Accuracy and precision of electrical permittivity mapping at 3T: the impact of three mapping techniques.

PURPOSE

To investigate the sequence-specific impact of amplitude mapping on the accuracy and precision of permittivity reconstruction at 3T in the pelvic region.

METHODS

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 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 bias relative to the true 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 of 0.2% of the average value. As regards precision, in vivo and phantom measurements were comparable.

CONCLUSIONS

Our simulation framework quantitatively predicts the different impact of mapping techniques on permittivity reconstruction and shows high sensitivity of permittivity reconstructions to sequence-specific bias and noise perturbation in the map. These findings are supported by the experimental results.