A-Level Physics AQA 7408

The physics of diagnostic X-rays

Physical principles of the production of X-rays; maximum photon energy, energy spectrum; continuous spectrum and characteristic spectrum.

Rotating-anode X-ray tube; methods of controlling the beam intensity, the photon energy, the image sharpness and contrast, and the patient dose.

Image detection and enhancement

Flat panel (FTP) detector including X-ray scintillator, photodiode pixels, electronic scanning.

Advantages of FTP detector compared with photographic detection.

Contrast enhancement; use of X-ray opaque material as illustrated by the barium meal technique.

Photographic detection with intensifying screen and fluoroscopic image intensification; reasons for using these.

Absorption of X-rays

Exponential attenuation.

Linear coefficient μ, mass attenuation coefficient μ_m, half-value thickness $I = I_0 e^{-μx} μ_m = \dfrac{μ}{ρ}$

Differential tissue absorption of X-rays excluding details of the absorption processes.

CT scanner

Basic principles of CT scanner:

• movement of X-ray tube
• narrow, monochromatic X-ray beam
• array of detectors
• computer used to process the signals and produce a visual image.

Comparisons will be limited to advantages and disadvantages of image resolution, cost and safety issues. Students will not be asked about the construction or operation of the detectors.