title: A Monte Carlo evaluation of three Compton camera absorbers

authors: Uche, Chibueze Zimuzo

subjects: Compton camera

abstract: We present a quantitative study on the performance of cadmium zinc telluride (CZT), thallium-doped sodium iodide (NaI(Tl)) and germanium (Ge) detectors as potential Compton camera absorbers. The GEANT4 toolkit was used to model the performance of these materials over the nuclear medicine energy range. CZT and Ge demonstrate the highest and lowest efficiencies respectively. Although the best spatial resolution was attained for Ge, its lowest ratio of single photoelectric to multiple interactions suggests that it is most prone to inter-pixel cross-talk. In contrast, CZT, which demonstrates the least positioning error due to multiple interactions, has a comparable spatial resolution with Ge. Therefore, we modelled a Compton camera system based on silicon (Si) and CZT as the scatterer and absorber respectively. The effects of the detector parameters of our proposed system on image resolution were evaluated and our results show good agreement with previous studies. Interestingly, spatial resolution which accounted for the least image degradation at 140.5 keV became the dominant degrading factor at 511 keV, indicating that the absorber parameters play some key roles at higher energies. The results of this study have validated the predictions by An et al. which state that the use of a higher energy gamma source together with reduction of the absorber segmentation to sub-millimetre could achieve the image resolution of 5 mm required in medical imaging.

text: A Monte Carlo evaluation of three Compton camera absorbers We present a quantitative study on the performance of cadmium zinc telluride (CZT), thallium-doped sodium iodide (NaI(Tl)) and germanium (Ge) detectors as potential Compton camera absorbers. The GEANT4 toolkit was used to model the performance of these materials over the nuclear medicine energy range. CZT and Ge demonstrate the highest and lowest efficiencies respectively. Although the best spatial resolution was attained for Ge, its lowest ratio of single photoelectric to multiple interactions suggests that it is most prone to inter-pixel cross-talk. In contrast, CZT, which demonstrates the least positioning error due to multiple interactions, has a comparable spatial resolution with Ge. Therefore, we modelled a Compton camera system based on silicon (Si) and CZT as the scatterer and absorber respectively. The effects of the detector parameters of our proposed system on image resolution were evaluated and our results show good agreement with previous studies. Interestingly, spatial resolution which accounted for the least image degradation at 140.5 keV became the dominant degrading factor at 511 keV, indicating that the absorber parameters play some key roles at higher energies. The results of this study have validated the predictions by An et al. which state that the use of a higher energy gamma source together with reduction of the absorber segmentation to sub-millimetre could achieve the image resolution of 5 mm required in medical imaging.

year: 2011

title: Analysis of Amino Acids in Mānuka Honey

authors: Lloyd, Alicia Marie

subjects: Amino acid

abstract: Honey, a natural product produced by honeybees, has a complex matrix of sugars proteins, minerals, vitamins, enzymes and free amino acids. Amino acids, obtained from the nectar of plants, account for 50-30 mg/kg of honey, the most abundant of which is proline, a secondary amino acid originating mainly from the haemolymph of bees.
Three methods were investigated for the analysis of amino acids in honey. The first used HPLC-UV with pre-column derivatisation, the second HPLC-MS with hydrophobic interaction chromatography, and finally HPLC-MS with aTRAQ™ derivatisation.
The HPLC-UV method involves derivatisation of amino acids by OPA-MPA and FMOC. A fully automated injection program analysed seventeen primary amino acids in 19 minutes. Ultimately, the detection by UV had inadequate sensitivity, and the secondary amino acid proline could not be detected. The method was rejected for these main reasons.
ZIC-pHILIC chromatography paired with LC-MS-MS gave high-quality separation of twenty one amino acids, detected using scheduled MRM, in 10 minutes. Amino acid recovery out of vial was low for the majority, this variation originating from sample preparation. In vial loss of amino acids could not be recovered and so investigation into the last method was initiated.
The final method used an aTRAQ™ kit which labels amino acids with a Δ8 reagent for analysis and also provides Δ0 labelled internal standards for comparison. Forty eight amino acids and internal standards can be accurately detected by MRM’s in 18 minutes. Sample preparation was optimised for honey and the method was validated.
The amino acid content of ten honeys were compared to values obtained from Massey University. Small differences in the majority of amino acids were observed. Mānuka and clover honeys from this data set were also compared, it was found that phenylalanine and tyrosine were at much higher concentrations in clover honey.
Seven mānuka honeys stored in different conditions, warm and cold, were analysed. Applied statistical analysis with the hypothesis that the warm honeys would have lower amino acid concentrations than the cold, found this to be true for seventeen amino acids. Glutamine and then lysine were at decreased concentrations after warm storage in the most honey samples.
The amino acid content of honey, analysed by this method can be used to investigate: botanical origin of honey, speed of honey production/harvest, effect on DHA conversion, inaccurate labelling, and sugar syrup addition.

text: Analysis of Amino Acids in Mānuka Honey Honey, a natural product produced by honeybees, has a complex matrix of sugars proteins, minerals, vitamins, enzymes and free amino acids. Amino acids, obtained from the nectar of plants, account for 50-30 mg/kg of honey, the most abundant of which is proline, a secondary amino acid originating mainly from the haemolymph of bees.
Three methods were investigated for the analysis of amino acids in honey. The first used HPLC-UV with pre-column derivatisation, the second HPLC-MS with hydrophobic interaction chromatography, and finally HPLC-MS with aTRAQ™ derivatisation.
The HPLC-UV method involves derivatisation of amino acids by OPA-MPA and FMOC. A fully automated injection program analysed seventeen primary amino acids in 19 minutes. Ultimately, the detection by UV had inadequate sensitivity, and the secondary amino acid proline could not be detected. The method was rejected for these main reasons.
ZIC-pHILIC chromatography paired with LC-MS-MS gave high-quality separation of twenty one amino acids, detected using scheduled MRM, in 10 minutes. Amino acid recovery out of vial was low for the majority, this variation originating from sample preparation. In vial loss of amino acids could not be recovered and so investigation into the last method was initiated.
The final method used an aTRAQ™ kit which labels amino acids with a Δ8 reagent for analysis and also provides Δ0 labelled internal standards for comparison. Forty eight amino acids and internal standards can be accurately detected by MRM’s in 18 minutes. Sample preparation was optimised for honey and the method was validated.
The amino acid content of ten honeys were compared to values obtained from Massey University. Small differences in the majority of amino acids were observed. Mānuka and clover honeys from this data set were also compared, it was found that phenylalanine and tyrosine were at much higher concentrations in clover honey.
Seven mānuka honeys stored in different conditions, warm and cold, were analysed. Applied statistical analysis with the hypothesis that the warm honeys would have lower amino acid concentrations than the cold, found this to be true for seventeen amino acids. Glutamine and then lysine were at decreased concentrations after warm storage in the most honey samples.
The amino acid content of honey, analysed by this method can be used to investigate: botanical origin of honey, speed of honey production/harvest, effect on DHA conversion, inaccurate labelling, and sugar syrup addition.

year: 2015

title: What a difference a default setting makes

authors: Keegan, Te Taka Adrian Gregory

subjects: computer science

abstract: This paper examines the effect of the default interface language on the usage of a bilingual digital library. In 2005 the default interface language of a bilingual digital library was alternated on a monthly basis between Māori and English. A comprehensive transaction log analysis over this period reveals that not only did usage in a particular language increase when the default interface language was set to that language but that the way the interface was used, in both languages, was quite different depending on the default language.

text: What a difference a default setting makes This paper examines the effect of the default interface language on the usage of a bilingual digital library. In 2005 the default interface language of a bilingual digital library was alternated on a monthly basis between Māori and English. A comprehensive transaction log analysis over this period reveals that not only did usage in a particular language increase when the default interface language was set to that language but that the way the interface was used, in both languages, was quite different depending on the default language.

year: 2008