Hey, everybody, and welcome to the first video in a series on digital radiography. In this video, we will focus on the components of the cassettes used in computed radiography and how they work. Computed radiography, or CR, is a form of digital imaging that uses a cassette based system similar in many ways to conventional film based radiography. A thin, active layer within a protective cassette records and stores the X-ray energy as an unprocessed image, much like the film in traditional radiography when exposed to X-ray photons. Just like with film imaging, this initial exposure results in only what we will call a latent image and still needs to be processed into a usable radiograph. In computed radiography, this processing is done by a plate reader that will be discussed in another video. So now that we have the basics, let's take a close look at the components of the CR cassettes. The CR cassettes have protective outer cases and a photo stimulable phosphor called a PSP plate made up of five key components. These components are the protective layer, phosphor layer, conductive or anti-static layer, support layer or the base, and reflective or light shielding layer. These cassettes can come in different sizes and are typically constructed of hard plastics, light metals, and carbon fibers. The outer protective cassette only serves as a protective barrier and has no bearing on image production. The protective layer protects the phosphor layer, which is the active component of the plates. The conductive layer serves to ground the imaging plate and reduce electrostatic charge. The reflective layer serves to direct the emitted light in the imaging plate reader. The phosphor layer or active layer is the most important layer within the imaging plate. The phosphor layer, like the film in traditional radiography, is where the latent image will be produced. The phosphor layer is composed of extremely small particles that have the ability to both store and release energy. The most common phosphors are barium fluorohalide bromides and iodides with europium activators. It is these two components, the europium activated barium fluorohalide bromides and iodides, that will work together to capture the X-ray energy photons and create our latent radiographic image. X-ray photon energy is captured in the phosphor layer by energy transfer through a process called photoelectric absorption. This is a key interaction between X-ray photons and matter. So here's what happens. When the X-ray photon strikes one of the atoms in the phosphor layer, it ejects an inner shell electron and is absorbed. This energy from the absorbed X-ray photon excites the ejected electron, making it a photoelectron. During the photoelectric absorption, the number of photoelectrons produced in the phosphor layer is proportional to the number of X-ray photons that interact with it. These photoelectrons then interact with other nearby electrons within the phosphor, exciting them from a low energy valence band to a high energy conduction band. It's in the gap between the conduction band and the valence band that the europium activators in the imaging play act as electron traps known as F-centers. They trap and store the high energy electrons, and it is this stored energy that houses the information that makes up the latent radiographic image or stored X-ray image. The number of electrons trapped is proportional to the number of X-ray photons that interact with the imaging plate. The latent image remains stored within the individual phosphors, until being released by a laser light within the plate reader. In summary, computed radiography is an X-ray imaging system, which utilizes cassettes to capture latent radiographic images and process those latent images into a digital radiograph. The cassettes are made up of several layers along with an active phosphor layer, where the latent image is produced. X-ray photons interact with the phosphor atoms through a process called photoelectric absorption and excites the outermost shell electrons. The excess energy created in this process is stored within the imaging plate, creating the latent image.