Taking the X-rays

Once the body arrived at Bethesda, the medical staff on hand lifted it from the shipping casket and placed it on the autopsy table. Bethesda’s Chief Radiologist, Captain Lloyd Brown, was away at a radiology conference in Chicago. Dr. John Ebersole filled in and served as the autopsy's radiologist. He stood by along with two radiological technicians, Jerrol Custer, and Edward Reed. They had already transported a portable X-ray machine to the autopsy room. Ebersole’s function was to direct the taking of any requested X-rays and to assist the pathologists with interpretation and diagnosis. The two technicians operated the equipment, made the exposures, and ran them up to the X-ray department on the fourth floor and developed them.

The immediate priority for the Secret Service and FBI was to recover a bullet. Before the pathologists proceeded with the exam, Humes asked Ebersole to take a set of X-rays. These preliminary X-rays included one frontal and two lateral images of the skull. The pathologists noted only bullet fragments but no intact bullet in these films, so they asked the radiology staff to take films of the rest of the body. The primary purpose of these X-rays was to locate a bullet. Making images that, in Ebersole’s words, displayed "fine diagnostic detail" was a secondary concern.

Bethesda’s portable X-ray machine was an old General Electric 250. Its base was about 3-feet square and the tower containing the X-ray source was about 6 feet above the floor. The unit had wheels, but its weight of1500 to 2000 pounds made it difficult to move around. Once the body was ready for examination, Humes directed the radiology staff to take a frontal image of the skull.

Normally, the technician positions the body with the film in front of the face so that the X-ray beam passes from back to front, or Posterior-Anterior, or PA. Custer knew that he was not going to be able to turn the body over onto the stomach that night, so he and Reed just lifted the head and slid the film cassette under it. As a result, the image was an Anterior-Posterior or AP projection. This X-ray is often called "the AP" for short.

Rigor mortis and the instability of the head introduced a second complication. Rigor mortis left the head stuck tilted back approximately 30 degrees by Custer’s estimate. They tried propping the head up, but the severe fractures in back of the skull prevented them from raising the head the necessary amount. Thus, the AP image would be an upward projection, called a "Modified-Waters" projection. (A full Waters projection is 45 degrees upward, but PA rather than AP.)

The technicians then positioned the X-ray tube 44 inches above the film, aimed and collimated it, and then adjusted the energy level. Taking an X-ray is much like taking a quality photograph. The goal is capture as much detail and tonal range (from black, through gray, to white) of the subject as possible. The exposure must be set so that the region of interest does not appear too light or too dark on the film.

The film cassette is not drawn to scale in the diagram at the right. They are much thinner (shorter in the diagram). Also, the X-ray beam passes through the whole cassette irradiating both screens.

An X-ray beam’s strength is reduced as it passes through more tissue and as it passes through denser tissue. A beam passing through a head from left to right will pass through less tissue than a beam passing from front to back. To get a proper exposure on the film, the technicians measured the depth of the skull and set the energy level on the X-ray machine according to a chart attached to the side of the machine. They then activated the X-ray tube and made the exposure.

The X-rays fan out from the anode of the X-ray tube in a cone-shaped beam. Each ray travels in a straight line from the tube to the film cassette, however, the action of the high energy ray on the body can produce a new X-ray that travels at a random angle to the original ray. This stray radiation is called scatter and it strikes the film along with the original beam leaving a uniform image on the film called scatter fog. Fogging is undesirable because it reduces the contrast of the image.

To reduce scatter fogging, the technicians placed an X-ray filter grid before the film. The filter grid functions as Venetian blinds for X-rays. It is made of a series thin lead strips stood on end separated by strips of X-ray transparent material. Lead blocks X-rays and the arrangement of lead strips on the grid passes those rays coming straight down at the film cassette and blocks those coming at an angle. Since most of the scatter rays strike the film at odd angles, the grid effectively blocks these and reduces the amount of scatter fogging in the final image. Custer and Reed used grids that had 60 lead strips per inch. One artifact introduced by the grid is shadows of the lead strips. The shadows show up as fine lines across the X-ray. Some of these are visible in the enhanced X-rays the HSCA published.

X-ray film is not too much different than photographic black and white film. The film will react to X-rays in the same way it reacts to light. (Passing your undeveloped vacation film through the X-ray scanner at an airport causes the film to fog slightly). However, the radiation level required to form a good image is higher than desired for patient safety. To make more efficient use of the X-rays, the film cassette holds intensifying screens in contact with the film. These screens fluoresce or glow when struck by X-rays. The film records the visible light they generate much like any photographic film.

To increase the contrast of the image, that is, to allow a greater range of tonal values from dark to light, the X-ray film has an emulsion coating on both sides. The dual-emulsion also keeps the films physically flat without curl. The film cassette has two intensifying screens, one on each side of the film so that the same image forms on each emulsion.

After taking the preliminary X-rays, Custer and Reed carried the cassettes up to the Radiology Department on the fourth floor. To allow for the possibility that an X-ray did not develop satisfactorily, Reed loaded two film sheets in each cassette rather than the normal single sheet. To compensate for the extra film, he had to boost the X-ray energy level to make the screens glow brighter during exposure. (The diagram on this page shows only a single dual-emulsion film in the cassette.) If the first film did not turn out, he could hand-develop the other one. If the first copy was underexposed, for example, he could partially compensate by developing the second one a longer time.

Reed brought the cassettes into the dark room, removed one film sheet from each cassette and placed them in the Kodak M-3 automatic developer. 6 minutes later, he had the developed X-ray ready for use. Since the initial films were satisfactory, he did not need to develop the second copies and destroyed them by exposing them to room light.

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