Transcription
Hello everybody and welcome back.
Now today we are going to be looking at the various different x-ray detection systems that we have at our disposal. And in the next series of talks, I'm going to look at each one of these systems individually, showing you the process required in order to generate a radiograph that we will end up looking at and analyzing.
Now, x-ray detection systems detect x-rays that have been transmitted or scattered through a patient and convert that x-ray signal into an actual radiograph. Now, we can broadly classify x-ray detection systems into two main categories: screen-film radiography and digital radiography.
Now, when we talk about screen-film radiography, we are talking about the actual plastic film that we hold up to a light box. And that film has varying different optical densities, allowing different amounts of light through the film and creating the radiographic image that we see on the film. Now, this film cannot be manipulated digitally. It's not on a computer screen. It's a physical copy that we can carry around.
Digital radiography systems refer to the digital image that we are creating. The final radiograph will be available on a computer screen. And on that computer screen, that radiograph will have pixel values for each one of the pixels in that image. And because those pixels have a grayscale value, we can manipulate that image after we've taken the image. We can increase the contrast. We can increase the exposure to the image. We can digitally manipulate that image.
Now, we can further subdivide digital radiography into two separate categories, and this is where it sometimes gets a little bit confusing. The first category is known as computed radiography, and the second is called digital radiography. Now, this initial digital radiography is referring to the end product, a digital image. This second classification, digital radiography, refers to the way we process and store our image. The processing and storage of the x-ray images here in digital radiography happens in a digital manner. We are storing charging capacitors that can then be transferred to a computer. In computed radiography, we create a latent image in our computed radiography cassette that we can then process into a digital image. This is a manual process, the processing of this image that then converts this latent image into a digital image. So, the processing, the storage of the images in computed radiography is analog, and in digital radiography is digital.
Now, we can further subdivide x-ray detection systems into cassette-based systems and cassette-less systems. Both screen-film radiography and computed radiography require us to hold a cassette that we then place behind a patient. And once we've exposed that patient to x-rays, we can physically take that cassette away for processing in order to create our image. We don't get the image instantaneously on our computer screen. That cassette needs to be opened up, needs to be read out, and then we can create an image, be it a film that we can physically hold or a digital image that we've sent to our computer. In cassette-less systems, we can get an image almost instantaneously sent to our computer. Everything is digital in that pathway. We don't need a physical cassette that we take and process.
We can also subdivide the systems into those that require scintillation and those that don't. Now, scintillation is the process of converting x-ray energy into light, and that light energy is then used to create our x-ray image. So, our indirect digital radiography system and our screen-film radiography system both require scintillation. Computed radiography and direct digital radiography do not require scintillation.
Now, this scintillator layer here, we're going to look at in the process of fluorescence, immediately converting x-rays into light. This is a process we're going to look at. There's another process here called phosphorescence, where our x-ray energy is then later converted into light. And when there's that delay in conversion of x-rays to light, we call it phosphorescence, again, a process that we will look at when we look at computed radiography.
So, it's good to know when we take a step back that there are multiple different systems. We've got a screen-film radiography system, a computed radiography system, our indirect digital radiography system, which can either be using a CCD chip or a TFT array, or we can look at our direct digital radiography system, taking x-ray energy and directly converting it into an electronic signal on a TFT array that can be then processed on our computer screen.
So, we're going to start by looking at screen-film radiography. I'll take you through the steps that go into creating a film that we hold up to a light box. We'll look at the characteristic curve of that screen-film before heading to our digital radiography system. So, I'll see you all in that next talk. Goodbye everybody.