MRI apparatus with correction of envelope of RF pulse
According to one embodiment, an MRI apparatus includes an amplifier and processing circuitry. The amplifier amplifies an RF pulse and outputs the amplified RF pulse to an RF coil. The processing circuitry performs correction processing on an envelope of an RF pulse to be inputted to the amplifier so as to compensate nonlinear input-output characteristics of the amplifier. As to this correction processing, the processing circuitry selects a correction information item out of a plurality of correction information items prepared for a corresponding plurality of imaging conditions and performs the correction processing by using the selected information item.
1. An MRI apparatus, comprising:
an amplifier configured to amplify an RF pulse and output an amplified RF pulse to an RF coil; and
processing circuitry configured to perform correction processing on an envelope of an RF pulse to be inputted to the amplifier so as to compensate for nonlinear input-output characteristics of the amplifier,
wherein the processing circuitry is further configured to
select a correction information item out of a plurality of correction information items prepared for a corresponding plurality of imaging conditions, and
perform the correction processing on the envelope of the RF pulse by using the selected correction information item: and
wherein each of the imaging conditions is an average electric power of an RF pulse train defined in a pulse sequence.
2. The MRI apparatus according to claim 1 ,
wherein the processing circuitry is further configured to acquire waveform information of the RF pulse and information on an imaging condition from a sequencer, and to select the correction information item based on the waveform information of the RF pulse and the information on the imaging condition.
3. The MRI apparatus according to claim 1 ,
wherein the processing circuitry is further configured to generate the plurality of correction information items at, at least one of, a time when the MRI apparatus is installed, a time when a prescan is executed prior to imaging of an object, and a time immediately before start of a pulse sequence of imaging the object.
4. An MRI apparatus, comprising:
an amplifier configured to amplify an RF pulse and output an amplified RF pulse to an RF coil;
processing circuitry configured to perform correction processing on an envelope of an RF pulse to be inputted to the amplifier so as to compensate for nonlinear input-output characteristics of the amplifier; and
a detector configured to detect an amplified RF pulse outputted from the amplifier and to output a detected pulse as a detection RF pulse, wherein
the amplifier is configured to receive a reference RF pulse generated based on a digital signal and to output the amplified RF pulse as an output RF pulse to the RF coil by amplifying the reference RF pulse, and
the processing circuitry is further configured to
select a correction information item out of a plurality of correction information items prepared for a corresponding plurality of imaging conditions, and
perform correction processing by using the selected information item on an envelope of the reference RF pulse to be inputted to the amplifier such that an envelope of the output RF pulse outputted at a time of imaging an object matches the envelope of the reference RF pulse.
5. The MRI apparatus according to claim 4 ,
wherein the processing circuitry is further configured to measure gain linearity of the amplifier based on a difference between the reference RF pulse and the detection RF pulse before the time of imaging the object, and
each of the plurality of correction information items is generated based on the gain linearity.
6. The MRI apparatus according to claim 5 ,
wherein the processing circuitry is further configured to
generate a plurality of correction functions , as the plurality of correction information items, based on the gain linearity, which is different between the plurality of imaging conditions, to compensate for the nonlinear input-output characteristics of the amplifier for the corresponding plurality of imaging conditions,
select a correction function used for the correction processing, and
apply the correction processing to the reference RF pulse by using the selected correction function.
7. The MRI apparatus according to claim 6 ,
wherein the processing circuitry is further configured to generate the plurality of correction functions, which are mutually different, according to an average electric power of an RF pulse train defined in a pulse sequence.
8. The MRI apparatus according to claim 6 ,
wherein the processing circuitry is further configured to generate the plurality of correction functions, which are mutually different, according to a type of pulse sequence.
9. The MRI apparatus according to claim 5 ,
wherein the processing circuitry is further configured to
generate a plurality of correction tables, as the plurality of correction information items, based on the gain linearity, which is different between the plurality of imaging conditions, to compensate for the nonlinear input-output characteristics of the amplifier for the corresponding plurality of imaging conditions,
select a correction table used for the correction processing, and
apply the correction processing to the reference RF pulse by using the selected correction table.
10. The MRI apparatus according to claim 9 ,
wherein the processing circuitry is further configured to generate the plurality of correction tables, which are mutually different, according to an average electric power of an RF pulse train defined in a pulse sequence.
11. The MRI apparatus according to claim 9 ,
wherein the processing circuitry is further configured to generate the plurality of correction tables, which are mutually different, according to a type of pulse sequence.