Introduction: In X-ray imaging, collimator limits the useful X-ray beam to the part of the body under examination. Adjustable light collimators are most commonly used to limit the beam to protect other tissues from unnecessary radiation exposure. Collimation also reduces scattered radiation, which improves the contrast resolution of the X-ray image. With precise collimation, a small part of the patient's tissues will be irradiated, and the dose received will thus be lower. If the irradiated volume is large, much more scattered radiation is generated, which means poorer contrast resolution and also a higher patient radiation dose. The simplest accessory for narrowing the X-ray beam is a tube that is placed on an X-ray tube. If such tubes are narrow enough, we can get very good X-rays images. Today, we generally use the so-called depth apertures to collimate the X-ray beam. With them, we can collimate different-sized fields and adjust the beam width to the size of the examined area. Purpose: The purpose of this diploma work is to provide a detailed presentation of the collimator and its impact on the quality of the X-ray image and patient radiation dose. For easier understanding, the diploma work also provides a brief presentation of radiation and the effect of patient radiation dose in X-ray imaging, X-ray image quality, and X-ray machine components. The aim was to systematically review the existing literature and present the topic in more detail. When writing the diploma work, we will focus on the effect of the collimator on the patient/object radiation dose and, at the same time, on its effect on the X-ray image quality, more precisely, its contrast resolution. Methods: In the diploma work, we used a descriptive work method with a systematic literature review. We searched for literature in books as well as scientific and professional articles in Slovene and English. We mainly looked for articles on collimators, patient radiation dose, and the effect of collimation on X-ray image quality. The mentioned literature was searched from November 2020 to March 2021 in various Slovenian and foreign bibliographic databases. Results: We presented the findings of the articles used in the systematic literature review. Great emphasis was placed on dose reduction received when using the aperture, thus also improving the quality of the X-ray image. Despite the shift from analogue to digital systems, field collimation is still a major problem, resulting in unnecessary patient irradiation and poorer X-ray image quality. We also detected different collimation practices. Discussion and conclusion: In quite a few radiological practices, inappropriate use of aperture and thus inconsistency in compliance with the ALARA principle was detected. We found that collimation is neglected when using digital technology, due to the possibility of cropping the X-ray image in postprocessing. All studies found that X-ray image quality and patient radiation dose are improved with maximum possible collimation.
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