Transcription
Hello everybody and welcome back.
Now, over the last few talks, we've spent some time looking at the cassette-based radiography systems, our screen film radiography as well as our computed radiography. Both of which create a latent image within our cassette that we can then go and process in the future prior to seeing our final image.
Now, we're going to shift our attention to the digital radiography systems. Now, when we talk about digital radiography here, we're talking about the way in which we detect, store, process, and ultimately display these images. This all occurs electronically or digitally. There's no analog latent image that's created. We can see our image almost instantaneously.
Now, our digital radiography systems can be further subdivided into indirect and direct digital systems. In our indirect digital radiography systems, we require x-rays to first be converted to light, prior to that light energy creating an electronic signal. So, we need what is known as a scintillating layer. We need x-rays to be converted to light.
Our direct digital radiography systems can take that x-ray energy and directly convert them into an electronic signal that we can store and ultimately process into an image. So, we need this scintillating layer in our indirect radiography systems. And we've seen a scintillation layer before when we looked at screen film radiography. We saw those two intensifying screens that sandwiched our film, and that intensifying screen created multiple light photons from one x-ray photon. And all of that light energy was needed to deposit silver atoms onto our film itself.
So, let's take a moment now to look at this scintillation layer and see how it differs from the intensifying screen that we used in our screen film radiography. Now, in screen film radiography, we use gadolinium oxysulfide, this amorphous phosphor that had no repeating structure to it that created multiple light photons and spread them in all directions from a single x-ray photon.
Now, in digital radiography, we use cesium iodide. Now, cesium iodide is created in these long tubular crystal structures. We get these columns of cesium iodide here. Now, when an x-ray strikes our gadolinium oxysulfide, we get this isotropic release of light photons, multiple light photons that spread out as they travel through the intensifying screen. We can see the lateral spread that occurs here of these light photons, and we get a reduction in our spatial resolution. We get good signal, we get intense light signal, and we need that intensity in our screen film radiography because we need that energy in order for our silver atoms to be deposited on the film.
Now, our direct digital radiography systems are much more sensitive to light. We don't need that high light intensity. We are able to detect much lower intensities of light. What we want is improved spatial resolution, and our cesium iodide allows us to do that. A single x-ray photon is going converted into light, which is then funneled down onto a small area on our digital radiography detection system. So, cesium iodide has improved spatial resolution, but it creates a much less intense light signal. Our gadolinium oxy sulfide is firstly much cheaper, and it creates a lot stronger light signal at our detector level, but that comes at the cost of a loss of spatial resolution as those light photons spread out traveling through this phosphor.
So, our indirect digital radiography systems require the scintillation layer, and we use cesium iodide in that scintillation layer. That is what separates it from our direct digital radiography systems, and that's a common question that comes up in exams. What's the difference between indirect and direct digital radiography systems? And the main difference is this scintillation layer.
Now, if you are studying for your Radiology Part Ones or your registry exams, these types of questions I've collated into a question bank that I've linked down below. Otherwise, we're going to look at our first indirect digital radiography system known as the charged couple device, the ability to detect light and convert that into a radiograph. So, I'll see you all in that talk. Goodbye everybody.