Simultaneous multislice diffusion‐weighted MRI of the liver: Analysis of different breathing schemes in comparison to standard sequences

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Abstract
Purpose: To systematically evaluate image characteristics of simultaneous‐multislice (SMS)‐accelerated diffusion‐weighted imaging (DWI) of the liver using different breathing schemes in comparison to standard sequences.Materials and Methods: DWI of the liver was performed in 10 healthy volunteers and 12 patients at 1.5T using an SMS‐accelerated echo planar imaging sequence performed with respiratory‐triggering and free breathing (SMS‐RT, SMS‐FB). Standard DWI sequences served as reference (STD‐RT, STD‐FB). Reduction of scan time by SMS‐acceleration was measured. Image characteristics of SMS‐DWI and STD‐DWI with both breathing schemes were analyzed quantitatively (apparent diffusion coefficient [ADC], signal‐to‐noise ratio [SNR]) and qualitatively (5‐point Likert scale, 5 = excellent). Qualitative and quantitative parameters were compared using Friedman test and Dunn‐Bonferroni post‐hoc method with P‐values < 0.05 considered statistically significant.Results: SMS‐DWI provided diagnostic image quality in volunteers and patients both with RT and FB with a reduction of scan time of 70% (0:56 vs. 3:20 min in FB). Overall image quality did not significantly differ between FB and RT acquisition in both STD and SMS sequences (median STD‐RT 5.0, STD‐FB 4.5, SMS‐RT: 4.75; SMS‐FB: 4.5; P = 0.294). SNR in the right hepatic lobe was comparable between the four tested sequences. ADC values were significantly lower in SMS‐DWI compared to STD‐DWI irrespective of the breathing scheme (1.2 ± 0.2 × 10‐3 mm2/s vs. 1.0 ± 0.2 × 10‐3 mm2/s; P < 0.001).Conclusion: SMS‐acceleration provides considerable scan time reduction for hepatic DWI with equivalent image quality compared to the STD technique both using RT and FB. Discrepancies in ADC between STD‐DWI and SMS‐DWI need to be considered when transferring the SMS technique to clinical routine reading. J. MAGN. RESON. IMAGING 2016;44:865–879.

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