MAGNETIC RESONANCE IMAGING APPARATUS AND MAGNETIC RESONANCE IMAGING METHOD

Abstract

With the object of enhancing image quality, a transmission sensitivity distribution calculating part calculates a transmission sensitivity distribution by a double flip angle method. Next, a threshold processing part threshold-processes the calculated transmission sensitivity distribution. Further, an image correcting unit corrects an actual scan image using the transmission sensitivity distribution subsequent to the threshold processing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configurational diagram showing a construction of a magnetic resonance imaging apparatus 1 illustrative of an embodiment according to the present invention.

FIG. 2 is a block diagram illustrating an image generator 31 employed in the embodiment according to the present invention.

FIG. 3 is a block diagram depicting an image correcting part 133 employed in the embodiment according to the present invention.

FIG. 4 is a flow chart showing operation executed upon photographing an imaging area of a subject SU in the embodiment of the present invention.

FIG. 5 is a diagram illustrating the flow of data at the time of photography of the imaging area of the subject SU in the embodiment according to the present invention.

FIG. 6 is a diagram showing the relationship between a deviation σ_f of a transmission sensitivity distribution f(x, y) and an actually measured distribution of flip angles θ in the embodiment according to the present invention.

FIGS. 7 a, 7b, and 7c are actual scan images obtained with respect to the imaging area of the subject SU in the embodiment according to the present invention.

Claims

1. A magnetic resonance imaging apparatus which executes an actual scan for allowing an RF coil unit to transmit an RF pulse to an imaging area of a subject in a static magnetic field space and to receive a magnetic resonance signal generated in the imaging area to which the RF pulse is transmitted and which thereafter generates an actual scan image about the imaging area, based on the magnetic resonance signal acquired by the execution of the actual scan, said magnetic resonance imaging apparatus comprising: an image correcting unit which corrects the actual scan image,wherein the image correcting unit includesa transmission sensitivity distribution calculating part which calculates a transmission sensitivity distribution at the time that the RF coil unit transmits the RF pulse, in the imaging area, anda threshold processing part which threshold-processes the transmission sensitivity distribution calculated by the transmission sensitivity distribution calculating part, andwherein the actual scan image is corrected using the transmission sensitivity distribution threshold-processed by the threshold processing part.

2. The magnetic resonance imaging apparatus according to claim 1, wherein the image correcting unit includes a reception sensitivity distribution calculating part which calculates a reception sensitivity distribution at the time that the RF coil unit receives the magnetic resonance signal therein, in the imaging area and, wherein the actual scan image is corrected using the reception sensitivity distribution calculated by the reception sensitivity distribution calculating part.

3. The magnetic resonance imaging apparatus according to claim 2, further comprising: a reference scan execution section which executes a reference scan for allowing the RF coil unit to transmit an RF pulse to the imaging area in the static magnetic field space and to receive a magnetic resonance signal generated in the imaging area, prior to the execution of the actual scan, anda reference image generating unit which generates a reference image about the imaging area, based on the magnetic resonance signal obtained by the execution of the reference scan,wherein the RF coil unit includesa first RF coil anda second RF coil ununiform in reception sensitivity distribution as compared with the first RF coil in the imaging area,wherein the reference scan execution section executes, as the reference scan,a first reference scan for allowing the first RF coil to transmit an RF pulse to the imaging area at a first flip angle and to receive a magnetic resonance signal generated in the imaging area,a second reference scan for allowing the first RE coil to transmit an RF pulse to the imaging area at the first flip angle and allowing the second RF coil to receive a magnetic resonance signal generated in the imaging area, anda third reference scan for allowing the first RF coil to transmit an RF pulse to the imaging area at a second flip angle different from the first flip angle and to receive a magnetic resonance signal generated in the imaging area,wherein the reference image generating unit generates a first reference image, based on the magnetic resonance signal obtained by the execution of the first reference scan, generates a second reference image, based on the magnetic resonance signal obtained by the execution of the second reference scan, and generates a third reference image, based on the magnetic resonance signal obtained by the execution of the third reference scan,wherein the reception sensitivity distribution calculating part calculates a reception sensitivity distribution, based on the first reference image and the second reference image, andwherein the transmission sensitivity distribution calculating part calculates a transmission sensitivity distribution, based on the first reference image and the third reference image.

4. The magnetic resonance imaging apparatus according to claim 3, wherein the threshold processing part sets a threshold value, based on a deviation of the first reference image and a deviation of the third reference image and executes the threshold processing using the set threshold value.

5. The magnetic resonance imaging apparatus according to claim 4, wherein the reference scan execution section allows the first RF coil to transmit an RF pulse to the imaging area upon execution of the third reference scan in such a manner that the second flip angle reaches one-half of the first flip angle.

6. The magnetic resonance imaging apparatus according to claim 5, wherein the reference scan execution section carries out the first reference scan, the second reference scan and the third reference scan respectively by a gradient echo method.

7. The magnetic resonance imaging apparatus according to claim 3, wherein the first RF coil is a body coil, and the second RF coil is a phased array coil.

8. The magnetic resonance imaging apparatus according to claim 1, further comprising a display unit for displaying an image, wherein the display unit displays the actual scan image corrected by the image correcting unit.

9. A magnetic resonance imaging method of executing an actual scan for allowing an RF coil unit to transmit an RF pulse to an imaging area of a subject in a static magnetic field space and to receive a magnetic resonance signal generated in the imaging area to which the RF pulse is transmitted, and thereafter generating an actual scan image about the imaging area, based on the magnetic resonance signal acquired by the execution of the actual scan, said magnetic resonance imaging method comprising: an image correcting step for correcting the actual scan image,wherein said image correcting step includesa transmission sensitivity distribution calculating step for calculating a transmission sensitivity distribution at the time that the RF coil unit transmits the RF pulse, in the imaging area, anda threshold processing step for threshold-processing the transmission sensitivity distribution calculated by the transmission sensitivity distribution calculating step, andwherein the actual scan image is corrected using the transmission sensitivity distribution threshold-processed by the threshold processing step.

10. The magnetic resonance imaging method according to claim 9, wherein the image correcting step includes a reception sensitivity distribution calculating step for calculating a reception sensitivity distribution at the time that the RF coil unit receives the magnetic resonance signal therein, in the imaging area, and wherein the actual scan image is corrected using the reception sensitivity distribution calculated by the reception sensitivity distribution calculating step.

11. The magnetic resonance imaging method according to claim 10, further comprising: a reference scan executing step for executing, prior to the execution of the actual scan, a reference scan for allowing the RF coil unit including a first RF coil and a second RF coil ununiform in reception sensitivity distribution as compared with the first RF coil in the imaging area to transmit an RF pulse to the imaging area in the static magnetic field space and to receive a magnetic resonance signal generated in the imaging area, and a reference image generating step for generating a reference image about the imaging area, based on the magnetic resonance signal obtained by the execution of the reference scan,wherein in the reference scan executing step, a first reference scan for allowing the first RF coil to transmit an RF pulse to the imaging area at a first flip angle and to receive a magnetic resonance signal generated in the imaging area, a second reference scan for allowing the first RF coil to transmit an RF pulse to the imaging area at the first flip angle and allowing the second RF coil to receive a magnetic resonance signal generated in the imaging area, and a third reference scan for allowing the first RF coil to transmit an RF pulse to the imaging area at a second flip angle different from the first flip angle and to receive a magnetic resonance signal generated in the imaging area are executed as the reference scan,wherein in the reference image generating steps, a first reference image is generated based on the magnetic resonance signal obtained by the execution of the first reference scan, a second reference image is generated based on the magnetic resonance signal obtained by the execution of the second reference scan, and a third reference image is generated based on the magnetic resonance signal obtained by the execution of the third reference scan,wherein in the reception sensitivity distribution calculating step, a reception sensitivity distribution is calculated based on the first reference image and the second reference image, andwherein in the transmission sensitivity distribution calculating step, a transmission sensitivity distribution is calculated based on the first reference image and the third reference image.

12. The magnetic resonance imaging method according to claim 11, wherein in the threshold processing step, a threshold value is set based on a noise component of the first reference image and a noise component of the third reference image and the threshold processing is executed using the set threshold value.

13. The magnetic resonance imaging method according to claim 12, wherein in the reference scan executing step, the first RF coil transmits an RE pulse to the imaging area upon execution of the third reference scan in such a manner that the second flip angle reaches one-half of the first flip angle.

14. The magnetic resonance imaging method according to claim 13, wherein in the reference scan executing step, the first reference scan, the second reference scan and the third reference scan are respectively carried out by a gradient echo method.

15. The magnetic resonance imaging method according to claim 11, wherein a body coil is used as the first RF coil, and a surface coil is used as the second RF coil.

16. The magnetic resonance imaging method according to claim 9, further comprising a displaying step for displaying an image, wherein the actual scan image corrected by the image correcting step is displayed in the displaying step.

17. A method for reducing imaging artifacts using a Magnetic Resonance Imaging apparatus, said method comprising: performing a plurality of reference scans to generate a plurality of reference images;calculating a reception sensitivity distribution using at least two of the reference images;calculating a transmission sensitivity distribution using at least two of the reference images;performing an actual scan to generate an actual scan image; andprocessing the actual scan image using the reception sensitivity distribution and the transmission sensitivity distribution to reduce imaging artifacts in the actual scan image.

18. A method in accordance with claim 17 wherein performing a plurality of reference scans further comprises: performing a first reference scan to generate a first reference image;performing a second reference scan to generate a second reference image; andperforming a third reference scan to generate a third reference image.

19. A method in accordance with claim 18 further comprising: calculating the reception sensitivity distribution using the first and second reference images; andcalculating a first transmission sensitivity distribution using the first and third reference images

20. A method in accordance with claim 19, further comprising: threshold processing the first transmission distribution to generate a second transmission sensitivity distribution; andprocessing the actual scan image using the reception sensitivity distribution and the second transmission sensitivity distribution to reduce imaging artifacts.