Optical Materials for Medical Applications: an Overview of Ultrafast Emitting Oxidic Pr 3+ Scintillating Materials
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Optical Materials for Medical Applications: an Overview of Ultrafast Emitting Oxidic Pr3+ Scintillating Materials Cees Ronda1,2,3, Joanna Gondek4, Emilie Goirand4, Thomas Jüstel4, Marco Bettinelli5 and Andries Meijerink2, 1 Philips Research Europe-Aachen, Weisshausstrasse 2, D-52066 Aachen, Germany 2 Department of Condensed Matter, Debye Institute, Utrecht University, P. O. Box 80 000, 3508 TA Utrecht, The Netherlands 3 Zhejiang University, Centre for Optical and Electromagnetic Research, Hangzhou 310058, China 4 University of Applied Sciences Münster, Stegerwaldstr. 39 D-48565 Steinfurt, Germany 5 Department of Science and Technology, University of Verona, and INSTM, UdR Verona, Strada Le Grazie 15, 37134 Verona, Italy ABSTRACT This paper describes an investigation towards very fast emitting oxidic luminescent materials doped with Pr3+. Such materials have the potential to be applied as scintillators in Positron Emission Tomography. INTRODUCTION Luminescent materials converting X-rays or γ-rays into UV or visible photons (scintillators) are in the zenith of current interest. Equipment based on such materials can be used to detect radioactive material, f.i. at airports or borders. They can also be used for medical examinations, like for example in computed tomography (CT) or positron emission tomography (PET). Especially in PET, the materials have to fulfill harsh conditions, such as: a large stopping power, a very fast decay, the virtual absence of afterglow and a high light yield. In this paper, we first give a short overview of the medical imaging modalities CT and PET. We then concentrate on the development of luminescent materials for PET, translating the application requirements into material properties. We then describe our research on fast emitting oxidic Pr3+ doped scintillating materials. The paper ends with an outlook. THE IMAGING MODALITIES CT AND PET [rewritten from 1] In CT, the attenuation of X-rays through the body is measured as the source-detector combination rotates 360° in a plane around the patient (Figure 1). The X-ray tube and the detectors are rigidly coupled and the source-detector combination generally executes the 360o rotation within 1-2 seconds. The fan shaped beam consists of as many individual beams as there are detectors. The beam of X-rays passes through a cross sectional slice of patient and strikes the detector. In this way an anatomical image of the body is obtained. In modern CT machines, ceramic scintillators are used, i.e. the luminescent material is not single crystalline.
Fig. 1. Schematic outline of a CT machine. The object in the middle symbolises the patient. The small circle at the left is the x-ray source which generates a fan beam; on the right hand side, the position sensitive detector containing the ceramic scintillators is located.
In PET, the patient is first injected with a radioactive material that emits positrons. The positrons rapidly thermalize within the body tissue and the annihilation of each positron with an electron produces two 511 keV γ-r
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