Method and system for synchronizing a rotational eccentric mass with a magnetic resonance elastography scan
Inventors
Darwish, Omar • Neji, Radhouene • Gharib, Ahmed M. • Sinkus, Ralph
Assignees
Siemens Healthineers AG • Centre National de la Recherche Scientifique CNRS • Institut National de la Sante et de la Recherche Medicale INSERM • Universite Sorbonne Paris Nord • Universite Paris Cite • Kings College London • US Department of Health and Human Services
Publication Number
US-11821972-B2
Publication Date
2023-11-21
Expiration Date
2042-03-23
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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.
Core Innovation
The invention provides a method for synchronizing a rotational eccentric mass of a gravitational transducer used for magnetic resonance elastography (MRE) acquisition with a corresponding MRE scan carried out by a magnetic resonance imaging (MRI) system. This method involves starting the rotation of the eccentric mass at a set vibration frequency and the MRE scan at a set acquisition frequency, determining the rotational position of the shaft driving the eccentric mass at the start of an acquisition period, defining this as a reference position, calculating further reference positions depending on the burst count, and continuously monitoring and adjusting the rotational speed based on the comparison between current and expected positions.
The problem addressed is the instability and lack of synchronization between the mechanical excitation generated by the gravitational transducer (with its rotational eccentric mass) and the MRI system's data acquisition timing. Prior art gravitational transducers achieved benefits in linearity and reduced parasitic harmonics but lacked stability in the angular position of the eccentric mass throughout the MRE acquisition, which is critical for reliable and stable measurement outcomes.
By defining one or multiple reference positions and adjusting the rotational speed of the eccentric mass accordingly, the invention compensates for deviations in the gravitational transducer's rotation speed relative to the MRI system's acquisition frequency. This synchronization ensures the phase stability of the gravitational transducer vibrations with the MRI acquisition, enabling improved stability of mechanical excitations during MRE. The method accounts for gear ratios, burst counts, and uses start signals from the MRI system to trigger synchronization steps.
Claims Coverage
The patent includes multiple independent claims covering a method for synchronization, a stepper motor system, and a magnetic resonance imaging system incorporating these features.
Method for synchronizing rotational eccentric mass with MRE scan
A method involving starting the rotation of the eccentric mass and MRE scan at aligned frequencies, determining and defining reference rotational positions based on the burst count, continuously determining the current shaft position at acquisition period starts, and adjusting the rotational speed based on comparing current and expected positions to maintain synchronization.
Method including discard of dummy acquisition periods
After starting rotation and scan, discarding a predetermined number of acquisition periods as dummy shots before determining the rotational position to allow the eccentric mass to reach stable speed.
Adjustment of rotational speed based on angular position difference
Increasing or decreasing the rotational speed conditioned on the difference between expected reference position and current position, with logic to handle angular wrapping and maintain phase stability.
Driving the shaft with a stepper motor and flexible rotating axis
Using a stepper motor to drive the shaft, transferring rotation via a flexible rotating axis, enabling precise control of shaft motion for synchronization.
Calculating further reference positions based on burst count and gear ratio
Depending on the burst count and gear ratio, calculating multiple reference rotational positions which may be the same or alternate between several positions, to accommodate differing rotational relationships.
Triggering position determination by a signal from MRI system
Using a transistor-transistor-logic (TTL) or equivalent signal sent from the MRI system at acquisition cycle start times to trigger determination of shaft rotational position for synchronization.
Stepper motor with control unit and interface for synchronization
A stepper motor apparatus comprising an interface to receive start signals, vibration frequency, and burst count, and a control unit programmed to perform the synchronization method steps as described.
Magnetic resonance imaging system integrating stepper motor and gravitational transducer
An MRI system comprising the stepper motor driving a shaft that rotates the eccentric mass, the gravitational transducer, and an MRI scanner console configured to send synchronization signals at acquisition intervals to the stepper motor.
Non-transitory computer-readable medium storing a program for synchronization
A computer program product comprising instructions causing a control unit of a stepper motor MRE system to perform the synchronization method steps with the defined vibration frequency, reference position determination, and speed adjustments.
The claims cover a comprehensive synchronization method with control and feedback based on angular position, implementations in hardware and software, the integration in stepper motors and MRI systems, and address issues of phase stability by adjusting rotational speeds according to acquisition timing and burst counts.
Stated Advantages
Improved stability and synchronization of the gravitational transducer's mechanical excitations with the MRI acquisition.
Ensures phase stability of the rotational eccentric mass during the MRE examination for reliable and stable measurement results.
Compensation for deviations in rotational speed enabling linear mechanical excitation with reduced parasitic harmonics.
Facilitates synchronization using signals from the MRI system, providing highly accurate timing transfer to the gravitational transducer.
The use of dummy shots allows the gravitational transducer to accelerate safely to the required frequency before measurement.
Documented Applications
Magnetic resonance elastography scans of subjects, in particular liver MRE experiments.
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