Three-dimensional imaging of human cutaneous forearm
bite marks in human volunteers over a 5 day period
Mhairi de Sainte Croix [email protected]
Introduction
Data Acquisition and Analysis
Human bite marks are often sustained
during sexual, domestic or child abuse.
Currently, analysis of these marks involves
two-dimensional digital photography
techniques along with an expert forensic
odontologist opinion. When shown in court,
the images often focus too closely on the
bite mark and give little context to the
anatomical location of the injury. Additionally,
it is sometimes days before an examination
is carried out, allowing the injury pattern
and colour to alter, making it harder to
analyse. Our aim is to investigate 3D imaging
of bite marks and develop a reliable procedure
for experimental recreation.
The images are captured using a DI3D photogrammertry system, outputting a series of textured 3D models which correspond to each time
interval. The models are loaded in Autodesk Maya to complete position alignment adjustments where necessary, without any changes to
the geometry or texture of the original images. Autodesk Maya is then used to create virtual camera movements and seamless transition
between bite mark images over time. Rendering is completed using Maya’s Software Renderer, without additional lighting, again preserving
the original images. The final rendered image sequences are loaded into Adobe After Effects where they are placed on a timeline. It is here
where any extra 2D imagery (created in Adobe Photoshop) such as logos and timeline indicators are added. The completed animation
is exported as a video, ready for presentation.
Procedure
Preliminary Conclusions
Volunteers will be recruited through the Forensic and Legal Medicine BMSc course for this study. All volunteers will give fully
informed written consent and complete an anonymous medical questionnaire to assess their suitability. Participants identified as
having bleeding disorders or those who take anti-thrombolytic medications will be excluded from the study. This study will use a
recognised procedure for causing a bite mark and uses the same apparatus and techniques for causing a bite mark as 2013 study
on experimental bite marks by Chinni and Forgie1.
Before receiving an experimental bite mark, the forearm will be photographed as a control image. The arm will then be placed
within the frame, resting upon a secured, custom made arm board, with muscles relaxed. Dental casts mounted on a bite articulator
create the bite mark, while weight applied to the surrounding frame provides constant force for 15 seconds. The forearm maintains
constant position within the frame by gripping the arm board. After 15 seconds the weight is removed and the arm photographed
at 0 hours post-infliction. Due to the importance of taking photographs of injuries with the relevant body part in the same position
as it would have been during the incident, the forearm will be photographed while gripping the same arm board, this time mounted
on a tripod, in front of the photogrammetry system.
Subsequent images will then be taken at 3, 6, 24, 48, 72 and 96 hours post-infliction. In addition to these 3D images, once bruising
has become apparent 2D photographs will also be taken using a cross-polarisation lens filter on a DSLR camera to investigate its
use in highlighting subcutaneous bruising more so than regular imaging.
From the initial trial of the equipment and imaging
technique, progress is positive. The first change made
was to increase the weight sequentially, beginning at 10kg
and ending with 20kg. The latter gave a significantly longer
lasting bite mark that was able to be photographed for the
full 96 hour period. Secondly, we realised that placement
of the bite was crucial in determining the persistence of the
resulting mark. In future the procedure shall ensure that the
bite occurs over a more proximal region of the anterior
forearm than distal.
References
1Chinni,
S, Al-Ibrahim, A and Forgie, A. (2013) ‘A simple, safe, reliable and
reproducible mechanism for producing experimental bitemarks’, Journal of
Forensic Odonto-Stomatology. 31(1). pp 22-29.
Acknowledgments
With special thanks to supervisors Dr Ronnie Lowe, Dr Andrew Forgie for their continuing guidance
throughout this project. Additional thanks to Scott Dunbar, Dylan Gauld and the 3D Visualisation
Research Lab.