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Abstract:
Purpose/Introduction: By introducing of the higher static magnetic field, B1 + field distribution becomes inhomogeneous due to the shorter wavelength in tissue. Different experimental hardware and methods are used in order to reduce B1 + field inhomogeneity [1-3]. In this work we present a new antenna concept used for the first time as RF transmit coil at 9.4T. Antenna is used in two configurations which produce complementary B1 + field patterns that cover whole head region.
Subjects and Methods: Experiments were performed on a 9.4T MR scanner (Siemens Medical Solutions, Erlangen, Germany). The original antenna is described in [4] and is modified for operation inside of 9.4T scanner. Proposed antenna does not contain any lumped elements or matching circuits and all
antenna parts are made of copper. Antenna's geometry is shown in Fig. 1. Antenna consists of an ‘empty' rectangular
box that has five sides and is placed 2mm above ground plane. Ground plane size is 300x300mm and box size is 210x200x55mm. Two short copper straps connect box sides and ground plane. Antenna 1 and antenna 2 are used for RF excitation. The difference between them is in position of ground plane connections. Antenna 1 has ground plane
connections starting from the midpoint of the box sides while short straps of the antenna 2 are 7mm shifted from the midpoint (Fig. 1b). In measurement setup, antenna was placed at 15cm distance from the phantom's head.
Figure 2. Measured B1 + field patterns in central sagittal slice (uT/V) with antenna 1 (a) and antenna 2 (b).
Figs. 2a and 2b are initial measurement results with presented antennas. Different current distributions on antennas result in complementary B1 + field measured on a phantom. Replacement of short grounding straps with RF
MEMS switches is intended which would allow obtaining presented results with one antenna.
Discussion/Conclusion: A new antenna has been used for the first time as RF transmitting coil at 9.4T. Antenna is of very simple geometry without any lumped elements. Initial measurements performed with two antennas show B1 +
produced over large complementary parts of head. Producing a homogeneous B1 + field with one antenna is intended.
