In anthropology

In anthropology, opaque artifacts that have obscured texts pose significant challenges to anthropologists because trying to read the texts can cause irreversible changes to the physical structures of the artifacts where they are contained. As such, the anthropologist has to choose whether to destroy the artifact while trying to recover the text on the artifact or keep the artifact in the original state without discovering the text on the artifact. There are great numbers of fragile artifacts that have texts that cannot be read under visible light. These include Papyrus rolls, especially those that have gone through the carbonizing process. These scrolls are difficult to physically unroll without causing damage to them, and even when they are physically unrolled, they tend to sustain great damage that makes them unreadable. However, there is a technology capable of recreating a readable image of the text without unrolling it. Technologies such as Computed Tomography play a vital role in helping anthropologists decipher the content of unreadable artifacts.
Computed Tomography (C.T)
This is a non-destructive radio-imaging technique used to come up with 3D images and models of the object (Abel 2). Over the last forty years, CT scans have constantly been redesigned, and these new models are commonly known as generations. All the CT scans reconstruct cross sections digitally in what is commonly known as slices. These slices are stacked to come up with 3 dimensional volumes. The 3D volumes are then used to come up with virtual or computerized images of the artifacts. These 3D volumes can then be manipulated, dissected and even measured. As such, the morphological information that is present inside the fragile, valuable and rare artifacts can remain intact. Even though it is possible to create a quality virtual fossil using a computer, the process is time consuming, and the specimens may be difficult. The quality of those materials being scanned also determines the result of the scan.
This is a cutting edge analysis which could either specialize in destructive or nondestructive techniques of analysis. However, even the best CT analyst comes across difficult CT image artifacts that hide those areas that the technician conducting the scan is trying to analyze. There are various ways to reduce image artifacts but one needs to first understand the forms that these artifacts take.
Image Artifacts
These are the discrepancies that occur between the reconstructed values in the CT image compared to what the analyst is expecting based on the density of the material and on the geometry sample. These image artifacts manifest themselves on the scan as bright or as dark shadows that follow a certain predictable pattern. The CT image artifacts defects are caused by either CT imaging set up or things like beam hardening, scattering of radiation, and failure of the x-ray to penetrate. The first issue can be resolved by fixing the scan properly and with correct fixture. There are some artifacts that are dependent on the sample and they tend to be frustrating because they are mainly caused by beam hardening.
History of Micro-CT Scans in Archaeology
X-ray CT scans were first recorded in the early 1970’s (Hughes 59). In the year 1989, a newer generation of the CT scanner was introduced. In anthropology, CT scans are preferred because they are able to show the internal structures of the object in a way that is not destructive. As such, the posterity of the artifact remains. This technique is commonly used in the study of mummies. It has been particularly instrumental in studying ancient Egyptian artifacts found in the pyramids or adjacent tombs. Before the CT scanner became widely used in anthropology, the only way anthropologists were able to find out about the internal structures of the mummies was by dissecting them. This entailed unwrapping the mummies, which tampered with the artifact. With CT scanning, however, it is possible to effectively unwrap the mummy artifact without having to disturb the mummy’s body, its wrappings or the coffin. This is possible through virtual dissection. The X-ray dose used is low, and as such, it does not damage the artifacts. In addition to this, the images have spatial resolution and very minimal spatial distortion throughout the entire field of view. Therefore, anthropologists in contemporary times use CT scanning to get details they were unable to acquire with the ineffective past technologies.
Micro-CT Preparation
According to Abel, when preparing a virtual fossil for a CT scan, one needs to reduce blurring through application of noise reduction techniques (5). The next step involves a reduction in cupping through the application of beam hardening correction. After that, contrast should be increased through stretching the floating point range of the fossil Grey values. Other preparations include segmenting fossils from matrices through application of global thresholds and removal of adjacent matrices using a masking tool.
Beam Hardening
Measuring bone mineral density is very important when investigating skeletal integrity (Meganck). In per-clinical research, micro-CT’s are essential tools in measuring bone mineral density. The ability to measure bone mineral density (BMD) from Micro-CT’s is often biased by things such as beam hardening. The image acquisition process affects the results of the BMD measurements. Beam filtration is used to minimize the artifacts that result from the process. In fact, the in murine femora, the setup of the scans affect densitometry measurements in both cortical as well as trabecular bone measurements. Setting up a scan that minimizes the artifacts leads to a more accurate reading in the micro-CT scans. Bone mineral density allows for ash content measurements and also for the measurement of the mineral content in the bones.
It is imperative to understand that photon x-rays from a tube are made up of an entire spectrum of x-ray energies and not just the voltage in which the tube is set. A good example of this is how “even though the tube is set at 225kV, many of those photons tend to come out at relatively lower levels of energy which could be from 50-100keV” (Fleischmann.). In addition to this, each sample material tends to have its own coefficient that is dependent on the energy through which the x-ray photons pass. When the x-ray beams start to pass through and penetrate the material, the lower energy x-rays become attenuated and ultimately, the spectrum gets harder. In most CT’s, there is a reconstruction algorithm that automatically adjusts the non-linear hardening effects in a single material. However, it is much more difficult when there are many densities in one scan volume. As a result, there are shadows and streaks visible when one tries to image both the high and low density materials in one scan.
When the x-ray beam is hard, it often has higher energy and there will be less beam hardening affecting the images of the CT scans of the specimen. As such, the solution is to adjust the CT technique which will ultimately reduce the beam hardening artifacts (Boas ; Fleischmann 5). Consequently, one can opt to incorporate different scanning techniques and scanning parameters which could prove effective in reducing the onset of beam hardening artifacts. There are times when these beam hardening artifacts cannot be fully eliminated, especially when there are multiple difficult samples. In this case, it is very important that one understands the different forms an artifact has so that misinterpretation does not happen, especially when an artifact is labeled incorrectly as a defect or a crack. In some instances, the shades and the separating streaks may be so bad to the extent that whole region cannot be interpreted. When this occurs, it becomes impossible to work on the sample without needing to carry out another scan.
CT scans are much more superior to merely having a physical examination of the artifact since not only does it give information about the artifacts shape but also provides information about the internal shape (Hughes 59). This means that CT scans are more efficient than plain x-rays. In the case of a mummy, conducting a micro- CT scan helps to determine if a piece of jewelry is on the surface or on the wrappings or inside the mummy’s body. The CT is also able to provide information on the artifacts internal structure like the bones, amulets and other organs. All this is possible without even opening the artifacts, something desirable in anthropology.
Due to the harm presented by unrolling, non-invasive ways of imaging are the solution to that problem. They help to analyze these opaque artifacts. High resolution micro-CT imaging is a versatile tool that is both powerful in analyzing anthropological artifacts. However, in order to get a usable result from these Micro-CT images various factors such as the absorption characteristics of the artifact and the pigments involved matter. X-Ray imaging is however effective because it can be used for different inks. Another significant advantage of the x-ray is that it has high energy radiations that allow it to go through the full depth of a vast array of objects (Uldin 165). It is also possible to perform analysis on site because of the configuration and portability of the equipment. In the past, artifacts needed to be transported to specific locations where the bulky equipment was located, risking damage or theft.
Micro CT Scans allow the scholars to determine and date artifacts. This is a great advantage because the micro-CT imaging is not limited to textual content. The scans are carried out based on physical vowel dimensions and other measurements like the length of the scroll when it is unrolled. It is also possible to get the area of the scrolls under study. When the resolution is at its optimum, the scholar is able to see even the minor details like the size and even the nature of the joints in the sheets. Micro-CT scans also allow for assessment of the interior of the artifact to see if any damage has affected the object (Hughes 67). This damage could be as a result of fragmentation or insect damage. As such, more valuable analysis will take place without being affected by the changes caused by physical manipulation. In some circumstances, traditional autopsies are still needed but the micro-CT imaging will allow conservators to prepare well in advance and make the necessary plans with regards to the process.
CT scans have also been used to decipher some of the readings on clay tablets just like the scrolls ( Hughes 66). In fact, the researcher talks about how an Israeli team has successfully used CT scanning in order to read the writing on clay tablets that had been enclosed in clay envelopes. Other artifacts that can be evaluated using the method are bronze artifacts. In fact, Hughes continues to discuss how Italy came up with a cone beam CT system aimed at studying the multiple artifacts that hold archaeological importance in Italy. This is the kind of CT system that has an X-ray beam shaped like a cone and the ray falls on a two dimension detection system. The system holds a key advantage that the data is got faster compared to the typical CT scanner. It is also possible to perform CT scans on cremation urns in order to view the outlines of metal artifacts that have already rusted or began the process of disintegration. The use of technology in anthropology will continue to get more proficient with the advancement of technology.
Conclusion
Micro-CT imaging is a critical tool used to analyze fragile artifacts that bear text. This technology has come in handy for many anthropologists who previously struggled to analyze artifacts without risking further damage. Fragile artifacts have been a serious problem for conservators because physically manipulating the objects could damage them. The portable micro-CT is ideal if the intention is to carry out non-destructive analysis. It allows the analysis of an artifact on site rather than carrying it to a different location, often an urban place where analysis tools can be found. Over the years, the issue of the security or archaeological artifacts has been a problem. This means that artifacts are in danger of being lost to fire, theft and even wars. The use of CT scans together with photography is the most suitable way to facilitate posterity even if the artifacts get stolen or destroyed. Future development of the Micro-CT imaging technology will make analysis further easier for anthropologists.