Combination of integrated dynamic shimming and readout-segmented echo planar imaging for diffusion weighted MRI of the head and neck region at 3Tesla.

PURPOSE: To evaluate the performance of combined integrated slice-by-slice shimming and readout-segmented EPI (irsEPI) for diffusion-weighted MR imaging (DWI) of the neck at 3Tesla.

METHODS: This study was approved by the local ethics committee. An anthropometric phantom of the head/neck region incorporating compartments with different diffusivities was constructed. In vivo measurements were performed in 10 healthy volunteers. DWI of the phantom and volunteers was performed on a 3Tesla MR scanner using single shot EPI (sEPI), a prototype single shot EPI with integrated slice-by-slice shimming (iEPI), readout segmented EPI (rsEPI) and a prototype readout segmented EPI with integrated shimming irsEPI. Apparent diffusion coefficients (ADC) and spatial distortions of phantom compartments were quantified. For phantom and volunteer measurements, the presence of geometric distortions, signal losses, ghosting artifacts as well as overall image quality were visually assessed on a 4-point scale by two radiologists in consensus. In addition, failure of fat saturation was assessed in volunteer data.

RESULTS: Quantification of ADC within the phantom compartments was comparable using the different EPI techniques without significant variations. Using irsEPI, spatial distortions in phase-encoding direction were markedly reduced compared to iEPI, rsEPI and especially sEPI. irsEPI yielded significantly better overall image quality compared to sEPI, iEPI and rsEPI in phantom data as well as volunteer measurements. Markedly reduced geometric distortions and signal loss as well as better fat saturation were observed using irsEPI.

CONCLUSION: The use of irsEPI significantly improves image quality and reduces artifacts caused by magnetic field inhomogeneities in EPI based DWI of the head/neck at 3Tesla.