Digital radiography gives forensic odontology more bite
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.
Courting Disaster
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.
Douglas Page is a Science/Medical Writer and editor. He can be reached at
douglaspage@earthlink.net.
