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

We have discovered a new inorganic single crystal scintillator [1], lutetium oxyorthosilicate doped with cerium, Lu2(SiO4)O:Ce (or “LSO”), which has a unique combination of properties including high emission intensity, fast decay time, high density, and high atomic number. These properties result in excellent signal-to-noise, fast coincidence timing, high count-rate capability, and high detection efficiency making LSO superior to any other known scintillator for many applications. This new scintillator has several important advantages over the scintillator crystals currently used for the detection of gamma rays or X-rays in applications such as medical imaging, nuclear and particle physics, and geophysical exploration. Here we compare the properties of LSO to those of the two most widely used scintillators, namely thallium-doped sodium iodide and bismuth germanate.

A promising new scintillator: cerium-doped lutetium oxyorthosilicate

Measurements performed by a thermoluminescence sensitivity technique of the degree of metamorphism experienced by unequilibrated ordinary chondrites are reported. Samples of type 3 chondrites were ground and heated to 500 C to remove their natural thermoluminescence, then irradiated with either 50 krad from a Co-60 gamma ray source or 25 krad from a Sr-90 beta source. The resulting thermoluminescence measured as a function of temperature is found to differ as much among some type 3 chondrites as between type 3 and other types, leading to the proposal of scheme for subdividing type 3 ordinary chondrites based on their thermoluminescence sensitivity.

Measuring metamorphic history of unequilibrated ordinary chondrites

In PET, inorganic scintillator crystals are used to record gamma-rays produced by the annihilation of positrons emitted by injected tracers. The ultimate performance of the camera is strongly tied to both the physical and scintillation properties of the crystals. For this reason, researchers have investigated virtually all known scintillator crystals for possible use in PET. Despite this massive research effort, only a few different scintillators have been found that have a suitable combination of characteristics, and only 2 (thallium-doped sodium iodide and bismuth germanate) have found widespread use. A recently developed scintillator crystal, cerium-doped lutetium oxyorthosilicate, appears to surpass all previously used materials in most respects and promises to be the basis for the next generation of PET cameras.

https://jnm.snmjournals.org/content/jnumed/41/6/1051.full.pdf

Scintillation crystals for PET.

Gamma-ray and UV-excitation of cerium-doped rare-earth oxyorthosilicates (RE = Y, Gd, and Lu) has been used to investigate the emission mechanism for this family of scintillators. The data clearly indicate the presence of two different luminescence centers, which are attributed to cerium substitution in the two different rare-earth crystallographic sites. While this model explains much of the present and previous UV data, the gamma-ray induced emission from GSO requires a better understanding of the energy transfer between Gd and Ce.

Charles L. Melcher

Papers

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

A promising new scintillator: cerium-doped lutetium oxyorthosilicate

Measuring metamorphic history of unequilibrated ordinary chondrites

Scintillation crystals for PET.

UV and gamma-ray excited luminescence of cerium-doped rare-earth oxyorthosilicates