Method to determine the actual flip angle and method to adjust the transmitter voltage in a magnetic resonance apparatus

Patent metadata

Field	Value
Publication number	US-9476958-B2
Application number	US-201213422227-A
Country	US
Kind code	B2
Filing date	Mar 16, 2012
Priority date	Mar 16, 2011
Publication date	Oct 25, 2016
Grant date	Oct 25, 2016

Abstract

In a method to determine the actual flip angle in magnetic resonance tomography with continuous table feed, at least one echo signal is generated by a pulse sequence from which an actual flip angle is produced with at least one RF pulse of the sequence, and a gradient scheme is used in the direction of the continuous travel of the examination subject, the gradient scheme being designed such that its first moment disappears at the points in time of each echo signals used for the determination of the flip angle. Such a pulse sequence is also used in a method for adjustment of the transmitter voltage for RF pulses given continuous travel of the examination subject in a magnetic resonance apparatus.

First claim

I claim as my invention:

1. A method for operating a magnetic resonance system, comprising:
from a control computer, operating a magnetic resonance data scanner comprising a radio-frequency (RF) antenna arrangement and a gradient coil system to execute a pulse sequence that includes radiating at least one RF pulse from said RF antenna arrangement into an examination subject while said examination subject is continuously moving through the magnetic resonance data acquisition scanner in a direction of continuous travel, said at least one RF pulse giving nuclear spins in the examination subject a flip angle that causes the nuclear spins to emit at least one echo signal;
from said control computer, in said pulse sequence, also operating said gradient coil system to activate gradient magnetic fields in said magnetic resonance data acquisition scanner according to a gradient scheme that occurs in said pulse sequence between said at least one RF pulse and each echo signal caused thereby, and, in said control computer, configuring said gradient scheme with respect to said direction of said continuous travel to cause a first moment of said gradient scheme in the direction of said continuous travel to disappear at a point in time of each of said at least one echo signal;
in said control computer, analyzing said at least one echo signal, obtained after activating the configured gradient scheme, to determine an actual value of said flip angle; and
storing the actual value of the flip angle in a memory accessible by said control computer and making the stored actual value of the flip angle available from the memory, via the control computer, in electronic form for subsequent operation of said magnetic resonance data scanner to acquire magnetic resonance data from the examination subject.

2. A method as claimed in claim 1 comprising from said control computer operating said gradient coil system to switch spoiler gradients in said gradient scheme that suppress unwanted signals in a direction perpendicular to said direction of continuous travel.

3. A method as claimed in claim 1 comprising, from said control computer operating said RF antenna arrangement in said pulse sequence to radiate at least three RF pulses and thereby producing at least two echo signals.

4. A method as claimed in claim 3 comprising from said control computer, operating said magnetic resonance data acquisition scanner to acquire said magnetic resonance data by operating said gradient coil system to read out said echo signals under a readout gradient in said direction of continuous travel and to switch a slice selection gradient in said direction of continuous travel for at least one of said three RF pulses selected from the group consisting of a second of said at least three RF pulses and a third of said at least three RF pulses in said gradient scheme in a direction of said continuous travel.

5. A method as claimed in claim 4 comprising, from said control computer, operating said gradient coil system in said pulse sequence by switching a combination of gradient pulses in said pulse sequence as respective trapezoidal gradients with a same amplitude, said combination of gradient pulses being selected from the group consisting of a slice selection gradient for an RF pulse and a readout gradient for an echo signal immediately following said RF pulse, a readout gradient for an echo signal and a slice selection gradient for an RF pulse immediately following said echo signal, and respective readout gradients for two echo signals in immediate succession.

6. A method as claimed in claim 5 comprising configuring said gradient scheme in said control computer to give flat tops of respective slice selection gradients for a second and a third of said RF pulses in said pulse sequence, and flat tops of readout gradients for at least one echo signal read out before a last echo signal, of equal length.

7. A method as claimed in claim 5 comprising, in said control computer configuring said trapezoidal gradients in said gradient scheme such that the time duration of the flat top of a slice selection gradient from an isodelay point of the associated RF pulse to the end of the flat top coincides with the time duration of the flat top of an immediately following readout gradient up to a point in time of the associated echo, wherein the time duration of the right ramp of the slice selection gradient is equal to the time duration of the left ramp of the immediately following readout gradient and/or the time duration of the flat top of a readout gradient from the start of the flat top to the point in time of the associated echo coincides with the time duration of the flat top of an immediately following slice selection gradient up to the isodelay point of the associated RF pulse, wherein the time duration of the right ramp of the readout gradient is equal to the time duration of the left ramp of the immediately following slice selection gradient, and/or the time duration of the flat top of a readout gradient from the associated echo to the end of the flat top coincides with the time duration of the flat top of an immediately following readout gradient up to the point in time of the associated echo, wherein the time duration of the right ramp of the first of said readout gradients is equal to the time duration of the left ramp of the second of said readout gradients, wherein the respective 0th and 1st moment acquired from spins via these two (adjacent half) gradients between immediately successive points in time from the group of isodelay points of RF pulses associated with respective slice selection gradients and echo points in time of echoes to be read out is compensated via a symmetrical trapezoidal gradient whose center of symmetry lies in the middle between the respective immediately successive isodelay points in time or, respectively, points in time of the echoes.

8. A method as claimed in claim 1 comprising, from said control computer, operating said gradient coil system in said pulse sequence by switching no gradient in the direction of continuous travel of the examination subject.

9. A method as claimed in claim 1 comprising said at least one RF pulse from an RF transmitter, of said RF coil arrangement, operating according to a transmitter voltage, and determining a reference transmitter voltage for a reference RF pulse from said determined flip angle, relative to a current position of the examination subject in said continuous travel.

10. A method as claimed in claim 9 comprising, after positioning the examination subject on the patient bed, moving the patient bed to a first examination position in said magnetic resonance data acquisition scanner and determining said reference transmitter voltage for each successive position occupied by said patient bed and said patient during said continuous travel.

11. A magnetic resonance apparatus comprising:
a magnetic resonance data acquisition scanner comprising a patient table that is movable through said data acquisition unit and that is configured to receive an examination subject therein, and said scanner comprising a radio-frequency (RF) antenna arrangement and a gradient coil system;
a control computer configured to operate said magnetic resonance data acquisition scanner to execute a pulse sequence that includes radiating at least one RF pulse from said RF antenna arrangement into an examination subject while continuously moving said examination subject on the patient table through the magnetic resonance data acquisition scanner in a direction of continuous travel, said at least one RF pulse giving nuclear spins in the examination subject a flip angle that causes the nuclear spins to emit at least one echo signal;
said

Assignees

• Stemmer Alto
• Siemens Ag

Inventors

• Stemmer Alto

Classifications

• G01R33/586

  for optimal flip angle of RF pulses · CPC title

• A61B5/055

  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging · CPC title

• G01R33/56383 Primary

  involving motion of the sample as a whole, e.g. multistation MR or MR with continuous table motion · CPC title