The 5d level positions of the trivalent lanthanides in inorganic compounds

Positron emission tomography (PET) provides metabolic information that has been documented to be useful in patient care. The properties of positron decay permit accurate imaging of the distribution of positron-emitting radiopharmaceuticals. The wide array of positron-emitting radiopharmaceuticals has been used to characterize multiple physiologic and pathologic states. PET is used for characterizing brain disorders such as Alzheimer disease and epilepsy and cardiac disorders such as coronary artery disease and myocardial viability. The neurologic and cardiac applications of PET are not covered in this review. The major utilization of PET clinically is in oncology and consists of imaging the distribution of fluorine 18 fluorodeoxyglucose (FDG). FDG, an analogue of glucose, accumulates in most tumors in a greater amount than it does in normal tissue. FDG PET is being used in diagnosis and follow-up of several malignancies, and the list of articles supporting its use continues to grow. In this review, the ph...

Clinical Applications of PET in Oncology

The authors discuss a single-crystal inorganic scintillator, cerium-doped lutetium oxyorthosilicate (Lu/sub 2(1-x)/Ce/sub 2x/(SiO/sub 4/) or LSO). It has a scintillation emission intensity which is approximately 75% of NaI(Tl) with a decay time of approximately 40 ns. The peak emission wavelength is 420 nm. It has a very high gamma-ray detection efficiency due to its density of 7.4 g/cm/sup 3/ and its effective atomic number of 66. Its radiation length of 1.14 cm is only slightly longer than bismuth germanate (BGO). The scintillation properties of Ce-doped LSO are compared to NaI(Tl), BGO, and cerium-doped gadolinium oxyorthosilicate (GSO). In addition to desirable physical properties such as high density and high atomic number, LSO also processes a combination of high emission intensity and fast decay which together are superior to any other known single crystal scintillator. >

Cerium-doped lutetium oxyorthosilicate: a fast, efficient new scintillator

Garnets have the general formula of A3B2C3O12 and form a wide range of inorganic compounds, occurring both naturally (gemstones) and synthetically. Their physical and chemical properties are closely related to the structure and composition. In particular, Ce3+-doped garnet phosphors have a long history and are widely applied, ranging from flying spot cameras, lasers and phosphors in fluorescent tubes to more recent applications in white light LEDs, as afterglow materials and scintillators for medical imaging. Garnet phosphors are unique in their tunability of the luminescence properties through variations in the {A}, [B] and (C) cation sublattice. The flexibility in phosphor composition and the tunable luminescence properties rely on design and synthesis strategies for new garnet compositions with tailor-made luminescence properties. It is the aim of this review to discuss the variation in luminescence properties of Ce3+-doped garnet materials in relation to the applications. This review will provide insight into the relation between crystal chemistry and luminescence for the important class of Ce3+-doped garnet phosphors. It will summarize previous research on the structural design and optical properties of garnet phosphors and also discuss future research opportunities in this field.

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Ce3+-Doped garnet phosphors: composition modification, luminescence properties and applications.

The recent introduction of high-resolution molecular imaging technology is considered by many experts as a major breakthrough that will potentially lead to a revolutionary paradigm shift in health care and revolutionize clinical practice. This paper intends to balance the capabilities of the two major molecular imaging modalities used in nuclear medicine, namely positron emission tomography (PET) and single photon emission computed tomography (SPECT). The motivations are many-fold: (1) to gain a better understanding of the strengths and limitations of the two imaging modalities in the context of recent and ongoing developments in hardware and software design; (2) to emphasize that certain issues, historically and commonly thought as limitations of one technology, may now instead be viewed as challenges that can be addressed; (3) to point out that current state of the art PET and SPECT scanners can (greatly) benefit from improvements in innovative image reconstruction algorithms; and (4) to identify important areas of research in PET and SPECT imaging that will be instrumental to further improvements in the two modalities. Both technologies are poised to advance molecular imaging and have a direct impact on clinical and research practice to influence the future of molecular medicine.

PET versus SPECT: strengths, limitations and challenges

Czochralski growth of rare earth oxyorthosilicate single crystals

A scintillator for use as a gamma ray or like radiation detector is composed of a single crystal of cerium-activated lutetium oxyorthosilicate having the general formulation Ce 2x Lu 2 (1-x) SiO 5 . In a borehole logging application, the detector is mounted in a logging sonde with a high energy neutron source, for movement through a borehole traversing earth formations. Gamma radiation from the surrounding formations is detected and analyzed to provide information concerning hydrocarbons in the formations.

Lutetium orthosilicate single crystal scintillator detector

The renewed interest in time-of-flight (TOF) positron emission tomography (PET) has been accompanied by new research in the development of fast scintillators, mainly halides and/or lutetium-based compounds doped with Ce or Pr. In this work we measure some intrinsic properties of these materials, such as decay time and light output, which have a direct effect on time resolution, the key performance parameter for a TOF-grade detector. In particular, we report on measurements on LSO:Ce, LuAG:Pr, LuYAP:Ce, LaBr3:Ce and LaCl3:Ce. The scintillators are characterized in terms of absolute light yield, decay time, energy resolution, emission and excitation spectra, and time resolution. A new figure of merit to compare scintillators based on their performance in a TOF PET scanner is introduced. This figure of merit, the TOF effective sensitivity eta , includes both interaction probability and timing characteristics.

Comparison of Fast Scintillators With TOF PET Potential

Experimental studies of Lu2SiO5:Ce (LSO:Ce) crystals codoped with various concentrations of Ca (0, 0.1, 0.2, 0.3, and 0.4 at% in the melt) are presented. The scintillation and optical properties including photoluminescence decay, emission, excitation, absorption, afterglow and thermoluminescence properties are investigated as a function of Ca concentration. Experimental data show Ca codoping significantly reduces the trapped charge population in the crystal matrix. Hence, the scintillation decay time of LSO:Ce is shortened and the afterglow is suppressed. Thermoluminescence studies show a strong correlation between the integrated thermoluminescence intensity and the Ca concentration.

Effects of Calcium Codoping on Charge Traps in LSO:Ce Crystals

This work presents the results from experiments performed on Lu/sub 2/SiO/sub 5/:Ce (LSO:Ce). It looks for potential correlations of light yield nonproportionality and other scintillation properties such as intrinsic energy resolution with thermoluminescence properties. The analyzed samples were chosen from various crystal batches having significantly different properties. Single crystal LSO:Ce samples were coupled to an XP2020Q photomultiplier and to large area avalanche photodiodes and measured as a function of /spl gamma/-ray energy between 14.7 and 1770 keV at room temperature and also near liquid nitrogen temperature. To explain the experimental results obtained from spectrometric methods, the properties of the samples were further studied using thermoluminescence techniques within the temperature range from 250K to 600K. The relationships between data obtained from these two types of experiments are reported.

Charles L. Melcher

Papers

Czochralski growth of rare earth oxyorthosilicate single crystals

Lutetium orthosilicate single crystal scintillator detector

Comparison of Fast Scintillators With TOF PET Potential

Effects of Calcium Codoping on Charge Traps in LSO:Ce Crystals

Non-proportionality and thermoluminescence of LSO:Ce