TY - JOUR
T1 - Accuracy and precision of electrical permittivity mapping at 3T: the impact of three B1+ mapping techniques
AU - Gavazzi, Soraya
AU - van den Berg, Cornelis A. T.
AU - Sbrizzi, Alessandro
AU - Kok, H. Petra
AU - Stalpers, Lukas J. A.
AU - Lagendijk, Jan J. W.
AU - Crezee, Hans
AU - van Lier, Astrid L. H. M. W.
PY - 2019
Y1 - 2019
N2 - Purpose: To investigate the sequence-specific impact of B + 1 amplitude mapping on the accuracy and precision of permittivity reconstruction at 3T in the pelvic region. Methods: B + 1 maps obtained with actual flip angle imaging (AFI), Bloch–Siegert (BS), and dual refocusing echo acquisition mode (DREAM) sequences, set to a clinically feasible scan time of 5 minutes, were compared in terms of accuracy and precision with electromagnetic and Bloch simulations and MR measurements. Permittivity maps were reconstructed based on these B + 1 maps with Helmholtz-based electrical properties tomography. Accuracy and precision in permittivity were assessed. A 2-compartment phantom with properties and size similar to the human pelvis was used for both simulations and measurements. Measurements were also performed on a female volunteer’s pelvis. Results: Accuracy was evaluated with noiseless simulations on the phantom. The maximum B + 1 bias relative to the true B + 1 distribution was 1% for AFI and BS and 6% to 15% for DREAM. This caused an average permittivity bias relative to the true permittivity of 7% to 20% for AFI and BS and 12% to 35% for DREAM. Precision was assessed in MR experiments. The lowest standard deviation in permittivity, found in the phantom for BS, measured 22.4 relative units and corresponded to a standard deviation in B + 1 of 0.2% of the B + 1 average value. As regards B + 1 precision, in vivo and phantom measurements were comparable. Conclusions: Our simulation framework quantitatively predicts the different impact of B + 1 mapping techniques on permittivity reconstruction and shows high sensitivity of permittivity reconstructions to sequence-specific bias and noise perturbation in the B + 1 map. These findings are supported by the experimental results.
AB - Purpose: To investigate the sequence-specific impact of B + 1 amplitude mapping on the accuracy and precision of permittivity reconstruction at 3T in the pelvic region. Methods: B + 1 maps obtained with actual flip angle imaging (AFI), Bloch–Siegert (BS), and dual refocusing echo acquisition mode (DREAM) sequences, set to a clinically feasible scan time of 5 minutes, were compared in terms of accuracy and precision with electromagnetic and Bloch simulations and MR measurements. Permittivity maps were reconstructed based on these B + 1 maps with Helmholtz-based electrical properties tomography. Accuracy and precision in permittivity were assessed. A 2-compartment phantom with properties and size similar to the human pelvis was used for both simulations and measurements. Measurements were also performed on a female volunteer’s pelvis. Results: Accuracy was evaluated with noiseless simulations on the phantom. The maximum B + 1 bias relative to the true B + 1 distribution was 1% for AFI and BS and 6% to 15% for DREAM. This caused an average permittivity bias relative to the true permittivity of 7% to 20% for AFI and BS and 12% to 35% for DREAM. Precision was assessed in MR experiments. The lowest standard deviation in permittivity, found in the phantom for BS, measured 22.4 relative units and corresponded to a standard deviation in B + 1 of 0.2% of the B + 1 average value. As regards B + 1 precision, in vivo and phantom measurements were comparable. Conclusions: Our simulation framework quantitatively predicts the different impact of B + 1 mapping techniques on permittivity reconstruction and shows high sensitivity of permittivity reconstructions to sequence-specific bias and noise perturbation in the B + 1 map. These findings are supported by the experimental results.
UR - https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85063373794&origin=inward
UR - https://www.ncbi.nlm.nih.gov/pubmed/30737816
U2 - https://doi.org/10.1002/mrm.27675
DO - https://doi.org/10.1002/mrm.27675
M3 - Article
C2 - 30737816
SN - 0740-3194
VL - 81
SP - 3628
EP - 3642
JO - Magnetic resonance in medicine
JF - Magnetic resonance in medicine
IS - 6
ER -