Use of a novel Controlled Drift Detector for Diffraction Enhanced Breast Imaging
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Transcript of Use of a novel Controlled Drift Detector for Diffraction Enhanced Breast Imaging
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
Outline
• Principles and constraints of Diffraction Enhanced Breast Imaging (DEBI)
• The Controlled Drift Detector (CDD)• Results with monochromatic radiation• Future applications
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
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
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
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
The “ideal” detector for DEBI
• Low noise (single-photon counting)• Position sensitive• Spectroscopic capability
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
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
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
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
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
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
Acknowledgment
S. Pani was supported by a Marie-Curie Intra-European Fellowship (MEIF-CT-2004-007206) within the 6th European Community Framework Programme