ASLI YILDIRIM

Medical applications of particle physics

General characteristics of detectors (5th Chapter)ASLI YILDIRIMAPPLICATIONS OF PARTICLE PHYSICSMedical applications such as producing X rays, protons, neutrons for diagnostic or treatment purposes.Security such as nuclear waste monitoringIndustry Biomedicine

MEDICAL IMAGINGX RaysComputational TomographyMagnetic Resonance ImagingUltrasoundPositron Emission Tomography

MEDICAL IMAGINGX RaysComputational TomographyMagnetic Resonance ImagingUltrasoundPositron Emission Tomography

Positron Emission Tomography

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

Examples of radiotracer Radioactive chemical that can be injected into vein, swallowed or inhaledProduced in cyclotron

Positron Emission

Compton scattering and photoelectric absorptionPhoton can loose energy through Compton scattering and scattering changes direction of photon

Under certain energy levels, photon can be absorbed by an atom.

Detection

Scattered coincidence

After first detection, one of detected photons has undergone Compton scatteringRandom coincidence Two photon from different annihilation

PET DetectorPhoto sensor

Pre-AmplifierElectronics Scintillation crystalGamma raysIts converts gamma rays to optical photonsIt converts light into electrical signalIt prepares the signal for computational processing Scintillatior

Spatial resolution

Thinner detectors give better resolution and better images but they have lower sensivityThicker detectors improve sensitivity, but spatial resolution becomes worseDetectorsPMT

Solid state detectors

Photodiodes

Silicon PMT

PhotodiodesAvalanche photodiodes

PMT

SPMT

PD

SSDProperties of system Spatial resolution is 1- 5 mmDetection efficiency is higher than 30 % Time resolution is 1-10 nsEnergy resolution is about 20 % Can detect 107-108 eventsExpensive

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

General characteristics of detectors (5th Chapter)

Transfer all the radiation energy into detector mass, then we can observe it.SensivityCapability of producing signal for a given radiationCross section for ionizing reactionsDetector massDetector noiseProtective material

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

Response functionSpectrum of pulses observed in detector when monoenergetic beam is sent to detectorRelated to different interactions , design and geometryExample

Dead time Required time for detector to process an eventAll other electronics have their own dead times

Extendable-Nonextendable dead times

Extendable occurs when detector does not loose its sensitivity during dead timeNon-extendable occurs when detector looses its sensitivity during dead timeDetector efficiency Intrinsic EfficiencyRelated to radiation interacting with detector

Geometric EfficiencyRelated to part of the radiation which is intercepted by detector.

ReferencesW.R Leo, Techiniques for nuclear and particle physics experiments, pages 107-118http://depts.washington.edu/nucmed/IRL/pet_intro/toc.html, accessed on 11/14/2010www.bnl.gov/ncss/files/.../NucChemSummerSchool-072106-v2.ppt, accessed on 11/14/2010www.physics.usyd.edu.au/astromed09/Talks/Day2/Cherry_invited.ppt, accessed on 11/14/2010www.fnal.gov/gridfest/pdfs/benefits_factsheet.pdf, accessed on 11/14/2010www.physics.ucla.edu/~arisaka/.../Physics89_PET.pdf, accessed on 11/14/2010http://serc.carleton.edu/research_education/geochemsheets/techniques/CT.html, accessed on 11/14/2010http://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