An innovative 3D-3D superimposition for assessing anatomical uniqueness of frontal sinuses through segmentation on CT scans

Abstract

Anatomical uniqueness plays a significant role in the personal identification process of unknown deceased. Frontal sinuses have been widely used in the past decades for this purpose, mostly using 2D X-ray techniques. However, the modern 3D CT-based segmentation methods may help in developing novel and more reliable methods of identification. This study aims at assessing the anatomical uniqueness of frontal sinuses through the 3D model registration. Thirty subjects who underwent two maxillofacial CT scans (interval: 1 month to 5 years) were selected from a hospital database. Frontal sinuses were automatically segmented through ITK-SNAP open source software and the 3D models belonging to the same patient were automatically superimposed according to the least point-to-point difference between the two surfaces. Two hundred patients were randomly selected from the same database and undergo the same procedure to perform 200 superimpositions of frontal sinuses belonging to different individuals, equally divided between males and females (mismatches). Statistically significant differences of average root mean square (RMS) point-to-point distance between the group of matches and mismatches, as well as possible differences according to sex, were assessed through Mann-Whitney U test (p < 0.05). In the group of matches, RMS ranged between 0.07 and 0.96 mm (mean RMS 0.35 ± 0.23 mm), while in the group of mismatches, it ranged between 0.96 and 10.29 mm (mean RMS 2.59 ± 1.79 mm), with a statistically significant difference (p < 0.0001). Neither the matches nor the mismatches group showed statistically significant differences according to sex. This study proposes a novel 3D approach for the assessment of anatomical uniqueness of frontal sinuses, providing both morphological and quantitative analysis, and a new method of identification based on 3D assessment of frontal sinuses, applicable when ante-mortem CT scans are available.

Segmentation procedures for the assessment of paranasal sinuses volumes

“…The second type consists of FS segmentation to get 3D models that were imported on a 3D elaboration software (VAM) to perform registration and superimposition of models belonging to the same individuals (match) and to different individuals (mismatch), to calculate the average root mean square (RMS) point to point distance and obtain a chromatic map (Figure 7). 36 RMS values were statistically significantly different when 3D models of different subjects were superimposed, therefore this procedure was proposed for human identification when antemortem imaging datasets are available.…”

Does the choice of the reference model affect the results of 3D-3D superimposition procedure? A comparison of different protocols for personal identification

“…Among the others, the forensic applications were developed as well, with special attention to the elaboration of novel methods for personal identification [2,[5][6][7]13] to overcome and improve the traditional 2D-2D comparison or superimposition, usually based on images from conventional radiology [19]. According to the state of the art, 3D-3D superimposition techniques for personal identification have been applied to faces [20], teeth [7], palatal rugae [6] and frontal [5] and sphenoid sinuses [2]. Among the others, possible applications to frontal sinuses are of special interest: In fact, the size and morphological uniqueness of frontal sinuses have been extensively investigated for personal identification [2,5,[21][22][23][24][25] as these paranasal sinuses are among the most diversified anatomical structures and present different configurations even in homozygotic twins [26].…”

“…One of the most important advantages brought about by the introduction of CT scan concerns the chance of extracting a 3D model of the chosen anatomical structure, hence allowing a comparison based on the 3D surface of the anatomical structures, rather than on the mere bi-dimensional silhouette which can be appreciated through CT slice comparison, multiplanar reformation (MPR) process [3] images or conventional radiology. This type of comparison is usually performed through 3D-3D superimposition methods, where 3D models of the anatomical structures extracted from AM and PM CT scans through segmentation [4] are superimposed on each other, with quantification of the difference between the two structures [2,[5][6][7]. This technique represents an important improvement in comparison with traditional 2D-2D comparison usually performed on images from conventional radiology.…”

“…Registration consists in the movement of one of the two models to superimpose on the other one: This procedure is automatically performed by the 3D software according to the least point-to-point distance between isolated landmarks, a limited surface or even the entire surface of the 3D models [8][9][10][11]. Among these choices, the registration according to the entire surface is preferable, as it is an automatic procedure excluding the manual interaction due to the selection of reference landmarks and surfaces [2,5].…”

“…On the other hand, the calculation of distance between two 3D models is performed through the automatic creation of a bi-univocal relationship between specific points belonging to the two models, which then results in values of maximum, minimum, mean and RMS (root mean square) point-to-point distance. These parameters are then used to discern matches and mismatches [2,[5][6][7].…”