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Wednesday, May 31 • 3:30pm - 4:00pm
104. (Research & Technical Studies) The Use of CT Numbers to Quantitatively Classify Cultural Heritage Materials

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Brittany Dolph Dinneen, Dr. John A. Malko, Renee A. Stein

Conservators routinely document the structure of objects for the purposes of condition assessment, technical study, and treatment decision-making. X-radiography has provided conservators with the ability to generate images of otherwise inaccessible features such as closed cavities, internal armatures or other structural features of solid objects, in a nondestructive way. Computed tomography (CT) scanning provides an additional level of information, emitting x-rays in multiple planes and acquiring data at multiple angles to produce a three-dimensional reconstructed image, whereas the X-radiograph results in an image in which the three-dimensional information is superimposed into a two-dimensional format. In both X-radiography and CT scans image contrast, that is, areas of differing brightness, are related to the differences in X-ray attenuation (radiodensity) of the regions through which the x-rays travel. In X-radiography the superimposed nature of the image makes quantitation of radiodensity difficult. In CT scanning regions of the scanned object can be quantified by their radiodensity; this quantitation uses units called Houndsfield units, or CT numbers, which describe the radiodensity of a given volume relative to air (-1000) and water (0).

In spite of the proven capabilities of CT scans for imaging, however, scan output may still not provide enough visual evidence of morphology to characterize a material. Furthermore, visual interpretation of radiodensity is typically only semi-quantitative at best – allowing for only qualitative comparisons - and dependent on the parameters of the scan. We suggest that if the relationship between x-ray attenuation and material class is significant, the identification of a material or class of materials would be informed by comparing the assigned radiodensity of a determined region of interest to a table of known ranges for various cultural heritage materials (i.e. ceramics, stone, soil, clay, cellulosic organics, keratinous organics, etc.). Similar tables developed for medical diagnostics include CT numbers for fat, blood, muscle, gray and white brain matter, and different types of bone.

Potential applications include the characterization of materials in hidden cavities which may be unethical to open, or impossible to access, without irreversibly disturbing the exterior matrix. For example, many African power objects, such as minkisi, contain materials in bundles or otherwise hidden spaces. Other possible applications may be the material characterization of amulets hidden in mummy bundles and sealed opaque vessels with contents intact.


Speaker(s)
avatar for Brittany Dolph Dinneen

Brittany Dolph Dinneen

Conservator, Michael C. Carlos Museum
Brittany Dolph Dinneen is Assistant Conservator of Objects at Emory University’s Michael C. Carlos Museum. She has enjoyed conservation roles at the Smithsonian National Museum of African Art and National Museum of American History, the Kelsey Museum of Archaeology, and the National... Read More →

Co-Author(s)
avatar for Dr. John A. Malko

Dr. John A. Malko

Associate Professor of Radiology, Emory University
avatar for Renee A. Stein

Renee A. Stein

Conservator, Michael C. Carlos Museum
Renée Stein is Chief Conservator at the Michael C. Carlos Museum at Emory University where she oversees the treatment, preventive care, and technical analysis of the Museum’s diverse collections. Stein is also a Lecturer in the Art History Department and teaches courses on conservation... Read More →

Wednesday May 31, 2017 3:30pm - 4:00pm
Riverside West Exhibit Hall Exhibit Level, East Tower
  • Poster # 104

Attendees (7)