1. Very High Resolution Small Animal PET Don J. Burdette Department of Physics

2. What is PET? Answer: Cancerous cells have a higher metabolism than normal cells, thus PET scans detect cancer. Other Uses for PET include detection of Cardiovascular Disease, Alzheimer’s disease, Parkinson’s disease, epilepsy, and other neurological disorders. Other Uses for PET include detection of Cardiovascular Disease, Alzheimer’s disease, Parkinson’s disease, epilepsy, and other neurological disorders. PET stand for Positron Emission Tomography 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) 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 Unlike MRI and X-Ray (which image bodily structure) PET creates images of metabolic processes Question: Why is imaging metabolic processes important? An image of damaged heart (left) compared to a normal heart (right). The damaged heart has undergone a heart attack. Single slice Example of a PET image

3. How does PET work?

4. Typical Resolution of human full body scans about 10mm There exist other applications for PET technology outside human imaging

5. Small Animal PET Systems biomedical, pharmaceutical, and genetic manipulation researchbiomedical, pharmaceutical, and genetic manipulation research Mice are used as human disease modelsMice are used as human disease models A single mouse can be used to tract disease development and treatment (Important for genetically altered specimens)A single mouse can be used to tract disease development and treatment (Important for genetically altered specimens) Transgenic mouse showing cells with albumin gene switched on Uses of Small Animal PET systems: 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 Example of a Small Animal PET image

6. MicroPET R4 from University of Michigan’s PET center Consists of 8 X 8 array of individual LSO scintillation crystals coupled to 64- channel 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

7. Silicon Detectors Characteristics of ideal Silicon detector for use in PET: Thick detector to increase efficiency (1mm compared to typical 0.3mm thickness)Thick detector to increase efficiency (1mm compared to typical 0.3mm thickness) Small detection pads for excellent spatial resolutionSmall detection pads for excellent spatial resolution Custom made readout chips including an amplifier, and sample-hold switchCustom made readout chips including an amplifier, and sample-hold switch Chips have trigger logic to allow independent silicon operationChips 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

8. Experimental Set-up Mechanical Set-up In collaboration with the University of Michigan

9. 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…

10. Reconstructing the Data for a Simulated Disk Source Projection of previous image with and without filtering Blue line = unfiltered data Green line = filtered data The narrower the peak, the higher the resolution = sharper image

11. Reconstructing the Data for a Simulated Point Source Image of Disk Source after filtering and transforming back to position space

12. Reconstructing the Data for a Simulated Disk Source Original ImageFiltered Image

13. Experimental Results Our small animal PET set-up Our small animal PET set-up Resolution of 0.7mm Resolution of 0.7mm From microPET R4 set-up From microPET R4 set-up Resolution of 1.8mm Resolution of 1.8mm Images of Flourine-18 source contained in two 1.1-1.2mm capillary tubes with a wall thickness of 0.2mm.

14. 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. 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 efficiencyAdd a stack of silicon detectors to increase efficiency Improve rate capabilities by decreasing coincidence windowImprove 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) 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)

15. References Miles N. Wernick and John N. Aarsvold, editors. Emission Tomography: The Fundamentals of PET and SPECT. Elsevier, Acad Press, 2004. 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. 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. 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 Special Thanks to Neal Clinthorne, Klaus Honscheid, Harris Kagan, Sang-June Park, and Joseph Regensburger