JPS6260540A - X-ray 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 an X-ray CT apparatus that can obtain a computed tomography (CT) image of a subject at a desired time with a minimum exposure dose.

[Technical background of the invention]

In medical diagnosis using an X-ray CT device, for example, it is possible to perform a scan at a set time after injecting a contrast agent into a subject and observe changes in CT values of the same region over time due to blood flow within the subject. It is an extremely effective diagnostic method for discovering local blood flow abnormalities in a specimen, and the scanning method used for this purpose is called dynamic scanning. In this case, the timing, time interval, and number of scans to be performed are generally planned before the dynamic scan is performed. This kind of plan is called a dynamics cap plan.

By the way, in conventional X-ray CT devices that do not have slip rings, cables are used in the circuit that applies high voltage to the X-ray tube, so scanning with this device cannot perform arbitrary continuous rotation, and Since the tube must be rotated not only in a single direction but also in both forward and reverse directions, rotation, stopping, and reversal operations of the X-ray tube may also occur during dynamic scanning. It was not possible to start data collection from that time.

In recent years, there have been systems in which the X-ray tube rotates around the subject and energy is supplied to the X-ray tube via a slip ring, and devices in which the X-ray tube itself is fixed but are scanned electronically. A device in which a line beam rotates around the subject has been developed, and it has become possible to start data collection at any time and from any position, or to collect data after any time has elapsed.

In addition, necessary portions of data are cut out from data collected over a plurality of consecutive scan rotations and processed by an electronic circuit to obtain a reconstructed image.

[Problems with background technology]

When performing a dynamic scan with such an X-ray CT device, the operator manually inputs the scan start time into the device using manual means such as a keyboard, and the data processing means including the computer provided in the device inputs the scan start time at that time. It was determined whether or not scanning was possible.

Originally, an operator would like to obtain a reconstructed image at an arbitrarily specified time and observe the contrast effect appearing in that image. However, there is a problem in that the scan start time must be specified at the time of the scan, and the operation for that purpose is extremely complicated.

Furthermore, when there are multiple times to collect data, the scan times corresponding to those times may be included in the rotation, stop, or reversal time of the X-ray tube, etc. In such cases, There was a problem in that it was virtually impossible to collect data.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and involves establishing a dynamics cap plan in which the central time of image data to be reconstructed is specified in advance and the required data collection time is calculated based on this time. Accordingly, it is an object of the present invention to provide an X-ray CT apparatus that can obtain a reconstructed image at a desired time with a minimum exposure dose to a subject.

[Summary of the invention]

The outline of the present invention for achieving the above object is to collect X-ray transmission data obtained by irradiating an X-ray beam onto an object while continuously rotating around the object. Process X to obtain a reconstructed image of an arbitrary cross section of the object
A plan for controlling the dynamic scanning and data collection of a X-ray CT device using a dynamics cap plan obtained by determining a data collection time centered on an arbitrary specified time specified in advance. It is characterized in that it includes a creation processing section.

[Embodiments of the invention]

Examples of the present invention will be described in detail below.

The configuration of the embodiment apparatus shown in FIG. 1 will be explained below.

The X-ray tube 1 rotates while irradiating a fan-shaped X-ray beam 4 toward the subject 2. X′! There is an X on the outside of the orbit of IA tube 1.
A detector ring 3 concentric with the rotation center of the wire tube is fixedly arranged. The detector ring 3 has a large number of X-ray detection elements arranged at equal intervals. The X-ray beam that has passed through the object 2 enters the part of the detector ring 3 facing the X-ray tube 1, where it is converted into an electrical signal according to its intensity and sent to the data acquisition section (hereinafter abbreviated as DAS) 5. supplied to

On the other hand, a graticule (not shown) is arranged concentrically with the rotation center of the X-ray tube 1. This graticule has transparent parts and opaque parts arranged alternately, and the number of the graticules is, for example, twice the number of detection elements. The graticules are then converted into electrical pulses by a photosensor (not shown) working in synchronization with the X-ray tube 1. (below,
The graticule and the photosensor are referred to as a graticule sensor. ) This electrical pulse is transmitted to the rotation control section 7.
supplied to The rotation control section 7 controls the rotation of the X-ray tube 1 using pulses from the graticule sensor, and supplies these pulses to the DAS 5.

The DAS 5 samples the electrical signal supplied from the detector ring 3 in synchronization with the pulse from the graticule sensor, that is, in synchronization with the rotation of the X-ray tube l, converts it into a digital signal, and supplies it to the sorter 6. do. The sorter 6 sorts the continuous projection data into a fan-shaped beam (hereinafter referred to as a detector fan) that spreads from a certain detection element.
It is supplied to the interpolation unit 8. The interpolation unit 8 interpolates the detector fan data, which is spread out at even intervals with respect to the rotation center of the X-ray tube 1, so that it is spread out at even intervals when viewed from the detection element. The memory section 9 is connected to the DAS 5, the sorter 6, and the interpolation section 8, and assists them.

The detector fan data from the interpolation section 8 is sent to the convolver 10.
supplied to The convolver 10 performs a convolution operation to prevent blurring of the image when back projecting the detector fan data, and supplies the data to the bank projector 11.

The bank projector 11 backprojects the detector fan data subjected to convolution calculation in an image memory having a memory space corresponding to the coordinates of the cross section of the subject 2. This convolution back project is executed on the detector fan data supplied one after another and superimposed on the image memory to reconstruct the tomographic plane of the subject 2 and display it on the CRT 13.

The rotation control section 7 includes a scan plan creation processing section 14.
is connected, and the scan plan creation processing section 14 executes a dynamics cap run as shown in the flow chart shown in FIG. 2 based on the time specified by the input means 15 such as a keyboard.

Next, the operation of the apparatus configured as described above will be explained with reference to an explanatory diagram showing the execution procedure of a dynamics cap run and the operation timing of each part of this apparatus shown in FIG.

The operator operates the input means 15 to start the dynamics cap run and select the required time t as step 1.
Input il+12+t*3+...

As step 2, the scan plan creation processing unit 14 calculates these specified times j il+ j fi2+ t i
Data collection start time t centered on 3+ . . . ,.

Lst2r tss3+..., data collection end time t
□I+1siltQi: Set l+... as the data collection time. However, ts++=j□−Aα+jss2
=j! □-Aα, M5i3=”s3'Aαr tai
l =t$1 +'Aα* jas! ""jtz+
'/Sα+ tQs3 = t13 +V2α,
α is a time width that can be set arbitrarily.

Next, the scan plan creation processing unit 14 performs a third step at a specified time jz (j, *+, Lst.

t, 3. Data collection end time t□1(...) at data collection end time t□1(...)
L ail+ j *sZ+ j es3+...) and look at the next specified time.

Data collection start time j is+++ at (ts□+ tl:l+ ...) (t8゜+ j isl
+...), and if the data collection end time t0□ is later than the data collection start time jsi (il+1) on the time axis, this data collection end time tas and the data collection start time jsi+4゜1 is deleted, and the period from the data collection start time j sii to the data collection end time L s+t (!+) is set as the actual data collection time at this time and the process moves to the next step.

On the other hand, if the data collection end time t, □ is earlier than the data collection start time Lsi(t.,) on the time axis, the difference between the two on the time axis is determined, and the data collection start time tss( Then, it is determined whether the difference between the data collection end time t and li is sufficiently large.

Then, if the difference between the two mentioned above is sufficiently large, a gantry rotation speed reduction is programmed. On the other hand, if the above-mentioned difference between the two is not so large, a program is created that prohibits the gantry rotation speed from decreasing.

Next, the scan plan creation processing unit 14 simulates the heat load on the X-ray tube 1 during execution of all scan plans,
If the result is good, the program created in step 3 as described above is displayed on the CRT 13 or a separate display means (not shown) in step 5, and is also stored in the memory built in the scan plan creation processing section 14. register.

On the other hand, if the result of simulating the heat load on the X-ray tube 1 is determined to be defective, a message requesting replanning is displayed on the CRT 13 or a separate display means.

In this way, a dynamics cap run is created in the scan plan creation processing section 14, and the rotation control section 7
is a scan plan creation processing unit 1 based on this dynamics cap run according to a plan execution instruction from an operator.
In response to the signal from 4, the gantry including the X-ray tube 1 and the detector ring 3 is started, the high speed steady rotation 2 rotation speed is controlled, and the dynamics cap run as step 6 is executed while controlling the stopping operation.

Note that the data collection time (t is + ~ t @ fil + t □
2~tasz+t□3~t1113+...), calculate the exposure dose at each data collection time, display these exposure doses and the total exposure dose that is the sum of these exposure doses, and register it in the memory. Also executed are the following:

A dynamic scan is performed on the object 2 by executing the dynamics cap run, and the detector ring 3
The electrical signals sent from the DAS 5 are sampled by the DAS 5 and then sent to the sorter 6, the interpolator 8, the convolver 10. Through a series of processing via the pack projector 11 and image memory 12, the reconstructed image is displayed on the CRT 13.

In this case, as shown in FIG. 3, if the data collection end time tasl centered at the specified time jsl is later than the data collection start time tsi□ centered at the specified time t,2, the above-mentioned dynamics cap plan is Collected data from data collection start time t8□ to data collection end time tss+ is obtained as collected data based on data collection start time t8□ to data collection end time tss+ to data collection end time t8□ and data collection start. Time t si
A cutout process is performed from z to data collection end time t, 2 to obtain reconstructed images each centered at the designated time jll+F□.

It goes without saying that the present invention is not limited to the embodiments described above, and that various modifications can be made within the scope of the invention.

For example, in a dynamic scan using a contrast agent such as in a dynamic study, the peak value and time to reach the peak are often important diagnostic parameters among the time changes in CT values due to the blood flow of the contrast agent, and the standard The time to reach the target peak is often known in advance depending on the site, contrast agent, etc., so in such cases, enter that time or a value with a certain range around that time as the data collection time. If you do so, you can more reliably obtain tomographic images at peak times.

Furthermore, in the embodiment described above, the specified time j Sl+ tl
Although we have explained the case where Z+L i3+ .
It is also possible to specify a period from t2 to a certain time t2. Needless to say, in such a case, the time interval is automatically set in the scan plan creation processing section.

〔Effect of the invention〕

According to the present invention described in detail above, since the dynamic scan and data collection control of this apparatus is performed based on the dynamics cap plan created in the scan plan creation processing section, unnecessary X
It is possible to provide an X-ray CT apparatus that can obtain a reconstructed image at a desired time with the minimum necessary exposure dose without performing radiation exposure.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a flowchart showing a dynamics cap run created by the plan creation processing section of the device and a dynamic scan procedure executed by this dynamics cap run. , FIG. 3 is a timing chart showing a procedure for executing a dynamics cap run and a procedure for processing collected data by the apparatus. DESCRIPTION OF SYMBOLS 1... X-ray tube, 2... Subject, 3... Detector ring, 5... DAS (data acquisition unit), 6... Sorter, 7... Rotation control unit, 8... ...Interpolation unit, 9...Memory unit, 10...Convolver, 11...Back projector, 12...Image memory, 13...CR
T. 14... Plan creation processing section, 15... Input means. Figure 3

Claims (1)

[Claims] X-ray transmission data obtained by exposing the object to an X-ray beam while continuously rotating around the object is collected, and this X-ray transmission data is processed to reconstruct an image of an arbitrary cross section of the object. In an X-ray CT device that obtains a An X-ray CT apparatus characterized by comprising a plan creation processing section for controlling.