Reduction of a High-field Dielectric Artifact with Homemade Gel

Abstract

We developed an original dielectric-equivalent gel (Japanese Patent Application ID: P2004-236876A, February 6, 2003 pad that could improve inhomogeneous images caused primarily by B 1 homogeneity on a high-tesla magnetic resonance (MR) system. Made easily from various ingredients, our gel could reduce interference from radiofrequency waves at an object's surface and show changes in B 1 inhomogeneity. We herein assess the gel's eŠect using a plastic-bottle phantom on a 3T MR system.

New high dielectric constant materials for tailoring theB1+distribution at high magnetic fields

“…The use of pads with high dielectric constant has also been demonstrated at 3 T and is in common clinical practice at many institutions for routine body imaging at 3 T. For example, Sreenivas et al [27] used 4-L bags filled with water, doped with between 20 and 50 mM manganese salts. Similar work has been reported in phantoms by Takayama et al [28] and Sunaga et al [29], who designed a gel with dielectric constant similar to tissue for improved impedance matching to human skin. The basic mechanism by which the RF spatial distribution can be altered using such external high-dielectric structures, summarized by Yang et al [26], follows from one of Maxwell's equations:…”

Permittivity and performance of dielectric pads with sintered ceramic beads in MRI: early experiments and simulations at 3 T

“…In a growing number of applications, high dielectric materials have been used to improve the local sensitivity and/or homogeneity of the radiofrequency (RF) magnetic ( B 1 ) field in human MRI (1–13). For example, simple aqueous and gel‐based pads of dielectric materials have been used to improve local sensitivity in head imaging at 3 and 7 T (4, 10) or image homogeneity in abdominal imaging at 3 T (1–3).…”

“…In a growing number of applications, high dielectric materials have been used to improve the local sensitivity and/or homogeneity of the radiofrequency (RF) magnetic ( B 1 ) field in human MRI (1–13). For example, simple aqueous and gel‐based pads of dielectric materials have been used to improve local sensitivity in head imaging at 3 and 7 T (4, 10) or image homogeneity in abdominal imaging at 3 T (1–3). Brain imaging with pads of distilled water or a suspension made by calcium titanate (CaTiO 3 ) powder in distilled or deuterated water placed beside the head have shown a significant increase in signal‐to‐noise ratio (SNR) in the area of the temporal lobe at 7 T (4, 6, 7).…”

“…Based on this understanding, until wavelength effects (such as field nulls) become a factor, higher permittivity materials should produce greater enhancement. The dielectric materials used in MRI research tend to have relative permittivity higher than that of biological tissue on average, from aqueous solution or gel‐based material (1–4) with 50 < ε r < 80, to solid material in slurry form (6, 7, 11) with 100 < ε r < 350.…”

“…Flexible dielectric pads have been used in MRI for years (12) and at least three types of dielectric materials have been introduced: gel‐based (1, 3), liquid water‐based (2, 4, 10), and solid particulates in water creating a slurry (5, 6, 13). In earlier research (1–13), for a given volume of material, the slurries show the greatest effect on RF field distribution and SNR enhancement due to their high ε r . Creation of slurries with still higher permittivity could facilitate greater effects or require lower volumes of material.…”