Method and system for synchronizing a rotational eccentric mass with a magnetic resonance elastography scan

A stepper motor configured to drive a rotational eccentric mass of a gravitational transducer used for a magnetic resonance elastography acquisition carried out by a magnetic resonance imaging system, wherein the rotation of the eccentric mass is driven by a shaft, the stepper motor comprising:

• an interface configured to (i) receive signals at regular intervals, the signals indicating a start time of an acquisition period of the magnetic resonance elastography acquisition, (ii) receive a set vibration frequency of the eccentric mass, the vibration frequency being set such that one or an integer number of rotational periods of the eccentric mass equals an acquisition period, the integer number being a burst count, and (iii) receive the burst count;
• a control unit configured to control the stepper motor and comprising programming instructions to carry out the following steps in order to synchronize the eccentric rotational mass with the received signals:
• (a) starting the rotation of the eccentric mass at the set vibration frequency;
• (b) when receiving a signal indicating the start time of an acquisition period, determining the rotational position of the shaft;
• (c) defining the determined rotational position as first reference position, which the shaft is expected to occupy at the start time of at least some of the subsequent acquisition periods;
• (d) depending on the burst count, calculating further reference positions that the shaft is theoretically expected to occupy at the start time of each subsequent acquisition period, wherein the further reference positions are (i) the same as the first reference position, or (ii) alternate between several positions;
• (e) at the start time of each subsequent acquisition period of the magnetic resonance scan, determine a current rotational position of the shaft;
• (f) after each determination of the current rotational position, compare the determined current rotational position with the expected reference position, and decrease or increase the rotational speed of the rotational eccentric mass based on the comparison.

A magnetic resonance imaging system, comprising:

• a stepper motor configured to drive a rotational eccentric mass of a gravitational transducer used for a magnetic resonance elastography acquisition carried out by a magnetic resonance imaging system, wherein the rotation of the eccentric mass is driven by a shaft, the stepper motor comprising:
• an interface configured to (i) receive signals at regular intervals, the signals indicating a start time of an acquisition period of the magnetic resonance elastography acquisition, (ii) receive a set vibration frequency of the eccentric mass, the vibration frequency being set such that one or an integer number of rotational periods of the eccentric mass equals an acquisition period, the integer number being a burst count, and (iii) receive the burst count;
• a control unit configured to control the stepper motor and comprising programming instructions to carry out the following steps in order to synchronize the eccentric rotational mass with the received signals:
• (a) starting the rotation of the eccentric mass at the set vibration frequency;
• (b) when receiving a signal indicating the start time of an acquisition period, determining the rotational position of the shaft;
• (c) defining the determined rotational position as first reference position, which the shaft is expected to occupy at the start time of at least some of the subsequent acquisition periods;
• (d) depending on the burst count, calculating further reference positions that the shaft is theoretically expected to occupy at the start time of each subsequent acquisition period, wherein the further reference positions are (i) the same as the first reference position, or (ii) alternate between several positions;
• (e) at the start time of each subsequent acquisition period of the magnetic resonance scan, determine a current rotational position of the shaft;
• (f) after each determination of the current rotational position, compare the determined current rotational position with the expected reference position, and decrease or increase the rotational speed of the rotational eccentric mass based on the comparison;
• a gravitational transducer with an eccentric rotational mass, wherein the rotation of the eccentric mass is driven by a shaft, and the shaft is driven by the stepper motor;
• and
• a magnetic resonance scanner including a console for controlling the magnetic resonance scanner,
• wherein the console is configured to transmit a signal at regular intervals to the stepper motor, the signal indicating the start time of an acquisition interval.

A non-transitory computer-readable medium having stored thereon a computer program product for synchronizing a rotational eccentric mass of a gravitational transducer used for a magnetic resonance elastography acquisition with a corresponding magnetic resonance elastography scan carried out by a magnetic resonance imaging system, wherein the rotation of the eccentric mass is driven by a shaft, and the shaft is driven by a stepper motor,

• wherein the computer program comprises instructions to cause a control unit of a stepper motor magnetic resonance elastography system to:
• (a) start the rotation of the eccentric mass at a set vibration frequency and the magnetic resonance elastography scan at a set acquisition frequency, wherein the vibration frequency is set such that one or an integer number of rotational periods of the eccentric mass equals an acquisition period, wherein the integer number is a burst count;
• (b) at a start time of an acquisition period of the magnetic resonance scan, determine the rotational position of the shaft;
• (c) define the determined rotational position as first reference position, which the shaft is expected to occupy at the start time of at least some of the subsequent acquisition periods;
• (d) depending on the burst count, calculate further reference positions that the shaft is expected to occupy at the start time of each subsequent acquisition period, wherein the further reference positions are (i) the same as the first reference position, or (ii) alternate between several positions;
• (e) at the start time of each subsequent acquisition period of the magnetic resonance scan, determine a current rotational position of the shaft;
• (f) after each determination of the current rotational position, compare the determined current rotational position with the expected reference position, and decrease or increase the rotational speed of the rotational eccentric mass based on the comparison.