Stretchable self-tuning MRI receive coils based on liquid metal technology (LiquiTune)

Abstract

Magnetic resonance imaging systems rely on signal detection via radiofrequency coil arrays which, ideally, need to provide both bendability and form-fitting stretchability to conform to the imaging volume. However, most commercial coils are rigid and of fixed size with a substantial mean offset distance of the coil from the anatomy, which compromises the spatial resolution and diagnostic image quality as well as patient comfort. Here, we propose a soft and stretchable receive coil concept based on liquid metal and ultra-stretchable polymer that conforms closely to a desired anatomy. Moreover, its smart geometry provides a self-tuning mechanism to maintain a stable resonance frequency over a wide range of elongation levels. Theoretical analysis and numerical simulations were experimentally confirmed and demonstrated that the proposed coil withstood the unwanted frequency detuning typically observed with other stretchable coils (0.4% for the proposed coil as compared to 4% for a comparable control coil). Moreover, the signal-to-noise ratio of the proposed coil increased by more than 60% as compared to a typical, rigid, commercial coil.

Silicone‐based materials with tailored MR relaxation characteristics for use in reduced coil visibility and in tissue‐mimicking phantom design

“…Three geometrically identical coils were fabricated as previously outlined. 6 The polymer substrate was fabricated using i) pure Ecoflex 00-30 silicone polymer and Ecoflex 00-30 mixed with Magnevist at a ratio of, ii) 1:20, and iii) 1:10 (Figure 5a). S 11 parameters and unloaded quality factors were measured using a vector network analyzer (Keysight, E5071C, Colorado Springs, CO).…”

“…[10][11][12] Novel research into innovative coil designs often involves the use of new materials that can be visible on MR images. 6 It would be a clear impediment to limit the selection of coil materials based on visibility and could severely limit the potential of these novel designs. A universal solution to reduce signal intensity in arbitrary coil materials is paramount.…”

“…In our previous work 6 we designed a stretchable RF receive coil at 3 T using Ecoflex silicone polymer. While considering potential materials for the stretchable coil, we looked at the polymers most commonly used in microfluidic and soft actuator device manufacturing, such as Sylgard, Elastosil, DragonSkin, and Ecoflex 7–9 .…”

“…In MR imaging, it is commonly undesirable to see the outline of the RF coil used because the expectation is for the focus to be on the anatomy and extra efforts are made to reduce any background noise for certain ultrashort echo time applications 10–12 . Novel research into innovative coil designs often involves the use of new materials that can be visible on MR images 6 . It would be a clear impediment to limit the selection of coil materials based on visibility and could severely limit the potential of these novel designs.…”

Characterization of a Low-Profile, Flexible, and Acoustically Transparent Receive-Only MRI Coil Array for High Sensitivity MR-Guided Focused Ultrasound

“…In this paper, we aim to improve both imaging sensitivity and acoustic transparency in one apparatus by presenting a very thin, low-profile, receive-only 8-channel head coil (FUS-Flex) operating at 3T. The design is inspired by stretchable [ 34 ], [ 35 ], flexible [ 36 ]–[ 40 ] and lightweight [ 41 ] coil technologies, offering a coil array with full conformity to the head. The novelty of our work lies in the use of very thin (~1 mm) RF elements (providing low interaction with the acoustic field), and the use of higher channel count than currently available in the literature, increasing the available imaging SNR, the sensitivity of the coil and improving/enabling parallel imaging.…”