Disadvantages of CT

Perhaps the greatest disadvantage of CT scanning applications in anthropology and archaeology is the size of the equipment. CT scanners are most often fixed units within an imaging facility, and accessibility to scanning equipment can be problematic. Since CT scanners were designed to diagnose injury and disease in living people, patient imaging takes precedence over the examination of mummified remains. Getting time to use a scanner often necessitates working late at night or during a period when patients are not scheduled. There are dedicated research centers where a CT scanner may be available, but that is the exception.

Another disadvantage is the potential cost of using the equipment. A center may charge a fee for scanner time to compensate for the tremendous operating costs previously discussed. Living patients can be scheduled on a 64-slice scanner every 5 or 10 min. The short interval is due to several factors. First, the precise region to be scanned within the patient is known. In addition, preset protocols eliminate the need for the technologist to spend a lot of time determining the technical factors required to scan the region requested. Without specific target regions within a mummy, the CT examination can take an hour or more, the equivalent of 6 or 12 paying patients.

Mobile CT scanners are available and are mounted in tractor-trailers. These units hold promise for fieldwork, but the remains or artifact still need to be moved into the scanning gantry. There are also portable CT scanners available, but even these units are extremely heavy and the subjects still need to be moved into the scanner. Anytime the subject is moved, there are the risks of damaging the remains or moving whatever is inside those remains around, altering the internal context. Even if the subject is already out of context, for example, at a museum, it would still need to be moved into the scanner. If mummified human remains are to be placed in a scanner that is used for patients, care must be taken not only to protect the scanner environment from the mummy but also protect the mummy from contaminants in the imaging center environment. A method that has served to stabilize the mummy for transport and protect the environment was first demonstrated to us by Gino Fornaciari, a paleopathologist, during a field project in Popoli, Italy. The study necessitated transporting a mummy from a crypt to the imaging facility. The mummy was first protected by wrapping it in acid-free paper and then sealed in a continuous sheet of clear plastic film (Figure 3.42). This procedure stabilized the mummy for transport and protected the CT scanner environment and the mummy. The remains never had to be unwrapped at the scanner site as CT technology images are captured through most existing materials.

Another major disadvantage associated with CT scanning is the misapplication of settings. After careful transport of the subject to the scanner, suboptimal data collection can result from individuals operating the CT unit who are inexperienced in examining mummified remains. As demonstrated by our experience with the mummy from the Barnum Museum, the technologist may need to spend hours using trial and error to locate the correct algorithm that will result in the most useful diagnostic images.

CT scanners have been designed for use on living people and have preset protocols, or algorithms, "built in" for data manipulation. These protocols, designed for hydrated tissue, were intended to increase the patient throughput and, ultimately, the productivity of the imaging facility. A bone algorithm increases edge enhancement, while soft tissue algorithms decrease edge enhancement and apply edge smoothing. Unfortunately, these protocols do not always select the best algorithms for dehydrated or mummified remains. Also, the specific protocols vary among the many manufacturers of CT equipment. A

Figure 3.42 Mummy wrapped in acid-free paper, then "sealed" with a continuous plastic wrap, cushioned, and gently strapped for travel by ambulance. The plastic wrap decreases the potential for contamination of the CT imaging equipment as well as the mummy.

skilled paleoimager must apply the protocols creatively to acquire optimal images from mummified remains.

In a field situation, a systems specialist from the manufacturer may be sent along to operate the instrumentation. These individuals may have little experience with the CT scanning of living humans and no experience with CT imaging of mummified human remains. Proper data collection requires the skills of a specially trained paleoimager knowledgeable about various imaging modalities, manipulation strategies for data collection for anthropological and archaeological research, mummification methods, and burial practices. Unfortunately, radiologists do not generally possess these skills.

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