Ultra-flexible and light-weight 3-channel coaxial transmission line resonator receive-only coil array for 3T
Michael Obermann1, Lena Nohava1,2, Sigrun Goluch-Roat1, Michael Pichler1, Jürgen Sieg1, Jacques Felblinger3, Jean-Christophe Ginefri2, and Elmar Laistler1

1Division MR Physics, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria, 2IR4M (Imagerie par Résonance Magnétique et Multi-Modalités), UMR 8081, Université Paris-Sud/CNRS, Université Paris-Saclay, Orsay, France, 3Université de Lorraine, Inserm, IADI, Nancy, France


An ultra-flexible light-weight coaxial coil array with compact interfaces is introduced. The interfaces consist of components for tuning, active detuning, matching and preamplifier decoupling. Bench and MR tests of the array are presented and the robustness with regard to bending is demonstrated.


Transmission line resonators1 have been studied for various applications2,3. Lately, a new concept using coaxial cables with one gap of the inner and the outer conductor was introduced4,5. These self-resonant coils have good geometrical decoupling characteristics over an extended overlap range. In combination with thin coaxial cables, this design is well suited for applications where coil flexibility is advantageous, i.e. especially when anatomical inter-subject variability is large or the shape of the region of interest is changing during the measurement. Here, an ultra-flexible 3-channel receive-only one-gap coaxial coil array with compact interfaces is presented.


Three one-gap coaxial coils with diameter dcoil = 80 mm were made from very thin coaxial cable (Siemens Rx cable, Stark Contrast, Erlangen, Germany) with an inner conductor diameter of 0.2 mm, an outer conductor diameter of 0.9 mm. The interface contains tuning, active detuning, matching as well as preamplifier decoupling combined in one compact layout (15x45x10 mm³) (Fig. 1). To obtain the optimal overlap dopt, S21 was measured on the network analyzer (E5061B, Keysight Technologies, Santa Rosa, CA, USA) while the center-to-center distance between two coils was varied between 30 and 160 mm. The three coaxial coils were then centered at the corners of an equilateral triangle with side length dopt (Fig. 2a). To keep the geometry roughly unaltered upon bending, the coils were woven into a wide-meshed textile tissue. This mesh was sewn onto an additional 2 mm foam padding and an outer layer of medical synthetic leather for stability, component protection, and electrical insulation (Fig 2b, top textile layers not shown). To evaluate robustness w.r.t bending, the S-parameter matrix was measured in flat and bent position on a torso phantom filled with tissue-equivalent gel3. The noise correlation matrix was calculated from MR noise-only data with the array in flat configuration on the phantom. To demonstrate the flexibility of the array, two T2-weighted double echo 3D MR scans were performed on a pineapple with the array either positioned laterally (Fig. 4a) with TR = 15.98 ms, TE = 5.35 ms, α = 25° and on the bottom of the fruit (not shown) using TR = 14.97 ms, TE = 4.85 ms, α = 25°.

Results and Discussion

A picture of the implemented array is shown in Fig. 2b. The optimal overlap was determined to be dopt ≈ 62 mm (Fig. 3a), which is similar to the optimal overlap described by Zhang et al., i.e. dopt ≈ 0.78 dcoil. The S-parameter matrices for the flat and bent setup are very similar (Fig. 3b,c). Noise correlation values < 4% were obtained, as demonstrated in Fig. 3d. The pineapple was nicely depicted in the MR scans (Fig. 4b,c). The total weight of one coil element including interface and preamplifier is about 12 g, excluding the textile enclosure. With the specific weight of the 4-layer textile used (≈ 2 kg/m²), adding array cabling (≈ 0.5 m per channel, ≈ 3.2 g/m), cable traps (≈ 5 g/channel), and additional components for fixation on the patient (≈ 200 g), we can extrapolate a total weight of ≈ 1 kg for a 32-channel version of such an array, making it a comfortably wearable device for patients.


An ultra-flexible and light-weight 3-channel receive-only coaxial coil array for 3T MRI with compact interfaces implemented on flexible textile is presented. The robustness of matching and decoupling upon bending was demonstrated, rendering such coil elements promising candidates for larger flexible arrays for applications, where anatomical inter-subject variability is large, e.g. in breast MRI.


This project was funded by the Austrian/French FWF/ANR grant, Nr. I-3618, “BRACOIL“, and Austrian/French OeaD WTZ grant FR 03/2018.


1 Gonord P et al. Parallel-Plate Spit-Conductor Surface Coil: Analysis and Design. Magn Reson Med 1988;6(3):353–358.

2 Frass-Kriegl R et al. Multi-turn multi-gap transmission line resonators – concept, design and first implementation at 4.7 T and 7 T. J Magn Reson 2016;273:65-72.

3 Hosseinnezhadian S et al. A flexible 12-channel transceiver array of transmission line resonators for 7T MRI. J Magn Reson 2018;296:47-59.

4 Zhang B et al. A high-impedance detector-array glove for magnetic resonance imaging of the hand. Nat Biomed Eng 2018;2:570–577.

5 Laistler E, Moser E. Handy magnetic resonance coils. Nat Biomed Eng 2018;2:557-558.


Figure 1: (a) Schematics of the interface consisting of tuning, active detuning, matching and preamplifier decoupling, combined on one circuit board. (b) A picture of the implemented interface with connected preamplifier (r.h.s) and the coil (shown partly on the bottom left).

Figure 2: (a) Layout of the coil array. The centers of the coils are positioned on the corner of an equilateral triangle with side length dopt which represents the optimal overlap from Fig. 3a. (b) Photograph of the implemented ultra-flexible 3-channel array.

Figure 3: (a) Determining the optimal overlap distance dopt. (b), (c) S-parameter matrix of the 3-ch coaxial coil array on a flat and bent position on the torso phantom, respectively. (d) Noise correlation matrix.

Figure 4: (a) Experimental setup with the array positioned on the side of a pineapple. (b) Sagittal scan with the array positioned laterally, (c) and on the bottom of the fruit.

Proc. Intl. Soc. Mag. Reson. Med. 27 (2019)