From Novel g-2 Fast Calorimetry
to a Superior PET Scanner
Bill Worstell
Chief Technology Officer
PhotoDetection Systems, Inc.
Talk Overview
• What PET/CT is and why it is important
– Brief Summary of Clinical Context
• The PDS PET/CT and its connection with
Experimental High-Energy Physics
– Detector Design + Implementation
– Data Analysis/Processing + Image Algorithms
• The Future of PET/CT
– Molecular Imaging + Molecular Medicine
PET Physics
Measure positions
and energies of
coincident
particles which
generate
triggers –
sound familiar?
FDG-PET
• All of clinical
PET is currently
FDG-PET
• FDG developed
at Brookhaven
National
Laboratory
• Nearly all tumors
are FDG-avid
Clinical Applications of
PET in Oncology
•
•
•
•
Diagnosis
Biopsy guidance
Staging
Radiation Therapy
Planning
• Monitoring Response
to Therapy
• Monitoring for
Recurrence
Monitoring Response to
Targeted Therapy
PET/CT Hybrid Scanners
Anatomical plus Functional
Imaging -> Fusion Imaging
CT Image
gives anatomy
PET Image
gives function
(-> in-vivo
Quantitative
Biochemistry)
PET is now a $1B/year business,
Up from ~$10M/year in 1998
PET/CT was first commercially
introduced in 2002, and now makes
Up nearly 100% of the PET market
Distinguishing Features of
PDS PET component of PET/CT
• Highest Sensitivity
available
• Largest bore available
(only 90cm PET/CT)
• Matches highest clinical
spatial resolution available
• Lowest cost to manufacture
• Simple interfaces to
alternative multislice CTs
Largest Bore PET/CT available
Patient Bore
(cm)
PDS Resolve 90
90
GE Discovery ST
70
CTI/Siemens pico-3D
70
CTI/Siemens Hi-Res
70
Philips Gemini
63
Manufacturer/Model
Large-bore CTs have been
introduced to satisfy the needs
of radiation therapy planning
applications – there is as yet no
comparably large-bore PET/CT.
Highest Sensitivity
PET/CT system
• Double the axial field
of other scanners
(32cm vs 16cm)
– Larger coverage
– Larger acceptance
Manufacturer Model
PDS
GE
Siemens
Siemens
Philips
Sensitivity
(kcps/MBq)
Resolve 90
18.1
Discover ST
9.1
Biograph LSO
6.4
Hi-Rez
5.3
Gemini
4.4
511keV

• High stopping power
• Clinical applications:
– Lower injected dose
– Emerging radiotracers
length
Highest PET/CT
Image Quality
CTI: Low resolution
• Meets or exceeds the
performance of competitive
systems as quantified by
NEMA standard tests and
direct imaging comparisons
GE: Non-uniform
intensity
6.35
5.56
2.38
4.76
3.18
3.97
PDS PET/CT
CTI Hi-Res
PDS: High resolution
and uniform intensity
BU Physics Prototype Work
Antecedent work:
• Muon g-2 fiber
calorimeter prototypes
• SSC fiber calorimeter
prototypes
• BU wavelengthshifting fiber PET
prototypes
– Patent filed 1995
– Photonics Center spinoff start-up 2000
Principle of Wavelength-Shifting
Fiber Optic PET Readout
• Wavelength-shifting fiber
readout technology
familiar and proven by
tile calorimeter groups
for many years.
• Combination with Anger
Logic readout is costeffective and robust at
high event rates.
5. Other photons pass
through mixer to
photomultiplier tube
2. Interaction
in crystal
releases blue
photons
1. Gamma ray enters
crystal from positron
annihilation
4. Fibers
carry
green light
to sensors
3. Fiber absorbs blue
photons and
fluoresces green
Commercial embodiment
of WLS fiber readout
44 field-replaceable optics modules
11 field-replaceable electronics modules
11 parallel readout commercial PCs
PDS/Analogic PET/CT Prototype
Key to High Sensitivity and
Low Cost: CsI(Na) Scintillator
• CsI(Na) developed
at Kharkhov in
collaboration with
Budker Instititute
in Novosibirsk
• Much lower cost
to manufacture
than alternatives
– Low melting point
– Low cost raw
materials
• But slower decay
Accurate High-Throughput Data
Acquisition and Signal Processing
• Fully digital, including
digital triggering (unique
to PDS)
• Digital waveform signal
processing
• Fully buffered to eliminate
downstream deadtime
effects
• Cost-effective
Programmable Logic
Array Design
Key to High-throughput
Data Processing:
Parallel Readout
• Unique to PDS
design
• Organizes lines-ofresponse into ordered
pairs.
• Uniformly distributes
data acquisition and
data processing
workload
• Built on a
commercial off-theshelf Linux cluster
1
2
11
10
3
9
4
5
8
3 slaves
6
7
1
2
11
10
3
9
4
5
8
7
3 masters
6
Optimal Use of Measured Data -Diversity Signal Processing
• List mode event data
packet:
( xi , yi , zi );( x j , y j , z j ); Ei , E j , ti, j
Total
• Weight each event by
probability it is a True
• Mathematically optimal
statistical treatment of
diverse events
• Unique to PDS
Trues + Scatters
Randoms
Statistically principled
fully-3D Maximum-Likelihood
Image Reconstruction
• Factorized
precalculated
formulation unique to
PDS
• Based on previously
unnoticed symmetry
• Custom hardware
parallel processing
reconstruction
accelerator
Continuous Bed
Motion combined
with fully-3D
reconstruction
• Coordinate transformation
to “virtual detector” which
is co-moving with patient.
• PDS first to combine this
with fully 3D reconstruction
Physical Detector
Front View
SSpace
S
Physical Detector
Side View

Virtual Detector
Side View
Axial Direction
ZSpace
Z

Physical Detector
Side View
Virtual Detector
Side View
The Future of PET/CT
• The Multi-slice CT revolution
• Radiation Therapy applications of
PET/CT
• New and Emerging Radiotracers
– Molecular Imaging and Molecular Medicine
– Personalized Medicine
PET/CT and new
Multi-slice CTs
Customers are demanding top
CT performance in PET/CTs, with
Cardiac applications leading the way.
(CT Angiography)
PET/CT and Radiation Therapy
• IMRT – Intensity
Modulated Radiation
Therapy directs beams
with greater accuracy
• IGRT – Image Guided
Radiation Therapy
gives direction by
imaging organs at
delivery time
• FIGRT – Functional
Image Guided
Radiation Therapy on
the near horizon
Emerging
HighSpecificity
Radiotracers
Ga-68 DOTATOC
binds to somatostatin
receptors overexpressed
by neuroendocrine
tumors
PET and Molecular Imaging
Things I Learned From Larry
• Love what you’re doing and let it show
– It’ll make people want to join your team
• Talk fast, life is short
– Assume your audience is quick on the uptake
• Put your best foot forward
– No one else will do it for you
• Swing for the fences
– Who knows how many at-bats you’ll get