Dr. Ahmed Najm Abstract The photoelectric effect is one of the fundamental interactions between X-rays and matter and plays an important role in radiographic image formation and contrast. This interaction occurs when a bound electron in an atom completely absorbs the energy of an incident photon, resulting in the ejection of the electron and absorption of the photon. The probability of the photoelectric effect occurring depends mainly on the photon energy and the atomic number of the material. Therefore, absorption varies among tissues and materials with different atomic compositions. This difference contributes to differential attenuation, which represents an important basis for contrast in radiographic images. This article aims to explain the physical principle of the photoelectric effect and demonstrate its role in improving radiographic contrast, while highlighting the importance of contrast media in diagnostic applications. **Introduction** X-rays interact with matter through several mechanisms, with the photoelectric effect and Compton scattering being among the most important interactions within the range of diagnostic radiography. Differences in the amount of radiation absorbed by tissues result in differential attenuation, which is one of the fundamental factors responsible for variations in the intensity of radiation reaching the detector and, consequently, for the formation of image contrast. The photoelectric effect is particularly important in radiography because it results in the complete absorption of the incident photon. Its probability of occurrence is higher in materials with a high atomic number and at relatively low photon energies. Therefore, this interaction is directly related to the ability of an imaging system to demonstrate differences between various tissues and materials. **Physical Principle of the Photoelectric Effect** The photoelectric effect occurs when an X-ray photon interacts with an electron bound to one of the energy levels of an atom, transferring all of its energy to the electron. If the photon energy is sufficient to overcome the electron binding energy, the electron is ejected from the atom and is known as a photoelectron. The relationship can be expressed in a simplified form as follows: **Kinetic Energy of the Photoelectron = Photon Energy − Electron Binding Energy** After the electron is ejected, another electron from a higher energy level may transition to fill the vacancy created. This process may result in the emission of characteristic X-rays or Auger electrons. **The Photoelectric Effect and Radiographic Image Contrast** As X-rays pass through the human body, the amount of radiation absorbed varies according to the composition, density, atomic number, and photon energy of the tissues. The photoelectric effect results in complete photon absorption and can therefore increase the difference in radiation intensity between different regions of the body. This effect is clearly demonstrated in bone imaging, as bones contain elements with a higher effective atomic number than soft tissues. This results in greater X-ray absorption and causes bones to appear more radiopaque, or whiter, on radiographic images. This property can also be utilized through the use of contrast media containing elements with relatively high atomic numbers, such as iodine and barium. These materials increase absorption in specific regions and enhance their visibility during diagnostic examinations. **Discussion and Conclusion** The photoelectric effect is an important interaction for understanding radiographic image formation, as it is directly associated with differential attenuation, which contributes to image contrast. In general, the probability of its occurrence increases as photon energy decreases and the atomic number of the material increases. From an applied perspective, controlling the energy of the X-ray beam and selecting appropriate exposure parameters are important for achieving a balance between image quality and radiation dose. In addition, the use of high-atomic-number contrast media can enhance the visualization of certain anatomical structures or organs during diagnostic examinations. **Conclusion** The photoelectric effect plays an important role in the formation of radiographic contrast through the complete absorption of photons, with its probability of occurrence depending on photon energy and the atomic number of the material. Understanding this interaction helps radiologic technology students interpret differences in X-ray absorption among tissues and understand the role of contrast media in diagnostic imaging. Therefore, the photoelectric effect represents an important physical foundation for understanding the relationship between radiation interactions, image quality, and radiographic contrast. **References** – Bushong, S. C. *Radiologic Science for Technologists: Physics, Biology, and Protection*. Elsevier. – Hendee, W. R., & Ritenour, E. R. *Medical Imaging Physics*. Wiley-Liss. – Allisy-Roberts, P. J., & Williams, J. *Farr’s Physics for Medical Imaging*. Elsevier. – Sprawls, P. *Physical Principles of Medical Imaging*.