Magnetic resonance imaging apparatus with segmented data acquisition
To provide an imaging technique suitable for acquiring an image with reduced artifacts due to differences in signal intensity. An MR apparatus 100 acquires, in data acquisition periods A 1, A 2, and A 3, data at part of grid points lying closer to a high-frequency region RH within a low-frequency region RL, and data at part of grid points lying closer to the low-frequency region RL within the high-frequency region RH. On the other hand, in a data acquisition period B, it acquires data at another part of grid points lying closer to the high-frequency region RH within the low-frequency region RL, and data at another part of grid points lying closer to the low-frequency region RL within the high-frequency region RH.
1. A magnetic resonance apparatus comprising a scanning section configured to conduct a scan for acquiring data at grid points contained in a first region in k-space and acquiring data at grid points contained in a second region adjacent to said first region, wherein said scanning section acquires:
in a first data acquisition period in which acquisition of data at grid points in k-space is conducted, data at part of a first plurality of grid points lying closer to said second region within said first region, and data at part of a second plurality of grid points lying closer to said first region within said second region; and
in a second data acquisition period in which acquisition of data at grid points in k-space is conducted, data at grid points of said first plurality of grid points other than those at which data are acquired in said first data acquisition period, and data at grid points of said second plurality of grid points other than those at which data are acquired in said first data acquisition period;
said magnetic resonance apparatus further comprising a determining unit configured to determine grid points for which data are to be acquired in said first data acquisition period and grid points for which data are to be acquired in said second data acquisition period;
wherein said determining unit comprises a numbering unit configured to assign numbers to grid points in k-space; a defining unit configured to define a border between said first and second regions; and an exchanging unit configured to exchange numbers assigned to part of said first plurality of grid points with those assigned to part of said second plurality of grid points; and
wherein said scanning section acquires in said first data acquisition period, data at grid points whose numbers are not exchanged by said exchanging unit within said first region, and data at grid points whose numbers are exchanged by said exchanging unit within said second region, and in said second data acquisition period, data at grid points whose numbers are exchanged by said exchanging unit within said first region, and data at grid points whose numbers are not exchanged by said exchanging unit within said second region.
2. The magnetic resonance apparatus as recited in claim 1 , wherein said determining unit comprises a sorting unit configured to sort numbers for a third plurality of grid points, said third plurality of grid points including grid points whose numbers are not exchanged within said first region and grid points whose numbers are exchanged within said second region.
3. The magnetic resonance apparatus as recited in claim 2 , wherein said scanning section acquires, in said first data acquisition period, data at each of said third plurality of grid points according to numbers for said third plurality of grid points after being sorted by said sorting unit.
4. The magnetic resonance apparatus as recited in claim 2 , wherein said sorting unit sorts numbers for said third plurality of grid points so that a grid point has a greater number as it lies farther from a center of k-space.
5. The magnetic resonance apparatus as recited in claim 1 , wherein said exchanging unit exchanges a number for each grid point chosen from within said first region so that the number for the grid point is decremented by α, with a number for each grid point chosen from within said second region so that the number for the grid point is incremented by β.
6. The magnetic resonance apparatus as recited in claim 5 , wherein said exchanging unit changes a value of α according to a distance between each grid point in said first region and said border, and a value of β according to a distance between each grid point in said second region and said border.
7. The magnetic resonance apparatus as recited in claim 6 , wherein the value of α is equal to the value of β.
8. The magnetic resonance apparatus as recited in claim 1 , wherein said numbering unit assigns a number to a grid point in k-space based on a distance between the grid point and the center of k-space.
9. The magnetic resonance apparatus as recited in claim 1 , wherein said scan has another first data acquisition period for acquiring data at the same grid points as those in said first data acquisition period.
10. The magnetic resonance apparatus as recited in claim 1 , wherein said second data acquisition period is divided into a plurality of data acquisition periods, and said scanning section acquires data at mutually different grid points in said plurality of data acquisition periods.
11. The magnetic resonance apparatus as recited in claim 1 , wherein said first region is a low-frequency region including the center of k-space, and said second region is a high-frequency region.
12. The magnetic resonance apparatus as recited in claim 1 , wherein said scanning section performs in said first data acquisition period, a first sequence for acquiring data at part of said first plurality of grid points and data at part of said second plurality of grid points, and in said second data acquisition period, a second sequence for acquiring data at grid points of said first plurality of grid points other than those at which data are acquired in said first data acquisition period, and data at grid points of said second plurality of grid points other than those at which data are acquired in said first data acquisition period.
13. The magnetic resonance apparatus as recited in claim 12 , wherein said scanning section performs in said first data acquisition period, said first sequence after applying a fat suppression pulse, and in said second data acquisition period, said second sequence after applying a fat suppression pulse.
14. The magnetic resonance apparatus as recited in claim 13 , wherein a plurality of fat suppression pulses are applied in said first or second data acquisition period.
15. The magnetic resonance apparatus as recited in claim 12 , wherein said scanning section performs in said first data acquisition period, a first navigator sequence for acquiring navigator echoes containing information on subject's respiration, and said first sequence after performing said first navigator sequence, and in said second data acquisition period, a second navigator sequence for acquiring navigator echoes containing information on subject's respiration, and said second sequence after performing said second navigator sequence.
16. The magnetic resonance apparatus as recited in claim 12 , wherein said scanning section performs in said first data acquisition period, a first blood flow suppressing sequence for reducing blood flow signals, and said first sequence after performing said first blood flow suppressing sequence, and in said second data acquisition period, a second blood flow suppressing sequence for reducing blood flow signals, and said second sequence after performing said second blood flow suppressing sequence.
17. The magnetic resonance apparatus as recited in claim 1 , wherein said scanning section conducts a scan on a subject to which a contrast medium is administered.
18. The magnetic resonance apparatus as recited in claim 1 , further comprising an image producing unit for producing an image based on the data at grid points in k-space acquired in said first data acquisition period and the data acquired in said second data acquisition period.