7 Tesla MRI: Proton imaging and RF pulse design

The research group focuses on MR proton imaging in humans at ultrahigh field (UHF) of 7 Tesla with a special interest in body imaging at this field strength. Due to the short radiofrequency (RF) wavelength, the spatial distribution of the magnetic component of the RF field (B1+), which is necessary for the imaging process, is highly inhomogeneous. This yields inhomogeneous signal and contrast distributions in the body (see Figure), making a diagnosis difficult or impossible. To counteract this effect, we use multi-transmit (Tx) body coils in combination with parallel transmission (pTx) techniques and dedicated RF pulses.
The spatial variation of the B1+ field can be altered by pTx and thereby homogeneous flip angles of the proton spins can be achieved, which homogenizes the contrast. A special focus of the working group is the use of the "MRExcite" body coil (RF arrays), which, unlike conventional transmit coils, is not placed locally on the body, but is installed in the scanner behind the bore liner. This coil contains 32 Tx channels (multi-channel transmit systems) and thus offers a higher degree of freedom for pTx compared to most local coils. One of the goals of the research group is to take advantage of the system and to evaluate the benefits and challenges of 7 Tesla body imaging for future clinical applications.