摘要
BackgroundRespiration-induced phase shift affects B-0/B-1(+) 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.
PurposeTo examine whether interleaved acquisition during calibration scanning could improve pTx repeatability and image homogeneity.
Study TypeProspective.
SubjectsNine healthy subjects.
Field Strength/Sequence7T MRI with a two-channel RF transmission system was used.
AssessmentCalibration scanning for B-0/B-1(+) mapping was performed under sequential acquisition/free-breathing (Seq-FB), Seq-BH, and interleaved acquisition/FB (Int-FB) conditions. The B-0 map was calculated with two echo times, and the B-1(+) 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 TestsA paired t-test with Bonferroni correction for multiple comparisons was used.
ResultsThe intersession CV/SDs for the B-0/B-1(+) 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 ConclusionUsing interleaved acquisition during calibration scans of pTx for 7T brain MRI improved the repeatability of B-0/B-1(+) mapping, AFI, and GRE images, without BH. Level of Evidence: 1 Technical Efficacy Stage 1 J. Magn. Reson. Imaging 2017.