Simultaneous B 1+ homogenization and specific absorption rate hotspot suppression using a magnetic resonance phased array transmit coil

In high‐field MRI severe problems with respect to B  1+ uniformity and specific absorption rate (SAR) deposition pose a great challenge to whole‐body imaging. In this study the potential of a phased array transmit coil is investigated to simultaneously reduce B  1+ nonuniformity and SAR deposition. This was tested by performing electromagnetic simulations of a phased array TEM coil operating at 128 MHz loaded with two different homogeneous elliptical phantoms and four dielectric patient models. It was shown that the wave interference of a circularly polarized RF field with an ellipse and a pelvis produces largely identical B  1+ and electric field patterns. Especially for obese patients, this results in large B  1+ nonuniformity and global areas with elevated SAR deposition. It is demonstrated that a phased array transmit coil can reduce these phenomena. The technique was especially successful in suppressing SAR hotspots with a decrease up to 50%. The application of optimized settings for an ellipse to the patient models leads to comparable results as obtained with the patient‐specific optimizations. This suggests that generic phase/amplitude port settings are possible, requiring no preinformation about patient‐specific RF fields. Such a scheme would, due to its simultaneous B  1+ homogenization and extra SAR margin, have many benefits for whole‐body imaging at 3 T. Magn Reson Med 57:577–586, 2007. © 2007 Wiley‐Liss, Inc.