Clinical Use of Photon Counting Detectors in CT
Medical Photon Counting in Israel
D spect
NM
CT
Module manufacturer
Swift
Jerry Arenson- Haifa CT Eng Mgr
Reuven Levinson
CT Engineering
GE Healthcare
Haifa, Israel
Shaike Maoz
Baruch Rosner
Lev Greenberg
Jenia Kuksin
( !
Zimam Romman
Daniel Rubin
"#
Galit Naveh
Shalom Rosenberg
!
) *'+,
Ofer Benjaminov
Dept. of Diagnostic Imaging
Rabin Medical Center
Tel Aviv, Israel
$% &'
Technology Paths to Dual-Energy CT Acquisition
80 kVp
Goals of Spectral CT
Simultaneous Collection of Energy Information
# X-rays
2 Tubes + 2 Detectors
Tube Spectra
140 kVp
140
SIEMENS
80
Dual-Source
# X-rays
1 Tube + 1 Detector
Tube Spectra 140 kVp
• Boost in resolution and dose
efficiency
80
Fast Switching
# X-rays
Detector Absorption
1
2
PHILIPS
Energy
L
L
H
# X-rays
Detector Energy Bins
Low
light
charge)
Spectral CT Detector
charge)
(X-ray
Incident X-ray
Photon
Scintillator
Incident X-ray
Photon
bias
Semiconductor
Light
photons
electron-hole
pairs
− digital counting of individual
x-ray photons
Dual-Layer
Energy Discriminating Detector
− smaller pixels with minimal loss in
‘dead-space’
• Eliminate electronic noise floor
Energy
1 2
(X-ray
− outdates detector slicing technology
140
80 kVp
Standard CT Detector
• Intrinsic simplicity
Energy
Dual-Layer Detector
Alcyone
Ventri
MBI
• Gateway to ultimate MD tissue
characterization
− maximize energy separation
− simultaneous collection for precise
temporal registration
Photodiode
electron-hole
pairs
Charge
Integrating DAS
Charge Pulse
Counting
DAS
High
Energy
Photon
Counting
/
GE /
Spectral CT:
Pulse Counting Electronics
direct conversion sensor
common
cathode
discriminators
pixilated
anode
current
compensation
• Incoming photon pulses stripped
off flowing detector current
• Pulse heights proportional to
keV
• Threshold discriminators trigger
high or low digital counters
pulse counters
Digital
output
shaper / filter
X-ray
photon
Optimum Imaging
Performance
D/A
-
Digital
output
preamplifier
D/A
“energy” thresholds
voltage
current
voltage
voltage
HV
dark/bias
current
CT Detector Challenges
photo-current
X-ray on
Photon pulses ‘riding’
on photo-current and
bias current
time
‘zero’ electronic noise floor
Precise energy separation
Simultaneous energy acquisition
Fully adjustable energy bins
Supports multiple (>2) energy
acquisition
•
•
•
•
•
threshold
level
test input
+
Clean Digital Signal
Processing
X-ray on
time
Photon pulses following
base-line restoration
X-ray on
time
X-ray on
time
• Count rates >100 Mcps/mm2
• Demanding stability
requirements
Narrow bi-polar pulses Digital pulses trigger counter
Photon-Counting CT system:
detector imaging parameters
Optimal Spectral CT Performance:
Paths to High-Flux X-ray Photon Counting
• Smaller pixels
• Today’s high-power scanners deliver
>100 Mcps/mm2 count rates at the detector
CT
Pixel size
Sub-pixelization
1mm
4x 0.5mm
• Faster photon-counting DAS
1x1 mm2
Multi-slice Geometry
2D (1000x32)
Flux rate (cps/mm2)
105-108
Counts/view (1 msec)
102-105
No. of bins
• Future systems expected to double this
requirement
20nsec shaper
Channel still hasn’t
reached saturation at
50 Mcps
• Hybrid Counting/Integrating
NO = 5
Mcps
Non-paralyzable detector
response and linearization
calibration ameliorate
pile-up issues
2
Linear Integration
High Flux Readout
Low-Energy Bin
Photon Counting
High-Energy Bin
NO = 3.5 Mcps
• Layered Photon-Counting
Low-Energy Bin
NO is when
OCR=ICR/2
High-Energy Bin
/
GE /
Swift Spectral CT Main Components
• 100% simultaneous dual-energy acquisition
• High-resolution direct-conversion detector
array
• Ultra-dose-efficient photon-counting detection
• GPU-based recon and display system
First Swift Phantom Scan (May 10, 2006)
A very happy hour
Wood
Swift: The World’s First EDCT Scanner
Swift 32-slice Spectral CT system
Aculon
Recon and Display
console
Teflon
Iodine
Air
Aluminum
bowtie
Pixilated
detector array
& ASICs
Plug&Play
all-digital
DAS
15 cm FOV
15 cm FOV
Water
VCT-64 gantry
GPU
technology
First Swift Patient Scanning (May 2007)
Axial
Curved
AVA
V. Endoscopy
New images in dual energy CT
2D MIP
Images
Conventional CT (HU)
Dual Energy
VR & Bone LM
VR With Hard Plaque Removal
3D MIP
Radial MIP
monoE (mono-energetic equivalent (HU))
VNC (material density image (mg/cc))
Iodine (material density image (mg/cc))
Scan parameters: Helical, 32x0.625 mm, 140 kVp, 14 mA (eff), 1-sec rotation, pitch=0.5
/
GE /
Theory (dual energy)
Proc, Recon and Images in dual Energy
Attenuation basis functions
•Basis processes: Photo-electric (w/o K-edge) & Compton Scatter
Image Space Recon
Non- linear processing
µT(E 1)= µPE(E1)+ µComp(E1)
µT(E 2)= µPE(E2)+ µComp(E2)
CT IMG
(E1)
FBP
Prep data (E1)
Raw data (E1)
•Basis Materials: Al, Delrin
µAl(E)= xPEµPE(E)+ xComp µComp(E)
Prep data (E2)
Raw data (E2)
µDelrin(E)= yPE µPE(E)+ yComp µComp(E)
Material Decomposition
2 basis function => 2 unknowns (amount of each component) => 2 measurements @
2 different energies
m
Bea
har
Projection Space Recon
Raw data (E1)
I2= exp(- L Al µ Al(E2)-LDel µDel(E2)
2-Material Basis
Decomposition
CT IMG
(E2)
FBP
FBP
Material density image A
FBP
Material density image B
Linear
combinations
Raw data (E2)
Inversion
Material density
images
ing
d en
Prep data (E1, E2)
I1= exp(-LAl µ Al (E1)-LDel µDel(E1)
(I1, I2)= G(LAl, LDel)
Linear
combinations
MonoE
(LAl, LDel )=G-1(I1, I2)
Aluminum image
Aculon image
Source/Detector: influence on dose efficiency
2M-PPU Cal
Factor
Phantom scan
Al prep
Ac prep
Aculon (Acetal) ~50 HU
Iodine [mg/ml]
Calcium (CaCl2) [mg/ml]
H2O
Al image
Ac image
I
10
14cm diam.
H2O
BH-free B&W image
I
15
I
20
I
20
I
30
Phantom
legend
Air
Ca
80
I
10
Ca
160
H2O
Ca
80
Ca
240
I
30
H2O
Ca
320
B&W monoenergy image
Status (vs Conventional CT)
Function form
Detector DQE
Same; except low flux performance
required for low energy beam
Empirical detector data
Bin energy separation
NEW: does not exist in single energy
EL, EH
Bin flux ratios
NEW: does not exist in single energy
f L, f H
Conventional CT
σ 2= (1 / N ) DQE
Dual Energy
σ 2g
σ 2g
A
B
Tkaczyk et al, SPIE 2009 (7258-15)
µ 2 B ( EH ) µ 2 B ( E L )
1/ N
=
(µ A ( EL )µ B ( EH ) − µ A ( EH )µ B ( EL ))2 µ 2 A ( EH ) µ 2 A ( E L )
Bin energy
separation
f -1(L)
f -1(H)
DQE
Bin flux ratios
/
GE /
Energy separation/bin flux ratio
Variance vs flux (photon-counting vs energy integrating)
Energy Integrating
Photon Counting
Pile-up
Electronic
noise
Carotid Arteriography
Mono-energetic Images
Mono60
Mono75
Mono100
/
GE /
Virtual Non-contrast Imaging
Virtual Non-contrast Imaging
Now you see it.
Now you don’t
Swift Clinical Studies:
Swift Clinical Studies:
VNC Performance
Abdominal Imaging
Energy Integrating
TUE-MCI
Delay-MCI
Delay-VUE
Spectral CT
Virtual
Unenhanced
processing
removes iodine
while
preserving
calcium.
Photon Counting
15 min delay
from contrast
injection images
displayed with
and w/o iodine.
Excreted
Contrast
Medium
No need for
pre-contrast
study.
Pre-contrast images
Calcified Structure Vs. Excreted Contrast
Medium
Calcified
Structure
/
GE /
Swift Clinical Studies:
Full FOV Abdominal Imaging
Mono 82KeV +
C
World’s 1st
Spectral CT
abdominal study
Z-map*
images
MCI-70 keV
*Color-mapping according to tissue
atomic number
Mono 82KeV +
C
Mono 82KeV + C
/
GE /
Mono 82KeV + C
VNC (+C)
VNC – True Unh
VNC Performance
AI: Can VNC (+C) replace conventional (-C)?
VCT -C
VNC -C
Iodine
VNC (+C)
Mono 82KeV + C
VNC +C
VNC +C
Lesion
Fat
Muscle
VNC -C
21
-87
58
VNC +C
19
-85
54
-4
31 /
GE /
-2
32 /
GE /
/
GE /
Adrenal Lesion
Conventional CT vs Dual Energy CT
(µ vs material density)
VCT (-C)
MCI (-C)
VNC (-C)
VNC (+C)
MCI (+C)
Subject 1 (Rt. Adrenal Les ion)
22
23
20
18
25
23
Subject 2 (Lt. Upper Lesion)
-2
-2
2
1
35
Delayed MCI
N/A
Subject 2 (Lt. Lower Lesion)
30
22
20
19
60
N/A
Subject 2 (Rt Upper Les ion)
-12
-15
-14
-14
31
N/A
Subject 3 (Rt. Adrenal Les ion)
3
-5
4
5
40
19
Subject 7 (Lt. Adrenal Les ion)
3
5
7
5
57
5
Subject 8 (Rt. Adrenal Les ion)
-2
5
2
-5
45
14
Subject 8 (Lt. Adrenal Les ion)
-3
-10
1
8
30
0
Average
5
3
5
5
40
12
Complete specificity: k-edge CT
Liver
Spleen
Aorta
Muscle
Retro. Fat
Gall Bladder
Portal vein
conv CT-C
VNC -C
51.1
55.0
42.2
49.2
34.2
45.4
34.0
48.6
-101.0
-83.6
17.0
19.4
37.2
36.1
(Gd contrast)
Partial Spec.
No Specificity
Single
Dual (Photo-Electric)
Gd contrast
Soft tissue
calcium
Soft tissue
No Gd contrast
calcium
Complete
Spec.
Partial Spec.
Gd Contrast only
Soft tissue
calcium
No Gd contrast
Dual
(Compton)
Triple (kedge)
Overlayed Gd contrast
w/ Single Energy image
/
GE /
Complete specificity – PET /CT
Summary
• Results on clinical trials show equivalent image
quality for single energy scanning and potential for
low-dose scanning
• PC delivers a single-tube, single-detector
configuration for high-quality dual energy CT
imaging
• PC provides a path for future k-edge imaging
' Great are the lights God created
Pleasant is their radiance in all the world
CT
PET
PET/CT
-
.
0
Thank you for your attention
/
GE /