title: Reduced scan time three-dimensional FLAIR using modulated inversion and repetition time.
abstract: BACKGROUND
  The purpose of this study is to design and evaluate a new reduced scan time three-dimensional (3D) FLuid Attenuated Inversion Recovery (FLAIR) sequence.
  
  
  METHODS
  The 3D FLAIR sequence was modified so that the repetition time was modulated in a predetermined smooth manner (3D mFLAIR). Inversion times were adjusted accordingly to maintain cerebrospinal fluid (CSF) suppression. Simulations were performed to determine SNR for gray matter (GM), white matter (WM), and CSF. Fourteen volunteers were imaged using the modified and product sequence. SNR measurements were performed in GM, WM, and CSF. Mean value and the 95% confidence interval ([CI]) were assessed. Scan time for the 3D FLAIR and 3D mFLAIR sequences was measured.
  
  
  RESULTS
  There was no statistically significant difference in the SNR measured in GM (P value = 0.5; mean SNR = 42.8 [CI]: 38.2-45.5 versus 42.2 [CI]: 38.3-46.1 for 3D FLAIR and 3D mFLAIR, respectively) and WM (P value = 0.25; mean SNR = 32.1 [CI]: 30.3-33.8 versus 32.9 [CI]: 31.1-34.7). Scan time reduction greater than 30% was achieved for the given parameter set with the 3D mFLAIR sequence.
  
  
  CONCLUSIONS
  Scan time for 3D FLAIR can be effectively reduced by modulating repetition and inversion time in a predetermined manner while maintaining the SNR and CNR of a constant TR sequence.
authors: Radiology and Imaging Sciences, Clinical Center, National Institutes of Health, Bethesda, Maryland, USA.
authors: Neville D
authors: ND
authors: Gai
authors: John A
authors: JA
authors: Butman
mesh_terms: D000465:Algorithms; D001921:Brain / Q000033:anatomy & histology*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors; D055815:Young Adult
keywords: 3D FLAIR; modulated inversion time; modulated repetition time; scan time reduction; variable repetition time