What MicroCT Discovered
Every historical artifact holds a unique story. Perhaps it is a tale of an individual life forgotten over the centuries or insight into the cultural behavior of a long-defunct society. Forensic archaeologists have the fascinating but painstaking task of studying such artifacts, of analyzing trace amounts of evidence in a search for hidden clues to connect seemingly unrelated details into a coherent picture of our past. Modern technology has provided these scientists with many powerful tools. But how do forensic archaeologists blend the past with today’s advanced technology?
The recent discovery of a silver reliquary at an archaeological site at Jamestown, the first permanent English settlement in America, provides a textbook example.
Click here to hear about the experience from Micro Photonics’ staff.
Jamestown Rediscovery archaeologists recently identified the site of the first of church built at Jamestown (in 1608). Inside the remains of the foundation of the church, they discovered four graves, believed to be those of four important original settlers of the colony. Within one of the graves, the archaeologists found a small silver box (approximately 2”x5”) that warranted further study – and would need advanced technology to fully unlock its mysteries.
We here at Micro Photonics were first presented with this unique project by the FBI Lab in Quantico, VA, which had been working with Jamestown Rediscovery to investigate the contents of the silver box. An initial 2D radiograph taken at the FBI Lab had identified two dense objects of unknown material inside the box. Scientists there suggested that Jamestown Rediscovery seek high resolution 3D images, specifically micro-CT images, of the box and its contents. Such images would be able to provide better clarity of, and more information about, the two objects, including a possible classification of their surface.
And that is where Micro Photonics became involved.
David Givens and Michael Lavin from Jamestown Rediscovery hand- carried the silver box to our imaging lab in Allentown, PA, to take advantage of our advanced X-ray Micro Computed Tomography technology. We conducted an initial scan of the box on the SkyScan 1173 High Energy Desktop Micro-CT, hoping to resolve more details of the two dense objects. What we found surprised us all.
The first reconstruction (NRecon software – Bruker) of the silver box not only showed the full contours of the two dense objects inside, which looked as if they might have been conjoined at one point, but also revealed seven fragments of bone! That the box contained bone fragments truly surprised David and Michael – and dramatically shifted their thinking about the importance of their find. Further analysis of the trabecular structure of the fragments hinted that the bone fragments probably came from a large mammal. Because bone is lighter in density than silver (the box) and the two dense objects(lead possibly), the fragments had been obscured in the background of the single 2D radiograph taken at the FBI lab. Only by scanning in 3D on a high resolution micro-CT were the bone fragments able to be discerned. With vital information about its contents revealed through micro-CT, the silver box became a more intriguing and more historically significant artifact; Jamestown Rediscovery could now say it was a reliquary.
Read more about the contents of the box.
Figure 1. Silver box and contents
How does micro-CT help forensic archaeologists?
Micro-CT is a non-destructive, non-invasive technique that allows a detailed look at an artifact while preserving its fundamental integrity. It does not alter the state of conservation or preservation of an object. In the case of the Jamestown reliquary, micro-CT scanning allowed the box to be examined in its natural state, before any restoration procedures were undertaken. Furthermore, it allowed exploration of the internal contents without having to physically open the object, which could have possibly damaged the box itself and/or its contents. This was a crucial consideration given the rarity and historical significance of the artifact. As micro-CT technology progresses, it may be possible to re-examine the silver box in a whole new way in the future.
How Does Micro Computed Tomography Allow Internal Visualization?
Micro-computed tomography (µCT) is an imaging technique that uses a series of radiograph images to reconstruct the internal structure of objects without actually having to physically destroy the specimen. These images are generated by determining the quantity of X-rays absorbed throughout the volume of the object being tested.
CT technology has been used extensively in the medical field for decades. If you or someone you know has had a CAT scan (i.e., CT), then you have experienced the same technology as micro-CT. Common uses of hospital scanners are to image broken bones or other injuries where the extent of the damage or affliction is not known. The major difference between clinical CTs and micro-CTs is the scale at which the images are taken. Typically a clinical CT scanner has a resolution in the range of 0.300mm – 0.600mm pixel size, whereas micro-CT scanners have ranges around 0.001 – 0.020mm pixel size, or 150-600X the resolution in every direction!
To learn more about how micro-computed tomography works, check out How Does A MicroCT Scanner Work
What more can be learned from micro-CT data?
Micro-CT images provide more than just a visual inspection and depiction of an object; they provide crucial information that can lead to further analysis and discovery.
Through careful digital analysis of the micro-CT images of the contents of the Jamestown reliquary, it was possible to create virtual models through CTVox (Bruker Micro-CT) and ScanIP (Simpleware, UK). These 3D models render the surface of virtual objects with tiny connected points in what is called a mesh model. Transforming the micro-CT data of the reliquary’s contents into a mesh model allowed for exporting to a 3D printer. Thus, detailed, actual size plastic replicas of the two halves of the ampulla and seven bone fragments could be printed out and painted, inviting a “hands-on” experience with the these objects. For more details on this process visit – How It Was Done.
Figure 2. STL models (Left), 3D Printed Models, 3D Printed Models after painting