An Anchoring and Steering Device for Wireless In Vivo Surveillance of Nasopharyngeal Carcinoma1
Hongliang Ren, Chwee Ming Lim, Justin S. Y. Tan, Jun Xiang Wang, Mu Lin, Vanessa Mak Wei-Lin, Dhashni D O Manogaran · Journal of Medical Devices · 2014
Nasopharyngeal carcinoma (NPC) is an endemic cancer in Southeast Asia, including Singapore. Diagnosis of NPC is usually made on nasal endoscopy to evaluate the nasopharynx and confirmed on biopsy. The stage of cancer is made following imaging studies like the computer-tomography or magnetic resonance imaging. Patients with NPC often present with a neck mass, epistaxis, or hearing loss. Due to the “deep” and relatively inaccessible nature of the nasopharynx, most NPC patients are diagnosed in the advanced stage of disease. Therefore, early diagnosis of NPC and early detection of recurrent disease in previously treated NPC patients will enhance the cure rates of this cancer and this can be indicated by early features, including morphological changes for experienced clinicians.The probability of recurrence of NPC is the highest during the following two years of treatment [1]. It is, therefore, paramount that constant surveillance of the nasopharyngeal region be done during this time period, based on morphological changes. This article is focused on surveillance, which will provide valuable clues for NPC diagnosis. Consequently, there exists a need for a biocompatible device that has the capability to remain secured in the nasal cavity for a couple of years, without causing airway blockage, to continuously capture images of the nasopharyngeal region for monitoring purposes.In this paper, we explore a solution to the above problem. A device was invented for the purpose of monitoring the nasopharynx. This paper will illustrate the concept and working principles behind the said device and also the preliminary tests done to ascertain the practicality of the device.The invention is an in vivo device for anchoring and steering a wireless camera module that can be secured to the vomer bone of the patient skull. The wireless camera module investigated in our prior study [2] can slot seamlessly into the extruded camera casing of the device as shown in Fig. 1. This camera casing allows the camera to have a wide viewing angle.As shown in Fig. 2, in order for rotation to function, a nylon string is connected to the camera module at the top and bottom of the camera module shaft. At the top, the nylon string is coiled around the beam in one direction (clockwise). At the bottom, it is coiled in the opposite direction (counterclockwise). Therefore, when the strings are pulled to rotate the camera to the left, the other string will be coiled around the camera module shaft, to allow rotation of the camera back to the right when pulled.The device has a slight curvature to the main shaft that allows for the device to smoothly glide along the floor of the nose, through the nasal cavity, until it can be clamped onto the vomer bone. The U-shaped front end of the anchoring shaft functions to secure the device onto the vomer bone. The nose is then pierced at the septum cartilage before a screw and nut are used to secure the device in place.In order to verify mechanical strength of the anchoring device, mechanical tests were performed to the shaft using the Instron 3345 machine and Series IX software, an electromechanical tester and analysis software, respectively, as shown in Fig. 3. The tests indicate how secure the camera module can be anchored onto the vomer bone through the proposed anchoring device.To verify the feasibility of the design concept of the anchorage device, the prototype was tested on a skull model, as shown in Fig. 4, where the camera casing part was panning right with respect to the vomer bone. The tests simulated realistic clinical procedures include insertion, anchoring, panning, and finally device detaching.Figure 5 shows the captured sample image using our device. In terms of evaluating the anchoring strength, the results of our mechanical tests are shown in Figs. 6 and 7. Figure 6 shows that a 151 N force is required to pull the device out from its secured position. Figure 7 shows that the weakest part of our device, the hook, fractures under a load of 34.9 N. Both these forces are highly unlikely to be experienced inside the nose, thereby translating to a low probability of device failure while in operation.It is noteworthy that the result correlates to the type of material being used. Objet VeroclearTM was used as the material of choice in our prototype simply because it was the only rapid-prototyping material that has behavioral properties most similar to what is desired.Table 1 shows the prototype device specifications. The size of the first prototype turned out less than ideal owing to the fragile nature of Objet VeroclearTM. In order to compensate for this inherent fault, the dimensions were increased to strengthen the structure of the device and will be miniaturized if we change the material to titanium alloy in the future work. The expected size, particularly the shaft cross section should be small enough for easy insertion along the nostril, and thus increase patient comfort.It is noteworthy that the experiment values in the above figures are based on the prototype made from Objet VeroclearTM, a material much weaker in mechanical strength and ductility [3] than the proposed Grade 5 titanium alloy, Ti6Al4V [4]. It is expected that using Ti6Al4V will allow this device to be much more robust. Hence, all values stated in Table 1 are projected to increase significantly, with the exception of angle of view and deployment time which are not dependent on the material used for construct.While the early prototype results show much potential and promise, more can be done to improve on this current design. This includes incorporating an electrical rotation system for a less manual and more precise panning of the camera as well as improving on the ergonomic aspect through implementing an extendable anchoring shaft system, so as to accommodate for the anatomical variation of the nasal cavity that comes with individuals.