## 1 Introduction
Therefore, wearing comfort and appearance are improved compared to conventional BC hearing aids. In cases of aural atresia, the signals are transmitted to the cochlea necessarily via the skull bone. The signals are percutaneousally delivered to the cartilaginous tissues in a manner similar to conventional BC hearing aids. For conventional BC hearing aids, high contact pressure can reduce the attenuation of the transmission. In contrast, the transducer in CC hearing devices is usually placed without a static force. However, it can provide sufficient audiological benefits for daily use [16; 17; 18]. The aided thresholds of CC hearing devices are better than those of ADHEAR [19]. The performances of CC hearing devices in speech recognition are comparable to those of BC devices, such as BAHA, although the aided thresholds were slightly higher [20]. They have been clinically used in Japan since 2017, and approximately 80% of patients with aural atresia purchased and continuously used CC hearing devices after daily use on trial [17]. There are three types of transducers utilized in CC hearing devices. The first type is a simple transducer that is fixed using double-sided tape. The other two transducers are the ear chip-attached and ear chip-embedded types (Figure 1) [14]. One of the differences between them is their size. The ear chip-embedded type can be chosen when the ear chip is large enough to embed the transducer. The stability of the transducer can be improved in the order of simple, ear chip-attached, and ear chip-embedded types. In a previous study, the continuous use rate increased in the same order [21]. Thus, the ear chip types are usually employed, if possible. In the process of CC hearing device fitting, taking an ear impression is required to create the ear chip to couple the transducer to the ear, similar to an ear mold or shell. There is a big variation in the shape of the ear among patients with microtia and aural atresia. Furthermore, otolasty also results in a big variation. The stable fixation of the transducer on the aural cartilage is considered important to achieve sufficient benefit. Therefore, the shape of the ear chip can influence the benefit. Meanwhile, when patients with aural atresia visit the hospital, some patients undergo a computed tomography (CT) scan of the ear for diagnosis. CT scans precisely describe the local anatomical structures. Particularly, the boundary between the tissues and air can be clearly described. Therefore, if CT was performed, CT images may be utilized for CAD to create ear chips instead of ear impressions, and the risks related to taking the ear impression can be avoided. Considering the cost and risk of radiation exposure, CT examination is not appropriate for creating ear impressions. However, if CT was already performed for other purposes, the creation of an ear chip utilizing CT images may become one of the options. In contrast, the reproduction of the structure designed using the CT image may be inferior to that of the ear impression because of the limitation of the resolution depending on the slice width. In this study, the ear chip of the CC hearing device was designed not only via ear impression but also via CT images of patients with aural atresia who underwent a CT scan of the ear. Aided thresholds and subjective evaluations were compared between both methods. This exploratory study aimed to investigate whether CT images can be used for CAD to create hearing devices.