[Magnetic resonance imaging artefacts and fixed orthodontic attachments]. / Les appareils orthodontiques collés doivent-ils être déposés systématiquement avant un examen d'imagerie par résonance magnétique (IRM) ?∗.

OBJECTIVES: 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. MATERIALS AND METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.

Magnetic resonance imaging artefacts and fixed orthodontic attachments.

BACKGROUND/OBJECTIVES: 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. MATERIALS/METHODS: 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. RESULTS: 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). CONCLUSIONS/IMPLICATIONS: 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.

Surgical trauma after sequential insertion of intracochlear catheters and electrode arrays (a histologic study).

HYPOTHESIS: To evaluate histologically the risk of trauma to intracochlear structures after sequential insertion of an intracochlear catheter and an electrode array. BACKGROUND: A previous computed tomographic scan-based study demonstrated that introduction of a flexible disposable intracochlear catheter for drug delivery to a distance of up to 15 mm was feasible and showed no radiologic evidence of basilar membrane trauma. METHODS: Fifteen fresh human temporal bones were prepared for cochlear implantation. We sequentially performed the introduction of the catheter, the injection of 15 µl of an iodine solution into the scala tympani via the catheter, and the removal of the catheter in 14 temporal bones, and finally, 2 types of electrode array (Flex EAS and Flex Soft) from MED-EL, were inserted into 10 temporal bones. The bones were fixed and embedded in methylmethacrylate to cut the undecalcified temporal bones parallel to the modiolus axis with the electrode array in place, and each histologic section was photographed to document the location and extent of trauma in the cochlea. RESULTS: No specific damage (Grade 0 trauma) to cochlear structures occurred in 12 temporal bones, and elevation of basilar membrane (Grade 1 trauma) occurred in 2 cases. The electrode array was positioned in the scala tympani under the basilar membrane in all temporal bones, with one exception, in which the Flex Soft electrode array deviated behind the spiral ligament and into the scala vestibuli apically (Grade 3 trauma). CONCLUSION: The infusion of an iodine solution within an intracochlear catheter and the subsequent insertion of an electrode array was shown to be feasible and often atraumatic.

Radiologic study of a disposable drug delivery intracochlear catheter.

HYPOTHESIS: 1) To assess the insertion characteristics of a disposable intracochlear catheter; and 2) to assess radiologically cochlear trauma induced by delivery catheter and electrode arrays. BACKGROUND: A catheter was designed to enter the scala tympani up to 15 mm and to acutely deliver pharmacological agents during cochlear implantation. METHODS: A cadaveric study was conducted in accordance to national regulation. Thirteen fresh temporal bones were evaluated radiologically. The intracochlear catheter used in this experiment has the same outer dimensions and profile as a standard MED-EL cochlear implant electrode array. We performed sequentially the introduction of the catheter, the injection of an iodine solution into the scala tympani via the catheter, the removal of the catheter, and finally an electrode array insertion. Ten to 15 µl of an iodine solution was injected into the scala tympani at depth of 15 mm. Four CT scans were sequentially performed after each step. RESULTS: The disposable intracochlear catheter could easily be inserted in all specimens. An insertion at depth of 15 mm was easily achieved every time. CT scans demonstrated that the iodine solution injected stayed in the scala tympani in all specimens. This was interpreted as indirect evidence of the integrity of the basilar membrane. CONCLUSION: Drug delivery during cochlear implantation using a flexible disposable intracochlear catheter has been demonstrated to be feasible and without radiological evidence of basilar membrane trauma to a distance of up to 15 mm, as demonstrated in 13 temporal bones.

Fusion of MRIs and CT scans for surgical treatment of cholesteatoma of the middle ear in children.

OBJECTIVE: To evaluate the efficiency of diffusion-weighted magnetic resonance imaging (MRI) and high-resolution computed tomographic (CT) scan coregistration in predicting and adequately locating primary or recurrent cholesteatoma in children. DESIGN: Prospective study. SETTING: Tertiary care university hospital. PATIENTS: Ten patients aged 2 to 17 years (mean age, 8.5 years) with cholesteatoma of the middle ear, some of which were previously treated, were included for follow-up with systematic CT scanning and MRI between 2007 and 2008. INTERVENTIONS: Computed tomographic scanning was performed on a Siemens Somaton 128 (0.5/0.2-mm slices reformatted in 0.5/0.3-mm images). Fine cuts were obtained parallel and perpendicular to the lateral semicircular canal in each ear (100 × 100-mm field of view). Magnetic resonance imaging was undertaken on a Siemens Avanto 1.5T unit, with a protocol adapted for young children. Diffusion-weighted imaging was acquired using a single-shot turbo spin-echo mode. To allow for diagnosis and localization of the cholesteatoma, CT and diffusion-weighted MRIs were fused for each case. RESULTS: In 10 children, fusion technique allowed for correct diagnosis and precise localization (hypotympanum, epitympanum, mastoid recess, and attical space) as confirmed by subsequent standard surgery (positive predictive value, 100%). In 3 cases, the surgical approach was adequately determined from the fusion results. Lesion sizes on the CT-MRI fusion corresponded with perioperative findings. CONCLUSIONS: Recent developments in imaging techniques have made diffusion-weighted MRI more effective for detecting recurrent cholesteatoma. The major drawback of this technique, however, has been its poor anatomical and spatial discrimination. Fusion imaging using high-resolution CT and diffusion-weighted MRI appears to be a promising technique for both the diagnosis and precise localization of cholesteatomas. It provides useful information for surgical planning and, furthermore, is easy to use in pediatric cases.

Contributions of reformatted computed tomography and panoramic radiography in the localization of third molars relative to the maxillary sinus.

OBJECTIVE: The aim of this clinical study was to seek an answer to the question of whether CT gives better qualitative and quantitative information as compared to panoramic radiograph when deciding on extraction of upper impacted third molars. STUDY: The study concerned 34 third molars appearing in direct relation with the sinus on the panoramic radiograph for which a CT scan had been recommended. For each case, the panoramic radiograph was compared with the CT scan for 5 evaluation criteria. RESULTS: The CT scan was more precise than the panoramic radiograph by 1.67 mm for measurement of the level of impaction of the third molar, by 12.44 degrees for measurement of the third molar displacement, by 0.74 mm for bone height separating the third molar roots and the sinus, and by 2.26 mm for the length of roots in the sinus. The CT scan was equally accurate for measurement of the distance separating the crowns of second and third molars in 34 cases. CONCLUSIONS: This study confirms the gain in precision for the CT scan as compared with conventional techniques. The CT scan therefore presents advantages when considering the extraction of upper third molars by providing both qualitative and quantitative information liable to bear on the diagnosis and therapeutic management.

CT-assisted surgery in choanal atresia.

OBJECTIVE: To limit restenosis after surgical repair of choanal atresia. MATERIAL AND METHODS: A total of 20 children (age range 3 days to 11 years) with choanal atresia underwent surgical repair using a microdebrider via an intranasal approach. Surgery was guided by CT. Mitomycin was administered at the end of the procedure. RESULTS: An average of 1.7 procedures per child were required. CT combined with peroperative endoscopy revealed postoperative neo-osteogenesis and insufficient bone resection. CONCLUSIONS: CT-assisted intranasal repair led to extended bone resection of the atretic plate, the predominant cause of which was restenosis resulting from neo-osteogenesis.

Computer-assisted navigation system in pediatric intranasal surgery.

OBJECTIVES: To introduce a computer-assisted navigation system and to evaluate its application in pediatric sinusonasal surgery. METHODS: A commercially available wireless passive marker system that allows the calibration and tracking of virtually any instrument was adapted to children and used during pediatric endoscopic sinusonasal surgery. RESULTS: The headset localizer that was initially used in computed tomographic scanning was not well accepted by children. Correlation of the preoperative computed tomographic scan to the actual patient was made possible by a laser device. Setup time was able to be decreased from an initial 20 minutes to 3 minutes. The average recording accuracy was 1.1 mm. The advantages of the system became apparent as experience increased in cases involving sinus polyposis, choanal atresia, nasopharyngeal fibroma removal, tumor biopsy, and minimally invasive maxillary, frontal, and sphenoidal surgery. CONCLUSIONS: The computer-assisted navigation system was used first as a control system and then, as experience increased, as a true surgical guide. Indications for its use also increased. Pediatric intranasal surgery was performed using 2 complementary guides: an endoscopic view and a computed tomographic view of the instrument's position.