|Year : 2017 | Volume
| Issue : 3 | Page : 120-127
Unfolding the Mysterious Path of Forensic Facial Reconstruction: Review of Different Imaging Modalities
Mansi Khatri, Deepankar Misra, Shalu Rai, Akansha Misra
Department of Oral Medicine and Radiology, Institute of Dental Studies and Technologies, Kadrabad, Modinagar, Uttar Pradesh, India
|Date of Web Publication||24-Oct-2017|
Department of Oral Medicine & Radiology, Institute of Dental Studies and Technologies, Kadrabad, Modinagar, Uttar Pradesh - 201201
Source of Support: None, Conflict of Interest: None
Forensic facial reconstruction (FFR) is the technique that combines art and science to recreate the antemortem appearance of an individual in order to recognize and identify the decedent. Over the years, many techniques of FFR and imaging modalities that provide the basic data for FFR have evolved. There is always a considerable debate and confusion regarding the advantages and limitations of these techniques. The aim of this review is to summarize the different techniques of FFR and emphasize the role of radiological techniques including cone beam computed tomography in it.
Keywords: Cone beam computed tomography, forensic facial reconstruction, three-dimensional reconstruction
|How to cite this article:|
Khatri M, Misra D, Rai S, Misra A. Unfolding the Mysterious Path of Forensic Facial Reconstruction: Review of Different Imaging Modalities. MAMC J Med Sci 2017;3:120-7
|How to cite this URL:|
Khatri M, Misra D, Rai S, Misra A. Unfolding the Mysterious Path of Forensic Facial Reconstruction: Review of Different Imaging Modalities. MAMC J Med Sci [serial online] 2017 [cited 2018 Feb 19];3:120-7. Available from: http://www.mamcjms.in/text.asp?2017/3/3/120/217116
| Introduction|| |
Over the years, many new techniques have evolved for the identification of deceased individuals. Out of these techniques, the commonly used are the comparison of antemortem and postmortem data by using clinical records, radiographs, or DNA. Still the identification of severely mutilated bodies poses a challenge. These cases limit the identification process of sex, stature, and build. Such are the cases in which facial reconstruction comes as a ray of hope. As the face of an individual has several exclusive features and, thus, is of great importance in identification and recognition of a person.
This article attempts to evaluate the efficacy of different methods and imaging modalities for forensic facial reconstruction (FFR). FFR is a technique based on both scientific standards and artistic skills to rebuild a face onto a skull to recreate the antemortem appearance of an individual in order to recognize and identify the decedent. It is also known as “forensic facial approximation.” It is seen as a connecting link between the sculpting art and science. Facial reconstruction does not bring about absolute reproduction of the facial details of the deceased, but a relative likeness is definitely achieved. The practical application of this reconstruction procedure includes the study of war or crime victims, victims of mass disaster, facial reconstruction from cadavers, and for archeological purposes. It is also used in the identification of criminals and victims.
| History of Facial Reconstruction|| |
Preservation of skull as a memory of the deceased dates back to Neolithic age, showing the essentiality of skull bone in facial appearance, but the soft tissue that includes skin, muscle, and fat is not less significant. In 1996, Farkas described how the minor variations in facial proportions can change the individuality of the face. Laura Verzé in the review on history of FFR found that the first scientific facial reconstruction was attempted by the Swiss-born German anatomist Wilhelm His in 1895.
They also found that during Renaissance period, wax models of faces were used by artists such as Michelangelo to study anatomy and for other documentation purposes. The first three–dimensional (3D) facial reconstruction was attempted by His and Kollman (1898) by reconstructing the face of a stone-age woman. Welcker, a German physiologist and anatomist, documented average tissue depth by studying cadavers. He inserted a small surgical blade into various anthropometric landmarks on the face and then measured the depth of penetration. This is called “Welcker Facial Reconstruction Technique.”
The advent of the twentieth century brought a revolution in the field of facial reconstruction, as the computers could completely change the methods of reconstruction. In the year 1916, first successful attempt of facial reconstruction by medico-legal experts was done in United States of America.,
| Methods of Facial Reconstruction|| |
The skeletal structure and osteological analyses of the skull give essential information about the facial morphology, but these are not enough when used alone. Modeling soft-tissue structures covering the skull is a significant part of the process of facial reconstruction.
FFR can be achieved by two basic techniques. These are two-dimensional (2D) and 3D facial reconstructions. Each of these techniques is further divided into (1) manual and (2) automated techniques.
Traditionally Russian and American manual methods of facial reconstruction have been described in the literature ([Figure 1]). These methods were 2D and 3D manual methods employing impressions and clay-modeling techniques. In this technique, the impressions of the skull were made, and casts were fabricated over which different landmark pins were applied. Various facial features were carved over the casts/models obtained using clay according to their anatomical positions. Later, the models were painted and hair was applied, and pictures of the final models were taken. These were relatively simple and fast reconstruction techniques that gave rough identity to an individual. Another method called Manchester method was proposed by Neave and developed by Wilkinson. These reconstruction techniques use soft facial parts made of wax and other artificial substances that are directly placed over the clay model. The photographs of the fabricated model are then taken and provided to the medico-legal experts. Although these methods were relatively simple and easy to perform, these had some disadvantages.
|Figure 1: Steps of manual method of forensic facial reconstruction: 1) Replicated skull with landmarks and already reconstructed eye socket and nose structure. 2) Advanced reconstruction of the soft facial parts. 3) Crude model of the face. (courtesy: K Kreutz et al. Dtsch Arztebl 2007;104(17):1160–5)|
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Limitations: Time consuming, technique sensitive, and expensive as the placement of modeled muscles on the skull requires lot of skill.,
3D facial reconstruction relies on the principle of building a “face” onto the skull based on the application of mean tissue thicknesses for given anatomical landmarks.
The aims of computer aided facial reconstruction are as follows:
- To make a model (actual or virtual) of the skull and arrange the soft tissues on to the prepared model of skull model.
- To form a database with average soft-tissue depth with the use of various invasive and noninvasive imaging modalities ([Figure 2]).
|Figure 2: Stepwise automated Computerized facial reconstruction. (courtesy: Claes P et al. Forensic Science International 2010;201:138–145.)|
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- Enables better visualization of the anatomical and pathological state by providing high degree of quality and resolution.
- Provides 3D imaging of 2D objects by using soft-tissue depth markers and algorithms that lay down mesh-like face over these anatomic structures.
- Completely noninvasive procedure as it allows virtual manipulation, simulation; bone sectioning in a virtual space, thus preserving the original object.
- Allows sequential other reconstructions on the same skull by using different facial templates from the same database.,
- As stated by Lee et al., computerized method of FFR uses a limited database to extract information using templates of pregenerated faces. Therefore, the end results in computer-aided facial reconstruction might be prejudiced as they would resemble the pregenerated facial template only. He further advocated that this limitation could be overcome by means of a statistical average model, prepared from average of a large database.
- It is technique sensitive, may face a number of intraoperative imaging limitations, and requires highly trained specialists for interpretation of the images obtained.
Different imaging modalities used for computer-aided facial reconstruction: For hard- and soft-tissue imaging
Nowadays, the data used are commonly obtained using computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound in which the two latter techniques are considered low risk and noninvasive.
On the contrary, such soft-tissue thickness data described above have certain limitations including the following:
- The studies previously reported reliability due to insufficient sample size.
- Previously conducted studies have restricted comparative tissue thickness data for different age groups, sex, ancestry, and build.
- There is lack of standardization of landmark sites employed by different studies to obtain soft-tissue depth data (especially when using different methodologies).
Children and adolescents undergoing the orthodontic treatment are routinely subjected to lateral cephaograms. Studies have measured the soft-tissue thickness with the help of these radiographs.
The limitations of this radiograph include soft-tissue depth data that are obtained in the midline area only. Therefore, any soft-tissue depth data lateral to these landmarks cannot be obtained and evaluated with respect to significance to age, sex, and ancestry.
Vanezis et al. and Claes et al. introduced the use of CT in FFR. In this method, all the defects and natural orifices of the skull are blocked before a scanning procedure to make an anthropological assessment of the skull. Then a virtual copy of the skull is obtained by scanning the skull using the CT. Later landmark tags are used as an aid to add soft facial parts to this virtual skull copy, and then facial features are inserted ([Figure 3]).
|Figure 3: 3Dimensional computerized facial reconstruction procedure following the combination method. (courtesy: Lee WJ et al. J Forensic Sci. March 2012;57(2): 318–327.)|
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Various standard software are available that make facial reconstruction accessible to a wide range of people without the need of experts.
- CT scanners can image both the internal hard-tissue structures and the external cutaneous covering allowing a complete assessment of facial morphology.
- It is also useful in assessment of soft-tissue thickness.
- CT scan is widely available in all areas of the world
- CT scan is also indicated routinely for many conditions, giving a chance to record soft-tissue thickness simultaneously to create a database in these patients without adding any extra radiation.
- Use of CT scan is a comparatively expensive technique.
- The devices expose patients to high amounts of radiation.
- CT craniofacial scans do not allow determining dental morphology accurately because of artifacts from metallic restorations or orthodontic brackets.
Cone beam computed tomography
The most recent modified form of CT is the cone beam CT (CBCT). It offers affordable 3D craniofacial reconstructions, with a reduced radiation exposure. CBCT systems have been developed specifically for the maxillofacial region. It was introduced in dentistry in the 1990s. Their different field of views (FOV) allows an efficient imaging of the skull including most of the landmarks used in cephalometric analysis together with a 3D volumetric rendering of the external facial surface.
In a study conducted by Sforza et al., where they reviewed various imaging technologies to study three dimensional facial morphology useful in facial reconstruction found that there was a decrease in the error rate in various studies on facial reconstruction after the use of CBCT from 2000 to 2006.
CBCT plays a significant role in a number of forensic studies today ([Figure 4]).,, This methodology utilizes various landmarks that are well defined points on the head and may be classified as cephalometric and craniofacial. Cephalometric points are corresponding marks on the surface of skin, whereas craniofacial landmarks are placed on the skull. Hwang et al. constructed a database on CBCT for facial soft-tissue thickness using midline and bilateral soft-tissue landmarks as described by De Greef et al. ([Figure 5]).
|Figure 4: 3 D reconstructed CBCT Image of skull along with facial soft tissue construction (courtesy : C. Sforza et al. Journal of Anthropological Sciences|
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|Figure 5: Craniofacial landmarks (courtesy: Galzi PJ, Mullins A (2016) Case Study: 3D Application of the Anatomical Method of Forensic Facial Reconstruction. J Forensic Res 7: 350)|
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By reducing the restoration-related artifacts, CBCT further improves accuracy of facial reconstruction for that individual by recording the site and type of the restorations. Dental fillings provide useful identification to that particular person and can be very helpful in identification on comparison with antemortem records available. Dental CBCT can readily confirm the presence of restorations and prostheses, root canal filling materials, and denture clasps and wires for enforcement in both dry- and soft-tissue-attached skulls during their forensic analysis and are thus useful in reconstruction of face.
- Noninvasive procedure producing 3D images.
- Ability to restrict size of exposed area by using different FOV thereby reducing overall radiation dose.
- Lack of superimposition.
- Absence of geometric distortion. Measurements made on the images are accurate.
- Software to analyze images are user friendly and have multiple tools that help to modify scanned images.
- It provides multiplanar reconstruction mode for images. Images can be visualized in different windows, that is, axial, coronal, saggital, and 3D-reconstructed images.
- Different rendering tools are available. These are (1) maximum intensity projection, (2) surface rendering, (3) soft-tissue density, and (4) different color schemes.
- Imaging of dentomaxillofacial region can be performed accurately avoiding image artifacts arising from metallic dental restorations and appliances. “Virtopsy” along with fluoroscopic system in CBCT was introduced by Pohlenz et al. and had the advantage of obtaining isocentric fluoroscopic images that can overcome the errors of artifacts due to metallic restorations on CBCT images and could also provide better visualization of soft tissues.
- The soft tissues are not as accurately visible in CBCT images as in MRI and ultrasonography (USG).
- The resolution of CBCT images is not as high as that of CT scan’ a the energy of x-rays used in CT scan is of high intensity compared with CBCT.
Magnetic resonance imaging
MRI was introduced in forensics for evaluation of soft-tissue depths to overcome the shortcomings of CT.
- MRI is more accurate than CT images for obtaining the soft-tissue depths.
- It is also useful to demonstrate atrophy or hypertrophy of the muscles and soft tissues as it gives immense details about structural features also.
- It is a nonionizing radiation. Hence, risk of radiation exposure hazards can be avoided.
- Aulsebrook et al. suggested that MRI gives accurate information only about soft tissues; underlying bone details may be lost.
- MRI is relatively expensive procedure.
- This modality is not readily accessible, and thus it does not contribute in forming database of the normal individuals with different facial characteristics.
Lebedinskaya et al. utilized ultrasound for measuring the soft-tissue thickness of 1695 faces of 10 different ethnic groups and contributed to form a successful database in the former Soviet Union.
- It is the safest method to measure soft-tissue depths. It has proved to be an economical and easily accessible technique.
- Nonionizing radiation, thus avoiding hazardous effects of radiation.
- Relatively cheap and easily available in clinical setups.
- It is an operator sensitive technique and requires highly trained radiologist to obtain soft-tissue data.
- USG images are of poor resolution and, once obtained, cannot be manipulated.
This is a noncontact surface imaging technique and is useful to capture 3D images of the object ([Figure 6]).
|Figure 6: Three-dimensional reproduction of the facial soft tissues of a woman obtained by laser scanning (three-dimensional polygonal mesh, and homogenous surface rendering) (courtesy : C. Sforza et al. Journal of Anthropological Sciences. 2013;91:159–184.)|
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In this method, the image of face is obtained after a 360 degree rotation. A “wireframe” matrix is constructed over the image and tissue-depth measurements are obtained. Digitized images of facial features not predicted by the skull contours (nose, eyes, and mouth) are later added by separate means to generate a wireframe face on which color and texture are subsequently applied to achieve the final mode of reconstructed face.
- Although laser scanning is a general technique for scanning the outer surface of 3D objects, the skull surface is very complex to reconstruct on the basis of laserline projections.
- These scanners have a limited scanning resolution, such that very small details of the skull are not acquired or copied.
Digital stereophotogrammetry technology
This is a useful computer-aided technology of FFR, which provides superior quality “external surface” photographs, coupling a color facial image (texture) with a 3D mesh of the analyzed surface., These systems are capable of accurately reproducing the surface geometry of the face and map realistic color and texture data onto the geometric shape resulting in a life-like appearance ([Figure 7]).
|Figure 7: Three-dimensional reproduction of the facial soft tissues of a normal 20-y old woman obtained by a stereophotogrammety (courtesy : C. Sforza et al. Journal of Anthropological Sciences. 2013;91:159–184.)|
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- It is a safe, noninvasive, fast (typical scan time 2 ms) modality.
- It does not require a physical contact between the instrument and the face.
- It can record and reproduce only the external body surface permitting 3D measurements of the external (soft tissues, in the living persons) structures.
Cevidanes et al. and Hammond and Suttie described fusion imaging for complete assessment of patients during FFR using combination of CT scans and 3D facial images obtained by optical method. The CT scans provide a detailed image of the skeletal surfaces and volumes, and 3D facial images offer additional information about color and surface texture as well as higher resolution of soft-tissue surfaces.
| Conclusion|| |
After weighing the benefits and limitations of each modality, we conclude that CBCT is useful for capturing quantitative information about the facial soft tissues and hard tissues as it provides distinct advantages with minimal invasiveness, quick capture speeds (often under one second), high precision, and accuracy and the ability to archive images for subsequent analyses.,, These systems provide safe, speedy, and reliable data at the time of mass disaster scenarios and crime scenes.
Faces reconstructed with this technique closely resemble the face of the individual. Thus, after detailed evaluation, CBCT emerged as the practically most useful imaging modality for FFR.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]