CN103083031A - Spiral scanning image reconstruction method and device and computer program product for computed tomography (CT) device - Google Patents
Spiral scanning image reconstruction method and device and computer program product for computed tomography (CT) device Download PDFInfo
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- CN103083031A CN103083031A CN2011103583906A CN201110358390A CN103083031A CN 103083031 A CN103083031 A CN 103083031A CN 2011103583906 A CN2011103583906 A CN 2011103583906A CN 201110358390 A CN201110358390 A CN 201110358390A CN 103083031 A CN103083031 A CN 103083031A
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Abstract
The invention discloses a spiral scanning image reconstruction method and device and a computer program product for a computed tomography (CT) device. According to the method, the CT device comprises multi-row detectors, the multi-line detectors comprise a narrow detector with a small row height and a wide detector with a large row height. The method comprises the steps of performing pre-weighting processing on projection data obtained from the multi-row detectors so as to enable the projection data obtained from the narrow detector to have the same slice direction sensitivity curve as the projection data obtained from the wide detector; directly performing interpolation processing on the projection data undergoing pre-weighting processing to ignore different row heights between the narrow detector and the wide detector; and performing back projection processing on the projection data undergoing the interpolation processing so as to obtain a reconstructed CT image. Artifacts in the spiral scanning CT image can be greatly reduced or eliminated through the spiral scanning image reconstruction method and device and the computer program product for the CT device.
Description
Technical field
Present invention relates in general to CT (Computed Tomography, computer tomography technology) field, relate more particularly to a kind of method for reconstructing, device and computer program of the helical scanned image for CT equipment.
Background technology
Usually, CT equipment scans the certain thickness aspect in human body a part with X-ray beam, is received the X ray that sees through this aspect by detector, the X ray that receives is carried out opto-electronic conversion, analog digital conversion, then obtain the CT image through after image reconstruction.
Helical scanning is one of common scan mode of CT equipment, and it makes scanning speed greatly improve.But what be associated with helical scanning is to occur pseudo-shadow in the CT image, the pseudo-shadow of windmill shape for example, stepped pseudo-shadow.
The basic reason of pseudo-shadow is the axial interpolation error of z.Usually use interpositioning in the CT image reconstruction process.General choice and operation comes reconstructed image near the data of image z shaft position when interpolation, and no matter these data come from which row's (at once) detector of detector array.Like this, rebuild the required data of piece image and come from multi-detector, because the angle of difference row detector image data is different, cause image periodic error to occur when rebuilding.Rebuild the row of the needed detector of piece image by the pitch decision of helical scanning, therefore the order of severity of pseudo-shadow is directly proportional to pitch, and pitch is larger, and pseudo-shadow is more serious.
In the CT image, the existence of various pseudo-shadows has had a strong impact on the quality of CT image.
Summary of the invention
Therefore, need a kind of CT image rebuilding method that can reduce or eliminate the pseudo-shadow in helical scanning CT image.
According to an aspect of the present invention, the invention provides a kind of method for reconstructing of the helical scanned image for CT equipment, wherein said CT equipment comprises the multirow detector, described multirow detector comprises having the high narrow detector of less row and have the high wide detector of larger row (high at once is not homogeneous, the capable height of partial row is wider, the capable height of partial row is narrower), described method comprises:
The data for projection that obtains from described multirow detector is carried out pre-weighting process, so that the data for projection that obtains from narrow detector has the identical slice direction sensitivity curve of data for projection that obtains with detector leniently;
Data for projection after pre-weighting is processed directly carries out interpolation processing and the different rows ignored between narrow detector and wide detector is high; And
Data for projection after interpolation processing is carried out back projection process the CT image that obtains rebuilding.
According to one embodiment of present invention, wherein, described pre-weighting is processed and is comprised the following operation of each data for projection execution:
If pending data for projection obtains from narrow detector, to this pending data for projection and from this narrow detector with string but the data for projection that at least one detector different rows obtains be weighted on average, and with weighted mean as corresponding data for projection after pre-weighting processing;
If pending data for projection leniently detector obtains, will the corresponding data for projection after pre-weighting is processed of the direct conduct of this pending data for projection.
According to one embodiment of present invention, wherein, described to this pending data for projection and be weighted average step from the data for projection that described at least one detector obtains and further comprise:
The corresponding weight coefficient of the data for projection of determining to be respectively used to this pending data for projection and obtaining from described at least one detector; And
Multiply by separately weight coefficient, then addition with this pending data for projection and from the data for projection that described at least one detector obtains.
According to one embodiment of present invention, wherein, the step of determining weight coefficient comprises determines corresponding weight coefficient so that the data for projection that obtains from narrow detector has identical section curve with the data for projection that detector leniently obtains.
According to one embodiment of present invention, wherein, the step of determining weight coefficient comprises calculates corresponding weight coefficient iteratively so that the full width at half maximum of slice direction sensitivity curve and equating of wide detector of the data for projection after pre-weighting is processed of narrow detector.
According to one embodiment of present invention, wherein, the data for projection that obtains from described at least one detector for adjacent from the detector that is derived from pending data for projection and with its data for projection that obtains at the detector with string.
According to one embodiment of present invention, wherein, also make in described iterative process for adjacent from the detector that is derived from pending data for projection and equal with its ratio at the respective weight coefficient of the data for projection that front detector and rear detector with string obtain after high half of row of detector add high half of the row of the detector that pending data for projection is derived from resulting and with high half of the row of front detector add high half of the row of the detector that pending data for projection is derived from resulting and ratio.
According to one embodiment of present invention, wherein, the row height of described wide detector is the high twice of row of described narrow detector, and wherein:
(1) if adjacent front detector row and the rear detector row of the detector that is derived from pending data for projection is narrow detector row,
(2) if the adjacent front detector row of the detector that is derived from pending data for projection is wide detector row, then detector row is narrow detector row,
And
(3) if the adjacent front detector row of the detector that is derived from pending data for projection is narrow detector row, then detector row is wide detector row,
Wherein, w
-1Be the weight coefficient of the data for projection that is used for obtaining at the detector with string from the detector that is arranged in described front detector row and is derived from pending data for projection, w
0For being used for the weight coefficient of described pending data for projection, w
1Weight coefficient for the data for projection that is used for obtaining at the detector with string from the detector that is arranged in described rear detector row and is derived from pending data for projection.
According to one embodiment of present invention, described back projection processes and comprises: the data for projection by matrix method, iterative method, filtered back projection's method or two-dimentional Fourier's reconstruction method after to interpolation processing carries out back projection and processes the CT image that obtains rebuilding.
According to one embodiment of present invention, wherein, described back projection processes and comprises:
Data for projection after interpolation processing is carried out convolutional filtering; And
The CT image of the data for projection of back projection after convolutional filtering to obtain rebuilding.
According to a further aspect in the invention, the another kind of method for reconstructing that is used for the spiral image of CT equipment is provided, wherein said CT equipment comprises the multirow detector, and described multirow detector comprises having the high narrow detector of less row and have the high wide detector of larger row, and described method comprises:
The data for projection that obtains from described multirow detector is directly carried out interpolation processing and the different rows ignored between narrow detector and wide detector is high; And
Data for projection after interpolation processing is carried out back projection process the CT image that obtains rebuilding.
According to another aspect of the invention, a kind of reconstructing device of the spiral image for CT equipment is provided, wherein said CT equipment comprises the multirow detector, and described multirow detector comprises having the high narrow detector of less row and have the high wide detector of larger row, and described device comprises:
Be used for the data for projection that obtains from described multirow detector is carried out that pre-weighting is processed so that the data for projection that obtains from narrow detector row has the parts of the identical slice direction sensitivity curve of the data for projection that obtains with detector row leniently;
For directly carrying out interpolation processing, the data for projection after pre-weighting is processed ignores the high parts of different rows between narrow detector and wide detector; And
Be used for the data for projection after interpolation processing is carried out the parts that back projection processes the CT image that obtains rebuilding.
According to one embodiment of present invention, wherein, described parts be used to carrying out pre-weighting processing comprise:
Be used in the situation that pending data for projection be from narrow detector obtain to this pending data for projection and from this narrow detector with string but be weighted average and with the parts of weighted mean as corresponding data for projection after weighting processing in advance at the data for projection that at least one detector of different rows obtains;
Be used in the situation that pending data for projection be leniently detector obtain will this pending data for projection directly as the parts of corresponding data for projection after weighting processing in advance.
According to one embodiment of present invention, wherein, described for to this pending data for projection and be weighted average parts from the data for projection that described at least one detector obtains and further comprise:
The parts of the corresponding weight coefficient of the data for projection that is used for determining being respectively used to this pending data for projection and obtains from described at least one detector; And
Being used for will this pending data for projection and multiply by separately weight coefficient, the parts of addition then from the data for projection that described at least one detector obtains.
According to one embodiment of present invention, wherein, the parts of the corresponding weight coefficient of described data for projection be used to determining to be respectively used to this pending data for projection and obtaining from described at least one detector are determined corresponding weight coefficient so that the data for projection that obtains from narrow detector has identical section curve with the data for projection that detector leniently obtains.
According to one embodiment of present invention, wherein, the parts of the corresponding weight coefficient of described data for projection be used to determining to be respectively used to this pending data for projection and obtaining from described at least one detector comprise: be used for calculating corresponding weight coefficient iteratively so that the parts that equate of the full width at half maximum of the slice direction sensitivity curve of the data for projection after pre-weighting is processed of narrow detector and wide detector.
In accordance with a further aspect of the present invention, provide a kind of computer program, it is configured to store the programmed instruction for carrying out on computer system, and described programmed instruction makes computer system carry out method as described in any one in claim 1-11.
Description of drawings
For to the more thorough understanding of present disclosure, below with reference to the following description of carrying out by reference to the accompanying drawings, in the accompanying drawings:
Fig. 1 is the schematic diagram that illustrates for the detector array of the CT equipment of embodiments of the invention;
Fig. 2 illustrates the schematic diagram that the merging in the contour interpolation method of prior art is processed;
Fig. 3 illustrates according to the pre-weighting processing in image rebuilding method of the present invention and the schematic diagram of interpolation processing step;
Fig. 4 A-4B is the schematic diagram that the how to confirm weight coefficient is shown;
Fig. 5 A-5B illustrates respectively the effect of the CT image that the image rebuilding method that utilizes prior art and image rebuilding method of the present invention obtain;
Fig. 6 A-6C illustrates respectively to utilize and carries out image rebuilding method that the prior art image rebuilding method of contour interpolation, the not contour interpolation of pre-weighted sum according to the present invention combine and according to of the present invention the use effect of the CT image that obtains of the image rebuilding method of contour interpolation not; And
Fig. 7 A-7B illustrates respectively the effect of a body CT image that obtains by the image rebuilding method of prior art and image rebuilding method of the present invention.
The specific embodiment
The below will describe specific embodiments of the invention in detail, but the present invention is not limited to following specific embodiment.
Fig. 1 shows the schematic diagram for the detector array of the CT equipment of embodiments of the invention.Just schematically show the row detector in the multiple row detector of z axle (being the rotating shaft of helical scanning) direction in Fig. 1.In fact, the detector of CT equipment can be multirow * multiple row detector.In Fig. 1, each detector in this row detector represents a detector row.As shown in Figure 1, detector array is listed in that to have different row on the z direction of principal axis high, and wherein the capable height of the detector row at the high narrower and two ends of the row of the detector row in the middle of the z direction of principal axis is wider.Detector with the high Δ h1 of narrower row can be called narrow detector, the detector that will have the high Δ h2 of wider row is called wide detector.But the detector array of Fig. 1 is a kind of example, and in fact the row of detector array is high can be other situation.
To carry out the initial data that the processing such as opto-electronic conversion, amplification, analog digital conversion can obtain CT scan from the data that detector collects, also referred to as scan-data or data for projection.For helical scanning, needed data for projection is carried out interpolation before carrying out back projection.At first the high inconsistent situation of row for detector usually merges processing in the prior art, is about to merge from the data for projection of several adjacent narrow detectors (in string), with the concordance of maintenance with the data of wide detector.As shown in Figure 2, the capable height of wide detector is high 2 times of the row of narrow detector, and the data for projection with two adjacent narrow detectors (in string) combines.Be equivalent to the data for projection set that collected by contour wide detector through the data for projection set that obtains after merging like this.Then, can carry out interpolation in the ranks to data for projection.Such interpolation method is called contour interpolation, namely first processes to obtain the data for projection of contour character to merging from the data for projection of contour detector not, and then carries out interpolation.Then the data for projection through interpolation processing is carried out back projection to obtain reconstructed image by matrix method, iterative method, filtered back projection's method or two-dimentional Fourier's reconstruction method.
The present invention adopts a kind of different image rebuilding method, and the method is compared the pseudo-shadow in removal of images better with said method.Image rebuilding method according to an embodiment of the invention will be described in detail belows.But in the following description, emphasis has been described the difference of the present invention and prior art, and known or more known treatment steps, do not do detailed description, in order to avoid obscure the present invention for those skilled in the art.
The present invention has introduced the treatment step of pre-weighting in image reconstruction process, and is different from the interpolation processing of contour interpolation based on this step.With reference now to Fig. 3,, it shows pre-weighting treatment step and interpolation processing step in image rebuilding method according to an embodiment of the invention.
The data for projection that obtains for never contour detector array (be detector have different row high), concrete pre-weighting treatment step is as follows: if pending data for projection obtains from narrow detector, to this pending data for projection and from this narrow detector with string but the data for projection that at least one detector different rows obtains be weighted on average, and with weighted mean as corresponding data for projection after pre-weighting processing; If pending data for projection leniently detector obtains, will the corresponding data for projection after pre-weighting is processed of the direct conduct of this pending data for projection.It is the identical slice direction sensitivity curve of data for projection that obtains with detector leniently for the data for projection that obtains from narrow detector is had that pre-weighting is like this processed, thereby makes the data that collect in all directions have concordance.
In a preferred embodiment, with this narrow detector with string but at least one detector in different rows refers to adjacent with this narrow detector and with the detector in string.In Fig. 3, data for projection P
m, P
n, P
oBe derived from narrow detector D
m, D
n, D
o, data for projection P
bDetector D comforts oneself
bP
bThe value P ' after pre-weighting is processed
bStill equal P
bP
mThe analog value P ' after pre-weighting is processed
mBe P
m, P
m-1(from D
mAdjacent and at D
mDetector D in row before
m-1), P
m+1(from D
mAdjacent and at D
mDetector D in row afterwards
m+1) weighted average of these three data for projection.Equally, P
nThe analog value P ' after pre-weighting is processed
nBe P
n, P
n-1(from D
nAdjacent and at D
nDetector D in row before
n-1), P
n+1(from D
nAdjacent and at D
nDetector D in row afterwards
n+1) weighted average of these three data for projection, P
oThe analog value P ' after pre-weighting is processed
oBe P
o, P
o-1(from D
oAdjacent and at D
oDetector D in row before
o-1), P
o+1(from D
oAdjacent and at D
oDetector D in row afterwards
o+1) weighted average of these three data for projection.
Can represent with following formula pre-weighting processing:
Wherein, P '
iFor to data for projection P
iThe data for projection that obtains after processing through pre-weighting, w
kBe weight coefficient, and
I, k are integer, P
i+k(k=1 or-1) be with from P
iThe detector that is derived from adjacent and with it at the data for projection with the detector in string.With w
kThe value data for projection that is defined as making the data for projection that obtains from narrow detector and detector leniently to obtain have identical section curve (slice profile).
Explain how to confirm weight coefficient w with reference to Fig. 4
kValue.In Fig. 4, with to the data for projection P in Fig. 3
nWhen carrying out pre-weighting processing, the weight coefficient of required calculating is that example describes.As mentioned above, P
nThe analog value P ' after pre-weighting is processed
nBe P
n, P
n-1(from D
nAdjacent and at D
nDetector D in row before
n-1), P
n+1(from D
nAdjacent and at D
nDetector D in row afterwards
n+1) weighted average of these three data for projection.As can be seen from Figure 3, D
n, D
n+1, D
n+1Be narrow detector.
Fig. 4 A is to from narrow detector D
nP
nWith the detector D that comforts oneself
bP
bThe value after pre-weighting is processed carry out the schematic diagram of convolution algorithm.In the first half of Fig. 4 A, the figure on the left side represents P
nPre-weighting process, i.e. P
n, P
n-1, P
n+1These three data for projection multiply by then addition of weight coefficient separately, and wherein three rectangles correspond respectively to this three data for projection, and rectangle wide is that the row of narrow detector is high, and the height of rectangle represents the size of the respective weight coefficient of data for projection.In the first half of Fig. 4 A, the figure on the right represents the convolution function for narrow detector.In the present embodiment owing to adopting linear interpolation, so this convolution function is the triangular wave function.The peak value of this function is 1, and width is high 2 times of the row of narrow detector.Symbol between convolution function and weighted mean " * " expression convolution algorithm symbol.In the latter half of Fig. 4 A, the figure on the left side represents P
bPre-weighting process, i.e. P
bMultiply by weight coefficient 1, wherein the rectangle in this figure wide is that the row of wide detector is high, and the height of rectangle represents P
bWeight coefficient 1.In the latter half of Fig. 4 A, the figure on the right represents convolution function for wide detector, and the peak value of this function is 1, and width is high 2 times of the row of wide detector.Equally, the symbol between convolution function and weighted mean " * " expression convolution algorithm symbol.Fig. 4 B is schematically illustrated through the resulting slice direction sensitivity curve of convolution algorithm.Because each weight coefficient is for the weighted average computing, so each weight coefficient sum should equal 1.Adjust iteratively the height of three rectangles in the left edge graph of Fig. 4 A the first half, i.e. the size of each weight coefficient can be so that P '
nSlice direction sensitivity curve and P '
bThe slice direction sensitivity curve have equal full width at half maximum (FWHM), each weighting coefficient values at this moment is namely suitable value.
In a preferred embodiment, also make in iterative process adjacent for the detector that is derived from pending data for projection and equal with its ratio at the respective weight coefficient of the data for projection that front detector and rear detector with string obtain after high half of row of detector add high half of the row of the detector that pending data for projection is derived from resulting and with high half of the row of front detector add high half of the row of the detector that pending data for projection is derived from resulting and ratio.Also can say, also to make ratio for the weight coefficient of the data for projection of front detector and the weight coefficient of the data for projection that is used for rear detector in iterative process be above-mentioned figure with the center of the rectangle of forward and backward detectors to the distance at the center of intermediate rectangular than inverse, we are called this relation the inverse relation of weight coefficient and distance.
For P
nPre-weighting process, carry out iterative computation with said method, the value that can draw corresponding each weight coefficient is:
W wherein
0Be pending data for projection P
nWeight coefficient, w
-1For from being positioned at and data for projection P
nThe detector D that is derived from
nIn adjacent previous row detector and and D
nAt the detector D with string
n-1The weight coefficient of data for projection, w
1For from being positioned at and D
nIn an adjacent rear row detector and and D
nAt the detector D with string
n-1The weight coefficient of data for projection.By top description as can be known, the value of each weight coefficient and data for projection is irrelevant, but the detector that is derived from the high relation of row wide, narrow detector, pending data for projection and adjacent with this detector and relevant in the type (being wide detector or narrow detector) with the detector in string.The value of each weight coefficient that the above determines is applicable to come from the pending data for projection of following such narrow detector: the front and back detector that this narrow detector is adjacent is all narrow detectors, and the capable height of narrow detector be in detector array the row of wide detector high 1/2nd.
For P
m, can determine each required weight coefficient by similar method.Be with the difference of top method, in three rectangles in the left edge graph of Fig. 4 A the first half, the width of rightmost rectangle should be adjusted into and wide detector D
m+1Row high corresponding; High half of row that the width of the initial point right-hand component of the triangular wave in the figure of Fig. 4 A the first half the right should be adjusted into wide detector add high half of the row of narrow detector resulting and, and the width of triangular wave initial point left-hand component is constant.By iterative calculation method recited above, can determine each weight coefficient and be:
Equally, these weight coefficients are applicable to come from the pending data for projection of following such narrow detector: the front detector that this narrow detector is adjacent be narrow detector then detector be wide detector, and the capable height of narrow detector be in detector array the row of wide detector high 1/2nd.
For P
o, can determine each required weight coefficient by similar method equally.Be with the difference of top method, in three rectangles in the left edge graph of Fig. 4 A the first half, the width of leftmost rectangle should be adjusted into and wide detector D
o-1Row high corresponding; High half of row that the width of the initial point left-hand component of the triangular wave in the figure of Fig. 4 A the first half the right should be adjusted into wide detector add high half of the row of narrow detector resulting and, and the width of triangular wave initial point right-hand component is constant.By iterative calculation method recited above, can determine each weight coefficient and be:
Equally, these weight coefficients are applicable to come from the pending data for projection of following such narrow detector: the front detector that this narrow detector is adjacent be wide detector then detector be narrow detector, and the capable height of narrow detector be in detector array the row of wide detector high 1/2nd.
Need to prove, the full width at half maximum that makes two slice direction sensitivity curves that the above mentions in describing equates not necessarily to instigate them definitely equal, also comprises making their approximately equals.
In superincumbent description, k=-1,0,1 is illustrated for example.But, those skilled in the art should be understood that, the value of k can be also other situation, for example, k can be from-2 to 2, at this moment still can determine suitable weighting coefficient values by iterative computation so that the slice direction sensitivity curve of the data for projection after the pre-weighting processing of narrow detector has with the slice direction sensitivity curve of the data for projection of wide detector the full width at half maximum that equates.In addition, the high relation of the row of wide detector and narrow detector also needs not to be the relation of 2 times, can be 3 times or other proportionate relationship.
Process through top pre-weighting, the data consistency in projection guaranteed, and also reduced the difference between projection, thereby helps to reduce the pseudo-shadow in reconstructed image.
Return to Fig. 3, after data for projection having been carried out above-mentioned pre-weighting processing, begin to carry out interpolation.As mentioned above, in the prior art, for from the data for projection of contour detector not, needed first to merge before interpolation.But, in the present invention, process owing to having carried out pre-weighting, therefore can need not to merge, ignore different rows between narrow detector and wide detector high and directly carry out interpolation in the ranks.
Through after interpolation processing, namely can carry out back projection to obtain reconstructed image to the data for projection after pre-weighted sum interpolation processing by the image reconstruction algorithm such as matrix method, iterative method, filtered back projection's method or two-dimentional Fourier's reconstruction method.
In the embodiment that describes, realized a kind of new image rebuilding method by pre-weighting being processed combine with not contour interpolation in the above.Experimental result shows, the pseudo-shadow in the CT image that obtains by such image rebuilding method is is effectively reduced or eliminated.
Fig. 5 A and 5B show respectively the effect of utilizing the CT image that two kinds of image rebuilding methods obtain.Fig. 5 A is corresponding to the prior art image rebuilding method that first merges, then carries out contour interpolation, and Fig. 5 B processes corresponding to pre-weighting according to the present invention the image rebuilding method that combines with not contour interpolation.Can find out, use the quality of the CT image that image rebuilding method of the present invention obtains higher, wherein the pseudo-shadow of windmill shape greatly reduces.
In addition, as another embodiment, also can dispense pre-weighting treatment step, and only use not contour interpolation processing, the different rows of namely initial data directly being carried out not contour interpolation processing and ignoring between narrow detector and wide detector is high, afterwards the data for projection after interpolation is carried out back projection with reconstructed image.
Fig. 6 A-C shows respectively the effect of the CT image that obtains by three kinds of image rebuilding methods.Fig. 6 A is corresponding to the prior art image rebuilding method that first merges, then carries out contour interpolation, and Fig. 6 B is corresponding to carrying out separately the not image rebuilding method of contour interpolation, and Fig. 6 C processes corresponding to pre-weighting the image rebuilding method that combines with not contour interpolation.Can find out, the pseudo-shadow in the CT image in Fig. 6 B has also greatly reduced, but owing to not having pre-weighting to process, the discordance of its data has been brought new pseudo-shadow-shadow.
Fig. 7 A and 7B illustrate respectively the effect of a body CT image that obtains by the image rebuilding method of prior art and image rebuilding method of the present invention.Fig. 7 A is corresponding to the prior art image rebuilding method that first merges, then carries out contour interpolation, and Fig. 7 B processes corresponding to pre-weighting according to the present invention the image rebuilding method that combines with not contour interpolation.Can find out, in the figure of Fig. 7 B, stepped pseudo-shadow greatly reduces.
The image rebuilding method that pre-weighting of the present invention is processed and not contour interpolation combines has adopted physically better sampling, can not affect the spatial resolution of z axle.This image rebuilding method not only reduces the pseudo-shadow in soft tissue area, can also reduce the pseudo-shadow in bone region.Image rebuilding method according to the present invention has been realized having improved resolution to having effective utilization of the narrow detector high than narrow row when reducing pseudo-shadow, and makes and can utilize larger pitch to scan, thereby can further improve scanning speed.And this image rebuilding method of the present invention can not introduced other pseudo-shadow, can not cause the deteriorated of other image quality factors such as resolution and noise yet.
Although the above-mentioned specific embodiments of the invention of having described by reference to the accompanying drawings, those skilled in the art can carry out various changes, modification and equivalent substitution to the present invention without departing from the spirit and scope of the present invention.Within these changes, modification and equivalent substitution all mean and fall into the spirit and scope that the claim of enclosing limits.
Claims (17)
1. method for reconstructing that is used for the helical scanned image of CT equipment, wherein said CT equipment comprises the multirow detector, and described multirow detector comprises having the high narrow detector of less row and have the high wide detector of larger row, and described method comprises:
The data for projection that obtains from described multirow detector is carried out pre-weighting process, so that the data for projection that obtains from narrow detector has the identical slice direction sensitivity curve of data for projection that obtains with detector leniently;
Data for projection after pre-weighting is processed directly carries out interpolation processing and the different rows ignored between narrow detector and wide detector is high; And
Data for projection after interpolation processing is carried out back projection process the CT image that obtains rebuilding.
2. method for reconstructing as claimed in claim 1, wherein, described pre-weighting is processed and is comprised each data for projection is carried out following operation:
If pending data for projection obtains from narrow detector, to this pending data for projection and from this narrow detector with string but the data for projection that at least one detector different rows obtains be weighted on average, and with weighted mean as corresponding data for projection after pre-weighting processing;
If pending data for projection leniently detector obtains, will the corresponding data for projection after pre-weighting is processed of the direct conduct of this pending data for projection.
3. method for reconstructing as claimed in claim 2, wherein, described to this pending data for projection and be weighted average step from the data for projection that described at least one detector obtains and further comprise:
The corresponding weight coefficient of the data for projection of determining to be respectively used to this pending data for projection and obtaining from described at least one detector; And
Multiply by separately weight coefficient, then addition with this pending data for projection and from the data for projection that described at least one detector obtains.
4. method for reconstructing as claimed in claim 2 or claim 3, wherein, the step of determining weight coefficient comprises determines corresponding weight coefficient so that the data for projection that obtains from narrow detector has identical section curve with the data for projection that detector leniently obtains.
5. method for reconstructing as claimed in claim 2 or claim 3, wherein, the step of determining weight coefficient comprises calculates corresponding weight coefficient iteratively so that the full width at half maximum of slice direction sensitivity curve and equating of wide detector of the data for projection after pre-weighting is processed of narrow detector.
6. method for reconstructing as claimed in claim 5, wherein, the data for projection that obtains from described at least one detector for adjacent from the detector that is derived from pending data for projection and with its data for projection that obtains at the detector with string.
7. method for reconstructing as claimed in claim 6, wherein, also make in described iterative process for adjacent from the detector that is derived from pending data for projection and equal with its ratio at the respective weight coefficient of the data for projection that front detector and rear detector with string obtain after high half of row of detector add high half of the row of the detector that pending data for projection is derived from resulting and with high half of the row of front detector add high half of the row of the detector that pending data for projection is derived from resulting and ratio.
8. method for reconstructing as claimed in claim 6, wherein, the row height of described wide detector is the high twice of row of described narrow detector, and wherein:
(1) if adjacent front detector row and the rear detector row of the detector that is derived from pending data for projection is narrow detector row,
(2) if the adjacent front detector row of the detector that is derived from pending data for projection is wide detector row, then detector row is narrow detector row,
And
(3) if the adjacent front detector row of the detector that is derived from pending data for projection is narrow detector row, then detector row is wide detector row,
Wherein, w
-1Be the weight coefficient of the data for projection that is used for obtaining at the detector with string from the detector that is arranged in described front detector row and is derived from pending data for projection, w
0For being used for the weight coefficient of described pending data for projection, w
1Weight coefficient for the data for projection that is used for obtaining at the detector with string from the detector that is arranged in described rear detector row and is derived from pending data for projection.
9. method for reconstructing as claimed in claim 1, wherein, described back projection processes and comprises: the data for projection by matrix method, iterative method, filtered back projection's method or two-dimentional Fourier's reconstruction method after to interpolation processing carries out back projection and processes the CT image that obtains rebuilding.
10. method for reconstructing as claimed in claim 1, wherein, described back projection processes and comprises:
Data for projection after interpolation processing is carried out convolutional filtering; And
The CT image of the data for projection of back projection after convolutional filtering to obtain rebuilding.
11. a method for reconstructing that is used for the spiral image of CT equipment, wherein said CT equipment comprises the multirow detector, and described multirow detector comprises having the high narrow detector of less row and have the high wide detector of larger row, and described method comprises:
The data for projection that obtains from described multirow detector is directly carried out interpolation processing and the different rows ignored between narrow detector and wide detector is high; And
Data for projection after interpolation processing is carried out back projection process the CT image that obtains rebuilding.
12. a reconstructing device that is used for the spiral image of CT equipment, wherein said CT equipment comprises the multirow detector, and described multirow detector comprises having the high narrow detector of less row and have the high wide detector of larger row, and described device comprises:
Be used for the data for projection that obtains from described multirow detector is carried out that pre-weighting is processed so that the data for projection that obtains from narrow detector row has the parts of the identical slice direction sensitivity curve of the data for projection that obtains with detector row leniently;
For directly carrying out interpolation processing, the data for projection after pre-weighting is processed ignores the high parts of different rows between narrow detector and wide detector; And
Be used for the data for projection after interpolation processing is carried out the parts that back projection processes the CT image that obtains rebuilding.
13. reconstructing device as claimed in claim 12, wherein, described parts be used to carrying out pre-weighting processing comprise:
Be used in the situation that pending data for projection be from narrow detector obtain to this pending data for projection and from this narrow detector with string but be weighted average and with the parts of weighted mean as corresponding data for projection after weighting processing in advance at the data for projection that at least one detector of different rows obtains;
Be used in the situation that pending data for projection be leniently detector obtain will this pending data for projection directly as the parts of corresponding data for projection after weighting processing in advance.
14. reconstructing device as claimed in claim 13 is wherein, described for to this pending data for projection and be weighted average parts from the data for projection that described at least one detector obtains and further comprise:
The parts of the corresponding weight coefficient of the data for projection that is used for determining being respectively used to this pending data for projection and obtains from described at least one detector; And
Being used for will this pending data for projection and multiply by separately weight coefficient, the parts of addition then from the data for projection that described at least one detector obtains.
15. reconstructing device as described in claim 13 or 14, wherein, the parts of the corresponding weight coefficient of described data for projection be used to determining to be respectively used to this pending data for projection and obtaining from described at least one detector are determined corresponding weight coefficient so that the data for projection that obtains from narrow detector has identical section curve with the data for projection that detector leniently obtains.
16. reconstructing device as described in claim 13 or 14, wherein, the parts of the corresponding weight coefficient of described data for projection be used to determining to be respectively used to this pending data for projection and obtaining from described at least one detector comprise: be used for calculating corresponding weight coefficient iteratively so that the parts that equate of the full width at half maximum of the slice direction sensitivity curve of the data for projection after pre-weighting is processed of narrow detector and wide detector.
17. a computer program, it is configured to store the programmed instruction for carrying out on computer system, and described programmed instruction makes computer system carry out method as described in any one in claim 1-11.
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