title: 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.
abstract: OBJECTIVE
  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.
  
  
  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.
  
  
  CONCLUSIONS
  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.
authors: Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, Switzerland. Electronic address: andreas.boss@usz.ch.
authors: Andreas
authors: A
authors: Boss
authors: Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, Switzerland.
authors: Borna
authors: B
authors: Barth
authors: Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, Switzerland.
authors: Lukas
authors: L
authors: Filli
authors: Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, Switzerland.
authors: David
authors: D
authors: Kenkel
authors: Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, Switzerland.
authors: Moritz C
authors: MC
authors: Wurnig
authors: Institute of Neuroradiology, University Hospital of Zurich, Switzerland.
authors: Marco
authors: M
authors: Piccirelli
authors: Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, Switzerland.
authors: Caecilia S
authors: CS
authors: Reiner
mesh_terms: D000328:Adult; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D017352:Echo-Planar Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D008099:Liver / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D009038:Motion; D010179:Pancreas / Q000000981:diagnostic imaging*; D011446:Prospective Studies; D012016:Reference Values; D015203:Reproducibility of Results; D059629:Signal-To-Noise Ratio; D013997:Time Factors
keywords: Diffusion-weighted imaging; Magnetic resonance imaging; Multiband; Simultaneous multi-slice