Simultaneous B1+ homogenisation and SAR hotspot suppression by a phased array MR transmit coil

C. A. van den Berg, B. van den Bergen, H. Kroeze, L. W. Bartels, J. J. Lagendijk Dept. of Radiotherapy, University Medical Centre, Utrecht, Utrecht, Netherlands, Dept. of Radiology, University Medical Centre, Utrecht, Utrecht, Netherlands Introduction The application of MR imaging at high field (B0 ≥ 3 T, f ≥ 128 MHz) faces considerable challenges with respect to uniformity of the RF magnetic excitation (B1 ) field and power deposition. Wave behaviour and penetration effects causing severe degradation of the image quality, have been reported both numerically and experimentally [1,2]. Furthermore, the stronger coupling of the RF field to small anatomical features with high dielectric contrast can lead to local high SAR values [3]. This concern has become more acute at high field MR imaging since the RF dissipation increases quadratically with the Larmor frequency.