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8/1/2018
1
Multi-energy CT using photon counting detectors
Katsuyuki “Ken” Taguchi
Russell H. Morgan Department of Radiology and Radiological Science
Johns Hopkins University School of Medicine
(Baltimore, MD)
AAPM 2018. K Taguchi (JHU)
Disclosure
■ No financial interest
■ Research grants and relationships– Siemens Healthineers JHU-2016-CT-1-01-Taguchi_C0022
– NIH R56 HL125680
– Previous: DxRay (NIH SBIRs), Philips (C-arm), Toshiba/Cannon (employee)
■ Former consultantship– Suzhou Bowing Medical Technologies, Life Saving Imaging Technology (LISIT),
JOB Corporation
2AAPM 2018. K Taguchi (JHU)
Outline
3AAPM 2018. K Taguchi (JHU)
Design types Groups Prototype CT (beta site installation)
“Standard” Siemens, Philips, GE, … Siemens (2014), Philips (2015), GE (2007)
“Anti-charge sharing” CERN (and MARS) MARS (–2018)
“Edge-on silicon” KTH Royal Institute of Tech (Sweden) KTH RIT (–2018)
■ Photon counting detectors (PCDs) and properties
■ Algorithms (data correction and image reconstruction)
■ System designs
■ Clinical applications
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Outline
4AAPM 2018. K Taguchi (JHU)
Design types Groups Prototype CT (beta site installation)
“Standard” Siemens, Philips, GE, … Siemens (2014), Philips (2015), GE (2007)
“Anti-charge sharing” CERN (and MARS) MARS (–2018)
“Edge-on silicon” KTH Royal Institute of Tech (Sweden) KTH RIT (–2018)
■ Photon counting detectors (PCDs) and properties
■ Algorithms (data correction and image reconstruction)
■ System designs
■ Clinical applications
Clinical applications
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There is no “killer application”
“What is the killer application?”
New generation CT has been developed for
6AAPM 2018. K Taguchi (JHU)
■ improving everything CT does (whole body)
■ adding new dimension to everything CT does
■ enabling new applications
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New generation CT has been developed for
7AAPM 2018. K Taguchi (JHU)
■ Improving everything CT does (whole body)
■ Adding new dimension to everything CT does
■ Enabling new applications
In 1998, MDCT with 4 detector rows
10 mm slice → 2–3 mm slice (→ 0.5 mm)Shorter scan duration, larger coverage, better resolution
2D slice-by-slice view → 3D view (coronal, sagittal, MIP, 3D)
Cardiac CT (coronary artery)
New generation CT has been developed for
8AAPM 2018. K Taguchi (JHU)
■ Improving everything CT does (whole body)
■ Adding new dimension (material info) to everything CT does
■ Enabling new applications
In 202x, PCD-CT with 3–6 energy windows
Contrast, contrast-to-noise, radiation dose, contrast dose,spatial reso, accuracy, quantitative values, CT radiomics
Simultaneous image-and-measure (IAM-XX), CT tissue biomarkers
Simultaneous multi-agent, molecular CT, personalized CT
Spatial resolution
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J. Baek, PMB 2013
Binned system High reso system
Binned detector High reso detector
Low reso detector High reso detector
MTF
NPS
MTF
NPS
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Spatial resolution
10A. Pourmorteza, Inv Rad 2018
Eff. (500 µm)2 Eff. (250 µm)2 Eff. (500 µm)2 Eff. (250 µm)2
Molecular CT
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Bi
D. Pan, Angew Chem Int Ed 2010
Simultaneous multi-agent imaging
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Gd → (10 min) → Iodine → PCD-CT scan
R. Symons, Int J Cardiovasc Imag 2017
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Simultaneous multi-agent imaging
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Gd → (10 min) → Iodine → PCD-CT scan
R. Symons, Int J Cardiovasc Imag 2017
Material-specific imaging for better diagnosis
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DWI
K. Taguchi, Inv Rad 2018
a b c
Normal
Edema
CT “X-map”
Acute ischemic stroke delineated clearly by water density images (for edema)
Dual-energy CT (Force). 68 yo, female, 40 min after symptom onset.
New generation CT has been developed for
15AAPM 2018. K Taguchi (JHU)
■ improving everything CT does (whole body)
■ adding new dimension (material info) to everything CT does
■ enabling new applications
In 202x, PCD-CT with 3–6 energy windows
Contrast, contrast-to-noise, radiation dose, contrast dose,spatial reso, accuracy, quantitative values, CT radiomics
Simultaneous image-and-measure (IAM-XX), CT tissue biomarkers
Simultaneous multi-agent, molecular CT, personalized CT
8/1/2018
6
Outline
16AAPM 2018. K Taguchi (JHU)
Design types Groups Prototype CT (beta site installation)
“Standard” Siemens, Philips, GE, … Siemens (2014), Philips (2015), GE (2007)
“Anti-charge sharing” CERN (and MARS) MARS (–2018)
“Edge-on silicon” KTH Royal Institute of Tech (Sweden) KTH RIT (–2018)
■ Photon counting detectors (PCDs) and properties
■ Algorithms (data correction and image reconstruction)
■ System designs
■ Clinical applications
PCDs (“Standard,” “ACS,” and “Edge-on Si”)
17AAPM 2018. K Taguchi (JHU) Table I of K Taguchi and J Iwanczyk, Med Phys, Vision 20/20 (2013)
PCD (“Standard” type)
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Incident x-ray
Convert a photon to
a charge cloud
Charge measured, counted,
and stored digitally
--
--
Amplifier
Counting
processing
Sensor (CdTe, CZT)
AAPM 2018. K Taguchi (JHU)
Courtesy of W. C. Barber
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AAPM 2018. K Taguchi (JHU)
PCD (“Standard” type)
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Shaper
Preamp
Counter2Digital output
Input
analog
pulses
Thresholds to pulse height comparators
DAC
Comparators
Counter1Digital outputDAC
CounterNDigital outputDAC
… …
w1 = n1 – n2
w2 = n2 – n3
w3 = n3
Time
n2
n1Threshold #1
Threshold #2
Threshold #3 n3Energy
PCD not flawless: Spectral distortion
■ Independent of x-ray intensities: Charge sharing, K-escape, Re-absorption, Compton scattering
■ Dependent on x-ray intensities: Pulse pileups
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Anode
Sensor
Charge sharing
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A 90 keV photon
time
60 keV
time
30 keV“Charge sharing”
AAPM 2018. K Taguchi (JHU)
Incident x-ray photons
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Anode
Sensor
Incident x-ray photons
Fluorescence x-ray emission (K-escape)
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A 90 keV photon
time
67 keV
time
23 keV
“K-escape”
Anode
Sensor
Re-absorption of fluorescence x-rays
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A 90 keV photon
time
67 keV23 keV
67 keV
23 keV
time
70 keV
Re-absorption of K-escape x-ray
Slower PCD
Faster PCD
Incident x-ray photons
Anode
Sensor
Compton scattering
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A 90 keV photon
time
50 keV30 keV
time
60 keV
“Compton scattering”
Slower PCD
Faster PCD50 keV
30 keV
10 keV
10 keV
Incident x-ray photons
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AAPM 2018. K Taguchi (JHU)
Spectral distortion
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Continuum:- Charge trapping- K-escape- Charge sharing- Compton scatter
0 20 40 60 80 100
Energy [keV]
Co
un
ts
Response to 59.5 keV photons (Am-241 source)
Photo peak
Noise floor
20 40 60 80 100
Energy [keV]120
Pro
bab
ility
[a.
u.]
Incident spectrum
Recorded spectrum
Anode
Sensor
Incident x-ray photons
Pulse pileups (count rate dependent)
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Time
Events on detector
Live
Dead
True pulses
Observed pulses
True
Recorded
Input count rate [Mcps]
Outp
ut count
rate
[M
cps]
10 20 30 40 500
10
Paralyzable detector
( =20 ns)
Non-paralyzable detector
( =20 ns)
True20
30
Count rate loss
Time
Pulse height (photon energy)
Pulse pileup spectrum
Energy [keV]
Pro
babili
ty
𝜏
PCD not flawless: Spectral distortion
■ Charge sharing, K-escape, etc.AlwaysLower energy, more countsSolution: Larger, slower PCD
■ Pulse pileupsOnly near skinsHigher energy, fewer countsSolution: Smaller, faster PCD
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200 400 600 800 1000 1200 1400 1600 1800
500
1000
1500
2000
25000
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2x 10
7
Φ16 cm
Detector channels (fan angles)
Pro
ject
ion
s (v
iew
an
gles
) 20
10
0
Count rates [Mcps]Heart
Synthesized from PCD
Measured by GOS-25 -20 -15 -10 -5 0 5 10 15 20 250
1
2
3
4
5
6
7
8
Lin
e in
tegr
als
Radial distance [cm]0 10-10
PCDs
Synthesized
Measured
Difference
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Spectral distortion: How to mitigate it?
■ Balanced design + PCD model + compensation algorithm
28AAPM 2018. K Taguchi (JHU)
X-ray focus
PCD
Ray
PCD pixels
Energy, E
nt(E)
nR(E)
Energy, E
Energy, E
n0(E)
Object, x(E)nt(E)
Bowtie filters
y={y1, y2, y3, y4}
Observed spectrum
Recorded counts
x={x1, x2, x3, x4}
Reconstruct images
Spectral distortion: How to mitigate it?
■ Balanced design + PCD model + compensation algorithm
29AAPM 2018. K Taguchi (JHU)
X-ray focus
PCD
Ray
PCD pixels
Energy, E
nt(E)
nR(E)
Energy, E
Energy, E
n0(E)
Object, x(E)nt(E)
Bowtie filters
y={y1, y2, y3, y4}
Observed spectrum
Recorded counts
x={x1, x2, x3, x4}
Reconstruct images
𝑥 𝐸 =
𝑚
𝑤𝑚Ψ𝑚 𝐸
x2
[cm-1]
Photon energy [keV]
Photoelectric
K-edge(Iodine)
Compton Scattering
Spectral distortion: How to mitigate it?
■ Balanced design + PCD model + compensation algorithm
30AAPM 2018. K Taguchi (JHU)
X-ray focus
PCD
Ray
PCD pixels
Energy, E
nt(E)
nR(E)
Energy, E
Energy, E
n0(E)
nt(E)Bowtie filters
y={y1, y2, y3, y4}
Observed spectrum
Recorded counts
Line integrals,Wj
𝑝 ො𝑦 𝑊
Estimate object W by maximizing the likelihood
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Spectral distortion: How to mitigate it?
■ Balanced design + PCD model + compensation algorithm
31AAPM 2018. K Taguchi (JHU)
(a) Truth (b) Without pulse pileup model (c) With pulse pileup model
WW 400 HU, WL 50 HU
Taguchi K, et al, IEEE MIC 2013
Outline
32AAPM 2018. K Taguchi (JHU)
Design types Groups Prototype CT (beta site installation)
“Standard” Siemens, Philips, GE, … Siemens (2014), Philips (2015), GE (2007)
“Anti-charge sharing” CERN (and MARS) MARS (–2018)
“Edge-on silicon” KTH Royal Institute of Tech (Sweden) KTH RIT (–2018)
■ Photon counting detectors (PCDs) and properties
■ Algorithms (data correction and image reconstruction)
■ System designs
■ Clinical applications
Spectral distortion: How to mitigate it?
■ Anti-charge sharing circuit (“CSM” in Medipix 3RX)
33AAPM 2018. K Taguchi (JHU) Courtesy of M. Campbell
55
The winner takes all CSMNon CSM
Spectrum
Th. Koenig, et al., IEEE TNS (2013).
8/1/2018
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Outline
34AAPM 2018. K Taguchi (JHU)
Design types Groups Prototype CT (beta site installation)
“Standard” Siemens, Philips, GE, … Siemens (2014), Philips (2015), GE (2007)
“Anti-charge sharing” CERN (and MARS) MARS (–2018)
“Edge-on silicon” KTH Royal Institute of Tech (Sweden) KTH RIT (–2018)
■ Photon counting detectors (PCDs) and properties
■ Algorithms (data correction and image reconstruction)
■ System designs
■ Clinical applications
Prototype PCD-CT systems
35AAPM 2018. K Taguchi (JHU)
Design types Groups Prototype CT (beta site installation)
“Standard” Siemens, Philips, GE, … Siemens (2014), Philips (2015), GE (2007)
“Anti-charge sharing” CERN (and MARS) MARS (–2018)
“Edge-on silicon” KTH Royal Institute of Tech (Sweden) KTH RIT (–2018)
■ Siemens (Mayo Clinic and NIH)
– Dual-source CT, PCD for 27.5 cm x 8–24 mm, EID for 50 cm
– (225 µm)2, 2 thresholds (staggered 4 thresholds), (450–900 µm)2 output
– 128x106 counts/s/mm2 with 13.5% loss, 256x106 with 25.2% loss
■ Philips (Louis Pradel University Hospital, Bron, France)
– Brilliance 64 CT, 16.8 cm x 2.5 mm
– (500 µm)2, 5 thresholds (*1)
– >150x106 counts/s/mm2 (*1)
1. R. Steadman, et al., Nucl Inst Meth Phys Res A (2017)
Prototype PCD-CT systems
36AAPM 2018. K Taguchi (JHU)
Design types Groups Prototype CT (beta site installation)
“Standard” Siemens, Philips, GE, … Siemens (2014), Philips (2015), GE (2007)
“Anti-charge sharing” CERN (and MARS) MARS (–2018)
“Edge-on silicon” KTH Royal Institute of Tech (Sweden) KTH RIT (–2018)
■ University of Canterbury, Christchurch, NZ (on site)
– Their own open gantry CT, PCD for ? cm x ? mm
– (110 µm)2, 8 thresholds, anti-charge sharing mode (Medipix3RX by CERN)
– 10–20x106 counts/s/mm2 with ?% loss
■ KTH Royal Inst of Tech, Stockholm, Sweden (on site)
– Philips CT(?), ? cm x ? mm
– (400 µm)x(500 µm), 8 thresholds/layer x 16 layers/pixel (KTH silicon strip det)
– 200x106 counts/s/mm2 with 2% loss, 600x106 with 25% loss
New York Times, July 17, 2018.https://www.nytimes.com/2018/07/17/health/3d-color-xrays-cern.html
8/1/2018
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Prototype PCD-CT systems
37AAPM 2018. K Taguchi (JHU)
Design types Groups Prototype CT (beta site installation)
“Standard” Siemens, Philips, GE, … Siemens (2014), Philips (2015), GE (2007)
“Anti-charge sharing” CERN (and MARS) MARS (–2018)
“Edge-on silicon” KTH Royal Institute of Tech (Sweden) KTH RIT (–2018)
■ University of Canterbury, Christchurch, NZ (on site)
– Their own open gantry CT, PCD for ? cm x ? mm
– (110 µm)2, 8 thresholds, anti-charge sharing mode (Medipix3RX by CERN)
– 10–20x106 counts/s/mm2 with ?% loss
■ KTH Royal Inst of Tech, Stockholm, Sweden (on site)
– Philips CT(?), ? cm x ? mm
– (400 µm)x(500 µm), 8 thresholds/layer x 16 layers/pixel (KTH silicon strip det)
– 200x106 counts/s/mm2 with 2% loss, 600x106 with 25% loss
H. Bornefalk, Nucl Inst Meth Phys Res A (2010)
Photon Counting Toolkit (PcTK, pctk.jhu.edu)
38
• “Spectral response” model of photon counting detectors
• Medical Physics 2018;45(5):1985–1998
• Matlab programs
• Available for academic research, free of charge
• Download and send the application
Probabilities
0.00
0.10
0.05
(a)Ver.3.2 E1=60keV
E1=90keV
E1=120keV
Recordedenergy,E3 (keV)0 6040 10080 14012020
(b)aBN
(d)vST (e)vBN
(f)m1 (g)m2 (h)m3 (i)m4
(j)fR,1 (k)fR,2 (l)fR,3 (m)fR,4
(n)ft,1 (o)ft,2 (p)ft,3 (q)ft,4
(a)aST aST=0.97 aST=1.00(c)
FPJ FPJ
Randomnumbergenerator
FBP FBP FBP FBP
Otherdata(Sec.2.C)(A)Init. x-rayspectrum(B)Initial#ofphotons(D)µk(E)of materialk(E)nCov3x3w byPcTK
(C)Material-specificsinograms
Material-specificimages
(j)fR,1
(n)f t ,1
Synthesized from the input images (a–b)
Reconstructed from noisy PCD data
Summary
39AAPM 2018. K Taguchi (JHU)
Design types Groups Prototype CT (beta site installation)
“Standard” Siemens, Philips, GE, … Siemens (2014), Philips (2015), GE (2007)
“Anti-charge sharing” CERN (and MARS) MARS (–2018)
“Edge-on silicon” KTH Royal Institute of Tech (Sweden) KTH RIT (–2018)
■ PCD-CT with 3–6 energy windows in Year 202x that
– Improves contrast, noise, spatial reso, quant. accuracy, etc.
– Add material-axis to 3-D images → How to use it effectively?
– Enables multi-agent CT, molecular CT, personalized CT
– No killer application!
■ Algorithms needed for data correction and image recon
8/1/2018
14
Acknowledgemnet
40AAPM 2018. K Taguchi (JHU)
Mayo Clinic■ Cynthia H. McCollough, Ph.D.■ Shuai Leng, Ph.D.■ Kishore Rajendran, Ph.D.
TITech■ Kenji Amaya, Ph.D.■ Kento Nakada, M.Sc.
JHU (my group)
■ Okkyun Lee, Ph.D.■ Somesh Srivastava, Ph.D.■ Jochen Cammin, Ph.D.■ Qiulin Tang, Ph.D.■ Zhihui Sun, M.Sc.■ Mengxi Zhang, M.Sc.
JHU ■ Eric C. Frey, Ph.D. ■ Benjamin M.W. Tsui, Ph.D.
Siemens Healthineers■ Steffen Kappler, Ph.D.■ Karl Stierstorfer, Ph.D.■ Christoph Polster, Ph.D.■ Thomas G. Flohr, Ph.D.■ Matthew K. Fuld, Ph.D.■ George S. K. Fung, Ph.D.
DxRay■ Jan S. Iwanczyk, Ph.D. ■ William C. Barber, Ph.D. ■ Neal E. Harsough, Ph.D.
New generation CT has been developed for
41AAPM 2018. K Taguchi (JHU)
■ Improving everything CT does (whole body)
■ Adding new dimension (material info) to everything CT does
■ Enabling new applications
In 202x, PCD-CT with 3–6 energy windows
Contrast, contrast-to-noise, radiation dose, contrast dose,spatial reso, accuracy, quantitative values, CT radiomics
Simultaneous image-and-measure (IAM-XX), CT tissue biomarkers
Simultaneous multi-agent, molecular CT, personalized CT