Mathematical modelling of the electric potential from cochlear implants for a new diagnosis tool

人工耳蜗通过替换内耳耳蜗中受损或缺失的传感器，使听力损失的人恢复听力。然而，有些人的植入物会出现持续的问题。准确诊断这些问题的原因往往是不可能的，这导致人们尽管植入了助听器，但听力却很差。听力损失是导致抑郁、痴呆和残疾的重要风险因素，据估计，听力损失给英国经济造成的损失为每年100亿至400亿英镑。人工耳蜗可以使更多的聋哑人受益，并有助于解决一个关键的社会挑战：减少晚年残疾的负担。然而，为了实现这一目标，我们需要新的诊断方法来确保植入物患者终身享有高质量的听力。这个项目将通过应用数学来开发一种诊断工具来改变人工耳蜗植入问题的诊断，这种诊断工具是由临床驱动的，并且是为临床设计的，它易于管理，并且患者能很好地忍受。人工耳蜗是将一系列金属电极插入耳蜗内。声音由耳朵上的一个单元捕获，该单元连接到头骨上的内部刺激器。刺激器使耳蜗阵列上的电极发出电流，激活听觉神经，向大脑发送被识别为声音的信号。电流和传递到大脑的信号可能会中断，从而导致听力下降或失声。来自电极的电流也会产生可以在头皮上检测到的电压。我们测量了植入人工耳蜗的人的这些电压，发现他们可以识别出植入物不再像预期的那样传递声音的问题。电信号的中断也会引起疼痛或不愉快的感觉。这些症状令人痛苦，难以解释或治疗，特别是当根本原因尚不清楚时。我们的目标是利用有限元方法建立一个人工耳蜗在人脑中运作的数学模型：这些方法广泛应用于医学和工业的许多领域。该模型将预测每个植入电极轮流产生电流时头皮上产生的电压。我们将使用现有数据和收集新数据，将这些预测与人工耳蜗植入者的数据进行比较，以验证模型。为了确保模型可以应用于不同头部形状的人，我们将研究模型头部不同特征的影响，比如它的形状，在我们的模型中捕捉正确的细节水平。为了诊断问题，我们将研究每个电极与头皮上特定位置的电压之间的关系。我们将描述全功能植入物的这种关系，然后将常见的问题，如植入物错位或疤痕组织的建立，纳入我们的模型。初步结果表明，在存在这些问题的情况下，哪个电极产生电流和头皮上的电压之间的关系发生了显著变化。这为使用这些关系诊断问题奠定了基础。我们的工作重点是开发一种可用于所有患者的临床测试，而之前的工作已经生成了少数个体的详细模型。人工耳蜗的使用寿命为20-25年，如果出现问题，可能会缩短使用寿命，或者需要进行额外的手术。这对病人和卫生预算都是有害的。显然需要一种可靠的诊断工具，这种工具可以在标准的临床环境中快速运行，并可用于成人和儿童，无论其语言技能或认知能力如何。该项目为开发一种可用于所有人工耳蜗诊所并最终通过远程医疗的有效测试铺平了道路。

Cochlear implants restore hearing in people with hearing loss, by replacing damaged or missing sensors in the cochlea in the inner ear. However, some people experience persistent problems with their implant. Precise diagnosis of the cause of these problems is often not possible, resulting in people with poor hearing despite having an implant. Hearing loss is a significant risk factor for depression, dementia and disability-affected life-years with an estimated cost to the UK economy of >£40billion/annum. Cochlear implants could benefit many more deaf people and help to address a key societal challenge: a reduction in the burden of disability in later life. However, for this to happen, we need new diagnostic approaches to ensure lifelong good quality hearing for people with implants. This project will transform the diagnosis of problems in cochlear implants by applying mathematics to develop a diagnostic tool that is driven by and designed for use in the clinic, that is easy to administer and that is well tolerated by patients. A cochlear implant is a series of metal electrodes, which are inserted into the cochlea. Sound is captured by a unit on the ear that is connected to an internal stimulator on the skull. The stimulator causes the electrodes on the array in the cochlea to emit electric currents which activate the auditory nerve, sending signals to the brain which are recognised as sound. Problems can occur that disrupt the electric current and the signal relayed to the brain, causing poorer hearing or loss of sound. The current from the electrodes also causes voltages that can be detected on the scalp. We have measured these voltages in people with cochlear implants and found that they can identify problematic cases where the implant is no longer relaying sound as expected. Disruption to the electrical signals can also cause pain, or unpleasant sensations. These symptoms are distressing and hard to explain or treat, particularly when the underlying cause is not clear. We aim to build a mathematical model of cochlear implants operating in the human head using finite element methods: these methods are widely applied in many areas of medicine and industry. The model will predict the voltages on the scalp that are generated in response to each implant electrode producing a current in turn. We will compare these predictions to data from people with cochlear implants to validate the model, using existing data as well as collecting new data. To ensure the model can be applied to different people with differently shaped heads, we will study the effects of varying characteristics of the model head, such as its shape, capturing the right level of detail in our model. To diagnose problems, we will study the relationship between each electrode and the voltage at specific locations on the scalp. We will describe this relationship for fully functional implants, and will then incorporate common problems, such as misplaced implants or build-up of scar tissue, into our model. Preliminary results show that the relationship between which electrode produces the current and the voltage on the scalp changes significantly in the presence of such problems. This lays the foundation for using these relationships to diagnose problems. Our work focuses on the development of a clinical test that can be used on all patients, whereas prior work has generated detailed models of a few individuals. Cochlear implants have a lifespan of 20-25 years, and problems can reduce this lifespan or result in additional surgery being needed. This is detrimental both to the patient and health budgets. There is a clear need for a reliable diagnostic tool that is quick to run in a standard clinical environment and usable in adults and children, irrespective of language skills or cognitive abilities. This project paves the way for the development of a validated test that can be used in all cochlear implant clinics and ultimately, via telemedicine.