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

Patent metadata

Field	Value
Publication number	US-11821972-B2
Application number	US-202217702212-A
Country	US
Kind code	B2
Filing date	Mar 23, 2022
Priority date	Mar 23, 2022
Publication date	Nov 21, 2023
Grant date	Nov 21, 2023

Abstract

The present disclosure is directed to techniques 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. The method includes starting the rotation of the eccentric mass at a set vibration frequency and the magnetic resonance elastography scan at a set acquisition frequency; determining the rotational position of the shaft; defining the rotational position as first reference position; calculating further reference positions. At the start time of each subsequent acquisition period, determining the current rotational position of the shaft; comparing the determined current rotational position with the theoretically expected reference position and decreasing or increasing the rotational speed of the rotational eccentric mass based on the comparison.

First claim

What is claimed is:

1. A method 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, the method comprising:
(a) starting 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, and wherein the integer number is a burst count;
(b) at a start time of an acquisition period of the magnetic resonance scan, 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 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, determining a current rotational position of the shaft;
(f) after each determination of the current rotational position, comparing the determined current rotational position with the expected reference position, and decreasing or increasing the rotational speed of the rotational eccentric mass based on the comparison.

2. The method according to claim 1 , wherein after starting the rotation of the rotational eccentric mass and the magnetic resonance scan, a predetermined number of acquisition periods is discarded as dummy shots before the rotational position of the shaft is determined at the start time of a further acquisition period.

3. The method according to claim 1 , wherein in step (f) the rotational speed of the shaft is increased:
(i) if the difference between the respective expected reference position and the determined current position is greater than zero and greater than 7E, or (ii) if the difference between the respective reference position and the current position is less than zero and greater than −π; and
wherein in step (f) the rotational speed of the shaft is decreased:
(i) if the difference between the respective reference position and the current position is greater than zero and less than 7E, or (ii) if the difference between the respective reference position and the current position is less than zero and less than −π.

4. The method according to claim 1 , wherein in step (f) the rotational speed of the shaft is increased or decreased by a fixed amount in each acquisition period.

5. The method according to claim 1 , wherein the shaft is driven by a stepper motor, and the rotation of the shaft is transferred to the gravitational transducer via a flexible rotating axis.

6. The method according to claim 5 , wherein the rotation of the shaft is translated to rotational eccentric mass of the gravitational transducer with a gear ratio of 1 or higher, such that the rotational eccentric mass rotates faster than the shaft.

7. The method according to claim 6 , wherein in step (d), the further reference positions that the shaft is expected to occupy at the start time of each subsequent acquisition period is determined on the basis of the burst-count and the gear ratio.

8. The method according to claim 7 , wherein:
if the gear ratio is three and the burst count is 3, the further reference positions are the same as the first reference positions, and
if the burst count is 4 or 5, the further reference positions alternate between three different rotational positions.

9. The method according to claim 1 , wherein step (e) is triggered by a signal received from the magnetic resonance imaging system at the start time of each acquisition cycle via a transistor-transistor-logic.

10. A method according to claim 1 , wherein the magnetic resonance elastography scan is of a subject.

11. 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.

12. 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

Assignees

• Siemens Healthcare Gmbh
• Centre Nat Rech Scient
• Inst Nat Sante Rech Med
• King S College London
• Dept of Health and Human Services
• Univ Paris Xiii Paris Nord Villetaneuse
• Univ Paris

Inventors

• Darwish Omar
• Neji Radhouene
• Gharib Ahmed M
• Sinkus Ralph

Classifications

• G01R33/56358 Primary

  Elastography · CPC title

• G01R33/30

  Sample handling arrangements, e.g. sample cells, spinning mechanisms · CPC title

• H02P8/08

  Determining position before starting · CPC title

• H02P8/22

  Control of step size; Intermediate stepping, e.g. microstepping · CPC title

• A61B5/0051

  by applying vibrations · CPC title