title: Breath-holding during the Calibration Scan Improves the Reproducibility of Parallel Transmission at 7T for Human Brain.
abstract: OBJECTIVE
  The B0 and B1+ maps required for calculation of the radiofrequency (RF) pulse of parallel transmission (pTx) are obtained in calibration scans; however, they may be affected by respiratory motion. We aimed to compare the reproducibility of B0 and B1+ maps and gradient echo (GRE) images of the brain scanned with pTx at 7T between free-breathing (FB) and breath-holding (BH) conditions during the calibration scan.
  
  
  METHODS
  Nine healthy volunteers were scanned by 7T MRI using a two-channel quadrature head coil. In the pTx calibration scans performed with FB and BH, the B0 map was obtained from two different TE images and the B1+ map was calculated by the Bloch-Siegert method. A GRE image (gradient-recalled-acquisition in steady state) was also obtained with RF shimming and RF design of pTx with spoke method, as well as quadrature transmission (qTx). All the scans were repeated over five sessions. The reproducibility of the B0 and B1+ maps and GRE image was evaluated with region-of-interest measurements using inter-session standard deviation (SD) and coefficient of variation (CV) values. Intensity homogeneity of GRE images was also assessed with in-plane CV.
  
  
  RESULTS
  Inter-session SDs of B0 and B1+ maps were significantly smaller in BH (P < 0.01). Inter-session CVs of GRE images were significantly smaller in qTx than BH and FB (P < 0.01, both); however, the CVs of BH were significantly smaller (P < 0.01). In-plane CVs of FB and BH with RF shimming were not significantly different with qTx; however, CVs of FB and BH with RF design were significantly smaller than those of qTx (P < 0.05 and P < 0.01, respectively).
  
  
  CONCLUSIONS
  BH could improve the reproducibility of B0 and B1+ maps in pTx calibration scans and GRE images. These results might facilitate the development of pTx in human brain at 7T.
authors.affiliation: Department of Radiation Medicine, Hokkaido University Graduate School of Medicine.
authors.forename: Taisuke
authors.initials: T
authors.lastname: Harada
authors.forename: Kohsuke
authors.initials: K
authors.lastname: Kudo
authors.forename: Ikuko
authors.initials: I
authors.lastname: Uwano
authors.forename: Fumio
authors.initials: F
authors.lastname: Yamashita
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kameda
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Matsuda
authors.forename: Makoto
authors.initials: M
authors.lastname: Sasaki
authors.forename: Hiroki
authors.initials: H
authors.lastname: Shirato
mesh_terms: D000328:Adult; D001921:Brain / Q000000981:diagnostic imaging*; D062485:Breath Holding; D002138:Calibration; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D015203:Reproducibility of Results