CN100453044C - CT beam sclerosis correcting method based on original projection sine diagram - Google Patents
CT beam sclerosis correcting method based on original projection sine diagram Download PDFInfo
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Abstract
The present invention relates to a CT beam sclerosis correcting method based on an original projection sinogram. The present invention comprises the following steps: (1) making trisubstituted CT scanning, and obtaining the original projection sinogram arranged into a matrix shape; (2) making the correction of dark current and discordance of the original projection sinogram; (3) searching the minimum value of each line pixel projection value of the original projection sinogram; (4) defining a group of positive real number correction coefficient of which the value is less than 1; (5) subtracting the product of the corresponding line minimum value obtained by the step (3) and the corresponding line correction coefficient obtained by the step (4) from the projection value of each line pixel of the projection sinogram and implementing projection beam hardening correction of all the lines; (6) feeding the corrected projection sinogram into a CT reconstructed dynamic library. The present invention does not need aforehand modeling scanning and calculation, and does not be limited by scanning objects and scanning conditions; the correction process is simple and real-time without a special correcting hardware.
Description
Technical field
The present invention relates to a kind of CT beam hardening correction method, particularly, belong to the CT technical field based on the CT beam hardening correction method of original projection sinogram.
Background technology
In the X ray CT system, x-ray source sends X ray, pass a certain cross section of object to be detected from different perspectives, the detector that is positioned over the radiographic source opposite is accepted in respective angles, then according to each angle ray decay in various degree, utilize certain algorithm for reconstructing and computer to carry out computing, reconstruct the ray line attenuation coefficient distribution map image in the detected cross section of object, thereby realize nondestructively reproducing the features such as Media density, composition and configuration of object in this cross section by reconstruction from projections imaging.
What CT algorithm for reconstructing hypothesis x-ray source sent is the monoenergetic spectrum X-ray beam.Actual CT system has polychrome power spectrum X-ray beam, and this hypothesis is not being met.When heterogeneous x ray bundle and matter interaction, more low-energy x-ray photon is preferentially by material absorbing, and the photon attenuation of higher-energy is less, along with the increase of transillumination thickness, the beam effective energy moves to the high-energy direction, the beam more difficult decay that becomes, more " firmly ", Here it is beam hardening.Beam hardening is rebuild to CT and is brought serious problems.Utilization is based on the algorithm for reconstructing of monochromatic rays hypothesis, and it is littler than actual value to rebuild the object line attenuation coefficient that obtains, and reconstructed image can produce the pseudo-shadow of evil mind (being also referred to as the pseudo-shadow of cup-shaped).These artefacts often cause pathological tissues such as tumor to be failed to pinpoint a disease in diagnosis medically; Industrial, then blind crack, defective such as loose are covered up.
Suppress the method for the pseudo-shadow of sclerosis, be called the beam hardening correction method.Beam hardening correction has been the research focus of international CT imaging field since 1975 always.At present, bearing calibration mainly is divided into monoenergetic and dual intensity two big classes.The dual intensity method is represented line attenuation coefficient with Compton scattering, photoelectric effect and section species distribution function, estimates monochromatic projection with the polychrome projection under twice different-energy, and then reaches gauged purpose.Because in operational complexity, this method seldom is used in engineering practice.The monoenergetic method only needs an object scanning, is easy to realize that practical application effect is also relatively good, has therefore obtained extensive studies.
The monoenergetic method is divided into pre-treatment and post processing two classes according to the difference of processing sequence.Pre-treating method is directly done correction to original projection sinogram, and then utilizes monochromatic algorithm for reconstructing to rebuild; Post-processing approach then at first utilizes monochromatic algorithm for reconstructing that original projection sinogram is rebuild, and then the image that reconstruction obtains is carried out hardening correcting.
The basic line of postprocessing correction method is: according to certain criterion, the image that reconstruction is obtained carries out threshold value to be cut apart, and determines hardened scanning angle and zone can take place; Then, in above-mentioned scanning angle and zone, utilize the re-projection technology, generating does not have the sclerosis projection, replaces the original projection sinogram corresponding data; At last, utilize monochromatic algorithm for reconstructing to rebuild again to proofreading and correct the back projection sinogram.It is consuming time that post-processing approach exist to calculate, shortcomings such as image information loss, though many post-processing approachs have appearred in the world, really can be for practical application also should consider pre-treating method.
The pre-treating method common itinerary is: by scanning some special die bodys, set up the hardening curve at certain detected object; According to certain criterion calculated correction function; According to this function projection sinogram is adjusted, finished hardening correcting.Yang Min etc., correction ray hardened in the CT reconstruct is studied, optical technology, 2003, Vol.29 (2): the fitting process that proposes among the 177-182. is typical pre-treatment beam hardening method, it proofreaies and correct thinking: under a certain testing conditions, with the polychrome beam material of the same race of different-thickness is carried out transillumination, set up the relation curve of polychrome beam transillumination data and transillumination thickness, again this curve is carried out match, from zero this curve is done tangent line then,, thereby set up the correction relationship of actual polychrome beam data and monochromatic beam data with the relation of this tangent line as monochromatic beam transillumination data and transillumination thickness thickness.Under certain condition, this method can produce calibration result preferably to single object of planting the material formation, but there is following defective in it: (1) correction program is loaded down with trivial details, at the different scanning object, need carry out modeling scanning and calculating separately; (2) the calibration model effectiveness depends on the condition of scanning, and condition changing need carry out modeling scanning and calculating again; (3) calibration model is affected by noise, proofreaies and correct the back signal noise ratio (snr) of image and descends; (4) being corrected image must be made of single material of planting.
Summary of the invention
Technology of the present invention is dealt with problems and is: at the above-mentioned shortcoming of present beam hardening correction method existence, a kind of CT beam hardening correction method based on original projection sinogram is provided, this method belongs to the beam hardening correction method of transmission-type X ray third generation CT, this method correction mass height, do not need to carry out in advance modeling scanning and calculating, not limited by the sweep object and the condition of scanning, and correction program is simple, real-time, does not need specific correction hardware.
Technical solution of the present invention: based on the CT beam hardening correction method of original projection sinogram, its characteristics are may further comprise the steps:
(1) carries out three generations's CT scan, obtain to be arranged in the original projection sinogram of matrix;
(2) dark current and the discordance of carrying out original projection sinogram proofreaied and correct;
(3) minima of each row pixel projection value of search projection sinogram;
(4) determine one group less than 1 arithmetic number correction coefficient;
(5) with the projection value of each row pixel of projection sinogram, deduct the product of the corresponding row minima and the corresponding row correction coefficient that step (4) obtains of step (3) acquisition, finish all row projection pencil sclerosis and proofread and correct;
(6) will proofread and correct the back projection sinogram and send into CT reconstruction dynamic base.
Principle of the present invention is based on true and two mathematical theorems of following three physics:
The physics fact 1: when beam hardening takes place when, at i projection angle, the intensity I that detector j gathers through object decay back ray
2(i is j) greater than ideal tensile strength I
1(i, j).(the I that is used to rebuild
0(i)/I
2(i, j)) will be less than real (I
0(i)/I
1(i, j)).Wherein, I
0(i) i projection angle of expression, undamped transmitted intensity.
The physics fact 2: when beam hardening took place, it is long more that beam passes the object path, and it is serious more to harden, and it is many more that the transmitted intensity that detector is accepted departs from ideal tensile strength.Available mathematical expression sublist is shown:
I
21(i，j)/I
22(i，j)＞I
11(i，j)/I
12(i，j)
I
21(i is j) for passing the object path than long time, the ideal ray intensity that detector is accepted;
I
12(i is j) for passing the object path more in short-term, the actual transmitted intensity that detector is accepted;
I
22(i is j) for passing the object path than long time, the actual transmitted intensity that detector is accepted;
The physics fact 3: same object section, under the different scanning angle, its decay total amount to ray is identical.Available mathematical expression sublist is shown:
N is the number of detector; M is the scanning angle number of divisions.
Mathematical theorem 1: establish A, B, C ∈ R
+, and A＞B＞(C+1)＞1, then there is following relation: ((A-C)/(B-C))＞(A/B).
Proof: by hypothesis AC＞BC is arranged, so ,-AC＜-BC, so, AB-AC＜AB-BC,
So A (B-C)＜B (A-C), so, A/B＜(A-C)/(B-C) is arranged;
Conclusion must be demonstrate,proved.
Mathematical theorem 2: establish A, B, C, D ∈ R+, and A＞B＞(C+1)＞1, then there is following relation in B＜D: ((A-C)/(B-C))/(A/B)＞((A-C)/(D-C))/(A/D).
Proof: by hypothesis DC＞BC is arranged, so ,-DC＜-BC, so, BD-BC＞BD-CD,
So AB (D-C)＞AD (B-C), so, B/A (B-C)＞D/A (D-C) is arranged
So, ((A-C)/(B-C))/(A/B)＞((A-C)/(D-C))/(A/D);
Conclusion must be demonstrate,proved.
Analyze the true and mathematical theorem of above-mentioned physics as can be known: the A in the above-mentioned theorem, B, D are considered as I in the actual projection
0(i), I
22(i, j), I
12(i, j), C is considered as a corrected value relevant with original projection, then mathematical theorem 1,2 hardening phenomenon that causes of the correcting physics fact 1,2 just in time.So, the reality projection of hardening is deducted a value relevant with original projection, just can approach the preferred view value preferably.Be familiar with in view of the above, it is as follows to propose bearing calibration of the present invention:
I
C(i，j)＝I
O(i，j)-K(i)×min(I
O(i，j))
Wherein, I
O(i, j) before the expression hardening correcting, under i the scanning angle, j the transmitted intensity signal that detector is gathered;
I
C(i, j) behind the expression hardening correcting, under i the scanning angle, j the transmitted intensity signal that detector is gathered;
Under i scanning angle of K (i) expression, the hardening correcting coefficient; Min () expression is got minima to the one dimension projection sequence.
Determine K (i) according to physics true 3, method is as follows:
Wherein, I
O(i, j) before the expression hardening correcting, under i the scanning angle, j the transmitted intensity signal that detector is gathered;
Max () expression is got maximum to one-dimension array;
C:[0.5 0.8] between constant, rule of thumb selected.
The present invention's advantage compared with prior art is as follows:
(1) the present invention determines each scanning angle correction coefficient separately owing to extract sclerosis information from the original projection of each scanning angle, so calibration model has higher effectiveness, and the correction mass height;
(2) trimming process only relates to the computings such as adding, subtract of original projection, so correction rate is higher, correction program is real-time;
(3) do not need to carry out in advance modeling scanning and calculating, not limited by the sweep object and the condition of scanning, do not need specific correction hardware, so proofread and correct more simple;
(4) correction does not need prior modeling, so it is little influenced by projection noise, the correction signal to noise ratio is higher.
Description of drawings
Fig. 1 is a hardening calibration method flow chart of the present invention;
Fig. 2 is a scanning object when only being made of a kind of material (aluminum), uses the projection sinogram and the filtered back projection's algorithm for reconstructing that do not carry out beam hardening correction, rebuilds the CT image that obtains;
Fig. 3 is a scanning object when only being made of a kind of material (aluminum), adopts projection sinogram and filtered back projection's algorithm for reconstructing after the present invention proofreaies and correct, rebuilds the CT image that obtains;
Fig. 4 is projection sinogram and the filtered back projection's algorithm for reconstructing after the ray hardened bearing calibration of match of the documents in the employing background technology is proofreaied and correct, and rebuilds the CT image that obtains;
Fig. 5 is that Fig. 3 and Fig. 4 reconstructed image corresponding row are rebuild the gray value comparison curves;
Fig. 6 is that scanning object is by three kinds of materials (aluminum, density 1.000g/cm
3Pure water, density 1.005g/cm
3Saline) when constituting, use the projection sinogram and the filtered back projection's algorithm for reconstructing that do not carry out beam hardening correction, rebuild the CT image that obtains;
Fig. 7 is that scanning object is by three kinds of materials (aluminum, density 1.000g/cm
3Pure water, density 1.005g/cm
3Saline) when constituting, use projection sinogram and filtered back projection's algorithm for reconstructing after the present invention proofreaies and correct, rebuild the CT image that obtains;
Fig. 8 is that Fig. 3 and Fig. 4 reconstructed image corresponding row are rebuild the gray value comparison curves.
The specific embodiment
As Fig. 1, concrete implementation step of the present invention is as follows:
(1) scanned object is positioned over three generations's CT scan system rotation inspection platform, guarantees that object is covered by fan-beam under arbitrary scanning angle;
(2) with the fan-beam ray that forms through collimation object is implemented transillumination, simultaneously, the inspection platform rotates at the uniform velocity continuously, the detector that is made of a plurality of detection channels that are arranged in linear array, cross the ray projection of object with the transmission of fixed sample speed continuous acquisition, obtain many group one-dimensional signals;
(3) when the inspection platform revolved three-sixth turn, detector stopped sampling, and inspection platform and radiographic source stop simultaneously, promptly finish three generations's CT scan one time;
(4) many groups one-dimensional signal that step (2) is obtained piles up, and is arranged in matrix, forms the original CT projection sinogram.Wherein, the data that on behalf of same detection channels, the string of matrix gather in 360 degree, the delegation of matrix represents under a certain scanning angle, the data that all detection channels are gathered;
(5) during no ray, (2), (3) and (4) method form the details in a play not acted out on stage, but told through dialogues projection set by step, and the details in a play not acted out on stage, but told through dialogues projection is averaged by row, obtain one dimension details in a play not acted out on stage, but told through dialogues projection array D;
(6) object is removed from scan table, guaranteed no any object between radiographic source and linear array detector;
(7) set by step (2), (3) and (4) method form the bright field projection, and the bright field projection is averaged by row, obtain one dimension bright field projection array L;
(8) L is deducted D, finish the bright field dark current correction, obtain L1;
(9) ask the meansigma methods of L1,, obtain one-dimension array U with meansigma methods each value divided by L1;
(10) the projection each row of data that step (4) is obtained deducts D, finishes dark current correction;
(11) the projection each row of data that step (10) is obtained multiply by U, finishes discordance and proofreaies and correct.
(12) there is one-dimension array A in the minima of each row pixel projection value of the projection sinogram obtained of search step (11) with them;
(13) each all pixel projection value of row of the projection sinogram obtained of calculation procedure (11) and, there is one-dimension array B in they;
(14) there is array B divided by array B maximum in each value of array B with the result;
(15) array B and array A corresponding data multiply each other, and there is array A in the result;
(16) all pixel projection values of the i with projection sinogram capable (i is the positive integer from 1 to N, and N is the total line number of projection sinogram) deduct array A i (i is the positive integer from 1 to N, and N is array A data sums) data;
(17) repeat above-mentioned steps (16), deduct last data of array A, form and proofread and correct the back projection sinogram up to all pixel projection values of last column of projection sinogram;
(18) above-mentioned projection sinogram is sent into CT and rebuild dynamic base.
Fig. 2-Fig. 5 has provided the concrete correction example that object to be detected only is made of a kind of material (aluminum).Fig. 2 rebuilds the CT image that obtains for using projection sinogram and the filtered back projection's algorithm for reconstructing that does not carry out beam hardening correction; Fig. 3 rebuilds the CT image that obtains for using projection sinogram and filtered back projection's algorithm for reconstructing of beam hardening correction of the present invention; Fig. 4 is projection sinogram and the filtered back projection's algorithm for reconstructing after the ray hardened bearing calibration of match of the documents in the employing background technology is proofreaied and correct, and rebuilds the CT image that obtains; Fig. 5 is that Fig. 3 and Fig. 4 corresponding row are rebuild grey scale curve relatively.Fig. 5 mid point is scribed ss the gray value of Fig. 2 the 256th row pixel; Heavy line is the gray value of Fig. 3 the 256th row pixel; Fine line is the gray value of Fig. 4 the 256th row pixel.Compare three curves as can be known, calibration result of the present invention is best.Calculate, the signal to noise ratio of Fig. 2, Fig. 3 and Fig. 4 is respectively: 24.9,38.6 and 12.4, show the present invention proofread and correct the back signal to noise ratio the highest.
Fig. 6-Fig. 8 has provided the concrete correction example that object to be detected is made of three kinds of materials (aluminum, the pure water of density 1.000g/cm3, the saline of density 1.005g/cm3).Fig. 6 rebuilds the CT image that obtains for using projection sinogram and the filtered back projection's algorithm for reconstructing that does not carry out beam hardening correction; Fig. 7 rebuilds the CT image that obtains for using projection sinogram and filtered back projection's algorithm for reconstructing of beam hardening correction of the present invention; Fig. 8 is that Fig. 6 and Fig. 7 corresponding row are rebuild grey scale curve relatively.Fig. 8 mid point is scribed ss the gray value of Fig. 6 the 256th row pixel; Heavy line is the gray value of Fig. 7 the 256th row pixel.Relatively two curves as can be known, the present invention is obvious to the beam hardening correction effect of the object that is made of multiple material.
Claims (4)
1, based on the CT beam hardening correction method of original projection sinogram, it is characterized in that comprising the following steps:
(1) carries out three generations's CT scan, obtain to be arranged in the original projection sinogram of matrix;
(2) dark current and the discordance of carrying out original projection sinogram proofreaied and correct;
(3) minima of each row pixel projection value in the projection sinogram that after overcorrect, obtains of search step (2);
(4) determine one group less than 1 arithmetic number correction coefficient;
(5) projection value of each row pixel of the projection sinogram that step (2) is obtained after overcorrect deducts the product of the corresponding row correction coefficient that corresponding row minima that step (3) obtains and step (4) obtain, and finishes all row projection pencil sclerosis corrections;
(6) projection sinogram is sent into CT and is rebuild dynamic base after the correction that step (5) is obtained.
2, the CT beam hardening correction method based on original projection sinogram according to claim 1, it is characterized in that: described step is carried out three generations's CT scan in (1), and the step that acquisition is arranged in the original projection sinogram of matrix is:
(a) scanned object is positioned over three generations's CT scan system rotation inspection platform, guarantees that object is covered by fan-beam under arbitrary scanning angle;
(b) with the fan-beam ray that forms through collimation object is implemented transillumination, simultaneously, the inspection platform rotates at the uniform velocity continuously, the detector that is made of a plurality of detection channels that are arranged in linear array, cross the ray projection of object with the transmission of fixed sample speed continuous acquisition, obtain many group one-dimensional signals;
(c) when the inspection platform revolved three-sixth turn, detector stopped sampling, and inspection platform and radiographic source stop simultaneously, promptly finish three generations's CT scan one time;
(d) many groups one-dimensional signal that step (b) is obtained piles up, and is arranged in matrix, forms the original CT projection sinogram, wherein, the data that on behalf of same detection channels, the string of matrix gather in 360 degree, the delegation of matrix represents under a certain scanning angle, the data that all detection channels are gathered.
3, the CT beam hardening correction method based on original projection sinogram according to claim 1 is characterized in that: the dark current and the gauged step of discordance of carrying out original projection sinogram in the described step (2) are:
(a) scanned object is positioned over three generations's CT scan system rotation inspection platform, guarantees that object is covered by fan-beam under arbitrary scanning angle; During no ray, the inspection platform rotate at the uniform velocity continuously, by the detector that a plurality of detection channels that are arranged in linear array constitute, with the continuous acquisition projection under no ray situation of fixed sample speed, organizes one-dimensional signals obtain more; When the inspection platform revolved three-sixth turn, detector stopped sampling, and the inspection platform stops; The many groups one-dimensional signal that obtains is piled up, be arranged in matrix, form the details in a play not acted out on stage, but told through dialogues projection, wherein, the data that on behalf of same detection channels, the string of matrix gather in 360 degree, the delegation of matrix represents under a certain scanning angle, the data that all detection channels are gathered; The details in a play not acted out on stage, but told through dialogues projection is averaged by row, obtain one dimension details in a play not acted out on stage, but told through dialogues projection array D;
(b) object is removed from scan table, guaranteed no any object between radiographic source and linear array detector;
(c) with the fan-beam ray that forms through collimation detector is implemented irradiation, simultaneously, the inspection platform rotates at the uniform velocity continuously, and the detector by a plurality of detection channels that are arranged in linear array constitute with fixed sample speed continuous acquisition ray projection, obtains many group one-dimensional signals; When the inspection platform revolved three-sixth turn, detector stopped sampling, and inspection platform and radiographic source stop simultaneously; The many groups one-dimensional signal that obtains is piled up, be arranged in matrix, form the bright field projection, wherein, the data that on behalf of same detection channels, the string of matrix gather in 360 degree, the delegation of matrix represents under a certain scanning angle, the data that all detection channels are gathered; The bright field projection is averaged by row, obtain one dimension bright field projection array L;
(d) L is deducted D, finish the bright field dark current correction, obtain L1;
(e) ask the meansigma methods of L1,, obtain one-dimension array U with meansigma methods each value divided by L1;
(f) the projection each row of data that step (1) is obtained deducts D, finishes dark current correction;
(g) each row of data of projection multiply by U behind the dark current correction that step (f) is obtained, and finishes discordance and proofreaies and correct.
4, the CT beam hardening correction method based on original projection sinogram according to claim 1 is characterized in that, the step of beam hardening correction is in described step (3), (4) and (5):
(a) there is one-dimension array A in the minima of each row pixel projection value of the projection sinogram obtained of search step (2) with them;
(b) each all pixel projection value of row of the projection sinogram obtained of calculation procedure (2) and, there is one-dimension array B in they;
(c) there is array B divided by array B maximum in each value of array B with the result;
(d) array B and array A corresponding data multiply each other, and there is array A in the result;
(e) capable all the pixel projection values of i with projection sinogram deduct i data of array A, and wherein, i is the positive integer from 1 to N, and N is the total line number of projection sinogram;
(f) repeating step (e) deducts last data of array A up to all pixel projection values of last column of projection sinogram, forms to proofread and correct the back projection sinogram.
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| CN103445803B (en) * | 2013-09-09 | 2015-09-30 | 深圳先进技术研究院 | Based on CT system beam hardening removing method and the system thereof of sinogram |
| CN104700377B (en) * | 2013-12-06 | 2019-07-30 | Ge医疗系统环球技术有限公司 | Obtain the method and apparatus that the beam hardening correction coefficient of beam hardening correction is carried out to computed tomography data |
| US10657679B2 (en) * | 2015-03-09 | 2020-05-19 | Koninklijke Philips N.V. | Multi-energy (spectral) image data processing |
| WO2020077592A1 (en) * | 2018-10-18 | 2020-04-23 | 清华大学 | Ct system energy spectrum inconsistency correction method |
| CN109887048B (en) * | 2019-01-30 | 2023-06-09 | 湖北锐世数字医学影像科技有限公司 | PET scattering correction method, image reconstruction device and electronic equipment |
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| 基于多色系统参数的CT硬化校正算法. 孙少华，高文焕，张丽，陈志强.清华大学学报（自然科学版），第42卷第12期. 2002 * |
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