crowns composed of different materials with prepared teeth and titanium implants. Resin, metal-ceramic, ceramic and zirconia crowns were fabricated and placed onto the prepared teeth on a human cadaver head or titanium implants with prosthesis abutments on a dry human mandible. The samples were scanned on a 1.5 T MRI apparatus, and artifact areas were defined as the signal intensity and signal loss adjacent to the prosthesis and measured by a threshold tool with ImageJ2x. Data were analyzed using SPSS 22.0. Resin, ceramic, zirconia, and precious metal-ceramic crowns barely produced artifacts on the cadaver skull (p > 0.999). By contrast, pure Ti and nonprecious metal-ceramic crowns created significant artifacts (p < 0.001). The average artifacts reduction of double Au-Pt and Ag-Pd metal-ceramic crowns combined with titanium implants and abutments was 79.49 mm2 (p < 0.001) and 74.17 mm2 (p < 0.001) respectively, while artifact areas were increased in double Co-Cr and Ni–Cr metal-ceramic crowns by 150.10 mm2 (p < 0.001) and 175.50 mm2 (p < 0.001) respectively. Zirconia, ceramic and precious metal-ceramic crowns induce less MRI artifacts after tooth preparation while precious metal-ceramic crowns alleviate artifacts in combination with titanium implants.

Isman O., Isman E.

We evaluated the in vitro detection sensitivity of orthodontic materials (serving as foreign bodies) using panoramic radiography, cone beam computed tomography (CBCT), magnetic resonance imaging (MRI), and ultrasonography. Five different orthodontic materials served as foreign bodies: titanium–molybdenum alloy wire (TMA; ORMCO, Orange, CA, USA; 0.017 × 0.025 in in cross-sectional dimensions and 1 cm long); stainless steel bracket tooth #34 (American Orthodontics, Sheboygan, WI, USA); a monocrystalline, sapphire ceramic bracket tooth #34 (Skyortho Dental Supplies Medical, China); a polycrystalline alumina clear bracket, Damon clear bracket tooth #34 (ORMCO); and a 1 × 1 × 0.1 cm polyurethane-based thermoplastic material, Invisalign clear aligner (Align Technology, San Jose, CA, USA). Panoramic radiography, CBCT, MRI, and ultrasonography were used, and four observers scored all findings independently. The TMA and stainless steel bracket were visualised in all fields by panoramic radiography and CBCT. The sapphire and Damon brackets were very clear on CBCT. The Invisalign in air was evident only on CBCT. MRI was unable to identify any material in muscle. Ultrasonography detected the TMA, sapphire bracket, and the Invisalign in muscle but only the TMA on bone. Panoramic radiography does not reveal nonmetallic orthodontic equipment in air and reveals them only poorly in muscle. CBCT was the optimal imaging modality for all materials in all fields except for the Invisalign in muscle and bone. CBCT was the only method that revealed the Invisalign in air. MRI and ultrasonography should be used to detect orthodontic materials in muscle.

Tran L.T., Sakamoto J., Kuribayashi A., Watanabe H., Tomisato H., Kurabayashi T.

Objectives: To evaluate the effects of syngo WARP on reducing metal artefacts from dental materials. Methods: Short tau inversion recovery (STIR) with syngo WARP [a dedicated metal artefact reduction sequence in combination with view-angle-tilting (VAT)] was performed using phantoms of three dental alloys: cobalt–chromium (Co–Cr), nickel–chromium (Ni–Cr), and titanium (Ti). Artefact volumes and reduction ratios of black, white and overall artefacts in the standard STIR and syngo WARP images with several different parameter settings were quantified according to standards of the American Society for Testing and Materials F2119-07. In all sequences, the artefact volumes and reduction ratios were compared. The modulation transfer function (MTF) and contrast-to-noise ratio (CNR) were also measured for evaluation of image quality. Results: In standard STIR, the overall artefact volume of Co–Cr was markedly larger than those of Ni–Cr and Ti. All types of artefacts tended to be reduced with increasing receiver bandwidth (rBW) and VAT. The effect of artefact reduction tended to be more obvious in the axial plane than in the sagittal plane. Compared with standard STIR, syngo WARP with a matrix of 384 × 384, receiver bandwidth of 620 Hz/pixel, and VAT of 100 % in the axial plane obtained reduction effects of 30 % (white artefacts), 45 % (black artefacts), and 38 % (overall artefacts) although MTF and CNR decreased by 30 and 22 % compared with those of standard STIR, respectively. Conclusions: syngo WARP for STIR can effectively reduce metal artefacts from dental materials.

Ogura I., Sugawara Y., Nagata K., Watanabe M.

Aims Dental magnetic attachments with satisfactory retentive force and stability are now commercially available for dental treatment. The aim of this study was to investigate a new phantom for evaluation of the artifact on magnetic resonance (MR) imaging by a dental magnetic attachment keeper. Material and Methods We developed a new keeper removable phantom for evaluation of the artifact on MR imaging. A keeper was inserted in an acrylic pole in a PET bottle. The keeper from acrylic pole of the phantom was removable. The keeper with saline solution in the PET bottle with a head and neck coil underwent MR imaging at our university hospital. We measured the real size (unit: mm) of artifact of the phantom with the keeper using a DICOM viewer. Furthermore, the size of artifact of a patient's image with the same three keepers in the mouth was measured on the image using the DICOM viewer, too. Results In MR images of the phantom with a keeper, the maximum size of artifact on axial T1-weighted, T2-weighted and STIR images were 78 mm, 85 mm, and 67 mm, respectively. Regarding MR images of the patient with three keepers, the maximum size of artifact on axial T1-weighted, T2-weighted and STIR images were 106 mm, 111 mm and 100 mm, respectively. Conclusions We investigated a new keeper removable phantom for evaluation of the artifact on MR imaging. The phantom can be used to evaluate the artifact on MR imaging by a dental magnetic attachment keeper.

Chockattu S.J., Suryakant D.B., Thakur S.

Felemban D., Verdonschot R.G., Iwamoto Y., Uchiyama Y., Kakimoto N., Kreiborg S., Murakami S.

Objectives: Our goal was to assess MR image uniformity by investigating aspects influencing said uniformity via a method laid out by the National Electrical Manufacturers Association (NEMA). Methods: Six metallic materials embedded in a glass phantom were scanned (i.e. Au, Ag, Al, Au–Ag–Pd alloy, Ti and Co–Cr alloy) as well as a reference image. Sequences included spin echo (SE) and gradient echo (GRE) scanned in three planes (i.e. axial, coronal, and sagittal). Moreover, three surface coil types (i.e. head and neck, Brain, and temporomandibular joint coils) and two image correction methods (i.e. surface coil intensity correction or SCIC, phased array uniformity enhancement or PURE) were employed to evaluate their effectiveness on image uniformity. Image uniformity was assessed using the National Electrical Manufacturers Association peak-deviation non-uniformity method. Results: Results showed that temporomandibular joint coils elicited the least uniform image and brain coils outperformed head and neck coils when metallic materials were present. Additionally, when metallic materials were present, spin echo outperformed gradient echo especially for Co–Cr (particularly in the axial plane). Furthermore, both SCIC and PURE improved image uniformity compared to uncorrected images, and SCIC slightly surpassed PURE when metallic metals were present. Lastly, Co–Cr elicited the least uniform image while other metallic materials generally showed similar patterns (i.e. no significant deviation from images without metallic metals). Conclusions: Overall, a quantitative understanding of the factors influencing MR image uniformity (e.g. coil type, imaging method, metal susceptibility, and post-hoc correction method) is advantageous to optimize image quality, assists clinical interpretation, and may result in improved medical and dental care.

Akutagawa M., Emoto T., Tokitani T., kinouchi Y.

Beau A., Bossard D., Gebeile-Chauty S.

Objectifs : Les appareils orthodontiques sont souvent déposés avant les examens d’imagerie par résonance magnétique (IRM) car ils sont réputés pour produire des artefacts. Le but de cette étude était de trouver les indications exactes de dépose de différents types d’appareils fixes lors de la visualisation de quatre zones spécifiques de la tête et du cou. Matériel et méthode : 60 patients nécessitant un examen IRM de la tête pour raisons médicales se sont portés volontaires pour cette étude. Un appareil fixe parmi quatre types d’appareils (boîtiers en acier inoxydable, boîtiers en titane, boîtiers en céramique à gorge métallique et fils de contention en acier inoxydable) a été assigné à chaque patient. Chaque patient a subi deux examens à 1,5 T : avec un «échantillon de cire vide» et avec un échantillon de cire contenant l’appareil. Les arcs n’ont pas été étudiés car leur dépose avant un examen est aisée. Deux radiologues ont évalué les images de chaque patient pour chacune des zones anatomiques étudiées : sinus maxillaire, cavité buccale, articulations temporo-mandibulaires et fosse cérébrale postérieure. Résultats : Les boîtiers en acier inoxydable ont rendu la totalité des images ininterprétables (100 %). Les boîtiers en titane, les boîtiers en céramique à gorge métallique et les fils de contention en acier inoxydable ont causé des artefacts seulement au niveau de la cavité buccale (pour 20 %, 16,65 % et 86,65 % des sujets). Conclusion : Ces résultats montrent que les boîtiers en céramique à gorge métallique et les boîtiers en titane ne doivent pas toujours être déposés avant un examen d’IRM de la tête et du cou, selon la zone anatomique étudiée. Les fils de contention métalliques ne devraient être déposés que si la cavité buccale est étudiée. Les boîtiers en acier inoxydable devraient être systématiquement déposés avant un examen d’IRM de la tête et du cou.

Zhou D., Wang S., Wang S., Ai H., Xu J.

Magnetic resonance imaging (MRI) compatibility of three early transition metal (ETM) based alloys was assessed in vitro with agarose gel as a phantom, including Zr-20Nb, near-equiatomic (TiZrNbTa)90 Mo10 and Nb-60Ta-2Zr, together with pure tantalum and L605 Co-Cr alloy for comparison. The artifact extent in the MR image was quantitatively characterized according to the maximum area of 2D images and the total volume in reconstructed 3D images with a series of slices under acquisition by fast spin echo (FSE) sequence and gradient echo (GRE) sequence. It was indicated that the artifacts extent of L605 Co-Cr alloy with a higher magnetic susceptibility (χv ) was approximately 3-fold greater than that of the ETM-based alloys with χv in the range of 160-250 ppm. In the ETM group, the MRI compatibility of the materials can be ranked in a sequence of Zr-20Nb, pure tantalum, (TiZrNbTa)90 Mo10 and Nb-60Ta-2Zr. In addition, using a rabbit cadaver with the implanted tube specimens as a model for ex vivo assessment, it was confirmed that the artifact severity of Nb-60Ta-2Zr alloy is significantly reduced in comparison with the L605 alloy. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 377-385, 2018.

Murakami S., Verdonschot R.G., Kataoka M., Kakimoto N., Shimamoto H., Kreiborg S.

Metallic compounds present in the oral and maxillofacial regions (OMRs) cause large artefacts during MR scanning. We quantitatively assessed these artefacts embedded within a phantom according to standards set by the American Society for Testing and Materials (ASTM).Seven metallic dental materials (each of which was a 10-mm3 cube embedded within a phantom) were scanned [i.e. aluminium (Al), silver alloy (Ag), type IV gold alloy (Au), gold-palladium-silver alloy (Au-Pd-Ag), titanium (Ti), nickel-chromium alloy (NC) and cobalt-chromium alloy (CC)] and compared with a reference image. Sequences included gradient echo (GRE), fast spin echo (FSE), gradient recalled acquisition in steady state (GRASS), a spoiled GRASS (SPGR), a fast SPGR (FSPGR), fast imaging employing steady state (FIESTA) and echo planar imaging (EPI; axial/sagittal planes). Artefact areas were determined according to the ASTM-F2119 standard, and artefact volumes were assessed using OsiriX MD software (Pixmeo, Geneva, Switzerland).Tukey-Kramer post hoc tests were used for statistical comparisons. For most materials, scanning sequences eliciting artefact volumes in the following (ascending) order FSE-T1/FSE-T2 < FSPGR/SPGR < GRASS/GRE < FIESTA < EPI. For all scanning sequences, artefact volumes containing Au, Al, Ag and Au-Pd-Ag were significantly smaller than other materials (in which artefact volume size increased, respectively, from Ti < NC < CC). The artefact-specific shape (elicited by the cubic sample) depended on the scanning plane (i.e. a circular pattern for the axial plane and a "clover-like" pattern for the sagittal plane).The availability of standardized information on artefact size and configuration during MRI will enhance diagnosis when faced with metallic compounds in the OMR.

Zhou D., Wang S., Wang S., Ai H., Xu J.

Several bulk metallic glasses (BMGs) were selected to in vitro assess their magnetic resonance imaging (MRI) compatibility with agarose gel as a phantom, in terms of the extent of susceptibility artifacts in magnetic resonance image. The investigated metals include the Au49Ag5.5Pd2.3Cu26.9Si16.3, Zr61Ti2Cu25Al12, Cu50.4Ni5.6Ti31Zr13 and Ti47Cu38Zr7.5Fe2.5Sn2Si1Ag2, together with pure titanium (CP-Ti) and Co–28Cr–6Mo alloy (ASTM-F799) for comparison. The artifact extent in MR images was quantitatively characterized according to the total volume in reconstructed 3D images with a series of slices under acquisition by fast spin echo (FSE) sequence and gradient echo (GRE) sequence. As indicated, artifact severity of the BMGs is much less than that of the CoCrMo alloy. The AuAgPdCuSi BMG manifested the smallest artifact among the four BMGs, while the TiCuZrFeSnSiAg BMG is comparative to the CP-Ti. The MRI compatibility of BMGs is ranked as a sequence of the Au-, Zr-, Cu- and Ti-based alloys. Dependence of material magnetic susceptibility on artifact extent is also the case of the BMGs, even though it does not follow a simple linear relationship within a range of Δχv = 30–180 ppm. These findings are of interest to reveal that the BMGs are potentially applied in the fields associated with an interventional MRI for MRI-guided surgeries.

Noureddine Y., Bitz A.K., Ladd M.E., Thürling M., Ladd S.C., Schaefers G., Kraff O.

Over the last decade, the number of clinical MRI studies at 7 T has increased dramatically. Since only limited information about the safety of implants/tattoos is available at 7 T, many centers either conservatively exclude all subjects with implants/tattoos or have started to perform dedicated tests for selected implants. This work presents our experience in imaging volunteers with implants/tattoos at 7 T over the last seven and a half years. 1796 questionnaires were analyzed retrospectively to identify subjects with implants/tattoos imaged at 7 T. For a total of 230 subjects, the type of local transmit/receive RF coil used for examination, imaging sequences, acquisition time, and the type of implants/tattoos and their location with respect to the field of view were documented. These subjects had undergone examination after careful consideration by an internal safety panel consisting of three experts in MR safety and physics. None of the subjects reported sensations of heat or force before, during, or after the examination. None expressed any discomfort related to implants/tattoos. Artifacts were reported in 52 % of subjects with dental implants; all artifacts were restricted to the mouth area and did not affect image quality in the brain parenchyma. Our initial experience at 7 T indicates that a strict rejection of subjects with tattoos and/or implants is not justified. Imaging can be conditionally performed in carefully selected subjects after collection of substantial safety information and evaluation of the detailed exposure scenario (RF coil/type and position of implant). Among the assessed subjects with tattoos, no side effects from the exposure to 7 T MRI were reported.

Beau A., Bossard D., Gebeile-Chauty S.

Orthodontic appliances are often removed before magnetic resonance imaging (MRI) scans because they are known to produce artefacts. The purpose of this study was to find the exact indications for removal of various fixed attachments when imaging four specific areas of the head and neck.Sixty patients requiring an MRI scan of the head for medical reasons volunteered for this investigation. One of four different types of fixed attachments (stainless steel brackets, titanium brackets, ceramic brackets with metal slots, and stainless steel retainers) were assigned to a patient. Each patient had two scans at 1.5 T: with an 'empty wax jig' and with a wax jig including the attachment. Archwires were not investigated as they are easily removed before a scan. Two radiologists evaluated the scans of each patient and each of the four areas under investigation: maxillary sinus, oral cavity, temporomandibular joints, and posterior cerebral fossa.Stainless steel brackets always caused non-interpretability of all anatomic areas (100 per cent). Titanium brackets, ceramic brackets with metal slots, and stainless steel retainers caused artefact in the oral cavity only (for 20, 16.65, and 86.65 per cent of the subjects).Our results show that ceramic brackets with metal slots and titanium brackets do not always have to be removed before MRI scans of the head and neck, depending on the area under investigation. Metal fixed retainers should only be removed if the oral cavity itself is under investigation. Stainless steel brackets should always be removed before MRI scans of the head and neck.