 Let's briefly touch on the T2 characteristics of central region nodules. They're pretty much the same as nodules that we've been discussing previously, but here's the challenge. You know, in the peripheral zone, the normal signal intensity is bright. So anything that's dark at least gets your attention. If it's wedge-shaped, non-mass-like, linear, septated, punctate, we don't worry about it. We toss it aside. But if it's round or bulging, and it has some minor criteria with it, that's easy. But in the central zone, everybody's got bright nodules. Those are easy because they're bright. Most cancers are not bright unless you have a mucinous tumor, which is not very common. But what about all these dark hyperplastic nodules? That presents a problem. So if they're very round, very well-defined, and you can see a dark rim around them, which I look for, those are a pyrrads 2. If I see a nodule, and most of it is well-defined, but part of it is a little ill-defined, that's when you get into the pyrrads 3, especially if some of the other criteria are somewhat supportive. That is when you get thrown into the pyrrads 3 no man's land designation. But you just saw an example of a patient that had involvement in the central region of the prostate gland, where there was a very lenticular-shaped area, especially as we got down low in one of the prior vignettes, the last vignette. As we got down low, you saw lenticular involvement and a ratio of the entire anatomy, both the central anatomy, the surgical capsule, and even the peripheral zone. All of them were completely wiped away. And that made the diagnosis, that makes the diagnosis of pyrrads 4 in the transitional zone and central region a lot easier. And then pyrrads 5, same thing, except you have size. Diffusion weighted MRI. That's what you came to hear about. D-W-I-M-R. Here's how it works. Let's take the example of a stroke. When you have a stroke, the water that is normally micro-diffusing in your brain along white matter tracks goes into the damaged cell membrane of a neuron, and it gets trapped there. It can't move around. And that's why you get diffusion restriction in a stroke. So that's one example of diffusion restriction, but it's only one. What happens if you have desmoplasia? Firmness. Scar tissue that is elucidated by a tumor, but yet there's increased water in the region from the tumor. Or for other reasons, like hyperperfusion or hypervascularity. Then the water may be restricted in its movement. But you might say to me, well, what about a scar? Why doesn't a scar versus a tumor, because both of them are going to have desmoplasia, why doesn't a scar give you diffusion restriction? How much water is there in a scar? It doesn't have water in it. So when you have water and desmoplasia together, like you have in a tumor, you get restriction of that water. That's another reason. Third reason. Viscosity. Where is that demonstrated? In two examples you know about from your experience in neuroradiology. Abscess. Epidermal. So that's easy. You know, if you get something really viscous in the prostate gland, really thick, then you could be in a situation where there is diffusion restriction. And a prostate abscess would be just that scenario. So let's take the situation where we have a Pirates I designation just for DWI. We have no abnormality whatsoever on the diffusion weighted image. Now let's talk about the diffusion weighted image for a second. How do you make the diffusion weighted image? You start out with what we call a reference image. There's something you're going to see called B. What does B stand for? B stands for the power and the efficiency and the rapidity on and off of the diffusion gradients. The higher the power and the faster you turn them on and off, the more sensitive they are for micro molecular motion. So you can play with those gradients in increments. It's kind of easy to think about it as B0, you don't have mon, your reference image, which is really a T2 weighted echoplane or image, 400, 800, 1200, 1600. And you could plot a curve and see what the behavior of diffusion is as you change that B value. You'll also see people do it asymmetrically. 0, 50, 150, 450, 900, 1600. So you can play around with those numbers a little bit, but the more points you have on the diffusion plot, the more accurate you're going to be in planning and assessing how aggressive a lesion is. And the brighter it gets as the B value goes up, the more likely a tumor is to be aggressive. And that plays into the DWI assessment. So the B value is something you should pay very careful attention to. It's usually in the upper left-hand corner of the image. As that B value goes up, cancers and things that really restrict diffusion are going to get brighter and brighter. But that's not the whole story. Because then you can take each pixel and you can measure the velocity of micro molecular movement per pixel. And when you restrict diffusion, what happens to that velocity? It goes down, right? There's no movement or less movement. The lesser the velocity, the lower the pixel plot, the darker the plot. So on the ADC map, if you have velocities that are very restricted, the signal is now going to be the opposite of the DWI image. The map is going to be low. And believe it or not, sometimes the parametric map will be positive, but the DWI is negative. So you absolutely have to have them both, and you have to look at them both. Pirates, too. The ADC map is more sensitive than the DWI. So the ADC map may show a little indistinct low signal intensity, but the DWI is normal. Very common. You see this a lot in people with BPH, benign, prostatic hyperplasia. Pirates, three. You've got some low signal on the ADC map, but it's not inordinate. In other words, it's very mild, and the DWI is kind of all over the place. There may be a few areas that are very high, a few areas that are a little bit high, and a few areas that are in between. In other words, no man's or no woman's land. DWI, Pirates 4. Here you've got a definite area of hyperintensity on the multi-parametric map, also known as the ADC map, and there is a clear, definitive, matching area of hyperintensity on its accompanying DWI image as the B value goes up. So the higher the B value, the brighter and brighter and brighter and brighter the cancer gets. So if it's high in the beginning and it gets lower and lower and lower and lower, that's not so good for your diagnosis of cancer. It's a little counterintuitive. The nice thing about DWI is, as the B value goes up, the signal of everything goes down, but the only thing that tends to persist is the thing that is diffusion restricted. And many of you have learned that from using diffusion elsewhere. Pirates 5, easy, same as a 4, but greater than 1.5 centimeters in overall size, either on the ADC map or on the DWI. And there may or may not be extra prosthetic extension. All right, let's move on now to the next Pirate's 2.0 designation. If you want to take a ride with us, and it's been yet, and that is the DCE MRI.