In silico intravascular optical coherence tomography (IVOCT) for quality assured imaging with reduced intervention.

In the clinical application of intravascular optical coherence tomography (IVOCT), it is necessary to flush opaque blood during image acquisition. However, there are no specific standards for how to perform low-dose but effective flushing. In this study, computational fluid dynamics (CFD) and optical models were integrated to numerically simulate the complete process of IVOCT, which includes blood flushing with normal saline followed by image acquisition. Moreover, an intermittent injection scheme was proposed, and its advantages over the conventionally adopted scheme of continuous injection were verified. The results show that intermittent injection can significantly reduce the dosage of normal saline (reduced by 44.4%) with only a slight sacrifice of image quality (reduced by 8.7%, but still acceptable). The developed model and key findings in this work can help surgeons practice optimized IVOCT operations and potentially lead to improved designs of the IVOCT equipment.

Real-time spatial quantification of gastric acid diffusion in whey protein gels with different NaCl concentrations by wide-field fluorescence microscopy.

Gastric acid diffusion and penetration constitute an essential process in the structural breakdown and enzymatic hydrolysis of solid food during digestion. This study aimed to quantify the real-time diffusion and spatial distribution of gastric acids in whey protein isolate (WPI) gels in the presence of 0-0.05 M NaCl during simulated digestion using a wide-field fluorescence microscope. For all the gels regardless of NaCl concentration, the outer surface rapidly developed a near-saturated layer, resulting in a higher normalized gastric acid concentration in the outer layer than in the inner layer. The pH decrease was more significant for the gels at a higher NaCl concentration (i.e., 0.05 M) due to the formation of a more discontinuous and looser network structure that would facilitate acid diffusion into the gel matrix and decrease the gel buffering capacity. Consistently, the effective diffusion coefficient (DA) estimated via the Fick diffusion model was 6.19 × 10-10 m2/s for 0.05 M WPI-RITC gels, significantly higher than 0.015 M (4.46 × 10-10 m2/s) and 0 M (3.54 × 10-10 m2/s) gels. The present study has provided a quantitative understanding of the diffusion process and spatial distribution of gastric acids within the WPI gel matrix in real-time during in vitro gastric digestion as influenced by NaCl concentration.