Instant Film

At this point it should be clear that conventional film has a number of disadvantages in a field application. Even though large quantities of film may be easily acquired as a donation, the need for a darkroom, chemistry, and water make it tremendously problematic. In addition, even if automatic processing is available, the occasional need to repeat films will result in the examination of fewer specimens. Because x-ray and visible light are both forms of electromagnetic radiation, photographic films and papers used for photographic prints can be used to record radiographic images. Since Polaroid provided a solution for medical imaging over 50 years ago, it seemed the logical choice. Through the mid-1980s, old Polaroid medical imaging systems could be found in storage at many major medical centers.

In a 1986 study of a mummy known as the "Soap Lady" at the College of Physicians Mütter Museum in Philadelphia, Pennsylvania, the Polaroid system made it possible to complete a radiographic examination of the mummy on-site (Conlogue et al. 1989). Although several medical imaging centers were within a few miles of the museum, the mummy was too fragile to be transported. A donated 30-year-old x-ray unit was brought to the site for the study, but processing the images would have to be done at a medical center. Since the relative speed of Polaroid intensifying screens matched the speed of the conventional radiographic screen cassette, the exposure factors for different regions of the

Figure 2.24 The 4 x 5 in. (10 x 12.7 cm) Polaroid Type 53 film of a femoral head and neck. Note the detail resolution of the trabecular pattern.

body were established with the Polaroid system. Using the Polaroid technical factors, over a dozen conventional 14 x 17 in. (35.5 x 43 cm) radiographs were obtained without having to repeat any exposures. Unfortunately, Polaroid discontinued the manufacturing of the film for its imaging system in 1990.

In 1997, once again the need for a nonconventional radiographic film recording media was necessary for the establishment of a field radiographic facility at an anthropological site in Peru (Conlogue and Nelson 1999). Polaroid Type 53 photographic film provided a partial solution to the problem. Since it was a film intended for photographic applications, it could not be used with an intensifying screen, but only as a nonscreen image receptor. The two major disadvantages were that nonscreen imaging required extremely long exposures, often many seconds long and the limited size of the 4 x 5 in. (10 x 12.5 cm) film. However, the film was large enough to image small structures, such as a femoral head to determine trabecular patterns in age determination (Figure 2.24) or mandibles to access dental development and pathology (Figure 2.25). Although it did not completely eliminate the need for conventional radiographic film, it did reduce the number of films that needed to be processed and established the value of Polaroid in the field.

A representative (Phalen 1998, personal communication) for a Polaroid distributor suggested a larger-format (8 x 10 in. [20.3 x 25.4 cm]) product that could be used with an intensifying screen system introduced in 1984 and manufactured by Calumet Photography. The system, targeted for use by veterinarians, podiatrists, and bomb squad personnel, also had two types of film available. Because the films were photographic products, the film sensitivity was indicated in ISO (International Organization for Standardization) and the European equivalent DIN (Deutsche Industrie Norm) units (Redsicker 2001). The faster the film, the higher the ISO/DIN. Unlike x-ray film, which is orthochromatic, that is, sensitive to only specific wavelengths of light, photographic film is panchromatic and therefore reacts to the entire spectrum of visible light. Type 804, Polapan® Pro 100, was the slower, more detailed film (100 ISO) described as a glossy finish, medium contrast with a key application identified as professional photography proofing (Polaroid, a). Type 803 (800 ISO)

Figure 2.25 three views of an infant mandible on 4 x 5 in. (10 x 12.7 cm) Polaroid type 53 film.

was described as a high-speed, glossy finish, medium contrast with a broader range of key applications including microscopic imaging, copy stand photography, and x-ray bomb detection (Polaroid, b).

The authors have used both the Type 804 and the Type 803 in field imaging settings with excellent results. It is important to realize the differences in the application of the two Polaroid Type films. The slower speed, Type 804, loaded into the cassette provided excellent detail. Since Type 803 is more sensitive, it was better suited for situations when there wasn't sufficient space for the cassette and the nonscreen approach was necessary. For example, if the technique required for a Type 804 film loaded into the cassette required a 2 s exposure, that same film would need 200 s for the same nonscreen exposure. However, because the Type 803 requires 1/8 the exposure time as the Type 804, only a 25 s exposure would be necessary. Not only is less time required to produce the image, but also the reduced exposure time has the additional advantage of prolonging the life of the x-ray tube.

In a laboratory situation, an object or specimen similar to that which will be encountered in the field can be used to determine the optimal exposure factors for the Polaroid and conventional radiographic film/screen systems. A conversion factor can then be calculated. Once in the field, the appropriate technique can be determined with the Polaroid system, the conversion factor applied, and a series of conventional films can be taken with the adjusted technique. At the end of the day, the exposed films can be transported to a facility for batch processing, saving valuable on-site research time.

There were three drawbacks to using Polaroid film as a field image receptor: limited size (4 x 6 or 8 x 10 in.; 10 x 15.2 or 20.3 x 25.4 cm), cost (about $15.00 per sheet for the larger size), and the need to ship it to the country where the study was to be conducted. The cost made it prohibitive for large-scale projects. Even with those considerations, the instant film yielded excellent detail and eliminated the need for a darkroom and wet processing chemistry. The ideal system for fieldwork would be a filmless digital x-ray system, which will be discussed in Chapter 3. However, recently an even greater disadvantage materialized. As of May 2008, Polaroid stopped manufacturing Type 804 and 803 films.

The experience with the Polaroid suggested that other photographic products may also provide satisfactory images. In order to eliminate the problems associated with shipping materials outside of the United States, a photographic product that would be available universally was sought. It was decided to test Ilford MGIV photographic print paper. As a photographic product, it was sensitive to a panchromatic spectrum of light similar to the Polaroid photographic products. As a comparison, one sheet of the 8 x 10 in. (20 x 24.5 cm) Ilford paper was loaded into the Polaroid cassette, and another sheet loaded into a 100-speed conventional radiographic cassette. Following each exposures, the paper was placed into a cylindrical Unicolor® eight real day light processor (Figures 2.26A and 2.26B) and developed with Ilford PQ Universal developer with agitation of 30 s. The developer was drained and fixer poured into the tank and agitated for another minute. After the fixer was poured off, the paper was washed in the tank for 5 min. The resulting images demonstrated that the Ilford paper placed into the Polaroid cassette provided an excellent image (Figure 2.27A). However, because the conventional radiographic screen emitted ortho-chromatic light, the resulting image with the Ilford paper in the x-ray film holder was unsatisfactory (Figure 2.27B). An additional test was carried out with the Ilford paper in a nonscreen film holder (Figure 2.28) with excellent results (Figure 2.29).

It certainly would be impractical to carry out an entire study using the photographic print paper; however, the paper has several applications. Once the satisfactory kVp and mAs, have been established for the photographic paper, a conversion factor for conventional radiographic film can be calculated. This reflects the procedure described previously for the 1986 study of the Soap Lady.

In addition, "on-the-spot" images can be obtained to check positioning before conventional radiographs are taken. If the positions need to be altered, it can be done without the delay of having to wait for the conventional radiographs to be processed.

Figure 2.26A Unicolor® day light processor.
Figure 2.26B Photograph showing the orientation of the Ilford photographic paper (arrow) within the unicolor® tank.
Figure 2.27A Lateral skull radiograph using Ilford photographic paper loaded into a Polaroid cassette.
Figure 2.27B Lateral skull radiograph using Ilford photographic paper loaded into a cassette with conventional radiographic intensifying screens.
Figure 2.28 Positioning the Ilford paper in a nonscreen film holder.
Skoliose Rdiografie

Figure 2.29 Lateral skull radiograph with Ilford paper loaded into a nonscreen film holder. Positioning

Even if the most sophisticated facilities are available, poor positioning of the remains will render the images of little value. Proper positioning can minimize the effects of superimposition of shadows, one of the principal disadvantages of conventional radiography. Wrapped mummified remains present the greatest challenge, particularly if they are in a flexed position. Without the ability to visually identify landmarks, the first image only documents the relative position of internal structures. From that x-ray, a skilled radiographer should be able to determine how to manipulate the mummy bundle to achieve the required position.

Even if the remains are in an extended position, subtle manipulation of the remains may be required. For example, if a suspected structure, such as a fracture, is noted on a projection (Figure 2.30A), the body can be rotated into an imaging perspective that will more clearly visualize the region in question (Figure 2.30B). In situations where the remains cannot be safely rotated, the x-ray tube and the image receptor can be positioned to achieve the same results (Figures 2.31A, 2.31B, and 2.31C).

For skeletal material, the task is less formidable. Since the bones can be placed directly onto the image receptor, there should be no questions as to the position. For both the mummified and skeletal remains, imaging projections should be identical to those used in medical imaging. There are volumes dedicated to describing proper position methods (Frank and Ballinger 2003) for the entire body, and the information should be used as references for any paleoimaging study.

The most valuable projection of the skull is the lateral. In many cases, it will reveal characteristics that indicate the sex of the individual, such as presence or absence of a

Figure 2.30A An AP radiograph of the right hip of a Guanajuato mummy (MH7) with an apparent fracture (arrows) of the pelvis.

browridge and external occipital protuberance, and it will provide an overview of the dentition. To obtain a lateral projection of the skull, the interpupillary line should be perpendicular (Figure 2.32A), and midsagittal lines should be parallel to the image receptor (Figure 2.32B). Positioning can present a problem in cases where there has been intentional cranial modification.

In order to more completely evaluate the dentition, right and left oblique projections of the mandible and maxilla may be necessary. However, to obtain these views, particularly on flexed remains, a great deal of manipulation of the x-ray tube and image receptor will be necessary (Figure 2.33). For the optimal images, the side of the mandible and maxilla of interest should be parallel to the image receptor. The opposite side should be rotated to eliminate superimposition.

There are several methods to acquire an anterior-posterior (AP) (Figures 2.34A and 2.34B) or posterior-anterior (PA) (Figure 2.35) projection of the skull. Taking into considerations the objectives of the study, a radiologist should be consulted to determine which projection would most clearly demonstrate the structures desired.

In cases of mummified remains, an AP or PA and lateral projections of the chest and abdomen should be acquired. Although dehydrated soft tissue structures are not usually visualized on conventional radiographs, when those tissues are calcified, such as lymph nodes or plaque within arteries, they are clearly seen (Figure 2.36). The lateral view will not only provide a second projection to assist in determining the spatial location of any

Figure 2.30B With the body rotated, the extent of the fractures (arrows) became clearly delineated.
Figure 2.31A An AP chest radiograph taken of the Soap Lady mummy at the Mütter Museum of the College of Physicians. Because the radiograph is a two-dimensional image, it is not possible to determine the exact location of the large radiopaque object in the chest.
Figure 2.31B Because the mummy could not be rotated, the cassette (arrow) was angled beneath the table to obtain an oblique projection.
Soap Lady Mummy

Figure 2.31C the oblique radiograph of the chest conclusively demonstrated that the radiopaque object (arrow) was located outside of the mummy's body along the posterior aspect of the back.

Soap Lady Mummy

Figure 2.32A For a lateral projection of the skull, the interpupillary line (A) should be perpendicular to the plane of the film (B). Although there appears to be a great deal of distance between the skull and the film, with a slow speed intensifying screen, the image will be magnified without a tremendous loss of detail.

Figure 2.32A For a lateral projection of the skull, the interpupillary line (A) should be perpendicular to the plane of the film (B). Although there appears to be a great deal of distance between the skull and the film, with a slow speed intensifying screen, the image will be magnified without a tremendous loss of detail.

Figure 2.32B The midsagittal line (A) should be parallel to the plane of the film (B) to minimize rotation on a lateral skull projection.

Figure 2.33 Since the mummified remains are immobile, positioning for an oblique mandible is complex. The center ray of the x-ray beam (A) must be directly beneath the side farthest from the film. To enhance separation of the mandibular bodies, the plane of the film (B) should be slightly angled, 15° to 20°, from a plane parallel to the sagittal plane of the skull (C).

Figure 2.33 Since the mummified remains are immobile, positioning for an oblique mandible is complex. The center ray of the x-ray beam (A) must be directly beneath the side farthest from the film. To enhance separation of the mandibular bodies, the plane of the film (B) should be slightly angled, 15° to 20°, from a plane parallel to the sagittal plane of the skull (C).

calcifications but will also afford a prospective of the spine with less superimposition (Figure 2.37).

The mummy's joints, including shoulders, wrists and hands, hips, knees and ankles, should also be radiographed. An attempt should be made to obtain as close as possible to AP or PA projections of the joints to document degenerative changes. With the exception of remains in a flexed position and possibly hands and wrists on extended mummies,

Canthomeatal

Figure 2.34A For an AP projection of the skull, the line extending from the outer canthus of the eye to the external auditory meatus, known as the canthomeatal line (A) should be perpendicular to the plane of the film (B). The center ray of the x-ray beam (C) should be directed through the midpoint of the browridge, the glabella, and perpendicular to the film plane.

Figure 2.34A For an AP projection of the skull, the line extending from the outer canthus of the eye to the external auditory meatus, known as the canthomeatal line (A) should be perpendicular to the plane of the film (B). The center ray of the x-ray beam (C) should be directed through the midpoint of the browridge, the glabella, and perpendicular to the film plane.

Skull Centering
Figure 2.34B The resulting AP skull projection. It will be noted that the orbital content in this projection is obscured by the petrous ridges projected into the structure.

superimposition should not be a problem. In order to eliminate superimposition, a non-screen film holder may be placed underneath the hands and wrists (Figures 2.38A and 2.38B).

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