In the framework of the Clear-PEM project for the construction of a high-resolution scanner for breast cancer imaging, a very compact and dense frontend electronics system has been developed for ...readout of multi-pixel S8550 Hamamatsu APDs. The frontend electronics are instrumented with a mixed-signal Application-Specific Integrated Circuit (ASIC), which incorporates 192 low-noise charge pre-amplifiers, shapers, analog memory cells and digital control blocks. Pulses are continuously stored in memory cells at clock frequency. Channels above a common threshold voltage are readout for digitization by off-chip free-sampling ADCs. The ASIC has a size of
7.3
×
9.8
mm
2
and was implemented in a AMS
0.35
μ
m
CMOS technology. In this paper the experimental characterization of the Clear-PEM frontend ASIC, reading out multi-pixel APDs coupled to LYSO:Ce crystal matrices, is presented. The chips were mounted on a custom test board connected to six APD arrays and to the data acquisition system. Six 32-pixel LYSO:Ce crystal matrices coupled on both sides to APD arrays were readout by two test boards. All 384 channels were operational. The chip power consumption is 660
mW (3.4
mW per channel). A very stable behavior of the chip was observed, with an estimated ENC of
1200
–
1300
e
-
at APD gain 100. The inter-channel noise dispersion and mean baseline variation is less than 8% and 0.5%, respectively. The spread in the gain between different channels is found to be 1.5%. Energy resolution of 16.5% at 511
keV and 12.8% at 662
keV has been measured. Timing measurements between the two APDs that readout the same crystal is extracted and compared with detailed Monte Carlo simulations. At 511
keV the measured single photon time RMS resolution is 1.30
ns, in very good agreement with the expected value of 1.34
ns.
Visceral leishmaniasis (VL) is a serious tropical disease that affects
approximately 500 thousand people worldwide every year. In the
Americas, VL is caused by the parasite Leishmania (Leishmania) ...infantum
chagasi mainly transmitted by the bite of the sand fly vector
Lutzomyia longipalpis. Despite recent advances in the study of
interaction between Leishmania and sand flies, very little is known
about sand fly protein expression profiles. Understanding how the
expression of proteins may be affected by blood feeding and/or presence
of parasite in the vector's midgut might allow us to devise new
strategies for controlling the spread of leishmaniasis. In this work,
we report the characterization of a vacuolar ATPase subunit C from L.
longipalpis by screening of a midgut cDNA library with a 220 bp
fragment identified by means of differential display reverse
transcriptasepolymerase chain reaction analysis. The expression of the
gene varies along insect development and is upregulated in males and
bloodfed L. longipalpis, compared to unfed flies.
We developed a rapid and simple method to identify single-nucleotide polymorphisms (SNPs) in the human mitochondrial tRNA genes. This method is based on a universal, functionalized, self-assembled ...monolayer,
XNA on Gold chip platform. A set of probes sharing a given allele-specific sequence with a single base substitution near the middle of the sequence was immobilized on chips and the chips were then hybridized with fluorescence-labeled reference targets produced by asymmetric polymerase chain reaction from patient DNA. The ratio of the hybridization signals from the reference and test targets with each probe was then calculated. A ratio of above 3 indicates the presence of a wild-type sequence and a ratio of below 0.3 indicates a mutant sequence. We tested the sensitivity of the chip for known mutations in tRNA
Leu(UUR) and tRNA
Lys genes and found that it can also be used to discriminate multiple mutations and heteroplasmy, two typical features of human mitochondrial DNA. The
XNA on Gold biochip method is a simple and rapid microarray method that can be used to test rapidly and reliably any SNP in the mitochondrial genome or elsewhere. It will be particularly useful for detecting SNPs associated with human diseases.
Performance and quality control of Clear-PEM detector modules Amaral, Pedro; Carriço, Bruno; Ferreira, Miguel ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2007, Letnik:
580, Številka:
2
Journal Article
Recenzirano
Clear-PEM is a dedicated PET scanner for breast and axilla cancer diagnosis, under development within the framework of the Crystal Clear Collaboration at CERN, aiming at the detection of tumors down ...to 2
mm in diameter. The camera consists of two planar detector heads with active dimensions 16.0×14.5
cm
2. Each head has 96 Clear-PEM detector modules consisting of 32 LYSO:Ce pixels with dimensions 2×2×20
mm
3 packed in a 4×8 BaSO
4 reflector matrix compressed between two Hamamatsu S8550 APD arrays in a double-readout configuration for Depth-of-Interaction (DoI) determination.
The modules are individually measured and characterized before being grouped into Supermodules (comprised of 24 modules). Measured properties include photo-peak position, relative gain dispersion, energy resolution, cross-talk and DoI resolution. Optical inspection of matrices was also performed with the aid of a microscope, to search for pixel misalignments and matrix defects. Modules’ performance was thoroughly evaluated with a 511
keV collimated beam to exactly determine DoI resolution. In addition, a fast quality control (QC) procedure using flood irradiations from a
137Cs source was applied systematically. The overall performance of the 24 detector modules complies with the design goals of the Clear-PEM detector, showing energy resolution around 15%, DoI resolution of about 2
mm and gain dispersion among pixels of 15%.
Trypsin and chymotrypsin serine proteases are the main digestive proteases in Diptera midguts and are also involved in many aspects of the vector–parasite relationship. In sand flies, these proteases ...have been shown to be a potential barrier to
Leishmania growth and development within the midgut. Here we describe the sequence and partial characterization of six
Phlebotomus papatasi midgut serine proteases: two chymotrypsin-like (Ppchym1 and Ppchym2) and four trypsin-like (Pptryp1–Pptryp4). All six enzymes show structural features typical to each type, including the histidine, aspartic acid, and serine (H/D/S) catalytic triad, six conserved cysteine residues, and other amino acid residues involved in substrate specificity. They also show a high degree of homology (40–60% identical residues) with their counterparts from other insect vectors, such as
Anopheles gambiae and
Aedes aegypti. The mRNA expression profiles of these six proteases vary considerably: two trypsin-like proteases (Pptryp1 and Pptryp2) are downregulated and one (Pptryp4) upregulated upon blood feeding. The two chymotrypsin-like enzymes display expression behavior similar to that of the early and late trypsins from
Ae. aegypti.
Toxorhynchites mosquitoes have an exclusively phytophagous feeding habit as adults, which leads to significant differences in their morphophysiology compared with haematophagous mosquitoes. However, ...the molecular mechanisms of digestion in this mosquito are not well understood. In this study, RNA sequencing of the posterior midgut (PMG) of the mosquito Toxorhynchites theobaldi was undertaken, highlighting its significance in mosquito digestion. Subsequently, a comparison was made between the differential gene expression of the PMG and that of the anterior midgut. It was found that the most abundant proteases in the PMG were trypsin and chymotrypsin, and the level of gene expression for enzymes essential for digestion (such as serine protease, α-amylase and pancreatic triacylglycerol lipase) and innate immune response (including catalase, cecropin-A2 and superoxide dismutase) was like that of haematophagous mosquitoes. Peritrophin-1 was detected in the entire midgut, with an elevated expression level in the PMG. Based on our findings, it is hypothesized that a non-haematophagic habit might have been exhibited by the ancestor of Tx. theobaldi , and this trait may have been retained. This study represents a pioneering investigation at the molecular level of midgut contents in a non-haematophagous mosquito. The findings offer valuable insights into the evolutionary aspects of feeding habits in culicids.
ClearPEM is a rotating, dual planar detector PET system dedicated to breast and axilla imaging that needs data corrections in order to improve quantification and lesion detectability. Since the ...scanner does not have CT nor transmission sources, we are implementing data corrections that use emission-only data. Also, since in this work we are using an iterative list-mode reconstruction algorithm that projects the data directly through a 3D grid of points, all the corrections are applied in image space. We describe the current implementation and validation of image-based corrections for normalization, scatter, attenuation and randoms. Normalization correction uses sensitivity images generated by backprojecting data from a planar source. Energy-based scatter correction is applied using the Estimation of Trues Method because this method does not require information about attenuating media and takes into account the activity outside the FOV. Attenuation correction is calculated from the segmentation of the breast in the emission images. Randoms correction is performed by subtraction of a smoothed image obtained from the backprojection of the delayed coincidences. The implementation of other corrections is also being pursued in order to obtain fully quantitative images in breast imaging.
Slope Failures in Tertiary Expansive OC Clays Ortigao, J. A. R; Loures, T. R. R; Nogueira, C ...
Journal of geotechnical and geoenvironmental engineering,
09/1997, Letnik:
123, Številka:
9
Journal Article
Recenzirano
This paper deals with slope stability in a oddly behaved, expansive, overconsolidated, stiff Tertiary clay of São Paulo, Brazil. The properties were not fully recognized until a recent major failure ...occurred during excavation on a 26-m-high, 250-m-wide slope constructed for the new Carvalho Pinto Motorway. A comprehensive site investigation was carried out and involved laboratory and in situ tests and successfully employed the Marchetti dilatometer. Back analyses of failures showed two different mechanisms, one leading to shallow failure in tertiary clays owing to expansion, followed by surface degradation or slaking. The other mechanism was lack of shear strength in the clay to resist stresses imposed by a high and steep slope. This paper gives site investigation data, discusses the causes, and back analyses of failures, and presents the final slope design.
Celotno besedilo
Dostopno za:
DOBA, FGGLJ, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
40.
Long-term stability of the Clear-PEM detector modules Amaral, Pedro; Bruyndonckx, Peter; Carriço, Bruno ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2007, Letnik:
571, Številka:
1
Journal Article
Recenzirano
Experimental evaluation of the imaging system Clear-PEM for positron emission mammography, under development within the framework of the crystal clear collaboration at CERN, is presented in terms of ...its long-term stability. The detector modules and experimental setup are described. Time evolution results of signal yield, energy resolution, depth-of-interaction and inter-channel crosstalk for a reference detector module are reported.
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