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Purposes: To provide abdominal contrast-enhanced MR image synthesis, we developed an gradient regularized multi-modal multi-discrimination sparse attention fusion generative adversarial network (GRMM-GAN) to avoid repeated contrast injections to patients and facilitate adaptive monitoring. Methods: With IRB approval, 165 abdominal MR studies from 61 liver cancer patients were retrospectively solicited from our institutional database. Each study included T2, T1 pre-contrast (T1pre), and T1 contrast-enhanced (T1ce) images. The GRMM-GAN synthesis pipeline consists of a sparse attention fusion network, an image gradient regularizer (GR), and a generative adversarial network with multi-discrimination. The studies were randomly divided into 115 for training, 20 for validation, and 30 for testing. The two pre-contrast MR modalities, T2 and T1pre images, were adopted as inputs in the training phase. The T1ce image at the portal venous phase was used as an output. The synthesized T1ce images were compared with the ground truth T1ce images. The evaluation metrics include peak signal-to-noise ratio (PSNR), structural similarity index (SSIM), and mean squared error (MSE). A Turing test and experts’ contours evaluated the image synthesis quality. Results: The proposed GRMM-GAN model achieved a PSNR of 28.56, an SSIM of 0.869, and an MSE of 83.27. The proposed model showed statistically significant improvements in all metrics tested with p-values < 0.05 over the state-of-the-art model comparisons. The average Turing test score was 52.33%, which is close to random guessing, supporting the model’s effectiveness for clinical application. In the tumor-specific region analysis, the average tumor contrast-to-noise ratio (CNR) of the synthesized MR images was not statistically significant from the real MR images. The average DICE from real vs. synthetic images was 0.90 compared to the inter-operator DICE of 0.91. Conclusion: We demonstrated the function of a novel multi-modal MR image synthesis neural network GRMM-GAN for T1ce MR synthesis based on pre-contrast T1 and T2 MR images. GRMM-GAN shows promise for avoiding repeated contrast injections during radiation therapy treatment.

Purposes: To provide abdominal contrast-enhanced MR image synthesis, we developed an image gradient regularized multi-modal multi-discrimination sparse-attention fusion generative adversarial network (GRMM-GAN) to avoid repeated contrast injections to patients and facilitate adaptive monitoring. Methods: With IRB approval, 165 abdominal MR studies from 61 liver cancer patients were retrospectively solicited from our institutional database. Each study included T2, T1 pre-contrast (T1pre), and T1 contrast-enhanced (T1ce) images. The GRMM-GAN synthesis pipeline consists of a sparse attention fusion network, an image gradient regularizer (GR), and a generative adversarial network with multi-discrimination. The studies were randomly divided into 115 for training, 20 for validation, and 30 for testing. The two pre-contrast MR modalities, T2 and T1pre images, were adopted as inputs in the training phase. The T1ce image at the portal venous phase was used as an output. The synthesized T1ce images were compared with the ground truth T1ce images. The evaluation metrics include peak signal-to-noise ratio (PSNR), structural-similarity-index (SSIM), and mean-squared-error (MSE). A Turing test and experts’ contours evaluated the image synthesis quality. Results: The proposed GRMM-GAN model achieved a PSNR of 28.56, an SSIM of 0.869, and an MSE of 83.27. The proposed model showed statistically significant improvements in all metrics tested with p-values

In Chapter one, an acid assisted closed vessel microwave digestion procedure was developed for the treatment of fine airborne particulate matter that allows elemental iodine to be solubilised simultaneously with metallic elements. This procedure is an improvement over existing methods as it allows the iodine to be safely digested from the filter media (polypropylene or cellulose) in less than one hour and achieve up to 70–100 % recoveries, without requiring an overnight pre-digestion step or the addition of reducing agents, with a microwave temperature of 185 °C and the use of 65 % HNO3 in the digestion media. A range of filters were investigated to determine the material that has the best properties for microwave digestion that also enabled the deposited iodine present in total suspended particles (TSP) to be rapidly fully digested and quantitatively analysed using inductively coupled plasma-mass spectrometry (ICP-MS). This developed method has shown to be possible in the analysis of metallic elements with iodine of interest without the need of a separate chemical preparation steps. The following Chapters 3 and 4 are based on the analysis of radioactive isotopes of uranium and plutonium with the use of a quadrupole ICP-MS with a general introduction on radionuclide analysis in Chapter 2. Unlike other mass-spectrometric methods (eg,, Sector-field ICP-MS or Multi-collector ICP-MS), the quadrupole ICP-MS is a cost-effective (easier maintenance) analytical instrument with good sensitivity to sub-ppb levels In Chapter 3, plutonium analysis, in particular 238Pu, was performed with a non-radiometric method. 238Pu is an alpha emitter and hence can be analysed successfully with alpha spectrometry, which does not have any spectral interference although it is a very slow alpha emitter and requires a relatively long counting time. However, mass spectrometric analysis of 238Pu faces isobaric interference with interfering 238U which cannot be resolved. Therefore, in this chapter, a mass spectrometric method that uses an experimentally derived algebraic correction factor was developed that requires sample pretreatment with TEVA and UTEVA resin cartridges to separate the plutonium (TEVA) and uranium (UTEVA) in the sample. The proposed developed method was shown to be more effective when enriched uranium (weapon grade) was added into the sample prior to the resin-based separation steps. In chapter 4, analysis of uranium isotope samples has usually been performed in a clean-room facility due to the presence of natural uranium in the environment that can potentially contaminate the sample. However, a clean room facility is not available in many laboratories that also carry out ICP analysis. There is also a lack in understanding of the potential contributors to natural uranium contamination, which can be identified through analysis of the process blanks. In this study, the process blanks were analysed in parallel to all samples to enable blank corrections to be performed for every step of the sample treatment processes. A significant portion of the natural uranium contamination was found to derive from reagents and consumables. The capability of analysis of different enrichment levels of uranium samples were evaluated by varying the amount of samples spiked during the sample preparation technique (lithium borate fusion) and assessed with the related relative uncertainties at the various mass point of spiked samples. The thesis ends with a concluding Chapter 5. ​Doctor of Philosophy (SPMS)

A comprehensive one-year study on the rainwater and particulate matter in ambient air of Singapore was performed and reported in this thesis. The rainwater composition and monthly trends were analyzed with the use of various analytical techniques, which includes Ion-chromatography and Inductively-Coupled Plasma Mass Spectrometry (ICP-MS). The pH and electrical conductivity (EC) of the rainwater collected were monitored concurrently as it has a close relation to the PSI index reported by the National Environmental Agency (NEA) of Singapore. The rainwater samples were collected in both sites, NTU and Hougang. These two sites have different distinctive environment. NTU, located in the western part of Singapore is surrounded with industries and refineries, which contribute pollutants to the atmosphere. Whereas, Hougang is a residential area with minimal industrial activities, however, the sampling site is close to the main road with moderate to heavy traffic. It was found in this study that the rainwater collected in NTU is high in content for trace metals related to refineries and industrial activities whereas rainwater samples collected in Hougang contain trace metals related to traffic. The pH of the rainwater samples collected in NTU is lower than Hougang with an averaged pH of 4.53 and 4.61 respectively. The higher averaged pH collected in Hougang would suggest the presence of less acidic ions present in the rainwater which is responsible for acid rain. The acidic ions contained in rainwater can be attributed to the release of SOx and NOx by industries located in the western part of Singapore where NTU is in close proximity to Jurong Island and Tuas. The particulate matter suspended in ambient air of western Singapore are studied with the use of ICP-MS for the analysis of trace metals present in the particulate matter filters collected. Two high-volume air samplers are located on level 6 roof, School of Physical and Mathematical Sciences building. The sample preparation of these filters, were performed by microwave acid-digestion prior to ICP-MS analysis. The enrichment factors (EF) calculated for the trace metals analyzed suggest that most elements come from anthropogenic sources. The calculated EF with values of EF > 10 are B, Sc, Zn, Ga, Se, x Ru, Pd, Ag, Cd, Sn, Ba, Re, Os, Ir, Pt, Au and Bi. Similarly, these elements have EF >10 in the rainwater samples collected in NTU. Since these elements generally are present in low amount in the earth crust’s hence, the presence of anthropogenic sources would greatly enrich the presence of such elements. Master of Science

A slight modification in the reaction conditions allows for selective aziridination or amination of the title compounds.

A method to prepare α-acyl-β-amino acid and 2,2-diacyl aziridine derivatives efficiently from Cu(OTf)(2) + 1,10-phenanthroline (1,10-phen)-catalyzed amination and aziridination of 2-alkyl substituted 1,3-dicarbonyl compounds with PhI═NTs is described. By taking advantage of the orthogonal modes of reactivity of the substrate through slight modification of the reaction conditions, a divergence in product selectivity was observed. In the presence of 1.2 equiv of the iminoiodane, amination of the allylic C-H bond of the enolic form of the substrate, formed in situ through coordination to the Lewis acidic metal catalyst, was found to selectively occur and give the β-aminated adduct. On the other hand, increasing the amount of the nitrogen source from 1.2 to 2-3 equiv was discovered to result in preferential formal aziridination of the C-C bond of the 2-alkyl substituent of the starting material and formation of the aziridine product.

Understanding the interactions between pathogen, crop and vector are necessary for the development of disease control practices of vector-borne pathogens. For instance, resistant plant genotypes can help constrain disease symptoms due to infections and limit pathogen spread by vectors. On the other hand, genotypes susceptible to infection may increase pathogen spread owing to their greater pathogen quantity, regardless of their symptom status. In this study, we evaluated under greenhouse conditions the relative levels of resistance (i.e. relatively lower pathogen quantity) versus tolerance (i.e. less symptom severity) of 10 commercial grapevine (Vitis vinifera) cultivars to Pierce's disease etiological agent, the bacterium Xylella fastidiosa. Overall, no correlation was detected between pathogen quantity and disease severity, indicating the existence of among-cultivar variation in plant response to infection. Thompson Seedless and Barbera were the two most susceptible among 10 evaluated cultivars. Rubired showed the least severe disease symptoms and was categorized as one of the most resistant genotypes in this study. However, within each cultivar the degree of resistance/tolerance was not consistent across sampling dates. These cultivar and temporal differences in susceptibility to infection may have important consequences for disease epidemiology and the effectiveness of management protocols.