Migraine is a socioeconomic burden, whose pharmaceutical and invasive treatment methods may have troublesome side-effects. A wearable neuromodulator targeting frontal nerve branches of trigeminal nerve may provide an effective solution to suppress or treat migraine. Such solutions have had limited efficacies. In this paper, using computational models, the relationship of this lack of efficacy to some neural variations is investigated. The results indicate that due to neuro-anatomic variations, different current levels may be required to achieve a sufficient level of neural stimulation. Thus, an optimized design should consider such variations across the patient group.
Objective. Conventional treatment methods for migraine often have side effects. One treatment involves a wearable neuromodulator targeting frontal nerves. Studies based on this technique have shown limited efficacy and the existing setting can cause pain. These may be associated with neuroanatomical variations which lead to high levels of required stimulus current. The aim of this paper is to study the effect of such variations on the activation currents of the Cefaly neuromodulator. Also, using a different electrode orientation, the possibility of reducing activation current levels to avoid painful side-effects and improve efficacy, is explored. Approach. This paper investigates the effect of neuroanatomical variations and electrode orientation on the stimulus current thresholds using a computational hybrid model involving a volume conductor and an advanced nerve model. Ten human head models are developed considering statistical variations of key neuroanatomical features, to model a representative population. Main results. By simulating the required stimulus current level in the head models, it is shown that neuroanatomical variations have a significant impact on the outcome, which is not solely a function of one specific neuroanatomical feature. The stimulus current thresholds based on the conventional Cefaly system vary from 4.4 mA to 25.1 mA across all head models. By altering the electrode orientation to align with the nerve branches, the stimulus current thresholds are substantially reduced to between 0.28 mA and 15 mA, reducing current density near pain-sensitive structures which may lead to a higher level of patient acceptance, further improving the efficacy. Significance. Computational modeling based on statistically valid neuroanatomical parameters, covering a representative adult population, offers a powerful tool for quantitative comparison of the effect of the position of stimulating electrodes which is otherwise not possible in clinical studies.
Migraine is a prevalent and highly disabling disorder. The pharmaceutical and invasive treatment methods have troublesome side effects and associated risks, hence undesirable. Transcutaneous supraorbital neuromodulation has been shown to potentially suppress episodic migraine attacks yet results have low efficacy. This inconclusive response may be associated with neuroanatomical variations of patients which may be investigated using computational models. Model complexity is a limiting factor in implementing such techniques. This paper investigates the effect of model complexity on fiber activation estimates in transcutaneous frontal nerve stimulati on. It is shown that the model can be simplified while minimally affecting the outcome.
The electro anatomy of the cochlea plays a crucial role in hearing, where damage to the cochlea may cause hearing loss. Cochlear implants provide hearing to severe or profound hearing-impaired individuals. The accurate insertion of electrodes into the cochlea is important. If misplaced it may lead to further damage (insertion trauma). Visual inspection of the electrode array insertion is limited and relies on the experience of the surgeon. Assisted real time guidance in positioning the electrode array in the cochlea during insertion is needed. Using an advanced computational model of the cochlea accounting for different tissue layers, impedance variations at different electrode distances from the cochlear wall were simulated. Preliminary simulations suggest that the variations may be used to detect the proximity of the electrodes to the cochlea wall.
The cochlear implantable neuromodulator provides substantial auditory perception to those with severe or profound impaired hearing. Correct electrode array positioning in the cochlea is one of the important factors for quality hearing, and misplacement may lead to additional injury to the cochlea. Visual inspection of the progress of electrode insertion is limited and mainly relies on the surgeon's tactile skills, and there is a need to detect in real-time the electrode array position in the cochlea during insertion. The available clinical measurement presently provides very limited information. Impedance measurement may be used to assist with the insertion of the electrode array. Using computational modeling of the cochlea, and its local tissue layers merging with the associated neuromodulator electrode array parameters, the impedance variations at different insertion depths and the proximities to the cochlea walls have been analyzed. In this study, an anatomical computational model of the temporal region of a patient is used to derive the relationship between impedance variations and the electrode proximity to the cochlea wall and electrode insertion depth. The aim was to examine whether the use of electrode impedance variations can be an effective marker of electrode proximity and electrode insertion depth. The proposed anatomical model simulates the quasi-static electrode impedance variations at different selected points but at considerable computation cost. A much less computationally intensive geometric model (~1/30) provided comparative impedance measurements with differences of <2%. Both use finite element analysis over the entire cross-section area of the scala tympani. It is shown that the magnitude of the impedance varies with both electrode insertion depth and electrode proximity to the adjacent anatomical layers (e.g., cochlea wall). In particular, there is a 1,400% increase when the electrode array is moved very close to the cochlea wall. This may help the surgeon to find the optimal electrode position within the scala tympani by observation of such impedance characteristics. The misplacement of the electrode array within the scala tympani may be eliminated by using the impedance variation metric during electrode array insertion if the results are validated with an experimental study.
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