Linear Diode Array (LDA) Detector
The linear diode array detector is comprised of individual photo diodes arranged into a line; it is used to detect different levels of light as they pass through its field of view. To obtain a 2d image from and LDA it is necessary to move the object being imaged or move the detector. One has probably observed the movement of the LDA in your copy machine. The LDA and the light scan the page as they move. In scan mode the paper is fed into the machine and scanned as the paper moves across the LDA.
LDA resolution is determined by the size of each photo diode, the scintillator material and scatter radiation. The sizes of LDA pixels range from 50 microns to as large as .4 mm for some CT applications. However, it is important to know that there is the ability to select your pixel size to match your application. Typically you will select the pixel pitch, pixel diffusion width, height, number of pixels and active length. The selection of scintillator material and the thickness of the material provides optimum light conversion for different x-ray energies. On can usually select GOS:Tb, CsI:Tl, CdWO4, etc... Some detectors are arranged to follow the curve of the X-ray beam angle. By doing, so one can optimize the X-ray beam energy.
LDA Advantages and Disadvantages
The advantages of the LDA is the removal of much of the scatter radiation that is created during the CT scan or any other applications. The LDA also can be configured to be as long as needed. In some cases the LDA for high energy CT scanning systems can be 4000 mm. The LDA has some disadvantages as well including longer scanning times when compared with cone bean CT using a Flat panel.
High Energy Basic System performance data:
Source: 9 MeV Linac, max. 32 Gy/min @ 7.8 MeV
Detector: Line Detector Array [LDA] - 4,000 mm length,
400 µm pixel pitch
Turntable: Payload 10 t
Max. FOV: 5,000 mm height,
3,200 mm diameter [Offset CT]
Image source: © Fraunhofer IIS/Kurt Fuchs