Apparatus and method for context-oriented iterative reconstruction for computed tomography (CT)
A method and apparatus is provided to iteratively reconstruct a computed tomography (CT) image using a spatially-varying content-oriented regularization parameter, thereby achieving uniform statistical properties within respective organs/regions and different statistical properties (e.g., degree of smoothing and noise level) among the respective organs/regions. For example, less smoothing and sharper features/resolution can be applied within a lung region than within a soft-tissue region by using a smaller regularization parameter value in the lung region than in the soft-tissue region. This can be achieved, e.g., using a minimum intensity projection to suppress/eliminate sub-solid nodules in the lung region. The content-oriented regularization parameter can be generated by reconstructing an initial CT image, which is then segmented/classified according to organs and/or tissue type. Segmenting the image and generating the content-oriented regularization parameter can be integrated into one process by applying an HU-to-β mapping to the CT image.
1. An apparatus, comprising:
circuitry configured to
obtain projection data representing an intensity of X-ray radiation for a series of projection images of attenuation through an object, the series of projection images being acquired at respective projection angles,
reconstruct a first computed tomography (CT) image from the projection data,
classify the first CT image into a plurality of regions corresponding to respective organs and/or tissue types,
determine respective first regularization parameters corresponding to the plurality of regions, and
reconstruct, using the projection data and the first regularization parameters, a second CT image using a regularizer that is scaled by the respective first regularization parameters in corresponding regions of the plurality of regions,
wherein the circuitry is further configured to
classify the first CT image by generating a minimum intensity projection (MIP) image based on a minimum value in an axial direction of a stack of slices of the first CT image, the stack of slices of the first CT image being taken in axial planes, and
determine the first regularization parameters using the first CT image to determine the first regularization parameters of pixels of the first CT image within a first range of radiodensity, and using the MIP image to determine the first regularization parameters of pixels of the first CT image within a second range of radiodensity, a radiodensity in the first range of radiodensity being greater than a radiodensity in the second range of radiodensity.
2. An apparatus, comprising:
circuitry configured to
obtain projection data representing an intensity of X-ray radiation for a series of projection images of attenuation through an object, the series of projection images being acquired at respective projection angles,
reconstruct a first computed tomography (CT) image from the projection data,
classify the first CT image into a plurality of regions corresponding to respective organs and/or tissue types,
determine respective first regularization parameters corresponding to the plurality of regions, and
reconstruct, using the projection data and the first regularization parameters, a second CT image using a regularizer that is scaled by the respective first regularization parameters in corresponding regions of the plurality of regions,
wherein the circuitry is further configured to
determine the first regularization parameters using a piece-wise linear mapping from values of radiodensity to values of the first regularization parameters, the piece-wise linear mapping being applied to pixels of the first CT image that have a radiodensity within a first range of radiodensities,
generate a minimum intensity projection (MIP) image based on a minimum value in an axial direction of a stack of slices of the first CT image, the stack of slices of the first CT image being taken in axial planes, and,
for pixels of the first image having a radiodensity outside of the first range of radiodensities, apply the piece-wise linear mapping to the MIP image to determine the first regularization parameters.
3. An apparatus, comprising:
circuitry configured to
obtain projection data representing an intensity of X-ray radiation for a series of projection images of attenuation through an object, the series of projection images being acquired at respective projection angles,
reconstruct a first computed tomography (CT) image from the projection data,
classify the first CT image into a plurality of regions corresponding to respective organs and/or tissue types,
determine respective first regularization parameters corresponding to the plurality of regions, and
reconstruct, using the projection data and the first regularization parameters, a second CT image using a regularizer that is scaled by the respective first regularization parameters in corresponding regions of the plurality of regions,
wherein the circuitry is further configured to determine the first regularization parameters, wherein the first regularization parameters, when used to reconstruct the second CT image, cause greater smoothing in a soft tissue region of the plurality of regions than in a lung region of the plurality of regions.
4. A method, comprising:
obtaining projection data representing an intensity of X-ray radiation for a series of projection images of attenuation through an object, the series of projection images being acquired at respective projection angles,
reconstructing a first computed tomography (CT) image from the projection data;
classifying the first CT image into a plurality of regions corresponding to respective organs and/or tissue types,
determining respective first regularization parameters corresponding to the plurality of regions, and
reconstructing, using the projection data and the first regularization parameters, a second CT image using a regularizer that is scaled by the respective first regularization parameters in corresponding regions of the plurality of regions,
wherein the determining of the first regularization parameters is performed using a piece-wise linear mapping from values of radiodensity to values of the first regularization parameters, the piece-wise linear mapping being applied to pixels of the first image that have a radiodensity within a first range of radiodensities,
the method further comprising:
generating a minimum intensity projection (MIP) image based on a minimum value in an axial direction of a stack of slices of the first CT image, the stack of slices of the first CT image being taken in axial planes, and
for pixels of the first image having a radiodensity outside of the first range of radiodensities, applying the piece-wise linear mapping to the MIP image to determine the first regularization parameters.
5. A method, comprising:
obtaining projection data representing an intensity of X-ray radiation for a series of projection images of attenuation through an object, the series of projection images being acquired at respective projection angles;
reconstructing a first computed tomography (CT) image from the projection data;
classifying the first CT image into a plurality of regions corresponding to respective organs and/or tissue types;
determining respective first regularization parameters corresponding to the plurality of regions; and
reconstructing, using the projection data and the first regularization parameters, a second CT image using a regularizer that is scaled by the respective first regularization parameters in corresponding regions of the plurality of regions;
wherein the first regularization parameters, when used to reconstruct the second CT image, cause greater smoothing in a soft tissue region of the plurality of regions than in a lung region of the plurality of regions.
6. A non-transitory computer-readable storage medium including executable instruction, wherein the instructions, when executed by circuitry, cause the circuitry to perform the method according to claim 4 .