Ticept: Wideband Electrical Properties Tomography by Tissue Composition Assessment With Quantitative ¹H²³Na³⁹K Multinuclear MRI

Purpose: 

To develop a noninvasive method for estimating dielectric properties over a wide frequency range from 50 to 600 MHz. Existing methods are limited in accuracy and provide single-frequency results. Furthermore, accurate knowledge of dielectric properties becomes more important, since medical device design and safety evaluation increasingly rely on computational modeling-based evaluation. 

Methods: 

Tissue composition assessment was performed to find the most important factors for the dielectric properties, which were sodium, potassium, and water. These were measured with a 3D acquisition-weighted density-adapted stack-of-stars scheme ((Formula presented.) Na and (Formula presented.) K) and an inversion recovery turbo spin echo sequence ((Formula presented.) H). Measurements were conducted in muscle-representative phantoms and six healthy volunteers. These measurements were used as input for mixture models, which were used to correlate the dielectric properties of the mixture with its constituents. Four different mixture models were tested to assess the feasibility of this method. 

Results: 

With the Maxwell–Garnett mixture model, a 7.9% error in the real relative permittivity and a 4.0% error in the effective conductivity are found for the phantoms. The in vivo values are in a similar range to those reported in literature. 

Conclusion: 

We presented the feasibility of estimating dielectric properties over a wide frequency band with quantitative MRI, leading to a new method: (Formula presented.) H (Formula presented.) Na (Formula presented.) K-TiCEPT. A discrepancy can be observed in the 50–200 MHz range, but the data aligns with literature from 200–600 MHz. These results show substantial intersubject differences in effective conductivity (29%), supporting the need for an accurate method to provide in vivo dielectric tissue properties.