title: 7T MRI-Histologic Correlation Study of Low Specific Absorption Rate T2-Weighted GRASE Sequences in the Detection of White Matter Involvement in Multiple Sclerosis.
abstract: BACKGROUND
  The high value of the specific absorption rate (SAR) of radio-frequency (RF) energy arising from the series of RF refocusing pulses in T2-weighted (T2-w) turbo spin echo (TSE) MRI hampers its clinical application at 7.0 Tesla (7T). T2-w gradient and spin echo (GRASE) uses the speed from gradient refocusing in combination with the chemical-shift/static magnetic field (B0) inhomogeneity insensitivity from spin-echo refocusing to acquire T2-w images with a limited number of refocusing RF pulses, thus reducing SAR.
  
  
  OBJECTIVE
  To investigate whether low SAR T2-w GRASE could replace T2-w TSE in detecting white matter (WM) disease in MS patients imaged at 7T.
  
  
  METHODS
  The .7 mm3 isotropic T2-w TSE and T2-w GRASE images with variable echo times (TEs) and echo planar imaging (EPI) factors were obtained on a 7T scanner from postmortem samples of MS brains. These samples were derived from brains of 3 female MS patients. WM lesions (WM-Ls) and normal-appearing WM (NAWM) signal intensity, WM-Ls/NAWM contrast-to-noise ratio (CNR) and MRI/myelin staining sections comparisons were obtained.
  
  
  RESULTS
  GRASE sequences with EPI factor/TE = 3/50 and 3/75 ms were comparable to the SE technique for measures of CNR in WM-Ls and NAWM and for detection of WM-Ls. In all sequences, however, identification of areas with remyelination, Wallerian degeneration, and gray matter demyelination, as depicted by myelin staining, was not possible.
  
  
  CONCLUSIONS
  T2-w GRASE images may replace T2-w TSE for clinical use. However, even at 7T, both sequences fail in detecting and characterizing MS disease beyond visible WM-Ls.
authors.affiliation: Vanderbilt University Institute of Imaging Science, Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN.
authors.forename: Francesca
authors.initials: F
authors.lastname: Bagnato
authors.forename: Simon
authors.initials: S
authors.lastname: Hametner
authors.forename: David
authors.initials: D
authors.lastname: Pennell
authors.forename: Richard
authors.initials: R
authors.lastname: Dortch
authors.forename: Adrienne N
authors.initials: AN
authors.lastname: Dula
authors.forename: Siddharama
authors.initials: S
authors.lastname: Pawate
authors.forename: Seth A
authors.initials: SA
authors.lastname: Smith
authors.forename: Hans
authors.initials: H
authors.lastname: Lassmann
authors.forename: John C
authors.initials: JC
authors.lastname: Gore
authors.forename: Edward B
authors.initials: EB
authors.lastname: Welch
mesh_terms: D065638:Absorption, Radiation; D000328:Adult; D000368:Aged; D000465:Algorithms; D001921:Brain / Q000473:pathology*; D056324:Diffusion Tensor Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D009103:Multiple Sclerosis / Q000473:pathology*; D015588:Observer Variation; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D013223:Statistics as Topic; D066127:White Matter / Q000473:pathology*
keywords: 7.0 Tesla magnetic resonance imaging; Multiple sclerosis; T2- weighted gradient and spin echo imaging; T2-weighted turbo spin echo imaging; white matter lesions