What Is Radiography?

Radiography is the technique of creating images by passing ionizing radiation through an object and recording the spatial pattern of transmitted or scattered radiation on a detector. The result is a two-dimensional projection, or a set of projections reconstructed into a three-dimensional volume, that reveals internal structure without physical disassembly. The field divides broadly into medical radiography, which supports clinical diagnosis and treatment guidance, and industrial radiography, which detects flaws in manufactured components and infrastructure. Both branches share the same underlying physics but differ substantially in regulatory requirements, detector technology, and the nature of the objects imaged.

X-rays are the predominant radiation source, generated by accelerating electrons toward a metal target in a vacuum tube. The resulting bremsstrahlung and characteristic X-ray spectrum is shaped by tube voltage (kilovoltage peak, kVp) and filtration, which together determine the photon energy range reaching the subject. Higher energies penetrate thicker or denser materials but reduce soft-tissue contrast. Industrial applications also use gamma sources such as iridium-192 and cobalt-60 for field work where a portable electrical source is impractical.

Diagnostic and Digital Radiography

Diagnostic radiography produces images of the human body to identify fractures, lesions, foreign bodies, and pathological changes in bone or soft tissue. The transition from film-screen systems to digital detectors over the past three decades has improved dose efficiency, enabled electronic image distribution, and opened the door to computer-aided detection algorithms. Two principal digital detector technologies are in wide use: computed radiography (CR), which reads photostimulable phosphor plates with a laser scanner, and direct or indirect flat-panel detectors, which convert X-rays to charge directly in amorphous selenium or via a scintillator coupled to amorphous silicon photodiodes.

The American College of Radiology's practice parameters set performance expectations for image quality, patient dose, and quality assurance in clinical radiography. Dual-energy subtraction imaging and tomosynthesis, a limited-angle form of tomographic reconstruction, extend the diagnostic capability of planar radiography without the full dose and complexity of computed tomography.

Computed Tomography

Computed tomography (CT) acquires a series of X-ray projections at many angles around the patient or object, then uses filtered back-projection or iterative reconstruction algorithms to compute cross-sectional images. Modern multi-detector CT scanners can acquire hundreds of thin slices in a single breath-hold, enabling high-resolution three-dimensional visualization of complex anatomy. CT colonography, cardiac CT, and CT angiography are established clinical applications. Iterative reconstruction techniques, as reviewed in research published through IEEE Transactions on Medical Imaging, reduce image noise at lower tube currents, supporting dose reduction without sacrificing diagnostic quality.

CT is also used in industrial settings for dimensional metrology and internal flaw detection in castings, welds, and assemblies, a practice known as industrial CT scanning.

Industrial Radiography

Industrial radiography inspects welds, castings, pipelines, and aerospace components for cracks, porosity, inclusions, and dimensional deviations. Film-based methods are being displaced by digital detector arrays and computed radiography panels, which provide faster throughput and immediate digital archiving. Gamma-ray sources are favored for field inspection of thick steel structures because their compact geometry allows placement inside pipes or vessels where X-ray tubes cannot fit. Regulatory requirements in most jurisdictions mandate source security, worker dosimetry, and controlled exposure areas. ASTM and ASME standards define acceptance criteria and procedure requirements for industrial radiographic inspection.

Applications

• Chest and skeletal radiography in emergency and primary care settings
• Mammography for breast cancer screening programs
• Weld inspection in pipeline construction and pressure vessel fabrication
• Dimensional verification of turbine blades and castings using industrial CT
• Cargo and luggage screening at ports and airports using high-energy X-ray systems
• Structural assessment of bridges, aircraft fuselages, and reinforced concrete