Computed Tomography CT scan

Each of the previously described imaging techniques collects 2D data, which can at times raise new questions about the dimensions of an object or anomaly and its precise location and relationship to other structures within the subject. CT scans, as described in Chapter 3, collect data digitally as an x-ray source circles the object. The images are produced and presented as slices, much like sliced bread, or in volumes. Each slice can be of varied thickness, depending on operator settings. Basically, the thinner the slice, the more precise the data. Each slice can then be examined for anomalies and an idea of its exact location and size can be obtained. The CT image has a much higher resolution than standard radiography, potentially yielding more information. The slices can be postprocessed and manipulated digitally by stacking the slices and creating a 3D image that can be further manipulated to show only specific densities like bone, effectively removing the skin and organs in order to study the skeletal system. The image can be remanipulated to study just the surface characteristics of the mummified remains. Image manipulation can "strip" away wrappings to "see" what lies beneath without needing to unwrap. Newer methods include manipulating the image to create a virtual "fly-through" of hollow structures within the subject. The virtual fly-through technique produces an image similar to videoendoscopy and can see into places that the VE cannot if there is no access route for the VE. In an attempt to develop a field procedure similar to the virtual fly-through in a laboratory setting, we compared the images obtained from the CT fly-through technique with standard endoscopic images. The VE was directed to collect images of specific structures within the cranial vault of a mummified Peruvian head. The CT virtual fly-through technique was also employed to

Figure 4.21 Image comparisons between CT fly-through imaging (left panels) and the corresponding videoendoscopy images (right panels).

create images of those same endocranial structures. We found that the images were comparable, with the endoscopic images being less subject to digital drop-out as the CT system "smoothes" the data collected (Figure 4.21). Additionally, the endoscopic image demonstrated a truer color representation than did the CT system (Posh and Beckett 2000).

Although CT is a powerful imaging tool, its major drawback is its size. Although there are "portable" units available, the instruments are not easily transported, often weighing 1000 lb (453.59 kg) or more. This necessitates bringing mummies or artifacts to the imaging center, whether that is in a medical facility or in the back of a tractor-trailer truck. This increases the risk of damage to the mummy or artifact that could potentially altering the spatial relationships among anatomical landmarks. Transporting the mummy to an imaging facility may also cause movement of artifacts within burial bundles, altering the internal context and decreasing the interpretability of the data collected by altering their original associations. An ideal complementary application using videoendoscopy with CT scanning is that of CT-guided biopsy or artifact retrieval procedures. The CT scan can help direct the endoscope to the precise location of the target structure, reducing the procedure time while increasing accuracy.

Was this article helpful?

0 0

Post a comment