JP2701355B2 - How to improve ECT images - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a method for improving image quality of an ECT (emission computer tomography) image.

[Prior art]

The ECT obtains a distribution image of RI (radioactive isotope) administered into a subject by image reconstruction processing using a computer. In other words, radiation emitted from the RI inside the subject to the outside of the subject is detected by a radiation detector placed outside the subject to obtain projection data, and the projection data is convolved with a smoothing filter, for example. After integration, the image is reconstructed by back projection. In this case, conventionally, data is uniformly filtered over the entire field of view.

[Problems to be solved by the invention]

However, when a uniform filter is applied over the entire field of view as in the prior art, the spatial resolution of an ECT (positron ECT) image using a positron-emitting nuclide, as shown in FIG. In both the tangential direction (dotted line) and the center, it is best near the center, and as the distance from the center increases, the spatial resolution in the radial direction deteriorates. As a result, the quantitative value is different between the central part and the peripheral part of the visual field, and an image obtained by reconstructing a point source having the same size is the fourth one.
As shown in the figure, distortion of the image occurs such that the periphery becomes larger in the radial direction. This development has higher spatial resolution,
Also, the smaller the diameter of the detector ring becomes, the more significant the problem becomes. The characteristics of the S / N ratio of the uniform image of positron ECT are the sixth.
As shown in the figure, for example, in the case of a uniform phantom having a diameter of 30 cm, the S / N ratio at the center is the worst, and the closer to the periphery, the better. This is because the more the radiation from the RI at the center, the greater the rate of absorption by the subject itself. According to the present invention, the spatial resolution of an ECT image can be made uniform between the central part and the peripheral part, and the S / N ratio of the central part can be improved, and the quantitative value can be made uniform near the entire visual field. An object of the present invention is to provide a method for improving an image.

[Means for Solving the Problems]

In order to achieve the above object, in the method for improving an ECT image according to the present invention, a filter which is a function of a distance from the center of the visual field is applied to projection data collected as a sinogram in a radial direction of the sinogram. After that, an image reconstruction process is performed.

[Action]

A filter, which is a function of the distance from the center of the field of view,
For example, a smoothing filter is used in which the longer the distance from the center is, the less the rounding is. This filter is applied to raw data as projection data collected as a sinogram before image reconstruction processing, in the radial direction of the sinogram, and then subjected to image reconstruction processing.
For this reason, an operation of simply performing a filtering process on the raw data arranged as sinograms is added, so that the processing can be performed easily without increasing the processing load. And by this processing, they correspond to different spatial resolutions in the radial direction and connection direction, or correspond to different spatial resolutions in the radial direction in the radial direction and different S / N ratios in the radial direction, so that they are uniform in all fields of view. It is possible to correct so that

【Example】

Next, an embodiment in which the present invention is applied to a positron ECT image will be described with reference to the drawings. In FIG. 1, projection data is collected by a data collection device 1 from a radiation detector (not shown). This data is stored in the storage device 2, sent to the filter processing device 4 via the CPU 3, and after being subjected to the filtering process, back-projected by the back projector 5 and the reconstructed image is displayed on the display device 6. . In this embodiment, the filter processing device 4 applies a smoothing filter to raw data (sinogram) stored in the storage device 2. That is,
A smoothing filter as shown in FIG. 2A is subjected to convolution integration in a direction L from the center for each angle θ with respect to a sinogram as shown in FIG. 2B, and the shape of this filter depends on L. Thus, the function of L is such that the smaller the L is, the less the rounding is, and the larger the L is, the less the rounding is. Therefore, the smoothing effect in the radial direction is large at the central portion and is small at the peripheral portion, and the resolution is uniform in the radial direction (L direction). As a result, for example, we collect data when the point source is placed in a cross,
Then, the image obtained by image reconstruction is a faithful reproduction of the original image as shown in FIG. 3, and the spatial resolution is constant in both the radial direction and the connection direction without changing according to the distance from the center. It turns out that it becomes. On the other hand, when the smoothing filter is fixed, the image is blurred in the radial direction and expanded as shown in FIG. 4 as described above. In addition, stronger in this center,
Due to the weaker smoothing effect at the periphery, the S / N ratio at the center of the originally poor value is particularly improved. As a result, the S / N ratio also approaches uniform over the entire field of view. In the above description, a smoothing filter is used as a filter, but a differential filter may be used.
In this case, the differential filter is subjected to convolution integration with respect to the sinogram in the L direction, and the shape of the differential filter is made such that the spatial resolution in the radial direction increases as L increases. As a result, the spatial resolution in the radial direction becomes uniform over the entire field of view, and the S / N ratio at the peripheral portion becomes uniform at the center, so that the S / N ratio approaches uniform over the entire field of view. In the above description, the filtering process is performed on the sinogram. However, the filtering process may be performed on the image after the back project. In this case, it is necessary to change the shape of the filter in the radial direction and the tangential direction, and to change the shape of the filter in the radial direction according to the distance from the center. Further, it is also possible to perform the same filtering process on images continuous in the body axis direction. In the above, we explained about positron ECT image,
The same can be applied to a single font ECT image.

【The invention's effect】

According to the method for improving an ECT image of the present invention, the spatial resolution of the image can be made uniform between the central portion and the peripheral portion, and between the radial direction and the tangential direction, and the S / N ratio can be improved over the entire visual field. And the quantification can be improved over the entire visual field.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2A is a diagram showing a filter shape, FIG. 2B is a diagram showing a sinogram on which this filter is operated, and FIG. FIG. 4 is a diagram showing an image obtained by the conventional filter processing, FIG. 5 is a graph showing a spatial resolution characteristic in the conventional positron ECT image, and FIG. 6 is an S / N in the conventional positron ECT image. 4 is a graph showing specific characteristics. 1 ... data collection device, 2 ... storage device, 3 ... CPU,
4 ... Filter processing device, 5 ... Back projector,
6 Display device.

Claims (1)

(57) [Claims] An image reconstruction process is performed on a projection data collected as a sinogram by applying a filter functioning as a function of the distance from the center of the visual field in the radial direction of the sinogram. How to improve ECT images.