Use of a novel Controlled Drift Detector for Diffraction Enhanced Breast Imaging
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Use of a novel Controlled Drift Detector for Diffraction Enhanced Breast Imaging
S. Pani, G. Royle, R. Speller – University College London, Department of Medical Physics and Bioengineering
A. Castoldi, A. Galimberti, C. Guazzoni – Politecnico di Milano and INFN, Sezione di Milano
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Outline
• Principles and constraints of Diffraction Enhanced Breast Imaging (DEBI)
• The Controlled Drift Detector (CDD)• Results with monochromatic radiation• Future applications
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Conventional Breast Imaging
• The main limitation of conventional mammography is the small difference between the attenuation coefficients of fibroglandular tissue and carcinoma
fibrous IDC
PC Johns and MJ Yaffe, Phys Med Biol 1987
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Diffraction Enhanced Breast Imaging (DEBI)
• DEBI is based on the detection of the diffraction pattern produced by coherently scattered X-rays
• The diffraction pattern of normal and neoplastic breast tissue are significantly different
G. Kidane et al., Phys Med Biol 1999
=1/ sin (/2)
=1.1 nm-1=1.7 nm-1
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Energy-dispersive DEBI
• Polychromatic beam• Scattered photons at a
given angle are detected with a HPGe detector
Can be used with a conventional source
Several values of the momentum transfer can be investigated simultaneously
× Non position sensitive
21
E1 E2
HPGe
incoming beam
collimator
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Synchrotron radiation DEBI
• Monochromatic radiation• Different values of the
momentum transfer are achieved by changing either E or
Position sensitive technique× Difficult implementation on
conventional sources
monochromaticbeam
diffractedbeam
multi-hole collimator
low-noise CCD
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The “ideal” detector for DEBI
• Low noise (single-photon counting)• Position sensitive• Spectroscopic capability
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The Controlled Drift DetectorPolitecnico/INFN Milano, MPI Munich
• Prototype characteristics:– 3.96 x 6.12 mm2, – pixel size180 µm2 – Thickness 300 µm– Edrift: 400 V/cm Frame rate:
50 kHz
• Energy resolution:– 2.15 keV FWHM @18 keV,
room temperature (high leakage current)
• Combines the pixel structure of a CCD with the fast readout typical of a SDD
• Integration time ~ 1-6 µs– High frame rate– Low thermal noise in
tegr
atio
n ph
ase
read
out
phas
e
A Castoldi et al., IEEE TNS 1997
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Experimental set-up at ELETTRA
• Goniometer at 9 degrees for diffraction images
• Beam energy 18 keV (=1.1 nm-1) and 26 keV (=1.7 nm-1)
• Multi-hole collimator (500 µm hole - 500 µm spacing)
• Both transmission and diffraction images
phantom
CDD + collimator
y translation
x translation stagegoniometer + vertical adjustment
monochromaticX-ray beam
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CDD spectra
0E+0 2E+4 4E +4 6E+4 8E+4energy (eV)
1E+0
1E+1
1E+2
1E+3
1E+4
1E+5
1E+6
coun
ts
E=18 keV (TrSam pA)
E=26 keV (Sam pD )
E=18 keV (Sam pC )
E=18 keV (Sam pA)
E=18 keV (TrSam pC )
Tr – plexi1 18 keV
Diff – plexi1 18 keV
Tr – plexi2 18 keV
Diff – plexi2 18 keV
Diff – plexi2 26 keV
pile-up 3rd harmonic
4th harmonic
• Images were obtained by integrating – The counts
within a 5 keV window
– The full spectrum
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Meat sample 1Thickness ~ 5 mm
Transmission 18 keV
Diffraction 18 keV
Transmission 26 keV
Diffraction 26 keV
CONTRAST 5 keV (%)
29±2
48±3
12±1
30±3
CONTRAST Full spect (%)
28±2
49±4
11±1
30±2
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Meat sample 2Thickness ~ 5 mm
CONTRAST 5 keV(%)
33±3
46±5
11±1
29±2
Transmission 18 keV
Diffraction 18 keV
Transmission 26 keV
Diffraction 26 keV
CONTRAST Full spect (%)
34±3
44±4
10±1
27±2
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Conclusions and perspectives
• The performance of the CDD in its application to DEBI was tested with a monochromatic source
• No significant difference was observed between full-spectrum/photopeak integration, BUT
• In the future: use of the CDD for DEBI with conventional sources– Energy dispersive, position-sensitive DEBI
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Acknowledgment
S. Pani was supported by a Marie-Curie Intra-European Fellowship (MEIF-CT-2004-007206) within the 6th European Community Framework Programme