CN102121908B - CT (computed tomography) system and signal processing method thereof - Google Patents

Abstract

The invention relates to a CT (computed tomography) system and a signal processing method thereof. The CT system comprises an X-ray source array and a small-sized flat panel detector (FPD) which are coaxially arranged in the horizontal direction, wherein, the X-ray source array comprises an electronic scanning ray source and a collimator metal target which are connected together; the X-ray source array and the small-sized FPD array are respectively fixed on two ends of a rotatable support; and the X-ray source array and the small-sized FPD which are positioned on the two ends of the rotatable support rotate around an object along a circular or spiral trace. Another X-ray array can form a three-dimensional array by means of a carbon nano X-ray source placed around a scanned object, wherein, the X-ray source array generated by the carbon nano X-ray source and the small-sized FPD form the CT system. The invention further provides an image compression and reconstruction method for the new CT scanning system.

Description

A kind of CT system and signal processing method

Technical field

The present invention relates to the new design of CT system and new image rebuilding method, particularly a kind of CT system and signal processing method.

Background technology

The structural representation of existing CT system as shown in Figure 1, it has used large-area detector, and 40X30cm is generally arranged ², improved production cost and the volume of instrument, simultaneously owing to wholely cover scanned object, thus large to the radiation dose of scanning object, human body is caused in various degree injury.

Recently the latest developments of information theory, the compressed sensing principle in optimum or near optimum signal reconstruction, particularly not exclusively has been proved to be its superior part in the reconstruct of linear measurement.These theories are very fast to be applied in the nuclear magnetic resonance image reconstruction by reorganization.And the present invention adapts for the first time and use these theories in the CT system.

Summary of the invention

The object of the invention is to, for the radiological dose that overcomes traditional CT system scan patient time of exposing thoroughly long, and the problem such as scattering effect, thus a kind of CT system and signal processing method are proposed.

In order to realize the foregoing invention purpose, its unique design is pattern of rows and columns of x-ray source, and the scanning beam track arranges.This is so that the sampling of object can reach best.Another unique distinction of invention is its restructing algorithm, and particularly the compressed sensing of its use is in optimizing sampling plan.This new system can be used for medical treatment, as: the scanning of human brain or human body, or industrial scanner (as: flaw of equipment, damage, fatigue) also can be used for extinct plants and animal recovery or archeological research etc.System has reduced the size of X ray flat panel detector, thereby has effectively reduced production cost and the volume of instrument.

A kind of CT system that the present invention proposes is characterized in that, described CT system comprises: x-ray source array and Small-scale Flat detector, described x-ray source array and the coaxial setting of Small-scale Flat detector horizontal direction.

Described x-ray source array comprises: the one scan radiographic source, described flying spot source links to each other with a collimating apparatus metallic target, this collimating apparatus metallic target for generation of and limit X ray and can only lead to the Small-scale Flat detector;

Wherein, described x-ray source array and described Small-scale Flat detector array are separately fixed at the two ends of a rotatable support, and by the motion of support, described x-ray source array and Small-scale Flat detector are around object synchronous rotary motion to be scanned.

Described collimating apparatus metallic target, this collimating apparatus metallic target are used for the fan-beam district that guarantees that each forms a cover part object by x-ray source and the Small-scale Flat detector in certain hole of collimating apparatus metallic target for opening uniformly the sheet metal in some holes.

Described Small-scale Flat detector adopts the photon counting detection array that is used for the fast recording scan-data, and this photon counting detection array comprises several little semiconductor detectors that are positioned on the Small-scale Flat detector.

Described x-ray source array, all right, form a cubical array x-ray source by being placed on scanned some carbon nanometer x-ray sources on every side.

Described x-ray source array, its arrangement mode is obtained by optimization method, determines the position of each point source by random alignment and experiment effect.

Described optimization method specifically comprises following steps:

1) position of x-ray source produces by simple computer mould quasi-random;

2) corresponding collection signal is simulated in the position of respective sources by existing CT simulator program, substitution 1);

3) the CT image is obtained by the method for reconstructing that this patent is mentioned at last;

4) calculate the suffered radiation dose of patient, this dosage can be reduced to the number that is proportional to x-ray source;

5) repeatedly by above 1)～4) described in analog computation, can obtain the curved line relation of x-ray source position and picture quality and the suffered radiation dose of patient, and can determine thus the arrangement mode of best x-ray source.

The signal processing method of a kind of CT system, described CT system comprises: x-ray source array and Small-scale Flat detector, described x-ray source array and the coaxial setting of Small-scale Flat detector horizontal direction; The object that described method is used for this CT system scan of reduction forms image output, and the method specifically comprises following steps:

11) set x-ray source array scanning object, object is carried out stochastic sampling;

12) the Small-scale Flat detector records the data that sampling obtains;

13) data that obtain for sampling adopt the compression of images method for reconstructing to recover the scanning object image, specifically comprise following steps:

At first try to achieve the sparse conversion of object with derivative or second derivative, concrete formula is as follows:

Or

Wherein, the object that the representative of f function is scanned, and

It then is the sparse conversion of scanned object;

Then, at restrictive condition (Af-y) ^T(Af-y)=0, or (Af-y) ^T(Af-y)＜and ε, lower sparse conversion with the L1 norm minimizes, and reduction is the object of sampling not exclusively, forms image output; Wherein, matrix A is the projection matrix of CT, and y is the data of detector record.

Described minimized method comprises interior point method, Newton iteration method, method of conjugate gradient or Iterative conditional modes method, and concrete formula is as follows:

$\underset{\∀f}{\min }{\left|\right|\mathrm{\φ}\left(f\right)\left|\right|}_{l1},s.t.{\left|\right|\mathrm{Af}-y\left|\right|}_{l2}^2\≤\mathrm{\ϵ}.$

In addition, the progress of nanometer technology, the particularly generation of carbon nano-tube x-ray source are so that use the X ray array to become possibility in the CT system.A plurality of x-ray sources are pressed certain pattern arrange, thereby this invention can realize stochastic sampling so that the theory of compressed sensing is able to abundant application in CT scan.Except the nanometer x-ray source, use the scanning beam x-ray source of special design collimating apparatus also can be used to provide similar X ray array.The benefit of this scanning beam x-ray source is the cheap of it.It with this invention in the minimonitor that uses together so that the price of whole system is very cheap.

The invention has the advantages that, it can be so that patient greatly reduces suffered radiological dose and sweep time, this invention provides high resolving power, low radiation, high time resolution (real-time graphics), and possible multispectral image treatment technology, this for diagnosis and radiation therapy particularly the precise positioning radiation therapy (IGRT) of emerging high-end image control be very useful.

Description of drawings

Fig. 1 is the traditional CT structural representation;

Fig. 2 is CT structural representation of the present invention;

Fig. 3 is the working method synoptic diagram of a kind of concrete CT of the present invention system;

Fig. 4 is the concrete structure of a kind of CT of the present invention system, comprises the flying spot source, collimating apparatus metallic target and Small-scale Flat detector;

Fig. 5 is the runing rest synoptic diagram of a kind of CT of the present invention system.

Embodiment

The present invention is further described below in conjunction with accompanying drawing, but should not limit protection scope of the present invention with this.

1. multi-source and minimonitor CT configuration

A Configuration Design that the CT system is new has been adopted in this invention.It has used a plurality of x-ray sources position, i.e. x-ray source array and small-sized detector.This design greatly reduces the cost of whole system.

As shown in Figures 1 and 2, accompanying drawing 1 has shown the Configuration Design of conventional CT scanner, and it has used large-area detector, and 40X30cm is generally arranged ², accompanying drawing 2 has shown CT scanner design of the present invention, its detector area is reduced to 1/10th of conventional CT.

Its x-ray source is positioned at different positions, thereby each group x-ray source and detector have formed a little fan-beam district, has covered the part of scanning object.In scanning process, x-ray source array and detector are around object along a circle or spiral trajectory rotates, as shown in Figure 3.

Little detector and X-ray beam cover and have reduced the Cape Town scattering effect of electronics, thereby have improved the reconstructed image quality.

2. random sampling technique

We notice, when using this new structure design, scanning object is covered by X-ray beam is whole at each crevice projection angle and unlike conventional design, this so that radiation dose greatly reduce.In general this means the picture quality variation simultaneously, because the minimizing of the data that gather.If but we carefully select the projection of X-ray beam, and use effective restructing algorithm, scanned object can be restored fully.Theoretical according to compressed sensing, the natural selection of an X-ray beam is exactly the stochastic sampling for linear measurement.Use this sampling, object can out effectively utilize the data that gather by Perfect Reconstruction as far as possible from the X ray projection, reduce mediocre tail degree.If the words that the sparse conversion of object exists.In fact this conversion can change existing by the gradient variable that minimum total variances (TV) normalization comes.We propose to increase degree of rarefication with second derivative in this external this invention, and this is so that reconstruction result is more perfect accurately, and we can describe in detail below.The stochastic sampling mode can be verified by experiment, in case determine that same mode can be recycled and reused for other object or patient.

3. compressed sensing reconfiguration technique

Because measure the sampling wretched insufficiency of (x-ray imaging), it is unlikely and very unsettled using conventional contravariant to bring the reduzate body.Therefore reconstruct need the extra information of scanned object, i.e. priori.In this invention, this priori is exactly " sparse " character of object.It for example has been proved to be in human body and other object in a lot of occasions is reliably, and has been applied in the Magnetic resonance imaging of human body.We need to find a kind of conversion so that be sparse in the space of object after conversion.Here we use derivative and the second derivative of mentioning in the past.The compressed sensing technology shows, uses by the L1 norm of sparse object, and we just can reduce object fully from incomplete sampled measurements.Equation below we have derived thus solves the problem that L1 optimizes.

${\left|\right|\mathrm{\φ}\left(f\right)\left|\right|}_{l1}=\∫\sqrt{f_x^2+f_y^2+f_z^2}\mathrm{dxdydz}---\left(1\right)$

$\underset{\∀f}{\min }{\left|\right|\mathrm{\φ}\left(f\right)\left|\right|}_{l1}s.t.{\left|\right|\mathrm{Pf}=s\left|\right|}_2^2\≤\mathrm{\ϵ},---\left(2\right)$

Equation (1) also can substitute with following equation

${\left|\right|\mathrm{\φ}\left(f\right)\left|\right|}_{l1}=\∫\sqrt{f_{\mathrm{xx}}^2+f_{\mathrm{yy}}^2+f_{\mathrm{zz}}^2}\mathrm{dxdydz}---\left(3\right)$

The object that the f function representative here is scanned, and

It then is sparse conversion.Satisfying under the prerequisite of projection theorem, minimize

Can realize optimized reconstructed image.The algorithm of optimizing generally can solve with several alternative manners, such as interior point method, Newton iteration, conjugate gradient method and iterated conditionmode method.

4. scanning beam contrasts carbon nano-tube X ray array

In case " at random " pattern of sampling is determined, x-ray source need to be aligned to certain pattern and realize sampling.We can impact at a plurality of targets with the electron scanning bundle of Electromagnetic Control and extremely realize it.

Such system comprises a rotatable support of CT, so the synoptic diagram of runing rest such as Fig. 5, this system also comprises a scan source and detection array on the other side, as shown in Figure 4.

This scan source and detector have a common axle, identical sweep limit.Detector can laterally done narrowlyer.An electron beam is passed the radiogenic transmission target utmost point by electromagnetic guide in gatherer process, rest on each collimating apparatus hole after, thereby the restriction X ray can only lead to detector.Detector array is done each x-ray source position and is read, and forms the two dimensional image of a partial view.The radiogenic scanning of rotation that in contrast to support is very fast.Transmitting the target utmost point is made of the W-Re film take beryllium as base material.Photon counting detection array on support C type arm is a kind of detector of direct conversion hysteria.It is that a kind of 4 * 4 detector array of tiling mixes, and each mixing comprises that a CdZnTe is attached to a semi-conductor chip that is used for photon detection and counting.

Radiogenic rapid scanning requires very fast reading speed, and this is that each detector will be done data and read because to each radiographic source position.Use photon counting to require very fast counting rate (will reach millions of countings of the every channel of per second).The detector of photon counting can reach this speed.The detector of photon counting also has an extra benefit, in contrast to the detector of energy integrated-type, and it can increase the quantum efficiency of detection.

Recently scientist's success produced X ray with carbon nano-tube.This technological breakthrough may be to radiology, and radiating medical and airdrome luggage scanner produce revolutionary impact.In the x-ray system of routine, electronics discharges from the tungsten filament of heating, and accelerates in vacuum tube until impact metallic target and extremely go up and produce X ray.Because X ray produces from single source, 3-D view processes such as CT scan is very complicated.After nanotube had been arranged, spatial digitizer can not use tungsten filament with a series of nanotubes structures.After adding voltage, by an a kind of quantum effect of emission, each nanotube electron emission of being called.Such system is considered to be fit to 3-D scanning, adds or remove voltage because utilize, and the speed of single nanotube switch can arrive the millisecond rank.

The present invention also can be in conjunction with new nanometer technology, rather than uses the method for above-mentioned electron scanning bundle.The nanometer x-ray source can be placed on the scanned array that forms a three-dimensional on every side, then is activated by certain order, thereby produces the inswept human body of a series of X ray.Electronization open and close the Mechanical Moving that can produce scanning beam and not need instrument.This scanning technique can provide real time 3-D image to process fast enough, thereby helps improve the tumor-localizing in beta ray therapy.This nanotube can be more expensive than conventional X-ray tube, but the saving that needs than present CT on plant equipment is a lot.

5. the arrangement of track while scan and x-ray source

This invents the design that important aspect is the scanning beam track, or the position of corresponding nanotube x-ray source.This has determined speed and the suffered radiation dose of patient of sampling, and prior picture quality.As mentioned above, sampling pattern is very important in the compressed sensing theory, and optimum pattern decides by experiment.This optimum method also depends on restructing algorithm, and this is also contained in this invention.

The method utilizes the computer random digital-to-analogue to intend producing the position of x-ray source, and by existing CT simulator program, corresponding collection signal is simulated in the position of substitution respective sources.The CT image is obtained by the method for reconstructing that this patent is mentioned at last.Simultaneously, the suffered radiation dose of patient can be reduced to the number that is proportional to x-ray source.By repeatedly repeating above analog computation, can obtain the curved line relation of x-ray source position and picture quality and the suffered radiation dose of patient, and can determine thus the arrangement mode of best x-ray source.

It should be noted last that above embodiment is only unrestricted in order to technical scheme of the present invention to be described.Although with reference to embodiment the present invention is had been described in detail, those of ordinary skill in the art is to be understood that, technical scheme of the present invention is made amendment or is equal to replacement, do not break away from the spirit and scope of technical solution of the present invention, it all should be encompassed in the middle of the claim scope of the present invention.

Claims (2)

1. the signal processing method of a CT system, described CT system comprises: x-ray source array and Small-scale Flat detector,

Described x-ray source array and the coaxial setting of Small-scale Flat detector horizontal direction, described x-ray source array forms a cubical array x-ray source by being placed on scanned some carbon nanometer x-ray sources on every side;

Described x-ray source array, its arrangement mode is obtained by optimization method, and the method specifically comprises following steps:

At first, produce the primary position of x-ray source with the computer mould quasi-random; Then by existing CT simulator program, the primary position of substitution respective sources is simulated corresponding collection signal, and obtains the CT image with method for reconstructing; Calculate at last the suffered radiation dose of patient, this dosage can be reduced to the number that is proportional to x-ray source; Repeatedly by above-described analog computation, obtain the curved line relation of x-ray source position and picture quality and the suffered radiation dose of patient, and can determine thus the arrangement mode of best x-ray source;

In scanning process, x-ray source array and Small-scale Flat detector center on object along a circle or spiral trajectory rotation;

Described x-ray source array comprises: the one scan radiographic source, described flying spot source links to each other with a collimating apparatus metallic target, this collimating apparatus metallic target for generation of and limit X ray and can only lead to the Small-scale Flat detector, described Small-scale Flat detector adopts the photon counting detection array that is used for the fast recording scan-data, this photon counting detection array comprises several little semiconductor detectors that are positioned on the Small-scale Flat detector, wherein, described x-ray source array and described Small-scale Flat detector array are separately fixed at the two ends of a rotatable support, motion by support, described x-ray source array and Small-scale Flat detector are around object synchronous rotary motion to be scanned

The object that described method is used for this CT system scan of reduction forms image output, and the method specifically comprises following steps:

1) sets x-ray source array scanning object, object is carried out stochastic sampling;

2) the Small-scale Flat detector records the data that sampling obtains;

3) data that obtain for sampling adopt the compression of images method for reconstructing to recover the scanning object image, specifically comprise following steps:

At first try to achieve the sparse conversion of object with derivative or second derivative, concrete formula is as follows:

${\left|\right|\mathrm{\φ}\left(f\right)\left|\right|}_{L1}=\∫\sqrt{f_x^2+f_y^2+f_z^2}\mathrm{dxdydz}$ Or ${\left|\right|\mathrm{\φ}\left(f\right)\left|\right|}_{L1}=\∫\sqrt{f_{\mathrm{xx}}^2+f_{\mathrm{yy}}^2+f_{\mathrm{zz}}^2}\mathrm{dxdydz};$

Wherein, the object that the representative of f function is scanned, and || φ (f) || _L1It then is the sparse conversion of scanned object;

Then, at restrictive condition (Af-y) ^T(Af-y)=0, or (Af-y) ^T(Af-y)＜ε under, the sparse conversion of L1 norm is minimized, reduction is the object of sampling not exclusively, forms image output; Wherein, matrix A is the projection matrix of CT, and y is the data of detector record.

2. signal processing method according to claim 1 is characterized in that, described minimized method comprises interior point method, Newton iteration method, method of conjugate gradient or Iterative conditional modes method, and concrete formula is as follows:

$\underset{\∀f}{\min }{\left|\right|\mathrm{\φ}\left(f\right)\left|\right|}_{L1},s.t.{\left|\right|\mathrm{Af}-y\left|\right|}_{L2}^2\≤\mathrm{\ϵ}.$

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