Under the surface: Dual Energy Computed Axial Tomography

sarcofago Low Res!


A modern approach to diagnostic art restoration allows non-destructive techniques that do not alter the works of art that are analyzed. For this reason, X-rays are widely used and, in recent years, computerized axial tomography, better known as CT, has come to be a key resource in the diagnostic art restoration process.

This technique allows researchers to analyze the artifacts with a three-dimensional reconstruction, providing high spatial resolution and a very high resolution in density. The technology of three-dimensional reconstruction has been widely used for the study of artifacts of historical and artistic value. In the Vatican Museum’s case, however, researchers have made use of a new type of medical CT, which is based on the principle of Dual Energy. The operation is similar because it scans the same structure, but with two X-ray tubes simultaneously with different voltage. The information the researchers receive from the dual-energy X-ray is compared with a known density, such as water and iodine, and in this way provides information about the inner structure of the object with respect to a monoenergetic object.

Recently, two small mummies and an Egyptian sarcophagus from the necropolis of Luxor (800 BC) were scanned. The dual-energy CT made it possible to not only investigate the interior of the two mummiettes, but also to create three-dimensional models to be dissected and investigated from every point of view. Through this process, a thin tin foil in the grout of the face, which would normally have been impossible to detect, was discovered. The discovery of the lamina revealed both mummies to be false historical artifacts, likely from the 19th Century. The dual-energy CT scan of the sarcophagus provided a great deal of  evidence supporting the argument that the cover is composed of material reuse. The CT scan is capable of showing the  assembly technique of the layers, but is also able to separate the different layers through densitometric measurement of materials (wood and stucco), using filters already set for medical use. Through this intensive process, researchers have learned some very useful and innovative techniques for the study of important historical and artistic artifacts.

The aim of this project is to gain access to this capability of dual-energy CT in order to differentiate the various densities of materials in order to study in detail the assembly and polychrome paint film of any work. With the help of this tool, researchers will be able to distinguish each pigment according to its densitometric characteristics, and then will be able to dissect the paint film by identifying the precise location of the pigmented layer on it. Today, no laboratory instrument has this capability, so obtaining this tool will be extremely beneficial to the work of the Vatican Museums restoration teams.