First DQE measurment of 500 m thick Si

First DQE measurment of 500 µm thick Si hybrid pixel sensor with Photon counting readout for X-ray medical imaging M. Caria, J. Chaput, L. Sarry, B. Surre IWORID 2004 -- B. SURRE Glasgow

Introduction • Aim: to measure system DQE following a standart protocole • Requirements: – IEC 62220 -1 – RQA 5 (~ 70 k. Vp) – Flat field corrected data IWORID 2004 - B. SURRE 2

Establishment of Standard X-ray spectrum • Adjust k. Vp of generator to get RQA 5 spectrum such as: Spectrum Added filtration (mm Al) HVL (mm Al) RQA 3 10 7 RQA 5 21 7. 1 RQA 7 30 9. 1 RQA 9 40 11. 5 IWORID 2004 - B. SURRE 3

Measurement geometry IWORID 2004 - B. SURRE 4

Tube calibration @ RQA 5 IWORID 2004 - B. SURRE 5

Set up ? • Well known Photon counting chip = MEDIPIX 2 (chip set just above the noise) • Bump bonded with 500 µm thick Si detector Thanks to the MEDIPIX collaboration • MUROS 2 interface • Medisoft IWORID 2004 - B. SURRE 6

Depletion voltage 20 % overdepletion 120 V IWORID 2004 - B. SURRE 7

Conversion function • Pixel size 55 x 55 µm² • Fluence: 91 #/(pixel. µGy) • Slope: 5. 9 count/(pixel. µGy) • G=6. 5% IWORID 2004 - B. SURRE 8

MTF (ESF) Angle α • N = 1/tan(α) = 12 • Oversampling = 0. 055 mm/12 IWORID 2004 - B. SURRE 9

SNR ? • 20 flood images to compute the flat field coefficients IWORID 2004 - B. SURRE 10

ESF, RQA 5, 10 m. As IWORID 2004 - B. SURRE 11

7. Step (300 pts), RQA 5, 10 m. As Step(x)=ESF(x-x_shift)-ESF(x) IWORID 2004 - B. SURRE 12

DFT(Step) (300 pts), RQA 5, 10 m. As MTF(f)=|DFT(real step, f)|/|DFT(perfect step, f)| IWORID 2004 - B. SURRE 13

DFT(Step) (300 pts), RQA 5, 10 m. As MTF(f)=|DFT(real step, f)|/|DFT(perfect step, f)| IWORID 2004 - B. SURRE 14

DFT(Step) (300 pts), RQA 5, 10 m. As MTF(f)=|DFT(real step, f)|/|DFT(perfect step, f)| IWORID 2004 - B. SURRE 15

MTF, RQA 5, 10 m. As IWORID 2004 - B. SURRE 16

MTF, RQA 5, 10 m. As IWORID 2004 - B. SURRE 17

MTF, RQA 5, 10 m. As Presampling resolution: 7. 7 lp/mm Visible detail limit = 0. 3 IWORID 2004 - B. SURRE 18

NPS @ RQA 5 dose IWORID 2004 - B. SURRE 19

NTF² @ RQA 5 IWORID 2004 - B. SURRE 20

DQE @ RQA 5 DQE(f) = Gx. MTF²/NTF² IWORID 2004 - B. SURRE 21

NPS considerations & calculation • Can we consider our results correct? >>> Calculations and simulations… IWORID 2004 - B. SURRE 22

Experimental NPS dose IWORID 2004 - B. SURRE 23

Simulated NPS dose IWORID 2004 - B. SURRE 24

NPS comparison: sim & exp IWORID 2004 - B. SURRE 25

1 -D NPS comparison, 2 directions IWORID 2004 - B. SURRE 26

1 -D NPS comparison IWORID 2004 - B. SURRE 27

1 -D NPS comparison Interpolation increases the low frequencies IWORID 2004 - B. SURRE 28

Conlusions • DQE has been calculated on 500 µm thick Si, bonded to a MEDIPIX 2 chip • A standard measure protocol have been used • DQE is not so evident to find… • How to improve this DQE ? (remember medicine) • Next step: comparison with detectors of different thickness, study in parallel with detectors from the market, further calculations… IWORID 2004 - B. SURRE 29

Acknowledgements • The MEDIPIX collaboration • J. CHAPUT, M. CARIA • L. SARRY • You, for your attention IWORID 2004 - B. SURRE 30