Simultaneous multi-slice echo planar diffusion weighted imaging of the liver and the pancreas: Optimization of signal-to-noise ratio and acquisition time and application to intravoxel incoherent motion analysis.

Purpose: To optimize and test a diffusion-weighted imaging (DWI) echo-planar imaging (EPI) sequence with simultaneous multi-slice (SMS) excitation in the liver and pancreas regarding acquisition time (TA), number of slices, signal-to-noise ratio (SNR), image quality (IQ), apparent diffusion coefficient (ADC) quantitation accuracy, and feasibility of intravoxel incoherent motion (IVIM) analysis.

Materials And Methods: Ten healthy volunteers underwent DWI of the upper abdomen at 3T. A SMS DWI sequence with CAIPIRINHA unaliasing technique (acceleration factors 2/3, denoted AF2/3) was compared to standard DWI-EPI (AF1). Four schemes were evaluated: (i) reducing TA, (ii) keeping TA identical with increasing number of averages, (iii) increasing number of slices with identical TA (iv) increasing number of b-values for IVIM. Acquisition schemes i-iii were evaluated qualitatively (reader score) and quantitatively (ADC values, SNR).

Results: In scheme (i) no differences in SNR were observed (p=0.321-0.038) with reduced TA (AF2 increase in SNR/time 75.6%, AF3 increase SNR/time 102.4%). No SNR improvement was obtained in scheme (ii). Increased SNR/time could be invested in acquisition of more and thinner slices or higher number of b-values. Image quality scores were stable for AF2 but decreased for AF3. Only for AF3, liver ADC values were systematically lower.

Conclusion: SMS-DWI of the liver and pancreas provides substantially higher SNR/time, which either may be used for shorter scan time, higher slice resolution or IVIM measurements.