Impact of tissue properties on time-dependent alterations in apparent diffusion coefficient: a phantom study using oscillating-gradient spin-echo and pulsed-gradient spin-echo sequences

Abstract

Purpose: The purpose of this study was to investigate whether the changes in apparent diffusion coefficients (ADCs) due to differences in diffusion time reflect tissue properties in actual measurements of phantoms.

Materials and methods: Various n-alkane phantoms and sucrose/collagen phantoms with various collagen densities were set up with and without polyvinyl alcohol (PVA) foam with an average pore diameter of 300 μm. Thus, n-alkanes or sucrose/collagen represented substrate viscosity and the presence of PVA foam represented tissue structure with septum. Diffusion-weighted images with various diffusion times (7.71-60 ms) were acquired using pulsed-gradient spin-echo (PGSE) and oscillating-gradient spin-echo (OGSE) sequences. The ADCs of the phantoms with and without PVA foam were calculated.

Results: The ADCs of some of the phantoms without PVA decreased with diffusion times decreased. In the n-alkane phantoms, only C₈H₁₈ showed significantly different ADCs depending on the use of PVA foam in the OGSE sequence. On the other hand, sucrose/collagen phantoms showed significant differences according to diffusion time. The ADCs of the phantoms decreased as the molecular size of the n-alkanes or collagen density of the sucrose/collagen phantom increased. Compared to phantoms without PVA foam, the ADC of the phantoms with PVA foam decreased as the diffusion time increased.

Conclusion: Changes in ADCs due to differences in diffusion time reflect tissue properties in actual measurements of phantoms. These changes in ADCs can be used for tissue characterization in vivo.

Keywords: ADC; Diffusion time; Oscillating-gradient spin-echo; Phantom; Spatial restriction.

Fig. 1

N-alkane phantoms. a A bottle containing only one n-alkane solution. b A bottle containing one of the n-alkane solutions and polyvinyl alcohol sponge. c To improve the local magnetic field uniformity, each of the phantoms was surrounded by rice

Fig. 2

The images of purified-water phantoms. Upper row, PVA-free; lower row, PVA-300. From left column to right column of the images, diffusion time = 60, 40, 20, 15.31, 10.52, and 7.71 ms

Fig. 3

The mean apparent diffusion coefficients of the n-alkanes phantoms with different diffusion times. In all the n-alkane phantoms with PVA free, the ADC values decreased as the diffusion time decreased (p < 0.05). In all the n-alkane phantoms except C₁₆H₃₄ with PVA-300, the ADC values increased as the diffusion time decreased (p < 0.05). In the PGSE sequence, the mean ADCs of the PVA-free phantoms were significantly higher (p < 0.05) than those with PVA-300 at each diffusion time. In the OGSE sequence, none of the mean ADCs of the n-alkane phantoms, except C₈H₁₈, were not significantly different. There were few differences in the mean ADCs between PVA-free and PVA-300 conditions

Fig. 4

The mean apparent diffusion coefficients of sucrose/collagen phantoms with different diffusion times. In the purified-water phantom and some sucrose/collagen phantoms with PVA free (#1, #2), the ADC values decreased as the diffusion time decreased (p < 0.05). In all the sucrose/collagen phantoms with PVA-300, the ADC values increased as the diffusion time decreased (p < 0.05). For all diffusion times, the mean ADCs of the PVA-free phantoms were significantly higher (p < 0.05) than those with PVA-300