So why is this periodic table of elements important? Starting at the top left and working your way across the table until the bottom right, you will see the atoms increasing in size and weight. Where these elements fall on the table gives us the physical properties that we use to make x-rays, alter x-ray energies, and use as protection from x-rays. The numbers in the upper left of each box is the atomic number of each element. This represents the number of protons, which is what makes each element unique. The numbers on bottom of each box represents the atomic weight of the element, which is the number of protons and neutrons added together. The yellow boxes are just some common elements used in x-ray, and the blue boxes are just some common contrast agents used to enhance radiographic exams. Tungsten (W), atomic #74, is used in the actual making of x-rays inside the x-ray tube. Copper (Cu) and Aluminum (Al) are commonly used as filters inside the x-ray housing. Filters are important as they filter out unwanted x-rays (we'll get into more on that later). This results in decreased patient exposure. Barium (56) is used in the study of the intestinal tract and Iodine (53) is used in the intestinal tract as well as the vascular system. If any of you have had a CT exam where you needed to drink something, it was either Barium or Iodine...and tasted great! Depending on the type of machine and the x-ray quality required, many other elements can be used as well. In mammography, where the energy level does not need to be as high, it is common to use elements like Silver (Ag), Molybdenum (Mo), Gold (Au), and Rhodium (Rh). Do you need to know all of these elements? No. The ones that are colored should be the ones you need to familiarize yourself with. You'll catch onto it as we go.