JP3061392B2 - Gamma camera device - Google Patents

Description

The present invention relates to a gamma camera apparatus that converts fan beam projection data into parallel beam projection data and then performs image reconstruction.

(Prior Art) A gamma camera (detector) for detecting gamma rays emitted from a subject through a fan beam collimator is arranged around the subject injected with a chemical containing a radioisotope (RI). SPECT (Single Photo'n Em) is a gamma camera device that reconstructs images after collecting fan beam projection data by rotating the gamma camera 360 degrees.
Ission Computed Tomography) devices are known. Since the gamma camera of this SPECT apparatus has a two-dimensional direction detection function, a multilayer tomographic image can be obtained by collecting data once in a 360-degree direction.

In such a SPECT apparatus that performs image reconstruction based on fan beam projection data, for the purpose of performing image reconstruction by a relatively simple method, this is converted into parallel beam projection data without directly using fan beam projection data. After the conversion, so-called fan-para conversion, image reconstruction is generally performed using the parallel beam projection data.

In this case, the matrix size of the projection image (fan beam projection image) based on the collected fan beam projection data and the pitch of the data collection angle (hereinafter simply referred to as angle) are the matrix size and angle of the parallel beam projection data after fan-para conversion. Is set the same as The conventional matrix size of the fan beam projected image is 128
× 128 is the maximum. However, in order to improve the spatial resolution (resolution) in order to obtain excellent image information, it is necessary to reduce the pixel size. Therefore, it is required to increase the pixel size to the next higher matrix size of 256 × 256. .

(Problems to be Solved by the Invention) By the way, if the matrix size of the fan beam projected image is increased to 256 × 256 in the prior art in order to improve the resolving power, the data amount when performing the fan-parallel conversion process is greatly increased, so There is a problem that a memory having a large capacity is required and the processing speed is considerably reduced (reduced to about 1/4).

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a gamma camera device capable of performing fan-para conversion processing without increasing the data amount.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a method for converting fan beam projection data collected by a gamma camera rotating around a subject into parallel beam projection data. In a gamma camera device that performs image reconstruction, the ratio of the gamma camera field size to the matrix size at the time of collecting fan beam projection data and the ratio of the effective field size to the matrix size after conversion to parallel beam projection data are substantially the same. In such a case, a data collection unit is provided in which the matrix size and the angle at the time of collecting the fan beam projection data and the matrix size and the angle after the conversion into the parallel beam projection data are made different from each other. is there.

(Operation) The matrix size when collecting fan beam projection data is set to, for example, 256 × 256, and the angle is set to 2 degrees or 4 degrees. On the other hand, the matrix size after fan-parallel conversion is set to, for example, 128 × 128, and the angle is set to 4 degrees or 6 degrees.
In this way, by selecting each matrix size and angle while maintaining a predetermined relationship, it is possible to suppress an increase in the data amount without deteriorating the image information at the time of the fan-parallel conversion, and also reduce the processing speed. Can be prevented.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 are a front view and a side view showing a SPECT apparatus according to an embodiment of the present invention, particularly showing a type of apparatus for obtaining a tomographic image of a head. Reference numeral 1 denotes a couch having a top plate 3 for supporting the subject 2, and the height of the top plate 3 in the vertical direction Z is adjustable by a height adjustment mechanism 4, and the position in the horizontal direction X is also adjusted. It is free. The subject 2 has its head fixed by a headrest 5 and lays on the top 3 with a drug containing a radioisotope (RI) injected into the body. Reference numeral 6 denotes a gantry provided with a dome 7 for guiding the subject 2, and around the dome 7, three rotatable unger-type gamma cameras 8 a and 8 b for detecting gamma rays emitted from the subject 2. , 8c are arranged 120 degrees apart from each other as shown in FIG.

Here, the area surrounded by the diameter R and the depth 1 in the dome 7 is the effective field of view for gamma ray detection. Reference numeral 10 denotes a gamma camera field of view and has a dimension of U [mm]. Reference numeral 11 denotes an effective field of view and has a dimension of R [mm]. Each of the gamma cameras 8a, 8b, 8c is equipped with a fan beam collimator 9a, 9b, 9c as shown in FIG. These fan beam collimators 9a, 9b, 9c are arranged in a horizontal direction X along the subject 2.
Has a large number of gamma ray guide holes 13 arranged so as to focus on the focal line 12, and the guide holes 13 are formed in a direction parallel to the horizontal direction Y orthogonal to the horizontal direction X. .

In this configuration, the three gamma cameras 8a, 8b, and 8c rotate around the subject 2 by 120 degrees, respectively, so that the fan beam collimators 9a, 9b, and 9c extend 360 degrees from the periphery of the subject 2. Fan beam projection data due to gamma ray incidence is collected through each guide hole 13, and a fan beam projection image is obtained. This fan beam projection image is converted into a parallel beam projection image by fan-parallel conversion, and then reconstructed to obtain a tomographic image (SPECT image).

In this embodiment, the gamma camera field of view 10 shown in FIG.
Using the dimension U of the effective field of view 11 and the dimension R of the effective field of view 11, data is collected according to the principle as shown in FIG. 5, a fan-para conversion is performed, and then reconstruction is performed to obtain a tomographic image. That is, as shown in FIG. 5, a matrix size of 256 × 256 in which the parallel beam direction and the fan beam direction are equal is obtained as the fan beam projection data. In this case, the dimension of one side of one pixel (pixel) of the matrix is U / 256 [mm / pixel]. Next, the fan beam projection data is subjected to a fan-parallel conversion to convert only the fan beam direction into a parallel beam, thereby obtaining a matrix size of 128 × 128 as the parallel beam projection data. In this case, the dimension of one side of one pixel of the matrix is P / 128
[Mm / pixel]. It is assumed that the focal length F is set to, for example, 400 mm. By performing the fan-para conversion based on such a principle, processing can be performed without increasing the data amount. The fan beam projection data is
As shown in the figure, it is two-dimensional data, and becomes parallel data in the parallel beam direction. Therefore, fan-para conversion is performed only in the fan beam direction, and U / 256 is applied in the parallel beam direction.
Although the length changes by the ratio of R / 128 to, the fan-parallel conversion is performed at the same time as the commonly arranged data in the parallel beam direction.

Next, the operation when data is collected according to the present embodiment will be described with reference to the flowchart of FIG.

First, as one procedure A, 256 × 2
Collect fan beam projection data in 56 matrix sizes. As the collection conditions, projection data for every two degrees is collected from the 360-degree direction as in step b (180 projections). Then, as in step c, 128 × 1
The projection data at every 4 degrees is collected in a matrix size of 28 and the fan-para conversion is performed (90 projections). Next, as in step d, parallel data is reconstructed with a matrix size of 128 × 128 to obtain a tomographic image.

On the other hand, as a second procedure B, as in the above procedure, fan beam projection data is collected with a matrix size of 256 × 256 as in step a. Collect data from 360 degrees (90 projections). Then, as in step f, projection data is collected at intervals of 6 degrees with a matrix size of 128 × 128 and fan-parallel conversion is performed (60).
Projection). Next, similar to the above procedure, as in step d, parallel data is reconstructed with a matrix size of 128 × 128 to obtain a tomographic image. In any procedure, the relationship of U / 256 ≒ R / 128 is maintained.

As described above, in the embodiment of the present invention, as the first procedure A, fan beam projection data collected at an angle of every two degrees with a matrix size of 256 × 256 is obtained at the time of fan-para conversion.
Data is collected at an angle of 4 degrees with a matrix size of 128 × 128 and converted to parallel beam projection data. As a second procedure B, fan beam projection data is collected at a matrix size of 256 × 256 at an angle of 4 °, and data is collected at an angle of 6 ° at a matrix size of 128 × 128 at the time of fan-para conversion. To convert the data into parallel beam projection data. By performing the fan-para conversion process with the combination of the acquisition conditions of the fan beam projection data and the parallel beam projection data, it is possible to suppress an increase in the data amount without deteriorating the image information.

In other words, assuming that a matrix size of 256 × 256 and 12 bits are set as an example of information in the depth direction, when collecting parallel beam projection data of 180 projections every two times, a data capacity of about 20 (MB) is required. Becomes However, by reducing the matrix size to 128 × 128 as in procedure A of the present embodiment, the data capacity becomes 1 /
The data volume can be further reduced by 1/2 by converting the data to parallel beam projection data by collecting data of 90 projections every 4 degrees and reducing the data volume to 1/8 in total. The capacity can be reduced.

Also, as in procedure B of this embodiment, when data is collected for 60 projections every 6 degrees and converted into parallel beam projection data, the data capacity can be further reduced. Therefore, according to the present embodiment, a large-capacity memory is not required, so that the cost can be reduced by that much, and the processing speed can be prevented from lowering due to no remarkable increase in the data capacity. Moreover, since the fan-para conversion can be performed without deteriorating the image quality (resolution, artifacts, etc.) of the image, the diagnostic performance is not reduced.

[Effect of the Invention] As described above, according to the present invention, the fan-parallel conversion is performed by appropriately combining the acquisition conditions of the fan beam projection data and the parallel beam projection data, so that the data amount can be increased. Can be processed.

[Brief description of the drawings]

1 and 2 are a front view and a side view showing an embodiment of the gamma camera device of the present invention, FIG. 3 is a front view showing a main part of the device of this embodiment, and FIG. FIG. 5 is a perspective view showing a fan beam collimator used, FIG. 5 is an explanatory diagram showing the principle of fan-parallel conversion by the apparatus of this embodiment, and FIG. 6 is a flowchart showing the procedure of fan-parallel conversion by the apparatus of this embodiment. 1 ... bed part, 6 ... stand part, 8a, 8b, 8c ... gamma camera (detector), 9a, 9b, 9c ... fan beam collimator, 10 ... gamma camera field of view, 11 ... effective field of view, 13 ... Gamma ray guide hole.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01T 1/164 H04N 5/225 H04N 5/32

Claims (3)

(57) [Claims] 1. A gamma camera device that converts fan beam projection data collected by a gamma camera rotating around a subject into parallel beam projection data and then performs image reconstruction. The relationship between the matrix size at the time and the relationship between the effective visual field size and the ratio of the matrix size after conversion to parallel beam projection data is maintained to be substantially the same, and the matrix size and angle at the time of fan beam projection data collection A gamma camera device comprising: a data collection unit that changes a matrix size and an angle after conversion into parallel beam projection data. 2. The matrix size and angle at the time of collecting fan beam projection data are set to 256 × 256 and 2 degrees, respectively, and the matrix size and angle after conversion to parallel beam projection data are set to 128 × 128 and 4 degrees, respectively. Claim 1 set
A gamma camera device as described. 3. The matrix size and angle when collecting fan beam projection data are set to 256.times.256 and 4 degrees, respectively, and the matrix size and angle after conversion to parallel beam projection data are set to 128.times.128 and 6 degrees, respectively. Claim 1 set
A gamma camera device as described.