Method and magnetic resonance apparatus for determination of excitation profiles from excitation pulses
In a method for determining excitation profiles from excitation pulses in a magnetic resonance, a homogeneous phantom is placed within the measurement volume of the magnetic resonance apparatus, at least one measurement data set of the phantom is acquired by operating the apparatus with a test pulse sequence composed of one excitation pulse, of which the excitation profile is to be determined, and a test gradient that is already activated on at full strength while the excitation pulse (A) is irradiated. The intensity profile of at least one acquired measurement data set in the direction in which the test gradient was switched on is determined in a processor, and the excitation profile of the excitation pulse is determined from the calculated intensity profile. The determined excitation profile is saved.
1. A method for determining an excitation profile of excitation pulses radiated in a magnetic resonance apparatus, comprising:
placing a homogeneous phantom within a measurement volume of a magnetic resonance apparatus;
acquiring at least one magnetic resonance measurement data set, having an intensity profile, from the phantom by operating the magnetic resonance apparatus according to a test pulse sequence that comprises an excitation pulse that produces an excitation profile in the phantom, and a test gradient that is activated at full strength while said excitation pulse is radiated;
providing said measurement data set to a computerized processor and, in said processor, automatically determining the intensity profile of said at least one measurement data set in a direction in which said test gradient is activated;
in said processor, determining said excitation profile, produced in the phantom by said excitation pulse, from the determined intensity profile; and
making the determined excitation profile available in electronic form at an output of said processor.
2. A method as claimed in claim 1 comprising activating said test gradient in a readout direction along which said magnetic resonance data set is read out in said test sequence.
3. A method as claimed in claim 1 comprising determining said intensity profile by determining an intensity time curve within said phantom in said direction in which said test gradient is activated.
4. A method as claimed in claim 1 comprising operating said magnetic resonance apparatus with a strength of said test gradient in said test sequence selected to cause a characteristic area of said excitation profile to be reproduced in the measurement data set representing said phantom.
5. A method as claimed in claim 1 comprising operating said magnetic resonance apparatus to acquire at least two measurement data sets with said test sequence, with different gradients being activated in said test sequence respectively for acquiring said two measurement data sets, and determining said intensity profile from said at least two measurement data sets.
6. A method as claimed in claim 5 comprising determining said excitation profile from respective individual intensity profiles of said at least two different measurement data sets.
7. A method as claimed in claim 1 comprising radiating said excitation pulse as a rectangular pulse in said test sequence.
8. A method as claimed in claim 1 comprising employing, as said phantom, a phantom having a size in said direction in which said test gradient is activated that corresponds to a resolution of said magnetic resonance apparatus.
9. A magnetic resonance apparatus comprising:
a magnetic resonance data acquisition unit;
a homogeneous phantom placed within a measurement volume of the magnetic resonance apparatus;
a control unit configured to operate said data acquisition unit to acquire at least one magnetic resonance measurement data set, having an intensity profile, from the phantom according to a test pulse sequence that comprises an excitation pulse that produces an excitation profile in the phantom, and a test gradient that is activated at full strength while said excitation pulse is radiated;
a computerized processor provided with said measurement data set, said computerized processor being configured to automatically determine an intensity profile of said at least one measurement data set in a direction in which said test gradient is activated;
said computerized processor being configured to determine said excitation profile, produced in the phantom by said excitation pulse, from the determined intensity profile; and
said computerized processor being configured to make the determined excitation profile available in electronic form at an output of said processor.
10. A non-transitory, computer-readable data storage medium encoded with programming instructions, said storage medium being loaded into a computerized control computer of a magnetic resonance apparatus that also comprises a magnetic resonance data acquisition unit, said programming instructions causing said control computer to:
operate the data acquisition unit to acquire at least one magnetic resonance measurement data set, having an intensity profile, from a homogeneous phantom placed within a measurement volume of the data acquisition unit, according to a test pulse sequence that comprises an excitation pulse that produces an excitation profile in the phantom, and a test gradient that is activated at full strength while said excitation pulse is radiated;
determine the intensity profile of said at least one measurement data set in a direction in which said test gradient is activated;
determine the excitation profile, produced in the phantom by said excitation pulse from the determined intensity profile; and
make the determined excitation profile available in electronic form at an output of said processor.