CN102074276A - Filter for filtering x-rays and x-ray computed tomography - Google Patents

Abstract

The invention relates to a filter (15) for filtering X-rays emitted from an X-ray source (16), which uses an X-ray detector (7) to detect the X-rays (8); the X-ray detector (7) comprises detector elements (24) arranged as detector lines (25, 26, 27) and detector rows (28, 29); detector signals of the detector element (24) are weighted in the way that the detector signals from the outer detector lines (26, 27) in relation to the middle detector line (25) are weighted down, when an image of an object (P) through which the detector signals pass is reconstructed; the filter (15) is configured to cause the X-rays (8) to be absorbed or attenuated by the filter (15) based on the weighting of the detector signals during the reconstruction or on the weighting function used during the reconstruction. The invention further relates to an X-ray computed tomography (1) with the filter (15).

Description

Be used to filter the filtrator and the X ray computer tomograph of X ray

Technical field

The present invention relates to be used to filter the filtrator of the X ray that sends from x-ray source, use X-ray detector to detect this X ray.In addition, the invention still further relates to X ray computer tomograph with this type of filtrator.

Background technology

X-ray apparatus is particularly taken the X ray computer tomograph about the measurement data of a plurality of health layers of patient simultaneously, has X-ray detector respectively for this reason, and this X-ray detector has a plurality of detector line that formed by detector element.Typically, the X-ray detector of this type of multilayer X ray computer tomograph is extending between the 4cm to 16cm on the direction of system's axle of X ray computer tomograph or z axle.In third generation X ray computer tomograph, X-ray detector is arranged opposed to each other with x-ray source on the rotatable portion of the frame of X ray computer tomograph, sends X ray from the common taper of described x-ray source ground in the direction of X-ray detector.

In so-called scanning, take patient's X ray projection from different projecting directions, for can from write down in this scan period owing to rebuild the faultage image or the 3D rendering of Measuring Object the measurement data of the X ray of taper and the X-ray detector that presents according to so-called Cone-Beam geometric configuration, it is available to have a reconstruction algorithm different strictnesses and approximate.For example, can use approximate Weighted Filtered Back Projection (WFBP weighted filtering back projection) as reconstruction algorithm, this is at people such as K.Stierstorfer " Weighted FBP-a simple approximate 3D FBPalgorithm for multislice spiral CT with good dose usage for arbitrary pitch ", describes among (2004) 2209 to 2218 pages of the Phys.Med.Biol.49.

With the same in the Cone-Beam of other non-strictness reconstruction algorithm, in this image of rebuilding pseudo-shadow appears.In weighted filtering back projection, these pseudo-shadows can be suppressed significantly, and this measurement data that is positioned at the detector line of more lateral on the z direction by will be from the observing of X-ray detector the time obtains by the downward weighting of weighting function.At people's such as K.Stierstorfer " Weighted FBP-asimple approximate 3D FBP algorithm for multislice spiral CT with good doseusage for arbitrary pitch ", the suitable weighting function W that proposes among (2004) 2209 to 2218 pages of the Phys.Med.Biol.49 _Q(q) be:

Wherein:

Q is [0; 1] selectable weight between, and

Q is the variable that is used for detector line.

Course for this weighting function of different weight Q has been shown among Fig. 1 on the detector line of X-ray detector, it forms people such as visible K.Stierstorfer " Weighted FBP-a simpleapproximate 3D FBP algorithm for multislice spiral CT with good dose usage forarbitrary pitch ", (2004) 2209 to 2218 pages of Phys.Med.Biol.49.X-ray detector at this from q=[-1; + 1] extend, q=0 represents detector centre when wherein observing on the z direction, and q=+/two outermost detector line of-1 expression.Littler by making in the reconstruction of the method for reconstructing that uses weighted filtering back projection from the measurement data or the detection signal contribution of the detector line that is positioned at the more lateral, pseudo-shadow is able to reduce very doughtily.But relatively, dose efficiency also is lowered in undesirable mode, does not contribute to imaging effectively because be applied to the part of patient's x-ray dose.From people's such as K.Stierstorfer " Weighted FBP-a simple approximate 3D FBP algorithm formultislice spiral CT with good dose usage for arbitrary pitch ", the Fig. 2 that obtains among (2004) 2209 to 2218 pages of the Phys.Med.Biol.49 illustrates the dose efficiency course for different weight Q.Obvious from Fig. 2, weight Q selects more for a short time, and then dose efficiency is low more.

Summary of the invention

Therefore, the technical problem to be solved in the present invention is, provides the filtrator of the X ray computer tomograph that is used for X ray and is used for aforementioned type, but makes improver amount efficiency when rebuilding radioscopic image.

According to the present invention, this technical matters solves by a kind of filtrator that is used to filter the X ray that sends with general conical from x-ray source, use X-ray detector to detect this X ray, described X-ray detector has the detector element of detector line of being arranged to and detector columns, the detector signal of described detector element or measurement data are weighted into when the image reconstruction of the object that is passed and make and to use weighting function will be positioned at the downward weighting of detector signal of the detector line of more lateral from the detector line with respect to the centre of detector element especially, and wherein filter configuration is to make X ray depend on the weighting of detector signal when rebuilding or depend on when rebuilding that employed weighting function is filtered that device absorbs or decay.

The inventor has recognized that, that the detector line with respect to the centre of X-ray detector is positioned at the more lateral and its detector signal when rebuilding by weighting downwards and therefore when rebuilding the littler detector element of contribution may have more quantum noise.Therefore, x-ray source can be associated with following filtrator, the X ray that this filtrator will point to the detector line of more lateral is decayed before it passes Measuring Object or is partly absorbed, and makes the x-ray dose that not only is applied to Measuring Object but also the x-ray dose in the detector element of the detector line of more lateral be lowered.Can improve the dose efficiency when rebuilding radioscopic image in this way, before passing Measuring Object, always be absorbed at least in part because be not used in the X ray of reconstruction.At this, correspondingly depend on the weighting of detector signal or depend on that correspondingly the weighting function of each reconstruction algorithm carries out by absorption or the decay of filtrator for X ray.

According to a kind of variant of the present invention, the filtrator that is used for the X ray computer tomograph is provided, wherein, this filter arrangement centers on system's axle or the rotatable part of z axle frame, and, make that being positioned at X ray that the detector line of z direction more lateral sends from the direction with respect to the detector line of centre depends on the weighting of detector signal when rebuilding or depend on that when rebuilding employed weighting function is filtered that device absorbs or decay with respect to the detector line orientation of arranging perpendicular to the z axle of the X-ray detector on the rotatable portion that is arranged in frame.

According to one embodiment of the present invention, filtrator has square basic configuration or basic structure, have the middle channel shaped depression of in square long limit, moving towards that is arranged in, obtain the wedge-like portion in the both sides, center thus, described wedge-like portion has and keep equal xsect on the length of filtrator.The length axle of square basic configuration or basic structure is perpendicular to the z axle of X ray computer tomograph and be parallel to the longitudinal axis orientation of X-ray detector approx.Filtrator makes the channel shaped depression point to x-ray source with respect to the layout of x-ray source usually.

According to another embodiment of the invention, filter design is a single-piece.Alternatively, the wedge-like portion of filtrator on the z direction promptly the longitudinal axis transverse to filtrator be configured to scalable.Therefore filtrator can be regulated coupling with the different diaphragm of the diaphragm that is associated with x-ray source.

According to another kind of variant of the present invention, constructed the filtrator in the reconstruction that is applied to use weighted filtering back projection (WFBP) reconstruction algorithm, wherein weighting function is:

Wherein, Q is [0; 1] selectable weight between, and q is [1; + 1] variable that is used for detector line that changes between wherein be the detector line of centre when q=0, and when q=1 or q=-1 for being positioned at outermost detector line.Filtrator is constructed so that correspondingly X ray depends on weighting function W by the absorption or the decay of filtrator _Q(q) carry out.

The course of filter thickness on its xsect preferably determined according to following formula:

$d\left(q\right)=-\frac{1}{\mathrm{\μ}\left(E\right)}\ln W_Q\left(q\right)$

Wherein, μ (E) is the attenuation coefficient that is used for the material of filtrator, and it depends on the ENERGY E of employed X ray.In being generally used for the heterogeneous X-ray spectrum of computer tomography instrument, for example can suppose average or effective energy.

If use aforementioned given equation to calculate the course of filter thickness d (q) on its xsect for different Q, then may in the edge extent of filtrator, obtain big relatively thickness.But filtrator can not be configured to any thickness, because otherwise filtrator needs the excessive structure space on the rotatable portion of frame.Therefore, in a kind of variant of the present invention, the maximum ga(u)ge of filtrator is between 1cm to 10cm.

According to a kind of variant of the present invention, filtrator has aluminum or aluminum titanium alloy material.

Technical matters of the present invention also solves by a kind of X ray computer tomograph, and described computer tomography instrument comprises aforesaid filtrator.

Description of drawings

Embodiments of the invention illustrate in subsidiary synoptic diagram.Each figure is:

Fig. 1 shows the weighting function W for the weighted filtering back projection of different Q values _Q(q) course,

Fig. 2 shows for the weighting function W shown in Fig. 1 _QThe course of dose efficiency (q),

Fig. 3 shows a kind of X ray computer tomograph,

Fig. 4 shows the vertical view of X-ray detector of the X ray computer tomograph of Fig. 3,

Fig. 5 shows the X-ray equipment of the X ray computer tomograph of Fig. 3,

Fig. 6 shows the z shaped filters of the X-ray equipment of Fig. 5,

Fig. 7 shows the xsect course for the z shape filtrator of different Q values,

Fig. 8 show Fig. 7 z shape filtrator different xsect courses X ray decay course and

Fig. 9 shows no z shape filtrator, uses the course of the dose efficiency of actual z shape filtrator and desirable z shape filtrator.

Identical in the accompanying drawings or function components identical provides all the time with identical reference marker.Diagram in the accompanying drawing is schematically, but not forcibly draws in proportion.For illustrated X ray computer tomograph 1 among Fig. 3, limit hereinafter and not only to discuss prevailingly and understand degree of the presently claimed invention.

Embodiment

X ray computer tomograph 1 shown in Figure 3 comprises the frame 2 that has stationary part 3 and center on system's axle or z axle 5 rotatable parts 4.Rotatable portion 4 has x-ray system in the situation of this embodiment of the present invention, described x-ray system is included in X-ray equipment 6 and the X-ray detector of arranging opposed to each other on the rotatable portion 47.In service at X ray computer tomograph 1, send X ray 8 from X-ray equipment 6 in the direction of X-ray detector 7, described X ray 8 passes measuring object and by the form collection of X-ray detector 7 with detector signal or measurement data.

In Fig. 4, have a plurality of detector element 24 that are arranged to detector line 25,26,27 and detector columns 28,29 according to the X-ray detector shown in the vertical view 7, wherein detector columns is moved towards on the z direction of principal axis, and detector line is moved towards perpendicular to the z direction of principal axis on the φ direction and therefore.Intermediate detector row 25 places are labeled as q=0, and two outermost detector line 26 and 27 places are labeled as q=-1 and q=+1.X ray computer tomograph 1 is the multilayer or the X ray computer tomograph of cutting into slices more.

X ray computer tomograph 1 has the patient's bed 9 that is used to support examine patient P in addition.Patient's bed 9 comprises bed seat 10, is provided as the patient support plate 11 that in fact supports patient P and is arranged on the described bed seat 10.Patient support plate 11 is with respect to bed seat 10 scalable on the direction of system's axle 5, make that they can be in patient P be introduced in the opening 12 of frame 4, described opening 12 defines columniform measurement field at present, is used for for example taking with spiral scan the 2D X ray projection of patient P.Use the image computer 13 of X ray computer tomograph 1 to carry out to the computing that utilizes the 2D X ray projection that x-ray system takes and based on the reconstruction of tomographic image, 3D rendering or the 3D data set of the projection of 2D X ray, described image computer 13 illustrates described tomographic image or 3D rendering on display device 14.

In the situation of this embodiment of the present invention, use weighted filtering backprojection reconstruction algorithm and use weighting function W by image computer 13 _Q(q) rebuild.For at this improving agent amount efficiency, in particular for the value improving agent amount efficiency of Q＜1, it is so-called z shape filtrator 15 that X-ray equipment 6 has filtrator according to the present invention.

In Fig. 5, typically explain the layout of z shape filtrator 15 in X-ray equipment 6.Under the situation of this embodiment of the present invention, X-ray equipment 6 comprises the x-ray source 16 with X-ray tube form, is sent the X ray of approximate taper by the focal point F of described x-ray source 16.For block (Einblendung) on X-ray detector 7, X-ray equipment 6 has diaphragm 17.Be provided with Bowtie filtrator 18 in described diaphragm 17 back, described Bowtie filtrator 18 will filter on the φ direction changeably by the X ray that diaphragm 17 arrives usually.Be provided with z shape filtrator 15 in Bowtie filtrator 18 back.

In Fig. 6, typically show the typical structure of z shape filtrator 15.Z shape filtrator 15 self has square basic structure, and provides the channel shaped depression 19 in the middle of being arranged in, and described depression 19 is extended on the direction of the longitudinal axis L of z shape filtrator 15.The both sides of channel shaped depression have the wedge- like portion 20,21 of extending on y direction, its xsect is constant on the direction of longitudinal axis L.The form of z shape filtrator 15 forms the X ray 8 of the outer detector row (being detector line 26,27 etc.) that points to X-ray detector 7 of should absorbing at least in part or decay because from the measurement data of the detector element of these detector line or these detector line when rebuilding always by weighting function W _Q(q) by weighting downwards.Therefore z shape filtrator 15 is orientated the z axle that makes its longitudinal axis L be substantially perpendicular to X ray computer tomograph 1 and arranges, and be positioned at plane with the central shaft M of X-ray detector 7 as much as possible, wherein longitudinal axis L and central shaft M mutual orientation approx perpendicular to z axle orientation.

The actual configuration of z shape filtrator 15 depends on reconstruction algorithm and depends on use therein for weighting function or weight from the measurement data of the outer detector row of X-ray detector 7 especially.

As mentioning, in the situation of this embodiment of the present invention, image reconstruction is undertaken by using weighted filtering back projection and following weighting function:

Wherein, Q is [0; 1] selectable weight between, and q is [1; + 1] variable that is used for detector line that changes between wherein be the detector line of centre when q=0, and when q=1 or q=-1 for being positioned at outermost detector line.

For should be taken into account, design z shape filtrator makes that the decay A of the X ray that causes by z shape filtrator should be as well as possiblely corresponding to weighting function W _Q(q).Therefore, set up:

$A_Q\left(q\right)=\frac{I}{I_0}{e}^{-\mathrm{\μ}\left(E\right)d\left(q\right)}=W_Q\left(q\right)$

Obtain thus, for the thickness d (q) of the z shape filtrator relevant with q:

$d\left(q\right)=-\frac{1}{\mathrm{\μ}\left(E\right)}\ln W_Q\left(q\right)$

Wherein, μ (E) is the attenuation coefficient that is used for the material of z shape filtrator, and it depends on the ENERGY E of X ray.Obvious by equation d (q), the thickness course of filtrator and therefore its xsect or by absorption or the decay of filtrator for X ray depend on the weight or weighting or the weighting function that use when rebuilding.

In this embodiment of the present invention, z shape filtrator is formed by aluminium and from the X ray energy of 80keV.For this situation, the μ value is approximately 0.545/cm.

Under this boundary condition, can for different weight Q use equation for d (q) with the detecting device width as [1; 1] the mobile variable q between calculate as illustrated course in Fig. 7 be the thickness d of the z shape filtrator of unit with cm, wherein q=0 has provided the intermediate detector row, and q=+/-1 has provided two outermost detector line.Step size computation according to 0.2 is for [0; The course of the Q value 1].In addition, when calculating, make the predesignating of maximum ga(u)ge that z shape filtrator only should have 3cm, because otherwise z shape filtrator required structure space in X-ray equipment 6 or on the rotatable portion 4 of frame 2 is excessive.The amplification of structure space makes the opening 12 of frame 2 dwindle, and this is undesirable.

In Fig. 8, pass through the course of z shape filtrator for different weight Q for the decay A of X ray for explaining to show.In the zone corresponding to the outer detector row of X-ray detector 7 of z shape filtrator, be constant for the decay of X ray, because the thickness of z shape filtrator reaches 3cm herein, make decay be not less than about 0.19 value.

At this, improved the variances sigma of quantum noise by z shape filtrator ²No z shape filtrator, then the variance of quantum noise is calculated as:

${\mathrm{\σ}}^2=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{\left[{\tilde{W}}_Q\left(q_i\right)\right]}^2\·{{\mathrm{\σ}}_i}^2$

Wherein

${\tilde{W}}_Q\left(q_i\right)=\frac{W_Q\left(q_i\right)}{\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{W}_Q\left(q_i\right)}$

Wherein

$\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{\tilde{W}}_Q\left(q_i\right)=1$

And i=1 ..., N is 1 ..., N irradiation S from the different x-ray projection _i, for the signal S of calculating chart picture point they are added and:

$S=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{\tilde{W}}_Q\left(q_i\right)\·S_i$

X-ray dose at this is:

$D=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{D}_i$

Use z shape filtrator, obtain the change of following situation with respect to no z shape filtrator now.The signal S ' of the independent irradiation of measuring with z shape filtrator _{F, i}With the quantum noise variances sigma ' _F.i ²Satisfy following formula:

S′ _F，i＝A _Q(q _i)·S _i

With

σ′ _F，i ²＝A _Q(q _i)·σ _i ²

For as in the situation of no z shape filtrator, obtain same valid signal strengths, signal is calculated correction with respect to independent irradiation:

${S^{\′}}_{F,i}\→S_{F,i}=\frac{{S^{\′}}_{F,i}}{A_Q\left(q_i\right)}\≡S_i$

With this, with respect to independent irradiation, the quantum noise variance of corrected signal raises according to following formula

${{{\mathrm{\σ}}^{\′}}_{F,i}}^2\→{{\mathrm{\σ}}_{F,i}}^2=\frac{{{{\mathrm{\σ}}^{\′}}_{F,i}}^2}{A_Q{\left(q_i\right)}^2}\≡\frac{{\mathrm{\σ}}_i^2}{A_Q\left(q_i\right)}$

And the quantum noise variance is calculated as:

${{\mathrm{\&sigma;}}_{\mathrm{<figure-callout\; id="2"\; label="F"\; filenames="HSA00000353695900021.png,HSA00000353695900022.png"\; state="\{\{state\}\}">F</figure-callout>}}}^2=\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{\left[{\tilde{W}}_Q\left(q_i\right)\right]}^2\&CenterDot;{{\mathrm{\&sigma;}}_{F,i}}^2=\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{\left[{\tilde{W}}_Q\left(q_i\right)\right]}^2\&CenterDot;\frac{{\mathrm{\&sigma;}}_i^2}{A_Q\left(q_i\right)}$

But according to following formula, required x-ray dose reduces:

$D_F=\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{A}_Q\left(q_i\right)\&CenterDot;D_i$

If use aforementioned z shape filter condition now:

A _Q(q)＝W _Q(q)

And limit:

$C:=\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{W}_Q\left(q_i\right)$

Then, under identical useful signal, obtain following quantum noise variance or following accumulated dose for the situation of using z shape filtrator:

${{\mathrm{\&sigma;}}_{\mathrm{<figure-callout\; id="2"\; label="F"\; filenames="HSA00000353695900021.png,HSA00000353695900022.png"\; state="\{\{state\}\}">F</figure-callout>}}}^2=\frac{1}{{\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="HSA00000353695900021.png,HSA00000353695900022.png"\; state="\{\{state\}\}">C</figure-callout>}}_2}\&CenterDot;\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{W}_Q\left(q_i\right)\&CenterDot;{\mathrm{\&sigma;}}_i^2$ With $D_F=\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{W}_Q\left(q_i\right)\&CenterDot;D_i$

Compare with the situation of not using z shape filtrator,

With $D=\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{D}_i$

Immediately as seen, the product of dosage and quantum noise variance for the situation of using z shape filtrator always smaller or equal to the situation of not using z shape filtrator.This means, by stipulating:

A _Q(q)＝W _Q(q)

Dose efficiency may raise usually according to formed z shape filtrator, and affirms not variation.

In Fig. 9 the course of the dose efficiency of three different situations of different Q values being shown in pitch (Pitch) as mean value is that diagram is gone up in 1 complete helix scanning.The course of the dose efficiency of the no z shape filtrator of reference marker 30 expressions.The course of the dose efficiency when reference marker 31 is to use aforementioned z shape filtrator, the maximum ga(u)ge of described z shape filtrator is 3cm.The course of the dose efficiency when at last, reference marker 32 is to use the desirable but z shape filtrator that can't make up in the reality.

As can be seen from Fig. 9, be 0.6 o'clock for example in the Q value, use the z shape filtrator of value design for this reason, compare with no z shape filtrator, under identical picture quality, obtain about 14% dosage saving.

Preferably, z shape filtrator 15 forms single-piece, at certain extension of X-ray detector 7 on the certain width of X-ray detector 7 on the z direction, the φ direction and for example typical effectively X ray energy design of 80keV, wherein carries out most CT scan.At this, the effective X ray energy of 80keV is represented the typical 120kV X-ray spectrum of tungsten anode, wherein carries out most CT scan at present.

But alternatively, can implement adjustable z shape filtrator, wherein wedge-like portion 20 with 21 on the z direction mutual relative scalable.Wedge- like portion 20 and 21 also can be moved mutually with deviating from opposite directions or, so that influence the decay of X ray on the z direction.

The thickness of z shape filtrator can be depending on material and changes, but should not surpass 10cm.Except that aluminium, aluminum titanium alloy also is suitable material, and wherein this is enumerated and is not understood that completely.

For saving structure space, z shape filtrator also can be embodied as structural unit with the Bowtie filtrator.

The present invention in preamble according to the weighting function W of weighted filtering back projection _Q(q) describe.But the present invention is not restricted to this weighting function.But can conceive and also can use other weighting function W in combination in practice with other reconstruction algorithm _Q(q), as long as satisfy A to be similar to well _Q(q)=V _Q(q).

Claims (10)

1. filtrator (15) that is used for filtering the X ray (8) that sends from x-ray source (16), utilize X-ray detector (7) to detect this X ray (8), described X-ray detector (7) has the detector line of being arranged to (25,26,27) and detector columns (28,29) detector element (24), the detector signal of described detector element (24) is weighted into when the image reconstruction of the object that is passed (P) and makes and will be positioned at the detector line (26 of more lateral from the detector line (25) with respect to the centre, 27) the downward weighting of detector signal, wherein, described filtrator (15) is constructed so that X ray (8) depends on the weighting of detector signal when rebuilding or depends on that employed weighting function is absorbed or decay by this filtrator (15) when rebuilding.

2. filtrator according to claim 1, described filtrator is that X ray computer tomograph (1) provides, wherein, described filtrator (15) is arranged in centering on system's axle (5) or the rotatable part of z axle (5) (4) of frame (2), and detecting device (25 perpendicular to z axle (5) layout with respect to the X-ray detector (7) on the rotatable portion that is arranged in frame (2) (4), 26,27) row is directed, make that being positioned at the X ray (8) that the detector line (26,27) of z direction more lateral sends from the direction with respect to the detector line (25) of centre depends on the weighting of detector signal when rebuilding or depend on that employed weighting function is absorbed or decay by this filtrator (15) when rebuilding.

3. filtrator according to claim 1 and 2, described filtrator has square basic configuration or basic structure, have the channel shaped depression (19) in the middle of square vertical upwardly extending being arranged in, obtain wedge-like portion (20 thus in the both sides, center, 21), it is at the square xsect that equates of keeping on vertically.

4. according to each described filtrator in the claim 1 to 3, described filtrator forms single-piece.

5. filtrator according to claim 3, the wedge-like portion of described filtrator be mutually relative scalable on the z direction.

6. according to each described filtrator in the claim 1 to 5, described filter configuration wherein has for weighting function for being applied in the reconstruction of using weighted filtering back projection (WFBP) reconstruction algorithm:

Wherein:

Q is [0; 1] selectable weight between, and

Q is [1; + 1] variable that is used for detector line that changes between wherein be the detector line of centre when q=0, and when q=1 or q=-1 for being positioned at outermost detector line.

7. filtrator according to claim 6, wherein, the course of thickness d (q) on its xsect of described filtrator (15) obtained by following formula:

$d\left(q\right)=-\frac{1}{\mathrm{\&mu;}\left(E\right)}\ln W_Q\left(q\right)$

Wherein, μ (E) is the attenuation coefficient that is used for the material of filtrator, and described attenuation coefficient depends on the ENERGY E of X ray.

8. according to each described filtrator in the claim 1 to 7, the maximum ga(u)ge of described filtrator is between 1cm to 10cm.

9. according to each described filtrator in the claim 1 to 8, described filtrator has aluminium or aluminum titanium alloy material.

10. X ray computer tomograph, it has according to each described filtrator (15) in the claim 1 to 9.

Images