Using the brightest X-ray source in the Western Hemisphere, Northwestern Medicine scientists directed a narrow beam of high-energy X-rays through an ancient mummy, aiming to reveal secrets about ancient Egyptian bone nanostructure that could help modern medicine better predict who might be at risk of fracture.
Led by Stuart Stock, PhD, research professor of Cell and Molecular Biology, the team used the Advanced Photon Source at Argonne National Laboratory to explore the structure of the mineral constituents of the mummy’s bones without disturbing the mummy’s wrappings. The findings of the investigation will be included in a January exhibition at the Block Museum of Art on the Evanston campus.
“We have some preliminary findings about the various materials, but it will take days before we tighten down the precise answers to our questions,” Stock said.
The project has its roots in the Block Museum exhibition; a gallery of Roman-Egyptian mummy portraits from the ancient city of Tebtunis. The portraits will be on loan from the University of California, Berkeley, but the 1,800-year-old mummy was a late addition to the exhibition after Block museum curator Essi Ronkko stumbled upon it while researching materials at the Garrett-Evangelical Theological Seminary on the Northwestern University campus.
As it turns out, the mummy was from the same time period as the Berkeley collection and was originally excavated from a site nearby, according to Stock.
“Quite by chance, my colleagues found a mummy that has its portrait still attached, unlike the Berkeley collection providing the bulk of the exhibit,” Stock said.
The exhibit curators, wanting to discover what was inside without disturbing the delicate portrait and wrappings, contacted Stock to arrange a CT scan at Northwestern Memorial Hospital. Stock agreed to perform the scan, but wanted to go further: taking the mummy to Argonne National Laboratory to analyze bone nanostructure using X-ray diffraction.
Bone contains a high density of nanocrystals and the periodic arrangement of atoms within these nanocrystals scatter X-rays in different directions. The angles at which the X-rays diffract and the intensities of the different diffracted beams reveal information about the object’s structure, according to Stock.
“If you know the angles and relative intensities of these diffracted beams, then you can identify what material it is — it’s like a fingerprint,” Stock said. “As far as I know, no one has tried to non-invasively interrogate what’s inside an object like this.”
Stock was most interested in bone competence, a measure of bone strength which becomes critical in osteoporosis.
The most significant determinant of bone competence is mineral density — the more mineral you have in your bones, the more they resist fracture. However, a significant number of older individuals who have fractures also have bones with high mineral density. According to Stock, some of this unexpected fracture risk is explained by poorly structured trabecular bone — the porous bone that is present at the ends of long bones — but that does not account for the whole discrepancy. Instead, it may be that the quality of the bone tissue varies.
“There are epidemiological studies that say peak muscle mass and bone mass are protective through life, particularly for women,” Stock said. “I wanted to compare populations who had an active lifestyle with our more modern sedentary populations — is there a difference in bone quality?”
Comparing the mineral nanostructure of the mummy’s bones with that of the bones of modern-day humans may quantify the benefits of an active lifestyle, improving clinicians’ ability to predict who is at risk for a fracture and enhancing preventative care.
“Right now in osteoporosis, we can look at bone density and trabecular bone structure and maybe predict fracture risk correctly 80 percent of the time,” Stock said. “We need to improve our predictive ability to around 95 percent, so we’ve got to track down additional factors.”
In addition to bone composition, Stock and colleagues will use X-ray diffraction patterns to identify other objects within the mummy’s wrapping, matching the patterns measured at Argonne with the patterns of other materials such as gold or rock.
“We have confirmed that the shards in the brain cavity are likely solidified pitch, not a crystalline material,” Stock said. “We are also investigating her teeth, a scarab-shaped object and what look like wires near the mummy’s head and feet.”
The findings from the synchrotron experiment, CT scan and other analyses will help investigators and historians better understand the life and death of this Roman mummy, according to Marc Walton, research professor of materials science and engineering at the McCormick School of Engineering.
“We’re basically able to go back to an excavation that happened more than 100 years ago and reconstruct it with our contemporary analysis techniques,” Walton said. “All the information we find will help us enrich the entire historic context of this young girl mummy and the Roman period in Egypt.”