Quantification of age-related changes in midsagittal facial profile using Fourier analysis: A longitudinal study on Japanese adult males
Introduction
The quantitative information held in the human face is a valuable indicator of identity in forensic science. It is particularly useful in the identification of the living such as criminals and missing persons or the identification of the deceased such as victims of mass disasters. The quantitative analysis of age-related changes in the face can aid with person identification.
Pre-existing photographic records of the face are necessary sources for the identification process. However, recent photographic reference records captured at the time of investigation are not always available. In such situations, the investigator is challenged by predicting how the face of a person under investigation would look like after some period of time. With the recent development of 3D imaging technology, there have been successful attempts to quantify and predict changes in facial topography induced by growth [1] and ageing [2]. Although facial features in adulthood are generally more stabilised when compared to the changes taking place during craniofacial growth, it has been reported that facial topography may be subject to some skeletal modifications brought about by ageing [[3], [4], [5], [6]] and obesity [7].
Age-related changes in facial morphology are attributed to changes in the facial soft tissues and residual remodelling in the underlying facial skeleton. It is often supposed that body growth is not noticeable beyond the critical age of 18–19 years [8]. However, studies using 3D CT scans of people from young adulthood to old ages revealed age-related angular changes in the midfacial skeleton [[3], [4], [5], [6]]. Although it was reported that some residual facial growth especially in the lower third of the face still occurs in young adult males and that facial growth is almost completed in females after the age of 15 years [9], age-related changes later than 25 years of age were found more intense in females [3,5]. Generally, age-related soft tissue changes are due to loss of volume and skin atrophy [10,11]. Age-related changes can also follow, to a lesser extent, underlying skeletal changes [12,13]. Changes in facial topography can also be attributed to non-ageing factors such as obesity [7].
The process of facial identification is often challenged further by the lack of direct frontal views, e.g. where surveillance footage only shows a lateral view of the face. Moreover, the only facial identity records available at many dental practices are lateral cephalograms which only show the soft-tissue profile of the face. Therefore, analysis of facial profile can be also important to the identification process.
Various methods exist for quantifying the facial profile. While direct anthropometric parameters such as angles and measurements were used in some studies [[14], [15], [16]], others used more advanced mathematical methods such as Procrustes superimposition, principal component analysis [17] and Fourier analysis [13,[18], [19], [20], [21], [22], [23]].
Fourier shape analysis decomposes contours or curvatures into harmonic functions defined by Fourier descriptors [24]. Fourier shape analysis is a mathematical method based on converting a curved outline such as the midsagittal profile of the face into an infinite successive sine and cosine functions amenable to quantitative statistical description, comparison and analyses [25]. Fourier analysis has been used to quantify human facial profiles [[19], [20], [21], [22], [23],26,27]. Most of the articles that employed Fourier analysis in studying longitudinal changes in facial profile focused on changes occurring during growth and development [19,26,28]. Studies using Fourier analysis to quantify age-related changed in adulthood have been very limited [13,20]. Ferrario et al. [20] used Fourier harmonic analysis to quantify and longitudinally evaluate the facial profiles of 14 adult subjects after 10 years. They computed the areas enclosed in each facial outlines and measured the difference in the area between pre and post ageing profiles. Ferrario et al. [20] reported significant age-related changes in facial profile in men and women. On the other hand, Kapur et al. [13] used lateral cephalograms of 77 subjects to extract the facial profiles. They then applied Fourier analysis to measure age-related longitudinal changes over a nine-year interval. They reported the greatest change between the upper and lower lips and the least change at the tip of the nose.
The limited literature quantifying age-related changes in facial profile through Fourier analysis has been limited further to small numbers of subjects uncategorised into age groups, the aim of the present study was to employ Fourier analysis to quantify age-related changes in facial profiles across three 10-year-long age groups.
Section snippets
Description of data used in the study
The present study is based on a joint collaboration between Melbourne Dental School (MDS) in Australia and the National Research Institute of Police Science (NRIPS) in Japan. Based on the collaboration, MDS burrowed from NRIPS a cohort of 688 three-dimensional facial scans of Japanese young and middle aged adults. The 3D scans had been acquired as part of an ongoing NRIPS research project titled “Ongoing research into improving the system for predicting age-related change in facial images
Results
The results of the inter-examiner reliability (error of the methods) are displayed in Table 2. All Pearson’s correlation coefficients were ≥0.88, which indicates a high level of reliability between the two examiners and the two methods for the extraction of the midsagittal facial profiles from the 3D scans.
Fig. 1 shows the anatomical reproduction of all possible midsagittal contours from the mean coefficients of the whole baseline sample at all possible harmonic levels. H1 represents the
Method error
The high level of inter-examiner reliability can also be considered as a high level of reliability between two different methods for the extraction of the profiles from 3D facial scans.
Quantification of midsagittal facial profile
The details of the facial profile were fully reconstructed from a Fourier series truncated at the level of the 20th harmonic with the harmonic levels higher than H20 contributing insignificantly to the profile shape. This finding is consistent with the previous similar studies [20,22,23]. The last midsagittal
Conclusions
Fourier analysis is a useful morphometric approach to quantify age-related changes in mid-sagittal soft-tissue features of the face. However, where age-related variations in midsagittal features are generally small across the young and middle aged adults in the study sample, it is recommended that the capacity of Fourier analysis to quantify age-related facial changes be tested further on the midsagittal features of the elderly and on other parasagittal and transverse facial features.
Declarations of interest
None.
Acknowledgements
The authors acknowledge the following bodies / institutions for their contribution to the study:
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Jordan University of Science and Technology (JUST), as the experimental part of this study had been conducted at Melbourne Dental School while the first author was on paid sabbatical leave from JUST.
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The National Research Institute of Police Sciences (NRIPS) – Japan for their collaboration and the provision of the 3D scans.
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Charles Sturt University (CSU) – Australia, for providing all the electronic
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