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Solid State Digital Photon Counting PET/CT Instrumentation and Technology

Jun Zhang, PhD, DABR

Assistant Professor

Wright Center of Innovation in Biomedical Imaging

Department of Radiology

The Ohio State University Wexner Medical Center

AAPM2017 Scientific Symposium: Emerging and New Generation PET: Instrumentation, Technology, Characteristics and Clinical Practice

Aug 2 Wednesday 10:45am – 11:15pm

Disclosure

Philips Healthcare (Cleveland, OH) provided the pre-commercial investigational PET/CT system (Vereos).

DPC PET/CT (Vereos, Philips Healthcare) at OSU

Pre-commercial release unit of digital photon counting PET/CT system (Vereos, Philips Healthcare) operational at The Ohio State University (PI: Michael V Knopp, MD, PhD) since October 2014. PET detector technology moving from PMT to solid state DPC is a technology leap.

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PMTs Light

Spreading

High Energy Photon

Positioning Logic

Digital One-to-One coupling

DPC tile

Scintillation photon

Analog Many-to-many coupling

Crystal

Analog PMT

Scintillation photons

Digital Photon Counter High Energy

Photon

Scintillator Crystals

From PMT to Solid State DPC

Vereos PET Detector Geometry

18

1

2

3

5

6

7

=

=

=

=

} 010101101

=

===

==

==

=

===

==

=

23,040 x 3,200

Biggest contribution to the overall sensor DCR is caused by only a small percentage of the cells such as ~10 % cells responsible for 70-80% DCR.

Disabling high DCR cells on small active sensor area leads to significantly reduced overall sensor DCR.

1. Philips Vereos PET/CT Whitepaper

2. Haemisch Y, et al. Physics Procedia. 2012;37:1546–1560

DPC Data Acquisition Sequence

Digital Photon Counting

Digital Time of Flight

1:1 Coupling

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Energy Resolution

0.0%

2.0%

4.0%

6.0%

8.0%

10.0%

12.0%

14.0%

16.0%

18.0%

20.0%

Energy resolution (%)

9.5

10

10.5

11

11.5

12

FWHM=11.2%

460 480 500 520 540 560 580

Energy [keV]

En

erg

y R

es

olu

tio

n

[% F

WH

M]

7

8

9

10

11

12

13

14

15

Ener

gy R

eso

luti

on

(% F

WH

M)A B

-400 -200 0 200 400

Timing [ps]

FWHM = 312 ps

-400 -200 0 200 400

Timing [ps]

324ps FWHM

321

321.5

322

322.5

323

323.5

324

324.5

325

Tim

ing

Re

so

luti

on

[ps

FW

HM

]

322 ps FWHM

310

312

314

316

318

320

322

324

326

328

330

Timing Resolution (ps)

Axial FOV

18F18F

22Na point source

0 20 40 60 80

02

00

40

06

00

80

01

00

0

Avg Singles Rate [Mcps]

Tim

ing

Re

so

luti

on

[ps

FW

HM

]

Vereos PET/CTGemini TF (ref 7)

Experimental setup (ref 7)

JNM 48(2007) 471

TOF Timing Resolution

NEMA NU 2 2012 Spatial Resolution

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FWHM FWTM

at 1cm at 10cm at 20cm at 1cm at 10cm at 20cm

Axial 4.31 4.79 6.17 8.51 9.48 10.82

Transverse (Radial) 4.01 4.64 5.86 8.37 8.97 10.46

Transverse (Tangential) 4.01 4.41 4.99 8.37 8.98 10.37

NEMA NU 2 2012 Spatial Resolution

where R is the overall spatial resolution, Kr – a scale factor, Ri the intrinsic resolution determined by crystal width, Rp the error due to positron range, Ra the error from noncollinearity, and Rl is the decoding error (anger logic positioning

localization). For DPC PET, Rl is zero due to that 1:1 coupling eliminates need for position decoding.

𝑅(𝐹𝑊𝐻𝑀) = 𝐾𝑟 × 𝑅𝑖2 + 𝑅𝑝

2 + 𝑅𝑎2 + 𝑅𝑙

2

1. WW Moses. Nucl Instrum Methods Phys Res A. 2011; 648 (Supplement 1): S236–S240

2. Jun Zhang, Michael V Knopp. J Nucl Med 2017; 58 (supplement 1): 1322

= 𝐾𝑟 × 𝑅𝑖2 + 𝑅𝑝

2 + 𝑅𝑎2

Compared to conventional photo-multiplier PET systems, spatial resolution of the SiPM digital photon counting PET system is NOT affected by A. Crystal size B. Positron Range C. Noncollinearity / Acollinearity D. Localization decoding

SAM Question

Answer: (D) 1:1 coupling eliminates need for position decoding

0 10 20 30 40 50 60 70 800

50

100

150

Slice Number

Se

ns

itiv

ity c

ps

/MB

q

0cm10cm

A B

0 2 4 6 8 10

05

10

15

20

25

Activity at Measurement Time [mCi]

Eff

ec

tiv

e S

en

sit

ivit

y [k

cp

s/M

Bq

]

Vereos PETAnalog PET Courtesy of Philips

NEMA NU 2 2012 Sensitivity

Average at 0 and 10cm: ~5.6 kcps/MBq

0 10 20 30 40 50 60 70 800

50

100

150

Slice Number

Se

ns

itiv

ity c

ps

/MB

q

0cm10cm

A B

0 2 4 6 8 10

05

10

15

20

25

Activity at Measurement Time [mCi]

Eff

ec

tiv

e S

en

sit

ivit

y [k

cp

s/M

Bq

]

Vereos PETAnalog PET

Axial Sensitivity Profile

𝐒𝐞𝐟𝐟(𝐀) = 𝐒𝐍𝐄𝐌𝐀(𝐀) × 𝑮𝐓𝐎𝐅

𝑮𝐓𝐎𝐅 =𝟐𝑫

𝒄𝚫𝐭= time-of-flight gain

Budinger. JNM 24(1): 73-78

NEMA PET Sensitivity Phantom (Data Spectrum Corporation, Hillsborough, NC)

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Activity Concentration (kBq/mL)

NEC

R (

kcp

s)

0

500

1000

1500

2000

2500

0 10 20 30 40 50

Ra

te (

kcp

s)

Activity Concentration (kBq/mL)

Total Randoms TRUE Scatter

0

50

100

150

200

0 10 20 30 40 50R

ate

(k

cps)

Activity Concentration (kBq/mL)

NECR Scatter Fraction

A B

30%

0 10 20 30 40 50 60 70

05

01

00

15

02

00

Activity Concentration [kBq/mL]

NE

CR

(1r)

[kcp

s]

OSU System

3 x V1

V1, 27cm

V1, 35 cm

Peak NECR = 157 kcps @ 51 kBq/mL TOF peak NECR = 641 kcps @ 51kBq/mL

NEMA NU 2 2012 NECR and Scatter

0 10 20 30 40 50 60 70

02

00

40

06

00

80

0

Activity Concentration [kBq/mL]

TO

F E

ffe

ctive

NE

CR

(1r)

[kcp

s]

OSU System

3 x V1

TOF

Effe

ctiv

e N

ECR

(kcp

s)

Measured TOF Gain - OSU = 325 ps G = 4.1 V1 = 316 ps G = 4.2 Analog ~ 500 ps 2.7

NECR = T2 / (T + S + R)

For a 48cm diameter object, an estimated sensitivity gain and the SNR improvement of the digital photon counting TOF PET (320ps, 4.8cm uncertainty) compared to nonTOF PET are about A. 5.0 and 5.0 B. 10.0 and 10.0 C. 10.0 and 3.2 D. 10.0 and 5.0

SAM Question

Answer: (C) 𝑮𝐓𝐎𝐅 =

𝟐𝑫

𝒄𝚫𝐭=

𝑫

𝚫𝒙 = time-of-flight gain

G SNR =

𝑫

𝚫𝒙

40.7

59.1 63.070.1

81.9 86.3

0

20

40

60

80

100

10 13 17 22 28 37

Co

ntr

ast

(%)

Sphere (mm)

9.2

7.45.8

4.63.6

2.7

0

2

4

6

8

10

12

10 13 17 22 28 37

Bac

kgro

un

d V

aria

bili

ty

(%)

Sphere (mm)

NEMA NU 2 2012 Image Quality

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Phantoms IQ

39

89

8.5

2.8

10 37

%

SPHERE SIZE (MM)

Sphere Contrast (%) Background Variability (%)

0.0000.1000.2000.3000.4000.5000.6000.7000.8000.9001.0001.100

2 5 8 11 14 17 20 23 26 29 32 35 38 41 44 47 50 53 56 59 62 65 68 71 74 77 80

SUV

me

an

Slice #

Alpha-Bravo Uniformity SUV Axial Profile - Brain 256FOV 2.2035mCi F18 @ 8:45am on 09/19/2014, phantom on the table, acq started at

10:49am, SUVmax=0.98, SUVmin=0.89, SUVmean=0.97, % variance=8.76%

LBR= 16

LBR= 32

Vereos Gemini

Specifications Vereos Gemini TF 64

Detector Design Direct Photon Counting PMT Anger Logic

Ring Diameter (mm) 764 764

Crystal LYSO LYSO

Crystal Size (mm3) 4 x 4 x 19 4 x 4 x 22

# of Detector Elements 23,040 420 PMT

Crystal-Detector Coupling 1:1 multi : multi

Transaxial FOV (mm) 256 / 576 / 676 256 / 576 / 676

Axial FOV (mm) 164 180

Overlap in Axial FOV 39% 53%

Energy resolution (%) 11 12.3

Energy calibration 1:1 multi : multi

Timing Resolution (ps) 320 550

Timing Calibration 1:1 multi : multi

Coincidence window (ns) 2.0 / 4.0 / 4.6 2.0 / 4.0 / 4.6

Reconstruction Algorithm 3D OSEM TOF 3D OSEM TOF, 3D Ramla

Reconstruction Matrix (pixel) up to 676 x 676 up to 338 x 338

Reconstruction Voxel (mm3) 64 / 8 / 1 64 / 8

# Voxels per slice up to 456,976 up to 107,584

Resolution Recovery PSF No PSF

System Specifications: DPC vs PMT

PMT PET vs DPC PET

Vereos Gemini

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Non-TOF 325ps TOF

Non-TOF TOF Non-TOF TOF

550ps 4mm PET 325ps 4mm PET

PMT PET vs DPC PET

PET Image Resolution (Recon)

Spacing (mm) 4 x 4 x 4

Volume (mm3) 64

FOV = 576mm 144 x 144 matrix

FOV = 676mm 169 x 169 matrix

FOV = 256mm N/A

# Voxels of V N (e.g., 20,736)

PSF & Filter on/off

Recon 3D TOF OSEM

2 x 2 x 2

8

288 x 288 matrix

338 x 338 matrix

128 x 128 matrix

8N (e.g., 165,888)

on/off

3D TOF OSEM

1 x 1 x 1

1

576 x 576 matrix

676 x 676 matrix

256 x 256 matrix

64N (e.g., 1,327,104)

on/off

3D TOF OSEM

4 4

4

2 2

2

1 1 1

4x4x4 mm3 2x2x2 mm3 1x1x1 mm3

Small Lesion Detectability with Less PVE

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Vereos (1mm3) Gemini (64mm3)

Lesion Detectability with Less PVE

A B C

D E F

A B C

D E F

A B C

D E F

A B C

D E F

A B C D E F

PET/CT Gemini TF 64 Gemini TF 64 mCT mCT Vereos Vereos

XY resolution 2mm 2mm 1mm 1mm 2mm 1mm

Slice Thickness 2mm 2mm 3mm 3mm 2mm 1mm

FDG Injected 4.3mCi 5.0mCi 10.0mCi 12.0mCi 13.9mCi 13.9mCi

Uptake time 45min 45min 50min 49min 118min 118min

Acquisition Time 10min 10min 10min 10min 90sec 90sec

A B C D E F

PET/CT Gemini TF 64 Gemini TF 64 mCT mCT Vereos Vereos

XY resolution 2mm 2mm 1mm 1mm 2mm 1mm

Slice Thickness 2mm 2mm 3mm 3mm 2mm 1mm

FDG Injected 4.3mCi 5.0mCi 10.0mCi 12.0mCi 13.9mCi 13.9mCi

Uptake time 45min 45min 50min 49min 118min 118min

Acquisition Time 10min 10min 10min 10min 90sec 90sec

A B C D E F

PET/CT Gemini TF 64 Gemini TF 64 mCT mCT Vereos Vereos

XY resolution 2mm 2mm 1mm 1mm 2mm 1mm

Slice Thickness 2mm 2mm 3mm 3mm 2mm 1mm

FDG Injected 4.3mCi 5.0mCi 10.0mCi 12.0mCi 13.9mCi 13.9mCi

Uptake time 45min 45min 50min 49min 118min 118min

Acquisition Time 10min 10min 10min 10min 90sec 90sec

Vendor A

A B C D E F

PET/CT Gemini TF 64 Gemini TF 64 mCT mCT Vereos Vereos

XY resolution 2mm 2mm 1mm 1mm 2mm 1mm

Slice Thickness 2mm 2mm 3mm 3mm 2mm 1mm

FDG Injected 4.3mCi 5.0mCi 10.0mCi 12.0mCi 13.9mCi 13.9mCi

Uptake time 45min 45min 50min 49min 118min 118min

Acquisition Time 10min 10min 10min 10min 90sec 90sec

Vendor B

Brain PET

90s/bed FDG

2mm Brain of 256FOV

Wholebody 576FOV

4mm Brain of WB 2mm Brain of WB

Brain PET Redefinition – Speed, Convenience, Dose, IQ

10min FDG

1mm Brain of WB

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WB PET Redefinition

30s/bed 60s/bed 75s/bed 90s/bed

WB NaF PET

120s/bed 120s/bed 120s/bed

12s/bed 12s/bed 12s/bed

Clinical Ultrafast PET

90s/bed 15min

30s/bed 5min

9s/bed 1.5min

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Low Dose FDG PET

NIH R01 PIs: Knopp, Zhang

Clinical Post 90Y Microsphere Radioembolization

Bremsstrahlung SPECT/CT DPC PET

A – 10min/bed; B - 7min/bed

A

B

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39% (9bed) 27% (8bed) 20% (7bed) 0% (6bed)

2.5mCi; NaF; 90s/bed; 110cm

39% 27% 20% 0%

• 1:1 coupling eliminates need for position decoding • Timing and energy calibrations per crystal • Improved timing resolution • Reduced dead time • Increased count rate performance • Early digitization eliminates as much as possible

analog noise and distortion.

Highlights

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A B C D E F

How much SiPM DPC Detector Coverage Do We Really Need?

A B C

D E F

Full ring detectors

50% detector reduction

33% detector reduction

25% detector reduction

40% tile-ring reduction

50% detector reduction

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Clinical Evaluation

• This research was supported by the Ohio Third Frontier OSDA TECH 09-028 (PI: Michael V Knopp, MD PhD) and NCI R01CA195513 (PI: Michael V Knopp, MD PhD; Jun Zhang, PhD)

• Philips Healthcare provided the pre-commercial investigational PET/CT system (Vereos) hardware and technical support

• Wright Center of Innovation in Biomedical Imaging (PI: Michael V Knopp, MD PhD)

Acknowledgement

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Thank You