Collimators are optical devices used to narrow a beam of particles or waves. They help ensure that the emitted rays are parallel, which is essential in various applications like telescopes, lasers, and medical imaging. By reducing the spread of the beam, collimators improve the accuracy and quality of measurements or images. In radiology, collimators are particularly important as they limit the exposure of radiation to specific areas, enhancing patient safety. They can be found in X-ray machines and CT scanners, where they help focus the radiation on the target area, minimizing unnecessary exposure to surrounding tissues.