Image processing apparatus, image processing method, and magnetic resonance imaging apparatus
An image processing apparatus according to an embodiment includes processing circuitry. The processing circuitry determines, with respect to each of the pixels included in a magnetic resonance image, a shift amount from the position of the pixel to a position where ringing artifacts will be reduced and performs a ringing correction to correct the ringing artifacts occurring in the magnetic resonance image on the basis of the determined shift amounts. The processing circuitry estimates, with respect to each of the pixels, a local amplitude of ringing artifacts, and performs the ringing correction on the magnetic resonance image while determining the shift amount of each of the pixels so as to be approximately continuous with the shift amounts of adjacently positioned pixels, sequentially in descending order starting with pixels having a higher local amplitude on the basis of the estimated local amplitudes of ringing artifacts.
1 . An image processing apparatus, comprising:
processing circuitry configured to
acquire a magnetic resonance image; and
determine, with respect to each pixel of pixels included in the magnetic resonance image, a shift amount from a position of the pixel to a position where ringing artifacts will be reduced, and perform a ringing correction to correct the ringing artifacts occurring in the magnetic resonance image based on the determined shift amounts, wherein
the processing circuitry is further configured to
estimate, with respect to each pixel of the pixels included in the magnetic resonance image, a local amplitude of the ringing artifacts occurring in the magnetic resonance image, and
perform the ringing correction on the magnetic resonance image based on a result of estimating the local amplitudes of the ringing artifacts, while determining the shift amount of each pixel of the pixels included in the magnetic resonance image so as to be approximately continuous with the shift amounts of adjacently positioned pixels, sequentially in descending order starting with pixels having a higher local amplitude of the ringing artifacts.
2 . The image processing apparatus according to claim 1 , wherein the processing circuitry is further configured to:
generate, as the result of estimating the local amplitudes of ringing artifacts, a ringing map indicating the local amplitude of ringing artifacts with respect to each of the pixels included in the magnetic resonance image, and
perform the ringing correction on the magnetic resonance image based on the ringing map, while determining the shift amount of each of the pixels included in the magnetic resonance image, sequentially in descending order starting with the pixels having a higher local amplitude of the ringing artifacts.
3 . The image processing apparatus according to claim 2 , wherein the processing circuitry is further configured to perform the ringing correction on the magnetic resonance image and generate a ringing map based on a difference image between an image before an initial ringing correction and an image after the initial ringing correction.
4 . The image processing apparatus according to claim 1 , wherein the processing circuitry is further configured to;
set a first threshold value related to the local amplitude of ringing artifacts,
determine, with respect to each of a first set of the pixels of which the local amplitude is equal to or higher than the first threshold value, the shift amount so as to be close to the shift amounts of the adjacently positioned pixels, and
determine, with respect to each of a second set of the pixels of which the local amplitude is lower than the first threshold value, the shift amount so as to be close to the shift amounts of the adjacently positioned pixels, and subsequently adjust the determined shift amounts for the second set of the pixels so that the shift amounts gradually diminish, sequentially in descending order starting with pixels of the second set of the pixels having a higher local amplitude.
5 . The image processing apparatus according to claim 4 , wherein the processing circuitry is further configured to;
set a second threshold value smaller than the first threshold value, and
set the shift amount to 0 for each of the pixels of which the local amplitude of ringing artifacts is lower than the second threshold value.
6 . The image processing apparatus according to claim 4 , wherein the processing circuitry is further configured to:
set threshold values based on a range of amplitudes of ringing artifacts across the magnetic resonance image, in combination with a number of pixels included in the magnetic resonance image, and
compute a residual range of amplitudes of ringing artifacts after excluding trivially low amplitudes, or extremely high amplitudes, or both, as the range of amplitudes of ringing artifacts to consider when setting the threshold values.
7 . The image processing apparatus according to claim 6 , wherein the processing circuitry is further configured to:
set a reference amplitude value based on the range of amplitudes of ringing artifacts across the magnetic resonance image, in combination with the number of pixels included in the magnetic resonance image; and
set the threshold values by multiplying the reference amplitude value by predetermined constant parameters, one for each threshold.
8 . The image processing apparatus according to claim 1 , wherein the processing circuitry is further configured to iteratively improve an accuracy of the estimated local amplitudes and a quality of the ringing correction by re-estimating the local amplitudes of ringing artifacts and performing a ringing correction twice or multiple times.
9 . An image processing method, comprising:
acquiring a magnetic resonance image; and
determining, with respect to each pixel of pixels included in the magnetic resonance image, a shift amount from a position of the pixel to a position where ringing artifacts will be reduced and further performing a ringing correction to correct the ringing artifacts occurring in the magnetic resonance image based on the determined shift amounts, wherein
the performing of the ringing correction includes
estimating, with respect to each pixel of the pixels included in the magnetic resonance image, a local amplitude of the ringing artifacts occurring in the magnetic resonance image, and
performing the ringing correction on the magnetic resonance image based on a result of estimating the local amplitudes of the ringing artifacts, while determining the shift amount of each pixel of the pixels included in the magnetic resonance image so as to be approximately continuous with the shift amounts of adjacently positioned pixels, sequentially in descending order starting with pixels having a higher local amplitude of the ringing artifacts.
10 . A magnetic resonance imaging apparatus, comprising:
processing circuitry configured to
generate a magnetic resonance image; and
determine, with respect to each pixel of pixels included in the magnetic resonance image, a shift amount from a position of the pixel to a position where ringing artifacts will be reduced and perform a ringing correction to correct the ringing artifacts occurring in the magnetic resonance image based on the determined shift amounts, wherein
the processing circuitry is further configured to
estimate, with respect to each of the pixels included in the magnetic resonance image, a local amplitude of the ringing artifacts occurring in the magnetic resonance image, and
perform the ringing correction on the magnetic resonance image based on a result of estimating the local amplitudes of the ringing artifacts, while determining the shift amount of each pixel of the pixels included in the magnetic resonance image so as to be approximately continuous with the shift amounts of adjacently positioned pixels, sequentially in descending order starting with pixels having a higher local amplitude of the ringing artifacts.