Ionizing radiation applied to archeology and forensic techniques

There are several procedures for acquiring computed tomography and magnetic resonance imaging that are very useful in the study of corpses and objects, which is why the application of this equipment in archeology and forensic medicine has become popular in recent years. The three-dimensional reconstruction, through the associated software of said equipment, allows a very useful interactive visualization, since it allows discerning between the different internal tissues. On the other hand, through morphometry the shape and dimensions of the organs are determined, and with densitometry, for example, bone densities are calculated.

For example, for a pelvic CT acquisition of a patient, typical parameters are 130 kV and 130 mA·s. In the case of objects and corpses, time is no longer a variable, since there is no need to fear irradiating more than what is regulated. So you can adjust the parameters to get better quality, even if it means giving more doses than you would with live subjects.

To obtain a good image quality, it is important that the photoelectric effect is dominant, since a large part of the initial energy is absorbed. This effect depends on the atomic number (Z) and the energy (E) like Z4/E3, that is, it is the majority effect at low energies. But on many occasions, low energy radiation is not enough to pass through the desired material well. In such a case, one option is to increase the energy of the radiation source but then, as shown in figure 1, the Compton effect comes into play which introduces scattered photons, causing the image to lose contrast.

In the event of acquiring images of people, according to the ALARA criteria, the radiation levels administered must be as low as reasonably possible. However, when we are interested in acquiring images of objects or corpses, there is no concern about the administered dose. So how do archeology and forensic radiology teams operate? Using high power produces regular images, so high exposure times (mA s) are set. As I said above, since the typical problems in patients such as breathing and overdosing do not occur, it does not matter that the acquisition is slow. In this way it is possible to obtain a very well contrasted image in all the densities of the body being studied and also with very high resolution. The price to pay is a slight increase in noise in the images, so it is normal to make several acquisitions.

Any CT and MRI available in a hospital are useful for performing these imaging studies. In the case of TCs, there is a preference for using dual RX sources with simultaneous dual detectors. In the case of NMR, the higher the magnetic field, the better image quality (preferably ≥ 3T).

One of the main differences of imaging techniques compared to other techniques is that the studied body is not manipulated or damaged, since radiation is not invasive. This is a great advantage, just remember the damage that was done when unwrapping the Egyptian mummies to proceed with their study (or, what is sadder, sometimes for mere fun). The most famous of these calamities is that of Pharaoh Tutankhamun (Tut for friends, year 1311 BC), whose mummy is fractured at all its joints. Today, thanks to CT and MRI studies, we have an approximate idea of what he looked like and many other facts about his life and death have also been determined. For example, we know that Tut died at the age of 19, that he had no evidence of malnutrition, and that his height was approximately 1.70 m.

It is precisely in the field of archeology where forensic radiology is experiencing great development. Currently it is possible to see images obtained through these techniques in some museums and interact with them, resulting in a very didactic exhibition. As an example, I leave you a video from the British Museum in London where this technique is explained applied to a case that is currently exhibited in its Egyptian collection (see Figure 3). By the way, I also take this opportunity to recommend that you go visit it, admission is free and it's worth it.

A very curious case is that of an Egyptian mummy belonging to the Ptolemaic dynasty, about 2,250 years old, from the National Archaeological Museum of Lisbon. Right from the start it is a unique piece, but its importance increased when the researcher Carlos Prates diagnosed him with prostate cancer in 2011 when he observed sclerotic lesions in the vertebrae and pelvis, suggestive of metastasis of said cancer, already at a very advanced stage ( see Figure 4).

It is not the only case, cancer was also diagnosed in a corpse of a Russian king from 2700 years ago. These studies show that prostate cancer is not a new disease caused by modern lifestyle or pollution, but genetic.

Another curious case is that of a Buddhist monk, about 1000 years old, who after being mummified was covered with so much gold leaf that it looked like a sculpture. Apparently, what the monk, while alive, left written in his last wishes, was done, but with the passage of time that is forgotten and… luckily they did not decide to crack the sculpture to verify it, because what a scare they could have been carried. Although there are those who say that the monk is not dead, but plunged into a deep sleep, so perhaps after all if they should have worried about the dose in this case.

There are also times when archaeologists find CT very useful in determining the characteristics as well as the causes of death of mummified animals. For example, the case of a certain baby elephant that died of suffocation by ingesting sediment is famous. Possibly the little elephant fell into a swamp or quagmire and couldn't get out. This discovery provides information on the existence of said wetland and, therefore, on the climatic characteristics of that time (see Figure 5).

In summary, forensic autopsy (also known as virtopsy) should be considered not only as a post-mortem procedure (which complements but does not replace traditional autopsy), but as a way of examining body parts in an interactive way. It is a very useful technique when a reproducible, precise and non-invasive forensic anatomical examination is required. The main application lies in forensic pathology (study of injuries and causes of death, injury trajectories…), thanatology (biochemical study with MRI, post-mortem angiography with CT), identification of skeletal remains and forensic anthropology (review what they give of the Egyptian mummies).