title: Optimal b Values for Generation of Computed High-b-Value DW Images.
abstract: OBJECTIVE
  The purpose of this study was to investigate the optimal b values required for the generation of computed high-b-value DW images.
  
  
  METHODS
  Brain DWI was performed for eight subjects using 16 b values, ranging from 0 s/mm(2) to 5000 s/mm(2). The fractional value as the turning point between the fast and slow components was determined using a diffusion decay curve. Image contrast in the white matter, gray matter, thalamus, putamen, and lateral ventricle was compared between the acquired high-b-value images and the computed high-b-value images derived from various b value images. In addition, the signal-to-noise ratio of each computed image and acquired image was measured and compared.
  
  
  RESULTS
  The fractional values obtained from the diffusion decay curve were between 1200 and 1800 s/mm(2). Image contrast in all regions was nearly equivalent between the acquired and computed high-b-value images when b values higher than the fractional value were used, whereas image contrast was significantly different between the two sets of images when b values lower than the fractional value were used (p < 0.05). The computed images derived from low-b-value images showed a higher signal-to-noise ratio, compared with the acquired images.
  
  
  CONCLUSIONS
  Optimal b values should be considered when acquiring images for the derivation of computed DW images.
authors.affiliation: 1 Graduate School, Gunma Prefectural College of Health Sciences, 323-1, Kamioki-machi, Maebashi, Gunma, Japan.
authors.forename: Akio
authors.initials: A
authors.lastname: Ogura
authors.affiliation: 2 Department of Radiology, National Hospital Organization Matsumoto Medical Center, Matsumoto, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Koyama
authors.affiliation: 1 Graduate School, Gunma Prefectural College of Health Sciences, 323-1, Kamioki-machi, Maebashi, Gunma, Japan.
authors.forename: Norio
authors.initials: N
authors.lastname: Hayashi
authors.affiliation: 3 Department of Radiology, Jichi Medical University Hospital, Tochigi-ken, Japan.
authors.forename: Isamu
authors.initials: I
authors.lastname: Hatano
authors.affiliation: 4 Department of Radiology, Gunma Saiseikai Maebashi Hopital, Gunma, Japan.
authors.forename: Kohki
authors.initials: K
authors.lastname: Osakabe
authors.affiliation: 5 Department of Radiology, Tokyo Metropolitan Tama Medical Center, Tokyo, Japan.
authors.forename: Natsumi
authors.initials: N
authors.lastname: Yamaguchi
mesh_terms: D000328:Adult; D001921:Brain / Q000033:anatomy & histology*; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D059629:Signal-To-Noise Ratio
keywords: biexponential decay; computed DWI; image contrast; optimal b value; signal-to-noise ratio