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Seal head

Anders Persson

Download this image from Wellcome Collection.

Computed tomography (CT) scan of the head of a seal. Virtual 'slices' were taken of the seal using X-rays. These were then used to create a 3D digital model that can be rotated, sliced and magnified as required to obtain a desired view. Different colours and degrees of transparency can also be applied to the various tissues. In the upper image, the skin has been made opaque to reveal surface details such as skin texture and whiskers, which are visible on the face of the animal. In the lower image, the skeleton has been made opaque and different layers of skin and fat tissue have been made partly see-through to reveal the bone of the skull underneath. This technique is extremely useful for noninvasively investigating and diagnosing medical conditions and for performing virtual autopsies.

How was this image created?

This dead seal was imaged to study its anatomy in more detail. Conventional CT, which uses a single X-ray source, was used to scan the animal in a series of virtual 'slices'. These were then digitally reconstructed using a 3D volume rendering technique to produce a digital model that can be rotated, sliced and zoomed into as required. Within the model different colours and degrees of transparency can be applied to different tissues - including fat, bone, parenchymal organs and contrast-enhanced vessels, as well as air - to increase the visual differentiation between them. Anders described the process as being "like painting in oil - you mix opacities and colours, and this can be time consuming."

How is this technology being used?

This is a noninvasive imaging technique that can be used on living animals and people, for instance to study anatomy, diagnose medical conditions and perform virtual autopsies. In a clinic setting the technology can be used together with contrast agents (angiography) to enable the visualisation of blood vessels and their contents. For example, it can be used to render vessel calcifications in a different colour to vessel contents, or to verify the success of a procedure post-operation (such as the insertion of a stent). Scans can be performed in seconds with patients only being exposed to very low doses of radiation. Alternatively, in forensic investigations a corpse can be virtually explored to determine the cause of death, or the contents of an object or package looked at without compromising any evidence, and the results then used to inform how a post-mortem examination might be carried out.