Magnetic resonance imaging apparatus and its control method

1. A magnetic resonance imaging apparatus comprising:

a phased array coil including a plurality of local coils;

a pre-scanning unit which pre-scans, before image scanning, an area including at least part of an image scanning area;

a determination unit which determines whether each of the local coils is abnormal, based on signals output from the local coils during pre-scanning; and

an information supply unit which supplies a user with information indicating an abnormal local coil, if the determination unit determines that the local coils include the abnormal local coil.

2. The magnetic resonance imaging apparatus according to claim 1 , wherein:

the local coils have sensitivity areas, each of the sensitivity areas overlapping with at least one of other ones of the sensitivity areas;

the pre-scanning unit pre-scans an area including the entire image scanning area, using those ones of the local coils which have sensitivity areas each including part of the image scanning area; and

the determination unit compares signals output from those local coils used for pre-scanning by the pre-scanning unit, thereby determining whether the local coils include the abnormal local coil.

3. The magnetic resonance imaging apparatus according to claim 2 , wherein the determination unit includes:

a computation unit which computes, as a comparative value set for each one of those local coils used for the pre-scanning, a ratio of an average of top intensity levels of signals output from said each one of those local coils and corresponding to all slices of the pre-scanning by said each one of those local coils, to an average of bottom intensity levels of the signals output from said each one of those local coils and corresponding to all the slices, the computation unit alternatively computing, as the comparative value, a sum of intensity levels of the signals corresponding to all the slices; and

a unit which determines that one of the local coils corresponding to the comparative value is the abnormal local coil, if the comparative value is lower than a maximum value set for the comparative value, by a preset degree of the maximum value.

4. The magnetic resonance imaging apparatus according to claim 1 , wherein the information supply unit causes a display unit to display an image indicating which of the local coils is the abnormal local coil.

5. The magnetic resonance imaging apparatus according to claim 4 , wherein the image indicates, on an image indicating an arrangement of the local coils, which of the local coils is the abnormal local coil.

6. The magnetic resonance imaging apparatus according to claim 1 , further comprising a unit which performs the image scanning using those ones of the local coils which are other than the abnormal local coil, if the determination unit determines that the local coils include the abnormal local coil.

7. The magnetic resonance imaging apparatus according to claim 1 , wherein:

each of the local coils is a quadrature coil for synthesizing signals of two orthogonal channels; and

the determination unit determines that each of the local coils is abnormal, also when an intensity ratio between the signals of the two channels falls outside a preset range.

8. The magnetic resonance imaging apparatus according to claim 1 , wherein:

each of the local coils is a quadrature coil for synthesizing signals of two orthogonal channels; and

the determination unit determines that each of the local coils is abnormal, also when a preset value is less than an intensity ratio between signals acquired before and after synthesis.

9. A magnetic resonance imaging apparatus comprising:

a phased array coil including a plurality of local coils;

a wide-area coil having a sensitivity area which includes sensitivity areas of the local coils;

a pre-scanning unit which pre-scans, before image scanning, an area including at least part of an image scanning area;

a determination unit which determines whether each of the local coils is abnormal, based on signals output, during pre-scanning, from the local coils and the wide-area coil at substantially a same scanning position; and

an information supply unit which supplies a user with information indicating an abnormal local coil, if the determination unit determines that local coils include the abnormal local coil.

10. The magnetic resonance imaging apparatus according to claim 9 , wherein the determination unit determines whether each of the local coils is abnormal, based on an intensity ratio of the signal output from each of the local coils, to the wide-area coil.

11. The magnetic resonance imaging apparatus according to claim 9 , wherein:

the pre-scanning unit pre-scans an area including the entire image scanning area, using those ones of the local coils which each include part of the image scanning area; and

the determination unit determines whether each of those local coils used for the pre-scanning is abnormal.

12. The magnetic resonance imaging apparatus according to claim 9 , wherein the information supply unit causes a display unit to display an image indicating which of the local coils is the abnormal local coil.

13. The magnetic resonance imaging apparatus according to claim 12 , wherein the image indicates, on an image indicating an arrangement of the local coils, which of the local coils is the abnormal local coil.

14. The magnetic resonance imaging apparatus according to claim 9 , further comprising a unit which performs the image scanning using those ones of the local coils which are other than the abnormal local coil, if the determination unit determines that the local coils include the abnormal local coil.

15. The magnetic resonance imaging apparatus according to claim 9 , wherein:

each of the local coils is a quadrature coil for synthesizing signals of two orthogonal channels; and

the determination unit determines that each of the local coils is abnormal also when an intensity ratio between the signals of the two channels falls outside a preset range.

16. The magnetic resonance imaging apparatus according to claim 9 , wherein:

each of the local coils is a quadrature coil for synthesizing signals of two orthogonal channels; and

the determination unit determines that each of the local coils is abnormal, also when a preset value is less than an intensity ratio between signals acquired before and after synthesis.

17. A method of controlling a magnetic resonance imaging apparatus with a phased array coil including a plurality of local coils, comprising:

pre-scanning, before image scanning, an area including at least part of an image scanning area;

determining whether each of the local coils is abnormal, based on signals output from the local coils during pre-scanning; and supplying a user with information indicating an abnormal local coil, if it is determined that the local coils include the abnormal local coil.

18. The method according to claim 17 , wherein:

the local coils have sensitivity areas, each of the sensitivity areas overlapping with at least one of other ones of the sensitivity areas;

an area including the entire image scanning area is scanned, using those ones of the local coils which have sensitivity areas each including part of the image scanning area; and

signals output from the local coils used for pre-scanning are compared, thereby determining whether the local coils include the abnormal local coil.

19. The method according to claim 18 , wherein the determining whether each of the local coils is abnormal includes:

computing, as a comparative value set for each one of those local coils used for the pre-scanning, a ratio of an average of top intensity levels of signals output from said each one of those local coils and corresponding to all slices of the pre-scanning by said each one local coil, to an average of bottom intensity levels of the signals output from said each one of those local coils and corresponding to all the slices, alternatively computing, as the comparative value, a sum of intensity levels of the signals corresponding to all the slices; and

determining that one of the local coils corresponding to the comparative value is the abnormal local coil, if the comparative value is lower than a maximum value set for the comparative value, by a preset degree of the maximum value.

20. The method according to claim 17 , wherein for supplying the information, an image indicating which of the local coils is the abnormal local coil is displayed on a display unit.

21. The method according to claim 20 , wherein the image indicates, on an image indicating an arrangement of the local coils, which of the local coils is the abnormal local coil.

22. The method according to claim 17 , wherein the image scanning is performed using those ones of the local coils which are other than the abnormal local coil, if it is determined that the local coils include the abnormal local coil.

23. The method according to claim 17 , wherein:

each of the local coils is a quadrature coil for synthesizing signals of two orthogonal channels; and

each of the local coils is determined abnormal also when an intensity ratio between the signals of the two channels falls outside a preset range.

24. The method according to claim 17 , wherein:

each of the local coils is a quadrature coil for synthesizing signals of two orthogonal channels; and

it is determined that each of the local coils is abnormal, also when a preset value is less than an intensity ratio between signals acquired before and after synthesis.

25. A method of controlling a magnetic resonance imaging apparatus with a phased array coil including a plurality of local coils, and a wide-area coil having a sensitivity area which includes sensitivity areas of the local coils, comprising:

pre-scanning, before image scanning, an area including at least part of an image scanning area;

determining whether each of the local coils is abnormal, based on signals output, during pre-scanning, from the local coils and the wide-area coil at substantially a same scanning position; and

supplying a user with information indicating an abnormal local coil, if it is determined that the local coils include the abnormal local coil.

26. The method according to claim 25 , wherein the determining whether each of the local coils is abnormal includes determining whether each of the local coils is abnormal, based on an intensity ratio of the signal output from each of the local coils, to the wide-area coil.

27. The method according to claim 25 , wherein:

the pre-scanning includes pre-scanning an area including the entire image scanning area, using those ones of the local coils which each include part of the image scanning area; and

the determining whether each of the local coils is abnormal includes determining whether each of those local coils used for the pre-scanning is abnormal.

28. The method according to claim 25 , wherein for supplying the information, an image indicating which of the local coils is the abnormal local coil is displayed on a display unit.

29. The method according to claim 28 , wherein the image indicates, on an image indicating an arrangement of the local coils, which of the local coils is the abnormal local coil.

30. The method according to claim 25 , wherein the image scanning is performed using those ones of the local coils which are other than the abnormal local coil, if it is determined that the local coils include the abnormal local coil.

31. The method according to claim 25 , wherein:

each of the local coils is a quadrature coil for synthesizing signals of two orthogonal channels; and

each of the local coils is determined abnormal also when an intensity ratio between the signals of the two channels falls outside a preset range.

32. The method according to claim 25 , wherein:

each of the local coils is a quadrature coil for synthesizing signals of two orthogonal channels; and

it is determined that each of the local coils is abnormal, also when a preset value is less than an intensity ratio between signals acquired before and after synthesis.