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Purpose/Introduction: Homogeneous excitation at field strengths as high as 9.4T is achieved by RF shimming approaches using parallel transmission through an array of independent RF coils. An actively detunable transmit array
with 16-elements arranged in two rows of 8-elements each was built for this purpose[1]. Receive-only coil arrays constructed using close fitting helmets provide significant gain in SNR over volume coils[2]. In this work, we design
a 31-channel receive-only head array which operates in combination with the 16-element transmit array[1].
Subjects and Methods: Experiments were performed on a Siemens 9.4T whole body MR scanner with a head gradient insert. 31-receive elements were arranged in 4 rows on a tight fitting helmet. The top 2 rows have 10-elements
each and there were 7-elements on the 3rd row and 4-elements on the 4th row. 10mm spacing was provided between the elements of the same row and they were decoupled inductively. The bottom row was rotated in such a way that it could be geometrically overlapped with 2 adjacent elements from the top row(Fig. 1). Even though our scanner is equipped with 32-receive channels, an additional element was not added to one of the bottom 2 rows to preserve the left-right symmetry in the receive array.
In addition to a protection fuse, the coil elements have 6 fixed and one variable capacitor. Low noise, small footprint preamplifiers (WanTcom Inc. USA) were installed on the coil. The coil is matched to 50-Ohms using a tissue equivalent phantom. Cable traps were incorporated before and after the preamplifier and an additional trap was installed on each of the 8-channel receive cable.
Results: Unloaded-Q of a single isolated loop was 158. The coil is sample noise dominated and the QUL/QL was 10 or more depending on the distance to the load. Active detuning during transmit was better than -33dB. Maximum coupling measured in the loaded condition was -12.2dB. The low impedance preamplifier provided -21dB of decoupling [3]. Figure 2 shows the field map acquired with and without the receive array. Initial in-vivo results shown in Fig.3 demonstrate high SNR and whole brain coverage at 9.4T.
