To develop a novel radio-frequency (RF) concept for ultra-high field (UHF) human magnetic resonance imaging (MRI) based on a coaxial resonant cavity. Methods: A two-channel slotted coaxial cavity RF applicator was designed for human head MRI at 9.4T. Physical dimensions made the proposed conducting structure resonant at the required frequency without tuning lumped elements. Numerical electromagnetic modeling was used to optimize the design. RF safety was assessed with two representative human body models. MR experiments on a 9.4T scanner included gradient echo images and mapping of a circularly polarized RF magnetic field in the human head phantom. Results: The simulations and the phantom MR experiments agreed both qualitatively and quantitatively. The design was relatively simple, robust and required only a few additional reactive elements for the applicator's input impedance matching. The transmit efficiency and homogeneity of the excitation field were only 20% and 4% lower compared to a conventional 8-channel head array. Conclusion: The coaxial RF applicator was feasible for human MRI at UHF and required no lumped elements for its tuning. Imaging performance of the RF applicator was only moderately lower compared to the conventional transmit array, but would be sufficient to provide an anatomical reference for the heteronuclei MRI. Significance: An alternative approach with the minimal involvement of lumped elements becomes feasible to design volume-type RF coils for UHF human MRI.
Bibliographical noteFunding Information:
Manuscript received September 21, 2018; revised November 21, 2018; accepted January 10, 2019. Date of publication February 1, 2019; date of current version September 18, 2019. This work was supported in part by Grants NIH P41EB015894, NIH S10 RR25437, NIH P30 NS076408, and NIH R21 EB009133, in part by the WM KECK Foundation, NWO-Veni 2009 Grant of Dr. C.A.T. van den Berg, Gov-erment of Russian Federation under Grant 08-08, in part by the Ministry of Education and Science of the Russian Federation (Zadanie No. 3.2465.2017/4.6), and in part by the Government of the Russian Federation through the ITMO Fellowship and Professorship Program. (Corresponding author: Georgiy Solomakha.) G. Solomakha is with the ITMO University, St. Petersburg 197101, Russia (e-mail:,email@example.com).
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- Coaxial radio-frequency applicator
- resonant cavity
- ultra high field