all right i've had a few questions about aec that i think we could maybe easily clear up kind of quickly um so aec stands for automatic exposure control what is the aec where is it i think are some also easy answers that will help you sort of navigate these questions um your aec is something that can help you as a technologist to produce consistent radiographic images from patient to patient despite their size or pathology it's really uh it's meant to help you where is the adc uh it is in your wall bucky and table bucky the aec is not in the image receptor itself right when you go to do portable x-rays you can't use your photo timing option right you have to set your own mass in kvp you have to be in your rooms with a table bucky or a wall bucky to have access to your aec and so you know as technologists you can either set your own technique or you can photo time i think of it as a car you have an automatic or a manual you decide textbook wise if you're using aec you as the technologist are setting the kvp the ma and you're selecting which chambers or photocells you'll you'll see the terminology sort of both you want to use for your exam you and i both know that when you click pa chest the settings come up on your screen and i understand that you are not going i want to use 117 kv at this ma station and i choose these cells most of this is done for us already and i understand that but textbook-wise that's what it's doing your aec is using an ionization chamber that determines the exposure time it will terminate the exposure when that anatomy is fully penetrated so if you get a question about what you are setting as a technologist you're not setting the mass you set the ma station but not the mass because the s the seconds is determined by the abc there is a minimum response time it's the shortest exposure time possible and that's one millisecond there are a couple advantages to aec there's decreased exposure um repeat rates there's decreased patient exposure because of you know not trying to determine your appropriate mass that you might need for that patient department efficiency with less repeats because of exposure errors or just some advantages of adc the photo cells which i think are it's an old term we're using ionization chambers now but photocells is something you might see also your text that the facility might call them and if you look on the outside of your buckys it's either going to be a three cell format or a five most of the older machines only have three so you have a two outer one center cell set up this is the most common um some of our newer machines have a five cell option um two outer upper ones and um lower and then still a center cell if you have clover learning or the radtech boot camp um account there are two videos that i think are great on aec it's under the radiography image production um settings okay the ionization chamber where is it it is behind the patient but in front of the image receptor remember it's not in your image receptor it's in front of it and has to be in the wall that you use the ionization chamber is going to interact with the exit radiation which is the radiation that is passing through your patient exiting the patient and then before it reaches your reaches your receptor here so there is air in the ionization chamber which is ionized and an electric charge is then um created where you place your chambers or what chambers you select and where you place your anatomy is extremely important aec is great if used properly but if not used properly it will cause errors so you need to think of your anatomy of interest when you are deciding which chambers to use and when you're centering the chambers over that anatomy okay so some examples that you might get asked possible questions would be um you know what are your common photo cell options or ionization chambers for a pa chest you know for phs we use the two outer cells most often well what happens if you choose the center cell will you get overexposed or underexposed you would get an over exposed chest because you are placing sternum thoracic spine and everything in between over the center cell you are asking that equipment to penetrate fully and turn off when it's done it's going to do that for you because that's its job but what you fail to do as a technologist is place your part of interest over the correct cells or number one you didn't choose the correct cells so your lungs which are your area of interest are overexposed lateral lateral cervical spine which is why for all of my students we don't use photocells or photo timing for c-spine because the likelihood that you're directly over that cell is probably a little bit slim to none if you get that anatomy right over that cell it's going to help you it's going to give you an accurate image but what happens if you're not if the part is in front of that cell and basically it's got air it's going to shut off too early and you're going to get it under exposed image okay so if technologists fail to center the part over the cell or they choose the wrong cells we're going to get an error on the content specs list density settings and i think these density controllers are not something commonly used anymore for me that learned on film we use them quite a bit and the concept being your mas controlled your density of your radiograph and we know that's you know not a term we're using these days anymore but if you are using your aec you do a lateral chest x-ray it comes out light and you want to repeat it but you want it to be a little bit darker well when you're using your aac you can't set your mass so what you could do is you could use the density settings and they're usually a plus one or plus two or minus one or minus two and you could use the density settings and ask the auc can you try again and make it a little darker this time and so those were those density settings um i know a lot of you haven't ever seen them or use them but the next time you're doing a lateral chest look on your control options and see what you have available to you the backup timer aec has a backup timer it's used to prevent over exposure to the patient protect your equipment it's a safety measure so there is a backup timer in case it does not turn off at the appropriate sort of exposure time it's going to be set to at least 150 percent to 200 percent over what it expects the exposure time to be for that part if the timer is set too short it will be an underexposure so for my students there's one room at 3300 main street that when you make a lateral chest x-ray and a large patient i'll say aec over it's because it doesn't bump up it doesn't see your patient if you have a large patient you should be bumping that up the maximum mas allowable is 600 mass so if you get a question about a backup timer that's what that is factor changes so if you increase your ma setting your exposure time will decrease and you all know mass reciprocity right how do you calculate mass it's m a times seconds you know that these factors work opposite each other if your seconds go up for say a breathing exposure your ma station has to go down if you want a shorter exposure time for say pediatrics or you're trying to prevent motion you're going to decrease your seconds your ma has to go up remember they work opposite of each other right if your kvp increases your exposure time will also decrease if your sid increases your exposure time will increase it's got to work a little harder to get there if you increase your density setting again your exposure time is going to increase disadvantages well aec is wonderful but it's not a magical unicorn okay so you have to use it properly or set up your settings properly for it to actually help you so we already talked about accuracy of positioning of the cells choosing the correct cell putting the part over the cell some other things that could cause um an error with aec could be prosthetic devices so like your hip replacement or spinal hardware if we know these are there um we need to be aware of where our um chamber selection is or set a manual technique it could be pathology um large amounts of fluid can affect the aec accuracy like pleural effusion if most of these lungs are filled with fluid and we're placing those cells maybe too low into the fluid then it'll change our accuracy with exposures as well collimation can allow um can cause also an error too so if you don't call me if your field is wide open it's going to allow for too much scatter to reach the image receptor those ionization chambers are going to fill faster the more um kind of light field you use so just be aware of that collimation i think is something simple that we can do to improve our image reduce scatter reduce patient dose make sure ac is going to work properly and things like that so basic stuff right exposure index or range a lot of times we use ei number um but remember the exposure indicator is specific to each type of equipment and um as technologists you should be aware of the exposure range for the equipment that you're using it's specific to cr and dr as well so cr for example if you're using a fuji cr plate um fuji cr uses a sensitivity number and an s number we should know that the range is an inverse relationship meaning a high number that's over say 600 is actually an under exposure it didn't use enough technique a low number say 75 or below is too much technique it's an overexposure digital radiography or dr has a direct relationship meaning if your number is high use too much if your number's low you didn't use enough so i think digital is a little bit easier to remember each equipment um like i think shimatsu is an ei um i think it's ge is a dei cannon is a rex um after is like a log mean or something like that i can't remember all of them and i don't think you need to worry too much about those sort of specific names but the relationship for dr is direct cr is inverse and just basics right under exposure would be uh referred to as you know not using not using enough you didn't use enough technique you didn't get enough x-ray photons to the part so usually it's not enough mass remember your mas controls your number of x-ray photons terminology you would see that would go under under exposure would be quantum model quantum noise or image noise it's got a grainy or like sandy appearance see how this one is really fuzzy versus this one it's clear so this is not enough mass it's an under exposure overexposure we refer to as saturation so your technique was too high you saturated that part with too many x-ray photons um we tend to lose some soft tissue detail here or the soft tissue might get burnt out it might be very gray very low contrast because we've over exposed it so it'll look a little bit different than those that are familiar with film but with the digital system it's it's not really too dark too light it's grainy over saturated so i hope that helps