title: Combined acquisition technique (CAT) for neuroimaging of multiple sclerosis at low specific absorption rates (SAR).
abstract: OBJECTIVE
  To compare a novel combined acquisition technique (CAT) of turbo-spin-echo (TSE) and echo-planar-imaging (EPI) with conventional TSE. CAT reduces the electromagnetic energy load transmitted for spin excitation. This radiofrequency (RF) burden is limited by the specific absorption rate (SAR) for patient safety. SAR limits restrict high-field MRI applications, in particular.
  
  
  METHODS
  The study was approved by the local Medical Ethics Committee. Written informed consent was obtained from all participants. T2- and PD-weighted brain images of n = 40 Multiple Sclerosis (MS) patients were acquired by CAT and TSE at 3 Tesla. Lesions were recorded by two blinded, board-certificated neuroradiologists. Diagnostic equivalence of CAT and TSE to detect MS lesions was evaluated along with their SAR, sound pressure level (SPL) and sensations of acoustic noise, heating, vibration and peripheral nerve stimulation.
  
  
  RESULTS
  Every MS lesion revealed on TSE was detected by CAT according to both raters (Cohen's kappa of within-rater/across-CAT/TSE lesion detection κCAT = 1.00, at an inter-rater lesion detection agreement of κLES = 0.82). CAT reduced the SAR burden significantly compared to TSE (p<0.001). Mean SAR differences between TSE and CAT were 29.0 (± 5.7) % for the T2-contrast and 32.7 (± 21.9) % for the PD-contrast (expressed as percentages of the effective SAR limit of 3.2 W/kg for head examinations). Average SPL of CAT was no louder than during TSE. Sensations of CAT- vs. TSE-induced heating, noise and scanning vibrations did not differ.
  
  
  CONCLUSIONS
  T2-/PD-CAT is diagnostically equivalent to TSE for MS lesion detection yet substantially reduces the RF exposure. Such SAR reduction facilitates high-field MRI applications at 3 Tesla or above and corresponding protocol standardizations but CAT can also be used to scan faster, at higher resolution or with more slices. According to our data, CAT is no more uncomfortable than TSE scanning.
authors.affiliation: Department of Neuroradiology, University of Heidelberg, Heidelberg, Germany.
authors.forename: Armin
authors.initials: A
authors.lastname: Biller
authors.affiliation: Research Center for Magnetic-Resonance-Bavaria (MRB), Wuerzburg, Germany.
authors.forename: Morwan
authors.initials: M
authors.lastname: Choli
authors.affiliation: Research Center for Magnetic-Resonance-Bavaria (MRB), Wuerzburg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Blaimer
authors.affiliation: Research Center for Magnetic-Resonance-Bavaria (MRB), Wuerzburg, Germany.
authors.forename: Felix A
authors.initials: FA
authors.lastname: Breuer
authors.affiliation: Research Center for Magnetic-Resonance-Bavaria (MRB), Wuerzburg, Germany; Department of Experimental Physics 5, University of Wuerzburg, Wuerzburg, Germany.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Jakob
authors.affiliation: Department of Neuroradiology, University of Heidelberg, Heidelberg, Germany; FMRIB Centre, University of Oxford, Oxford, United Kingdom.
authors.forename: Andreas J
authors.initials: AJ
authors.lastname: Bartsch
mesh_terms: D000328:Adult; D017352:Echo-Planar Imaging / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D060733:Electromagnetic Radiation; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000175:diagnosis* / Q000473:pathology; D059906:Neuroimaging / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D011835:Radiation Protection