JPS5920152A - Data treatment of ct apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a data processing method for a dart scan type OCT apparatus.

[Technical backbone of the invention]

In general, a CT display device, for example, an X-ray CT instrument W (hereinafter simply CTi)
In this case, an X-ray tube and an X-ray detection device are used, which are placed opposite each other with the subject in between.The X-ray tube is for fan beam irradiation, and the X-ray detection device is a
In order to accommodate the spread of the fan beam, an X-ray detector equipped with a large number of X-ray detectors is used.
A scanning method is used in which a beam is emitted and the transmission data is collected, so when obtaining a tomographic image of an organ that moves significantly, such as the heart, it is necessary to eliminate artifacts (false images) corresponding to the scanning time. It was happening. Such artifacts can be reduced by shortening the scanning time, but since the scanning of the CT device d is performed using a mechanical rotation mechanism, one scanning takes at least about 2 seconds. For the heart whose pulse period is approximately 0.9 to 1.0 seconds, artifacts due to the scanning time are eliminated and a tomographic image of the heart in a nearly constant state during the diastole or systole can be clearly visualized. I couldn't do it.

Therefore, in the past, the Guitide scan method was used for CT.
A device t was proposed.

This method focuses on the fact that the heart repeats almost the same beats periodically, and if the state of the heart's synchronization at a certain period is taken as the first beat, then the R wave, which is omitted from the electrocardiogram, can be measured. Collect X-ray velocity transmission data corresponding to the phase of pulsation based on the internal period (hereinafter referred to as pulsation period) by multiple scans,
II! by X-ray transmission data corresponding to the same predetermined phase among the collected X-ray transmission data! II image reconstruction is performed, and a cross section If of a constant track of the heart corresponding to this predetermined phase is obtained.
It is designed to be superior to the n-image. In other words, if we perform r xm projections (c projections) while sequentially changing the angle of view in − tanshi, the phase of the pulsation in each projection will be different, but the same phase will occur for every several projections. Therefore, each projection at the same phase is obtained by scanning multiple times,
The image is reconstructed from these images to obtain a tomographic image of the heart in a constant state.

Here, an example of the conventional Guitide scan method will be specifically explained.

First, in one scan, the X-ray tube is rotated 360 degrees around the subject.
It is assumed that X-ray transmission data is collected by rotating the device, and the set meal time required for this is 4.5 seconds. Further, it is assumed that scanning is performed eight times in succession, and the scanning pause time for each scanning amount is 1.5 seconds.

It is assumed that the heartbeat is repeated at a constant interval of 09 seconds. .

Scanning performed based on these conditions can be shown in the time chart of FIG. Note that (al indicates scanning, and (bl indicates heartbeat).

Since the heart repeats the same movement periodically, as can be seen from Figure 1, which detects the electrocardiogram and records and compares the electrocardiograms, the heart tissue changes during one scan period of the CT machine. The same interlocking state will appear five times.

If we divide the state of one cardiac movement into 10 parts, we get
The heart changes its interlocking state every 0.9/10=0.09 seconds, resulting in one beat in 10 motion states.

In this case, in one scan, 10 different motion states are performed over 360 degrees around the heart, and for one motion state of the heart, the rotation angle of the X-ray tube is 360°/10. -Only 36″ of X-ray transmission data f
``Only 1/10th of the total amount of data can be done for one of the heart's linked states.''
This means that only the data obtained by multiplying the amount of time is the cargo movement.

This means that when scanning is performed multiple times, if the position of the heart beat and the rotation position of the X-ray tube are shifted for each scan, more information can be obtained regarding one motion state of the heart. This means that it is possible to obtain X-ray transmission data from different angles, which means that clear tomographic images can be obtained.

By the way, according to this method, if we consider a certain phase, one scan will yield 1/10 angle data, and if each scan is completely out of phase, then the angle will be 1/10.
Data for all angles can be obtained in one scan.

However, the probability of this happening is very low, and normally, even if scanning is performed 10 times, it is not possible to obtain data over the entire angle because the angles overlap.

That is, missing data occurs in terms of angle.

Of course, if the number of scans is increased, missing data can be reduced, but this increases the radiation dose for the subject, so it is not preferable to increase the number of set meals unnecessarily.

On the other hand, if reconstruction is performed with missing data present, artifacts will occur, which is not desirable.

Therefore, in the diuted scan method, the problem is how to fill in this missing data.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and
To provide a CT table device capable of optimally interpolating missing data when the number of scans is reduced in scan type CT Hft, thereby reducing X-ray exposure, and causing no artifacts.

[Summary of the invention]

- That is, in order to achieve the above object, the present invention performs multiple radiation scans at predetermined angles on a region to be imaged where almost the same pulsation is periodically repeated, and obtains radiographic data of the region to be imaged. In a CT table apparatus that performs 1LI image re-groove based on radiographic pigs that are in the same phase of the pulsation of the imaging region among the radiographic data collected over time, - (b) scanning is performed. Within the period, projections with the same heart shape and deafness occur, and each projection between these same projections has a slightly different heart state.
Evaluation coefficients are assigned to each factor that affects the image quality of the reconstructed CT image, such as time and angle deviation with respect to the phase difference, and one radiation of each detector in each projection obtained by multiple scans is assigned. The transmission data is evaluated using the evaluation coefficient, and the radiation transmission data of the necessary projection positions in i song 1 elephant reproduction 1 @ 1j39 are selected in order from the important ones for evaluation, and the CT image is reconstructed based on this. This allows us to obtain the same radiographic data from each projection position obtained through as few scans as possible for an imaging object that repeats several beats during one scan period, such as the heart. Image reconstruction is performed using radiographic data of each projection as close as possible to the phase of .
To make it possible to select radiation transmission data in a projection whose phase is shifted to an extent that does not impair image quality even for projections that do not have the same phase among the projections required for image reconstruction.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 2 to 5.

FIG. 2 (al is a map of actual data when scanned multiple times by rotation method OCTMM) IJ lux is shown. The matrix shows the detector rows on the horizontal axis and the projection rows on the vertical axis, and if the number of projections in one scan is r, the number of detectors is 512 O.
This shows that in a CT device, the projection data of a matrix of 512Xr is incremented by 1 for one scan, and by performing the first scan, ..., the nth scan, and the nth scan, the projection data of 512XrXn is obtained. ing.

As mentioned above, the heart may be in the same state several times during one scan due to its movement, and the projections in this state are shown here as A and m. Rotation method (7) In CT'Jit, data for one project is collected at the same time!
And if the m projection is a projection in the diastolic phase! The data of all the detectors for the projection and m-projection all show values that match the diastolic phase. ! Since the data of the projection and the breast projection are in the same phase in the heart motion, an evaluation value of 1w is given, for example. ! Each projection between the heartbeat and the breast projection is shifted from the specified phase. The projections have a and b respectively.
, c, . . . h.

The specific value of this a%h is determined empirically.

For example, there is a method in which the phase is decreased by 0.1 every time the phase shifts by one projection.

In this case, a = h = Q, 9 b''g = 0.8 C-f = 0.7 d = e = 96. Also, in the case of the diastolic phase of the heart, the movement is slow before the specified phase. , and the latter one is sharp.

Considering that point, for example, a=0.9, b=0.8, c=0.75,
d=0.75゜h=0.95, g=0.9,
It may be determined that f=0.85 and e=Q, 8.

In this way, a % h is determined empirically. Similarly, evaluation values are determined for the second to nth scans.

Next, a data group is created using the opposing beams.

Rotation method using fan beam is 3rd generation C
This third-generation CT scan has a scan rate of 36
If this is done over 0°, there will be almost identical beams that are 180 degrees opposite each other, as shown by Xb and xb' in FIG. Here, this will be referred to as the opposing beam. In Fig. 4, XT is the X-ray tube, 0 is the rotation center of the X-ray tube XT, and xb, xb'' are the X-ray beams. Expressing this relationship mathematically, φ (θ, φ) = φ (θ −π+2φ, −φ)・・・・・・
+1) Here, θ is the position of the X-ray tube, and φ is the angle from the center of the beam.

There is a relationship between FIG. 2(b) shows the data matrix of the opposing beams created from equation (1). As is clear from equation (1), the detector arrays for the actual data and the opposing beam data are in reverse order. In other words, the relationship is as follows. Also, the data of the same projection of real data becomes a diagonal Ata array with opposing beams.

However, in actual OCT devices, θ and φ are not continuous but discrete. Therefore, the opposing beam is determined by interpolation from multiple pieces of data. There are various interpolation methods, for example, 1 of 2 points.
If we perform the next interpolation, φ(k, n)=φ(j, 513-n)x(1-i)
+φ(J+1, 513-n), x 1 where j is an integer and i is the decimal part, 255.5-n j-H k −-, −−−−)−□・・・・・・・・・・・・
(2) △θ Δφ △θ: Angular displacement interval of projection Δφ: Angular interval of the detector.

FIG. 5 shows an example of evaluation coefficients for opposing beams.

If the evaluation coefficient of the n-th detector of the projection to @ is A, the person is determined empirically. For example A= (1-i)
X (evaluation value of j projection) + IX (evaluation value of j+1 projection) (3) where i,
j is i and j in the above equation (2).

As a result of the above, actual data and an evaluation table regarding the opposing beams were obtained.

Next, all data for one scan is divided into n
Select from n actual data and n opposing beam data. The data to be selected is the data having the largest evaluation coefficient among the evaluation coefficients. Even if the evaluation coefficients are the same, either one or the average is used. If a CT image is reconstructed from the Daite 9 data V selected in this way, a high quality CT image can be reconstructed for the designated phase.

Next, the sum of the evaluation coefficients of the data used for reconstruction is determined. This is taken as the evaluation coefficient of CT (Jl).

The digitized scan method is asynchronous to the heartbeat and C
Since the T device scans, the variation in missing data is not constant. Therefore, CT1m! , time if the evaluation coefficient is below a certain value? The image is large and cannot be said to be an image of the heart that corresponds to the phase.

Therefore, when the value of the CT image evaluation coefficient is less than a certain value, it is possible to make a decision such as redoing the scanning.

Although only actual data and opposing beam data have been described here, the present invention can also be applied to cases where the number of interpolated data is increased by other methods.

As explained above, according to the present invention, high-quality images can be reconstructed using a CT scanner using the guided scan method.
Furthermore, the reconstructed CT image can be evaluated.

〔Effect of the invention〕

As described in detail above, the present invention collects radiographic data of the imaged area over time by performing multiple radiation scans at predetermined angles on the area to be imaged in which almost the same beats are repeated periodically. Among the collected radiation velocity data, the CT table apparatus performs image reconstruction based on the radiographic data in the same phase of the pulsation of the imaging region. Utilizing the fact that the same projections occur, and each projection between these same projections has a slightly different state of the heart,
For each projection, an evaluation coefficient corresponding to the phase of the heart is assigned, for example, a deviation time from the phase, an angular deviation, etc., and each factor that affects the +un quality of the reconstructed CT image is given an evaluation coefficient, and multiple scans are performed. Evaluate the number-paired radiation transmission data of each detector in each projection determined by 46 using the evaluation coefficient, and sequentially select the radiation transmission data of each projection position necessary for image reconstruction from those that are important for evaluation. Based on this, we reconstructed the CT image by performing as few scans as possible on the object eye, which can repeat several beats during one scan period, such as the heart. Image reconstruction can be performed using the radiation transmission data of each projection that is as close to the same phase as possible from among the obtained radiation transmission data of each projection position. Since it is possible to select radiographic data from projections with phases as close to each other as possible even for projections with no objects, it is possible to reproduce high-quality images with a small number of set meals. [b32
It is possible to provide a CT table device data processing method having excellent features such as being able to evaluate a reconstructed image based on all evaluation values of data used in the process.

[Brief explanation of the drawing]

Fig. 1 is a time chart for explaining the relationship between scans and pulsations in a CT table device, Fig. 2 is a diagram for explaining the relationship between data in each scan and phase with respect to pulsations, and Fig. 3
The figure is a diagram to explain the relationship of evaluation coefficients to actual data, Figure 4 is a diagram to explain the X-ray transmission data of the same X-ray path scaled by an opposing beam in third generation CT, and Figure 5 is a diagram to explain the relationship between evaluation coefficients and actual data. FIG. 2 is a diagram for explaining an example of an evaluation coefficient for opposing beams. 1st Axis Patent Attorney Takehiko Suzue Figure 2 Figure 3 Figure 4 XT Figure 5

Claims (1)

[Scope of Claims] +11 Radiation transmission data of the imaged area is collected over time by performing multiple ray projections at predetermined angles on the imaged area where the same pulsations are periodically repeated. , in a CT table device that performs image reconstruction based on the radiation transmission data in the same phase of the pulsation of the radiographed region among the collected radiation transmission data, Φ is added to the several pairs of radiation transmission data for each angle.
A CT image is repurchased by having an evaluation coefficient corresponding to the J phase, evaluating the specified radiographic data using the RiJ evaluation coefficient, selecting the most important ones for evaluation, and using them for re+a532. CT table device data processing method characterized by +2) CT image re-I! OCT according to claim 1, characterized in that the sum of evaluation values of all data used for 14 images is used as the evaluation value for determining the quality of the CT image.
How the device processes data.