Several techniques have been developed for detecting radiation: the ionization chamber; scintillation counter, and proportional counter tube.   However, very few have been established for detecting a radiation image two-dimensionally: photo-film, the two-dimensional proportional counter tube, X-ray image intensifier and X-ray TV.   Among these, the means most widely used in various fields is photo-film.   The differences between the Imaging Plate and photo-film are clearly illustrated characteristically in Figure 5, depicting the detection of beta rays from radioactive isotope ³²P.

Figure 5: Comparison of characteristics between Imaging Plate and photographic methods (for autoradiography).
      The abscissa is radiation of a standard sample of ³²P (beta rays 1.7 MeV) used for exposure, measured by liquid scintillation counter.   The left ordinate is the amount of luminescence from the imaging plate.   The right ordinate is the blackened density of photo-film.   The visible limitation is the limit necessary to distinguish between the "presence and absence" of an image, and is generally about 1/10 of the determination limit.

      Similar characteristics are obtained with other beta rays of different energies, electron rays, X-rays, and gamma-rays.

      The features of the Imaging Plate method become clear when compared with other radiation image sensors.

1. Ultrahigh sensitivity.   Several ten times more sensitive than film, and several thousand times depending on the sample.
2. Wider dynamic range.   A wider range of 10⁴ to 10⁵ over the 10² range of the photographic method.
3. Superior linearity.   The fluorescence emission is proportional to the dose in the entire range.
4. Higher spatial resolution.   When compared with other electronic systems, a higher pixel density can be designed to meet the system purpose though less freely than film.
5. Digital electric signals are directly available from the reader.   Computer processing or combination with other electronic systems is easy.
6. Due to an integral-type detector, the IP method produces less detection counting errors even at a high flux density, which often happen with pulse-type detectors such as the proportional counter tube and scintillation counter.
7. The accumulated background can be erased before use.

      The Imaging Plate method, replacing the conventional radiation image sensors, not only visualizes the latent radiation image with a high sensitivity through the digital process of conventional radiation image sensors, but also makes it possible to quantify the position and intensity of the radiation image.