Comparison of three-dimensional surface scanning techniques for capturing the external ear

Abstract

Congenital facial anomalies, such as microtia (malformation of the external ear), lead to significant psychosocial effects starting from early childhood. Three-dimensional (3D) scanning and advanced manufacturing are being investigated as a cheaper and more personalised method of fabricating reconstructive treatments for patients compared to traditional approaches. To date, most case studies have used expensive 3D scanners, yet, there is potential for low-cost devices to provide comparable results. This study aimed to investigate these different approaches. Both ears of 16 adult participants were scanned with three devices: Artec Spider (Artec Group), Intel® RealSense™ (Intel), and the Apple iPhone® 7 (Apple Inc.) combined with photogrammetry using 90, 60 and 30 photographs. The scanning time, processing time, accuracy, completeness, resolution and repeatability of each technique were assessed using the Artec Spider as a reference scanner. Our results show that the iPhone had the longest processing time however, this decreased nine-fold when reducing the number of photos from 90 to 30. There was no significant difference in the accuracy, completeness or repeatability of the iPhone scans with 90 photographs (1.4 ± 0.6 mm, 79.9%, 1.0 ± 0.1 mm), 60 photographs (1.2 ± 0.2, 79.3%, 0.9 ± 0.2 mm) or 30 photographs (1.2 ± 0.3 mm, 74.3%, 1.0 ± 0.2 mm). The Intel RealSesne performed significantly worse in each parameter (1.8 ± 03 mm; 46.6%, 1.4 ± 0.5). Additionally, the RealSense had significantly lower resolution with not enough detail captured for the application. These results demonstrate that the ear can be accurately 3D scanned using iPhone photographs. We would recommend capturing between 30 and 60 photographs of the ear to create a scan that is accurate but without the downfall of long processing time. Using these methods we aim to provide a more comfortable setting for the patient and a lower-cost and more personalised ear prosthesis.

Keywords

• 3d scanning
• photogrammetry
• advanced manufacturing
• microtia
• ear reconstruction
• ear prosthesis