Data Acquisition Electronics for Positron Emission Tomography William W. Moses Lawrence 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 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 Photon Detectors Radionuclide decays by emitting a positron (  + ).  + annihilates with e – from tissue, forming back-to-back 511 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)

MRI & PET Images of Epilepsy MRI “Sees” Structure with 0.5 mm Resolution PET “Sees” Metabolism with 4.0 mm Resolution MRIPET

Combine PET & CT (Oncology) CT ImagePET ImageFused ImagePost-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) Image courtesy of Gustav von Schulthess, University Hospital, Zurich Anatomy from X-Ray CT, Function from PET

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? 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t

Numbers Detector Modules (25 cm 2 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 Module Decode Crystals Using Anger Logic (Light Sharing) X-Ratio Y-Ratio Profile through Row 2 Array of Scintillator Crystals Photomultiplier Tubes

Position Identification Y X E=A+B+C+D Y=(A+B)/E X=(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 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 YesNo E

Time Stamp “Raw” Time Stamp is Digitized Time Since Last Time Slice Boundary Each Crystal Assumed to Have a Different (But Constant) Propagation Delay Propagation Delays Measured w/ Positron Source and 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 a Different (But Constant) Propagation Delay Propagation Delays Measured w/ Positron Source and 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 Coincidences Break Time Into Slices (100–250 ns / slice) Search for Singles Within  t max (4–12 ns) in Each Slice Greatly Reduces Combinatorics Break Time Into Slices (100–250 ns / slice) Search for Singles Within  t max (4–12 ns) in Each Slice Greatly Reduces Combinatorics Time Slice 1Slice 2Slice 3Slice 4Slice 5Slice 6 Single  t max Coincidence Single Coincidence Single Coincidence Single Coincidence Not Coincidence

Siemens & 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 Scintillator Crystal Array

Chord Siemens & GE System Architecture Detector Board Detectors Multiplexer Board 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 Detector Board Multiplexer Board Position Time Position Time Position Time Energy Position Time Energy

Philips 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” Scintillator Crystal Array

Chord Philips System Architecture Detector Board Detectors Coincidence Board Processing Board Host PC Position & Energy Computed Only for Coincidences Bidirectional Data Flow  Handshaking Position & Energy Computed Only for Coincidences Bidirectional Data Flow  Handshaking Detector Board Time Coincidence ADC Output PMT ID Position Energy Position Energy

Typical Front End Architecture PMTs Corrections Done In Real Time, Outputs Singles Events B Gain Adjust, Integrate Sum Gain Adjust, Integrate Gain Adjust, Integrate Gain Adjust, Integrate Sum ADC V in V ref ADC V in V ref A C D ADC V in V ref Crystal Lookup (X & Y  ID) Energy Validation (E & ID  511?) Time Stamp (T & ID  T Stamp) Event Formatting CFD TDC +5V A+B B+D Y X E T Logic

Siemens Implementation (~1995) PMTs Analog Done w/ Discretes, Digital Done w/ Custom ASIC B Gain Adjust, Integrate Sum Gain Adjust, Integrate Gain Adjust, Integrate Gain Adjust, Integrate Sum ADC V in V ref ADC V in V ref A C D ADC V in V ref Crystal Lookup (X & Y  ID) Energy Validation (E & ID  511?) Time Stamp (T & ID  T Stamp) Event Formatting CFD TDC +5V A+B B+D Y X E T Custom ASIC

Siemens Implementation (~2000) PMTs Analog Done w/ Custom ASIC, Digital Done w/ FPGA B Gain Adjust, Integrate Sum Gain Adjust, Integrate Gain Adjust, Integrate Gain Adjust, Integrate Sum ADC V in V ref ADC V in V ref A C D ADC V in V ref Crystal Lookup (X & Y  ID) Energy Validation (E & ID  511?) Time Stamp (T & ID  T Stamp) Event Formatting CFD TDC +5V A+B B+D Y X E T FPGA & Memory Custom ASIC

Siemens Implementation (~2005) PMTs Op-Amp  Free Running ADC, More Digital Done w/ FPGA B Gain Adjust, Anti-Alias Gain Adjust, Anti-Alias Gain Adjust, Anti-Alias Gain Adjust, Anti-Alias Sum ADC V in V ref A C D Crystal Lookup (X & Y  ID) Energy Validation (E & ID  511?) Time Stamp (T & ID  T Stamp) Event Formatting CFD TDC +5V A T FPGA & Memory Custom ASIC ADC V in V ref +5V B ADC V in V ref +5V C ADC V in V ref +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 Requirements 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 Same Tremendous Variation in How Outputs Are Combined  Combine Outputs in Firmware Tremendous Variation in How Outputs Are Combined  Combine 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) PMTs Analog Done w/ Discrete, More Digital Done w/ FPGA B Gain Adjust, Anti-Alias Gain Adjust, Anti-Alias Gain Adjust, Anti-Alias Gain Adjust, Anti-Alias ADC V in V ref A C D Crystal Lookup (X & Y  ID) Energy Validation (E & ID  511?) Time Stamp (T & ID  T Stamp) Event Formatting TDC +5V A FPGA & Memory ADC V in V ref +5V B ADC V in V ref +5V C ADC V in V ref +5V D Free-Running (80 MHz) TDC Discriminator

OpenPET System Architecture Detector Board Data Control Detectors 16 Analog Signals In Support Board PP 8 Boards In Digital Multiplexer 8 Boards In Coincidence P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 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 mm 3 LSO crystals 4 Hamamatsu R-9800 PMTs

Detector 2: SiPM Array Same Electronics with Very Different Type of Detector 16x16 array 3x3 mm 2 SiPMs 3x3x20 mm 3 & 3x3x30 mm 3 LSO Adapter Board 16x16 array to 16 Row & 16 Column Analog Sums Natural LSO Activity Pixel Intensity  Energy x Count Rate

Timing Resolution HPTDC (CERN) FPGA Test PulseTOF Module Pair 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 Open Source Hardware, Firmware, and Software Schematics, Gerbers, BOM,… Active User Community Share Software and Expertise Module, Calibration, DAQ, Display,… Spring Fall, 2010 Detector & Support Boards Available Work on Coincidence Board Begins