Why Give a Dead Man a Body Scan?

The forensic question before Thali tonight is whether or not the elderly woman inside the body bag was dead before she ended up under the chassis of a Volvo sports sedan the previous afternoon. The Volvo’s driver insists that he checked his rearview mirror before backing into the parking stall where the body was found. Given the woman’s age—70ish—the possibility of a prior heart attack or stroke seems plausible.


Thali’s research team began their examination of the body earlier in the day, as it lay face-up on the stone examining table in the forensic institute’s second-floor autopsy bay. Visualization specialist Ursula Buck and pathology resident Emin Aghayev prepared the body by affixing buttonlike reference markers across its surface and photographing it with a digital camera from nine angles. Using an overhead light and transparency, they then projected a numbered grid of black points across the body before initiating a computer-guided 3-D scan using cameras mounted on an overhead beam. Turning the body over, Buck and Aghayev repeated the procedure before placing the corpse in a bag and sending it, by private hearse, to the university’s Institute of Neuroradiology, several blocks away, for its MRI scan.


Magnetic resonance imaging has become fairly routine in medical diagnostics since its introduction in 1980. Using radio waves beamed through a powerful magnetic field, MRI produces 3-D internal images of unsurpassed detail. But the process remains far from automated, requiring operators to learn elaborate protocols to extract images from different types of body tissue. Complicating matters for the virtopsy project, MRI technologist Karin Zwygart has had to create special protocols to compensate for the lower body temperatures of Thali’s refrigerated research subjects. The cooler temperatures would otherwise wreak havoc on results, because the MRI machine operates by translating the signature vibrations emanating from the nuclei of different kinds of atoms. At cooler temperatures, these nuclear vibrations slow down.


On the plus side, the resulting images are of such clarity that they draw amazed inquiries from radiologists whenever Thali displays them at international conferences. “Not only do they not fidget,” he says of the corpses, “there is no beating heart, no circulating blood, no digestive motions to blur our images.”The body’s final appointment of the night brings it to the University of Bern’s Institute of Diagnostic Radiology. Here it passes through the doughnut-shaped hole of a CT scanner, which constructs 3-D images of the body from a series of x-ray slices. In the radiology suite’s darkened computer room, Peter Vock, director of the imaging institute, shares a computer with neuroradiologist Luca Remonda. As intent as schoolboys with a new videogame, the two men take turns clicking and dragging screen controls to manipulate the image on the monitor. Vock defines and deletes the CT scanner’s bed to leave the woman’s body suspended in midscreen. Slowly he melts away silvery layers of skin, muscle and connective tissue to reveal a bare white skeleton. He rotates the image, head over heels, pausing to note multiple rib fractures, a broken sternum, a shattered collarbone and crushed vertebrae. Then, layer by layer, he reassembles the body. When he reaches the level of fascia—midway between bare bones and full muscle—he stops again, intrigued by the abnormally high position of the woman’s stomach and the telltale indentation, like an overly tightened belt, around the organ’s midsection.


“We call this a collar sign,” Vock explains. “We think that perhaps the woman’s stomach was pushed up through a break in her diaphragm,” the large muscle that separates the lungs from the abdominal organs. To get a better look, Vock finishes reconstructing the torso and then slices down through its midsection, five millimeters at a click, until he discovers a dark gap in the white muscle of the diaphragm.


Vock turns the controls over to Remonda, and Thali asks the radiologist to look for signs of inhaled blood in the woman’s lungs. Earlier, during the MRI scan, Thali noted light areas in the woman’s muscle tissues. If this represented active bleeding, it would suggest that she was alive when the car crushed her body against the pavement. But postmortem injuries can produce some internal blood seepage. More telling would be a clear indication of aspirated blood—a confirmation that the woman was still breathing when she sustained the injuries.


Remonda is on his second or third slice through the lungs when the first white splotches appear. As he continues to click down through the tissues, each bright spot melts away, only to be replaced by others. Clearly, aspirated blood.


Remonda and Vock turn to Thali for his pronouncement as to probable cause of death. “Thorax instability secondary to crushing injuries,” he concludes: suffocation following rib fractures so massive that the victim was unable to take a breath.


The next morning Richard Dirnhofer, Thali’s boss and the director of the Institute of Forensic Medicine, will perform a conventional autopsy for confirmation. “It will be a bloody mess, to be sure,” Thali says with a grimace. “Nobody likes to show that to a jury.”At the same time that Dirnhofer is making his first cut, visualization specialist Buck will be hauling her surface-scanning equipment to the police garage where the suspect’s Volvo remains impounded. There she will create a 3-D computer image of the car’s surface, the same way she photographed the corpse. Buck and Thali will then bring the body and automobile together in cyberspace, matching wounds to car surfaces until they can determine the woman’s position as she sustained each of her injuries. Thali is particularly interested in how well the car’s rear bumper and trunk lid will match up against the gouges seen in the surface scan of the woman’s knees and the deep bleeding the MRI picked up in the muscles over her hips. “This is not some animation program using artificially created models,” Thali insists. “You are looking at real data from the original car, the original person, the original wounds and bones.” Depending on how the data match up, the driver could face manslaughter charges.