Rest in Peace

During our discussion of x-ray technology today, I thought Haseena brought up a good point when she asked whether the use of x-rays to identify jewelry in a mummy's tomb was damaging to the mummy's bones.  So I did a little googling and found recent investigations that were using full-body scanners (you know, the same ones causing all these privacy rights issues in airports) rather than x-rays to analyze mummies.

Traditionally, x-rays or CT scans are used to study mummies by identifying gender, age, injury, or disease. According to one study, these x-rays and CT scans apply ionizing radiation to the mummies that potentially interacts with the extremely fragile DNA.  The radiation causes a small amount of fragmentation of DNA. Don't worry though, this is insignificant for us because living organisms can quickly and easily repair this brief damage. Of course, our mummified friends aren't so lucky because their bodies can't repair the DNA.  The mummy DNA is already degraded and scarce, and x-rays are only making it worse.

Enter the full body scanner. A menace for airport security, but a potential solution for anthropologists. The technology used in the full body scanners is called Terahertz imaging. This applies non-ionizing radiation in the region between microwave and infrared on the electromagnetic spectrum, meaning that these waves have a longer wavelength than x-rays.  They are apparently harmless to human cells.

This diagram depicts a standard Terahertz (THz) spectroscopy system.  There is one lens that generates THz pulses, and a mirror focuses the emitted beam onto the sample at a specific position.  The beam is transmitted through the sample and is refocused onto the detector by a second mirror.  The detector records the time-delay of the pulsed signal as it passes through the sample. 

The THz imaging technique has both advantages and disadvantages. Its unique time-delay recording (which isn't possible with x-rays) can give information about the optical density of the material, aka tell us whether it's bone, soft tissue, or some kind of metal (jewelry).  Also, the THz device can obtain images at different frequencies at the same time.  Images with low frequencies show larger structures such as major arteries, while higher frequencies show more bone structure detail.  One complaint about THz is that its signalling doesn't work as well for thick samples, but this problem is mostly eliminated with mummies because all of the water in human bodies has dried up, leaving just the bones and dried tissue. The down side of THz imaging is that while it distinguishes bone vs. tissue, it doesn't differentiate for specific tissues types.  With x-rays, different soft tissues can be individually identified.

For mummies, at least, this full-body scan technique seems like a better solution.  And the mummies can't complain about their 4th amendment rights being violated, so it's all good.

http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1031&context=anthropologyfacpub
http://onlinelibrary.wiley.com/doi/10.1002/ajpa.21292/pdf