New Trends in PET Instrumentation

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New Trends in PET Instrumentation
William W. Moses Lawrence Berkeley National
Laboratory September 18, 2006
Outline

• Recent Advances
• Current Directions
• Future

This work was supported in part by the U.S. DOE
(contract No. DE-AC03-76SF00098) and in part by
the NIH (NIBIB grant No. R33-EB001928).
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Recent Advances in PET Instrumentation
PET in 1986
PET in 2006

• 8 mm Resolution
• 5 cm Axial Extent
• Cardiology / Neurology
• Academic Research

• 4 mm Resolution
• gt15 cm Axial Extent
• Oncology
• Routine Clinical

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Combine PET CT
CT Image
PET Image
Fused Image
Post-Therapy
Images courtesy of Stig Larsson, Karolinska
Institute

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

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Small Animal (Mouse) PET
FDG Heart
F Bone Scan

• 1 mm Spatial Resolution
• Basic Biological Research

Tumor Model
Images courtesy of Simon Cherry, UC Davis
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Small Animal (Mouse) PET / CT
CT Image
PET Image
Fused Image
Images courtesy of Simon Cherry, UC Davis
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Positron Emission Mammography
Image courtesy of M. Smith, D. Weisenberg, and S.
Majewski, Jefferson National Lab.

• PET Cameras Optimized to Image Breast Cancer
• Reduced Field of View
• Lower Cost (10x)
• Higher Performance (2x 30x)

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Prostate-Specific PET Camera
Images courtesy of Jennifer Huber, LBNL

• Focused on the Prostate
• Higher Efficiency Resolution than Conventional
  PET
• Uses 4x Fewer Detector Modules than Conventional
  PET

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Dual-Modality PET / Ultrasound Imaging
PET
Trans-RectalUltrasound (TRUS)
Merged PET / TRUS Image?
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PET / MRI Brain Scanner
Four 8x8 arrays of 2x2x20 mm LSO crystals read
out by 16 APDs (5x5 mm) and two 8 channel preamps
Scanner size 36 cm dia. x 20 cm FOV

• Challenging Technology PET MRI Systems
  Interfere
• Planned to Use for Neurology

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Conscious Small Animal (Rat) PET RATCAP
Image courtesy of Craig Woody,Brookhaven
National Laboratory

• Wearable PET Camera
• Planned to Use for Neurology

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Small Animal (Rat) PET / MRI Camera

• Standard Non-Magnetic Components
• LSO crystals
• Aluminum housing
• Fiberglass, kapton, plastic, silicon

• Special Non-Magnetic Components
• APDs (special pins)
• APD sockets
• Non-magnetic flex circuit board (substrate)
• Non magnetic electronic components (solder leads)

Image courtesy of Craig Woody,Brookhaven
National Laboratory

• Shielding from RF
• Aluminum housing
• Kapton cable carrying signals

• Non-Magnetic Version of RATCAP
• Planned to Use for Neurology

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Time-of-Flight in PET
c 30 cm/ns

• Use time-of-flight to localize source along line
  of flight.
• Time of flight information reduces noise in
  images.
• Variance reduction given by 2D/c?t.
• 500 ps timing resolution? 5x reduction in
  variance!

• Time of Flight Provides a Huge Performance
  Increase
• Biggest Improvement in Large Patients

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Statistical Noise in PET
If there are N counts in the image, SNR
Signals from Different Voxels are Coupled ?
Statistical Noise Does Not Obey Counting
Statistics
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Whole-Body TOF Simulations
2x106 Trues, 1x106 Randoms, Attenuation
IncludedOP-OSEM w/ TOF Extensions, 2 Iterations,
14 Subsets
Images courtesy of Mike Casey, Siemens Medical
Solutions

• Clear Improvement Visually
• Commercial TOF PET Camera Released by Philips

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Human PET Block Detector Design
4 PMTs (25 mm square)
Saw cuts direct light toward PMTs. Depth of cut
determines light spread at PMTs. Crystal of
interaction found with Anger logic (i.e. PMT
light ratio).
50 mm
Scintillator Crystal Block
50 mm
30 mm

• Measures Position, Energy, and Time
• Good Performance, Inexpensive, Easy to Pack

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Animal PETLSO Scintillator Position-Sensitive
PMTs
LSO Scintillator
Position-Sensitive PMTs
Compared to BGO
Compared to PMTs

• Higher Light Output
• Similar Attenuation Length
• Shorter Decay Time

• Many Pixels
• Similar Area
• Higher Cost
• More Dead Area
• Less Uniform

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What Can Be Improved?

• Energy Resolution
• Reduce Scatter Background
• Time Response
• Reduce Dead Time
• Improve TOF Performance
• Spatial Resolution
• Reduce Penetration Effects
• Need Volumetric Detector
• Cost

Array of Scintillator Crystals
Photomultiplier Tubes
Much More Work To Be Done!
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Improvements In Scintillators

• Combine Best Properties of
• LaBr330 Ce
• Timing resolution lt100 ps
• Energy resolution lt4
• LuI3Ce
• Light output gt100,000 ph/MeV
• PbWO4
• Density gt8 g/cc
• High atomic number
• Inexpensive

Image courtesy of Paul Lecoq, CERN
PET Performance Determined by Scintillator
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Improvements in Photodetectors
Avalanche Photodiode Array
Position-Sensitive APD
Hamamatsu Photonics

• High Quantum Efficiency
• GHz Bandwidth w/ Reasonable Gain
• Individual Small Pixels
• Practical (compact, reliable, inexpensive)

RMD, Inc.
Geiger Mode APDs (SiPMs) Also Show Promise
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Improvements In Electronics

• Timing Resolution
• Improve TOF Performance
• High-Performance CFD ASIC
• Multi-Channel
• Multi-Anode PMTs
• APD SiPM Arrays
• Volumetric Detectors
• 100,000 Pixels in Camera!
• Cost

Image courtesy of Jorgen Christianson, CERN
Electronics Must Keep Pace w/ Detectors
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Conclusion

• PET Instrumentation Has Improved Dramatically
• Routine Clinical Use w/ Merged X-Ray CT Image
• Small Animal
• Current Trends
• Multi-Modality (MRI, Ultrasound, Optical)
• Special Purpose (Disease-Specific) Cameras
• Time-of-Flight
• Future Improvements Require
• New Scintillators, Photodetectors, Electronics
• New Detector Camera Designs
• New Reconstruction, Data Analysis, Chemistry

Much More Work To Be Done!