title: Three-dimensional double-echo steady-state (3D-DESS) magnetic resonance imaging of the knee: establishment of flip angles for evaluation of cartilage at 1.5 T and 3.0 T.
abstract: BACKGROUND
  The effect of flip angle (FA) on synovial fluid and cartilage signal and on image contrast using three-dimensional double-echo steady-state (3D-DESS) sequence have only been performed with 1.0-T but not with 1.5-T or 3.0-T scanners.
  
  
  OBJECTIVE
  To identify the FA that gives the maximum synovial fluid and cartilage values, and to identify the FA at which maximum values of synovial fluid-cartilage contrast-to-noise ratio (CNR) in 3D-DESS sequences when 1.5-T and 3.0-T scanners are used.
  
  
  METHODS
  Using 3D-DESS with water-excitation pulse, mid-sagittal plane images of the knees of 10 healthy volunteers (5 men, 5 women; age range, 21-42 years) were obtained with FA varying from 10° to 90°. Synovial fluid signals, cartilage signals, and background were measured at each FA, and the FA that gave the highest synovial fluid and cartilage values was obtained. Synovial fluid-cartilage CNR was also calculated, and the FA that gave the largest CNR was obtained.
  
  
  RESULTS
  At 1.5 T, the maximum synovial fluid signal was at FA 90°, and the maximum cartilage signal was at FA 30°. Synovial fluid-cartilage CNR was highest at FA 90° (P < 0.05). At 3.0 T, the maximum synovial fluid signal was at FA 90°, and the maximum cartilage signal was at FA 20°. Synovial fluid-cartilage CNR was highest at FA 90° (P < 0.05).
  
  
  CONCLUSIONS
  In order to improve the visibility of cartilage itself, FA settings of 30° at 1.5 T and 20° at 3.0 T are apparently ideal. For observing the cartilage surface, the most effective FA setting is 90° for both 1.5 T and 3.0 T.
authors: Ishikawa Clinic, Kyoto, Japan. smoyari@yahoo.co.jp
authors: Susumu
authors: S
authors: Moriya
authors: Yukio
authors: Y
authors: Miki
authors: Yukako
authors: Y
authors: Matsuno
authors: Masayo
authors: M
authors: Okada
mesh_terms: D000328:Adult; D002358:Cartilage, Articular / Q000033:anatomy & histology*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007719:Knee Joint / Q000033:anatomy & histology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D012984:Software; D013582:Synovial Fluid