Performance Evaluation of Small Pixel-Sized Gd2O2S and CsI CMOS X-ray Detectors

Date

2025-01-01

Author

Mart, Yagiz
Aslan, Ahmet Arif
Buyukdemirci, Kaan
Lee, Denny
Akın, Tayfun
Camlica, Ahmet

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Flat panel X-ray detectors with thin-film t ransistors (TFT) a re w idely u sed i n X -ray m edical i maging applications. However, indirect X-ray detectors with TFT suffer f rom a n i nadequate s patial r esolution t hat i s required for some medical imaging procedures, where resolving fine d etails a t i ts e arly s tage p lays a c rucial r ole i n successful diagnosis such as breast imaging. Besides, indirect conversion X-ray detectors when incorporated with common types of scintillators, i.e. cesium iodide (CsI) or Gd2O2S, can meet the requirements of high fabrication yield and respectively lower costs. As an alternative to TFT read-out circuitry, complementary metal oxide semiconductor (CMOS) presents an attractive alternative, offering l ower i nherent e lectrical n oise a nd higher temporal resolution, enabling dynamic imaging at lower X-ray doses. The purpose of this work is to develop small pixel size indirect conversion CMOS X-ray detectors. The CsI-based detector features an active area of 1.1x0.8 cm2 and a pixel size of 20-µm, while the Gd2O2S-based detector has an active area of 1.5x1.5 cm2 and a pixel size of 20-µm. Both detectors comprise of 1024x1024 pixels with an image depth of 14 bits. However, the active area of the CsI-based detector is less than that of the Gd2O2S-based detector. To evaluate the spatial resolution of the detectors, the IEC 62220-1:2003 standard is followed. The modulation transfer function (MTF) of both detectors is examined experimentally by the slanted-edge method using the first t wo prototype CMOS detectors. The initial results indicate that the point at which the MTF reaches 50% is significantly higher for both indirect CMOS detectors compared to commercial CMOS and TFT detectors utilizing the same scintillators. Specifically, t he G d2O2S-based d etector a chieves 2.6 l p/mm, w hile t he C sI-based d etector reaches 4.7 lp/mm. Also, the preliminary images of the medical stent used for angiography operation obtained with the fabricated detectors demonstrate that the indirect conversion CMOS X-ray detectors can be a reasonable alternative to direct conversion X-ray detectors for some specific i maging o perations. I n a ddition t o M TF, noise power spectrum (NPS), and detective quantum efficiency (D QE) va lues ar e al so ex amined. Th is st udy is the first a ttempt t o e xplore o ur i ndirect C MOS X -ray d etectors a nd f urther s tudies w ill b e c arried o ut t o identify their potential application area in medical imaging procedures.

Subject Keywords

CMOS, DQE CsI, Gd2O2S, MTF, NPS, RQA5, TFT

URI

https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=105004573066&origin=inward
https://hdl.handle.net/11511/114686

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Department of Electrical and Electronics Engineering, Conference / Seminar