Maximum Absolute Sensitivity Research Articles

A novel Sm3+ singly doped LiCa3ZnV3O12 phosphor: a potential luminescent material for multifunctional applications.

The Sm3+ ion singly doped LiCa3ZnV3O12 (LCZV) phosphors were synthesized by a traditional high-temperature solid-state method. The luminescence characteristics of the as-prepared samples were studied by photoluminescence excitation and emission spectra. Under 343 nm excitation, the synthesized phosphors exhibited color controllable emission induced by the efficient energy transfer from VO43− groups to Sm3+ ions. Besides, the energy transfer efficiency was revealed to be about 58.4% when the dopant concentration was 4 mol%. By utilizing the as-prepared LCZV:Sm3+ phosphors, commercial BaMgAl10O7:Eu2+ blue-emitting phosphors and a near-ultraviolet light-emitting diode (LED) chip, a white LED device was fabricated. Under an injection current of 100 mA, the packaged LED device emitted pure white light with high color rendering index (88.4) and proper correlated color temperature (4320 K). By analyzing the thermal quenching behavior of the VO43− groups and Sm3+ ions, the optical thermometric behavior of the Sm3+-doped LCZV compounds was investigated. The maximum absolute sensor sensitivity and relative sensor sensitivity were found to be 0.25 K−1 and 1.8% K−1, respectively. Additionally, the emitting color of the studied samples was dependent on the temperature. Ultimately, the Sm3+-doped LCZV phosphors were potential candidates for indoor illumination, optical thermometry and safety signals in high temperature environments.

Self-calibrating optic thermometer based on dual-emission nanocomposite

A new approach to optical thermometers with high sensitivity was developed herein by using In2O3 quantum dots (QDs) emission as temperature detecting signal and Eu3+ ions emission as reference one. Originated from the diverse thermal quenching behavior between the defect-related emission of In2O3 QDs and 4f-4f transitions of Eu3+ ions, fluorescence intensity ratio of In2O3 to Eu3+ in nanocomposite exhibited excellent temperature sensing property in the range from 303 K to 543 K. The maximum absolute and relative temperature sensitivity can reach as high as 4.43 × 10−2 K−1 and 0.89% K−1, respectively. We believe that this work exploits an effective pathway for developing other innovative optical thermometers.

Optical temperature sensing behavior of Er[formula omitted]/Yb[formula omitted]/Tm[formula omitted]:Y[formula omitted]O[formula omitted] nanoparticles based on thermally and non-thermally coupled levels

Er3+/Yb3+/Tm3+ triply doped Y2O3 nanoparticles have been synthesized by solute combustion method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) demonstrate that the prepared particles are cubic Y2O3 phase with the average size of ∼49 nm. The blue (Tm3+: 1G4→3H6), green (Er3+: 2H11∕2, 4S3∕2→4I15∕2) and red (Er3+: 4F9∕2→4I15∕2) upconversion (UC) emissions are observed upon a 980 nm excitation. Applying the fluorescence intensity ratio (FIR) technique, the optical temperature sensing behaviors are studied based on thermally coupled levels (2H11∕2 and 4S3∕2 of Er3+) and non-thermally coupled levels (1G4(b) (Tm3+) and 2H11∕2 (Er3+)), respectively. The results show that the absolute sensing sensitivity is much higher in the entire experimental temperature range, when the non-thermally coupled levels with different temperature dependences (1G4(b) (Tm3+) and 2H11∕2 (Er3+)) are selected as the thermometric index. The maximum absolute sensitivity is found to be as high as ∼1640×10−4 K−1 at 573 K. This demonstrates that an optical temperature sensor with high performance can be designed based on the Er3+/Yb3+/Tm3+:Y2O3 nanoparticles.

NEMA NU-4 Performance Evaluation of the IRIS PET/CT Preclinical Scanner

This paper presents the performance assessment study of the PET component of the IRIS PET/CT according to the National Electrical Manufacturers Association NU 4–2008 standard. The IRIS PET/CT is a high-resolution integrated system for PET and CT imaging of small animals. We evaluated the performance of the PET system, carrying out the following measures: spatial resolution, sensitivity, counting rate capabilities, and image quality parameters. Furthermore, two examples of in vivo experiments are shown. The average energy resolution for a whole module is 14% at 511 keV. The maximum absolute sensitivity for a point source at the center of the field-of-view is 8.0 ± 1.1% for 250–750 keV energy window and 6.6 ± 1.0% for 350–750 keV. The scatter fraction for mouse-like and rat-like phantoms are 15.6% (250–750 keV) and 22.4% (350–750 keV), respectively. Recovery coefficients were measured with the image-quality phantom, providing good results with an image uniformity of 7%. The imaging performance of the IRIS PET are confirmed in the animal experiments. With the IRIS PET/CT, it was possible to derive the time activity curve for various regions of interest with time frame duration down to 5 s, thus enabling the possibility to derive the tracer input function.

Energy transfer, tunable emission and optical thermometry in Tb3+/Eu3+ co-doped transparent NaCaPO4 glass ceramics

Tb3+/Eu3+ co-doped glass ceramics containing NaCaPO4 nanocrystals were successfully synthesized via traditional melt-quenching route with further heat-treatment and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence spectroscopy. The energy transfer process of Tb3+→Eu3+ was confirmed by excitation and emission spectra and luminescence decay curves, and the energy transfer efficiency was also estimated. The results indicated that the efficient emission of Eu3+ was sensitized by Tb3+ under the excitation of 378nm, realizing tunable emission in the transparent bulk glass ceramics containing NaCaPO4 nanocrystals. Furthermore, optical thermometry was achieved by the fluorescence intensity ratio between Tb3+:5D4→7F5 (~542nm) and Eu3+:5D0→7F2 (~612nm). The maximum absolute sensitivity of 4.55% K−1 at 293K and the maximal relative sensitivity of 0.66% K−1 at T=573K for Tb3+/Eu3+ co-doped transparent NaCaPO4 glass ceramic are obtained. It is expected that the investigated transparent NaCaPO4 glass ceramics doped with Tb3+/Eu3+ have prospective applications in display technology and optical thermometry.

NEMA NU4-2008 Performance Evaluation of Albira: A Two-Ring Small-Animal PET System Using Continuous LYSO Crystals

Goals:This paper presents the performance review based on a dual-ring Positron Emission Tomography (PET) scanner being a part of Bruker Albira: a multi-modal small-animal imaging platform. Each ring of Albira PET contains eight detectors arranged as octagon, and each detector is built using a single continuous lutetium-yttrium oxyorthosilicate crystal and multi-anode photo multiplier tube. In two-ring configuration, the scanner covers 94.4 mm in axial- and 80´80 mm in trans-axial direction, which is sufficient to acquire images of small animals (e.g.mice) without the need of moving the animal bed during the scan.Methods:All measurements and majority of data processing were performed according to the NEMA NU4-2008 standard with one exception. Due to the scanner geometry, the spatial resolution test was reconstructed using iterative algorithm instead of the analytical one. The main performance characteristics were compared with those of the other PET sub-systems of tri-modal small-animal scanners.Results:The measured spatial resolution at the centre of the axial field of view in radial, tangential and axial directions was 1.72, 1.70 and 2.45 mm, respectively. The scatter fraction for the mouse-like phantom was 9.8% and for the rat-like phantom, 21.8%. The maximum absolute sensitivity was 5.30%. Finally, the recovery co-efficients for 5, 4, 3, 2, 1 mm diameter rods in image quality phantom were: 0.90, 0.77, 0.66, 0.30 and 0.05, respectively.Conclusion:The Bruker Albira is a versatile small-animal multi-modal device that can be used for variety of studies. Overall the PET sub-system provides a good spatial resolution coupled with better-than average sensitivity and the ability to produce good quality animal images when administering low activities.

A Novel Optical Thermometry Strategy Based on Diverse Thermal Response from Two Intervalence Charge Transfer States

In this work, a novel thermometry strategy based on the diversity in thermal quenching behavior of two intervalence charge transfer (IVCT) states in oxide crystals is proposed, which provides a promising route to design self‐referencing optical temperature sensing material with superior temperature sensitivity and signal discriminability. Following this strategy, uniform Tb3+/Pr3+:NaGd(MoO4)2 micro‐octahedrons are directionally synthesized. Originated from the diverse thermal responses between Tb3+‐Mo6+ and Pr3+‐Mo6+ IVCT states, fluorescence intensity ratio of Pr3+ to Tb3+ in this material displays excellent temperature sensing property in a temperature range from 303 to 483 K. The maximum absolute and relative sensitivity reaches as high as 0.097 K−1 and 2.05% K−1, respectively, being much higher than those of the previously reported optical thermometric materials. Excellent temperature sensing features are also demonstrated in the other Tb3+/Pr3+ codoped oxide crystals having d0 electron configured transition metal ions (Ti4+, V5+, Mo6+, or W6+), such as scheelite NaLu(MoO4)2 and NaLu(WO4)2, and monazite LaVO4 and perovskite La2Ti3O9, evidencing the universal validity of the proposed strategy. This work exploits an effective pathway for developing new optical temperature sensing materials with high performance.

Performance evaluation of the small-animal PET scanner ClairvivoPET using NEMA NU 4-2008 Standards

The aim of this study was to evaluate the performance of ClairvivoPET using NEMA NU4 standards.The ClairvivoPET incorporates a LYSO dual depth-of-interaction detector system with 151 mm axial field of view (FOV). Spatial resolution, sensitivity, counting rate capabilities, and image quality were evaluated using NEMA NU4-2008 standards. Normal mouse imaging was also performed for 10min after intravenous injection of 18F(-)-NaF. Data were compared with 19 other preclinical PET scanners.Spatial resolution measured using full width at half maximum on FBP-ramp reconstructed images was 2.16 mm at radial offset 5 mm of the axial centre FOV. The maximum absolute sensitivity for a point source at the FOV centre was 8.72%. Peak noise equivalent counting rate (NECR) was 415kcps at 14.6MBq ml−1. The uniformity with the image-quality phantom was 4.62%. Spillover ratios in the images of air and water filled chambers were 0.19 and 0.06, respectively. Our results were comparable with the 19 other preclinical PET scanners based on NEMA NU4 standards, with excellent sensitivity because of the large FOV. The ClairvivoPET with iterative reconstruction algorithm also provided sufficient visualization of the mouse spine.The high sensitivity and resolution of the ClairvivoPET scanner provided high quality images for preclinical studies.

Design and evaluation of the MAMMI dedicated breast PET

A breast dedicated positron emission tomography (PET) scanner has been developed based on monolithic LYSO crystals coupled to position sensitive photomultiplier tubes (PSPMTs). In this study, we describe the design of the PET system and report on its performance evaluation. MAMMI is a breast PET scanner based on monolithic LYSO crystals. It consists of 12 compact modules with a transaxial field of view (FOV) of 170 mm in diameter and 40 mm axial FOV that translates to cover up to 170 mm. The patient lies down in a prone position that facilitates maximum breast elongation. Quantitative performance analysis of the calculated method for the attenuation correction specifically developed for MAMMI, and based on PET image segmentation, has also been conducted in this evaluation. In order to fully determine the MAMMI prototype's performance, we have adapted the measurements suggested for National Electrical Manufacturers Association (NEMA) NU 2-2007 and NU 4-2008 protocol tests, as they are defined for whole-body and small animal PET scanners, respectively. Spatial resolutions of 1.6, 1.8, and 1.9 mm were measured in the axial, radial, and tangential directions, respectively. A scatter fraction of 20.8% was obtained and the maximum NEC was determined to be 25 kcps at 44 MBq. The average sensitivity of the system was observed to be 1% for an energy window of (250 keV-750 keV) and a maximum absolute sensitivity of 1.8% was measured at the FOV center. The overall performance of the MAMMI reported on this evaluation quantifies its ability to produce high quality PET images. Spatial resolution values below 3 mm were measured in most of the FOV. Only the radial component of spatial resolution exceeds the 3 mm at radial positions larger than 60 mm. This study emphasizes the need for standardized testing methodologies for dedicated breast PET systems similar to NEMA standards for whole-body and small animal PET scanners.

National Electrical Manufacturers Association NU-4 Performance Evaluation of the PET Component of the NanoPET/CT Preclinical PET/CT Scanner

The NanoPET/CT represents the latest generation of commercial preclinical PET/CT systems. This article presents a performance evaluation of the PET component of the system according to the National Electrical Manufacturers Association (NEMA) NU-4 2008 standard. The NanoPET/CT consists of 12 lutetium yttrium orthosilicate:cerium modular detectors forming 1 ring, with 9.5-cm axial coverage and a 16-cm animal port. Each detector crystal is 1.12 × 1.12 × 13 mm, and 1 module contains 81 × 39 of these crystals. An optical light guide transmits the scintillation light to the flat-panel multianode position-sensitive photomultiplier tubes. Analog-to-digital converter cards and a field-programmable gate array-based data-collecting card provide the readout. Spatial resolution, sensitivity, counting rate capabilities, and image quality were evaluated in accordance with the NEMA NU-4 standard. Energy and temporal resolution measurements and a mouse imaging study were performed in addition to the standard. Energy resolution was 19% at 511 keV. The spatial resolution, measured as full width at half maximum on single-slice rebinning/filtered backprojection-reconstructed images, approached 1 mm on the axis and remained below 2.5 mm in the central 5-cm transaxial region both in the axial center and at one-quarter field of view. The maximum absolute sensitivity for a point source at the center of the field of view was 7.7%. The maximum noise equivalent counting rates were 430 kcps at 36 MBq and 130 kcps at 27 MBq for the mouse- and rat-sized phantoms, respectively. The uniformity and recovery coefficients were measured with the image-quality phantom, giving good-quality images. In a mouse study with an (18)F-labeled thyroid-specific tracer, the 2 lobes of the thyroid were clearly distinguishable, despite the small size of this organ. The flexible readout system allowed experiments to be performed in an efficient manner, and the system remained stable throughout. The large number of detector crystals, arranged with a fine pitch, results in excellent spatial resolution, which is the best reported for currently available commercial systems. The absolute sensitivity is high over the field of view. Combined with the excellent image quality, these features make the NanoPET/CT a powerful tool for preclinical research.

Horizontal hall effect sensor with high maximum absolute sensitivity

The sensitivity of conventional Hall effect sensors is strongly limited by the well-known short-circuit effects. Many researches were devoted to reduce offset and noise, but few works were carried out to improve the sensitivity. Here, a new shape of integrated horizontal Hall effect device is presented. This particular shape has been developed in order to minimize the short-circuit effects in the sensor, allowing to reduce its length to width ratio and consequently to reduce its average resistance. Thus, the biasing current of this sensor can be significantly increased in order to obtain a higher absolute sensitivity than for conventional devices. Such a Hall effect device needs a specific biasing circuit which is also presented, first in a simple version and second in an improved one. A resolution of 32 μT has been reached on a bandwidth of 5 Hz to 1 kHz with a 39×9.2 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> sensor biased with a current of 2.07 mA, the corresponding absolute sensitivity being 195 mV/T. The maximal absolute sensitivity of a so shaped device can be increased as much as needed by increasing its width-to-length ratio, without loss on the current related sensitivity.

Luminescence properties of pyron red—A new molecular probe for protein research

The dependence of the luminescence of the new anionic dye Pyron Red (PR) on the polarity of the medium is investigated. Upon passage from an aqueous phase to a nonpolar phase, PR shows a shortwave shift of the fluorescence emission maximum from 675 to 650 nm and an increase in the fluorescence quantum yield from 0.03 to 0.54–0.70. When complexed with human serum albumin, PR shows fluorescence excitation and emission maxima at 525 and 625 nm and a fluorescence quantum yield of 0.8. In a comparison of the luminescence properties of PR with those of the well-known probes ANS and K35 in water and a complex with albumin, PR is shown to have the maximum absolute sensitivity but a lower fluorescence enhancement upon binding with a protein compared to ANS. A convenient criterion of the probe sensitivity toward binding with a protein that is defined as the ratio of the fluorescence intensities of the protein-bound and the free probe AF=Fb/Ff is proposed. The value of AF(35) for the PR probe ranks between those for the K35 probe with a low AF(18) and ANS with a high AF(105).

Application of Progress Curve Analysis to Enzyme Kinetic Studies Using Radioactive Measurements

Abstract Progress curve analysis has been tested as a method of estimating enzyme kinetic parameters when enzyme activity must be determined by using radiolabeled substrates. The initial concentrations of adenosine have been selected in order to achieve the maximum absolute sensitivity of adenosine with respect to the parameters of the equation. The results obtained show that this method gives the same results as initial-rate analysts and has the advantages that it is faster and cheaper. Kinetic parameter estimates of commercial adenosine deaminase, when [3H] adenosine is used as a substrate, are determined in order to prove the applicability of the procedure.

Dichroism and absorption by photoreceptors

Photoreceptor membrane is dichroic, i.e. its absorption depends on the direction of the electric vectorE of linearly polarised light. Dichroism depends on the arrangement and packing of the membrane (form dichroism) in addition to the orientation and dichroic properties of the chromophores associated with the membrane (intrinsic dichroism). 1. The amount of light absorbed by a photoreceptor depends on the orientation of the dipoles within its membrane. There is an optimum orientation for the photoreceptor to have a maximum absolute sensitivity tounpolarised light andthis orientation depends on the photoreceptor structure. In both vertebrate discs and fly rhabdomeres 1 to 6, the optimum dipole orientation is a random alignment within the plane of the membrane; while in fused rhabdoms the dipoles must be highly aligned with the microvillus axis for maximum absolute sensitivity to unpolarised light. Measurements of dichroism indicate that this optimum dipole orientation is indeed present in vertebrate outer segments, fly rhabdomeres 1 to 6 and the crustacean rhabdom. This furnishes strong evidence for the view that dipoles are orientated in the plane of the membrane to provide the majority of photoreceptors with maximum absolute sensitivity to unpolarised light. Membrane dichroism is only a secondary consequence of this objective [See Section VII]. 2. The measured side-on dichroism of vertebrate outer segments is shown to represent aproduct of form and intrinsic dichroism, where the form factor is approximately 1.6. MSP measurements must be corrected for form dichroism to obtain the intrinsic dichroism. 3. An extremely simple derivation is given for the dichroism of microvilli (rhabdomeric photoreceptor) membranes in which each miorovillus is treated as if constructed from 4 vertebrate outer segment discs. The analysis accounts for both form and intrinsic dichroism. 4. The dichroic ratio of microvilli is estimated using contemporary knowledge of membrane and its associated chromophores. We find that the long (dipole) axis of the chromophore shows preferential axial alignment whenever the dichroic ratio of microvilli exceeds 1.67 to 1. This is to be contrasted to the value of 2 to 1 determined from the ideal (but unrealizable) model of Moody and Parriss (1962). An alignment of about 17° with the microvillus axis gives a dichroism of about 10 to 1 while perfect alignment gives 20 to 1. 5. We propose that the microvillus is fluid membrane rolled into a cylindrical shell. The bending causes the preferential dipole alignment when the rhodopsin molecule is asymmetrical in the membrane plane; a spherical molecule is associated with random dipole orientation in thecunved microvillus. Thus, the shape of the rhodopsin molecule is postulated to be asymmetric in crustacea and spherical in fly 1–6 microvilli.