Method for simulation of an electric stimulation in an MR imaging system

A magnetic resonance imaging apparatus for obtaining an MR image from a plurality of signals and for simulation of an electric stimulation of a nerve system of a subject to be examined, which stimulation is generated by a rate of change of gradient fields, the simulation including filtering a differentiated gradient signal with a filtering function, deriving a stimulation signal from said filtered gradient signal, and comparing said stimulation signal with a predetermined stimulation threshold value for generating an indicator signal if said threshold value is exceeded, the apparatus comprising:

• a main field magnet;
• gradient coils;
• means for filtering the differentiated gradient signal with a filtering function including a first filter stage with a first bipolar filter for filtering the differentiated gradient signal and a first unipolar filter for parallel filtering said differentiated gradient signal and weighing means, in which both output signals are weighted, and adding means, in which the weighted output signals are added;
• means for calculating and vector combining time dependent and spatially dependent electric field components from each gradient coil axis based on gradient signals defined by a scanning sequence and filtered by the filtering means and the gradient coil properties resulting in a temporal diagram of the total electric field at various spatial locations within the gradient coils;
• means for calculating a stimulation probability at each location from said temporal diagram and said stimulation signal;
• means for comparing said stimulation probability with the stimulation threshold value at each location within the gradient coil and generating an indicator signal if said threshold value is exceeded.

A computer program product stored on a computer usable medium for forming an image by a magnetic resonance method including a method for simulation of an electric stimulation of a nerve system of a subject to be examined generated by a rate of change of gradient fields of a gradient coil of a magnetic resonance imaging system, the computer program product comprising a computer readable program storage medium storing instructions executable by a computer to control the execution of a plurality of steps comprising:

• filtering a differentiated gradient signal of said gradient coil with a filtering function, the filtering including filtering the differentiated gradient signal in a first stage with a first bipolar filter, parallel filtering said differentiated gradient signal in a first unipolar filter, and weighting the output signals of both first filters and adding the weighted output signals,
• deriving a stimulation signal from said filtered gradient signal,
• comparing said stimulation signal with a predetermined stimulation threshold value for generating an indicator signal if said threshold value is exceeded,
• calculation of time dependent and spatially dependent electric fields as defined by a scanning sequence and the gradient coil properties,
• vector combination of said calculated electric field components from each gradient coil axis resulting in a temporal diagram of the total electric field at various spatial locations within the gradient coil,
• calculation of a stimulation probability at each location from said temporal diagram and said stimulation signal, and
• comparing said stimulation probability with a stimulation threshold value at each location within the gradient coil;
• and
• generating said indicator signal if said threshold value is exceeded at any location within the gradient coil.