Materials and methods for higher performance screen-printed flexible MRI receive coils

Abstract

Purpose To develop methods for characterizing materials used in screen-printed MRI coils and improve SNR with new lower-loss materials. Methods An experimental apparatus is created to characterize dielectric properties of plastic substrates used in receive coils. Coils are fabricated by screen printing conductive ink onto several plastic substrates. Unloaded and sample loaded quality factor (QUnloaded/QLoaded) measurements and scans on a 3T scanner are used to characterize coil performance. An experimental method is developed to describe the relationship between a coil's QUnloaded and the SNR it provides in images of a phantom. Additionally, 3T scans of a phantom and the head of a volunteer are obtained with a proof-of-concept printed 8-channel array and the results are compared to a commercial 12-channel array. Results Printed coils with optimized substrates can exhibit up to 97% of the image SNR when compared to a traditional coil on a loading phantom. QUnloaded and the SNR of coils are successfully correlated. The printed array results in images comparable to the quality given by the commercial array. Conclusion With the methods and materials proposed, the SNR of printed coils approaches that of commercial coils while using a new fabrication technique that provides more flexibility and close contact to the patient's body.

Custom, spray coated receive coils for magnetic resonance imaging

“…Measured values were averaged over three trials to equal 200, 210 and 320 for PEEK, SBR and PS respectively. The Q unloaded value of the PEEK film was consistent with the previously reported results 10 , confirming the reliability of the testing setup. The PS film had the highest Q unloaded and was chosen as the dielectric for the custom MRI coils.…”

“…Careful selection of materials is essential for achieving high performing sprayed MRI coils. Losses determined by the coil materials and fabrication approach can be characterized by measuring the quality factor in the absence of a sample (Q unloaded), which is inversely related to the loss contribution from the coil 10 . Losses from both dielectric and conductor material can contribute to a decrease in Q unloaded and, consequently, compromise SNR.…”

“…One of the key factors determining signal-to-noise ratio (SNR) of MR images is the design of the receive coils that are used to collect RF signal and their proximity to the patient 6 – 8 . Particularly, placing coils close to the body has been shown to significantly improve SNR and, thus, diagnostic image quality 9 , 10 . However, commercially available receive coils are typically designed to accommodate the largest possible subjects and do not optimally fit every patient or subject.…”

“…While inkjet printing allows printing coils onto the flexible substrates, it requires many printing passes to achieve the desired conductivity for RF applications 15 . Corea et al developed highly flexible and lightweight receive coils that were fabricated using scalable and low-cost screen-printing approach 9 , 10 , 13 . This paved the way to new opportunities in imaging, particularly for pediatric patients for whom conventional adult coils are especially problematic.…”

Stitching Stretchable Radiofrequency Coils for MRI: A Conductive Thread and Athletic Fabric Approach

“…Typically, to enhance the signal-to-noise ratio (SNR), receive coil arrays are shaped to encompass a generalized form of the anatomy of interest. Fixed coil arrays are durable and designed for specific applications, e.g., brain imaging; however, multiple sizes are often desirable to facilitate a closer fit and maximize SNR [2].Researchers have identified flexible coils as a means to improve SNR, with recently-proposed flexible or bendable planar RF coil designs fabricating coil conductors using screen-printing technology [3], copper braid [4], [5], and custom coaxial cable [6], [7]. These designs are well-suited for wrapping coil elements around an elliptic cylinder, e.g., the torso or abdomen.…”