Cross-sections for the production of
181Re,
182mRe,
182gRe,
183Re,
184Re, and
186Re from proton bombardment of natural tungsten have been measured using the stacked foil technique for proton energies ...up to 17.6
MeV. Results are compared with the theoretical excitation functions as calculated by the EMPIRE II code (version 2.19) and experimental literature values. Results are in strong agreement with some of the previously reported literature as well at theoretical calculations for multiple reactions providing for more reliable estimates for the
186W(p,
n)
186Re reaction.
Our goal was to assess the utility of MR-PET image coregistration to quantify dopamine D2 receptors in striatum.
Twenty-nine normal subjects were investigated with PET and 11Craclopride and with MRI. ...D2 receptors were quantified using the ratio of the distribution volume in striatum to that in cerebellum. Measures obtained using regions selected directly from the PET images were compared with those obtained from MR images and then projected to coregistered PET images.
There were no differences between measures selected from the PET images (3.9 +/- 0.5) and those from the MR images (3.9 +/- 0.65). The values for these two measures were significantly correlated and corresponded to r = 0.9, p < 0.0001.
Regions of interest selected directly from PET images, where there is a large contrast between the region of interest and background, as for the case of dopamine D2 ligands, are almost identical to those obtained from coregistered MR images.
The ability to acquire high resolution anatomical data as well as quantitative functional information in vivo is becoming an increasingly important factor in the diagnosis of disease. Simultaneous ...acquisition of PET and MRI data would provide essentially perfect co-registration between the two images which is particularly important for tissues whose position and shape can change between sequential scans. RatCAP is a complete 3D tomograph that is designed to image the brain of an awake rat. A special MRI coil composed of 2 saddle elements working in quadrature mode was mounted on a Delrin cylinder specifically designed to fit inside the RatCAP but allowing the rat's head to be placed inside as well. Simultaneous PET/MRI images of the rat brain have been acquired in a 4 T MRI scanner using the RatCAP detector, with minimal effect on MRI images.
PET tracers and radiochemistry Schlyer, D J
Annals of the Academy of Medicine, Singapore,
03/2004, Letnik:
33, Številka:
2
Journal Article
Recenzirano
Odprti dostop
This paper provides a brief review of the radiochemistry of radiopharmaceuticals used in positron emission tomography (PET). It includes some history of PET, the basic formation of radionuclides in a ...cyclotron target, the processing of the precursor molecules into a useful PET radiotracer and the clinical significance and outlook for PET radiotracers. This review is based on a series of recent books and articles outlining the fundamental goals of PET and how radiochemistry plays a part in achieving these goals. It is also drawn from the literature that has been developed in PET over the last 30 years since PET became a research and valuable clinical tool. PET is a growing field and the clinical applications of the chemistry and technology have just begun to be explored. There is a great deal left to do in order to explore the full potential of PET in the clinic.
L-Deprenyl (Selegeline) is an enzyme-activated irreversible inhibitor of monoamine oxidase B (MAO B; EC 1.4.3.4). It is used to treat Parkinson's disease at a dose of 5 mg twice a day. Since enzyme ...inhibition is irreversible, the recovery of functional enzyme activity after withdrawal from L-deprenyl requires the synthesis of new enzyme. We have measured a 40 day half-time for brain MAO B synthesis in Parkinson's disease and in normal subjects after withdrawal from L-deprenyl. This is the first measurement of the synthesis rate of a specific protein in the living human brain. L-Deprenyl is currently used by 50,000 patients with Parkinson's disease in the United States and its use is expected to increase with reports that it may be beneficial in Alzheimer's disease. The slow turnover of brain MAO B suggests that the current clinical dose of L-deprenyl may be excessive and that the clinical efficacy of reduced dosing should be evaluated. Such an evaluation may have mechanistic importance as well as an impact on reducing the side effects and the costs arising from excessive drug use.
The effect of the foil material on the recovery of Xe-123 from the irradiation cell used for the measurement of the production of I-123 from the proton reaction on xenon-124 has been studied. The ...metal used for the foil can have a significant effect on the amount of Xe-123 which can be cryogenically pumped out of the irradiation cell at 30 min after the end of irradiation. Foils made from several metals and alloys were tested. Of these, the effect is most pronounced with "Havar" alloy foil where only 58% of the theoretically available activity was recovered. This effect should be considered and tested in the measurement of reaction cross-sections in irradiation cells and targets which have metal foils.
An improved procedure for producing 18Ffluoromethane (18FFM) in batches of several hundred mCi is reported. 18F prepared by the 18O (p, n) 18F reaction in a H2(18)O target is trapped on a small ...column of Dowex 1 (x 10) resin to allow recovery of H2(18)O. One new feature is elution of 18F- from the column with 3 mL of CH3CN containing 67 microL 1.5 M aqueous (Bu)4N+ OH-, after residual H2(18)O has been removed with dry CH3CN. This 18F- solution reacts with CH3I in the presence of Ag2O directly to give 18FFM, which is swept out of the reaction vessel with a stream of air, from which CH3I and other vapors are removed with a C18 SEP-PAK at room temperature. Another new technique is trapping of 18FFM on a second SEP-PAK cooled in ethanol/dry ice. After warming the SEP-PAK to room temperature, the trapped 18FFM can be recovered with either H2O or air. The improvements speed the preparation and minimize hands-on operations. The product has no detectable radiochemical impurities, and a specific activity of greater than 1 Ci/mumol. Non-radioactive CH3CN, CH3I and CH3OH are present at less than 0.2 mumol per batch.
Variation in gene regulation is ubiquitous, yet identifying the mechanisms producing such variation, especially for complex traits, is challenging. Snake venoms provide a model system for studying ...the phenotypic impacts of regulatory variation in complex traits because of their genetic tractability. Here, we sequence the genome of the Tiger Rattlesnake, which possesses the simplest and most toxic venom of any rattlesnake species, to determine whether the simple venom phenotype is the result of a simple genotype through gene loss or a complex genotype mediated through regulatory mechanisms. We generate the most contiguous snake-genome assembly to date and use this genome to show that gene loss, chromatin accessibility, and methylation levels all contribute to the production of the simplest, most toxic rattlesnake venom. We provide the most complete characterization of the venom gene-regulatory network to date and identify key mechanisms mediating phenotypic variation across a polygenic regulatory network.
Ecological stoichiometry uses information on a few key biological elements (C, N and P) to explain complex ecological patterns. Although factors driving variation in these elements are well ...established, expanding stoichiometric principles to explore dynamics of the many other essential elements comprising biological tissues (i.e. the ionome) is needed to determine their metabolic relationships and better understand biological control of elemental flows through ecosystems.
In this paper, we report observations of ionomic variation in two species of salamander (Ambystoma opacum and A. talpoideum) across ontogenic stages using specimens from biological collections of two wetlands sampled over a 30‐year period. This unique data set allowed us to explore the extent of ionomic variation between species, among ontogenic stages, between sites and through time.
We found species‐ and, to a lesser extent, site‐specific differences in C, N and P along with 13 other elements forming salamander ionomes but saw no evidence of temporal changes. Salamander ionomic composition was most strongly related to ontogeny with relatively higher concentrations of many elements in adult males (i.e. Ca, P, S, Mg, Zn and Cu) compared to metamorphic juveniles, which had greater amounts of C, Fe and Mn.
In addition to patterns of individual elements, covariance among elements was used to construct multi‐elemental nutrient balances, which revealed differences in salamander elemental composition between species and sites and changes in elemental proportions across ontogenic development. These multi‐elemental balances distinguished among species‐site‐ontogenic stage groups better than using only C, N and P.
Overall, this study highlights the responsiveness of consumer ionomes to life‐history and environmental variation while reflecting underlying relationships among elements tied to biological function. As such, ionomic studies can provide important insights into factors shaping consumer elemental composition and for predicting how these changes might affect higher‐order ecological processes.
Population decline and fragmentation often lead to reduced genetic diversity and population differentiation. Habitat destruction throughout Madagascar has caused population decline and extinction of ...many endemic species. Lemur populations, including those of the largest extant lemur,
Indri indri
, have been fragmented into remaining forest patches. We assessed the level of genetic diversity in indri populations in three protected reserves by genotyping a total of 43 individuals at 17 microsatellite loci. Genetic diversity in terms of heterozygosity was high in all three reserves, with no differences between reserves. Population structure and
F
ST
analyses revealed Analamazaotra Forest Station and the Torotorofotsy Conservation Area, which are separated by
ca
. 18 km to be genetically differentiated from each other with some admixture. Betampona Strict Nature Reserve, which is separated from the other reserves by
ca
. 130 km, exhibited clear population genetic differentiation, with no signs of admixture with the other reserves. Our genetic diversity estimates are similar to those for other Indridae in similar habitats and may reflect past rather than current population processes, given that populations have declined recently. Our results suggest that Betampona may be genetically isolated and that it is important to maintain gene flow between remaining populations to prevent loss of genetic diversity for the future conservation of
Indri indri
.
PDF
