Digital Radiography in Forensic Odontology
Sometime in the middle of a weekday morning next month, two furniture vans believed operated by terrorists enter opposite ends of New York’s Lincoln tunnel simultaneously. within seconds, both vehicles explode violently, partially collapsing the portals. Devastating fires spread the length of the tunnel from vehicle to vehicle, blocking the escape of those trapped between the blasts.
Emergency crews fight desperately to suppress the inferno, but over 250 people perish, either in the flames, the fumes, or trampled as surviving motorists stampede to avoid suffocation. When located, most of the victims are unrecognizable. A forensic odontology team is summoned, whose job is to identify human remains as quickly as possible. The team arrives with a recently adopted dental identification technology called digital dental radiography.
Digital radiography, used for a decade or more by radiologists in most large hospitals, has become the solution of choice in mass casualty situations where the number of victims overwhelms the ability of forensic medical examiners to quickly and accurately identify decedents.
“Digital radiography dramatically increases the quality and timeliness associated with the use of dental x-rays in forensic dental victim identifications, particularly when combined with computer-based dental chart matching software,” said Richard A. Weems, DMD, director of Oral and Maxillofacial Radiology at the University of Alabama, Birmingham, School of Dentistry. Weems was a member of the odontology team working the aftermath of the 2001 World Trade Center disaster.
Mass disasters such as the World Trade Center and the 1995 Oklahoma City bombing demonstrate that when the victims number in the hundreds or thousands the traditional plain film method of exposing radiographs and manually comparing dental records to determine identities is complicated, time-consuming, and sometimes even careless.
Weems said the biggest advantages of digital radiography are immediate image availability and the time saved by eliminating film developing and the nuisance of establishing a film processing lab at the scene of a disaster or maintaining one at the medical examiner's office.
New digital X-ray systems and portable X-ray tube heads allow odontology teams to work directly at the site of mass fatalities.
“On-site postmortem digital radiography accelerates the identification process,” said Scott R. Firestone, DDS, DABFO, an odontologist in the Suffolk County, NY Medical Examiner’s Office. “Portable computers and radiation sources allow for immediate identification at the site of the accident, with the body, if possible, still in place.”
On-site identification efforts are especially advantageous when the body has been burned or otherwise rendered susceptible to damage during transit. Secure satellite communication then allows images to be relayed to the command center.
Armed to the Teeth
Accurate forensic dental identification requires point-by-point comparison of a complete set of mouth x-rays, which can be as many as 18 to 21 images, in which all points of comparison must match exactly, or in which differences must be explainable.
“When film-based radiographs are used, this comparison is tremendously cumbersome, expensive, and time-consuming,” Weems said. With digital dental x-ray technology, it is possible to capture dental x-rays and compare them to existing digitized dental records much more efficiently. Digital technology enables the instantaneous side-by-side display of antemortem and postmortem radiographic images on a computer screen without the need for a conventional light box.
Digital images can also be digitally transmitted down the hall, across the street, or around the world, thus avoiding the delay of mailing or hand delivering dental records, which increases the ability of doctors to quickly consult without waiting for duplication, forwarding by snail-mail and the possible loss of images.
Firestone documents other advantages of digital radiography in mass casualty incidents in a recent paper (Journal of Homeland Security and Emergency Management, Vol 1, Issue 4, 2004).
“Decreased turnaround and increased productivity are the most important advantages of digital radiography during mass disaster dental identification,” he said. He also noted that the time factor helps to alleviate the causes of inadequate radiographs - operator error and human nature.
Human nature is an issue in mass fatality incidents because authorities and victims’ families demand identifications be made as soon and as accurately as possible. However, physically comparing film records can take several hours for each victim. This is where indifference can surface.
“The pressure for rapid results often results in a second-rate operating philosophy that ‘settles’ for results that are ‘good-enough,” Firestone said. With digital radiography, accuracy is maximized since the likelihood of acquiring a substandard set of radiographs is minimized.
Digital radiographs are compatible with the popular WinID dental identification matching system, written by dentist James McGivney, DMD, available free at http://www.winid.com/.
WinID software sorts through thousands of records and produces a ranked list of most-likely matches in seconds. The system was used in the aftermath of the WTC attack, where only fragments of dental remains were recovered.
“Such digital systems not only support mass disaster dental identification, but also function well in matching dental records from databases listing missing persons and unidentified bodies encountered in the routine activities of the medical examiner’s office,” Weems said.
The first use of digital dental radiography followed the crash of TWA Flight 800 off Long Island, NY, in July, 1996, in spite of resilient skepticism among many in the field. The greatest cultural fear was whether digital evidence could be accepted in court.
“We proved the naysayers wrong,” Firestone said. “There is now case law established for admitting digital images in court proceedings.”
Case law was established by two court cases of digital enhancement of fingerprints in State of Washington v. Eric Hayden (1995), wherein a homicide case was taken through a KellyFrye hearing in which the defense specifically objected on the grounds that the digital images were manipulated. The court authorized the use of digital imaging and the defendant was found guilty. In 1998 the Appellate Court upheld the case on appeal.
Also, in State of California v. Phillip Lee Jackson (1995), the San Diego Police Department used digital image processing on a fingerprint in a double homicide case. The defense asked for a KellyFrye hearing, but the court ruled this unnecessary on the argument that digital processing is a readily accepted practice in forensics and that new information was not added to the image.
Since the establishment of case law, digital radiography has become the gold standard in mass disaster dental identification, although as yet the American Board of Forensic Odontology makes no specific reference to digital radiography in its current guideline to human identification.
“Digital radiography is the next logical technological step to a well-established protocol involving film radiography,” said Bryan Chrz, DDS, DABFO, whose private forensic practice in Perry, OK, has been all digital since 1997. Chrz worked dental identification after the Oklahoma City Murrah Federal Building bombing and the WTC attack.
The U.S. armed forces dental identification units now use digital radiography instead of film. Digital radiography was used by the dental identification unit at Dover Air Force Base on September 11, 2001, to identify the victims from the flights that crashed in Pennsylvania and into the Pentagon, and is now an integral part of the portable morgue used by the Federal Emergency Management Agency’s Disaster Mortuary Response Team in mass disaster responses.
“In mass disaster identification situations, digital radiography becomes much more useful than conventional radiography,” said David Senn, DDS, DABFO, Director for the Center for Education and Research in Forensics at the University of Texas Health Science Center in San Antonio. Senn performed recovery and identification of the 2003 STS-107 Shuttle Columbia astronauts.
“The practicality and flexibility of digital radiography and digital photography greatly facilitate the forensic comparison process,” Senn said.
Digital radiographic images can be enhanced for optimal viewing, enlarged by a mouse-click to aid in visualizing characteristics more easily, permitting side-by-side digital comparisons of antemortem and postmortem radiographs.
“There are no technical or legal reasons why digital radiography should not be the standard method of producing dental radiographs of victim identification,” Firestone said.
Byte out of Crime
Digital imaging protocol has matured sufficiently to satisfy relevant legal issues. Image chain-of-custody is provided for by preserving the original image on unalterable archive media, such as read-only CDs or WORM (Write Once, Read Many) drives. Some imaging programs use secure tagged block file extensions which cannot be changed. If the image is modified, it must be saved as a different file extension.
“Then, steps of manipulation can be repeated in court to prove there was no fraudulent change performed,” Firestone said.
Media longevity is not a great concern. Most reports show digital media has a shelf life of several decades, ample to satisfy most jurisdictional requirements. Film may last longer but only in well controlled storage areas with temperature and humidity constantly monitored.
When digital material is copied in a lossless format a perfect copy is created, so if important digital material is backed-up, copied, or re-archived every 10-20 years using then-current technology, digital information can be retained indefinitely in original form.
The possibility of fraud stalks digital technology, the same as it does film. A 1999 study (J Am Dent Assoc. 1999 Sep;130(9):1325-9) illustrated the potential for fraudulent use of manipulated digital radiographic images.
The authors (Drs. Andrew Tsang, David Sweet, and Robert Wood) obtained periapical radiographs of teeth that contained small restorations or were unrestored from the files of three dental patients at a private dental practice. A flatbed scanner was used to digitize and import the radiographs into a computer. Using PhotoShop®, dental caries, large restorations, fractures, and periapical pathosis were added to the radiographs.
Insurance approval was then sought for restoration of the teeth in question using rootcanal therapy and fullcoverage crowns, approval for which was obtained in every case. The study did not mention that conventional film is just as susceptible to fraud.
“Digital imaging is no different than conventional imaging,” Chrz said. “It’s easy to scan film into a computer, use a computer aided design program to change the image, and then transfer it back onto film. An industrious criminal can alter or counterfeit images.” The final test remains the integrity of the examiner or witness, he said.
Image integrity is addressed by commercial digital radiographic software, which does not permit changes to image content. Users can only manipulate brightness and contrast.
“By protecting, maintaining, archiving the original images and enhancing exact digital copies only, the question of altered images is moot,” Chrz said.
Firestone’s paper contains several suggestions for the future of digital radiography in dental identification, including the formulation of protocols to standardize equipment, methods, and storage of information, as well as a protocol for reproducing antemortem radiographic position in the postmortem radiograph in order to prevent any question about manipulation of evidence.
The FBI’s Scientific Working Group for Digital Evidence is in the process of setting the standards for management of digital evidence. Although not completed, current status can be tracked at: http: //www.fbi.gov/hq/lab/fsc/backissu/april2000/swgde.htm.