PART 1.3 - CORE CONCEPTS
What is radiography?
Radiography is typically associated with the use of X-rays in medical imaging, although it has a wider remit of application. For example, X-rays may be used as non-destructive testing in industrial radiography for metal joinery and welding. Industrial radiography, as its name suggests, uses equipment of higher power to penetrate metal objects. Among other possible suggestions, the assessment of aeroplane wings comes to mind. There are direct applications of radiography in archaeological research, but also fossilised remains as this example of a middle Eocene primate demonstrates.
Example of X-rays being used to image middle Eocene primates (47.8 to 38 million years ago). Images reproduced from here.
Within the United Kingdom the discipline of radiography is closely aligned to the title of radiographer, which is a protected title requiring registration with the Health and Care Professions Council. This means that you are not legally entitled to call yourself a radiographer without state registration. The use of X-rays and who can operate them differs between countries based on legislation and training. I shall not be providing an overview of who can do what, but I will say that the medical imaging of living patients and those of forensic value (i.e. deceased) would be conducted by a state registered radiographer.
In comparison, you would not need to be registered with a regulatory body to use X-rays with archaeological specimens. In my opinion, the lack of formal training may lead to misuse, or misinformation through an absence of 'proper' imaging or inappropriate interpretation of images.
No matter what type of radiography you conduct, all will require the same basic equipment:
An X-ray generator (something that produces x-rays)
An X-ray receptor (something that receives the x-rays to produce an image)
A power source
Protective equipment for the operator (including a method of measuring dose)
I shall not go into the physics of how X-rays are produced now (phew!) as it is more pertinent to Part 2: Image Brightness/Contrast where we will explore the relationship between specimen density and image grayscale.
It is important to consider the radiation protection issues surrounding radiography and the use of ionising radiation. All radiation use implies a level of risk, with greater risks associated with longer exposure to radiation or higher radiation levels. Staff who use ionising radiation are required to monitor their radiation levels using dose badges. Within the United Kingdom we use the body badge to record our doses, but there are also similar variants with finger rings and glasses to record eye dose. For a detailed overview of radiation safety and protection, I recommend this StatPearl available here.
Examples of x-ray equipment:
The images below present different types of X-ray equipment throughout the last 100 years.
Videos:
The following videos have been created to help your understanding of X-rays and radiography. The first video shows you the old X-ray room at Canterbury Christ Church University (which has since been replaced). We use X-ray rooms on campus to teach the diagnostic radiography students and take X-rays within archaeology.
The second video introduces the key benefits and limitations of X-rays and how objects are shown as two-dimensional images. For an example of chemical film processing (of X-rays) visit this YouTube video.
* Please note, this was the old X-ray room at the university and has since been replaced.
The X-ray equipment seen in other archaeology units may be based on chemical film processing. I am lucky enough to have access to digital detector technology.
Main benefits of radiography:
Non-destructive
Non-invasive
Allows quantitative investigation
Other benefits of radiography:
Relatively cheap (when compared to computed tomography)
Provides an objective permanent record
Produces digital files that can be -
Manipulated to improve image quality, discern subtle structures or extract additional information
Stored more efficiently than physical film
Shared more efficiently between users (intranet or internet)
Main limitations of radiography:
'Only' black and white
Representation of entire object as a two-dimensional image.
Not all objects can be X-rayed successfully
Image interpretation requires suitable training
Reading task
Read the short chapter 'The Basics of X-rays' by Guillermo Avendaño Cervantes in their book titled Technical Fundamentals of Radiology and CT (2016).
The chapter can be found using this link. The whole chapter is shown on the website, alternatively it can be downloaded as a PDF for offline reading.
This chapter ties together many of the concepts of physics and medical imaging equipment described above, with a little more detail on some aspects.
Estimated reading time: 11 minutes
