Very High Resolution Small
Animal PET
Don J. Burdette
Department of Physics
What is PET?
PET stand for Positron Emission Tomography
 It is a leading medical imaging technique (more than 200,000 PET scans in
over 700 institutions performed last year in the US)
 Unlike MRI and X-Ray (which image bodily structure) PET creates images of
metabolic processes
Question: Why is imaging metabolic processes important?

Answer: Cancerous cells have a
higher metabolism than normal
cells, thus PET scans detect
Example of a PET image
cancer.
Other Uses for PET include detection
of Cardiovascular Disease,
Alzheimer’s disease, Parkinson’s
disease, epilepsy, and other
neurological disorders.
An image of damaged heart (left)
compared to a normal heart (right).
The damaged heart has undergone
a heart attack. Single slice
How does PET work?
How does PET work?
• Typical Resolution of human full body scans about 10mm
• There exist other applications for PET technology outside human imaging
Small Animal PET Systems
Uses of Small Animal PET systems:
•
•
•
biomedical, pharmaceutical, and
genetic manipulation research
Mice are used as human disease
models
A single mouse can be used to
tract disease development and
treatment (Important for
genetically altered specimens)
Example of a Small Animal
PET image
Challenges for Small Animal PET:
• Need resolution of less than 1mm
• Lower doses, high efficiency
Possible Solutions:
• smaller detection elements
• higher efficiency detectors
• Increase solid angle of the detector
Transgenic mouse showing
cells with albumin gene
switched on
MicroPET R4 from University of Michigan’s
PET center
• Consists of 8 X 8 array of individual
LSO scintillation crystals coupled to 64channel PMT
• 15 cm detection ring diameter
• Typical System resolution = 1.8 mm
• Image of two 1.1-1.2mm capillary
tubes filled with Flourine-18 source
Silicon Detectors
Characteristics of ideal Silicon
detector for use in PET:
•
•
•
•
Thick detector to increase efficiency
(1mm compared to typical 0.3mm
thickness)
Small detection pads for excellent
spatial resolution
Custom made readout chips including
an amplifier, and sample-hold switch
Chips have trigger logic to allow
independent silicon operation
Silicon Detector composed of an
array of 32 X 16 pads 1mm thick by
1.4mm X 1.4mm in area
• Small Detection Pixels yield
excellent spatial resolution of the
absorbed photons
• Timing resolution of 200ns
(Coincidence Window)
Americium-241 spectrum
collected by silicon detector
Experimental
Set-up
In collaboration with the
University of Michigan
Mechanical Set-up
Reconstructing the Data for a
Simulated Disk Source
Simple Back-Projection of the data (just drawing the lines)
Fourier transforming this image into frequency space…
Reconstructing the Data for a
Simulated Disk Source
• Blue line = unfiltered data
• Green line = filtered data
• The narrower the peak, the
higher the resolution = sharper
image
Projection of previous image with and without filtering
Reconstructing the Data for a
Simulated Point Source
Image of Disk Source after filtering and
transforming back to position space
Reconstructing the Data for a
Simulated Disk Source
Original Image
Filtered Image
Experimental Results


From microPET R4 set-up
Resolution of 1.8mm
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Our small animal PET set-up
Resolution of 0.7mm
Images of Flourine-18 source contained in two 1.1-1.2mm capillary tubes
with a wall thickness of 0.2mm.
Conclusion and Future Work
Our prototype Small Animal PET achieves a system
resolution below the 1mm goal demonstrating the
usefulness of silicon in Small Animal PET applications.
Future Work includes:
• Add a stack of silicon detectors to increase efficiency
• Improve rate capabilities by decreasing coincidence
window
This can be accomplished by taking advantage of the
Compton scattered photon and using a secondary
detector with faster coincidence timing (Silicon timing
200ns coincidence window, timing from some scintillation
crystals approach 60ns)
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References
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Miles N. Wernick and John N. Aarsvold, editors.
Emission Tomography: The Fundamentals of
PET and SPECT. Elsevier, Acad Press, 2004.
Glenn F. Knoll. Radiation Detection and
Measurement. John Wiley and Sons, Inc. 1989.
Christof Knoess. Performance evaluation of the
Micropet R4 pet scanner of rodents. Eur J Nucl
Med Mol Imaging, 2003.
Special Thanks to Neal Clinthorne, Klaus
Honscheid, Harris Kagan, Sang-June Park, and
Joseph Regensburger