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LUND UNIVERSITY LIBRARIES

Performance Assessment of Cerenkov Emission Imaging

Mellhammar, Emma (2013) MSFT01 20131
Medical Physics Programme
Medical Radiation Physics, Lund
Abstract (Swedish)
Laddade partiklar med hög energi kan ibland färdas snabbare än ljusets hastighet i det medium det för stunden befinner sig i. När detta sker, emitteras så kallat Cerenkovljus. Ljuset ligger inom det synliga spektret och kan alltså detekteras med vanlig kamerateknik.

Många av de radionuklider som används för nukleärmedicinska undersökningar och terapier emitterar högenergetiska laddade partiklar när de sönderfaller. Dessa kan få tillräckligt hög hastighet för att vid passage genom kroppen emittera Cerenkovljus.

Nukleärmedicinska radionuklider används även för prekliniska metoder och tidigare studier har visat att Cerenkov Luminance Imaging (CLI), en metod där man studerar det emitterade Cerenkov ljuset från försöksdjur injicerade med... (More)
Laddade partiklar med hög energi kan ibland färdas snabbare än ljusets hastighet i det medium det för stunden befinner sig i. När detta sker, emitteras så kallat Cerenkovljus. Ljuset ligger inom det synliga spektret och kan alltså detekteras med vanlig kamerateknik.

Många av de radionuklider som används för nukleärmedicinska undersökningar och terapier emitterar högenergetiska laddade partiklar när de sönderfaller. Dessa kan få tillräckligt hög hastighet för att vid passage genom kroppen emittera Cerenkovljus.

Nukleärmedicinska radionuklider används även för prekliniska metoder och tidigare studier har visat att Cerenkov Luminance Imaging (CLI), en metod där man studerar det emitterade Cerenkov ljuset från försöksdjur injicerade med radionuklider, skulle kunna användas för prekliniska studier av nukleärmedicinska terapier och läkemedel.

När ljus färdas genom vävnad kommer det spridas och absorberas och endast en liten del av ljuset, om något, kommer ta sig upp till ytan. Om man ska kunna kvantifiera vilken mängd radioaktivitet som gett upphov till ljuset, måste man ta reda på hur ljuset har påverkats av sin färd mot ytan.
I detta arbete utfördes så kallade fantommätningar för att studera hur spridning, absorption och djup i vävnad påverkar vilken mängd ljus man kan detektera. Fantomen bestod av mus-stora epoxiharts-block med olika optiska egenskaper som fick dem att absorbera och sprida ljuset olika mycket. Genom fantomen hade kanaler borrats med varierande avstånd till ytan för att simulera aktivitetsupptag på olika djup i en muskropp. Försöken gjordes med en ljustät låda som stänger ute vanligt ljus och en så kallad CCD-kamera monterad inuti lådan som kan detektera ljuset. Fantomen fylldes med radionukliden 18F, en vanlig nuklid vid PET-undersökningar och placerades i CLI-lådan. Bilder med varierande insamlingstid togs upprepade gånger under flera timmars tid, medan aktivitetsinnehållet i fantomen sönderföll.

För att jämföra CLI:s potential som nukleärmedicinsk bildverktyg utfördes Positronemissionstomografi (PET)-undersökningar av samma fantom med 18F i tre olika prekliniska PET-system, däribland det box-geometriska systemet Genisys4.
Resultaten visade att radiansen sjönk som funktion av djupet och för stigande absorptionsegenskaper i fantomens material. Spridande partiklar i fantomen ökade radiansen. Upplösningen blev sämre för ökande djup och för stigande mängd spridande partiklar. Absorberande material förbättrade upplösningen något.

Resultaten visade på de hinder som måste överbryggas för att CLI ska kunna användas som ett kvantitativt nukleärmedicinskt bildverktyg, eftersom ljuset som detekteras inte direkt kan översättas till ett radionuklidupptag i muskroppen. Först måste radiansen normeras mot en effektiv attenueringskoefficient som beskriver hur ljusets intensitet förändras på sin väg mot ytan. Dessutom kommer CLI bara kunna användas till ytligt belägna aktivitetsupptag, så som tumörer implanterade under huden på försöksdjur. (Less)
Abstract
Background: Cerenkov Luminescence Imaging detects the light emitted when a charged particle travels through a medium with a velocity greater than the phase velocity of light in that medium. The beta-particles emitted from many radionuclides used in nuclear medicine have sufficient kinetic energy to satisfy the requirement.

Purpose: This thesis aimed to examine the physical and optical properties affecting the radiance of Cerenkov radiation measured in the new imaging modality Cerenkov Luminescence Imaging (CLI). In difference to established preclinical imaging modalities detecting radionuclides such as Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT), CLI detects Cerenkov emission. This radiation... (More)
Background: Cerenkov Luminescence Imaging detects the light emitted when a charged particle travels through a medium with a velocity greater than the phase velocity of light in that medium. The beta-particles emitted from many radionuclides used in nuclear medicine have sufficient kinetic energy to satisfy the requirement.

Purpose: This thesis aimed to examine the physical and optical properties affecting the radiance of Cerenkov radiation measured in the new imaging modality Cerenkov Luminescence Imaging (CLI). In difference to established preclinical imaging modalities detecting radionuclides such as Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT), CLI detects Cerenkov emission. This radiation is within the optical spectral range, as opposed to high energy photons emitted as a product of the radioactive decay. Better understanding of these properties could possibly enable quantitative measurements of radionuclide uptake in animal tumor models.

Materials and method: Mouse-sized phantoms of varying scattering and absorbing properties with channels drilled at different depths were filled with 18F and imaged with a laboratory-built CLI-system. Images of varying exposure times were collected repeatedly during a number of half-lives of 18F. The radiance and FWHM were analyzed with MATLAB and the custom-made MATLAB-program OptiScope. For comparison to established imaging modalities, the phantoms were imaged in three different preclinical PET-systems, including the box-geometry system Genisys4 (Sofie BioSciences).

Results: The radiance of the Cerenkov radiation was found to be proportional to the activity present in the channels of the phantoms. Increasing depth of the cannels was found to decrease the radiance measured, as did increasing absorption coefficient. An increasing scattering coefficient was found to increase the radiance over the range examined. Increasing depth and scattering coefficient showed a broadening of the FWHM, while an increasing absorption coefficient narrowed the FWHM. The FWHM measured for a variety of depths down to 1 cm and varying scattering and absorption coefficients, ranged between 0.4- 3.8 cm.

Conclusion: CLI is limited by its complicated relationship between activity and radiance. Due to the many factors affecting the emitted light at the surface of the phantoms, the radiance could not directly be used as a quantitative measurement of the activity uptake. For this to be possible some form of normalization for the effective attenuation coefficient would be needed and the imaging could only be done for uptakes close to the surface of the subject. The coefficient could be assessed with an external light source.
CLI will never challenge PET as an equally efficient quantitative imaging modality for preclinical imaging, but could become a part of an imaging scheme where a combination of modalities is used to utilize the benefits of each system. (Less)
Please use this url to cite or link to this publication:
author
Mellhammar, Emma
supervisor
organization
course
MSFT01 20131
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
4192067
date added to LUP
2013-12-06 11:18:12
date last changed
2017-01-09 16:32:54
@misc{4192067,
  abstract     = {Background: Cerenkov Luminescence Imaging detects the light emitted when a charged particle travels through a medium with a velocity greater than the phase velocity of light in that medium. The beta-particles emitted from many radionuclides used in nuclear medicine have sufficient kinetic energy to satisfy the requirement.

Purpose: This thesis aimed to examine the physical and optical properties affecting the radiance of Cerenkov radiation measured in the new imaging modality Cerenkov Luminescence Imaging (CLI). In difference to established preclinical imaging modalities detecting radionuclides such as Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT), CLI detects Cerenkov emission. This radiation is within the optical spectral range, as opposed to high energy photons emitted as a product of the radioactive decay. Better understanding of these properties could possibly enable quantitative measurements of radionuclide uptake in animal tumor models.

Materials and method: Mouse-sized phantoms of varying scattering and absorbing properties with channels drilled at different depths were filled with 18F and imaged with a laboratory-built CLI-system. Images of varying exposure times were collected repeatedly during a number of half-lives of 18F. The radiance and FWHM were analyzed with MATLAB and the custom-made MATLAB-program OptiScope. For comparison to established imaging modalities, the phantoms were imaged in three different preclinical PET-systems, including the box-geometry system Genisys4 (Sofie BioSciences).

Results: The radiance of the Cerenkov radiation was found to be proportional to the activity present in the channels of the phantoms. Increasing depth of the cannels was found to decrease the radiance measured, as did increasing absorption coefficient. An increasing scattering coefficient was found to increase the radiance over the range examined. Increasing depth and scattering coefficient showed a broadening of the FWHM, while an increasing absorption coefficient narrowed the FWHM. The FWHM measured for a variety of depths down to 1 cm and varying scattering and absorption coefficients, ranged between 0.4- 3.8 cm.

Conclusion: CLI is limited by its complicated relationship between activity and radiance. Due to the many factors affecting the emitted light at the surface of the phantoms, the radiance could not directly be used as a quantitative measurement of the activity uptake. For this to be possible some form of normalization for the effective attenuation coefficient would be needed and the imaging could only be done for uptakes close to the surface of the subject. The coefficient could be assessed with an external light source.
CLI will never challenge PET as an equally efficient quantitative imaging modality for preclinical imaging, but could become a part of an imaging scheme where a combination of modalities is used to utilize the benefits of each system.},
  author       = {Mellhammar, Emma},
  language     = {eng},
  note         = {Student Paper},
  title        = {Performance Assessment of Cerenkov Emission Imaging},
  year         = {2013},
}