  Purpose: The aim of this work was to create tissue-mimicking gel phantoms
appropriate for diffusion kurtosis imaging (DKI) for quality assurance,
protocol optimization and sequence development.
  Methods: A range of agar, agarose and polyvinyl alcohol phantoms with
concentrations ranging from 1.0% to 3.5%, 0.5% to 3.0% and 10% to 20%,
respectively, and up to 3 g of glass microspheres per 100 ml were created.
Diffusion coefficients, excess kurtosis values and relaxation rates were
experimentally determined.
  Results: The kurtosis values for the plain gels ranged from 0.05 with 95%
confidence interval (CI) of $(0.029, 0.071)$ to $0.216(0.185, 0.246)$, well
below the kurtosis values reported in the literature for various tissues. The
addition of glass microspheres increased the kurtosis of the gels with values
up to $0.523(0.465, 0.581)$ observed for gels with the highest concentration of
microspheres. Repeat scans of some of the gels after more than six months of
storage at room temperature indicate changes in the diffusion parameters of
less than 10%. The addition of the glass microspheres reduces the apparent
diffusion coefficients (ADCs) and increases the longitudinal and transverse
relaxation rates but the values remain comparable to those for plain gels and
tissue, with ADCs observed ranging from $818(585, 1053) \times 10^{-6}$
mm$^2$/s to $2257(2118, 2296) \times 10^{-6}$ mm$^2$/s, and R1 values ranging
from $0.34(0.32, 0.35)$ 1/s to $0.51(0.50, 0.52)$ 1/s, and R2 values ranging
from $9.69(9.34, 10.04)$ 1/s to $33.07(27.10, 39.04)$ 1/s.
  Conclusions: Glass microspheres can be used to effectively modify diffusion
properties of gel phantoms and achieve a range of kurtosis values comparable to
those reported for a variety of tissues.
