 Hello friends, today we'll be speaking about the TLT badge, which means the Thermal Luminosin Dosimeter and this is the device that is used to calculate your radiation dose. So the idea behind this video is to make radiology students aware of how the TLT badge actually works and so that they can answer confidently in their examinations. So there are many devices that are used to capture radiation but the TLT badge is more superior and is used worldwide and why is it so? Because of the linearity of the response to doses, it is very sensitive to even low doses and it can be reused again and again. However, the disadvantage is no permanent reading is available and you don't get on the spot reading, hence you have to give it to the lab every three months and that's when the reading comes. So how exactly does this work? It is made up of a TLT cassette which is made up of high impact plastic and within it lies the TLT card. So we can just open it by sliding it down right here and you get this TLT card over here. If you see this TLT card discovered in the black paper to protect it from damage as well as from exposure to radiation from any open source and if you look around and feel this you can see a wee cut right at the top. This ensures that it is placed in the TLT cassette correctly. We also have a metal plate on which are three discs. So if you feel around the front and back there are three discs which are seen within that metal plate. You have of course a paper writing wrapper on top which tells you your name as well as the time period you are supposed to wear it. It's usually a quarter for diagnostic departments as well as a regular number from the company. There are three discs as you can feel here. They have been mechanically clipped onto this plate and they have been clipped onto holes that are about 12 mm in diameter. This plate is actually made up of aluminum and what we have are the calcium sulphate discs which are clipped onto it. So this is a personal monitoring radiation card and that number and the name ensures that you cannot exchange it. It's not transferable. It's just you who got to wear it at the time of using it in the radiation department. So the asymmetric wee cut that we just spoke about allows the loading of this card into the plate in an exact orientation so that those discs face exactly these filters as we're going to talk about right now. So the spot on top is the aluminum filter. It's one of plastic and the third one is open and we're going to find out why. So the first disc is actually D1 which is sandwiched between a pair of filter combination of 1 mm thick aluminum and 1 mm thick copper. The copper filter lies nearer to the disc. Disc 2 will lie behind this plastic. So it's sandwiched between a pair of 1.6 mm thick plastic filter. So you have the plastic filter here as well as the plastic filter over here. And disc 3 will lie under a circular oval window. So this is open here as well as open here. So D1 is between the aluminum and copper filter, D2, disc 2 between the two plastics which we see on either side and disc 3 is under circular open window. And why does it work this way to make the whole assembly energy independent? So the high energy x-ray and gamma dose can be measured from disc 1 which is here. The low energy x-ray and the gamma as well as the beta dose can be measured from disc 2. And low energy beta can be measured from disc 3. So what exactly is the disc? We can't really cut this open, but we know that the disc is a phosphor such as lithium fluoride or calcium fluoride in a solid crystal structure. And when this TLD batch is exposed to ionizing radiation at an ambient temperature, this radiation interacts with the phosphor crystal. And it deposits all or part of the incident energy in that material. Now some of the atoms in the material that absorb that energy become ionized, producing free electrons. And these electrons get trapped in that crystal lattice itself. At the end of three months, the entire card is taken back to the lab and they calculate the radiation dose. Now how exactly this radiation calculation is done? When we heat the crystal, it causes the crystal lattice to vibrate and it releases those trapped electrons in the process. As these electrons come back to a ground state, they release the captured energy from ionization as light. It is this light that is red using photomultiplier tubes and the photon's red is equal to the radiation striking the phosphor. This is red on glow curve charts. And based upon the glow curves observed on the TLD readers and subjective to the algorithms as per BRC in India, we can calculate the dose received by an individual. So what are the cutoff values? For the whole body for radiation workers, it is 20 millisieverts in a year and it should not be more than 100 millisieverts average over five years. For non-radation workers or the general public, it is 2 millisieverts in a year. For partial body, for the extremities, it has got to be 500 millisieverts in a year and for lens, it is 150 millisieverts. For reporting over exposure cases as per ARB rules and regulations, it should not be more than 10 millisieverts in a quarter for the chest and 250 millisieverts in a quarter for wrist. If the value is below recordable value of 0.05 millisieverts, your reading will come as zero. So where are you supposed to wear it? When a LED apron is being used, when you are using it in the intervention department, you've got to wear it under the LED apron at the chest level right here. However, for those who are working in interventional radiology for long periods of time, you should procure additional badges to be worn at the wrist.