PART 4.2 - PALEORADIOGRAPHY IN RESEARCH
Using DICOM files
Within medical imaging the vast majority of images are stored as Digital Imaging and Communications in Medicine files (DICOM). This is a file format used across different imaging technologies and equipment such as radiography, computed tomography, ultrasound, magnetic resonance imaging and so on. Whilst there are different makes and models of imaging machines, all imaging files should be in the same format so they can be shared easily between hospitals. For example, an X-ray taken using a Siemens machine could be exported and viewed on a General Electric system.
Within paleoradiography there are many benefits of using DICOM files as opposed to film. A Picture Archive and Communication System (PACS) is a database of DICOM images. The X-rays I obtain for my research isn't on a PACS system, as there are too few to warrant it, however large collections of medical images would need to be stored on servers with a PACS system.
Many commerical archaeology providers, and universities, still use chemical film radiography or those which print out the resultant images. It is possible to digitise the film/printed media. There are limitations though, the resolution may be different and the embedded data may be lacking. Interestingly, the utility of digitisation has been explored previously within archaeology / museum studies by O'Connor and Maher (2010). Although not open access, the article explains the benefits of converting old film into digital files for storage and viewing.
These videos explain what DICOM files are, and how they are used.
Benefits of DICOM files:
Image manipulation - The contrast and brightness of an image can be changed to demonstrate low or high density structures, or to potentially save the image from under or over exposure to X-rays. Images can be manipulated and exported as JPEG files for use in reports, emails or websites. DICOM files can be magnified or inverted according to viewing preference of the investigator.
Embedded data - DICOM files have integrated data which may include the place where the imaging was undertaken, the 'patient' name (or specimen details), along with date / time of imaging. Some systems also embed the exposure factors (kV / mAs) used at the time of imaging. Other details may be added to the image by the operator, for example I use a radiographic marker and annotate the radiographic projection and exposure values used.
Radiographic measurements - Another aspect of embedded data includes a spatial element to the files which allows direct measurement of the specimen, internal structure or parts thereof. This does not take into account any geometric unsharpness (image distortion) as a result of radiographic technique, but instead shows the distance according to the size of the detector originally used at the time of imaging. Measurements are normally shown in units of millimeters, although you can also measure the number of pixels per unit area (useful for photodensitometry).
Management, storage and sharing of images - Digital files are easier to store than physical film and may be shared remotely. The ability to adjust and export images as smaller files (e.g. JPEG) improves sharing of files. When I qualified as a diagnostic radiographer I remember the mass transition towards DICOM files and how all the physical film had to be digitised using an elaborate scanner. The availability of all DICOM files at a touch of a button also allows the investigator to compare X-rays relatively quickly, assuming that the files have been named and managed logically. PACS systems have allowed vast quantities of medical imaging to be available anywhere on a network, including across the internet.
As you may anticipate, I am biased towards the use of DICOM files for paleoradiography.
This may be due to my lack of involvement with chemical film radiography, although I am aware of several archaeological organisations which still use it due to the large financial cost of digital imaging.
In any case, I believe the future of research within paleoradiography is with the use of digital radiography and all the benefits that come with it.
