Spectral x-ray photon counting

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 1

ASIC Development for Energy Resolved Spectral Counting and Imaging of X-rays

S. Azman, W. Dang, C. Gheorghe, M. Gjetanger, T.M. Johansen,D. Meier, S. Mikkelsen, G. Mæhlum, J. Talebi, T. Ødegaard

Gamma Medica – Ideas (Norway) AS

CERN, 4.-6. April 2011

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 2

ASIC Designs Overview

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 3

Radiation Detector Design and Development for Science

JAXA, BepiColombo

ATHENA

Requirements, Preliminary

Specifications

Design Simulation

Implementation,Rule checks, simulation

Manufacture, Foundry

Assembly

Integration

Tests,Verification and

Validation

Science: e.g. space, physics

ASIC wafer

Radiation sensor

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 4

Abstract – ASIC for Spectral X-ray Photon Counting

We describe an integrated circuit (IC) for spectral counting and imaging of polychromatic x-rays.

The circuit has been designed for the readout of cadmium telluride (CdTe) radiation sensors with up to 64 pixel electrodes. Each readout channel contains a charge sensitive amplifier, up to 6 discriminators and 6 counters which increment when the amplitude exceeds a given threshold. The energy dynamic range is about 120 keV. Subsequently we designed and assembled camera prototypes from 1D-linear arrays of CdTe read out by 32 ASICs. We have tested the cameras with imaging phantoms and polychromatic x-rays in a micro-computed tomography (microCT) setup. We studied the use of the cameras for material separation, especially with gadolinium and iodine based contrast agents, for medical imaging. The presentation will focus on the ASIC design specifications which were originally set for industrial scanning, but also discuss the requirements for x-ray microCT and medical imaging.

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 5

Spectral X-ray Photon Counting - Principle

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 6

Spectral X-ray Photon Counting - Principle

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 7

ASIC Channel Architecture – 1 out of 32/64

Mikkelsen et al. (2008), Proc. IEEE NSS

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 8

ASIC Specifications

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 9

ASIC Floorplan, Padframe, Block Diagram

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 10

ASIC Block Diagram

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 11

Spectral X-ray Photon Counting – Applications

Security e.g. explosives

Food safety e.g. foreign objects

Separtion & sorting e.g. metals, waste....

NDT Medical

e.g. contrast agents Physics research

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 12

Spectral X-ray Counting Detector

X-ray Line Camera

Modules: CdTe + ASICs

Wang et al. (2009), Proc. IEEE NSS

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 13

Radiation Sensor - CdTe Crystal with Electrodes

0.4 mm Anode Pitch

3 mm

-500V

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 14

Spectral X-ray Counting Detector - Specifications

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 15

Photographs of X-ray Line Detector

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 16

Photographs of X-ray Line Detector

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 17

X-Ray Line Camera - Hardware Details

External COUNT signal synchronized with conveyor belt or CT system

1500 frames/seconds maximum (0.67 ms frames)

Short dead time between frames (40us)

Interface to PC through National Instruments I/O card

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 18

Example Material Identification – Luggage Phantom

Color coded based on the ratio of attenuation at two energies, [80,100] keV and [35,50] keV

Grey scale image based on attenuation at one energy

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 19

Food Safety - Pieces of Glass in Raisins

Dual-energy information, enhanced to ’see’ only glass and eliminate raisins

Grey scale image based on attenuation at one energy

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 20

Material Separation – Hard Disk Drive

Regions color coded based on attenuation ratio between high and low energy

Grey scale image based on attenuation at one energy

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 21

Count Rate and Spectra

Customer data

Mono-energetic x-rays

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 22

Spectral Distortion in Photon Counting Detector

Comparison between• GM-I Spectral Photon

Counting Detector• AMTEK CdTe

Spectrometer

Effects:• Energy resolution• Pulse pileup• Characteristic x-ray• Charge sharing

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 23

Charge Sharing

80 keVSummed Count rate Summed energy

Customer data

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 24

Spectra with Gd Contrast Agent

0.4

0.8

1.2

1.6

2

2.4

2.8

30 40 50 60 70 80 90 100

WaterPMMAPOMPTFECortical boneIodine solutionGd solution

Energy (keV)

Energy-dependent x-ray attenuation

Wang, 2011

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 25

CT Phantom Images and Energy Thresholds Trimming

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 26

Summary

We have built a X-ray Line Camera capable of Spectral X-ray PhotonCounting. The design is based on CdTe custom made ASICs.

The prototype cameras allow one to study the potentials of spectral x-ray photon counting.

It is important to understand and improve:

• Spectral response vs. count rate– Charge sharing in CdTe– Rate capability of CdTe pixels and ASIC, especially for CT

• Threshold uniformity and trimming

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 27

References

[1] S. Mikkelsen et al. (2008), ”An ASIC for Multi-Energy X-ray Counting”, Proc. IEEE NSS 2008.

[2] X. Wang et al. (2009), ”A Digital Line-Camera for Energy Resolved X-ray Photon Counting”, Proc. IEEE MIC 2009.

[3] X. Wang et al. (2011), “Material Separation in X-ray CT with Energy Resolved Photon Counting Detectors", Medical Physics (0094-2405), 3/1/2011. Vol.38,Iss.3;p.1534-1546.

[4] X.Wang et al. (2011), “MicroCT with energy-resolved photon-counting detectors2011“, Phys. Med. Biol. 56 2791–2816.

dirk.meier@gm-ideas.com 2011-April, CERN, SpecX-Ray Workshop 28

Acknowledgments

We like to thank our customers and collaborators.

and

X. Wang, E. Frey, K. Taguchi, B.M.W. Tsui at Johns Hopkins University

D. Wagenaar at Gamma Medica, Northridge

B. Sundal at Corentium, Norway

Thank you