Cinefluorography is the process of making X-ray motion films by photographing the image from a fluorescant screen, rather than by capturing the X-rays directly on the film emulsion. Typical clinical diagnostic applications are observing heart, circulation or swallowing disorders. It is useful for general speech research by revealing how articulator movements are coordinated to shape the entire vocal tract. A typical diagnostic or research application in speech pathology is the study of clefts. Methodology is concerned with issues like exposure and safety, and camera settings needed to resolve movement.
Early procedures required continuous X-ray emission, as though filming with light, and radiation exposures were consequently considerable (Subtelny et al. 1957). In the 1950s, a maximum dose of 20-25 roentgens was said to be acceptable by Lusted and Miller (1956). This is approaching the exposures used in clinical radiation treatment (in contrast to low exposures for diagnosis). In 1960, Moll estimated his radiation exposures to be 3.9 roentgens from filming at 24 frames/second for 3 minutes. A finer grain (but less sensitive) film emulsion for better image quality would have required exposures around 7.5 roentgens for the same motion film. Higher filming rates for better temporal resolution in order to capture rapid movements would have called for even more intense radiation. By the 1970s and 1980s, improved image intensifiers required far less radiation while emitting enough light for both fine-grain emulsions and faster camera speeds. Another technical advance was intermittent radiation bursts synchronized with the camera shutter, which obviated the former need for continuous radiation and reduced exposures considerably. Smaller radiation doses were also offered by X-ray microbeam systems (Kiritani et al. 1975a and 1975b), a method more suited to tracking individual articulators (usually defined by a small metal pellet) than to outlining the contours of the vocal cavities.
Shutter speed refers to the number of pictures taken per second, given as frames/second (a frame is one image on a strip or reel of film, or one image in a digital video recording). The tradition of the early cinema was to have shutter speeds in multiples of eight (8, 16, 24, 48 frames/second). A slow speed fails to arrest movement on one frame, giving a blurred image in consequence. A fast speed consumes more film, resulting in less talking time by the informant for the same radiation dose. A frame rate of 24/second fails to resolve and delimit speech manoeuvres with sufficient precision. This gave the impression that the speech articulators are never still. A lot can happen during 40 milliseconds in speech – an articulator can turn round and be on its way back again, or an occlusion can be missed completely between two frames at this speed. A minimum rate of 50 frames/second is essential for getting close to resolving speech movements. Our X-ray motion films were made at 75 frames/second. The articulators are seen to complete their excursions and then wait until called on to move again.