Development and evaluation of a microcapsule-based phantom simulating intra- and extracellular water diffusion

Objectives To develop a microcapsule-based phantom that simulates intra- and extracellular diffusion and to evaluate its microstructural validity using time-dependent diffusion-weighted imaging (DWI) metrics and limited spectrally edited diffusion (IMPULSED) modeling. Materials and methods Microcapsules with undecane cores and melamine resin membranes were fabricated in three diameter ranges and dispersed at different concentrations within an octane gel to create phantoms with controlled microstructure. DWI was performed using pulsed gradient spin-echo and oscillating gradient spin-echo research sequences with effective diffusion times of 5.8, 10.2, and 51.1 ms. Apparent diffusion coefficient (ADC), relative ADC (rADC), and incremental area under the curve (iAUC) were calculated. Microstructural parameters, including diameter, intracellular volume fraction ( f in ), intracellular diffusivity ( D in ), extracellular diffusivity ( D ex ), and cellularity were estimated using the IMPULSED model. Group differences were assessed using one-way ANOVA with Tukey’s post hoc test. Pearson’s correlation analysis was conducted to evaluate correlations between theoretical and estimated microstructural parameters. Reproducibility was assessed with Bland–Altman analysis according to repeated imaging of independently fabricated phantoms. Results ADC significantly decreased with increasing diffusion time in all microcapsule phantoms ( p < 0.001), whereas reference materials showed no time dependence. Higher microcapsule density resulted in lower ADC and higher rADC and iAUC. IMPULSED-derived diameters closely matched theoretical values ( r = 0.992). Estimated f in and cellularity strongly correlated with theoretical values ( r = 0.940 and 0.910). Reproducibility was good for ADC and IMPULSED-derived parameters. Conclusion This microcapsule-based phantom reproduces diffusion time-dependent restriction and enables quantitative validation of time-dependent DWI and IMPULSED-derived microstructural metrics. Key Points Question Validation of time-dependent diffusion MRI and microstructural models requires phantoms that reproduce both intra- and extracellular water diffusion under controlled conditions. Findings The microcapsule-based phantom reproduced diffusion-time-dependent restriction, and MRI-estimated diameters strongly correlated with theoretical diameters across tested conditions, with a Pearson correlation coefficient of 0.992. Relevance Statement The microcapsule-based phantom provides controlled intra- and extracellular diffusion environments for technical validation and standardization of quantitative MRI methods designed to characterize tissue microstructure.