PART 4.3 - PALEORADIOGRAPHY IN RESEARCH
Data extraction
What data can be extracted from radiographs?
When conducting paleoradiography the real question should be 'what is the research question?'.
Within commercial archaeology there is little room for experimental imaging, taking X-rays just for the sake of curiosity would not be cost effective. However, within a research or educational orientated environment the circumstances may be different. I am very fortunate with both time and access to radiography equipment to explore paleoradiography and develop my own radiographic technique for archaeological items. The end goal is to use the lessons learnt from my paleoradiography sessions to inform research, thus allowing a transition from curiosity-imaging towards a more formal objective-driven approach.
Drawing upon the previous three parts of this course, the following video provides an overview of the types of information that can be gathered using paleoradiography of archaeological specimens. I have provided examples from archaeological academic literature beneath. These are also listed within the Learning Resources section.
Are you conducting research which uses paleoradiography? Let me know.
Identification of pathologies, trauma or biological stress
At its simplest level, paleoradiography may be used to identify the presence or absence of pathologies, trauma or stress within bones. This relies upon the concept of radiographs as two-dimensional representations of three dimensional objects, and the benefit of radiography to demonstrate the internal structures of objects. Within the clinical context a reporting radiographer or radiologist would rely upon pattern recognition or being able to spot differences that indicate a deviation from the norm. This therefore highlights the importance of consistent radiographic technique (more notably radiographic views) to allow the investigator a reliable comparison to other radiographs with a confirmed diagnosis.
Cellular changes upon bones may indicate biological stress related to poor diet, developmental pathologies or degenerative changes (e.g. osteoarthritis). Depending upon the radiographic technique used, radiographs may be measured to provide indications of size, shape and angle of bone changes associated with pathologies or biological stress.
The study by van Schaik et al (2017) undertook paleoradiography of 213 18th-19th century skeletons from a church in London. The aim was to identify the presence of skeletal lesions - changes associated with cancer, infection or other diseases. The authors admit that visual inspection of the bones by a trained anthropologist provided the greatest detection rates of pathologies, but that characterisation of pathological spread or nature was complemented by radiographic imaging.
Harris lines provide an example of paleoradiography being used to estimate biological stress in an individual (see below). The influence of poor diet or illness causes an arrestment in bone growth, leading to a dense line across the long bones (best seen on tibia). The open access article by Beom et al (2014) provides an example of Harris line detection in a population of medieval Korean skeletons in comparison to modern equivalents.
Both tibiae from the same individual in medieval St Alban's, United Kingdom. Harris lines are more commonly seen in the distal tibia.
Example paleopathologies and conditions
The examples shown below are from Open Access published literature. These demonstrate the use of paleoradiography within archaeological research. These examples have been compiled as an appendix file available to download and within the Learning Resources section.
Estimation of age
Radiography of teeth may provide an estimation of age due to the predictable eruption rates of permanent teeth. As a child we have deciduous teeth (baby teeth) which fall out as we develop our adult (permanent) teeth. Whilst the visual inspection of dental remains of an adult may account for all teeth without the need for radiography, juvenile remains pose a greater challenge. In such instances the radiography of dental remains provides a great advantage for accurate aging. This is a large topic of forensic, anthropological and archaeological interest with many different methods and equations used to estimate age.
Dental wear has been mentioned in previous sections of this course and may indicate the age of the individual. The article by Mays, Sakrzewski and Field (2022) provides a recent re-evaluation of the scoring chart used for molar dental wear. The authors use remains from Neolithic to Post-Medieval Britain to examine tooth wear alongside estimated age at death. Although limited to British remains, the authors state that their scoring chart may be used with other populations.
Identification of corroded metal objects
Radiography may identify corroded metalwork and contribute towards the archaeological report. As mentioned within Part 1, identification of metal finds may be used as a triage method to decide which items would be cleaned and preserved and/or subjected to further analysis.
Caple and Garlick (2018) provide the best overview of paleoradiography being used with metalwork finds. The content of this article is more closely aligned with commercial archaeology, where radiography may highlight archaeological finds that warrant preservation. Depending upon the degree of geometric unsharpness, radiographs can also be used to measure specimens, such as internal dimensions. The chapter by Marie-Anne Loeper-Attia (2007) mentions the use of radiography when assessing metalwork corrosion. For those working with chemical-film processing systems, the article by Scott (1976) provides a good overview of X-ray and metalwork (you will need an institutional login for access).
Photodensitometry
Introduced within Part 2, photodensitometry can provide the investigator with a relative density when compared to a known quantity (the aluminium step-wedge). This is an old method of estimating bone density which has been superseded by DEXA scanners. In the distant past investigators would quantify the amount of light coming through an X-ray image to estimate bone density. Digital radiography has improved the accuracy and efficiency of the process, although the article by Manifold (2014) converted chemical film to a digital format to achieve the same result.
Within her study, Manifold examined 72 medieval skeletons from Cambridge and Gloucester (United Kingdom) to estimate bone density at different sections of the radius and femur. Her results suggest that densities differ greatly between individuals, but this may be due to taphonomic changes whilst interred within the ground.
Brickley (1997) provides her PhD thesis on bone density, which explains and compares photodensitometry with other methods for application with archaeological remains.
Radiogrammetry
Bone loss can also be estimated by measuring cortical bone thickness of the carpal bones. This was covered within Part 3 and relies upon an appropriate radiographic technique being deployed to minimise image distortion. Rather than comparing the density to aluminium, the method of radiogrammetry provide a thickness index, where a low index indicates osteoporosis (i.e. greater bone loss).
A procedural guide for radiogrammetry (using archaeological bones) is provided by Ives and Brickley (2004), although you will need access to the journal or pay for the article.
As recommended previously, Gilmour et al (2021) explores radiogrammetry with archaeological remains using digital radiography. Glencross and Agarwal (2011) provide an example of radiogrammetry data collection in a Neolithic Turkish population. Both articles require institutional access.
How can this data be used?
Again, this depends upon the research question posed by the investigator and the scope of the investigation. Does it relate to the in-depth analysis of one individual (as with the remains of King Richard III) or a population of individuals within one context? Paleoradiography of everyday items may provide indication of activities at a location or contribute towards an understanding or manufacture process.
Studies such as Hunt, Roberts and Kirkpatrick (2018) provide the wider picture of human pathologies, with a systematic review for the evidence of cancer within archaeological research. The application of paleoradiography may provide a robust tool for archaeological research in order to answer these larger questions about human existence.
Why is this important to paleoradiography?
Paleoradiography, as a tool of archaeological research, must be used appropriately whilst accepting the limitations of each method of data extraction. Performing radiographic imaging of items purely for curiosity is counterintuitive. Without investigation and dissemination of results the value of the images are limited to the individual who took them.
I accept there are other reasons for undertaking paleoradiography, such as the development of radiographic technique or for education purposes. For successful data extraction to occur the investigator must apply the correct method as necessary. This should take into account the key concepts covered within this course:
Radiographs as a two-dimensional representation of a three-dimensional object.
The relationship between specimen density and greyscale upon the radiograph.
The effect of geometric unsharpness upon image quality.
