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Figure 4: In indirect-conversion detectors,
the x-ray scintillator can be structured or unstructured. Structured
scintillators, which typically are crystalline cesium iodide, reduce the spread
of visible light; this improves spatial resolution and permits the use of
thicker scintillator materials for improved quantum detection.
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· It constructed by adding amorphous silicon photodiode circuitry and a scintillator as the top layers of the thin-film transistor sandwich.
· These layers replace the x-ray photoconductor layer that is used in direct-conversion devices.
· When x-ray strike the scintillator, visible light is emitted proportional to the incident x-ray energy.
· Visible light photons are then converted into an electrical charge by the photodiode array, and the charge collected at each photodiode is converted into a digital value by using the underlying readout electronics.
· Scintillator used can be either structured or unstructured.
· Unstructured scintillator
Ø Example : conventional fluorescent screens
Ø Visible light that is emitted in the material can spread to adjacent pixels and thereby reduce spatial resolution.
· Structured scintillator
Ø Consists of cesium iodide crystals that are grown on the detector.
Ø The crystalline structure, which consists of discrete and parallel “needles” approximately 5-10µm wide
Ø Light spreading is greatly reduced in a structured scintillator, thicker layers of this material can be used in the detector; this increases the number of x-ray photon interactions and thus the available visible light.
Ø The use of thicker layer of structured scintillators greatly increases the potential detective quantum efficiency that is achievable by using the detector, especially at higher imaging frequencies.
Simplified Operations :
Special appreciation to:
-Markus Korner, MD
-Christof H.Weber, MD
-Stefan Wirth, MD
-Klaus-Jurgen Pfeifer, MD
-Maximilian F.Reiser, MD
-Marcus Treitl, MD
-Markus Korner, MD
-Christof H.Weber, MD
-Stefan Wirth, MD
-Klaus-Jurgen Pfeifer, MD
-Maximilian F.Reiser, MD
-Marcus Treitl, MD
