X-ray CT scanner, image generation method, and image generation program
An image is generated where an edge of a structure in a subject is sharpened with reducing streak artifacts, within a short amount of time. X-rays at multiple angles are applied to the subject placed in imaging space, and a distribution of X-rays strength passing through the subject is detected to obtain raw data associated with multiple views. After smoothing the raw data associated with multiple views, image reconstruction is performed to generate a smoothed image of a predetermined region to be imaged in the imaging space. In the smoothed image, more intense sharpening process is applied to pixels in a region of a central part of the subject, than the pixels in a region of a peripheral part of the subject.
1. An X-ray CT system comprising,
a raw data acquisition part configured to acquire raw data obtained by applying X-rays to a subject placed in imaging space and by detecting a distribution of X-ray strength passing through the subject, the raw data being associated with multiple views at different X-ray irradiation angles to the subject,
an image reconstructor configured to apply a smoothing process to the raw data associated with multiple views, followed by image reconstruction to obtain a smoothed image of a predetermined region to be imaged in the imaging space,
a sharpening processor configured to apply more intense sharpening to pixels in a region of a central part of the subject in the smoothed image, than to pixels in a region of a peripheral part of the subject, and
a subject model generator configured to create a subject model that represents a form and position of the subject in the region to be imaged, in an approximate manner, by using one or more predetermined shapes and the position thereof,
wherein the sharpening processor brings the subject model into correspondence with the smoothed image, and applies more intense sharpening to pixels in the region of the smoothed image corresponding to the region of the central part of the predetermined shape of the subject model, than to pixels in the region of the smoothed image corresponding to the region of the peripheral part of the predetermined shape.
2. The X-ray CT system according to claim 1 , wherein,
the subject model generator selects the raw data of one or more views from the raw data associated with multiple views, and creates the subject model on the basis of a distribution of signal strength of the raw data thus selected.
3. The X-ray CT system according to claim 1 , wherein,
the predetermined shape of the subject model is an ellipse.
4. The X-ray CT system according to claim 1 , wherein,
the sharpening processor increases a degree of sharpening gradually from the peripheral part to the central part of the predetermined shape of the subject model.
5. The X-ray CT system according to claim 4 , wherein,
when the subject model includes two or more predetermined shapes, the sharpening processor increases the degree of sharpening gradually from the peripheral part to the central part, as to each of the predetermined shapes.
6. The X-ray CT system according to claim 2 , wherein,
the subject model generator selects the raw data of two or more views, from the raw data associated with multiple views, and creates the subject model.
7. The X-ray CT system according to claim 6 , wherein,
the raw data of two or more views selected by the subject model generator includes a vertical direction view and a horizontal direction view.
8. The X-ray CT system according to claim 6 , wherein,
the raw data of two or more views selected by the subject model generator includes a view inclined at a certain angle relative to the vertical direction view and a view inclined at a certain angle relative to the horizontal direction view.
9. An X-ray CT system comprising:
a raw data acquisition part configured to acquire raw data obtained by applying X-rays to a subject placed in imaging space and by detecting a distribution of X-ray strength passing through the subject, the raw data being associated with multiple views at different X-ray irradiation angles to the subject,
an image reconstructor configured to apply a smoothing process to the raw data associated with multiple views, followed by image reconstruction to obtain a smoothed image of a predetermined region to be imaged in the imaging space,
a sharpening processor configured to apply more intense sharpening to pixels in a region of a central part of the subject in the smoothed image, than to pixels in a region of a peripheral part of the subject, and
a pixel-value variation calculator configured to obtain a degree of variation of pixel values between the pixels that are adjacent to each other in the smoothed image, wherein,
the sharpening processor reduces the rate of sharpening for the pixels with a high degree of variation in pixel value, relative to the pixels with a low degree of variation in pixel value.
10. The X-ray CT system according to claim 9 , wherein,
the pixel-value variation calculator creates an image space model representing a distribution of the degree of pixel-value variation between pixels adjacent to each other in the smoothed image, and
the sharpening processor varies the degree of sharpening in response to the distribution of the degree of pixel-value variation of the image space model.
11. The X-ray CT system according to claim 2 , wherein,
the subject model generator places the predetermined shape at a position corresponding to a range where the signal strength distribution of the selected raw data is equal to or larger than a predetermined threshold, and creates the subject model.
12. The X-ray CT system according to claim 11 , wherein,
the subject model generator reduces the number of the predetermined shapes, by consolidating the range where the signal strength distribution is equal to or larger than the predetermined threshold, so that the number of predetermined shapes is equal to or less than a predetermined upper limit.