JPH0134057B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image reconstruction device that is effective for use in performing calculations for image reconstruction, for example, in an X-ray CT apparatus. More specifically, the present invention relates to an image reconstruction device that utilizes optical signals and is capable of processing two-dimensional operations in parallel by utilizing the spatial distribution of the optical signals.

In an X-ray CT device or the like, the amount of data for image reconstruction is extremely large, and processing this data to obtain an image requires an enormous amount of calculation. For this reason, a minicomputer equipped with an array processor for high-speed calculation is used for this arithmetic processing. On the other hand, the calculation method for the back projection calculation part is extremely difficult because the calculation result is two-dimensional, and it takes several hours when using a general minicomputer.
Further, even if a dedicated processor is used, it takes several tens of seconds.

FIGS. 1 to 4 are explanatory diagrams showing an example of the procedure of CT image reconstruction. Here, Translate−
The Rotate method (TR scan method) will be shown as an example.

In Fig. 1, the analyte (absorption coefficient μ(x,
y)) When H is irradiated with a single spectrum X-ray of intensity I ₀ , the perspective data P(θ, x) can be expressed by equation (1).

P (θ, x) = ∫ _l μ (x, y) dl ...(1) Such 1-view fluoroscopic data is obtained by, for example, a 511-channel X-ray detector; By sequentially rotating perspective data by, for example, 0.625° and obtaining data for all θ (0<θ<π), a total of 576 views of data are obtained.

Back Projection for image reconstruction
Prior to this, each view data is subjected to a convolution operation of a kernel function (correction function) as shown in FIG. 2, for example, in order to make a sharp image. Therefore,
The reconstructed image g(x,y) is expressed by the convolution of the original image f(x,y) and the kernel function h(x,y), and can be expressed by equation (2).

g (x, y) = ∫ ^∞ _-∞ ∫ ^∞ _-∞ f (x', y') ・h (x-x', y-y') x dx'dy' ...(2) However, x' , y′: distribution coordinate The convolution operation expressed by equation (2) is
It is a repeated product-sum operation, and is usually performed serially on a computer, and the calculations are enormous and take a long time. For example, the kernel function h(x,y)
If the term is 1000 terms, then 511 (channel) x 1000 (term) x 576 (view)
This requires a product-sum operation.

FIG. 3 shows an example of a one-view function after performing a convolution operation.

The data of each view subjected to convolution in this manner can be back-projected for all θ (576 views) to obtain a reconstructed image, as shown in FIG. Such a back projection operation transforms the reconstructed screen into l×
If there are m (for example, l = m = 320) pixels, first calculate which sensor each pixel receives for each view, and store the signal in the memory representing each pixel. . This is done for all 320x320 pixels.
The data for the next view is similarly stored (projected) in memory for 320 x 320 pixels. This is repeated for all 576 views.

The back projection calculation as described above is enormous and takes a long time.

The present invention provides an image reconstruction device that is useful when applying the above-mentioned back projection calculation to obtain a reconstructed image, using an optical signal.
It has a simple configuration and can perform high-speed calculations.

The present invention will be explained below by taking the apparatus shown in FIG. 5 as an example. Here, a case is shown in which back projection calculation for CT image reproduction is performed. In the figure, reference numeral 1 denotes an optical gate array element, in which 12 optical gates are arranged in the x-axis direction of the array.
This optical gate array element 1 is constructed by arranging a plurality of pairs of electrodes corresponding to the number of optical gates on a PLZT substrate, for example, and using two deflection plates whose deflection planes are perpendicular to each other to form a sound switch. Each optical gate has a light transmittance corresponding to the magnitude of the applied signal. 2 is an input drive circuit of this optical gate array element 1, which has a waveform P(θ, r) as shown in the figure.
A convolution signal is given, and the light transmittance of each light gate is controlled accordingly.
Each light transmittance is distributed in the x-axis direction (the direction in which the optical gates are arranged) corresponding to the convolution signal. Note that while the convolution signal shown in the figure has positive and negative polarities, the light transmittance of the optical gate array element has one polarity, so the convolution signal has positive and negative polarities. This difference in polarity is determined by driving the optical gate array element at a time different from the negative one.

This optical gate array element 1 is irradiated with light of uniform intensity from one surface side (in this case, the upper surface side), and from this optical gate array element 1, light is emitted from the optical gate array element 1 in the direction in which the optical gates are arranged (x-axis direction). In contrast, spatial light whose brightness is distributed in accordance with the convolution signal is emitted.

Reference numeral 3 denotes a two-dimensional optical sensor array, which is composed of a plurality of optical sensors arranged in l×m arrays, which is the same as the number of pixels to be reconstructed. As this optical sensor array, it is possible to use one with almost the same configuration as, for example, a CCD image sensor or a MOS image sensor, and each optical sensor corresponds to the amount of light irradiated to it during a certain period of time. It is configured to store the charges and read them out to the outside.

Figure 6 is an equivalent circuit of the two-dimensional optical sensor array 3, where one optical sensor is, for example, a photodetector diode.
This is represented by the parallel connection of D ₁ and capacitor C ₁ , and signals corresponding to the intensity of light received by each light receiving diode are sequentially stored in the capacitor.

Returning to FIG. 5, 4 is an output signal processing circuit for reading out signals from the two-dimensional optical sensor array 3. Reference numeral 5 denotes an angle changing means for the optical gate array coupled to the optical gate array element 1, which changes the relative angle between the optical gate array element 1 and the two-dimensional sensor array 3 (the arrangement direction of the optical gate array element and the arrangement direction of the optical sensor array). The function is to sequentially change the relative angle formed by the direction in the direction of arrow a at a pitch of, for example, 0.625° when both arrays are parallel.

The operation of the apparatus configured in this way will be explained next. First, in a relative position state where the arrangement direction of the optical gate array element 1 and the arrangement direction of the optical sensor array 3 match as shown in the figure, one view of data (convolution signal) is inputted to the optical gate via the drive circuit 2. In addition to the array element 1, each optical gate is controlled to have a light transmittance corresponding to each signal.
Here, in the optical gate array element, it is assumed that nonlinearity between the input signal and light transmittance, span, etc. are corrected by an appropriate correction circuit or feedback circuit. The light from the uniform light source that is irradiated onto the optical gate array element 1 passes through each light-transmissive optical gate of the optical gate array element 1 and is irradiated onto the two-dimensional optical sensor array 3 . In the two-dimensional photosensor array 3, each photosensor stores an amount of charge corresponding to the intensity of light irradiated thereon. Note that at this time, the intensity of the light from the uniform light source may be changed in inverse proportion to the X-ray pulse intensity of the view, and correction may be performed based on the change in the X-ray pulse intensity.

By the above operations, the first back projection (Back
−Projection) is completed. Next, the optical gate array angle changing means 5 rotates the optical gate array element 1, for example, by 0.625 degrees in the direction of arrow a. Then, in this positional relationship, a second backprojection is performed by the same operation as described above. At this time, the two-dimensional photosensor array 3 stores the charge amount obtained by the second back projection on the charge amount obtained by the first back projection. Hereinafter, in the same manner, the optical gate array element 1
is sequentially rotated by 0.625°, and backprojection is performed a total of, for example, 576 times (equivalent to one rotation).

When the back projection corresponding to one rotation or half a rotation is completed, the two-dimensional photosensor array 3 has the sum of the charges obtained by each back projection, and outputs these signals. Signal processing circuit 4
A reconstructed image can be obtained by taking it out through the .

Here, when the data of one view (convolution signal) has positive and negative polarities, first, the entire view is back-projected for one rotation only for the signal with a positive sign, and this is provided in the output signal processing circuit 4. Store it in a memory means, then perform back projection of the entire view by one rotation only for the negative sign signal,
By subtracting this value from the previously stored value, a reconstructed image is obtained. Note that this method requires two rotations to obtain one reconstructed image. Therefore, instead of this method, first add a bias signal to a convolution signal with positive and negative polarities to make a positive signal, back-project this for one revolution, and finally subtract the bias signal from the integration result. You may also do so.

Although the optical gate array element 1 side is rotated here, the two-dimensional optical sensor array 3 side may be rotated to sequentially change the relative angle. Moreover, various optical systems for parallelizing, enlarging, or reducing light beams may be interposed between each element.

The device according to the present invention performs back projection calculation using the spatial distribution of optical signals, and this calculation is performed at a speed ( By increasing this speed, the backprojection operation can be completed in less than one second, for example. Furthermore, if the operation of back-projecting while changing the relative angle is performed in synchronization with the rotation of the X-ray CT gantry, a reconstructed image can be obtained immediately after data collection.

Further, in the present invention, a light source that outputs light with uniform intensity in two-dimensional directions, a light gate array,
It is constructed by a combination of a two-dimensional optical sensor array and an angle changing means that changes the relative angle between the optical gate array and the two-dimensional optical sensor array, and can utilize the two-dimensional spatial distribution of optical signals. , errors due to variations in the characteristics of each optical gate and each optical sensor are averaged out by rotating the relative angle between the optical gate array and the two-dimensional optical sensor array by a certain amount, and the effect is that it no longer affects the reconstructed image. be.

[Brief explanation of drawings]

1 to 4 are explanatory diagrams and diagrams showing an example of a known CT image reconstruction procedure, FIG. 5 is a perspective view of the configuration of an example of the apparatus according to the present invention, and FIG.
This is an equivalent circuit of a photosensor array used in the device shown in the figure. DESCRIPTION OF SYMBOLS 1... Optical gate array element, 2... Input drive circuit, 3... Two-dimensional optical sensor array, 4... Output signal processing circuit, 5... Relative angle changing means.

Claims (1)

[Claims] 1. A light source that outputs light with uniform intensity in the two-dimensional directions of the x-axis and the y-axis, and a plurality of light gates arranged in the x-axis direction, and a plurality of light gates arranged from the light source on each of the light gates. An optical gate array that is irradiated with light of uniform intensity and has a light transmittance corresponding to the magnitude of the applied signal, and a plurality of optical sensors in the two-dimensional directions of the x-axis and the y-axis. a two-dimensional photosensor array in which a quantity of electricity corresponding to the amount of light transmitted through and irradiated through the optical gate array during a certain period of time is stored in each optical sensor; and the optical gate array and the two-dimensional optical sensor. angle changing means for sequentially changing the relative angle with the array from a state in which both arrays are parallel at an angle of a predetermined pitch; and convolution means corresponding to each position of each optical gate arranged in the x-axis direction of the optical gate array an optical gate drive circuit that applies a signal every time the angle changes at a predetermined pitch by the angle changing means, and drives the light transmittance of each optical gate array so as to be distributed in the x-axis direction in response to the convolution signal; Image reconstruction comprising: an output signal processing circuit that reads out electrical signals stored in each optical sensor of the two-dimensional optical sensor array when the relative angle between the optical gate array and the two-dimensional optical sensor array has rotated by a certain angle. Device.