Field Radiography Applications Considerations and Challenges General Considerations

Field radiography may be defined as a radiographic examination outside of an established imaging center. Contextual examples for field radiography include remote research facilities, tombs, caves, and museums. Considerations regarding field radiography instrumentation and technique are determined by two primary factors: the proposed location of the study and the specific research goals. Each of these factors in turn produces a wide variety of additional considerations to be addressed while planning the field-imaging project.

The first step in any research project is to define the objectives, and this is no different for a field-imaging study. If the objective of the project is to complete an imaging triage study of a group of mummies in a remote location outside the United States, the preparation will certainly be different than if the remains are housed in a nearby museum.

When determining which instrumentation to employ and what type and quantity of image receptors to use, the paleoimager must consider such variables as the following:

1. How many mummies and/or skeletons are associated with the project?

2. What will be the minimum projections required?

3. What is the predominant cultural practice with regard to mummification position, extended or flexed?

4. What is the nature of the travel required by the project?

5. How can the necessary equipment and supplies be kept to a manageable weight yet include everything that might be required?

6. What problems may be encountered when trying to transport x-ray film, since film packed in checked baggage will be subject to security x-ray inspection?

7. What are the issues surrounding the customs requirements for entering foreign countries and returning your equipment back into your country of origin?

8. Is a list describing the equipment and their serial numbers necessary?

9. Is a list of equipment all that will be needed or is additional official documentation required?

It is apparent that many considerations need to be taken into account in field radiography projects. These and other factors are addressed in the following sections.

Field Imaging: Specific Considerations The Radiographic Unit

Although selecting an x-ray unit may be based on what you can get as dictated by budget or donation, it cannot be stressed enough that the equipment needs to be operated by a trained radiographer with paleoimaging experience. After providing some training, on occasion the authors left equipment with researchers in the field, only to find that they did not anticipate the impact of their application on the unit itself. In one instance, while attempting a long exposure, the unit overheated and the filament broke, rendering the unit inoperable. Without proper knowledge of exposure settings, positioning, and safe unit operation, the results can be disastrous. There are several ways in which the tube can be cooled, but the key is in knowing how to achieve the imaging objectives without damaging the equipment.

A variety of challenges to conducting field radiographic work arise when planning and executing such expeditions. The instrumentation not only has to be compact and light enough to be transported, but also flexible enough to be able to adapt to any number of possible application situations. Dependability of the selected unit is critical. Many of the field challenges described in this chapter are applicable to conventional radiography applications in imaging centers as well, particularly in the forensic setting. Although the authors do not object to radiographic studies of mummified remains being conducted at imaging centers, we feel it is imperative that initial radiographs be conducted on site to determine if the mummy can be moved and if the preliminary data suggest that transportation and its inherent risks are warranted.

A new high-frequency-generated portable x-ray unit would certainly be the simplest approach to an x-ray source. At a cost of approximately $12,000, a MinXray HF 100/30 veterinary unit comes equipped with a collimator and laser-centering light. In addition, it is packed into a nearly indestructible transport case, and together they weigh less than 50 lb (23 kg). However, older operational x-ray units abound. Most, such as dental and mobile x-ray units, are low output, generally not greater than 15 mA and 80 kVp. Since mummified and skeletal remains only require 55 kVp and, due to the lack of motion, long exposure times are not a problem, these units certainly meet the needs of anthropological and archaeological research.

Older dental, medical, and veterinary portable units can usually be disassembled into two separate components, a control unit and an x-ray tube. These nonmounted components can be easily packed for transport and then reconfigured on-site to meet the imaging needs of the particular project.

Often, project directors in locations where there are large stores of mummified remains desire a permanently mounted radiographic unit at the research site. In some of these situations, a mounted x-ray tube is put in place. Unfortunately, a permanently mounted x-ray tube loses the flexibility of application needed. A fixed x-ray tube requires that the subject be brought to the unit and, frequently, the ability to angle the tube is sacrificed. Tube angulation is often necessary to place a body part parallel to the film. The preferred approach is to use a nonpermanently mounted system. This method allows the tube to be placed and directed as the case dictates. The nonmounted system permits unlimited angling, and therefore provides views that have greater interpretability. Additionally, the nonmounted system reduces or eliminates the need to move the subject to the unit, thereby permitting radiographic examination in virtually any remote location, such as within a tomb or a cave.

One particular unit that has been a real workhorse for our paleoimaging team is a 1952 Picker Field Army Unit that was originally used in the Korean conflict and is designed for rugged environments. The unit has two functional pieces and requires two carrying/ shipping cases, creating the need to add baggage-handling costs to each project. Another drawback is that it weighed over 80 lb! We now use a much lighter single-piece unit, the previously mentioned MinXray HF 100/30 veterinary unit.

Utilities

When using radiography in the field, electrical requirements for the equipment must be considered. Often, in remote regions there is no electricity. In other areas there may be electricity, but at best only fluctuating output during certain hours of the day, depending on factors such as the time of year and reservoir water levels required for power generation. We recall one unique power situation in Tucame, Peru, in which our power requirements were such that when we activated the radiographic equipment, the nearby town would experience a transient "brown out"!

Although electric power may be available, it may be a different voltage than required by the radiographic instrumentation. With these and other unexpected situations related to available power, researchers need to learn as much as they can about the available power and remain flexible with their protocols.

In cases where there is no power available, a gasoline- or diesel-powered 5000 W generator is the best option. When relying on a generator, it is important to estimate the potential usage and determine the additional fuel needs for the generator itself. These units are quite heavy and may require transportation into remote regions where no vehicle can travel. This can be accomplished either by carrying the generator or by fashioning a travois, which may be hauled by a beast of burden. In either case, additional manpower will be required for this task. In the case of travois transport, a mule wrangler may be needed as well. The generator is also useful as a backup power source in those regions where the electric power is only active during certain hours of the day.

In most countries, electricity is supplied at 220 V at 50 Hz (hertz or cycles per second). Equipment manufactured in the United States is designed for 110 V at 60 Hz. In order to use the lower voltage units outside the United States, an electrical transformer is required to adjust the current. Traveling with a transformer can be challenging, as it tends to add considerable weight to the overall equipment being transported. Newer transformers are available that are much lighter and, therefore, more practical.

Another important "utility" to consider is water. The availability of water for film processing is critical, as it is required to rinse conventional x-ray film once processed. Access to an ample water supply may be a challenge or, in some cases, the use of the local water may even reduce drinkable water supplies. Additionally, the particulate and mineral content in some local water may impact the final image when processing conventional film. The pH of water with a high mineral content may affect the chemistry used in manual processing. Since the fixer is acidic, the higher pH of the water will tend to neutralize the fixer and require more frequent replenishment of the chemical. In one remote location in the Osmore River Valley near Ilo, Peru, in an effort to conserve water and to create water that was free from minerals, we proposed and designed a water distillation system.

X-Ray Tube Support System

The x-ray tube will often require some mechanism by which the tube is suspended over or placed under the subject of study. The decision of where to place the x-ray tube should depend on a combination of concern for the fragility of the subject and, often more importantly, convenience. Although commercial support systems are available, they may weigh as much as a 100 lb (45 kg), adding extra unnecessary weight. Designing supports for the x-ray tube is a creative process; they can be a formal arrangement of specific metal tubes or an informal contraption that is made from whatever you have available to you.

A formal x-ray tube support system can be constructed from a series of aluminum electromechanical tubes (EMT) cut into 20 in. (50 cm) sections. Once the EMT system has been constructed, the x-ray tube can be secured to the support with duct tape or another suitable clamping system (Figure 2.5). This formal EMT system has the advantage of being flexible in its possible configurations and is quite sturdy, which is important with some of the heavier x-ray tubes. The major disadvantage is that the system, even when dismantled, is heavy and cumbersome, making transportation a greater challenge. Additionally, the set-screws in the hardware used to join the EMT sections can strip, requiring spare parts to be included with the supplies transported to the site.

Informal x-ray tube support systems can be fashioned with common items such as sawhorses, wooden posts, construction rebar, rocks, equipment cases, stacked chairs, and ladders found at the research location (Figures 2.6A and 2.6B). Instead of positioning the

Figure 2.5 The electromechanical tubing (EMT) frame supporting the x-ray tube (arrow).

Figure 2.6A The x-ray tube fastened to the pole with duct tape.

x-ray tube for anterior-posterior projections above the remains, the radiation source can be placed on the floor with the beam directed up for posterior-anterior projections (Figure 2.7). Since duct tape always seems to play a major role in the design of these informal x-ray tube support systems, sufficient quantities should be included with supplies.

Figure 2.6B X-ray tube placed on stacked chairs for a lateral projection of a mummy.
Figure 2.7 X-ray tube placed on the floor to project the x-ray beam vertically through the skull of the mummy called James Penn. The EMT frame was used to support the film holder.

Image Receptors

As described earlier in this chapter, image receptors come in a variety of shapes and sizes, and have set technical factors. Discarded cassettes can be easily found at medical centers or imaging equipment vendors. Optimally, a 14 x 17 in. (35.5 x 43 cm), 100-speed screen would be the best all-purpose choice. This size would cover a large area of the mummy or artifact, and if disarticulated skeletal remains are the study subjects, a number of bones will fit onto a single film. A 14 x 36 in. (35.5 x 91.4 cm) cassette would be a great find. Although that size film has become more difficult to locate (trifold versus single sheet), the greater challenge is loading it into the hanger for manual processing. The cassette can be loaded with two sheets of standard 14 x 17 in. (35.5 x 43 cm) film with 2 in. of screen uncovered (Figure 2.8). The primary advantage of the long cassette is that it covers a large area of the mummy in a single exposure. The principal disadvantage is that generally an SID of 72 in. (190.5 cm) is necessary for the radiation to cover the entire 14 x 36 in. (35.5 x 91.4 cm) cassette.

Conventional radiographic film/screen imaging systems can be problematic. Although expired film can be easily obtained, it may be difficult to match the speeds of the donated screens with expired film. The main disadvantage of a mismatched system is a change in the relative speed and, possibly, a loss of detail. However, if the film and the screen were donated, the financial savings are certainly worth the loss of a little detail and contrast.

When detail is necessary, such as an infant bundle, a nonscreen film holder should be used instead of the cassette equipped with intensifying screen. The resulting image will have greater detail and the textile wrappings and some soft tissue structures may be more clearly visualized (Figures 2.9A and 2.9B). If a nonscreen film holder cannot be located, one can easily be fashioned using the black plastic liner found in boxes of many brands of

Figure 2.8 Two 14 x 17 in. (35.5 x 43 cm) films placed into a 14 x 36 in. (35.5 x 91.4 cm) cassette. Note there were 2 in. (5 cm) on the right side of the cassette, where there is no film.

x-ray film (Figure 2.10). If the black bag liner is not available, one can be easily constructed. Cardboard or 1/8 in. (3.1 mm) Foamcore® can be used as a "stiff" base. The base is then placed into an "envelope" made of black swimming pool liner. The simple black bag film holder without the cardboard or foamcore has the advantage of being more flexible.

Using film without a cassette or screen has various applications. If the space behind the subject is too narrow to allow the passage of a cassette or there is no way to support the cassette behind the subject, nonscreened film can be slid into that space (Figure 2.11). The flexibility and lightweight nature of a nonscreen film holder can be utilized for projections, such as a lateral skull, that could not have been taken without a more complex, time-consuming approach (Figures 2.12A and 2.12B). Another application is when the goal is to image a very large area at one time. Using nonscreened film and allowing the film to overlap so that the images may be reconstructed during postprocessing will produce a single image of the large subject. The drawback to the nonscreened method is that the exposure time needs to be increased by a factor of 100. If a single long exposure were taken, the x-ray tube would overheat and result in permanent damage. Many shorter exposures must be

Figure 2.9A an AP (anterior-posterior) projection of the pelvis and legs of a Guanajuato infant mummy (M1M3) taken with a Polaroid screen cassette at 46 kVp and 1.2 mas.

Figure 2.9 B A similar projection of another Guanajuato infant mummy (GMo8), taken without the use of a screen, on Polaroid film at 46 kVp and 150 mas. Note the more defined appearance of the trabecular pattern in the right ilium with the nonscreen image. In addition, the film taken without the use of the screen provides visualization of the soft tissue structures of the legs.

Figure 2.9 B A similar projection of another Guanajuato infant mummy (GMo8), taken without the use of a screen, on Polaroid film at 46 kVp and 150 mas. Note the more defined appearance of the trabecular pattern in the right ilium with the nonscreen image. In addition, the film taken without the use of the screen provides visualization of the soft tissue structures of the legs.

taken to avoid the overheating potential, and additional care must be taken to keep the x-ray tube cool. The authors have used ice, cool packs, and in one case, chilled champagne to keep the tube cool (Figure 2.13).

Another image receptor system that was available, instant film, will be discussed following the description of film changing and processing challenges. The instant film eliminated many of these challenges, thereby streamlining the conventional imaging procedure.

Figure 2.10 an old commercially available nonscreen film holder on the right and the black plastic envelope removed from a box of film on the left. The latter can be used as a nonscreen film holder.
Figure 2.11 since the mummies were fastened to the wall, it was not possible to place a conventional cassette behind the mummy. Here, a Polaroid film packet was easily placed behind the thorax of a mummy (u1) in urbania, Italy.

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