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The Use of X-ray Computed Tomography Technologies in Forensic Anthropology.

Introduction

Postmortem radiologic imaging is indisputably valuable to medicolegal death investigations. As a non-destructive and non-invasive method of examining human remains, radiology allows visualization and diagnosis of internal body structures and can facilitate sorting human remains from nonhuman or non-skeletal material, personal identification, the assessment of trauma, and determination of cause of death in support of a forensic autopsy (Aghayev et al. 2008; Dirnhofer et al. 2006; Giraudo et al. 2011; Levy et al. 2006; Levy et al. 2007; Thali et al. 2010). Although traditional 2D radiography (film or digital) is still more widely available and more frequently utilized in postmortem surveys, the use of X-ray computed tomography (CT), which allows 3D reconstruction, visualization, and analysis of remains, has significantly increased in recent years in forensic death investigation (Baglivo et al. 2013; Hatch et al. 2014; Lynn & Fairgrieve 2009; Robson Brown et al. 2011; Thali et al. 2003a; Wade et al. 2011). CT technology is ideal for conducting nondestructive, non-invasive, and non-contact external and internal examination and measurement of bones and other evidence, especially when evidence must remain unmodified for future examination. Moreover, this can be done without the silhouette effect and superimposition of structures common in standard 2D radiography (Goldman 2007). CT is also becoming more frequently used in medical diagnostics, especially in surveys of the head, making CT scans more often available as a source of antemortem skeletal information in identification comparisons (Brough et al. 2015).

In many parts of Europe, the use of postmortem CT (PMCT) to supplement (or in some cases even replace) autopsy is rather routine (O'Donnell et al. 2007; Thali et al. 2003a, 2007). In Switzerland, for example, PMCT is performed in nearly 100% of death investigation cases (Thali et al. 2007). In the United States only a handful of medical examiners' offices routinely perform PMCT, and its use in anthropological investigations is even less frequent.

Forensic anthropological examinations are performed in a wide variety of settings. While some occur within a medical examiner's office, others take place in laboratories external to the medical examiner's office, including university, museum, and government laboratory-based operations. Anthropologists are commonly consulted to assist in matters of trauma analysis as well as personal identification, often through the use of comparative radiology, which is widely regarded as an effective and reliable means of personal identification (Christensen et al. 2014; Hatch et al. 2014). An advantage of PMCT in identification cases is that scans can be reformatted or rendered to match almost any antemortem medical image (Hatch et al. 2014), reducing the need for multiple imaging modalities. This is especially advantageous because of the wide variety of antemortem images that may be available for comparison such as 2D medical and dental radiographs from various projections, CT, or MRI. Likewise, PMCT is superior to 2D radiography for visualizing and analyzing bone trauma and patterned tool marks impressions, taphonomic effects, and variation of internal bone structures (Cattaneo et al. 2006; Robson Brown et al. 2011; Thali et al. 2003a).

Several types of CT systems are available today, including traditional medical or clinical scanners, submicron CT and nano CT scanners (also referred to as 3D X-ray microscopes), and industrial CT scanners. Submicron and nano CT systems use the same technology as medical CT scanners but at a much smaller scale that allows for greatly increased resolution --as great as 50 nm (0.00005 mm) resolution in some cases. However, these systems are typically only used to analyze very small objects (usually less than 20 mm) for research and are not practical for use by forensic anthropologists in PMCT examination of whole bones. While forensic anthropologists sometimes use medical CT systems to examine skeletal remains, a practical alternative for forensic anthropologists may be the use of industrial CT systems. These scanners are used to examine medium- to large-sized objects (up to 80 cm x 120 cm) with much greater spatial and contrast resolution than can be achieved with medical CT systems.

In this review we compare industrial and medical CT systems and describe some of the advantages (e.g., greater spatial and contrast resolution, geometric magnification, image quality and unsharpness, longer scan times) and limitations (i.e., cabinet size, object size restrictions, reconstruction artifacts and noise) to using industrial CT systems for PMCT inspection of skeletal remains by forensic anthropologists. In addition, we provide examples of industrial CT use in the FBI Laboratory and the Grady Early Forensic Anthropology Laboratory at Texas State University. Finally, we provide examples of some of the procedures or applications for the documentation, analysis, and visual representation that can benefit forensic anthropologists using PMCT in medicolegal death investigations. Overall, we aim to familiarize forensic anthropologists with some of the different CT technologies available and show how they may be useful forensic anthropological analyses.

Industrial CT Scanners

Although most people associate CT with medical and dental applications, these are not the only markets. On the contrary, CT is used for non-destructive testing of external and internal structures and components in a wide variety of industries, including aerospace, automotive, foundry, electronics, engineering, food, manufacturing, medical devices, metrology, military and defense, and plastics. Common industrial applications include inspection of parts for voids, cracks, or other defects; failure analysis; internal and external part measurement; reverse engineering; and 3D digitization (Castillo 2012). Virtually all of the CT systems used in these industries can be adjusted to parameters suitable for examining bone and can be used effectively by forensic anthropologists for research, digital reconstruction of fragmented bones, trauma analysis, biological profile development, and identification purposes.

The main components of an industrial CT system typically include the X-ray tube (radiation source), movable X-ray detector, and rotational stage/platform that are contained in a radiation-shielded cabinet (Noel 2008). Unlike open-tube CT systems, which require a specialized room with lead-lined walls, all the components of industrial CT systems are contained in the cabinet and can be used safely in public spaces of the laboratory. Hence they do not require specialized rooms to meet state and federal radiation safety regulations.

Medical CT systems typically use a fan-shaped X-ray beam and a line-type detector (single row of pixels) that are rigidly fixed on a gantry that rotates around the patient or object of interest. The table then moves forward to obtain scans in a spiral or helical progression. The system produces slices in the axial plane with only a small portion of the patient or object in the field of view (FOV). During reconstruction the slices are sequentially stacked by the computer.

In most cases, industrial systems use a cone-shaped X-ray beam and a fat-panel detector (matrix of pixels). However, collimated fan-shaped X-ray beams with a line-type detector are used in some systems. In order to achieve the desired orientation and magnification of the item being imaged, several of the components can be repositioned. The detector can be moved forward and backward as well as up and down. The rotational stage moves forward and backward as well as right and left. The X-ray tube is commonly restricted to motions in the up and down direction. Conebeam radiology emits radiation in the form of a cone from a small circular focal spot. To collect scans, the object of interest is placed on the rotational stage between the radiation source and the detector (Figure 1). The entire object is in the FOV in cone beam CT (CBCT). Geometric magnification of the object of interest can be obtained by adjusting the distance of the object from the X-ray source and the distance of the object from the detector. The X-ray photons emitted from the source pass through the object of interest while a sequence of 2D images is captured by the detector over a 360[degrees] rotation. Depending on the resolution needed, the number of images captured for a single CT scan typically range from 360 to 3,600, but more images can be captured in some applications to reduce noise (i.e., electronic interference that can degrade the image) (Noel 2008). After image acquisition, reconstruction algorithm software is used to reconstruct the 3D CT volume based on the entirety of the 2D images (Feldkamp et al. 1984). The reconstructed volume can be manipulated, and cutting planes can be inserted to visualize or measure the external and internal structures from any orientation. Files can be exported in a variety of nonproprietary formats, including DICONDE (a DICOM-compatible format), and therefore viewed and shared using standard medical DICOM viewers such as OsiriX and Mimics.

There are multiple advantages to using industrial CT system for PMCT in forensic anthropology. Some of these advantages include (1) greater penetration of dense materials such as dental fillings and medical devices than is possible with medical CT systems, (2) increased spatial and contrast resolution compared to medical CT systems, and (3) greater image quality than possible with medical CT systems or other 3D imaging methods. In addition, some industrial units are much smaller, more affordable, and possibly more accessible to smaller anthropology laboratories than medical CT systems, and they can be used safely in public spaces.

X-ray Source Penetration

Compared to medical CT scanners, industrial CT systems allow for greater penetration of dense materials such as dental fillings, medical devices, and the long edges of bone encountered by forensic anthropologists. Penetration is necessary to acquire quality data of structures (especially those with thicker edges) and is dependent on the energy of the photons (i.e., the voltage of the radiation source). Medical CT systems are commonly limited to certain dosages or tailored to specific diagnostic applications. Typically, the X-ray sources of medical CT systems are limited to maximum operating voltages of 120-140 kV, with an average operating energy nearer 70 kV, but industrial CT systems can have X-ray energies capabilities of 450 kV and higher. Given that health concerns (e.g., radiation dose) of the subject are not a problem in PMCT, industrial CT technologies permit the use of higher voltage and longer scan times for greater penetration of dense objects. For example, the ray photons must pass through a sizable thickness of bone on the edges of a cranium (Figure 2), which requires greater penetration to obtain quality images. In most cases, however, voltages greater than 225 kV are not needed for the examination of skeletal remains, which is a relatively low density material compared to metals used in industry. Penetration can also be increased by filtering or attenuating out low-energy X-ray photons. Filtering is easily accomplished on industrial CT scanners by adding filters such as copper, aluminum, or other metallic materials to the X-ray source to remove low-energy photons. The removal of low-energy or soft photons hardens the beam and increases penetration. In addition, scattering of photons (bouncing of photons off high density materials) can be reduced by putting a filter on the detector. If greater filtering is needed the bone can also be placed within a metallic cylinder to attenuate low-energy photons hitting the object of interest on the front side (tube side) and reducing scatter on the back side (detector side).

Resolution

The three types of resolution in CT are temporal, spatial, and contrast (Lin & Alessio 2009). Temporal resolution allows for the ability to resolve moving objects without blur. In medical CT, temporal resolution is important because the patient moves while breathing, and the heart beats. Obviously, temporal resolution is generally not of importance to forensic anthropologists examining skeletal remains provided the specimens are properly stabilized to prevent movement during the CT scan. Spatial resolution reflects the ability of the CT system to distinguish details such as distinct edges or differentiation between two or more adjacent features in the CT reconstruction. Contrast resolution is the ability to distinguish between features or objects based on density or attenuation properties. The greater the contrast, the easier it is to distinguish between structures with similar attenuation properties or material density. In CT, high-density objects are generally displayed as white, low-density materials are black, and intermediate-density structures are displayed as varying shades of gray. Both spatial and contrast resolution are important to the forensic anthropologist; unfortunately, however, there is a constant trade-off between spatial and contrast resolution when performing CT. The investigators must therefore balance the need for spatial and contrast resolution based on the features they want to observe.

Industrial CT systems provide considerably greater spatial resolution than medical CT units. For skeletal remains a resolution of 50 [micro]m (0.05 mm) or higher is preferred to differentiate and analyze trabeculae in bone, which is difficult to obtain using a medical CT system. Forensic anthropologists who have experience with medical CT scanning often think about resolution in terms of slice thickness. Higher resolution results in thinner slices that permit greater differentiation of closely associated structures such as trabeculae. In medical CT systems the slice thickness generally ranges from 0.625 mm to 3.0 mm, while the slice thickness from high-resolution industrial scanners is commonly less than 45 [micro]m (0.045 mm). Figures 3 and 4 provide examples of the greater spatial resolution that can be obtained using industrial CT systems. Such resolution would likely improve the ability to detect small fractures in forensic anthropological cases, since some very small fractures may be less than a single voxel in width using a medical CT scanner.

Spatial resolution in CT is primarily determined by the pixel size of the detector, the ratio of the distance between the source and the object and the object and the detector (geometric magnification), and the X-ray focal spot size (Goldman 2007; Romans 2011; Staude & Goebbels 2011). Industrial CT systems generally have detectors with square pixel sizes ranging from 100 to 400 [micro]m (0.1-0.4 mm), whereas medical CT systems have a pixel pitch of 0.625 mm or greater. The smaller the pixel size, the greater the spatial resolution that can be obtained. Focal spot size is the area on the radiation source where the electrons are converted to X-rays. The smaller the focal spot size the greater the resolution that can be obtained. Lower voltage industrial CT systems ([less than or equal to] 225 kV) can be equipped with nano-, micro-, or mini-focal cone tubes that provide superb spatial resolution with less geometric unsharpness (loss of definition). Micro-focus tubes can produce resolutions of less than 5 [micro]m (0.005 mm). In medical CT the focal spot size is usually 1 mm or greater. Medical CT systems also generally have a large field of view for imaging whole bodies with a rigidly fixed distance between the radiation source and the detector. As a result, the spatial resolution does not change depending on the size of the object of interest (Goldman 2007). However, in industrial CT systems the distance between the source and the object and the object and the detector can be manipulated to obtain geometric magnification and greater spatial resolution. For example, using a 200 [micro]m detector pixel size a 50 [micro]m resolution can be achieved with a 4x magnification. For most human bones a magnification of 40x can be obtained using industrial CT systems by focusing on the specific region of interest.

CT in general is ideal for visualizing low-contrast structures in an object, but the density and thickness of the material is a key component to contrast resolution (Goldman 2007; Romans 2011). Less dense and thinner materials have greater contrast sensitivity. Contrast resolution can be improved by any method that allows more photons to reach the detector. This is usually accomplished by collimation of the cone of radiation, decreasing the radiation voltage and increasing the current, using fixtures that produce less scatter, filtering to reduce X-ray scatter, binning pixels, or moving the detector closer to the source (Goldman 2007; Romans 2011; Staude & Goebbels 2011). Increasing the current strengthens the signal by intensifying the X-ray energy. Moving the detector closer to the radiation source increases the number of photons that hit the detector, but it reduces geometric magnification and therefore spatial resolution. This cannot be accomplished using medical CT systems. In most cases very little filtering is needed for bone, but if necessary metallic filters can be easily applied to the X-ray tube or detector. Many industrial CT systems also have the ability to pixel bin. Pixel binning is when the detector combines a 2 x 2 matrix of pixels to produce a larger pixel (Seeram 2016). For example, a 100 [micro]m detector can be converted to a 200 [micro]m detector to improve signal level and contrast resolution. Obviously, the drawback to pixel binning is a reduction in spatial resolution. Pixel binning is especially useful for improving contrast when higher kV is needed to penetrate dense objects or regions. Finally, contrast increases with the bit depth of the detector. The larger the bit depth, the greater the number of grayscale levels in the reconstructed image. Most industrial CT systems use 16-bit detectors that allow for 65,536 gray levels.

Image Quality and Visualization

One advantage of CT is the ability to easily visualize structures without superimposition or silhouette effects associated with traditional 2D radiography. However, if traditional radiography is necessary, it can be performed with industrial CT systems (Figure 5). In fact, real-time 2D imaging can be performed as the object rotates with industrial CBCT. In addition to the single view of radiographs, CT 3D reconstruction surface can be viewed from any orientation by adding clipping planes (Schorner 2012). The clipping planes allow investigators to scroll through the object to attain the best view of the region or structure of interest, which can be useful in the analysis of skeletal trauma or in examining features that may be useful for personal identification.

Industrial CT systems allow for superior image quality because of the high spatial and contrast resolution. As with medical CT systems, artifacts such as beam hardening, rings, and streaks can reduce the quality of the image (Scarfe & Farman 2008). Image quality can be improved by increasing the number of projections or images acquired, using frame averaging, using scanning modalities such as step-scanning, and using filtering algorithms during reconstruction. During the 360[degrees] rotation of the object, the number of images collected can be significantly increased using industrial CT systems, whereas in most cases the number of images that can be collected is fixed for medical CT systems. Most commonly, the number of images acquired by industrial CT as the object being scanned rotates 360[degrees] is 1,000 to 15,000, depending on the size of the detector and the contrast needed. Furthermore, scan modalities such as step-scanning, where the rotation stage stops before each image acquisition, reduces motion blur. Other parameters such as frame-averaging and post-processing filters can reduce noise. Prior to scanning with an industrial CT system, live or real-time averaging can be viewed in digital radiography to visualize how parameters such as the number of frames averaged affect the quality of the image.

Limitations

It should be noted that there are also several limitations of using industrial CT systems for anthropological applications. First, many industrial CT scanners are rather large, with steel and lead cabinets (100 square feet and 8 feet high) that can weigh more than 40,000 pounds. Another limitation of industrial CT is that possible object size is generally limited to the dimensions of the X-ray detector, making industrial CT systems impractical for whole-body imaging. However, helical or mosaic scan modalities can be used to increase the maximum size of the object that can be examined and are useful for imaging of entire long bones and whole pelvises (Cnudde & Boone 2013). Helical and mosaic modalities can also be used to increase magnification of small objects without loss of image quality. Finally, artifacts or distortion in the image that are not associated with the object being scanned can occur in CT. Common reconstruction artifacts include beam hardening, ring artifacts, and parallax, which have been described elsewhere (Cnudde & Boone 2013; Goldman 2007; Sinha et al. 2016). Fortunately, several pre-scanning and post-processing methods are available to mitigate these problems.

Examples of Industrial CT Systems in Anthropology Laboratories

Currently, the Federal Bureau of Investigation (FBI) Laboratory and Texas State University's Grady Early Forensic Anthropology Laboratory both utilize the North Star Imaging X5000 CT scanner (Figure 6) in postmortem forensic assessments of skeletal remains. These units are marketed primarily for nonmedical, industrial applications but are readily adaptable to use in anthropological settings. The large envelope allows for analysis of small to large bones.

Both the FBI's and Texas State University's units employ a cone beam microfocus X-ray tube with an adjustable operating voltage of 10-225 kV and a 16" x 16" 200 [micro]m (2,048 x 2,048 pixel matrix) PerkinElmer 16-bit fat-panel detector that can detect up to 30 frames per second. These machines are easily capable of obtaining a < 50 [micro]m resolution needed to visualize and analyze trabecular structure in bone. Under optimal conditions the unit can produce resolutions of approximately 5 [micro]m on small bones. The cabinet is 107 inches wide, 80 inches deep, and 92 inches tall. The part envelope can accommodate objects 32 inches in diameter and 48 inches tall. The accompanying workstation includes acquisition and proprietary reconstruction software.

A significant advantage of a CT system like the NSI X5000 in a setting such as the FBI Laboratory and Texas State University is that, unlike a medical CT, which is configured and dedicated to one or a few specific purposes, the machine has many other potential forensic applications. These alternative uses ensure a high utilization rate and more readily justifies the costs of its purchase and operation. In the FBI Laboratory the NSI system supports forensic examinations of manufactured products (Figure 7), objects with hidden compartments, explosive devices, timers, switches, airplane components, electronics, firearms and suppressors, and anthropological specimens of forensic interest. In addition, any law enforcement or medicolegal agency desiring a CT examination of skeletal remains as part of a medicolegal or criminal investigation may send specimens to the FBI for anthropological examination and/or CT scanning (all such examinations at the FBI Laboratory are provided free of charge). At Texas State University the CT system serves as shared equipment that can be used by researchers in a variety of academic disciplines. In anthropology the system is primarily used for forensic anthropology casework, skeletal biology research, 3D digitization, and internal structure measurements. Students trained to use the system also gain significant technological skills that benefit them throughout their careers. Texas State University also conducts CT for clients with academic, forensic, or industrial needs. Similarly, the FBI Laboratory occasionally performs CT analysis for other government agencies that have compelling needs and lack comparable capabilities.

Besides these two organizations, numerous other universities, museums, and businesses have high-resolution industrial CT systems that may offer scanning services. In most cases these organizations charge hourly to include the time to mount specimens, image data acquisition, and calibration of the scanner. Data acquisition (scan times) can vary considerably depending on the specimen size and resolution needed and can range from a few minutes to multiple hours. Image processing and analysis are usually charged separately.

The Use of Industrial CT in Forensic Anthropology

High-resolution PMCT has numerous potential applications in forensic anthropology. The purpose of the review is not to provide an exhaustive list of all possible usages but to highlight some of the casework and research applications. High-resolution PMCT is ideal for digital preservation of evidence and non-destructive 3D analyses that can be used to develop a biological profile, aid in identification, and interpret taphonomic and traumatic damage to bones. CT reconstructions can also be used for additive manufacturing (3D printing) to aid in 3D facial approximation and courtroom presentation.

Digital Images to Preserve Evidence

CT reconstructions can be used to accurately document bone and other evidence without damaging the specimen. Skulls and other bones with trauma and taphonomic damage, especially those with some soft tissue retention, can be scanned prior to processing to record the original damage and specimen integrity (Figure 8). The images can be transferred to other investigators or used for reevaluation at a later date (Errickson et al. 2014).

There are two main advantages to using CT over other external 3D optical or laser scanning methods for documentation. First, CT provides excellent resolution of both external and internal structure of the object of interest, whereas external scanners only record the surface features. Second, the quality of the images is not affected by the shape of the object or its surface characteristics (color, reflectivity, transparency, etc.). Depending on the shape of the object, valuable data can be lost with external 3D scanners when there are obstructions between the surface and the scanner's line of site (Errickson et al. 2014). However, since photons penetrate the surface during CT, there is no line-of-sight problem, and collection of the necessary data for reconstruction of obstructed features and shadow areas is not a problem.

3D Visualization, Reconstruction, and Additive Manufacturing

High-resolution CT reconstructions are ideal for visual inspection of bone and examining detailed anatomical structures, bone fractures, and pathologies. Figure 9 provides an illustration of visualization of internal and external structures of a human skull using clipping planes that can be obtained with high-resolution CT systems. Images can then be saved and used in forensic anthropological reports or for courtroom testimony. Errickson et al. (2014:135) point out that virtual images are ideal for court presentation because they provide accurate representations of the original specimen, can be manipulated in virtual space, and are "considerably less emotional than an autopsy photograph."

Visualization can also be improved by adding color and transparency with the CT software or by uploading the volume into graphics visualization software packages. Color is especially valuable for visualizing trauma, teeth, sinuses, or other features of interest (Figures 10 and 11). Multiple surfaces can also be viewed simultaneously, and surface transparency can be used to visualize internal structures (Figures 12 and 13).

The software and computers associated with most industrial CT systems include the ability to generate 3D surface renderings as point cloud or triangular mesh model files that can be exported to a 3D printer (Figure 14). The anatomically accurate and life-sized replica can be used in the courtroom to illustrate anatomical features or to demonstrate injury patterns with much greater demonstrative value than 2D photographs (Errickson et al. 2014). The 3D reconstruction can also be used as the basis for facial approximations or in skull-photo superimposition to exclude possible missing individuals (Lorkiewicz-Muszynska et al. 2013). The advantage of 3D replicas based on CT images compared to other sources such as white-light scanners is that the replica includes the internal structures of the bone. The 3D print based on CT images can be sectioned to examine internal structure and used during court appearances to help illustrate specific features without bringing the actual bones into the courtroom (Figure 15). For trauma cases with complete or comminuted fractures, replicas could aid in physical reconstruction of the scanned bone fragments or used for testimony and second opinions without jeopardizing the chain of custody.

CT reconstructions can also be used to digitally segment and reconstruct crushed or badly broken bones. Using graphics software, the CT scans can be processed to separate and label individual bones, and then surface models can be created for each bone. An algorithm can reft the segments (Mahfouz et al. 2016). CT scans of manually reconstructed bones can also serve to document and preserve reconstructions, especially in cases where bones and/or reconstructions are fragile (Figure 16).

Measurement of Internal and External Structures

Another use of CT reconstructions is to collect skeletal dimensions, and the agreement between dry bone and CT-derived measurements has been shown to be high (e.g., Stull et al. 2014). Because of the greater spatial resolution, industrial CT systems can provide much greater measurement accuracy and precision than medical systems. The advantage for forensic anthropologists is that any definable dimension on a skull or other bone can be measured using the 3D reconstruction. In addition, internal structures and angles such as femoral neck torsion can be accurately measured using CT (Mesqarzadeh et al. 1987). Moreover, CT scans allow the measurement not only of linear dimensions but also of volumes and surface areas.

Trauma and Taphonomic Analysis

Reconstructed CT volumes are ideal for the examination of trauma and providing information about the cause and manner of death. CT is excellent for detecting and measuring bone fractures as well as mapping fracture patterns that provide information about the forces and are useful in the analysis of tool-inflicted injuries. High-resolution CT can be used effectively to diagnose diseases (Ruhli et al. 2007; Wade et al. 2011), and CT reconstructions can be valuable in the evaluation sharp-force, blunt-force, and chop injuries (Robson Brown et al. 2011; Thali et al. 2003b; Wittschieber et al. 2016) (Figures 17-18). High-resolution CT also permits the association of bone alterations to the causal instrument, determination of the number of injuries, and the direction and angles of impact (Thali et al. 2003b; Wittschieber et al. 2016). Likewise, CT can be used to obtain high-resolution images of fracture surfaces to help evaluate taphonomic versus perimortem damage (Hentschel 2014; Figure 19).

Biological Profile and Identification

Images obtained from high-resolution CT are also useful for development of the biological profile. For example, age estimation of juveniles is much easier because the unerupted dentition can be viewed, measured, and examined (Figures 20 and 21). In addition, quantitative methods are being developed that model the bone surfaces of the pubic symphysis and other bones and provide an estimate of age that meets many of the expected evidence standards (Slice & Algee-Hewitt 2015). Point cloud data can also be used to obtain measurements for ancestry, sex, and stature estimation (Giurazza et al. 2012; Hale et al. 2014; Kanthem et al. 2015).

High-resolution CT scans are also useful for documenting, describing, and analyzing characteristics and structures that aid in exclusion or identification (Figures 22-24) and for comparison of antemortem and postmortem records for positive identification (Dedouit et al. 2014; Haglund & Fligner 1993; O'Donnell et al. 2011; Silva et al. 2011; Smith et al. 2002; Tatlisumak et al. 2011). CT images are superior to conventional radiography because structures are not superimposed in CT images, the structure can be viewed from multiple orientations, and anatomical structure can be precisely located. O'Donnell et al. (2011) report that CT contributed to the identification of 161 out of 164 missing persons in a mass disaster case in Australia. They also report that CT images of the bodies in body bags provided useful preautopsy information such as the presence of nonhuman remains, commingling, disfguration of bodies, and missing elements.

Research

Application of high-resolution CT has great potential usefulness for the types of research conducted by forensic anthropologists. In biological anthropology, CT has primarily been used in bone biomechanical and paleopathology studies (Barak et al. 2011; Frost 1999; Gosman & Ketcham 2009; Keaveny et al. 2001; Kivell 2016; Morgan 2014; Raichlen et al. 2015; Ruhli et al. 2007; Saers et al. 2016Wade et al. 2011). However, the range of study types that can be conducted in forensic anthropology is nearly endless. High- resolution CT has significant potential for studies on trauma patterns and mechanisms, taphonomic effects on bone, pathology diagnosis, bone growth and development, and methods for estimating the biological profile and positive identification. At Texas State University the CT system is currently being used in studies comparing long bone trabecular architecture of obese and non-obese (Gleiber et al. 2016) and mobility-impaired individuals (Gleiber & Wescott 2017). The system is also being used to examine changes in the trabecular structure and symphyseal face of the pubic bone associated with pelvic instability (Galea 2016) and the sternal rib end morphology to develop a quantitative method for the estimation of age (Schaefer 2016).

Conclusions

Computed tomography is an extremely useful tool in postmortem forensic examinations, and the use of CT for documentation, preservation, examination, and diagnosis in forensic anthropological examinations is strongly recommended and encouraged. In casework, images acquired via CT can be used to document the original condition of the remains, help develop the biological profile, examine unique individual characteristics, and be compared with a number of different imaging modalities (conventional X-ray, MRI, PET, and other) for comparison of antemortem and postmortem anatomical structures for positive identification. Virtual reconstructions are also ideal for courtroom presentation to help in the visualization of traumatic injuries or unique individual characteristics. The virtual images or 3D printed replicas produced from CT have extremely high demonstrative value without the emotive effect of autopsy photographs or actual specimens. The digital images can also be shared with other colleagues for a second opinion without chain-of-custody issues or referred to prior to trial to refresh the investigator's memory.

Forensic anthropologists may have a wider variety of CT options available to them than they are commonly aware of. In fact, the use of industrial CT systems for forensic anthropological research and casework has several advantages over medical CT systems. These systems have greater spatial and contrast resolution than is possible with traditional medical CT systems because of the greater flexibility in parameter settings, and the image quality is far superior to conventional radiography. Virtually any type of industrial CT scanner can be adjusted to effectively scan skeletal material, so anthropologists are not limited to medical CT in their examinations.

Not only is there variety in the types of CT scanners that laboratories could consider purchasing for themselves, but they may be able to leverage resources that already exist in their vicinity by developing relationships or partnerships with professionals in other offices or industries. Other organizations or industries may also find these opportunities educational, or may simply be happy to assist for the satisfaction of aiding with a forensic investigation. The use of more versatile machines may make it more cost- effective for a laboratory to purchase them, especially in cases where the device can serve multiple disciplines, thus reducing the potential need for and cost of multiple devices.

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Angi M. Christensen, PhD (a*) * Michael A. Smith, PhD (a) * Devora S. Gleiber, BA (b) * Deborah L. Cunningham, PhD (b) * Daniel J. Wescott, PhD (b)

(a) Federal Bureau of Investigation Laboratory, 2501 Investigation Parkway, Quantico, VA 22135, USA

(b) Department of Anthropology, Texas State University, 601 University Drive, San Marcos, TX 78666, USA

(*) Correspondence to: Angi M. Christensen, Federal Bureau of Investigation Laboratory, 2501 Investigation Parkway, Quantico, VA 22135, USA

E-mail: Angi.Christensen@ic.fbi.gov

Disclaimer: The views expressed are those of the authors and do not necessarily reflect the official policy or position of the FBI. Names of commercial manufacturers are provided for identification purposes only, and inclusion does not imply endorsement of the manufacturer or its products or services by the FBI.

Received 9 March 2017; Revised 14 April 2017; Accepted 10 May 2017

Forensic Anthropology Vol. 1, No. 2: 141-142

DOI 10.5744/fa.2018.0013
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Author:Christensen, Angi M.; Smith, Michael A.; Gleiber, Devora S.; Cunningham, Deborah L.; Wescott, Daniel
Publication:Forensic Anthropology
Article Type:Report
Date:Mar 22, 2018
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