8CH 19F/1H Transceiver Array for Lung Imaging at 7T (pTX)
Helmar Waiczies1, Andre Kuehne1, Armin M. Nagel2,3, Dennis Schuchardt1, Darius Lysiak1, Jan Rieger1, and Thoralf Niendorf1,4

1MRI.Tools GmbH, Berlin, Germany, 2Division of Medical Physics in Radiology, Cancer Research Center (DKFZ), Heidelberg, Germany, 3Diagnostic and Interventional Radiology, University Medical Center Ulm, Ulm, Germany, 4Berlin Ultrahigh FieldFacility (B.U.F.F.), Max Delbrück Center for Molecular Medicine, Berlin, Germany


Lung MR-Imaging is challenging due to low proton density in the lung. Ventilation can only be visualized directly using exogenous contras agents such as hyperpolarized noble gases or 19F-containing gasses as a “contrast agents”. This work proposes a multi-channel transmit and receive (TX/RX) radiofrequency (RF) coil that supports eight TX/RX channels (4 loop- and 4 dipole-elements) for 19F and 1H lung imaging at 7.0T using a pTX-array.


Diagnostic imaging of lung disorders is of high clinical relevance. MRI of the lung constitutes a challenge [1], due to low proton density. Consequently, lung ventilation is commonly visualized using hyperpolarized noble gases [2], sulphur hexafluoride (SF6) [3] or other exogenous agents. 19F-containing gasses presents a valuable alternative. In recognizing of this opportunity, this study proposes an eight channel 19F/1H transceiver array tailored for lung imaging at 7.0 T using a pTX-Array. The feasibility of the proposed RF coil array for 19F/1H-MRI is demonstrated in phantom experiments and in in vivo studies.

Materials and Methods

The RF coil consists of a planar posterior (Fig1. A) and an anterior (Fig1. B) section which is modestly curved to conform to an average chest. Each section contains 2 loops and two dipoles optimized for 19F (f=279 MHz, element size 300 x 50 mm²) and a RF-shield (Fig1 C). EMF-simulations were performed using CST Studio Suite 2014 (CST AG, Darmstadt, Germany) with a phantom (Fig 3 A), voxel model Duke (Fig. 2) and Ella (Virtual family, IT’IS Foundation, Zurich, Switzerland). B1+-shimming using simulated data was performed to improve the transmission field homogeneity at minimum SAR within a VOI covering the lung (Fig. 2). Local SAR averaged over 10g of tissue was calculated and the input power was adjusted to meet the limits of IEC 60601-2-33 Ed.3. This procedure was applied for the 19F- and 1H-frequency. Measurements were performed on a torso phantom containing Agarose-gel+NaCl and a cylindrical insert containing Galden (Apollo Scientific Ltd., Denton, Manchester, UK), a Perfluoropolyether, using a 7 T whole body MRI system with an 8-channel pTX-Array (Magnetom, Siemens, Erlangen, Germany). Two different phase settings where employed- phaseset 0: same phase setting for all channels, phaseset 1: phase setting deduced from EMF simulation of the human voxel models Duke and Ella. To validate the simulation a Bloch-Siegert B1-mapping technique was utilized[4] (Fig.3 B). 1H-MRI: 2D-FLASH, TR/TE=100/3.3ms, FA=20°, resolution=(0.78x0.78x5)mm3, avg=1 (Fig. 3 C). 19F-MRI: 2D-FLASH, TR/TE=20/3ms,FA=20°, resolution=(1.95x1.95x5)mm3, avg=32 (Fig. 3 D). Whole VOI coverage 19F 3D datasets were acquired with a density-adapted 3D radial acquisition technique [5]: TE=0.4 ms, TR=11 ms, TRO=7.1 ms, TX amplitude 115 V (~90% SAR) equivalent to a tip angle of 30-40°, number of projections=50000, averages=2, voxel size=(1.95x1.95x1.95) mm³, scantime = 18:20min (Fig. 4). In-vivo cardiac 1H imaging was performed using 2D CINE FLASH: matrix 256x256, TE=1.84 ms, TR=4.14 ms, voxel size (1.4x1.4x4.0) mm³, cardiac phases=30, total acquisition time=0:16 min. An MR stethoscope (EasyACT, MRI.TOOLS GmbH, Berlin, Germany) was employed for cardiac gating [6]


The reflection coefficients of the eight channels were less than -20dB@279MHz and less than -7dB@297MHz. The coupling between the channels was less than -12dB@279MHz and less than -20dB@297MHz. Maximum local SAR10g did not exceed the limits of 20 W/kg for an input power of 34 W for 279MHz and 297MHz. Whole body and partial body SAR were well below the IEC limits. The combination of independent loops and dipole-elements was of advantage for decoupling reasons. The outer loop-elements could be easier tuned and matched to the human body. The inner dipoles provided higher depth-penetration, which was instrumental to cover the entire VOI. B1+ mapping confirmed the transmission fields deduced from EMF simulations (Fig. 3+4). To demonstrate the in-vivo B1+ uniformity of the array for deep lying organs in the torso, cardiac and renal MR was conducted at 297 MHz (Fig. 5).


This work demonstrates the feasibility of an eight channel transceiver array tailored for 19F lung MRI. Our results show that the array can be also used for 1H imaging, therfore supports anatomical 1H imaging as well as functional 19F MRI of the lung in clinically acceptable scan times. The proposed eight channel 1H/19F transceiver RF coil array contributes to the technological basis for the clinical assessment of lung ventilation and pulmonary inflammation but also to research into the bio distribution and bioavailability of 19F-containing drugs. The results underscore the challenges of fluorine MR in humans and demonstrate that these issues can be offset by using tailored RF coil hardware. The benefits of such improvements would be in positive alignment with the technological requirements of further studies, that are designed to examine the potential of 19F MR to trace and quantify 19F-containing agents and drugs.


This project was supported in part (H.W.) by the German Federal Ministry of Education and Research, “KMU-innovativ”: Medizintechnik MED-373-046.


[1] Biederer, J. et al., 2012, Insights Imaging 3, 355–371
[2] Wild JM, et al., 2002, Phys Med Biol 47:N185–N190
[3] Scholz A-W, et al., 2009, Magn Reson Imaging 27:549–556
[4] F. Carinci, D. Santoro, et al., 2013, PloS One. 8
[5] Nagel, AM, et al., Magnetic resonance in, 2009, 62(6):1565–1573
[6] Frauenrath, T, et al., Journal of cardiovascular magnetic, 2010;12:67


Fig.1: EMF-simulation setup using the voxel-model „Duke“. (A) anterior section, (B) posterior section, (C) an axial cut through the center of the array depicting the position of the RF-shield

Fig. 2: 10g SAR and B1+-field results after B1-optimization using phaseset 1, the black outline depicts the optimization volume (lung).

Fig. 3: comparison of the two phasesets – phaseset 0 where all phases of the 8 channels are the same and phaseset 1, an optimized phaseset for lung-imaging (optimized on Duke and Ella, not on the phantom). (A) simulated B1-map, (B) measured B1-map, (C) gradient-echo 1H image, TR/TE=100/3.3ms, FA=20°, resolution=(0.78x0.78x5) mm3, avg=1, (D) 19F gradient-echo images of a cylinder containing Galden, using two different phase settings. TR/TE=20/3ms, FA=20°, resolution= (1.95x1.95x5) mm3, avg=32

Fig. 4: 19F 3D datasets acquired with a density-adapted 3D radial acquisition technique [5]: TE=0.4ms, TR=11ms, TRO=7.1ms, TX amplitude 115 V (~90% SAR) equivalent to a tip angle of 30-40°, number of projections=50000, averages=2, voxel size=(1.95x1.95x1.95) mm³, using two different phasesettings, top row: phaseset 0 – all phases the same, bottom row: phaseset 1, an optimized phaseset for lung-imaging (optimized on Duke and Ella, not on the phantom).

Fig. 5: (A)+(B): 2D CINE FLASH cardiac gated MR: matrix 256x256, TE=1.84ms, TR=4.14ms, voxel size (1.4x1.4x4.0) mm³, (C): 2D-FLASH, TR/TE=10/4ms, FA=40°, resolution=(1.09x1.09x8) mm3, avg=1, showing a coronal cross-section through the kidneys, using an eight channel transceiver array (4 loop- and 4 dipole-elements) phase optimized for 19F and 1H lung imaging at 7.0T pTX-array.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)