Abstract This article discusses the concept of image quality in digital radiography and the physical and technical factors that influence it. It addresses contrast, spatial resolution, noise, and image artifacts, as well as the effects of exposure parameters, focal spot size, distance, motion, detector characteristics, and digital image processing. The article also highlights the importance of quality assurance programs and objective and clinical assessment methods in obtaining images that are appropriate for the diagnostic task without unnecessarily increasing the patient's radiation dose. Keywords Image Quality; X-ray Imaging; Contrast; Spatial Resolution; Noise; Image Artifacts; Quality Assurance. Introduction A good diagnostic image is not simply one that has appropriate brightness or sharpness. Rather, it must contain the information necessary for the diagnostic task and allow clinically significant details and findings to be detected. Recent literature emphasizes the importance of evaluating image quality according to the intended diagnostic purpose while maintaining an appropriate balance between image quality and the radiation dose received by the patient. Contrast Contrast refers to the difference in signal intensity between two different regions of an image. It is influenced by several factors, including the natural contrast of tissues, X-ray beam energy, patient thickness, scattered radiation, and digital image-processing techniques. Contrast is one of the fundamental components of image quality, as it helps distinguish between tissues and structures with similar properties, thereby improving the ability to detect differences and pathological changes. Spatial Resolution Spatial resolution is defined as the ability of an imaging system to display small objects or closely spaced details separately and clearly. Spatial resolution is affected by several factors, including the focal spot size of the X-ray tube, imaging geometry, pixel size, digital detector characteristics, patient motion during imaging, and digital image-processing procedures. High spatial resolution is essential for demonstrating fine anatomical details that may be important in the diagnosis of certain medical conditions. Noise Noise refers to unwanted random variations in the signal that appear within an image and affect the visibility of diagnostic details. In digital radiography, the level of noise is closely related to the number of X-ray photons reaching the detector. Increasing the detected signal may reduce noise and improve image clarity; however, increasing radiation exposure without a diagnostic need should not be considered an objective in itself. Therefore, the goal should be to achieve an appropriate level of image quality for the required diagnostic task while keeping the radiation dose at the minimum level necessary. Image Artifacts and Motion Image artifacts may result from several factors, including patient motion during imaging, detector problems, increased scattered radiation, digital processing errors, or other technical errors occurring during the examination. These artifacts may obscure important diagnostic information or distort image details, thereby reducing the physician's confidence in image interpretation. Patient motion is an important cause of reduced image quality because it may produce image blurring and loss of fine detail. Therefore, proper patient positioning and immobilization should be ensured, and exposure time should be minimized whenever possible. Exposure and Geometric Factors X-ray tube voltage (kVp) affects the energy of the X-ray beam, its penetrating ability, and the resulting image contrast. In contrast, the tube current–time product (mAs) influences the quantity of X-ray photons produced and consequently affects image noise and radiation dose. Imaging distances, focal spot size, and the alignment of the patient, detector, and X-ray tube also influence geometric sharpness and overall image quality. Therefore, the appropriate selection of exposure parameters and imaging geometry is an essential component of obtaining high-quality diagnostic images while avoiding unnecessary radiation exposure. Digital Image Processing Digital image-processing techniques allow adjustments to image presentation, enhancement of specific details, improvement of contrast, and the application of noise-reduction algorithms to improve the visibility of different anatomical structures. However, digital processing cannot compensate for major errors caused by inappropriate exposure or poor patient positioning. In addition, improper use of image-processing techniques may conceal certain technical problems within the image. Therefore, digital processing tools should be used within appropriate quality-control and quality-assurance programs. Image Quality Assessment The quality of diagnostic images can be evaluated using a combination of objective and clinical methods. Objective methods include measurements of noise, spatial resolution, contrast, Modulation Transfer Function (MTF), Signal-to-Noise Ratio (SNR), and Contrast-to-Noise Ratio (CNR). In addition, clinical evaluation of the image is essential to determine whether it provides sufficient information for an accurate diagnosis. Scientific literature emphasizes the importance of relating image-quality indicators to the specific diagnostic task rather than relying on a single parameter to determine overall image quality. Conclusion Image quality in diagnostic X-ray imaging results from the interaction of multiple physical, technical, and human factors. These factors include X-ray beam characteristics, exposure parameters, imaging geometry, patient motion, detector characteristics, and digital image processing. The implementation of an effective quality assurance program contributes to the early detection of deviations and technical problems, improves imaging-system performance, reduces the need for repeat examinations, and minimizes unnecessary radiation exposure. Therefore, the primary objective is not to achieve the highest possible image quality regardless of radiation dose, but rather to obtain image quality that is sufficient and appropriate for the diagnostic task while achieving the best possible balance between diagnostic benefit and patient radiation dose. Almustaqbal University – The First University in Iraq