Challenges of pixelated scintillators in medical X-ray imaging
2008 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, Vol. 591, no 1, 291-295 p.Article in journal (Refereed) Published
In current X-ray detectors, spatial resolution is limited by optical photon diffusion in the scintillator layer. A method to prevent photons from reaching neighboring pixels is the embedding of opaque walls within the scintillator. The realization of a pixelated scintillator faces, several challenges to obtain a good imaging performance, especially a high detective quantum efficiency (DQE). To maintain a high X-ray absorption, a high volume fill-factor is required. Losses of secondary light quanta have to be kept to a minimum to maintain an acceptable gain. Moreover, the signal per primary X-ray quanta should have a low variation with the depth of interaction to avoid a high secondary quantum noise (Swank-noise). Light scatter inside the scintillator causes both enhanced light loss and Swank-noise. For this work, a pixelated scintillator has been built from electrochemically etched silicon pore arrays, which are filled with cesium iodide (CsI:Tl). With a pixel pitch of 50 mu m, wall thicknesses of 6.5 mu m and pore depths of nearly 400 mu m are achieved. The modulation transfer function is 40% at 4 lp/mm and 10-20% at 8 lp/mm. The ability of the pores to transport light quanta from their origin to the photodiode is expressed in a light guiding efficiency, which is determined as 6.5% in the better cases. The maximal DQE(0) is 0.28, while the X-ray absorption with the given thickness and fill-factor is 0.57. The difference is explained by high Swank-noise due to optical scatter inside the CsI-filled pores, in agreement to Monte-Carlo simulations of the photon transport inside the pore array structure.
Place, publisher, year, edition, pages
2008. Vol. 591, no 1, 291-295 p.
X-ray imaging, pore array, detective quantum efficiency, high aspect ratio, CsI
IdentifiersURN: urn:nbn:se:kth:diva-38090DOI: 10.1016/j.nima.2008.03.077ISI: 000257529300073ScopusID: 2-s2.0-44649189702OAI: oai:DiVA.org:kth-38090DiVA: diva2:436120
9th International Workshop on Radiation Imaging Detectors Location: Univ Erlangen, Nuremberg, GERMANY Date: JUL 22-26, 20072011-08-222011-08-222011-08-22Bibliographically approved