Screen-printed flexible MRI receive coils - PubMed (original) (raw)

Screen-printed flexible MRI receive coils

Joseph R Corea et al. Nat Commun. 2016.

Abstract

Magnetic resonance imaging is an inherently signal-to-noise-starved technique that limits the spatial resolution, diagnostic image quality and results in typically long acquisition times that are prone to motion artefacts. This limitation is exacerbated when receive coils have poor fit due to lack of flexibility or need for padding for patient comfort. Here, we report a new approach that uses printing for fabricating receive coils. Our approach enables highly flexible, extremely lightweight conforming devices. We show that these devices exhibit similar to higher signal-to-noise ratio than conventional ones, in clinical scenarios when coils could be displaced more than 18 mm away from the body. In addition, we provide detailed material properties and components performance analysis. Prototype arrays are incorporated within infant blankets for in vivo studies. This work presents the first fully functional, printed coils for 1.5- and 3-T clinical scanners.

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Conflict of interest statement

The authors declare no competing financial interests.

Figures

Figure 1

Figure 1. RF receive coil arrays proximity to body results in better image SNR.

(a) Conventional MRI receive arrays on the chest and head of a patient. (b) Cervical spine images of volunteer showing low-SNR when using a coil placed 8 cm away from the spine (left) and high SNR when placed against the skin (right). (c) Schematic representation of fabrication process of flexible printed coils. The screen is patterned with emulsion (blue) and shows the coil design. Ink (grey) is transferred to the substrate (white) during the screen-printing process. (d) Photograph of a printed flexible four-channel coil array fabricated on plastic film and integrated into an infant blanket. The inset shows how a printed coil is stitched into the fabric. (e) Concept drawing of an infant swaddle and hat with an integrated printed receive coil array.

Figure 2

Figure 2. Fabrication method and characterization of printed receive coils.

(a) Schematic of a printed coil showing tuning, Ct, and matching, Cm, capacitors. (b) Photograph of a printed coil. Inset highlights top-down view of printed capacitor. (c) Coil printing process flow showing two optional possible processes: printed dielectric or using the substrate as a dielectric. (d) Dependence of capacitance with top electrode area, dielectric thickness and ink composition. (e) Relative dielectric constant, measured at 127 MHz, as the volume of barium titanate in the ink is increased. High dielectric constant is achieved with barium titanate ink, while low dielectric constant is achieved with ultraviolet-curable ink. Error bars show standard deviation.

Figure 3

Figure 3. 1.5- and 3-T scanner receive coil SNR characterization.

(a) Normalized SNR versus depth into the phantom for coils fabricated with different permutations of printed components at 3 T, with schematic showing coil position 3 mm away from conductive fluid. Bar graph summarizes trends shown in relative SNR for each coil type. Dot on bar graph shows predicted SNR extracted from bench top quality factor measurements. (b) Relative measured (bars) and bench top-predicted (dots) image SNR of printed coils at 1.5 and 3 T. (c) Relative SNR for control and printed coils versus increasing coil offsets from the top surface of the phantom. Black dashed-dotted line highlights the position offset where the control coil shows equal SNR to the printed coils when the printed one has no offset from the top surface of the phantom. Light thin lines represent calculated best case performance when preamplifiers are added to the coil. Error bars show standard deviation. (d) Average normalized SNR profile for printed coils flexed around the surface of a curved saltwater phantom (blue) and placed on a flat phantom (red) at 3 T. Wide coloured bands indicate the s.d. across several coils.

Figure 4

Figure 4. In vivo imaging with flexible coil array at 3 T.

(a) Proof of concept, prototype of printed flexible four-channel receive array. (b) Sagittal cervical spine MRI image showing excellent penetration due to the conformity of the array. (c) Single-element MRI image of a knee. (d) Scan showing the expected improved penetration using a four-channel array wrapped around the leg of a volunteer. Highlighted areas show region of interest with higher SNR from increased field of view from array.

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