  Advanced diffusion MRI models are being explored to study the complex
microstructure of the brain with higher accuracy. However, these techniques
require long acquisition times. Simultaneous multi-slice (SMS) accelerates data
acquisition by exciting multiple image slices simultaneously and separating the
overlapping slices using a mathematical model. However, this slice separation
is not exact and leads to crosstalk between simultaneously excited slices.
Although this residual leakage is small, it affects quantitative MRI techniques
such as diffusion imaging.
  In this study, the effects of SMS acceleration on the accuracy of propagator
metrics obtained from the MAP-MRI technique was investigated. Ten healthy
volunteers were scanned with SMS accelerated multi-shell diffusion MRI
acquisitions. Group analyses were performed to study brain regions typically
affected by SMS acceleration. In addition, diffusion metrics from atlas based
fiber tracts of interest were analyzed to investigate how propagator metrics in
major fiber tracts were biased by 2- and 3-band SMS acceleration.
  Both zero-displacement metrics and non-Gaussianity metrics were significantly
altered when SMS acceleration was used. MAP-MRI metrics calculated from SMS-3
showed significant differences with respect to SMS-2. Furthermore, when shorter
TR afforded by SMS acceleration was used, the characteristics of this bias have
changed. This has implications for studies using diffusion MRI with SMS
acceleration to investigate the effects of a disease or injury on the brain
tissues.
