G. Mettivier , M.C. Montesi, P. Russo

04/25/23 4th International Workshop on Radiation Imaging Detectors, Amsterdam, The Netherlands 8-12 September 2002

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Design of a compact gamma camera

with semiconductor hybrid pixel detectors: imaging tests

with a pinhole collimator

G. Mettivier, M.C. Montesi, P. Russo

Università di Napoli “Federico II” and INFN Napoli, Italy


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Scope of the project

Design specifications of final system

•for Tc-99m ray tracer (140 keV) • Design and build a compact gamma camera

• using the medipix series of hybrid pixel detectors + collimator

• for sentinel lymph node (SLN) radio-guided surgery

• Spatial resolution 1-2 mm

• Medipix2 readout chip (256x256 pixels, 55 m pitch)

• CdTe pixel detector (1 mm thick)


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Scope of the present work

• Medipix1 chip (64x64 pixels, 170 m pitch)

• 300 m thick Silicon detector (low detection efficiency)

To perform preliminary evaluations of the spatial resolution attainable with a pinhole tungsten collimator

with the present imaging system


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20 40 60 80 100 120 140

0,01

0,1

1 CdTe 1 mm

Si 0.3 mm

Det

ectio

n ef

ficie

ncy

Photon energy (keV)


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Previous work Multi-hole collimator Setup

d

DSi Pixel detectorMedipix1 chip

Collimator

Point-like source

Chipboard or PGA

Spatial resolution0.6 mm FWHM

at 46 mm

Geometric efficiency2x10-5

Field Of View11 mm


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This work Experimental Setup

PinholeCollimator

Point-like source

PGA chip carrier

h

bSi pixel detector

Medipix1 chip


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Experimental Setup

7 mm

0.35 mm

Pinhole minimum diameter d = 0.35 mm (de = 0.57 mm)

Total (geometric+penetrative) on-axis efficiency S = de2 /16h2

de = effective diameterTotal FWHM spatial resolution Rs2 [ (h+b)de/b ]2 + (h/b)2 Ri2

Pinhole aperture = 90 deg

h

b


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0 13 25 38 50 63

0

13

25

38

50

63

0 125 250 375 500 625

0 13 25 38 50 63

0

13

25

38

50

63

0 50 100 150 200 250 300 350

0 13 25 38 50 63

0

13

25

38

50

63

0 25 50 75 100 125 150 175 200

0 13 25 38 50 63

0

13

25

38

50

63

0 25 50 75 100 125 150

Point-like Co 57 gamma source

(122 keV)

h = 16.5 mm h = 26.5 mm

h = 36.5 mm h = 46.5 mm

b = 7.5 mm

Results

t = 15 hEthr = 15 keV


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Results

10 20 30 40 50

10-6

10-5

10-4

10-3

10-2

d = 0.35 mm d = 2 mm Theory (de = 0.57 mm)

O

n-ax

is g

eom

etric

effi

cien

cy

Source-collimator distance (mm)

0.2 cps/kBq


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Results

0 10 20 30 40 500,0

0,5

1,0

1,5

2,0

O

n-ax

is re

solu

tion

FWH

M (m

m)

Source-collimator distance (mm)

D = 0.35 mm


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ConclusionsTested a prototype compact gamma camera

Imaging performance at 10 mm source-collimator distance

system sensitivity = 0.2 cps/kBq

FOV = 20 mm

Spatial resolution = 1 mm


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Future DevelopmentsUse of the Medipix2 readout ASIC (256x256 pixel, 55 micron pitch)

Bump-bonded to a 1 mm thick CdTe pixel

- Higher detection efficiency at 140 keV (30%)- Higher sensitivity (in the order of 1 cps/kBq)- Equal or better spatial resolution (1-2 mm)

Comparable with other prototype using arrays of scintillators

With respect to the present Medipix1 + Silicon detector:

- Detection threshold settable up to about 100 keV

Spatial resolution = 3.5 mm, FOV = 9 mm, Sensitivity = 10 cps/kBq (L. R. Mac Donald et al.)


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AcknowlegementThis work has been done in the framework of the activities of the Medipix2 collaboration (www.cern.ch/MEDIPIX) which comprises 16 European research institutions. The Medipix2 chip has been designed by CERN (Geneva, Switzerland). The MUROS2 interface has been designed by NIKHEF (Amsterdam, The Netherlands). The Medisoft 4 software system has been written by Universita' di Napoli Federico II and INFN (Napoli, Italy).

G. Mettivier , M.C. Montesi, P. Russo

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