In magnetic resonance-based electrical properties tomography (EPT), circularly polarized magnetic field B 1 from a transmit radiofrequency (RF) coil is measured and utilized to infer the electrical conductivity and permittivity of biological tissues. Compared with a quadrature RF coil, a multi-channel transmit coil provides a plurality of unique transmit B 1 patterns that help to alleviate the under-determinedness of EPT reconstruction problem, and it also allows to circumvent the 'transceive phase assumption' that fails at ultra-high-field MRI. Here, a new approach, contrast conformed electrical properties tomography or CONCEPT, is proposed based on the multi-channel transmission that retrieves electrical properties (EPs) by solving a linear partial differential equation with discriminated L 1 and L 2 norm regularization informed by intermediate EP gradient. The theory of CONCEPT and a fast reconstruction algorithm based on the alternating direction method of multipliers are described and evaluated using numerical simulations, phantom experiment, and analysis of in vivo human brain data at 7 T MRI. Compared with the multi-channel gradient-based EPT (gEPT) method, this new technology does not require receive-B 1 sensitivity profiles and does not rely on symmetry assumption regarding RF coil design and imaged target. Moreover, it is not dependent on external prior information, such as integration seed point or anatomical MRI, which can be sources of bias in reconstructed EP values. By deriving EPs from transmit B 1 profiles only, CONCEPT can be used with RF coils that include receive-only arrays with large channel count which can, in turn, offer substantial gains in signal-to-noise ratio. It also holds potentials to image unsymmetrical body organs and diseased brain. CONCEPT provides solutions for the practical problems during the implementation of gEPT, thus representing a more generalized framework in the context of multi-channel RF transmission.
Bibliographical noteFunding Information:
Manuscript received June 7, 2018; revised August 6, 2018; accepted August 8, 2018. Date of publication August 13, 2018; date of current version February 1, 2019. This work was supported in part by NIH under Grant R21 EB017069, Grant R01 MH114223, Grant R01 EB021027, Grant R01 NS096761, Grant R01 AT009263, Grant R21 EB014353, Grant P41 EB015894, Grant R01 EB011551, Grant S10 RR026783, and Grant NSF CBET-1450956, and in part by the WM KECK Foundation. (Corresponding author: Bin He.) Y. Wang is with the Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455 USA.
- B mapping
- Electrical properties tomography (EPT)
- alternating direction method of multipliers (ADMM)
- magnetic resonance imaging (MRI)
- multichannel transmission