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Phase-Contrast CT Captures Microscopic Details Of Mummy

September 25, 2018 -- What can today's radiology professionals learn from CT scans of the ancient past? Plenty, according to Swedish researchers, who used a technique called phase-contrast CT to reveal micron-sized details in a mummified hand and published their findings online September 25 in Radiology.

Volume-rendered reconstruction of the phase-contrast CT scan of a mummified hand (a). Axial view of the hand (b). Axial section of the third and fourth fingers (c). Image courtesy of RSNA.

Phase-contrast CT provided microscopic detail of soft-tissue anatomy in the mummified hand of an Egyptian boy who probably lived 2,400 years ago. The researchers believe the resolution of phase-contrast CT surpasses that of conventional CT by a factor of 100 -- and could someday be useful in the clinical realm.

The group, led by lead author and doctoral candidate Jenny Romell from KTH Royal Institute of Technology in Stockholm, acquired propagation-based phase-contrast CT scans of an ancient Egyptian mummy. They found that the high spatial resolution of this technique allowed them to discern tiny soft-tissue structures -- such as individual layers of skin, fat cells, and blood vessels -- at sub-0.01-mm resolution.

"The biggest advantage of phase-contrast CT is that we can image the soft tissue in situ, at high resolution (down to the cellular level) without damaging the sample, which is not possible with other methods," Romell told AuntMinnie.com. "We see phase-contrast CT as a natural complement to the existing methods for the investigation of mummies and other ancient remains."

Give CT A Hand

Clinicians and archaeologists have long studied mummified human anatomy through histology -- an invasive method that relies on the extraction of tissue samples, the authors noted. More recently, developments in imaging technology have led to the application of x-ray, CT, and micro-CT in the field as nondestructive options.

But however useful these imaging modalities are for visualizing hard tissues such as bones, they do not provide sufficient contrast to illustrate soft-tissue structures in high detail.

Conventional x-ray and CT are fundamentally limited in imaging soft tissue because they rely solely on the absorption of x-rays to create different degrees of contrast in an image. An alternative to this technique is phase-contrast CT, which measures the absorption of x-rays and also the phase shift of x-rays as they pass through tissue.

This form of propagation-based imaging enhances the contrast of soft tissue in CT scans and, thus, facilitates better differentiation between types of tissues. MRI is also capable of capturing soft tissue but is restricted to resolutions of approximately 1 mm, whereas phase-contrast CT hits resolutions of sub-0.01 mm (6 µm to 9 µm) -- ideal for identifying cellular-sized features.

Evaluating the technique in a laboratory setting, Romell and colleagues performed phase-contrast CT scans on an Egyptian mummy dated to around 400 B.C. They first acquired nine scans of distinct regions of the mummy's hand and then combined these scans into a single dataset using image reconstruction software (Octopus Reconstruction, XRE).

To get an even more detailed look, the group acquired a phase-contrast CT scan of just the tip of the mummy's middle finger. The reduced surface area enabled them to maximize phase contrast by using smaller equipment that provided greater magnification, as well as by increasing the exposure time per scan.