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

A novel way of measuring the non-proportional response of scintillation materials, using a Positron Emission Tomography (PET) scanner, has been developed and tested Using a Siemens Biograph mCT, a modified Compton coincidence technique is performed where the Compton scatter angular information data is collected by taking advantage of the fine angular sampling that is inherent to the PET scanner Using the scatter angle information, the energy deposited in the sampled scintillator can be calculated Comparing the calculated energy deposited versus the measured scintillator response yields the Compton electron non-proportional response

Measuring the non-proportional response of scintillators using a Positron Emission Tomography scanner

In this article, we report on crystal growth, density functional theory (DFT) calculations, and scintillation properties of TlCaX<inline-formula> <tex-math notation="LaTeX">$_{3} (X =$ </tex-math></inline-formula> Cl, Br, I). Crystals were grown by the vertical Bridgman technique in silica ampoules. Crystals of TlCaCl3, TlCaBr3, and TlCaI3 belong to the family of perovskites and have an orthorhombic crystal structure. All three compositions show bright emission under X-ray excitation peaking at 425, 470, and 545 nm, respectively. Light yield increases in the series Cl < Br < I [25 000–47 000 photons/MeV (ph/MeV)].

Crystal Growth, Density Functional Theory, and Scintillation Properties of TlCaX3 (X = Cl, Br, I)

To provide an additional scintillator material which has an increased light yield, increased energy resolution, increased proportionality, reduced light sensitivity, temperature dependence, a long decay time, a short decay time, and/or a shorter startup time.SOLUTION: A scintillator (for example, GdGaAlOor GdGaAlOor other rare earth elements, gallium, aluminum, and garnet) are co-doped with different ions so as to modify a scintillation light yield, a decay time, a startup time, energy resolution, proportionality and/or sensitivity to exposure. Further, there is provided a method for detecting gamma rays, X rays, cosmic rays, and particles having energy of 1 keV or larger using the co-doped garnet type scintillator itself, a radiation detector including the co-doped garnet type scintillator and its relative device, or the radiation detector.SELECTED DRAWING: Figure 1

Scintillation of garnet type scintillator and co-doping method for modifying optical characteristics

The main performance parameters in positron camera system design are sensitivity and spatial resolution. This paper concerns sensitivity, which is a function of the scintillation material, the solid angle subtended by the detector array, and the scintillator packing fraction. The solid angle can be increased by extending the axial extent of cylindrical detector systems. Most commercial positron camera systems are usually based on rings of detector blocks with lutetium oxyorthosilicate, LSO:Ce or LYSO:Ce, as the scintillator of choice. By adding more block detector rings, the solid angle increases while the detection efficiency remains fairly constant assuming the same crystal thickness. It has been shown that Ca co-doping of LSO:Ce reduces the scintillation decay time to ~ 30 ns with a light output over 30000 ph/MeV. This improvement may give a time-of-flight (TOF) advantage with time resolution of 500 to 600 ps or less. If we couple the count rate sensitivity of a large axial field-of-view (AFOV) system to the TOF sensitivity increase, we have the means to create examination times in the sub-minute range with no compromise in image quality. In the present study we have compared the existing Siemens molecular CT (mCT) systems to future 6, 8, 12, 20 and higher block ring systems with and without the TOF advantage. The mCT 4 block ring system has been used as a reference. The time for acceptable image quality with this system is then extrapolated to other systems based on planar sensitivity. However, the planar sensitivity is related to the solid angle, and reaches saturation for large AFOVs. This implies that there is an upper count rate sensitivity limit. A 20 block ring system may cover a 70 cm examination range at a certain planar count rate and could provide acceptable quality images in approximately 10 seconds by combining a high planar sensitivity count rate provided by the multi-ring feature, the high stopping power of LSO and the TOF gain due to the improved timing resolution.

Towards sub-minute PET examination times

The use of Cherenkov light production and timing for TOF PET has been suggested, and there are papers indicating the possibility to improve timing in this way The present paper, however, focuses only on count rate sensitivity issues by comparing a LSO-LSO system against a potential PbF2 system This has been accomplished by using a simple two detector set up first looking at LSO-LSO coincidences and then exchanging the LSO crystal on one of the channels with PbF2 and then extracting the coincidence sensitivity for a pure PbF2 system A simple comparison between the resulting LSO-LSO coincidence count rate and the PbF2-PbF2 coincidence count rate shows more than a 10 to 1 difference In addition we have evaluated the time resolution achievable with two different photo sensor combinations, PMT-PMT and PMT-SiPM Even if a time resolution of 50 ps may be possible to achieve in a PbF2 system, this requires very special photo sensors Our results with standard photo sensors indicate time resolutions of the order of ~250 ps If a 50 ps time resolution can be achieved, this may be equivalent to a 500 ps LSO system with 10 times higher sensitivity One must consider, however, the minimum number of counts needed in a 50 ps system to achieve reasonable image quality In addition to use very fast, photo sensors, these have to have high quantum efficiency from 250 nm up to 600 nm Possible photo sensors for Cherenkov PET may be MCP PMTs

Charles L. Melcher

Papers

Measuring the non-proportional response of scintillators using a Positron Emission Tomography scanner

Crystal Growth, Density Functional Theory, and Scintillation Properties of TlCaX3 (X = Cl, Br, I)

Scintillation of garnet type scintillator and co-doping method for modifying optical characteristics

Towards sub-minute PET examination times

Comparison of count rate sensitivity performance for a LSO-TOF system with a Cherenkov radiation based PbF 2 -TOF system