Two-dimensional x-radiography is often sufficient for looking at simple, relatively flat objects. But what happens when an object has multiple layers of information or overlapping parts? A coin with two faces is an example of such an object—a two-dimensional radiograph allows the viewer to pick up certain details of each face of the coin, but these details inevitably overlap. Similar issues may occur for other objects, such as a painting with multiple layers or a complex circuit board.
A Digitome exam was taken of an Alaska quarter to see if the two separate faces could be isolated, and it was successful. One distinct layer of the coin scan reveals the grizzly bear springing out of a rushing river and biting his catch—a salmon. Moving down through the coin, the face of George Washington is clear, but analysis of the words reveals that the radiographic image face is actually a mirror image of the real face! The coin had been placed with Washington’s face down on the image plate, so its shadow was flipped. (Imagine an ink stamp or the imprint of a boot in the mud.) In the video, after scanning, the coin is manually rotated and flipped by video software for ease of viewing.
The characters (text and numbers) on each face are visible albeit not completely clear. The designs on the coin are made through pressing blank copper-nickel alloy with imprints that outline the images and characters; the result is that any pressed coin has varying thicknesses and therefore different levels of attenuation (absorption or scatter of x-rays) across the coin. Characters are areas of greater thickness and Digitome distinguishes the changes in thickness on both faces from one another. Still, the characters on the quarter are somewhat difficult to resolve because of the limitations of resolution. Resolution is determined by the image plate used, the position of the object relative to the source and detector, and, in this instance, the size of the letters (on the order of millimeters).
Blackbeard’s infamous pirate ship, The Queen Anne’s Revenge (QAR), lay lost on the ocean floor off the North Carolina coast for almost 300 years. It was discovered in 1996, but most of the relics of colonial culture aboard its decks, such as specks of gold, glass beads, firearms and brass pins, remain hidden inside a thick crust of muddy sand and shells.
With the help of the Davidson Research Initiative, Ryan Kozlowski ’16 and Professor of Physics Dan Boye hope to shed some light on those items by using their Digitome non-destructive x-ray imaging system. Their examination of a half-dozen items from the pirate ship this month at the N.C. Department of Cultural Resources lab located at Eastern Carolina University could add to the evidence that this was indeed Blackbeard’s ship.
The NC Cultural Resources department’s QAR team has thus far retrieved, catalogued and stored 3,000 encrusted objects from the wreck. But the two-dimensional film x-rays of those objects they produce are not as revealing and helpful as a Digitome inspection can be.
The Digitome system, which was purchased by the Davidson physics department, gives students access to a cutting-edge imaging device. Professor Boye, who is managing the project, said the system has application in many liberal arts disciplines.
“Digitome Corporation wanted to see uses that may emerge when they put the Digitome system in the hands of liberal arts students rather than engineers,” Boye explained. “This is a great opportunity for us in applied physics research.”
The way in which the Digitome system creates a three-dimensional image of an object leads Boye to hail it as a “cross-disciplinary game changer” for Davidson. He said, “We believe we can apply Digitome to help understand topics of interest in the humanities and social sciences as well as the sciences.”
During the past school year two students learned the system and explored applications throughout the curriculum. Phillip Wall ’14 created an examination of a common gaming die that vividly displayed the system’s capabilities. The captured three-dimensional image began on the one-dot side of the cube. Wall then moved straight through the die until the six dots on the opposite side came into view on the screen. Through rotation and controlled movement, he revealed all the other sides of the die. “It’s a graphic way to demonstrate its volumetric capability,” Wall said.
Student researchers have experimented with a variety of objects in honing their examination techniques, including skulls of a baboon, a wolverine, a snapping turtle and a python. Examination of a novel Chinese ceramic wine cup revealed the internal structure of a self-priming siphon. An examination of a brittle prayer pouch from the library verified the existence of a scroll inside without having to open it.
Steven Keller ’14 provided support for a project by students in an animal physiology class taught by Professor of Biology Michael Dorcas. Keller examined the rate of mouse digestion when corn snakes are kept at different environmental temperatures, and he also examined flawed welds in steel plates.
Two other students are conducting Digitome research this summer. In preparation for work at the QAR Lab, Kozlowski has been creating high-resolution images of the nearly flat surface of coins, even when encased in over an inch of plaster. Rebecca Garner ’16 is making paintings with Old World pigments to see how the system might be used to reveal artistic techniques, modifications and even underpaintings.
Three Main Parts
“Digitome imaging can be done on a laptop,” explained Kozlowski ’15. The configuration at Davidson consists of three main parts. A source shoots x-rays into the cabinet. The object of the examination rests inside the cabinet on a circular plastic plate attached to the image plate. The object and image plate can be tilted and the plastic plate can be rotated to record as many as 32 different perspectives of the object, though just eight views are commonly captured. The system’s proprietary software immediately assembles the different views such that any mathematically-defined contour can be viewed.
Though the Digitome exams are most easily accomplished in the cabinet, the mounting fixture and image plate are removable and easily portable to remote locations such as a museum for off-site examination of fragile or valuable pieces. To test its portability, the team twice this spring took the system to a room-sized x-ray vault at Central Piedmont Community College. It allowed them to do a test examination with a moveable x-ray source, whereas in the past they employed a fixed source and moved the object. East Carolina University’s QAR Lab, where the Davidson team is working, is also room-sized.
Davidson students are a crucial part of the Digitome project because learning to properly use the system requires some training and experimentation, according to Kozlowski. “There are adjustments to make in frame rate, frame count, beam energy, gamma, contrast and histogram,” he explained. “Another challenge is learning to view with your mind’s eye an image in three dimensions rather than the usual two.”
Boye will continue to enlist students to learn the system so they can handle requests from other departments and external agents. He noted that the experience and skills they develop through using Digitome prepares them well for work with almost any imaging system, and gives them valuable experience for careers in a wide variety of fields. Last year’s student assistants prove that point. Steven Keller ’14 has been accepted into the UVA medical school for studies in biophysics and biomedical imaging, and Phillip Wall ’14 will be pursuing graduate work in medical physics at LSU.
Agreement Breaks Ground
Digitome Corporation is a tightly held 30-year-old business that has, until now, supplied its imaging devices almost exclusively to the defense industry and government-related organizations. One of their exams was instrumental in determining the cause of the Space Shuttle Columbia disaster, and led to the solution for the return to space after the grounding of the shuttle missions. Other Digitome Corporation examinations revealed that a music stand owned by Mozart had pieces screwed together with reverse threading, that the handle of an invaluable Japanese national treasure had been modified, and that the general absence of cracks in the intricate enamel of a Ming vase resulted from expansion joints on the inside surface. An examination of a jet engine turbine blade revealed cracks that could have been dangerous.
In a unique agreement facilitated by Digitome Corporation, the college has entered into a licensing agreement to sell Digitome systems and software to educational institutions and museums. Davidson will receive a percentage of the revenue on the sale. This is the first time Davidson has tried to set up a self-supporting, profitable entity.
“It’s a new venture for Davidson,” said Boye. “We received startup funds from the college to get the project rolling, but we’re expecting to be self-supporting soon. Revenues we generate will go back into the project, supporting student employment and training, equipment procurement, marketing and presentation of our findings at professional meetings.”
The system’s portability, cost, scalability, rapid results and ability to measure any aspect of tested subjects make it comparable if not superior to other imaging techniques such as computed tomography (CT), positron electron tomography (PET), ultrasound and magnetic resonance imaging (MRI).
Boye is inviting about two dozen museum curators and academicians to attend the first comprehensive Digitome marketing showcase, which will occur soon in Washington, D.C. Following that kickoff event, the system will be promoted online, and with demonstrations at Davidson and other locations.
Article written by Bill Giduz
Geodes are hollow, closed shells made of igneous or sedimentary rock. They generally form in cooling lava or in sedimentary geological structures over several thousand years. Though the mechanisms of void formation differ, the same process occurs in time for all geodes: water-carrying minerals, usually calcite (CaCO3), seeps into the microscopic pores of the shell and accumulate the inner lining that, in the final product, is a visually pleasing crystalline structure,.
Since these rocks are closed surfaces, the only practical ways to view the inner crystals are to break them or to use a form of imaging that makes use of light outside of the visible range like x-radiography. A two-dimensional x-ray image will be able to detect that the rock is hollow, but it will not necessarily include information about the varying thickness of the shell or the shape of the crystal lining. A Digitome volumetric exam, however, is able to detect the contour of the void within the rock in a non-destructive manner.
The elemental make-up and thinness of the geode shown in the video allow for easy penetration of x-rays that are relatively low in energy. The quartz is mainly silicon dioxide and the crystal lining’s most absorptive element is calcium, with an atomic number of 20. The exam in the video was taken with an x-ray beam of 80 kVp; metallic elements like iron, of atomic number 26, often require more energy for adequate penetration. Since calcium composes much of the geode, this material is a good model for concretions that would be found on the ocean floor in underwater archaeology excavations. In particular, the geode shown in the video was volumetrically examined to prepare for taking three-dimensional x-radiography exams of artifacts in concretions from the Queen Anne’s Revenge.
Scanning upward through the geode, it is evident that much of the rock is indeed hollow. Areas of particularly low or high thicknesses are identifiable through the exam and can be accurately located on the actual geode. Because of this, one could carefully break open the geode or open a small hole by accessing an area of weakness found in the 3D exam. This potentially provides the opportunity for a cleaner cut of the rock for museum display, personal use, or commercial purposes.