<aside>

Conventional radiography is the use of X-rays to produce 2D projectional images of the body, primarily for diagnostic purposes. It is the oldest and most widely used imaging modality, forming the foundation of diagnostic radiology.

</aside>

Physics Principle

• Based on differential absorption of X-rays by tissues depending on density and atomic number.

X-ray photons pass through the body:

• Dense structures (bone, calcification) → absorb more → appear white (radiopaque).
• Air-filled structures (lungs, bowel gas) → absorb less → appear black (radiolucent).
• Soft tissues → intermediate shades of gray.

![Computed radiography and its imaging mechanism. (a) The characteristic exposure curve of film-screen radiography (FSR, blue dotted line) and computed radiography (CR, red line). The film-screen radiography shows a linear exposure range of 10 : 1, and the digital radiography shows a linear exposure of 104 : 1. (b) Schematic diagram showing a typical computed radiography reader system and the corresponding image readout process. (c) Schematic diagram of the cross-section of the imaging plate (I). Scanning electron microscope (SEM) image of the structured (III) and unstructured (II) phosphors. (d) X-ray absorption spectra of thallium-doped cesium iodide (CsI: Tl, green), terbium-doped gadolinium oxysulphide (GOS: Tb, orange), and europium-doped barium fluobromide (BaFBr: Eu2+, blue) as a function of X-ray photon energy. (e) The physical process of photostimulation using BaFBr: Eu2+ phosphors. It can be divided into two steps, including radiation storage (light yellow) and photostimulated luminescence (light blue). The X-rays penetrating the object are absorbed by phosphors, creating a lot of electron-hole pairs, which subsequently migrate to emitting centers or are captured by metastable energy traps. Electrons and holes in the metastable energy traps absorb low-energy laser irradiation to overcome the energy barrier, escaping from the traps, followed by recombination at emitting centers to generate photostimulated luminescence.

Ou X, Chen X, Xu X, et al. Recent development in X-Ray imaging technology: future and challenges. Research. 2021;2021. doi:10.34133/2021/9892152](attachment:33a56294-7ce7-41ae-8d7c-fab21bc21749:image.png)

Computed radiography and its imaging mechanism. (a) The characteristic exposure curve of film-screen radiography (FSR, blue dotted line) and computed radiography (CR, red line). The film-screen radiography shows a linear exposure range of 10 : 1, and the digital radiography shows a linear exposure of 104 : 1. (b) Schematic diagram showing a typical computed radiography reader system and the corresponding image readout process. (c) Schematic diagram of the cross-section of the imaging plate (I). Scanning electron microscope (SEM) image of the structured (III) and unstructured (II) phosphors. (d) X-ray absorption spectra of thallium-doped cesium iodide (CsI: Tl, green), terbium-doped gadolinium oxysulphide (GOS: Tb, orange), and europium-doped barium fluobromide (BaFBr: Eu2+, blue) as a function of X-ray photon energy. (e) The physical process of photostimulation using BaFBr: Eu2+ phosphors. It can be divided into two steps, including radiation storage (light yellow) and photostimulated luminescence (light blue). The X-rays penetrating the object are absorbed by phosphors, creating a lot of electron-hole pairs, which subsequently migrate to emitting centers or are captured by metastable energy traps. Electrons and holes in the metastable energy traps absorb low-energy laser irradiation to overcome the energy barrier, escaping from the traps, followed by recombination at emitting centers to generate photostimulated luminescence.

Ou X, Chen X, Xu X, et al. Recent development in X-Ray imaging technology: future and challenges. Research. 2021;2021. doi:10.34133/2021/9892152

Image Acquisition

Film-Screen Radiography (historic “conventional”)

• Uses X-ray film and intensifying screens.
• Produces analog images.

Computed Radiography (CR, modern conventional system)

• Uses a photostimulable phosphor (PSP) plate inside an imaging cassette.
• After exposure, the cassette is placed in a CR reader, where a laser scans the plate, releasing stored energy as light.
• Light is digitized to form an image.
• PSP plate is then erased with white light and reused.

![Drawing illustrates a CR system based on storage-phosphor image plates. Image generation is separated into two steps. First, the image plate (IP) is exposed to x-ray energy, part of which is stored within the detective layer of the plate. Second, the image plate is scanned with a laser beam, so that the stored energy is set free and light is emitted. An array of photomultipliers collects the light, which is converted into electrical charges by an analog-to-digital (A/D) converter

Körner M, Weber CH, Wirth S, Pfeifer KJ, Reiser MF, Treitl M. Advances in Digital Radiography: Physical Principles and system Overview. Radiographics. 2007;27(3):675-686. doi:10.1148/rg.273065075](attachment:a91f992c-3414-47d8-a461-9e72d8b89020:image.png)

Drawing illustrates a CR system based on storage-phosphor image plates. Image generation is separated into two steps. First, the image plate (IP) is exposed to x-ray energy, part of which is stored within the detective layer of the plate. Second, the image plate is scanned with a laser beam, so that the stored energy is set free and light is emitted. An array of photomultipliers collects the light, which is converted into electrical charges by an analog-to-digital (A/D) converter

Körner M, Weber CH, Wirth S, Pfeifer KJ, Reiser MF, Treitl M. Advances in Digital Radiography: Physical Principles and system Overview. Radiographics. 2007;27(3):675-686. doi:10.1148/rg.273065075