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ASLI YILDIRIM

ASLI YILDIRIM. Medical applications of particle physics General characteristics of detectors (5 th Chapter). APPLICATIONS OF PARTICLE PHYSICS. Medical applications such as producing X rays, protons, neutrons for diagnostic or treatment purposes. Security such as nuclear waste monitoring

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ASLI YILDIRIM

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  1. ASLI YILDIRIM Medical applications of particle physics General characteristics of detectors (5th Chapter)

  2. APPLICATIONS OF PARTICLE PHYSICS • Medical applications such as producing X rays, protons, neutrons for diagnostic or treatment purposes. • Security such as nuclear waste monitoring • Industry • Biomedicine

  3. MEDICAL IMAGING • X Rays • Computational Tomography • Magnetic Resonance Imaging • Ultrasound • Positron Emission Tomography

  4. MEDICAL IMAGING • X Rays • Computational Tomography • Magnetic Resonance Imaging • Ultrasound • Positron Emission Tomography

  5. Positron Emission Tomography * After injecting radiotracer to human body, gamma rays produced and detected. * This information is transformed into images by using tomography tecniniques.

  6. PET images

  7. Examples of radiotracer • Radioactive chemical that can be injected into vein, swallowed or inhaled • Produced in cyclotron

  8. Positron Emission

  9. Compton scattering and photoelectric absorption • Photon can loose energy through Compton scattering and scattering changes direction of photon • Under certain energy levels, photon can be absorbed by an atom.

  10. Detection

  11. Scattered coincidence After first detection, one of detected photons has undergone Compton scattering

  12. Random coincidence Two photon from different annihilation

  13. PET Detector Gamma rays Photo sensor • → Scintillation crystal Pre-Amplifier Electronics Its converts gamma rays to optical photons It converts light into electrical signal It prepares the signal for computational processing

  14. Scintillatior • Spatial resolution

  15. Thicker detectors improve sensitivity, but spatial resolution becomes worse → → Thinner detectors give better resolution and better images but they have lower sensivity

  16. Detectors • PMT • Solid state detectors • Photodiodes • Silicon PMT Photodiodes Avalanche photodiodes PMT PD SPMT SSD

  17. Properties of system • Spatial resolution is 1- 5 mm • Detection efficiency is higher than 30 % • Time resolution is 1-10 ns • Energy resolution is about 20 % • Can detect 107-108events • Expensive

  18. Computed Tomography • Computed x-ray tomography is a technique in which the x-ray source and detector screen are moved in opposite directions • Also system moves around object to produce images slices that can be converted into 3d picture

  19. General characteristics of detectors (5th Chapter)

  20. Transfer all the radiation energy into detector mass, then we can observe it.

  21. Sensivity • Capability of producing signal for a given radiation • Cross section for ionizing reactions • Detector mass • Detector noise • Protective material

  22. Detector response Response is relation between radiation energy and output signal. Energy Resolution Ability of distinguish very close energy levels

  23. Response function • Spectrum of pulses observed in detector when monoenergetic beam is sent to detector • Related to different interactions , design and geometry

  24. Example

  25. Dead time • Required time for detector to process an event • All other electronics have their own dead times

  26. Extendable-Nonextendable dead times Non-extendable occurs when detector looses its sensitivity during dead time Extendable occurs when detector does not loose its sensitivity during dead time

  27. Detectorefficiency • Intrinsic Efficiency • Related to radiation interacting with detector • Geometric Efficiency • Related to part of the radiation which is intercepted by detector.

  28. References • W.R Leo, Techiniques for nuclear and particle physics experiments, pages 107-118 • http://depts.washington.edu/nucmed/IRL/pet_intro/toc.html, accessed on 11/14/2010 • www.bnl.gov/ncss/files/.../NucChemSummerSchool-072106-v2.ppt, accessed on 11/14/2010 • www.physics.usyd.edu.au/astromed09/Talks/Day2/Cherry_invited.ppt, accessed on 11/14/2010 • www.fnal.gov/gridfest/pdfs/benefits_factsheet.pdf, accessed on 11/14/2010 • www.physics.ucla.edu/~arisaka/.../Physics89_PET.pdf, accessed on 11/14/2010 • http://serc.carleton.edu/research_education/geochemsheets/techniques/CT.html, accessed on 11/14/2010 • http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/MedicalImaging/MedicalX-Rays/ucm115317.htm#5, accessed on 11/14/2010 • www.jsgreen.tamu.edu/427%205%20Medical%20imaging.ppt, accessed on 11/14/2010

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