Tomonori Fukuchi | Searcharxiv

arXiv2021

Monte Carlo simulation of molecular dynamics for amino acid production from carboxylic acid via C-14 beta-decay

To study the chemical origin of life, we investigated the amino acid production probability from radiocarbon (C-14)-containing carboxylic acid via beta-decay using a newly developed Monte Carlo simulator for molecular dynamics calculation. Using the simulation, we calculated the dynamical trajectory of N-14 recoiled via C-14 beta-decay in [3-C-14]propionic acid and evaluated the staying probability of N-14 in the compound, which is the glycinium (a protonated glycine) production probability from [3-C-14]propionic acid. The glycinium production probability was calculated to be 78.7% assuming static compound structures of [3-C-14]propionic acid and a glycinium C-N binding potential energy of 3.93 eV. From calculations with various binding potential parameters, a glycinium production probability of approximately 30% was expected by simulation in case of a loose C-N binding potential energy of 2-eV.

physics.chem-ph↗

arXiv2021

Image reconstruction method for dual-isotope positron emission tomography

We developed a positron emission tomography (PET) system for multiple-isotope imaging. Our PET system, named multiple-isotope PET (MI-PET), can distinguish between different tracer nuclides using coincidence measurement of prompt gamma-rays, which are emitted after positron emission. In MI-PET imaging with a pure positron emitter and prompt-gamma emitter, because of the imperfectness of prompt gamma-ray detection, an image for a pure positron emitter taken by MI-PET is superposed by a positron-γ emitter. Therefore, in order to make isolated images of the pure positron emitter, we developed image reconstruction methods based on data subtraction specific to MI-PET. We tested two methods, subtraction between reconstructed images and subtraction between sinogram data. In both methods, normalization for position dependence of the prompt γ-ray sensitivity is required in addition to detector sensitivity normalization. For these normalizations, we performed normalization scans using cylindrical phantoms of the positron-gamma emitters Sc-44m and Na-22. A long period measurement using the activity decay of Sc-44m (Half-life 58.6 hours) elucidated that the acquisition ratio between the prompt gamma-rays coincided with PET event and pure PET event changes on the basis of object activities. Therefore, we developed a correction method that involves subtraction parameters dependent on the activities, i.e., the counting rate. From analysis of dual-tracer phantom images, data subtraction in the sinogram data with sensitivity correction gives a higher quality of isolated images for the pure positron emitter than those from image subtractions. Furthermore, from dual-isotope (F-18-FDG and Sc-44m) mouse imaging, we concluded that our developed method can be used for practical imaging of a living organism.

physics.med-ph↗