Which Is the Optimal Anthropometric Method for Asian Noses: Conventional Rulers, Two-Dimensional Photographs, Three-Dimensional Imaging, or Computed Tomography?

Abstract

Most Asian noses have a bulbous tip, low radix, low dorsum, short columella, and thick skin envelope, which make rhinoplasty one of the most popular plastic surgery procedures among Asians. Nasal anthropomorphic measurements are required for planning and obtaining a pleasing aesthetic result in rhinoplasty.1 In addition, understanding the relative effect of individual treatments or techniques depends on accurate and objective nasal measurements. Several anthropometric methods have been applied, including conventional rulers, two-dimensional photographs, three-dimensional imaging, or computed tomography (Table 1). Table 1. - Advantages and Disadvantages of Nasal Measurement Methods Method Advantages Disadvantages Conventional rulers Accessible Imprecise, examiner-biased, unfavorable angular measurements Two-dimensional photographs Accessible, appearance record, favorable angular measurements Need to set scale manually, not applicable to the noses with low radix and alar hypertrophy Three-dimensional imaging High reliability, accuracy, time saving, low cost, no radioactivity, repeatability No tissue information, expensive imaging machine CT High reliability, accuracy, visible bone and soft tissue High cost, radioactivity CT, computed tomography. Anthropometric measurements are referenced to the standards established by Farkas et al.2 Conventional rulers, such as calipers and protractors, have proven to be time-consuming, examiner-biased, and extremely relying on patient cooperation. This is probably because of the difficulty in identifying anatomical landmarks with sufficient precision. In addition, the identification of some landmarks by individuals is somewhat subjective. As the nose is three-dimensional, it is also difficult to simulate some nasal angles, such as nasal tip angle and nasofacial angle, and measure them accurately with protractors. Two-dimensional photographs are routinely used to record changes before and after rhinoplasty. Linear measurements can be obtained using image processing software if the photographs contain a scale; otherwise, only angles can be measured. The accuracy of the measurements can be affected by many factors, such as lighting, camera angle, and distance relative to the patient. A large percentage of Asians have a low radix, and the landmarks of nasion points are not visible from lateral photographs, resulting in some nasal measurements—including nasal height, nasal length, nasofrontal angle, and nasofacial angle—not being able to be measured. Likewise, alar hypertrophy causes the subnasal points to be unrecognizable on lateral photographs and, consequently, the nasal depth and nasolabial angle cannot be measured. Three-dimensional imaging can produce high-resolution three-dimensional images by capturing and constructing topographic surface maps. Several studies have been performed using three-dimensional imaging for facial anthropometric measurements, and the method has proven to be highly accurate and reliable.3,4 Computed tomography has become an important tool for rhinoplasty because of its high efficiency to analyze and simulate nasal bone and soft tissue independently. The midsagittal images and axial images of computed tomography were used for nasal measurements previously, whereas the position of the head during the examination may affect the images. Besides, computed tomographic data can be used to generate three-dimensional images of the face to facilitate nasal measurements.5 The three-dimensional images can be moved and rotated to any view, and the nasal details can be magnified to identify the anthropometric landmarks. The scale of the three-dimensional image is defaulted by the machine with high precision, without the need to determine the scale manually as for two-dimensional photographs. Computed tomography allows precise acquisition of head tissue information, but the disadvantages of high cost and radioactivity prevent its routine use for nasal measurements. Although three-dimensional imaging can obtain only facial surface images, it is sufficient for nasal measurements. Compared to computed tomography, three-dimensional imaging has the advantages of time saving, low cost, no radioactivity, and repeatability. Overall, three-dimensional imaging is recommended for nasal measurements, especially for Asian noses. One day, three-dimensional scanning will replace direct measurements and two-dimensional photographs, because of its reliability, accuracy, repeatability, time saving, patient convenience, and low cost. DISCLOSURE The authors have no financial interest in any of the products or devices mentioned in this article.