data acquisition electronics for positron emission tomography

Data Acquisition Electronicsfor

Positron Emission Tomography

Data Acquisition Electronicsfor

Positron Emission Tomography

William W. MosesLawrence Berkeley National Laboratory

May 24, 2010

• PET Overview• PET Electronics Requirements & Trends• OpenPET Electronics

Outline:

• This work was supported in part by the U.S. DOE (contract No. DE-AC02-05CH11231) and in part by the NIH (NIBIB grant No. R01-EB006085).

• Thanks to S. Choong, C. Vu, and Q. Peng of LBNL, C. Jackson, S. Buckley, and N. Pavlov of SensL, M. Casey and J. Young of Siemens Medical Solutions, D. McDaniel of GE Medical Systems, and J. Karp of U. Penn.

Nuclear MedicineNuclear Medicine

• Patient injected with small amount of radioactive drug.

• Drug localizes in patient according to metabolic properties of that drug.

• Radioactivity decays, emitting gamma rays.

• Gamma rays that exit the patient are imaged.

•Well Established Clinical Technique•10 Million Studies Annually

•Well Established Clinical Technique•10 Million Studies Annually

Gamma Camera

Ring of PhotonDetectors • Radionuclide decays by

emitting a positron (+ ).

• + annihilates with e– from tissue, forming back-to-back511 keV photon pair.

• 511 keV photon pairs detected via time coincidence.

• Positron lies on line defined by detector pair.

• Detects Pairs of Back-to-Back 511 keV Photons• Use Computed Tomography to Form 2-D Image

• Detects Pairs of Back-to-Back 511 keV Photons• Use Computed Tomography to Form 2-D Image

Positron Emission Tomography (PET)Positron Emission Tomography (PET)

MRI & PET Images of EpilepsyMRI & PET Images of Epilepsy

• MRI “Sees” Structure with 0.5 mm Resolution

• PET “Sees” Metabolism with 4.0 mm Resolution

MRI PET

Combine PET & CT (Oncology)Combine PET & CT (Oncology)CT Image PET Image Fused Image Post-Therapy

•Anatomy from X-Ray CT, Function from PET•Current “Standard of Care”

•Anatomy from X-Ray CT, Function from PET•Current “Standard of Care”

Images courtesy of Stig Larsson, Karolinska Institute

Combine PET & CT (Cardiac)Combine PET & CT (Cardiac)

Image courtesy ofGustav von Schulthess, University Hospital, Zurich

Anatomy from X-Ray CT, Function from PETAnatomy from X-Ray CT, Function from PET

What Is A “PET Event”?(What Do You Need To Record?)

What Is A “PET Event”?(What Do You Need To Record?)

•Non-TOF PET: A Chord — Defined By Two End Points•Time-of-Flight PET: A Chord and t

•Non-TOF PET: A Chord — Defined By Two End Points•Time-of-Flight PET: A Chord and t

What Is The Electronics Concept?What Is The Electronics Concept?

• Identify “Singles Events”•Find Time Coincidences Between Singles Events w/ t

•“Coincident Event” = Pair of Singles Events (Chord)

• Identify “Singles Events”•Find Time Coincidences Between Singles Events w/ t

•“Coincident Event” = Pair of Singles Events (Chord)

• Position (crystal of interaction)

• Time Stamp (arrival time)

• Energy Validation (=511 keV?)

“Singles Event”

• Position (crystal of interaction)

• Time Stamp (arrival time)

• Energy Validation (=511 keV?)

“Singles Event”t

NumbersNumbers

• 150-300 Detector Modules (25 cm2 each) per Camera

• 100 kHz Typical Singles Rate per Module

• 1 MHz Maximum Singles Rate per Module

• 1 MHz Typical Coincidence Rate per Camera

• 4 MHz Maximum Coincidence Rate per Camera

• 1 ns fwhm Timing Resolution for Conventional PET

• 250 ps fwhm Timing Resolution for TOF PET

•Low Coincidence / Singles Ratio•Low Occupancy in Each Detector Module

Multiplex Singles Events

•Low Coincidence / Singles Ratio•Low Occupancy in Each Detector Module

Multiplex Singles Events

PET Detector ModulePET Detector Module

0500

1000150020002500300035004000

Counts

Decode Crystals Using Anger Logic (Light Sharing)Decode Crystals Using Anger Logic (Light Sharing)

X-Ratio

Y-Ratio

ProfilethroughRow 2

Array of Scintillator Crystals

Photomultiplier Tubes

1 2 3 4 5 6 7

8 9 10 11 12 13 14

15 16 17 18 19 20 21

22 23 24 25 26 27 28

29 30 31 32 33 34 35

36 37 38 30 40 41 41

43 44 45 46 47 48 49

50 51 52 53 54 55 56

Position IdentificationPosition Identification

1 2 3 4 5 6 7

8 9 10 11 12 13 14

15 16 17 18 19 20 21

22 23 24 25 26 27 28

29 30 31 32 33 34 35

36 37 38 39 40 41 42

43 44 45 46 47 48 49

50 51 52 53 54 55 56

Y

X

E=A+B+C+DY=(A+B)/EX=(B+D)/E

C

A

D

B

•Identify Crystal of Interaction Using Lookup Table•Position Given by Crystal ID

•Identify Crystal of Interaction Using Lookup Table•Position Given by Crystal ID

Energy ValidationEnergy Validation

•Yes/No Decision Based on Measured Energy•Individual Thresholds for Each Crystal

•Implemented Using Lookup Table

•Yes/No Decision Based on Measured Energy•Individual Thresholds for Each Crystal

•Implemented Using Lookup Table

0

2000

4000

6000

8000

10000

12000

14000

0 100 200 300 400 500

Counts per Bin

Pulse Height Bin

YesNo No

E

Time StampTime Stamp

• “Raw” Time Stamp is Digitized Time Since Last Time Slice Boundary

• Each Crystal Assumed to Have aDifferent (But Constant) Propagation Delay

• Propagation Delays Measured w/ Positron Sourceand Stored in a Lookup Table

• Crystal by Crystal Correction Factor Added to “Raw” Time

• “Raw” Time Stamp is Digitized Time Since Last Time Slice Boundary

• Each Crystal Assumed to Have aDifferent (But Constant) Propagation Delay

• Propagation Delays Measured w/ Positron Sourceand Stored in a Lookup Table

• Crystal by Crystal Correction Factor Added to “Raw” Time

TDC

CFD Master Clock

Time Slice Boundary

Clock

Start / Reset

Stop

From Central Timing BoardDetector Module

Identifying Time CoincidencesIdentifying Time Coincidences

•Break Time Into Slices (100–250 ns / slice)•Search for Singles Within tmax (4–12 ns) in Each Slice

•Greatly Reduces Combinatorics

•Break Time Into Slices (100–250 ns / slice)•Search for Singles Within tmax (4–12 ns) in Each Slice

•Greatly Reduces Combinatorics

Time

Slice 1 Slice 2 Slice 3 Slice 4 Slice 5 Slice 6

Single

Single

Single

Single

Single

tmax

Coincidence

Single

Single

Coincidence

Single

Single

Single

Single

Single

Single

SingleSingle

Single

Single SingleCoincidence

Coincidence

Single

Single

SingleSingle

CoincidenceNot Coincidence

Siemens & GE Detector TopologySiemens & GE Detector Topology

•4 PMTs to Decode Event Position• Independent Modules Operating in Parallel

•4 PMTs to Decode Event Position• Independent Modules Operating in Parallel

ScintillatorCrystal Array

Chord

Siemens & GE System ArchitectureSiemens & GE System Architecture

DetectorBoard

Detectors

MultiplexerBoard

Coincidence Host PC

• Position, Time, & Energy Computed for Each Trigger• All Data Flow is Forward No Handshaking

• Position, Time, & Energy Computed for Each Trigger• All Data Flow is Forward No Handshaking

DetectorBoard

MultiplexerBoard

Position

Time

Position

Time

Position

Time

Energy

Position

TimeEnergy

Philips Detector TopologyPhilips Detector Topology

•7–20 PMTs to Decode Event Position•Highly Coupled—Each PMT Used in Many “Modules”

•7–20 PMTs to Decode Event Position•Highly Coupled—Each PMT Used in Many “Modules”

ScintillatorCrystal Array

Chord

Philips System ArchitecturePhilips System Architecture

DetectorBoard

Detectors CoincidenceBoard

ProcessingBoard

Host PC

• Position & Energy Computed Only for Coincidences• Bidirectional Data Flow Handshaking

• Position & Energy Computed Only for Coincidences• Bidirectional Data Flow Handshaking

DetectorBoard

Time

Time

Coincidence

Coincidence

ADC Output

ADC Output

PMT ID

Position

Energy

Position

Energy

Typical Front End ArchitectureTypical Front End ArchitecturePMTs

Corrections Done In Real Time, Outputs Singles EventsCorrections Done In Real Time, Outputs Singles Events

B

Gain Adjust,Integrate

Sum




Sum

Sum

ADCVin

Vref

ADCVin

Vref

A

C

DADC

Vin

Vref

Crystal Lookup(X & Y ID)

EnergyValidation

(E & ID 511?)

Time Stamp(T & ID T Stamp)

Event FormattingCFD TDC

+5V

A+B

B+D

Y

X

E

T

Logic

Siemens Implementation (~1995)Siemens Implementation (~1995)PMTs

Analog Done w/ Discretes, Digital Done w/ Custom ASICAnalog Done w/ Discretes, Digital Done w/ Custom ASIC

B


Sum




Sum

Sum

ADCVin

Vref

ADCVin

Vref

A

C

DADC

Vin

Vref


EnergyValidation

(E & ID 511?)



+5V

A+B

B+D

Y

X

E

T

Custom ASIC


Analog Done w/ Custom ASIC, Digital Done w/ FPGAAnalog Done w/ Custom ASIC, Digital Done w/ FPGA

B


Sum




Sum

Sum

ADCVin

Vref

ADCVin

Vref

A

C

DADC

Vin

Vref


EnergyValidation

(E & ID 511?)



+5V

A+B

B+D

Y

X

E

T

FPGA & Memory

Custom ASIC


Op-AmpFree Running ADC, More Digital Done w/ FPGAOp-AmpFree Running ADC, More Digital Done w/ FPGA

B

Gain Adjust,Anti-Alias




Sum

ADCVin

Vref

A

C

D


EnergyValidation

(E & ID 511?)



+5V

A

T

FPGA & Memory

Custom ASIC

ADCVin

Vref+5V

B

ADCVin

Vref+5V

C

ADCVin

Vref+5V

D

Free-Running(~75 MHz)

• Nuclear Medicine Research Community Needs“Industrial-Strength” Electronics

• Needs Can Be Met By Single, Flexible Design!

• Nuclear Medicine Research Community Needs“Industrial-Strength” Electronics

• Needs Can Be Met By Single, Flexible Design!

Electronics System RequirementsElectronics System Requirements

Like Open Source Software!Like Open Source Software!

High-Performance•# of Channels, Rate, Energy, Timing, …

Very Flexible•Type of Detector, Camera Configuration,Event Word Definition

User-Modifiable•Schematics, Source Code, Knowledge Base

User-Friendly• Instructions, Documentation, Can Buy Boards

All Detector Outputs Look the SameAll Detector Outputs Look the Same

• Tremendous Variation in How Outputs Are CombinedCombine Outputs in Firmware

• Tremendous Variation in How Outputs Are CombinedCombine Outputs in Firmware

Voltage

Time

Extract Timing Signal from Leading Edge

Extract “Energy” from Area Under the Curve

100 mV – 2 V

OpenPET Implementation (~2010)OpenPET Implementation (~2010)PMTs

Analog Done w/ Discrete, More Digital Done w/ FPGAAnalog Done w/ Discrete, More Digital Done w/ FPGA

B





ADCVin

Vref

A

C

D


EnergyValidation

(E & ID 511?)


Event FormattingTDC

+5V A

FPGA & Memory

ADCVin

Vref+5V B

ADCVin

Vref+5V C

ADCVin

Vref+5V D

Free-Running(80 MHz)

TDC

TDC

TDC

Discriminator

Discriminator

Discriminator

Discriminator

OpenPET System ArchitectureOpenPET System Architecture

DetectorBoard

Data

Control

Detectors

16 AnalogSignals In

SupportBoard

P

8 Boards In

DigitalMultiplexer

8 Boards In

Coincidence

P

8 Boards In

Host PC

• Supports 256 Block Detectors (2048 With Multiplexers)• PSB + 8 DPBs Makes Nice Test Stand (32 Block Detectors)

• Supports 256 Block Detectors (2048 With Multiplexers)• PSB + 8 DPBs Makes Nice Test Stand (32 Block Detectors)

Detector 1: Conventional Block DetectorDetector 1: Conventional Block Detector

• Pre-Prototype Circuit Boards• Excellent Flood Map and Energy Resolution

• Pre-Prototype Circuit Boards• Excellent Flood Map and Energy Resolution

12% 11%

10%12%

12x12 array of 4x4x22 mm3 LSO crystals4 Hamamatsu R-9800 PMTs

Detector 2: SiPM ArrayDetector 2: SiPM Array

Same Electronics with Very Different Type of DetectorSame Electronics with Very Different Type of Detector

16x16 array3x3 mm2 SiPMs

3x3x20 mm3 &3x3x30 mm3 LSO

Adapter Board

16x16 arrayto

16 Row &16 Column

Analog Sums

Natural LSO Activity

Pixel Intensity Energy x Count Rate

Timing ResolutionTiming Resolution

HPTDC(CERN)

FPGA

Test Pulse TOF Module Pair

0

1 105

2 105

3 105

4 105

5 105

6 105

-400 -200 0 200 400

Counts per Bin

Time (ps)

255 ps fwhm

0

1 105

2 105

3 105

4 105

5 105

6 105

-200 -150 -100 -50 0 50 100 150 200

Counts per Bin

Time (ps)

90 ps fwhm

0

500

1000

1500

2000

2500

3000

-400 -200 0 200 400

Counts per Bin

Time (ps)

286 ps fwhm

0

500

1000

1500

2000

2500

-200 -150 -100 -50 0 50 100 150 200

Counts per Bin

Time (ps)

56 ps fwhm

• 16 Channel TDC in Cyclone II FPGA• Performance Good Enough for Time-of-Flight PET

• 16 Channel TDC in Cyclone II FPGA• Performance Good Enough for Time-of-Flight PET

Vision

Vision

http://OpenPET.LBL.govhttp://OpenPET.LBL.gov

data acquisition electronics for positron emission tomography

Documents

resolution pet

pet event

maximum singles rate

flight pet

digitized time

nontof pet

detector pair

maximum coincidence