Medical imaging is essential to modern clinical practice, providing anatomical and functional information for diagnosis and treatment decisions. As the use of X-ray imaging, computed tomography, fluoroscopy, and nuclear medicine increases, a balance must be maintained between image quality and patient radiation exposure. This article examines the role of medical physics in improving imaging quality while reducing unnecessary exposure to ionizing radiation. It reviews image-formation principles, factors affecting image quality, dose indicators, protocol optimization, and quality assurance. It also discusses the medical physicist’s responsibilities in equipment calibration, dosimetry, performance assessment, and radiation protection. Safe imaging is not achieved through indiscriminate dose reduction, but by obtaining image quality adequate for the clinical task with exposure kept as low as reasonably achievable. Medical physics; medical imaging; image quality; radiation dose; dose optimization; computed tomography; quality assurance; radiation protection. Medical imaging is a major application of physics in healthcare. Modalities include X-ray imaging, computed tomography (CT), fluoroscopy, magnetic resonance imaging (MRI), ultrasound, and nuclear medicine. Some modalities use ionizing radiation, whereas MRI and ultrasound do not. Although imaging provides substantial diagnostic benefits, inappropriate use of radiation-based techniques may cause unnecessary exposure. Examinations should therefore be justified and optimized so that clinical benefits are achieved while exposure is minimized . Medical physicists provide expertise that connects equipment performance with clinical requirements for image quality and patient safety. Physical Principles of Image Formation Medical image formation involves the interaction of physical energy or signals with body tissues, followed by detection and processing. In X-ray imaging, the beam is attenuated as it passes through tissues; attenuation depends on photon energy, tissue density, thickness, and atomic composition. For a monoenergetic beam, attenuation is described by I = I₀ e^(−μx), where I is transmitted intensity, I₀ is initial intensity, μ is the linear attenuation coefficient, and x is material thickness. In CT, measurements acquired from multiple angles are reconstructed into cross-sectional images. MRI signals arise from the response of hydrogen protons to a magnetic field and radiofrequency pulses, while ultrasound images are formed by processing echoes reflected from tissue interfaces. Factors Affecting Image Quality Key image-quality characteristics include contrast, spatial resolution, temporal resolution, noise, and artifacts. X-ray and CT performance is influenced by tube voltage (kVp), tube current and exposure time (mAs), focal-spot size, filtration, detector efficiency, slice thickness, and reconstruction algorithms. Increasing exposure may reduce noise but also increases patient dose. MRI image quality depends on signal-to-noise ratio, field strength, pulse sequences, and patient motion. Ultrasound image quality is affected by transducer frequency, imaging depth, gain, and focusing. Radiation Dose Indicators and Optimization In CT, indicators such as CTDIvol and DLP are used to monitor scanner output; neither alone provides a direct and precise estimate of absorbed dose to a specific organ in an individual patient. Dose-area product (DAP or KAP) may be used in projection radiography and fluoroscopy. Optimization includes selecting protocols appropriate to the clinical question, patient size, and age; adjusting kVp and mAs; limiting scan length; avoiding unnecessary repeat images; and applying dedicated pediatric protocols. Diagnostic reference levels (DRLs) support comparison and improvement of practice but are not individual patient dose limits . The goal is the lowest dose that provides diagnostically adequate image quality, not dose reduction at the expense of image usefulness. The Role of the Medical Physicist Medical physicists evaluate the physical performance of imaging systems and contribute to equipment selection, acceptance and commissioning tests, image-quality and dose measurements, calibration, and quality-control programmes. In CT, testing may include noise, uniformity, CT-number accuracy, spatial resolution, slice thickness, and dose indices. In X-ray and fluoroscopy systems, physicists assess tube output, voltage and timing accuracy, detector performance, dose indicators, and protective systems. They also help optimize protocols and investigate unusual exposures. Their responsibilities include patient-dose assessment, image quality, equipment calibration, optimization of radiation protection, and the physical aspects of quality assurance . Quality Assurance and Quality Control Quality control (QC) consists of technical tests and measurements used to verify equipment performance. Quality assurance (QA) is a broader system covering policies, responsibilities, procedures, documentation, training, and continuous improvement. A programme begins with acceptance testing and commissioning to establish baseline performance, followed by periodic tests of image quality, output constancy, parameter accuracy, detector performance, and display and processing systems. Results should be documented and compared with baseline values and tolerance limits. Deviations should be investigated and corrected. QA also includes protocol review, analysis of repeated images, dose monitoring, and staff training . Radiation Protection and Patient Safety Medical radiation protection is based on justification and optimization. Justification requires that an examination be clinically indicated and provide an expected benefit. Optimization requires appropriate image quality with exposure kept as low as reasonably achievable. Patient safety includes verifying identity, examination request, anatomical region, and protocol, while considering age, body size, and clinical condition. Staff protection includes appropriate shielding, distance, protective barriers, occupational monitoring, and continuous training. Dose limits do not apply to the intended medical exposure of patients in the same way as they apply to workers and the public . Recent developments include digital detectors, advanced reconstruction, dose-monitoring systems, and artificial intelligence. AI algorithms may reduce noise, accelerate acquisition, and support anatomical delineation, but require validation and monitoring for bias or synthetic image features that could affect diagnosis. Dual-energy and photon-counting CT are also developing and may improve material differentiation and photon efficiency in selected applications. Medical physicists remain essential in evaluating their effects on dose and image quality and verifying safety before clinical implementation . Medical imaging quality and patient safety are interdependent. An appropriate dose is one that produces image quality sufficient for the clinical task, not necessarily the lowest possible value. Medical physicists are central to achieving this balance through dosimetry, image-quality assessment, protocol optimization, equipment calibration, quality assurance, and radiation protection. Integrating medical physics into imaging teams, supported by continuous training and evaluation, can improve diagnostic performance, reduce unnecessary exposure, and enhance healthcare.