Effect of particle size on liver MRI R 2 * relaxometry: Monte Carlo simulation and phantom studies.

PURPOSE: To investigate the effect of particle size on liver R 2 * $$ {\mathrm{R}}_2^{\ast } $$ by Monte Carlo simulation and phantom studies at both 1.5 T and 3.0 T. METHODS: Two kinds of particles (i.e., iron sphere and fat droplet) with varying sizes were considered separately in simulation and phantom studies. MRI signals were synthesized and analyzed for predicting R 2 * $$ {\mathrm{R}}_2^{\ast } $$ , based on simulations by incorporating virtual liver model, particle distribution, magnetic field generation, and proton movement into phase accrual. In the phantom study, iron-water and fat-water phantoms were constructed, and each phantom contained 15 separate vials with combinations of five particle concentrations and three particle sizes. R 2 * $$ {\mathrm{R}}_2^{\ast } $$ measurements in the phantom were made at both 1.5 T and 3.0 T. Finally, differences in R 2 * $$ {\mathrm{R}}_2^{\ast } $$ predictions or measurements were evaluated across varying particle sizes. RESULTS: In the simulation study, strong linear and positively correlated relationships were observed between R 2 * $$ {\mathrm{R}}_2^{\ast } $$ predictions and particle concentrations across varying particle sizes and magnetic field strengths ( r ≥ 0.988 $$ r\ge 0.988 $$ ). The relationships were affected by iron sphere size ( p < 0.001 $$ p<0.001 $$ ), where smaller iron sphere size yielded higher predicted R 2 * $$ {\mathrm{R}}_2^{\ast } $$ , whereas fat droplet size had no effect on R 2 * $$ {\mathrm{R}}_2^{\ast } $$ predictions ( p ≥ 0.617 $$ p\ge 0.617 $$ ) for constant total fat concentration. Similarly, the phantom study showed that R 2 * $$ {\mathrm{R}}_2^{\ast } $$ measurements were relatively sensitive to iron sphere size ( p ≤ 0.004 $$ p\le 0.004 $$ ) unlike fat droplet size ( p ≥ 0.223 $$ p\ge 0.223 $$ ). CONCLUSION: Liver R 2 * $$ {\mathrm{R}}_2^{\ast } $$ is affected by iron sphere size, but is relatively unaffected by fat droplet size. These findings may lead to an improved understanding of the underlying mechanisms of R 2 * $$ {\mathrm{R}}_2^{\ast } $$ relaxometry in vivo, and enable improved quantitative MRI phantom design.

Accumulation and metabolism of selenium in the rare yeast Kazachstania unispora during the selenium enrichment process.

Selenium (Se)-enriched yeast is a good nutritional source for human being. Kazachstania unispora (K. unispora) has shown the positive physiological functionality for human health, whose potential for Se enrichment, however, remains elusive. This study demonstrated the ability of K. unispora to convert inorganic Se to organic Se, and then comprehensively investigated the accumulation and metabolism of Se in K. unispora. The results indicated that K. unispora can effectively accumulate organic Se, of which 95% of absorbed Se was converted to organic forms. Among these organic Se, 46.17% of them was bound to protein and 16.78% was combined with polysaccharides. In addition, some of the organic Se was metabolized to selenomethionine (30.26%) and selenocystine (3.02%), during which four low-molecular weight selenometabolites were identified in K. unispora. These findings expand the scope of Se-enriched yeast species, and provide useful knowledge for further investigation of Se enrichment mechanism in K. unispora.