Reducing the radio-frequency transmit field in a predetermined volume during magnetic resonance imaging

A method of operating a magnetic resonance imaging system for acquiring magnetic resonance data from a subject within an imaging zone, wherein the magnetic resonance imaging system comprises a radio-frequency transmitter for generating a radio-frequency transmit field for acquiring the magnetic resonance data using a radio-frequency antenna, wherein the radio-frequency transmitter has multiple transmit channels, wherein the radio-frequency antenna comprises multiple antenna elements, wherein each of the multiple transmit channels is adapted to connect to an antenna element chosen from the multiple antenna elements, wherein the method comprises the steps of:

• receiving a set of radio-frequency sensitivities, wherein the radio-frequency sensitivities are descriptive of the radio-frequency sensitivities of the multiple antenna elements when the subject is within the imaging zone;
• calculating a set of input drive scales for the multiple transmit channels in accordance with the radio-frequency sensitivities, wherein an input drive scale is descriptive of the amplitude and phase of radio-frequency transmit field generated by each of the multiple antenna elements, wherein the input drive scales reduce a magnetic field generated by the radio-frequency antenna within a predetermined volume to below a first predetermined value, wherein the predetermined volume is within the subject;
• wherein an electrically conductive object is located within the predetermined volume and wherein execution of the instructions further causes the processor to determine an orientation of the electrically conductive object using the preliminary magnetic resonance data, and wherein the set of input drive scales are further calculated at least partially using the orientation of the electrically conductive object and
• acquiring the magnetic resonance data using the magnetic resonance imaging system, wherein the radio-frequency transmit field is generated in accordance with the set of input drive scales.

A computer program product comprising machine executable instructions for execution by a processor configured for controlling a magnetic resonance imaging system, wherein the magnetic resonance imaging system is configured for acquiring magnetic resonance data from a subject within an imaging zone, wherein the magnetic resonance imaging system comprises a radio-frequency transmitter for generating a radio-frequency transmit field for acquiring the magnetic resonance data using a radio-frequency antenna, wherein the radio-frequency transmitter has multiple transmit channels, wherein the radio-frequency antenna comprises multiple antenna elements, wherein each of the multiple transmit channels are adapted to connect to an antenna element chosen from the multiple antenna elements, wherein execution of the instructions causes the processor to:

• receive a set of radio-frequency sensitivities, wherein the radio-frequency sensitivities are descriptive of the radio-frequency sensitivities of the multiple antenna elements when the subject is within the imaging zone;
• calculate a set of input drive scales for the multiple transmit channels in accordance with the radio-frequency sensitivities, wherein an input drive scale is descriptive of the amplitude and phase of radio-frequency transmit field by each of the multiple antenna elements, wherein the input drive scales reduce a magnetic field generated by the radio-frequency antenna within a predetermined volume to below a first predetermined value, wherein the predetermined volume is within the subject;
• wherein an electrically conductive object is located within the predetermined volume and wherein execution of the instructions further causes the processor to determine an orientation of the electrically conductive object using the preliminary magnetic resonance data, and wherein the set of input drive scales are further calculated at least partially using the orientation of the electrically conductive object and
• acquire the magnetic resonance data using the magnetic resonance imaging system, wherein the radio-frequency transmit field is generated in accordance with the set of input drive scales.