 So, why prostate MRI as opposed to say ultrasound or digital examination or serum PSA? First of all, serum PSA has a sensitivity of 36 percent for diagnosing prostate cancer. That just frankly is not good enough. Digital rectal examination is somewhere far south of that. And in terms of assessing tumors, we use histologic rating called the Gleason score. We'll talk about that at a separate time, but a Gleason score of seven or over is considered more aggressive, six or less, less aggressive, and that'll be a story for another section. Previously we used transurethral rectal ultrasound to biopsy and define aggressiveness of the Gleason with the histologic Gleason score. But those biopsies were not directed to any one specific ominous locus. They are somewhat random in character until MRI came along. So what are the indications for MRI? Probably the most important indication is surveillance in a low risk tier one individual. So what does a tier one mean? That is a separate vignette coming right up, but we're going to have three tiers of aggressiveness and risk. There'll be tier one, tier two, and tier three. Then we also can use MRI for staging. And the staging will help us identify not only how big the tumor is, but also it's histologic character because there's a correlation between the Gleason score and the appearance on MRI. Now let's go back to surveillance for a minute. Surveillance is used in tier one low risk individuals. So what does that give you? Well, if you can survey the prostate gland and assure that there's not an aggressive lesion and use a conservative method for following the gland, you avert the potential complications of intervention on the prostate gland with all the techniques that are available out there, starting with surgery. With surgery, the risk of having some ejaculatory dysfunction is as high as 60%. The risk of incontinence or leaking is as high as 30%. So if you don't need a procedure for an aggressive lesion, you shouldn't have one. And in the past, we have been operating on cancers that are less aggressive. So we've got surveillance, which can prevent you from having an unnecessary procedure, probably the most important indication of MRI by far, and then second is staging. And staging helps you not only decide the character of the tumor, but also what to do. Because if the stage is later stage, that's a different treatment than if it's early stage, even if they are both aggressive. So we've already talked about avoiding unnecessary surgery, let's take the converse. You've got somebody with a rising PSA and we know that the PSA goes up with age because the normal gland gets bigger, more normal gland, more PSA. So it may be a matter of how fast it rises, but the converse that we're referring to is what if the PSA is rising and there really is an aggressive cancer? How good is MRI at picking up Gleason 8s, 9s, and 10s? Really, really good. How good is it at picking up Gleason 1s, 2s, 3s, 4s, 5s? Not so good. And that's a good thing. Because we're not picking up or not registering a lot of these smaller or less aggressive cancers that should be surveyed for conversion to more aggressive character, which MR does really, really well. MR is used for biopsy, planning, and overlay. So instead of going into a gland, going through the rectum from the back here, and just randomly putting a needle in and saying, okay, I'll take 12 samples, one here, one here, one here, and so on, with MRI, you have directed access to that nodule. You overlay it on the ultrasound using it as a map and you can go directly to that locus and put your needle right where you see the abnormality. And the MR far more accurately shows you these loci than ultrasound ever could. So you have this very nice correlation between MR, truce, and where your needle should go. On top of that, you can take three-dimensional MRI, 3D MRI within sections, and you can volumetrically take a nodule, and then on a series of axial slices, you can simply trace the outside of the nodule from one slice to the next and get a volume of tumor and further assist the accuracy of that trans-urethral biopsy done under sonographic biopsy. The other thing you can use MRI for is recurrence. MR does pretty well in patients that have had prior partial treatments, including subtotal prostatectomies, prostatectomies, which is a more complete treatment, but many of the other treatments that include laser, heat ablation, extra corporation, and other newer techniques that alter the architecture of the prostate, but there are methods to assess tumor recurrence that we'll discuss at a separate date. So we've got surveillance is probably the most important aspect of MRI that's unique. The second most important is directing trans-urethral ultrasonographic biopsy. Probably the third most important is staging, and all of these combined will allow you to avoid unnecessary surgery or intervene if you need to intervene if you've got the landmark correlate of Eglison 8, 9, or 10, and we'll discuss what that correlate is. We also said that we're going to survey individuals that have Tier 1 disease or lower grade types of disease. There'll be three tiers, and we're going to discuss those tiers in a separate section.