MAGNETIC RESONANCE IMAGING DEVICE AND IMAGING PARAMETER DETERMINATION METHOD

• US 20160146910A1
• Filed: 07/23/2014
• Published: 05/26/2016
• Est. Priority Date: 08/27/2013
• Status: Active Grant

• Current Assignee: FUJIFILM Healthcare Corp. (Fujifilm Holdings Corporation)
• Original Assignee: Hitachi Medical Corporation (Hitachi, Ltd.)
• Inventors: Kaneko, Yukio, Soutome, Yoshihisa, Ochi, Hisaaki
• Granted Patent: US 10,241,161 B2
• Time in Patent Office: Days
• CPC Class Codes: A61B 2560/0266 for monitoring or limiting apparatus function
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61B 5/748 Selection of a region of interest, e.g. using a graphics tablet
• CPC Class Codes: G01R 33/288 Provisions within MR facilities for enhancing safety during MR, e.g. reduction of the specific absorption rate [SAR], detection of ferromagnetic objects in the scanner room
• CPC Class Codes: G01R 33/34046 Volume type coils, e.g. bird-cage coils; Quadrature bird-cage coils; Circularly polarised coils
• CPC Class Codes: G01R 33/3875 using correction coil assemblies, e.g. active shimming
• CPC Class Codes: G01R 33/4833 using spatially selective excitation of the volume of interest, e.g. selecting non-orthogonal or inclined slices
• CPC Class Codes: G01R 33/4835 of multiple slices
• CPC Class Codes: G01R 33/5612 Parallel RF transmission, i.e. RF pulse transmission using a plurality of independent transmission channels

Abstract

Provided is a technique capable of achieving safety and image quality at the same time in an MRI device using a transmission coil including plural channels. An SAR distribution is calculated, and an imaging parameter is determined for optimizing a radio frequency magnetic field distribution in an imaging region while suppressing a maximum value of an SAR to be equal to or smaller than a predetermined threshold value. The determined imaging parameter includes a radio frequency magnetic field parameter for specifying radio frequency pulses to be transmitted through each of the plural channels. The SAR distribution is calculated using a database that retains an electric field distribution of each of the plural channels for each subject model retained in advance.

Claims

1. A magnetic resonance imaging device comprising:

a transmission coil that includes a plurality of channels that respectively transmits radio frequency pulses to a subject;

an imaging parameter determiner that determines a predetermined imaging parameter among imaging conditions used in imaging the subject; and

an imaging unit that executes imaging using the determined imaging parameter,

wherein the imaging parameter determiner includes

a database that retains data capable of calculating a specific absorption rate distribution for each of predetermined subject models, and

an imaging parameter optimizer that determines the imaging parameter for optimizing a radio frequency magnetic field distribution in a region of interest while suppressing a maximum value of a local specific absorption rate to be equal to or smaller than a specific absorption rate threshold value using the data in the database, and

wherein the imaging parameter determined by the imaging parameter optimizer includes a radio frequency magnetic field parameter for specifying the radio frequency pulses to be transmitted through each of the plurality of channels.

2. The magnetic resonance imaging device according to claim 1,

wherein the imaging parameter optimizer determines the radio frequency magnetic field parameter according to predetermined optimization conditions, and

wherein the optimization conditions include a uniformity condition that the uniformity of the radio frequency magnetic field distribution is equal to or greater than a predetermined value, and a local specific absorption rate condition that a maximum value of the local specific absorption rate is equal to or smaller than the specific absorption rate threshold value, as restriction conditions.

3. The magnetic resonance imaging device according to claim 1,

wherein the imaging parameter determined by the imaging parameter optimizer further includes a specific absorption rate parameter which is an imaging parameter other than the radio frequency magnetic field parameter and affects a specific absorption rate,

wherein the imaging parameter optimizer includes

a high frequency magnetic field parameter optimizer that determines the radio frequency magnetic field parameter according to predetermined optimization conditions,

a specific absorption rate distribution calculator that calculates a specific absorption rate distribution using the determined radio frequency magnetic field parameter, the latest specific absorption rate parameter, and the data in the database whenever the radio frequency magnetic field parameter is determined, and

a specific absorption rate parameter adjuster that determines whether a maximum value of the calculated specific absorption rate distribution exceeds the specific absorption rate threshold value whenever the specific absorption rate distribution is calculated and adjusts, if the maximum value exceeds the specific absorption rate threshold value, the specific absorption rate parameter so that the maximum value of the specific absorption rate distribution is equal to or smaller than the specific absorption rate threshold value, and

wherein the optimization conditions include a uniformity condition that the uniformity of the radio frequency magnetic field distribution is equal to or greater than a predetermined value as a restriction condition.

4. The magnetic resonance imaging device according to claim 3,

wherein the specific absorption rate parameter adjuster further includes an imaging time determiner that calculates a time relating to imaging using the adjusted specific absorption rate parameter and determines whether the calculated imaging time is within an allowable range, and

wherein the imaging parameter optimizer changes, when it is determined by the imaging time determiner that the calculated imaging time is not within the allowable range, a threshold value for regulating the uniformity condition in the optimization conditions by a predetermined value, and makes the radio frequency magnetic field parameter optimizer to determine the radio frequency magnetic field parameter again.

5. The magnetic resonance imaging device according to claim 1,

wherein the imaging parameter determined by the imaging parameter optimizer further includes a specific absorption rate parameter which is an imaging parameter other than the radio frequency magnetic field parameter and affects the specific absorption rate,

wherein the imaging parameter optimizer includes

a radio frequency magnetic field parameter optimizer that determines the radio frequency magnetic field parameter according to predetermined optimization conditions,

a specific absorption rate distribution calculator that calculates a specific absorption rate distribution using the determined radio frequency magnetic field parameter, the latest specific absorption rate parameter, and the data in the database whenever the radio frequency magnetic field parameter is determined, and

a specific absorption rate parameter adjuster that determines whether a maximum value of the calculated specific absorption rate distribution exceeds the specific absorption rate threshold value and adjusts, if the maximum value exceeds the specific absorption rate threshold value, the specific absorption rate parameter in a predetermined range, and

wherein when the specific absorption rate parameter is changed, the imaging parameter optimizer makes the specific absorption rate calculator calculate the specific absorption rate distribution using the changed specific absorption rate parameter, determines whether a maximum value of the calculated specific absorption rate distribution using the changed specific absorption rate parameter exceeds the specific absorption rate threshold value, and repeats, if the maximum value of the specific absorption rate distribution exceeds the specific absorption rate threshold value, a process of changing a threshold value for regulating the uniformity condition in the optimization conditions by a predetermined value, a process of making the radio frequency magnetic field parameter optimizer to determine the radio frequency magnetic field parameter again, and a process of making the specific absorption rate distribution calculator to calculate the specific absorption rate distribution using the re-determined radio frequency magnetic field parameter, until the maximum value of the specific absorption rate distribution becomes equal to or smaller than the specific absorption rate threshold value.

6. The magnetic resonance imaging device according to claim 1,

wherein the radio frequency magnetic field parameter is at least one of an amplitude and a phase of the radio frequency pulse transmitted through each of the plurality of channels of the transmission coil.

7. The magnetic resonance imaging device according to claim 3,

wherein the specific absorption rate parameter is at least one of a repetition time and the number of slices.

8. The magnetic resonance imaging device according to claim 5,

wherein the specific absorption rate parameter is at least one of a repetition time and the number of slices.

9. The magnetic resonance imaging device according to claim 1,

wherein the data retained in the database includes an electric field distribution of each of the plurality of channels for each subject model, and

wherein the electric field distribution is a distribution when radio frequency magnetic field pulses having a predetermined amplitude and a phase as references is emitted once per unit time in imaging one slice.

10. The magnetic resonance imaging device according to claim 1,

wherein the imaging parameter optimizer further determines the imaging parameters so that at least one of a specific absorption rate and a signal value in a region where an artifact is generated is equal to or smaller than a predetermined value.

11. An imaging parameter determination method comprising:

determining a predetermined imaging parameter so that a radio frequency magnetic field distribution in a region of interest is optimized while suppressing a maximum value of a local specific absorption rate to be equal to or smaller than a specific absorption rate threshold value using data in a predetermined database,

wherein the imaging parameter includes a radio frequency magnetic field parameter for specifying radio frequency pulses to be transmitted through each of a plurality of channels of a transmission coil of a magnetic resonance imaging device, and

wherein the data retained in the database is data capable of calculating a specific absorption rate distribution for each subject model.

12. The imaging parameter determination method according to claim 11,

wherein the radio frequency magnetic field parameter is determined according to optimization conditions that include a uniformity condition that the uniformity of the radio frequency magnetic field distribution is equal to or greater than a predetermined value and a local specific absorption rate condition that a maximum value of the local specific absorption rate is equal to or smaller than the specific absorption rate threshold value, as restriction conditions.

13. The imaging parameter determination method according to claim 11, further comprising:

determining the radio frequency magnetic field parameter according to optimization conditions that include a uniformity condition that the uniformity of the radio frequency magnetic field distribution is equal to or greater than a predetermined value as a restriction condition;

calculating a specific absorption rate distribution using the determined radio frequency magnetic field parameter, and the data in the database; and

determining whether a maximum value of the calculated specific absorption rate distribution exceeds the specific absorption rate threshold value and adjusting, if the maximum value exceeds the specific absorption rate threshold value, a specific absorption rate parameter which is an imaging parameter other than the radio frequency magnetic field parameter and affects the specific absorption rate so that the maximum value of the specific absorption rate distribution is equal to or smaller than the specific absorption rate threshold value.

14. The imaging parameter determination method according to claim 13, further comprising:

calculating a time relating to imaging using the adjusted specific absorption rate parameter after the specific absorption rate parameter is adjusted; and

determining whether the calculated imaging time is within an allowable range and changing, when it is determined that the calculated imaging time is not within the allowable range, a threshold value for regulating the uniformity condition in the optimization conditions by a predetermined value to determine the radio frequency magnetic field parameter again.

15. The imaging parameter determination method according to claim 11, further comprising:

determining the radio frequency magnetic field parameter according to optimization conditions that include a uniformity condition that the uniformity of the radio frequency magnetic field distribution is equal to or greater than a predetermined value as a restriction condition;

calculating a specific absorption rate distribution using the determined radio frequency magnetic field parameter, and the data in the database; and

determining whether a maximum value of the calculated specific absorption rate distribution exceeds the specific absorption rate threshold value and adjusting, if the maximum value exceeds the specific absorption rate threshold value, a specific absorption rate parameter which is a parameter other than the radio frequency magnetic field parameter and affects the specific absorption rate in a predetermined range;

calculating the specific absorption rate distribution using the changed specific absorption rate parameter, and determining whether a maximum value of the calculated specific absorption rate distribution using the changed specific absorption rate parameter exceeds the specific absorption rate threshold value; and

repeating, if the maximum value of the specific absorption rate distribution exceeds the specific absorption rate threshold value, a process of changing a threshold value for regulating the uniformity condition in the optimization conditions by a predetermined value to determine the radio frequency magnetic field parameter again, and a process of calculating the specific absorption rate distribution using the re-determined radio frequency magnetic field parameter, until the maximum value of the specific absorption rate distribution becomes equal to or smaller than the specific absorption rate threshold value.