Impacts, causes and biofortification strategy of rice selenium deficiency based on publication collection.

Selenium (Se) deficiency in rice will result in a Se hidden hunger threat to the general public's human health, particularly in areas where rice consumption is high. Nevertheless, the impact scope and coping strategies have not been given sufficient focus on a worldwide scale. In order to evaluate the impacts, causes and biofortification strategies of Se-deficient rice, this study collected data from the publications on three themes: market survey, field sampling and controlled experiments. According to the market survey, global rice Se concentrations were 0.079 mg/kg on mean and 0.062 mg/kg on median. East Asia has a human Se intake gap due to the region's high rice consumption and the lowest rice Se concentration in markets globally. Total Se concentrations in East Asian paddy soils were found to be adequate based on the field sampling. However, over 70 % of East Asian paddy fields were inadequate to yield rice that met the global mean for rice Se concentration. The Se-deficient rice was probably caused by widespread low Se bioavailability in East Asian paddy fields. There were two important factors influencing rice Se enrichment including root Se uptake and iron oxide in soils. Concentrating on these processes is beneficial to rice Se biofortification. Since Se is adequate in the paddy soils of East Asia. Rather of adding Se exogenously, activating the native Se in paddy soil is probably a more appropriate strategy for rice Se biofortification in East Asia. Meta-analysis revealed water management had the greatest impact on rice Se biofortification. The risks and solutions for rice Se deficiency were discussed in our farmland-to-table survey, which will be a valuable information in addressing the global challenge of Se hidden hunger. This study also provided new perspectives and their justifications, critically analyzing both present and future strategies to address Se hidden hunger.

Tapered LSO arrays for small animal PET.

By using detectors with good depth encoding accuracy (∼2 mm), an animal PET scanner can be built with a small ring diameter and thick crystals to simultaneously obtain high spatial resolution and high sensitivity. However, there will be large wedge-shaped gaps between detector modules in such a scanner if traditional cuboid crystal arrays are used in a polygonal arrangement. The gaps can be minimized by using tapered scintillator arrays enabling the sensitivity of the scanner to be further improved. In this work, tapered lutetium oxyorthosilicate (LSO) arrays with different crystal dimensions and different combinations of inter-crystal reflector and crystal surface treatments were manufactured and their performance was evaluated. Arrays were read out from both ends by position-sensitive avalanche photodiodes (PSAPDs). In the optimal configuration, arrays consisting of 0.5 mm LSO elements could be clearly resolved and a depth of interaction resolution of 2.6 mm was obtained for a 20 mm thick array. For this tapered array, the intrinsic spatial is degraded from 0.67 to 0.75 mm compared to a standard cuboidal array with similar dimensions, while the increase in efficiency is 41%. Tapered scintillator arrays offer the prospect of improvements in sensitivity and sampling for small-bore scanners, without large increases in manufacturing complexity.

Continuous depth-of-interaction encoding using phosphor-coated scintillators.

We investigate a novel detector using a lutetium oxyorthosilicate (LSO) scintillator and YGG (yttrium-aluminum-gallium oxide:cerium, Y(3)(Al,Ga)(5)O(12):Ce) phosphor to construct a detector with continuous depth-of-interaction (DOI) information. The far end of the LSO scintillator is coated with a thin layer of YGG phosphor powder which absorbs some fraction of the LSO scintillation light and emits wavelength-shifted photons with a characteristic decay time of approximately 50 ns. The near end of the LSO scintillator is directly coupled to a photodetector. The photodetector detects a mixture of the LSO light and the light emitted by YGG. With appropriate placement of the coating, the ratio of the light converted from the YGG coating with respect to the unconverted LSO light can be made to depend on the interaction depth. DOI information can then be estimated by inspecting the overall light pulse decay time. Experiments were conducted to optimize the coating method. 19 ns decay time differences across the length of the detector were achieved experimentally when reading out a 1.5 x 1.5 x 20 mm(3) LSO crystal with unpolished surfaces and half-coated with YGG phosphor. The same coating scheme was applied to a 4 x 4 LSO array. Pulse shape discrimination (PSD) methods were studied to extract DOI information from the pulse shape changes. The DOI full-width-half-maximum (FWHM) resolution was found to be approximately 8 mm for this 2 cm thick array.

A prototype PET scanner with DOI-encoding detectors.

UNLABELLED: Detectors with depth-encoding allow a PET scanner to simultaneously achieve high sensitivity and high spatial resolution. METHODS: A prototype PET scanner, consisting of depth-encoding detectors constructed by dual-ended readout of lutetium oxyorthosilicate (LSO) arrays with 2 position-sensitive avalanche photodiodes (PSAPDs), was developed. The scanner comprised 2 detector plates, each with 4 detector modules, and the LSO arrays consisted of 7 x 7 elements, with a crystal size of 0.9225 x 0.9225 x 20 mm and a pitch of 1.0 mm. The active area of the PSAPDs was 8 x 8 mm. The performance of individual detector modules was characterized. A line-source phantom and a hot-rod phantom were imaged on the prototype scanner in 2 different scanner configurations. The images were reconstructed using 20, 10, 5, 2, and 1 depth-of-interaction (DOI) bins to demonstrate the effects of DOI resolution on reconstructed image resolution and visual image quality. RESULTS: The flood histograms measured from the sum of both PSAPD signals were only weakly depth-dependent, and excellent crystal identification was obtained at all depths. The flood histograms improved as the detector temperature decreased. DOI resolution and energy resolution improved significantly as the temperature decreased from 20 degrees C to 10 degrees C but improved only slightly with a subsequent temperature decrease to 0 degrees C. A full width at half maximum (FWHM) DOI resolution of 2 mm and an FWHM energy resolution of 15% were obtained at a temperature of 10 degrees C. Phantom studies showed that DOI measurements significantly improved the reconstructed image resolution. In the first scanner configuration (parallel detector planes), the image resolution at the center of the field of view was 0.9-mm FWHM with 20 DOI bins and 1.6-mm FWHM with 1 DOI bin. In the second scanner configuration (detector planes at a 40 degrees angle), the image resolution at the center of the field of view was 1.0-mm FWHM with 20 DOI bins and was not measurable when using only 1 bin. CONCLUSION: PET scanners based on this detector design offer the prospect of high and uniform spatial resolution (crystal size, approximately 1 mm; DOI resolution, approximately 2 mm), high sensitivity (20-mm-thick detectors), and compact size (DOI encoding permits detectors to be tightly packed around the subject and minimizes number of detectors needed).

Comparison of four depth-encoding PET detector modules with wavelength shifting (WLS) and optical fiber read-out.

We propose detectors for a laboratory positron emission tomography scanner specific for mouse imaging that utilizes fewer detectors and channels of electronics compared with existing designs. The detectors are based on lutetium oxyorthosilicate arrays, read out by orthogonal optical fibers placed on the top and bottom of the arrays. Depth of interaction (DOI) information is obtained from the ratio of the signals at either end of the array. Four different detector modules were evaluated, using different reflector materials and two types of optical fibers (wavelength shifting (WLS) fibers and clear optical fibers). The modules were compared in terms of flood histograms, energy resolution, DOI resolution and timing resolution. Energy resolution for single crystals at one irradiation depth was around 65% full-width half-maximum (FWHM). A DOI resolution of approximately 6 mm was obtained for the modules. Timing resolution was in the range of 5.1-7.8 ns. An array assembled in the laboratory and coupled with WLS fibers had the best DOI resolution; the same array with clear fibers had the best timing resolution and a commercially manufactured array and coupled with WLS fibers had the best energy resolution.

Measurements of wavelength shifting (WLS) fibre readout for a highly multiplexed, depth-encoding PET detector.

We are attempting to develop a laboratory PET scanner for mouse imaging that utilizes far fewer detectors and channels of electronics, thus reducing cost, whilst retaining state-of-the-art performance. The detectors are based on LSO arrays read out by wavelength shifting (WLS) fibres placed on the top and the bottom of the arrays. Depth of interaction information will be obtained from the ratio of the signals at either end of the array. For acceptable performance, it is critical to maximize collection of light photons from the ends of the fibres and to minimize the optical crosstalk between adjacent fibres. Factors which can affect the light collection and crosstalk were studied, including coupling materials between fibres and crystals, reflectors wrapped around the fibre sides and ends, fibre size and shape, and number of layers of fibre cladding. Properties of WLS fibres such as the transmission attenuation and transverse absorption were also studied. The light yield from 2 x 2 x 10 mm(3) LSO crystals collected from the end of a 2 x 2 x 30 mm(3) WLS fibre was up to 24% (typical values 16-20%) of that obtained by direct coupling of the LSO crystal. This light collection efficiency appears to be sufficient for decoding interaction position in these detectors.

Optimizing multicompression approaches to elasticity imaging.

Breast lesion visibility in static strain imaging ultimately is noise limited. When correlation and related techniques are applied to estimate local displacements between two echo frames recorded before and after a small deformation, target contrast increases linearly with the amount of deformation applied. However, above some deformation threshold, decorrelation noise increases more than contrast such that lesion visibility is severely reduced. Multicompression methods avoid this problem by accumulating displacements from many small deformations to provide the same net increase in lesion contrast as one large deformation but with minimal decorrelation noise. Unfortunately, multicompression approaches accumulate echo noise (electronic and sampling) with each deformation step as contrast builds so that lesion visibility can be reduced again if the applied deformation increment is too small. This paper uses signal models and analysis techniques to develop multicompression strategies that minimize strain image noise. The analysis predicts that displacement variance is minimal in elastically homogeneous media when the applied strain increment is 0.0035. Predictions are verified experimentally with gelatin phantoms. For in vivo breast imaging, a strain increment as low as 0.0015 is recommended for minimum noise because of the greater elastic heterogeneity of breast tissue.