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

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

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

MEDICAL IMAGING X Rays Computational Tomography Magnetic Resonance Imaging Ultrasound 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 inhaled Produced in cyclotron

Positron Emission

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.

Detection

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

Random coincidence Two photon from different annihilation

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

Scintillatior - Spatial resolution

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

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

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 events Expensive

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

General characteristics of detectors (5 th Chapter)

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

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

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

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

Example

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

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

Detector efficiency Intrinsic Efficiency Related to radiation interacting with detector Geometric Efficiency Related to part of the radiation which is intercepted by detector.

References W.R Leo, Techiniques for nuclear and particle physics experiments, pages accessed on 11/14/ accessed on 11/14/ accessed on 11/14/ accessed on 11/14/ accessed on 11/14/ accessed on 11/14/ EmittingProducts/RadiationEmittingProductsandProcedures/MedicalImaging/Medical X-Rays/ucm htm#5, accessed on 11/14/ EmittingProducts/RadiationEmittingProductsandProcedures/MedicalImaging/Medical X-Rays/ucm htm#5, accessed on 11/14/2010