An example of an indirect DR image receptor with high photoelectric capture of the remnant beam and a low amount of light spread is: AGdOS/a-Si (gadolinium oxysulfide/amorphous silicon) BCsI/a-Se (cesium iodide/amorphous selenium) Ca-Se (amorphous selenium) DCsI/a-Si (cesium iodide/amorphous silicon)
The answer is D.DR image receptor technology is subdivided into two main classifications: direct capture and indirect capture. A direct capture system is choice (C); it uses an amorphous selenium capture layer to convert the remnant beam directly to charges captured in a capacitor. Indirect systems are those that convert the remnant beam into visible light first, and then convert the light to electrons in an amorphous silicon layer. Choices (A) and (D) are both indirect capture devices. Of these, the CsI, with atomic numbers of 55 and 53, respectively, increase the probability of photoelectric absorption greatly. Additionally, CsI crystals grow in needle-like structures, and trap light photons in ways similar to fiber optic cable. For these reasons, (D) is a better answer than (A), as GdOS is a turbid phosphor unable to control the spread of the light signal. Lastly, choice (B) is not a common arrangement of capture and coupling layers would not effectively capture the image. The energy associated with visible light would not be sufficient to create ionizations in the amorphous selenium layer.
The indirect DR image receptor with high photoelectric capture of the remnant beam and a low amount of light spread is gadolinium oxysulfide/amorphous silicon (AGdOS/a-Si). The receptor is composed of two layers: The first layer, gadolinium oxysulfide (GdOS), is a scintillator that converts X-rays into visible light. The second layer, amorphous silicon (a-Si), is a photodiode array that converts the visible light into an electrical signal.
The high photoelectric capture of the remnant beam is due to the high atomic number of gadolinium (Z=64) in GdOS. This makes it more likely for X-rays to be absorbed in the scintillator layer, generating a higher signal-to-noise ratio. On the other hand, the low amount of light spread is due to the thin a-Si layer, which limits the diffusion of the visible light photons. This reduces blur and improves the spatial resolution of the image.
Other indirect DR image receptors with similar properties include cesium iodide/amorphous selenium (CsI/a-Se), amorphous selenium (a-Se), and cesium iodide/amorphous silicon (DCsI/a-Si). These materials have different trade-offs in terms of sensitivity, resolution, and cost, depending on the application.