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Necro-Radiology: Postmortem CT Scans Are On The Rise

Sat, 08/01/2009 - 4:00am
Douglas Page

Is Radiology Ready?

The efficacy of forensic postmortem computed tomography is no longer in dispute. What is still in question is whether radiologists proficient at interpreting clinical imaging of the living can be expected to be equally adept at rendering precise postmortem forensic findings without special training. There are major differences in the interpretation of postmortem and clinical imaging, yet no postmortem radiologic subspecialty exists.

Without special training, postmortem CT interpretations can easily be inaccurate. “A radiologist embarking on interpretation of postmortem CT or MRI is immediately aware that postmortem imaging is simply not the same as clinical imaging,” said Chris O’Donnell, MD, a radiologist at the Victorian Institute of Forensic Medicine, in Southbank, Victoria, Australia. Victoria is the world leader in postmortem CT usage. CT has been employed at the Institute over 10,000 times in the past five years.

There are many distinctions between imaging the dead and imaging the living. O’Donnell said established techniques of oral and intravenous contrast administration are not possible with the deceased, thus interpretation of thoracic and abdominal cavities is problematic.

“Also, bodies are often not positioned orthogonally on the scan table due to rigor, anatomy can change dramatically in shape due to lack of blood pressure, blood elements sediment out after circulation ceases, and lividity and intravascular clot is seen as a normal change after death,” he said.

There’s more.

The process of decomposition and putrefaction leading to abnormal gas formation can be confusing and lead to incorrect diagnosis if not fully understood, he said. There is still debate about the origin and distribution patterns of this gas and the contributions of trauma, cardiopulmonary resuscitation, and putrefaction to the presence of such gas.

“Pathologies rarely seen in the living are commonplace to the forensic pathologist and must also be recognized by the radiologist,” O’Donnell said. In addition, forensic pathological terminology differs from that used in the clinical field. Radiologists and forensic pathologists also approach injury cause and effect from different directions.

“The clinical radiologist is very much concerned with the visceral effects of trauma, such as identifying sites of tissue disruption and hemorrhage in order for appropriate treatment to be instituted, whereas issues of causation are paramount to the forensic pathologist, who must decide how injury has occurred and the mechanisms of that injury, as well as the ultimate effect,” O’Donnell said.

The bottom line is, clinical radiologists seldom exposed to postmortem cross-sectional imaging are at risk of misinterpreting postmortem findings, particularly if they adhere to the rules of clinical radiological analysis.

Dead Reckoning
There is a solution. In order to more fully understand postmortem CT and MRI and how they contribute to the autopsy process, O’Donnell recommends that radiologists work in a cooperative environment with forensic pathologists—in effect, creating a novel subspecialty he calls necro-radiology.

“The radiology community needs to embrace forensics or postmortem imaging will become the domain of forensic pathologists,” he said. O’Donnell argued the case for necroradiology in a recent issue of the journal Clinical Radiology (2008 Nov; 63 (11):118994).

According to O’Donnell, the necro-radiology subspecialty would fuse cross-sectional radiological imaging with postmortem pathology.

“Necro-radiology is best suited to radiologists with a background in general or trauma radiology who have an interest in the area of forensics,” he said.

O’Donnell believes postmortem CT imaging falls logically into radiology’s bailiwick since it incorporates the full range of radiological skills, from cross-sectional anatomy, macropathology, and 3D perception to mastery of modality physics and technology and their application in the detection of disease. Forensic pathologists possess a different skill set.

For necro-radiology to flourish as a forensic subspecialty in radiology, however, it will first require recognition by the governing radiological boards. Professional radiology organizations have already begun to provide forums for forensic discussion and exploration at international meetings. The 42,000-member Radiological Society of North America has not officially endorsed the idea of a new necro-radiology subspecialty, but the Society has recognized the need to begin educating its membership on forensic issues.

“The interpretive skills and techniques necessary in postmortem CT are unique compared to clinical imaging, so our professional societies are sponsoring courses on postmortem imaging,” said Angela Levy, MD, associate professor of radiology, Uniformed Services University in Bethesda, Maryland. A course in forensic imaging was offered by Levy at the RSNA annual November meeting the first time in 2007, and was repeated last year.

Levy said the goal of the course is to introduce the concept of using CT, and, to a lesser extent, MR and sonography, in postmortem imaging. She believes imaging is most useful in deaths from penetrating and blunt trauma, but is also useful in fire deaths and to screen the body prior to autopsy in nontraumatic deaths.

“Postmortem imaging is a field that has tremendous potential and room to grow within radiology, as well as within forensic medicine,” Levy said.

Without the blessing from organizations like RSNA, O’Donnell fears that those assuming the duties of nascent necro-radiology in the future will be forensic pathologists, which could ultimately cost forensics the extensive crosssectional expertise possessed by radiologists.

“Pathologists in centers with access to cross-sectional imaging are increasingly relying on radiology in the formulation of reports, and radiologists with a specialty interest in necro-radiology can have an important role to play in that process,” O’Donnell said.

Image Generation
Full-body CT scans generate up to 3,000 detailed, high resolution images. Radiologists or forensic pathologists then use special computer software to reconstruct the separate images into 3D views that can be displayed on monitors.

The forensic utility of postmortem CT is perhaps best illustrated at Dover Air Force Base, where military pathologists have routinely administered full-body scans to every casualty returned from the Iraq and Afghanistan wars since 2004.

Although MRI is much better at defining visceral structures and delineating pathology than CT, it is also much more expensive, more technically demanding, and more difficult to install in mortuary environments. Dover uses CT.

“Postmortem CT studies can be acquired in three to five minutes, and, when working with the deceased, we don’t need to be concerned about the amount of radiation dose or the presence of metal or foreign objects in the body,” said Navy Capt. Craig Mallak, MD, Chief Medical Examiner in the Armed Forces Medical Examiner System. In clinical imaging, artifacts caused by all kinds of metallic implants (teeth fillings, prostheses, fiducial markers) often impose limitations on the reliability of CT results.

Mallak said postmortem CT has not replaced conventional autopsy at Dover. It is not a stand-alone autopsy protocol. CT is merely a tool that adds efficiency to the overall autopsy process.

Pre-autopsy CT scanning allows the pathologist to plan aspects of the procedure in advance by identifying potential hazards, such as tuberculosis or sharp metal objects, and accurately locating foreign bodies like bullets or bomb fragments.

“CT can’t do it by itself, but it certainly makes what we do more precise,”

Mallak said. “It helps during the autopsy so we can do things quicker with a greater degree of accuracy.” Mallak said postmortem CT enables pathologists to evaluate anatomic areas of the body that are difficult to dissect or that are not routinely dissected at autopsy, such as facial bones, nasal passages and sinuses, the shoulders and upper extremities, and the outer pelvic, hip, spine, and lower extremities.

“CT enables fractures to be much better evaluated and studied than can be done at autopsy,” he said.

The multiplanar and three-dimensional capabilities of CT also enables precise localization of bullets and metal fragments in the body that must be recovered.

The use of postmortem forensic CT in military settings, however, can present several unique challenges, since scans of the deceased are performed soon after arrival, before subjects are stripped and cleaned.

“We started out with a standard 16-slice scanner, but soon discovered the 5-ft, 2-in table-run wasn’t long enough, the radiation source was never designed to scan full bodies one after another, and the tube opening wasn’t large enough to scan casualties in full body armor,” Mallak said.

GE Healthcare responded by designing a special scanner specifically for use at Dover. The machine is still 16-slice, but the tube is now more robust, the table-run is now 6-ft, 2-in, and the opening is larger.

Postmortem CT scan of  a U.S. soldier

Sputtering Acceptance
While there is no dispute over the value of postmortem CT, its acceptance in the U.S. continues to sputter. The reasons are generally economic in nature. Not even the FBI Laboratory uses postmortem CT/MRI imaging in forensic casework.

Few new facilities that include forensic CT suites are being built for medical examiners due to current economic pressures. Funding for CT scanners for medical examiners is expected to continue to be lean in the near future.

“Those CT scans that are done postmortem will be done using hospital or clinic scanners rather than ones dedicated for medical examiner or coroner use due to the high costs involved,” said forensic pathologist and medical examiner John D. Howard, MD, president of the National Association of Medical Examiners. New 16-slice scanners cost over $1 million, although recent online auction bids for used or refurbished 16-slice units were in the range of $185,000 to $340,000.

Installing CT suites in mortuary settings is by no means mandatory. Many medical examiners have established working relationships with nearby radiology clinics, where after hours scans and interpretations can be acquired.

“I anticipate that CT will be used more and more in the future as a part of postmortem examinations, but that progress in this area will be slow,” Howard said.

Howard speculates in the future postmortem CT scans will be increasingly used as a supplement to, but not as a replacement for, conventional autopsy.

“CT may also be used in the future as a screening tool to decide whether an autopsy is indicated—to rule in or rule out signs of internal injury that may need further evaluation by traditional autopsy,” he said.

Some studies have shown that when there are major injuries, such as those resulting from a motor vehicle accident, CT may provide enough information in a fraction of the time to justify avoiding the additional expense of a conventional autopsy altogether.

Douglas Page writes about forensic science and medicine from Pine Mountain, California.

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