title: Optimising diffusion-weighted imaging in the abdomen and pelvis: comparison of image quality between monopolar and bipolar single-shot spin-echo echo-planar sequences.
abstract: OBJECTIVE
  To compare geometric distortion, signal-to-noise ratio (SNR), apparent diffusion coefficient (ADC), efficacy of fat suppression and presence of artefact between monopolar (Stejskal and Tanner) and bipolar (twice-refocused, eddy-current-compensating) diffusion-weighted imaging (DWI) sequences in the abdomen and pelvis.
  
  
  METHODS
  A semiquantitative distortion index (DI) was derived from the subtraction images with b = 0 and 1,000 s/mm(2) in a phantom and compared between the two sequences. Seven subjects were imaged with both sequences using four b values (0, 600, 900 and 1,050 s/mm(2)) and SNR, ADC for different organs and fat-to-muscle signal ratio (FMR) were compared. Image quality was evaluated by two radiologists on a 5-point scale.
  
  
  RESULTS
  DI was improved in the bipolar sequence, indicating less geometric distortion. SNR was significantly lower for all tissues and b values in the bipolar images compared with the monopolar (p < 0.05), whereas FMR was not statistically different. ADC in liver, kidney and sacrum was higher in the bipolar scheme compared to the monopolar (p < 0.03), whereas in muscle it was lower (p = 0.018). Image quality scores were higher for the bipolar sequence (p ≤ 0.025).
  
  
  CONCLUSIONS
  Artefact reduction makes the bipolar DWI sequence preferable in abdominopelvic applications, although the trade-off in SNR may compromise ADC measurements in muscle.
authors: CR-UK and EPSRC Cancer Imaging Centre, Royal Marsden NHS Foundation Trust and Institute of Cancer Research, Downs Road, Sutton, Surrey, SM2 5PT, UK. Stavroula.Kyriazi@icr.ac.uk
authors: Stavroula
authors: S
authors: Kyriazi
authors: Matthew
authors: M
authors: Blackledge
authors: David J
authors: DJ
authors: Collins
authors: Nandita M
authors: NM
authors: Desouza
mesh_terms: D000005:Abdomen / Q000473:pathology*; D003952:Diagnostic Imaging / Q000379:methods; D004058:Diffusion; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D004129:Dimethylpolysiloxanes / Q000737:chemistry; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007668:Kidney / Q000473:pathology; D008099:Liver / Q000473:pathology; D010179:Pancreas / Q000473:pathology; D010388:Pelvis / Q000473:pathology; D019047:Phantoms, Imaging; D013154:Spleen / Q000473:pathology; D014018:Tissue Distribution
chemical_list: D004129:Dimethylpolysiloxanes