Evaluation of the neural response telemetry (NRT) capabilities of the nucleus research platform 8: initial results from the NRT trial.

The purpose of this study was to evaluate the performance of the new features of the Nucleus Research Platform 8 (RP8), a system developed specifically for research purposes The RP8 consists of a research implant, a speech processor and a new NRT software (NRT v4), and includes comparisons of the different artefact-cancellation methods, NRT threshold, and recovery function measurements. The system has new artefact-suppression techniques and new diagnostic capabilities; their performance has been verified in animal experiments. In this study, NRT data were collected from 15 postlingually deafened adult cochlear implant patients intraoperatively and up to 6 months postoperatively after switch-on. The initial investigation in two clinics in Europe focused primarily on the enhanced NRT capabilities Results from the trial in two European clinics indicate that NRT measurements can be obtained with lower noise levels. A comparison of the different artefact-cancellation techniques showed that the forward-masking paradigm implemented in the Nucleus 3 system is still the method of choice. The focus of this report is on recovery function characteristics, which may give insight into auditory nerve fiber properties with regard to higher stimulation rates.

Functional MR imaging of the auditory cortex with electrical stimulation of the promontory in 35 deaf patients before cochlea implantation.

BACKGROUND AND PURPOSE: Promontory testing is used for preoperative assessment of the auditory pathway before cochlear implantation. This method depends on patient cooperation and cannot be used in children or disabled persons. Promontory stimulation during functional MR imaging (fMRI) provides a new and objective method to test the integrity of the auditory pathway. To evaluate the method, we performed this prospective study in deaf adult patients. METHODS: fMRI of the auditory pathway with electrical stimulation of the promontory was performed in 35 profoundly deaf patients, bilaterally in seven. For safe stimulation inside the MR environment, a specially designed nerve stimulator was used. We acquired nine sections parallel to the sylvian fissure by using an echo-planar pulse sequence (1.5 T). To evaluate the number of pixels in the auditory cortex, areas were counted and the minimum confidence level (p(st) value) was determined. The auditory pathway was called intact when the minimal p(st) value was 10(-5) or when the minimal p(st) value was 10(-4) in at least five activated pixels. RESULTS: Images in 85% of patients reporting an auditory sensation showed activation of the contralateral auditory cortex. In the group of patients reporting no hearing sensation, images in 75% did not show activation. CONCLUSION: This method can prove the intactness of the auditory pathway and help the surgeon in decision making before cochlear implantation. However, a negative finding should not be interpreted as indicating a nonfunctioning auditory pathway. Additional technical refinements and experience are needed to further improve this method.

Virtual endoscopy of the middle ear: experimental and clinical results of a standardised approach using multi-slice helical computed tomography.

Virtual endoscopy (VE) enables non-invasive 3D endoluminal imaging of the middle ear by post-processing of CT data. To optimise the clinical application a standardised approach was evaluated in normal and pathologic cases. Data acquisition was performed using multi-slice helical CT in 20 normal patients and 15 patients with malformation or trauma. Virtual endoscopy of the tympanic cavity and 3D images of the ossicles were generated using surface and volume rendering. Qualitative assessment of the representation of anatomical structures was performed in normal patients. In 15 pathological cases the diagnostic benefit was evaluated by comparing the 3D images to the 2D images and intra-operative findings. In all 35 cases 3D imaging was possible using the standardised approach. The ossicular chain as well as the bony and soft tissue structures of the tympanic cavity were visualised in 20 normal patients. In 7 of 8 patients with malformation and 1 of 7 patients with trauma the original diagnosis was changed by 3D imaging. Standardisation and evaluation of the method in normal patients is essential as it enhances the diagnostic reliability. Virtual endoscopy facilitates understanding of the complex anatomy of the middle ear. In cases of suspected malformation and confirmed trauma it is helpful for diagnosis and surgical planning.