Flat detector

Some commercial detectors come with built-in procedures and software that automatically corrects for a flat detector response of every pixel4. For other detectors the necessary correction has to be carried out by the user. 

We have done explicit analysis to determine the error associated with the omission of the systematic shift caused by flat detector shape and location off the Rowland circle. This omission revealed a poor determination of the dispersion function and consequent errors of 100 ppm. Including this effect has allowed reduction of the dispersion function uncertainty to 20 ppm through the careful determination of systematic uncertainties. 

Figure 14 Ultraviolet-A and visible flat detectors. Abbreviation UV, ultraviolet.

Fig. 5.21. Aneurysm rupture during coiling of an acutely ruptured basilar tip aneurysm. Angio-CT (Flat-detector) before...

A number of expensive but very powerful analysers available on the market are based on Fraunhofer diffraction. An assembly of particles in a liquid or in a gas are illuminated by an expanded laser beam and the particle size distribution is derived from the measurement of the spatial distribution of the diffraction patterns on a flat detector behind the sample. 

Flat detectors, on the other hand, either avoid or at least reduce some of the major disadvantages of image intensifiers (Granfors et al. 2001 Bruijns et al. 2002 Busse et al. 2002 Choquette et al. 2001 Colbeth et al. 2001). The most important technical advantages of flat detectors are ... 

High detective quantum efficiency (DQE) across all dose levels, in particular for CsI/aSi-based flat detectors. 

A schematic view of an indirect converting flat detector based on Csl is presented in Fig. 3.1. An individual pixel is shown in detail, comprising a large photodiode and a small thin-film transistor (TFT). Pixel readout is initiated when the TFT is switched on. This causes the charge to flow to dedicated low-noise readout electronics, where it is ampflfied and subsequently converted into a digital signal. 

Flat detector technology is subject to further development and continuous improvement. Miniaturized electronics will allow for even thirmer and flghter detectors required for mobile or portable applications. Higher bit depths of 16 bits or even 18 bits wiU improve C-arm CT image quaHty, allowing it to further approach the low-contrast resolution of multi-sflce computed tomography (MSCT). 

Bruijns TJC, Bastiaens RJM, Hoornaert B, et al. (2002) Image quality of a large-area dynamic flat detector comparison with a state-of-the-art II/TV system. In Medical Imaging 2002 Physics of Medical Imaging. San Diego, pp 332-343... 

Technical Principles 560 Rotational C-Arm-Based Flat Detector CT (FD-CT) 560 FD-CT Versus Regular CT 562... 

Temporal response was no major concern in the design and development of flat detectors. Frame rates of five to ten images per second are typically available today for full matrix readout, which appears adequate for most fluoroscopic applications. Combining of pixels, the so-called binning process, allows for higher readout rates, e.g., up to 60 images per second with 4x4 binning, but at the expense of spatial resolution. 

Kalender WA, Kyriakou Y (2007) Flat-detector computed tomography (FD-CT). Eur Radiol 17 2767-2779... 

Flat detector technology has gained in acceptance over the conventional X-ray fihn because of its higher absorption efficiency and wider dynamic range. Furthermore, flat detectors are capable of direct, several frames... 

Kalender WA, Kyriakou Y (2007) Flat-detector computed tomography (FD-CT). Eur Radiol 17 2767-2779 Salem R, Lewandowski R, Roberts C etal. (2004) Use of Yttrium-90 glass microspheres (TheraSphere) for the treatment of unresectable hepatocellular carcinoma in patients with portal vein thrombosis. J Vase Interv Radiol 15 335-345... 

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