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DETECTORS FOR MEDICAL PHYSICS
Maria Giuseppina BisogniMaria Giuseppina BisogniUniversita’ di Pisa, Dipartimento di Fisica “E. Fermi”INFN Sezione di Pisa
Corso CLXXV - "Radiation and particle detectors“, Varenna, 20 - 25 Luglio 2009
Lectures Contents
� Radiation detectors for morphological imaging.
�Digital mammography
2
� Radiation detectors for functional imaging
�Multimodality Imaging: advantages and technological challenges.
Contents
� Foreword
� Digital Radiology
3
� Digital Radiology
� Digital Mammography
� Clinical CT
� Micro CT
The beginning
� 1895 Prof. Wilhelm Conrad Roentgen discovers X-rays
� Phosphor screens introduced early 20th century
� In the ‘70 years routine use of fluoroscopy with image intensifiers coupled to TV cameras
� In the ‘80 years 'the radiography becomes digital (imaging plates, CCDs, flat-panels, semiconductor detectors both
4
plates, CCDs, flat-panels, semiconductor detectors both amorphous and crystalline) M. Hoheisel, NIM A563 (2006) 215–224
Digital Radiographic Imaging
�Film-screen systems cons:� detection and display on the same medium
�Digital radiography features: �transmitted intensity pattern sampling (pixels)�transmitted intensity pattern sampling (pixels)
� spatial sampling (del, pixel)
3D reconstruction techniques
6
Alessandra Retico - SPIE Medical Imaging 2009
Computer Aided Detection
CAD input
CADI for internal nodule detection
CADJP for juxtapleural nodule detection
Alessandra Retico - SPIE Medical Imaging 2009 7
CAD output
Several imaging modalities …
� General radiography
� Angiography
� Digital Subtraction Angiography (DSA)
� Mammography
8
� Mammography
� Stereotactic biopsy
� Computed
Tomography (CT)
…with different requirements 9
Radio-graphy
Angio-graphy
Mammo-graphy
Stereo-Tactic biopsy
CT
Detector size (cm2)
43 x 43 30 x40 18 x 2424 x 30
5 x 9 4 x 70 size (cm ) 24 x 30
Pixel (µm) 125–165 150–400 50–100 <50 500
Resolution 12 bits 12 bits 12 bit 16 bit 20 bit
Frame rate Single shot < 1 s
< 60 f/s Single shot < 1s
Single shot < 1 s
1000 MB/s
Best Detector for ?
� Wrong approach: Detector driven
“I have the best detector for… what??”
10
� Right approach: Experiment driven
“I have this biological, medical, clinical experiment to
make with these requirements: � which is the best
detector to be used, built or developed ?”
Classification of Digital Radiology
� Computed Radiography (CR)� photostimulable phosphor Imaging plates
� Digital Radiography(DR)
11
� Digital Radiography(DR)� Indirect
� e.g. a-Si flat panel detector, CCD or CMOS based detectors
� Direct � a-Se flat panel detector
� single photon counting (e.g. hybrid detectors, MWPCs)
Charge Coupled Devices (CCD)
� Tecnology Metal Oxide Semiconductor (MOS)
� The charge produced is stored in a potential well
� Potential changes to make the charges shift from one pixel to the next in a given column
� Serial read-out with a clock con un clock
� Coupled to scintillators CsI(Tl) to improve efficiency
OPDIMA® Siemens
Read-out architectures for CCD14
CCD linear array
CCD camera system- Light loss- Demagnification
Reduced DQE→
a-Si Flat Panels for DR
� a-Si:H photodiodes (low dark current, high sensitivity to green light)
� Coupled to CsI phosphors to improve efficiency
15
from J. A. Seibert, UC Davis Medical Center, CA, USA
Scintillator: CsI:Tl needle crystals
� Thickness 550µm
� good X-ray absorption
� Needles act as light-guides
16
� Needles act as light-guides
� sharp MTF
� CsI:Tl emits green light
Scintillator
Read-Out Architecture
AddressingReadout
ADC
X-ray film: dynamic range18
Over-exposedUnder-exposed
8 mAs0.5 mAs 2 mAs 4 mAs 16 mAs 32 mAs 63 mAs
M. Overdick, Philips Research Labs – Aachen, IWORID 2002
Flat panel detector: dynamic range19
typical usage
M. Overdick, Philips Research Labs – Aachen, IWORID 2002
a-Se Flat Panels Direct DR
� alloyed a-Se with % As and with ppm Cl
20
from J. A. Seibert, UC Davis Medical Center, CA, USA
from J. A. Seibert, UC Davis Medical Center, CA, USA
alloyed a-Sewith % As (stabilizer, ↓ holes lifetime, ↑ e- lifetime) with ppm Cl (↑ holes lifetime, ↓ e- lifetime)
DIGITAL MAMMOGRAPHY
22
DIGITAL MAMMOGRAPHY
Mammography
� Tumour masses� Healthy tissue degeneration
� X-ray Attenuation properties
similar to healthy tissue
� Size > 5 mm
Microcalcifications� Microcalcifications
� Submillimetric calcium deposits
� Denser than gland and adipose tissues
� Cluster of microcalcificatons are tumour markers
nn
X rays
µ1µ1
µ2µ2tt
xx
Quantic Image
Detector Signal-Transfer properties
(depend on the object size!)
Detector Signal-Transfer properties
(depend on the object size!)
Physical Parameters
l2l1
n2n1Quantic Image
DigitalDetector
Detected Image
Image line profileImage histogram
Signal to Noise Ratio
n2n1
1 2
2 21 2
n nSNR
σ σ−=+
Only statistics fluctuations
25
n1
n2
x
( )( ) 1
11
ts NAe
SNR eR
µµ ε−
− ∆= −+
If SNR = k and (∆µ)s << 1 small 2
12 4
(1 )exp( )( )
( )
k R tN k
s
µε µ+≈
∆
ε= detection efficiency
Mammography
26
Tumour masses� Healthy tissue degeneration
� X-ray Attenuation properties
similar to healthy tissue
� Size > 5 mm
Microcalcifications• Submillimetric calcium deposits• Denser than gland and adipose tissues• Cluster of microcalcificatons are tumour markers
First Digital Mammography System27
� GE Senographe 2000D
� Revolution™ Flat Panel Digital Detector a-Si +CsI(Tl)
� 18x 24 cm2
Pixel: 100 x 100 µm2� Pixel: 100 x 100 µm2
� 12 bit resolution
� 11 years R&D
and 130 M$ investment
� First digital mammographic
system approved by FDA (2000)
Direct Digital Mammography28
� A-Se based flat panels
� SeleniaTM, LORAD-Hologic
� Mammomat NovationDR Siemens
� Active area 24 x 29 cm2� Active area 24 x 29 cm
� 70 µm pixel size
� Dual target X-ray tube: Mo/Mo, Mo/Rh, W/Rh for dose reduction
� Giotto Image MD Internazionale Medico Scientifica Srl (I.M.S. Bologna, Italy)
� active area 23.9 x 30.5 cm2
� pixel size of 85 µm
� Mo and Rh filter
Single Photon Counting (SPC) Systems29
� Noise suppression� Higher SNR or lower dose
� Low event rate applications
� Linear and wider dynamic range� Limited by counter saturation� Limited by counter saturation
� Energy discrimination� Compton events rejection
� X-ray fluorescence rejection
� “Energy weighting” suppression� Low energy photons weight less than high
energy ones in integrating systems
� In SPC systems all photons have same weight
First SPC commercial mammographic system30
Sectra MicroDoseTM
� Si strip detectors, 768 strips, 50 µm pitch
slight fan-out (to � slight fan-out (to compensate beam divergency), 2 cm long
� 500 µm thick
� “quasi” edge-on
(4º- 4.5º tilt angle)
� ~90% efficiency @ 30 keV
� ASIC:
� 128 channels
� counting rate/pixel: >1 MHz
Photon Counting in X-ray MammographyCourtesy of Mats Danielsson, Sectra Mamea AB ,Sweden (2009)
32
� M. Lundqvist et al., “Evaluation of a Photon-Counting X-Ray Imaging System”, IEEE Trans.Nucl.Sci. 48 (4), August 2001
SYRMEP Project (INFN GV, early ‘90)33
(ELETTRA Synchrotron, Trieste) Combined use of syncrotron light, new detectors and non-conventional imaging techniques aimed at the improvement of the image quality in mammography
Erik Vallazza – INFN Trieste – VCI 2007
Edge-on Si strip detector
� A silicon microstrip detector is used in the so called “edge-on” geometry matching the laminar geometry of the beam
� The absorption length seen by the impinging radiation is given by the strip length (~100% in 1 cm of silicon for 20 keV photons)
� Almost complete scattering rejection
� The pixel size is determined by the strip pitch (H) times the detector thickness (V)
� Drawback: the dead volume in front of the strip34
Phase contrast nylon wires
Contrast –detail phantom17 keV
35
� Phase contrast nylon wires
Integrated Mammographic Imaging Project� Technology Transfer project funded by the Italian Ministry for
Reseach (under law 46/82 article 10)
� Technologies originally developed for High Energy Physics experiments applied to mammographic and functional breast
36
experiments applied to mammographic and functional breast imaging
� Collaboration between national Universities, INFN and Industry
� Research lines� Gamma camera for scintimammography
� GaAs pixel detectors and bump bonding techniques
� Mammography system demonstrator based on GaAs pixel detectors
� High intensity Quasi-monochromatic X-rays source
Why GaAs ?
Photoelectric interaction probability ≈ 100% in the mammographic energy range (10 - 30 keV) for a 200µm thick GaAs crystal
The Medipix-1/PCC detection unit
38 GaAs Detector
Indium Bump -bonding
Detectors by AMS ItalyGaAs: 200 µm thickpixel 170 x 170 µm2
Schottky 150x150 µm2
channels 64 x 64total area 1.2 cm2
Electronic chip
Indium Bump -bondingBy AMS Italy
Input Preamp
LatchedComparator
Pulseshaper
ThresholdAdjust(3 bits)
TestInput
Cfb
Test(1 bit)
Ctest
Rst
AnalogReset
Mask(1 bit)
Shutter
Data
Clk
Clkout
1
0
01
Sel
Sel
Mux
Mux
ShiftReg
To lowerpixel
From upperpixel
Photon Counting Chip (PCC)MIC CERN SACMOS 1 µmFASELEC ZurigoPixel 170 x 170 µm2
Channels 64 x 64Area 1.7cm2 (active area =1.2cm2)Threshold adjust 3-bitPseudo-random counter 15-bit
httphttp:://medipix//medipix..webweb..cerncern..ch/MEDIPIXch/MEDIPIXhttphttp:://medipix//medipix..webweb..cerncern..ch/MEDIPIXch/MEDIPIX
Mammographic Demonstrator39
X ray tube
Pb collimatorMammographic
Head
Mammographic Head40
� The Detection Unit
� The assemblies have been produced and bump bonded by Alenia Marconi Systems (Roma)
� Each detection unit has been mounted in a protective case.
Aluminum nitride (AlN) substrate,LEXAN cover on top (not shown)
GaAs MPXI/PCCassembly
Step and Shoot41
� 18 x 24 cm2 exposure field
� 1D scanning
� 9 x 2 assemblies
� 26 exposures� 26 exposures
� “off-line” image reconstruction
1 cm
Some radiographs
Al disk 15 micron thickAl disk 15 micron thick
42
Radiograph of Al disks embedded in wax
In a lucite matrix (5 cm thick, 10 cm in diameter)
Dose 2 mGy
Radiograph of Al disks embedded in wax
In a lucite matrix (5 cm thick, 10 cm in diameter)
Dose 2 mGy
Al disk 15 micron thick
Contrast 0.8 %
Al disk 15 micron thick
Contrast 0.8 %
Tulip Radiograph
Image size 14 x 20 cm^2
Dose 2 mGy
Tulip Radiograph
Image size 14 x 20 cm^2
Dose 2 mGy
Image Quality Assessment
�Transfer Function Analysis
Protocol IEC 62220-1-2: "Medical electrical equipment -Characteristics of digital X-ray imaging devices - Part 1-2: Determination of the detective quantum efficiency -Detectors used in mammography"
� MTF, NNPS, DQE
�Contrast Threshold Analysis
Protocol EUREF: Perry N et al. L (eds), “ European Guidelines for
quality assurance in breast cancer screening and diagnosis –Fourth Edition”, Luxembourg (2006)
�Contrast-detail curves
SystemSystemPSF(x) = Point Spread Function
input = q(x)input = q(x) output = d(x)output = d(x)Space Invariant Linear Systems Theory Space Invariant Linear Systems Theory Space Domain
Modulation Transfer FunctionsModulation Transfer Functions
Space-Frequency Domain
T(u) = Characteristic Function
Modulation Transfer Function
∫∞
∞−
⋅= dxexLSFMTFxiνπν 2)()(
45
� It measures how much an imaging system affects
the amplitude of an input sinusoidal signal
� It is function of the spatial frequency
� Fourier transform of the Line Spread Function LSF(x)
C(x) = autocorrelation function of the signal variations ∆d(x) around the mean signal <d(x)>
Ergodic Wide-Sense Stationary process
Noise Power SpectrumNoise Power Spectrum
for Digital Imaging Systems...
flood imageflood imageflood imageflood image
Detective Quantum EfficiencyDetective Quantum Efficiency
)(
)()(
2
2
uSNR
uSNRuDQE
in
out=)(
)()(
2
uNNPSq
uMTFuDQE =
Fraction of Poisson-distributed quanta contributing to form the image
Degradation of information in the signal in the detector system.
Detective Quantum Efficiency
DQE( f ) = SNRout2
SNRin2
• DQE describes how the Signal to Noise Ratio varies
48
• DQE describes how the Signal to Noise Ratio varies
across the imaging system stages.
• It depends on the frequency through the MTF and the
NNPS, both frequency functions.
• At zero frequency, DQE(0) depends on the detection
efficiency and on the image variance
Mammographic Systems Comparison
49 System IMI Prototype Giotto IMS Fuji FCR 5000MA
GE Senographe 2000D
Detector Crystalline GaAs, a-Se Imaging plates Caesium Iodide. Detector Crystalline GaAs, Si
a-Se Imaging plates Caesium Iodide. TFT array
Electronic mode Single Photon Counting
TFT. Charge integration
Laser scanner TFT. Charge integration
Pixel pitch 170 micron 85 micron 50 micron 100 micron
Image matrix (pix) 1152 x 1536 2048x2816 3600 x 4800 1914 x 2294
Image size (cm) 18 x 24 17.4 x23.9 18 x 24 19 x 23
Beam (Target/Filter)
Mo/Mo Mo/Mo, Mo/Rh Mo/Mo Mo,Mo/Mo,Rh,Rh/Rh
Note Slot scanning Full field Full Field Full Field
CDMAM 3.4 Phantomresult of the project: "Quality Assurance in Mammography, Department of Radiology, University Medical Centre
Threshold Contrast Visibility
EUREF protocol Medical Centre Nijmegen, the Netherlands." By M.A.O. Thijssen, Ph.D., K.R. Bijkerk, M.Sc. and J.M. Lindeyer, B.Sc.Technical specifications
aluminum base containing gold discs of various thicknesses and diameters which are arranged in a matrix of 16 rows and 16 columns. Each square contains two identical discs (same diameter and thickness), one in the center and one in a corner.
Diameters from 0.06 mm to 2 mm.
Thickness: from 0.03 to 2 µm.
Phantom ImageParticular MGD 2 mGyImaged with 4 cmthick lucite layer
� EUREF protocol � Three experienced observers
determine the minimum contrast visible on two images
� Every observer must score two different images
� The results of the three observers must be averaged
Contrast detail CurvesDisk
Diameter(mm)
EUREF Acceptable value (micron)
EUREF Achievable value (micron)
IMI Thickness Threshold (µm) 1.58 mGy
IMI Thickness Threshold (µm) 2.21 mGy
2 mm 0.069 0.038 0.0375 0.0362
1 mm 0.091 0.056 0.0588 0.0475
0.50 mm 0.15 0.103 0.1537 0.1312
0.25 mm 0.352 0.244 0.3833 0.3417
Senographe200D data from:“EVALUATION AND CLINICAL ASSESSMENT OF DIGITAL MAMMOGRAPHY SCREENING USING THE GE SENOGRAPHE 2000D SYSTEM”, NHSBSP Equipment Report 0602, May 2006, Published by NHS Cancer Screening Programmes
0.1 mm 1.68 1.10 - -
Image QualityConfronto Senographe 2000D e dimostratore IMI in progress..
Disk Diameter(mm)
EUREF Acceptable value (contrast %)* [thickness (micron)]
EUREF Achievable value (contrast %)* [thickness (micron)]
IMI Th. Contrasts( %)* [thickness (µm)]
36 mAs
IMI Th. Contrast (%)*[thickness (µm)]
50 mAs
Senodgraphe 2000D Threshold Contrast
2 mm 1.05% [0.069] 0.55% [0.038 ] 0.53% 0.51% 0.65%
1 mm 1.4% [0.091] 0.85% [0.056] 0.82% 0.67% 1.00%
0.50 mm 2.35% [0.15] 1.6% [0.103] 2.14% 1.83% 1.84%
0.25 mm 5.45% [0.352] 3.8% [0.244] - - 4.15%
0.1 mm 23% [1.68] 15.8% [1.10 ] - - 16%0.1 mm 23% [1.68] 15.8% [1.10 ] - - 16%
Senographe200D data from:“EVALUATION AND CLINICAL ASSESSMENT OF DIGITAL MAMMOGRAPHY SCREENING USING THE GE SENOGRAPHE 2000D SYSTEM”, NHSBSP Equipment Report 0602, May 2006, Published by NHS Cancer Screening Programmes
MTF comparison53
Nyquist frequency MTF
Giotto Image MD 5.88 lp/mm 46 %
1.0
GE Senographe 2000DMedipix I 170 um pitch Fuji FCR 5000MA Giotto Image MD Medipix II 55 um pitch
Medipix II 9.1 lp/mm 60 %
GE Senographe 2000 D 5 lp/mm 20 %
FCR 5000MA 10 lp/mm 1 %0 5 10 150.0
0.5MT
F
lp/mm
Detective Quantum Efficiency
54
S.R. Amendolia et al., "Characterization of a mammographic system based on single photon counting pixel arrays coupled to GaAs x-ray detectors" Med. Phys. Volume 36, Issue 4, pp. 1330-1339 (April 2009)
Measurement of Detector DQE
0.7
0.6
0.5
0.4
Kodak CR 850 EHR-M Konica Regius 190 Fuji CR Profect GE Senographe DS Lorad Selenia Sectra MDM
0.3
0.2
0.1
0.0
DQ
E
109876543210Spatial frequency [mm-1]
* Monnin et al. Medical Physics, March 2007, Volume 34, Issue 3, pp. 906-914 S.R. Amendolia et al., "Characterization of a mammographic system based on single photon counting pixel arrays coupled to GaAs x-ray detectors" Med. Phys. Volume 36, Issue 4, pp. 1330-1339 (April 2009)
DQE for the system
Courtesy of Mats Danielsson, Sectra Mamea AB ,Sweden (2009)
Sectra 3D photon counting (Tomosynthesis)
Courtesy of Mats Danielsson, Sectra Mamea AB ,Sweden (2009)
Dual energy with photon counting technique
If one measures the pulse height in Photon Counting one can estimate the energy of each x-ray (color) and potentially enhance structures of clinical interest such as structures of clinical interest such as microcalcifications, e.g. using the so-called dual-energy technique
Photon Counting Enables Electronic Spectrum Splitting
6
8
10
12
14
16
18
Spectrum after breast
Flu
ence
(10
6 ph.
/cm
2 )
4
6
8
10
12
14Spectra after breast
Flu
ence
(10
6 pho
t/cm
2 )
10 15 20 25 30 35 40 450
2
4
6
Energy (keV)
Flu
ence
(10
0 10 20 30 400
2
4
Flu
ence
(10
Energy (keV)
Advantage 1: No high- and low-energy spectra overlapAdvantage 2: Single exposure
Fantom bilderLow energy image High energy image
Total image Dual energy subtraction
Bornefalk H, Lewin JM, Danielsson M, Lundqvist M. Single-shot dual-energy subtraction mammography with electronic spectrum splitting: Feasibility. Eur J Radiol 2006;60:275-278.
COMPUTED TOMOGRAPHY ( Clinical CT)
61
Originally called:
Computerized Axial Tomography (CAT)
Rotation givesmultiple projections
X-raytube
Thin fan beamof x-rays
Patient
Computed Tomography (CT)
Array of detectors(rare-earth doped ceramics
with photodiodes)
Patient(stationary)
Use 1D projectionas a template
Back projectionof pixel
brightness
PROJECTIONRECONSTRUCTION
http://www.colorado.edu/physics/2000/index.pl
Spiral CT: Scanning Principle63 Start of
spiral scanPath of continuouslyrotating x-ray tubeand detector
Kalender WA et al. Radiology 1989; 173(P):414 and 1990; 176:181-183
Direction of continuouspatient transport 0
0 t, s
z, mm
64
2424--row 16r ow 16--slice slice ‘adaptive / hybrid’ ‘adaptive / hybrid’
Array Detector’Array Detector’
1.5 mm 0.75 mm4 x 1.5
mm4 x 1.5
mm16 x 0.75
mm
16 x 0.75 mm@ 0.5 s
16 x 1.5 mm@ 0.5 s
12 x 0.75 mm@ 0.42 s
Courtesy of W. Kalender, ECR-2003
Axial Geometry evolution (z-direction)65
zz
MPR
1998: M=4 2002: M=16<1998: M=1
z
(drawn in an exaggerated way)
Courtesy of W. Kalender, ECR-2003
NOW 256 slices
MSCT
66
3D Isotropic Resolution in Spiral CT3D Isotropic Resolution in Spiral CTx/y-plane
0.1 mm0.2 mm0.3 mm
0.4 mm 0.5 mm 0.6 mm 0.7 mm
x
y
z-direction (MPR)
0.1 mm0.2 mm0.3 mm
0.4 mm 0.5 mm 0.6 mm 0.7 mm
z
y
1.1 mm 1.0 mm 0.9 mm 0.8 mm
1.2 mm 1.3 mm 1.4 mm 1.5 mm
y
1.1 mm 1.0 mm 0.9 mm 0.8 mm
1.2 mm 1.3 mm 1.4 mm 1.5 mm
Scans in UHR mode with 2 Scans in UHR mode with 2 ×××××××× 0.5 mm collimation, 0.5 mm collimation, Seff = 0.5 mm
y
Fuchs T, Krause J, Kalender WA. Physica Medica 2001; 17(3):129Fuchs T, Krause J, Kalender WA. Physica Medica 2001; 17(3):129--134134
68
Tube
Area detector CT – the future of CT
aSi Detector
C-Arm CT Flat Panel Detector CT
Cone beam CT
COMPUTED TOMOGRAPHY
69
COMPUTED TOMOGRAPHY ( MicroCT)
MicroMicro ComputedComputed TomographyTomography
((MicroMicro--CT, µCT)CT, µCT)
There is no unique definition for µCT!
Most used, but arbitrary�
Spatial resolution of better than 100 µm
� Rotating gantry or rotating object
70
� Rotating gantry or rotating object
� Circular or spiral data acquisition
� Fan- and cone-beam data acquisition
� X-ray tube or synchrotron radiation
� Developed medical
[and for industrial] applications
Micro Computed TomographyMicro Computed Tomography
(Micro(Micro--CT, µCT)CT, µCT)
Technical details and constraints
� As expensive as “economy class” CT used in clinical scanning
71
used in clinical scanning
� Small fields of measurement (typically. 5-50 mm)
� Very low power x-ray sources (typically 5-50 W)
� Long scan times (typically 5-30 minutes)
Medical Applications of MicroMedical Applications of Micro--CTCT
Organ / Disease
� Bone
� Teeth
72
Sample / Animal• Biopsies • Excised materials
� Teeth
� Vessels
� Cancer
• Excised materials • Small animals
(rats / mice)���� in vivo
ex-vivoin vitro
CCD Micro-tomographer
X-ray source ................ 20-100kV,10W, <5µm spot size or 20-80kV, 8W, <8µm spot size
X-ray detector ............. 10Mp or 1.3Mp cooled CCD fiber-optically coupled to scintillator
Detail detectability ...... <1µm with 10Megapixel camera, <2µm with 1.3 Megapixel camera
Maximum object size... 68mm in diameter with 10 Mp camera, 37mm - with 1.3Mp camera 1.3Mp camera
Reconstruction ............ single PC or cluster volumetric reconstruction (Feldkamp algorithm)
http://www.skyscan.be/products/1172.htm
3D Images
Object: mouseScanner: SkyScan1076 Image: full body mouse scan using
contrast agent, 35um isotropic voxel size35um isotropic voxel size
Object: mouse lung sampleScanner: SkyScan1172/100kV/10Mpusing contrast agent + CTan processing softwareImage: pseudo3D visualization (MIP) of lungs vascular structure, 5.7um pixel size
Benchtop Micro-CT75
cone beam
x-ray tube CCD detectorsample
axis of
high voltage
Benchtop MicroBenchtop Micro--CTCT76
Trabecular Structure
� 3D morphology� thickness
� separation
� structure model index
� anisotropy
77
30 years30 years30 years30 years� anisotropy
� Euler number
(ETH Zürich, Aarhus)
� 3D density(ESRF, Grenoble)
30 years30 years30 years30 years
70 years70 years70 years70 years
Courtesy of W. Kalender, ECR-2003
High-Resolution Micro-CT78
0.6
0.8
1.0
0 20 40 60 80 100
0.6
0.8
1.0
System MTF of transaxial slice
MTF
5 µm resolution @ 2 % MTF
0 20 40 60 80 1000.0
0.2
0.4
0.0
0.2
0.4
MTF
LP/mm10 µm tungsten wire7 µm voxel size
Courtesy of W. Kalender, ECR-2003
CMOS Flat Panels
� CMOS Monolithic Active Pixel Sensors (MAPS), developed for visible light imaging in visible light imaging in early ’90s, look very promising for application in medical imaging
G.Rizzo – IWORID-8 – Pisa, July 2-6 2006
79
Principle of Operation80
Signal generated by a particle is collected by a diode (n-well/p-epitaxial layer), then readout by CMOS electronics integrated in the same substrate… BUT :
Charge generated by the incident particle moves by thermal diffusion in the thin (~ 10 µm) p-
P-epitaxial layer ~ 10 mm
G.Rizzo – IWORID-8 – Pisa, July 2-6 2006
thermal diffusion in the thin (~ 10 µm) p-epitaxial layer
P-epi layer doping ~1015 cm-3
� not depleted
� carrier lifetime O(10 ms), small diffusion distance
P++ substrate gives a small contribution to the collected charge (very low carrier lifetime)
Typical collection time: ≤ 100 ns for small diode, faster with larger diodes.
Charge-to-voltage conversion provided by sensor capacitance -> small collecting electrode
(Monolithic active pixel sensor)MAPS CMOS Detector (detector and readout incorporated in the same layer)
• no bias voltages• charge diffusion• 100% fill factor
- charged particles
Epilayer
7/20/2009 LMB, CambridgeTurchetta et alNIM A458 (2001) 677-689
Substrate
CMOS: Single Pixel Readout
T1,T2, T3 are all transistors
7/20/2009 LMB, Cambridge
Comparison of CCD and CMOS Readout
7/20/2009 LMB, Cambridge
Single (or few) node readout, slower
Charge shifted along columns/row
Parallel readout, fasterCharge converted to voltage In pixel
Commercial CMOS Flat Panels
A small animal CT prototype:FasTac (Pisa)
85
X-ray source
• Fixed tungsten anode• Maximum voltage: 60 kV• Maximum power: 10 W• Measured focus size: 7 µm FWHM• Beam aperture: 32°
X-ray detector
• 1024 x 2048 pixels (48 µm each)• 5 cm x 10 cm active area• Maximum frame rate 2.7 fps• 10lp/mm resolution
MEDIPIX286
� 0.25 um IBM technology 33M transistors
� 256x256 pixels, 55 x 55 µm2 (65536 pixel/chip)
� Positive and negative input signals
� Preamplifier equipped with leakage current compensation circuit at pixel level
Max count rate/pixel: 1 MHz� Max count rate/pixel: 1 MHz
� Two leading edge discriminators, threshold adjustable at pixel level (3 bits resolution)
� “energy window” logic
� 13 bits Counter / shift register
� Read-out
� Serial: 100 MHz 9 ms/frame LVDS drivers, Fast Shift Register
� Parallel: 100 MHz 266 µs/frame bus 32 bit
� Dead area 55 µm on three sides
MPX2 designed by M. Campbell and X. Llopart (2000) of the microelectronics group CERN, in the framework of the international collaboration MEDIPIX2
http://medipix.web.cern.ch/MEDIPIX/
14111 µµm
16120
87
16120 µµm
MPX2 Bone studies on small animals
Transaxial Sagittal
1 mm
Panetta, D.: 8th International Workshop on Radiation Imaging Detectors – July 2-6 2006, Pisa – ITALY
Coronal
60 µµµµm
Conclusions
� Radiological Imaging � Morphological Imaging but not only !!
� CT is still a hot topic!
89
� CT is still a hot topic!
� There is Room for improvement :
� � Dose Reduction at the same image quality
� Better Image quality at the same dose
SINGLE PHOTON COUNTING � the FUTURE
THE END
90
THE END
Abstract #1
The development of radiation detectors in the field of nuclear and particle physics hashad a terrific impact in medical imaging since this latter discipline took off in late ’70with the invention of the CT scanners. The massive use in High Energy Physics of positionsensitive gas detectors, of high Z and high density scintillators coupled to Photomultiplier(PMT) and Position Sensitive Photomultipliers (PSPMT), and of solid state detectors hastriggered during the last 30 years a series of novel applications in Medical Imagingwith ionizing radiation. The accelerated scientific progression in genetics and molecular
91
with ionizing radiation. The accelerated scientific progression in genetics and molecular
biology has finally generated what it is now called Molecular Imaging. This field
of research presents additional challenges not only in the technology of radiationdetector, but more and more in the ASIC electronics, fast digital readout and parallel
software. In this series of three lectures I will try to present how High Energy
Physics and Medical Imaging development have both benefited by the cross-
fertilization of research activities between the two fields and how much they will takeadvantage in the future.
Abstract #2
With particular evidence to Medical Imaging I will address and discuss:
1 - The use of gas, scintillator and solid state detectors in digital radiology and digital mammography, clinical CT and small animal CT.
2 - The use of scintillators and PMT/PSPMTs in functional imaging and in particular:
92
2 - The use of scintillators and PMT/PSPMTs in functional imaging and in particular:
- For Molecular Imaging with PET and SPECT (clinical and preclinical);
- For Breast Cancer Imaging (PEM and SPEM, PEMT and SPEMT);
- For on line PET dosimetry in hadrontherapy .
3 - The impact of the novel solid state photomultipliers in Medical Imaging and the advent of multimodality imaging such as PET/CT and SPECT/CT, PET/MRI and SPECT/MRI.
Detector and Front-End� The Si Detector
� 256 to 1024 strips
� Strip length 2 cm
� 100 or 50 µm strip pitch
� Detector thickness: 300 µm
� Dead entrance window ~200 - 400 µm
� Detection efficiency: 80% (20 keV)
� The Mythen-II ASIC
� Evolution of the Mythen-I
� 0.25 µm UMC technology
� Upgrades:
� 24 bit counter
� re-design of the digital part
� 6-bit threshold trim DAC for each channel
� with proper optimization usable up to 3 MHz (work in progress)
93
MHz (work in progress)
94
ConeCone--beambeamSpiral CTSpiral CT(CSCT)(CSCT)
here:here:MM = 16= 16
• 0.5 s rotation• 0.5 s rotation• 16××××0.75 mm• 70 cm in 28 s• 1.4 GB rawdata• 1400 images
Whole body rat imaging95
Vessels� in vitro scans
� casting of vessels with Microfil (compound with lead chromate)
� applications
96
BrainBrain
KidneyKidneyapplications � heart
� kidney
� liver
� lung
MPRMPR MIPMIP Vol RendVol RendHoldsworth et al.: Trends Biotech. 2002 Holdsworth et al.: Trends Biotech. 2002 Wan et al: Comp Biol Med. 2002Wan et al: Comp Biol Med. 2002Ortey et al: Kidney Int. 2000Ortey et al: Kidney Int. 2000
KidneyKidney
TumorTumorHeartHeart
Muscle and Fat97
rat heart musclerat heart muscleorientation of fibersorientation of fibersJorgensen et al.: Jorgensen et al.: Am J Physiol 1998Am J Physiol 1998
Mouse in vivo scansMouse in vivo scansfat content and distribution changesfat content and distribution changesHildebrandt et al.: Hildebrandt et al.: J Pharmacol Toxicol Meth 2002J Pharmacol Toxicol Meth 2002
Cancer Research
Monitoring of Lung cancer growthby micro-CT
Resolution 150 µm
98DayDay
00
1010
tumor cell tumor cell injectioninjection
treatm. treatm. startstart
Resolution 150 µm
Scan time 5-7 min
here: no change intumor size
Kennel et al.: Med Phys. 2000
1212
1414
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