hello everybody and welcome back I hope you're all doing well today we're going to be looking at the anode heel effect we'll see what causes the anode heel effect what factors we can change in order to reduce the anode Hill effect and then look at how we can use this effect to our advantage when taking radiographs now in the last talk we looked at the focal spot and we saw that reducing the anode angle reduced our field size as well as reduced are effective focal spot size we also saw that our effective focal spot size actually changes throughout our field the closer we get to the anode side we get a smaller effective focal spot and as we move out towards our cathode side we get a bigger effective focal spot now today we're going to look at the anode heel effect and I don't want you to get confused with that variation in effective focal spot size and the anode heel effect so what exactly is the anode heel effect well the anode heel effect describes the variation or the difference in x-ray beam intensity between our anode side and our cathode side of our x-ray beam or of our field now this variation in x-ray beam intensity occurs because when we produce x-rays we're still going to go through this through the process of brainstorm or characteristic radiation x-rays are released in 360 Degrees they're isotropic they're released in all directions now a proportion of those x-rays will head out towards our patient those x-rays on the cathode side of our x-ray field have to travel through a relatively shorter distance of the anode than those on the anode side of our x-ray beam field now those that travel through the heel of our anode this area here is called the heel of anode will be attenuated more because they have to travel through a further distance and that's why this is called the heel effect the intensity of these x-rays leaving the anode is less than the intensity of those on the cathode side of our field and that's simply due to the distance that they had to travel through the anode now a common misconception is that our Electron Beam hits our anode and forms x-rays on the surface of our anode the x-rays are actually formed within our anode here and it's because these x-rays have to travel through differential distances depending on whether they're on the anode or the cathode side it leads to this variation in x-ray beam intensity so there are three parameters that we can change in order to manipulate the anode Hill effect now the first is the anode angle you can see that with a larger anode angle the distance at the anode side of our beam has to travel through the heel of the anode is less than for a smaller anode angle when we reduce our anode angle the heel or the effective heel gets bigger here and our anode side of our field has less intensity than it would in a larger anode angle reducing that anode angle increases the heel and increases our anode heel effect so if we want to reduce the anode Hill effect in our x-ray field we can increase our anode angle the second thing that changes our anode Hill effect is what's known as our source to image distance our source is where x-rays are produced where electrons interact with our tungsten in our anode and produce x-rays that is our source our image refers to where the image is created our detector or our cassette that is detecting x-rays they've passed through the patient and now they're now hitting our x-ray detector if you look at the variation here between the start of our detector and the end of our detector we are almost getting the full spectrum of varied intensities here if we move that detector away we increase our source to image distance as we move it away that variation between this end of our detector and this end of our detector is now less we are not getting these high energy or high intensity x-rays here and we've lost some of these low intensity X ratio that variation is less we've reduced our anode Hill effect by increasing our source to image distance now the last thing that we can do is change our field size we can do this by a process called collimation where we remove x-rays on the anode and cathode size of our field now this process collimation we're going to go through in two talks time and we'll see there are multiple benefits to collimation one of which is reducing the anode heal effect if we use our entire field here to create our image our detector will experience the entire range of intensities between our anode and cathode sites if we collimate that beam down to a small region that differential in intensity is much less if our detector was now detecting all of these x-ray beams so firstly we can change our anode angle increasing our anode angle reduces our anode Hill effect we can move our detector further away from the source and that will reduce the anode Hill effect and we can collimate or reduce the field size that we expose our patient to and that also will reduce the anode heel effect now the anode heel effect is not all bad we can use it to our advantage when we are x-raying certain portions of a patient certain regions in that image will be more dense than other regions so for here we can see that our pelvis which contains our pelvic bones and our pelvic organs that is more dense than our abdomen which mainly contains air and some abdominal organs there's less dense bone here in our abdomen we can use the more intense part of the beam that has better penetration to go through the more dense part of our patient the less intense part of the beam because of the anode Hill effect can then interact with the less dense part of our patient and the end point of that is that our detector has a more even exposure because the higher intensity beam is interacting with the higher density portion of our patient this can happen in our foot where our ankle is more dense and more thick than our forefoot and we can place the cathode side of our beam over the ankle the same happens in mammography where our chest wall is more dense than the periphery of the brain test we can place the Dan's chest wall on the cathode side of the beam and then as the breast is compressed and gets thinner that goes out towards our and outside of the beam so that summarizes the anode heel effect in a nutshell it describes the variation in x-ray beam intensities between the anode and cathode end of our field and it's due to the differential distances that the x-rays have to travel when leaving the anode the anode part of our beam has to go through a larger part of the anode hill now this is a very popular question when it comes to exams and it can be asked in multiple ways including how does it benefit us how do we reduce the anode heel effect and we're often asked to define and explain how the anodehe effect occurs these are the types of questions that come up in the question bank that I've Linked In the first line of the description below if that's something you're interested in go and check it out in our next talk we're going to cover a process called filtration a really important process when we're looking at x-ray physics we can reduce our x-ray dose while simultaneously improving our x-ray image so I'll see you all in that lecture goodbye everybody