MAGNETIC RESONANCE IMAGING APPARATUS AND CONTROL METHOD OF MAGNETIC RESONANCE IMAGING APPARATUS
A respiratory movement is monitored during imaging to detect the start of a respiratory stable period (expiration). After an R wave is detected, it is confirmed that the respiratory movement immediately before the R wave detection transitions to the respiratory stable period, and a main measurement is performed at a timing at which a cardiac time phase and a respiratory time phase of a subject are matched with each other, to acquire image data. The cardiac time phase for acquiring the image data is fixed, and a slice position of the main measurement is adjusted by using a respiratory movement displacement acquired immediately before the cardiac time phase fixation. As a result, the image data for two heartbeats can be acquired in a respiratory period after the entrance into the stable period while suppressing an influence of body movement.
1 . A magnetic resonance imaging apparatus comprising:
an imaging unit that collects a nuclear magnetic resonance signal generated from a subject, and performs a navigation measurement for detecting a respiratory movement of the subject and a main measurement for generating an image of the subject;
a measurement controller that controls the imaging unit;
a respiratory movement monitoring unit that monitors the respiratory movement of the subject by using a result of the navigation measurement, and transmits an accept signal and a reject signal to the measurement controller depending on whether a magnitude of the respiratory movement of the subject is inside or outside a preset gate window; and
a cardiac period monitoring unit that monitors a cardiac period of the subject, and generates a gate signal at an R wave occurrence timing of the cardiac period,
wherein the measurement controller consecutively executes the navigation measurement before and after the generation of the gate signal, and controls, in a case in which the gate signal is received from the cardiac period monitoring unit, the imaging unit to perform the main measurement after a preset delay time elapses in a case in which a most recent transition among transitions of a signal from the respiratory movement monitoring unit, which is generated during the navigation measurement before the reception of the gate signal, is a transition from the reject signal to the accept signal.
2 . The magnetic resonance imaging apparatus according to claim 1 ,
wherein the respiratory movement monitoring unit does not use a result of a navigation measurement most recent to the main measurement among the navigation measurements performed after the main measurement, for monitoring the respiratory movement.
3 . The magnetic resonance imaging apparatus according to claim 1 ,
wherein the measurement controller adjusts a slice position of the main measurement following a navigation measurement performed in the delay time by using a respiratory movement position obtained by the navigation measurement.
4 . The magnetic resonance imaging apparatus according to claim 1 , further comprising:
a prior information setting unit that sets the gate window of the respiratory movement,
wherein the prior information setting unit sets the gate window at a position in a stable period of the respiratory movement.
5 . The magnetic resonance imaging apparatus according to claim 4 ,
wherein the prior information setting unit sets the gate window so that a maximum value of the stable period of the respiratory movement is included.
6 . The magnetic resonance imaging apparatus according to claim 4 ,
wherein the prior information setting unit sets the gate window so that a position lower than a maximum value of the stable period of the respiratory movement is an upper limit value.
7 . The magnetic resonance imaging apparatus according to claim 4 ,
wherein the measurement performed by the imaging unit includes scano imaging for determining an imaging part of the subject, and the prior information setting unit determines a position of the gate window by using an image obtained by the scano imaging.
8 . The magnetic resonance imaging apparatus according to claim 4 , further comprising:
a UI unit that receives adjustment of a position of the gate window by a user,
wherein the respiratory movement monitoring unit reflects the adjustment received by the UI unit to change the position of the gate window set by the prior information setting unit.
9 . The magnetic resonance imaging apparatus according to claim 1 , further comprising:
a prior information setting unit that sets the delay time of the main measurement,
wherein the prior information setting unit determines the delay time by using a cine image obtained by cine imaging on a region including a heart of the subject as a target.
10 . A control method of a magnetic resonance imaging apparatus that collects a signal for generating a subject image as a main measurement in a case in which an electrocardiogram waveform and a respiratory movement waveform of a subject are in determined ranges, respectively, the control method comprising:
a step of consecutively executing a navigation measurement for detecting the respiratory movement waveform before and after the main measurement;
a step of monitoring a result of the navigation measurement, generating an accept signal in a case in which a magnitude of a respiratory movement is inside a set gate window, and generating a reject signal in a case in which the magnitude of the respiratory movement is outside the gate window; and
a step of, after an R wave of the electrocardiogram waveform is detected, in a case in which a most recent transition among transitions of a signal generated during the navigation measurement before the R wave is detected is a transition from the reject signal to the accept signal, starting the main measurement after a preset delay time.
11 . The control method of a magnetic resonance imaging apparatus according to claim 10 , further comprising:
a step of adjusting a slice position of the main measurement by using a result of a navigation measurement performed immediately before the main measurement.
12 . The control method of a magnetic resonance imaging apparatus according to claim 10 , further comprising:
a step of performing scano imaging; and
a step of acquiring information on the respiratory movement of the subject from a result of the scano imaging, and setting a position of the gate window.
13 . The control method of a magnetic resonance imaging apparatus according to claim 10 , further comprising:
a step of acquiring a cine image of a heart; and
a step of acquiring information on a cardiac period from the cine image, and determining the delay time.