Slice-specific phase correction in slice multiplexing
First Claim
1. A method that corrects a signal phase in a slice multiplexing data acquisition of magnetic resonance (MR) signals from a subject, wherein, for each of at least two slices of the object, from which MR signals are to be acquired in a slice multiplexing data acquisition sequence in which said at least two slices are respectively excited by radiating two radio-frequency (RF) pulses, each having a resonance frequency and the resonance frequencies differing from each other, in order to produce a different magnetization respectively in each of said at least two slices, while a slice selection gradient is activated, for a slice selection duration in a slice selection direction, said method comprising:
- calculating, in a processor, a linear phase error along said slice selection direction, said linear phase error arising from slice-specific linear field deviations that occur along the slice selection direction due to magnetic fields other than said slice selection gradient that act on said at least two slices in the slice selection direction;
additionally in said processor, for each of said two RF pulses, also calculating a time offset, relative to a middle of said slice selection duration, with an offset amount that corrects said calculated linear phase error when a combination of said two RF pulses is radiated at the calculated time offsets, with said combination of said two RF pulses modifying a gradient moment that acts on said different magnetizations occurring in said at least two slices during said slice selection duration;
operating an MR data acquisition scanner from said processor in order to execute said slice multiplexing data acquisition sequence, including radiating said two RF pulses respectively at times corresponding to the respective, calculated time offsets and with a partial temporal overlap of said RF pulses that are radiated, while activating said slice selection gradient in said slice selection direction, so as to acquire said MR signals with said linear phase correction produced by said gradient moment, without altering or augmenting said activated slice selection gradient; and
making the acquired MR signals available from the processor in electronic form, as a data file.
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Abstract
In a method to correct a signal phase in the acquisition of MR signals of an examination subject in a slice multiplexing method, in which MR signals from at least two different slices of the examination subject are detected simultaneously in the acquisition of the MR signals, a linear correction phase in the slice selection direction is determined for each of the at least two slices. An RF excitation pulse with a slice-specific frequency is radiated in each of the at least two different slices. A slice selection gradient is activated during a slice selection time period, during which the different RF excitation pulses are radiated in the at least two different slices, and the slice selection time period has a middle point in time in the middle of the slice selection time period, and the different RF excitation pulses temporally overlap for the at least two different slices. A time offset of the RF excitation pulse relative to the middle point in time for each of the RF excitation pulses is determined, such that a slice-specific correction gradient moment in the slice selection direction that corresponds to the linear correction phase of the respective slice acts on the magnetization of the respective slice.
33 Citations
13 Claims
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1. A method that corrects a signal phase in a slice multiplexing data acquisition of magnetic resonance (MR) signals from a subject, wherein, for each of at least two slices of the object, from which MR signals are to be acquired in a slice multiplexing data acquisition sequence in which said at least two slices are respectively excited by radiating two radio-frequency (RF) pulses, each having a resonance frequency and the resonance frequencies differing from each other, in order to produce a different magnetization respectively in each of said at least two slices, while a slice selection gradient is activated, for a slice selection duration in a slice selection direction, said method comprising:
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calculating, in a processor, a linear phase error along said slice selection direction, said linear phase error arising from slice-specific linear field deviations that occur along the slice selection direction due to magnetic fields other than said slice selection gradient that act on said at least two slices in the slice selection direction; additionally in said processor, for each of said two RF pulses, also calculating a time offset, relative to a middle of said slice selection duration, with an offset amount that corrects said calculated linear phase error when a combination of said two RF pulses is radiated at the calculated time offsets, with said combination of said two RF pulses modifying a gradient moment that acts on said different magnetizations occurring in said at least two slices during said slice selection duration; operating an MR data acquisition scanner from said processor in order to execute said slice multiplexing data acquisition sequence, including radiating said two RF pulses respectively at times corresponding to the respective, calculated time offsets and with a partial temporal overlap of said RF pulses that are radiated, while activating said slice selection gradient in said slice selection direction, so as to acquire said MR signals with said linear phase correction produced by said gradient moment, without altering or augmenting said activated slice selection gradient; and making the acquired MR signals available from the processor in electronic form, as a data file. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A magnetic resonance (MR) apparatus that corrects a signal phase in a slice multiplexing data acquisition of MR signals from a subject, said apparatus comprising:
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an MR data acquisition scanner; a processor; said processor being configured to operate said MR data acquisition scanner so as to execute a slice multiplexing data acquisition sequence wherein, for each of at least two slices of the object, MR signals are acquired in said slice multiplexing data acquisition sequence by said at least two slices being respectively excited by radiating two radio-frequency (RF) pulses, each having a resonance frequency and the resonance frequencies differing from each other, in order to produce a different magnetization respectively in each of said at least two slices, while a slice selection gradient is activated, for a slice selection duration in a slice selection direction; said processor being configured to calculate a linear phase error along the slice selection direction, said linear phase error arising from slice-specific linear field deviations that occur along the slice selection direction due to magnetic fields other than said slice selection gradient that act on said at least two slices in the slice selection direction; additionally in said processor, for each of said two RF pulses, also calculating a time offset, relative to a middle of said slice selection duration, with an offset amount that corrects said calculated linear phase error when a combination of said two RF pulses is radiated at the calculated time offsets, with said combination of said two RF pulses modifying a gradient moment that acts on said different magnetizations occurring in said at least two slices during said slice selection duration; said processor being further configured to operate said MR data acquisition scanner in order to execute said slice multiplexing data acquisition sequence, including radiating said two RF pulses respectively at times corresponding to the respective, calculated time offsets, while activating said slice selection gradient in said slice selection direction and with a partial temporal overlap of RF pulses said two that are radiated, so as to acquire said MR signals with said linear phase correction produced by said gradient moment, without altering or augmenting said activated slice selection gradient; and said processor being configured to make the acquired MR signals available from the processor in electronic form, as a data file.
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Specification