SAR hotspot reduction by temporal averaging in parallel transmission MRI

A magnetic resonance system comprising:

• N RF transmit elements, where N is a plural discrete number, disposed adjacent a patient receiving region;
• N RF transmitters, each connected with one of the RF transmit elements;
• a control processor programmed to control the transmit elements to apply a plurality of variations of a repetitive pulse by superposition in time of individual pulses from discrete independently controlled transmit elements during a magnetic resonance sequence, the variations of the repetitive pulse being configured to cause specific absorption rate (SAR) hot spot locations with subsequent applications of the repetitive pulse to generate SAR hot spots in locations of SAR low spots, wherein the SAR low spots are regions of low energy deposition;
• a magnetic resonance signal receive system configured to receive magnetic resonance signals generated by the magnetic resonance sequence;
• a resonance signal processor configured to process the received magnetic resonance signals;
• and
• a display configured to display results of the magnetic resonance signal processing.

A method of imaging, in which applying a magnetic resonance sequence includes a repetitively applied radiofrequency (RF) pulse capable of causing a specific absorption rate (SAR) hot spot, the method comprising acts if:

• determining locations of SAR hot spots and SAR low spots based on stored SAR simulation data, wherein the SAR low spots are regions of low energy deposition;
• determining a composition of the repetitive pulse to change the SAR hot spot locations with subsequent applications of the repetitive pulse to generate SAR hot spots in the location of SAR low spots;
• and
• varying the composition of the repetitive pulse based on the determined composition of the repetitive pulse.