Improvement of the repeatability of parallel transmission at 7T using interleaved acquisition in the calibration scan

• Published in: Journal of magnetic resonance imaging Vol. 48; no. 1; pp. 94 - 101
• Main Authors: Kameda, Hiroyuki, Kudo, Kohsuke, Matsuda, Tsuyoshi, Harada, Taisuke, Iwadate, Yuji, Uwano, Ikuko, Yamashita, Fumio, Yoshioka, Kunihiro, Sasaki, Makoto, Shirato, Hiroki
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.07.2018
• Subjects: 7 Tesla; Bloch−Siegert shift; Brain; Brain mapping; Calibration; Field strength; Homogeneity; Image acquisition; interleaved acquisition; Magnetic resonance imaging; Mapping; Medical imaging; Neuroimaging; parallel transmission; Reproducibility; Respiration; Scanning; Statistical analysis; Statistical tests; Bloch−Siegert shift; parallel transmission; interleaved acquisition; 7 Tesla
• ISSN: 1053-1807; 1522-2586
• DOI: 10.1002/jmri.25903

Background Respiration‐induced phase shift affects B0/B1+ mapping repeatability in parallel transmission (pTx) calibration for 7T brain MRI, but is improved by breath‐holding (BH). However, BH cannot be applied during long scans. Purpose To examine whether interleaved acquisition during calibration scanning could improve pTx repeatability and image homogeneity. Study Type Prospective. Subjects Nine healthy subjects. Field Strength/Sequence 7T MRI with a two‐channel RF transmission system was used. Assessment Calibration scanning for B0/B1+ mapping was performed under sequential acquisition/free‐breathing (Seq‐FB), Seq‐BH, and interleaved acquisition/FB (Int‐FB) conditions. The B0 map was calculated with two echo times, and the B1+ map was obtained using the Bloch‐Siegert method. Actual flip‐angle imaging (AFI) and gradient echo (GRE) imaging were performed using pTx and quadrature‐Tx (qTx). All scans were acquired in five sessions. Repeatability was evaluated using intersession standard deviation (SD) or coefficient of variance (CV), and in‐plane homogeneity was evaluated using in‐plane CV. Statistical Tests A paired t‐test with Bonferroni correction for multiple comparisons was used. Results The intersession CV/SDs for the B0/B1+ maps were significantly smaller in Int‐FB than in Seq‐FB (Bonferroni‐corrected P < 0.05 for all). The intersession CVs for the AFI and GRE images were also significantly smaller in Int‐FB, Seq‐BH, and qTx than in Seq‐FB (Bonferroni‐corrected P < 0.05 for all). The in‐plane CVs for the AFI and GRE images in Seq‐FB, Int‐FB, and Seq‐BH were significantly smaller than in qTx (Bonferroni‐corrected P < 0.01 for all). Data Conclusion Using interleaved acquisition during calibration scans of pTx for 7T brain MRI improved the repeatability of B0/B1+ mapping, AFI, and GRE images, without BH. Level of Evidence: 1 Technical Efficacy Stage 1 J. Magn. Reson. Imaging 2017.