A dual-energy CT image reconstruction method, system and computer-readable storage medium

Abstract

The present invention relates to the field of medical imaging, and in particular to a dual-energy CT image reconstruction method, system and computer-readable storage medium. The method comprises the following steps: obtaining the light signal Iair received by the detector when scanning air and scanning a patient when the tube voltage values ​​are KV1 and KV2 respectively based on the CT imaging system; kv1 、Iair kv2 and I kv1 ,I kv2 According to Iair kv1 、Iair kv2 and I kv1 ,I kv2 Calculate the patient's absorption value P at tube voltage values ​​KV1 and KV2 kv1 and P kv2 ; The P kv1 and P kv2 Corrected to monochromatic light P1 and P2; after polynomial decomposition of P1 and P2, the absorption values ​​P of two basic substances, water and iodine, are obtained respectively. water and P iodine According to P water and P iodine Reconstruct the base material map and calculate the required energy spectrum image based on the base material map. This calculation formula can ensure the accuracy of dual-energy imaging in the pure water part and avoid the situation where two large positive and negative water iodine components cancel each other out in the pure air part.

Description

Technical Field

[0001] The present invention relates to the field of medical imaging, and in particular to a dual-energy CT image reconstruction method, system and computer-readable storage medium. Background Art

[0002] The main components of the third-generation CT system include Tube, Collimator, and Detector. The X-ray tube emits X-rays, which are limited by the beam limiter to form a conical beam. The conical beam is irradiated on the detector, converted into an electrical signal by the detector, and converted into digital information by the data acquisition and conversion unit and stored in the image processing system. The image processing system generates an image displayed on the monitor through a series of correction algorithms and image reconstruction algorithms. In terms of cost and technical level, mainstream detectors use a detector formed by many detector modules arranged on an arc or polygonal surface. A matrix formed by regularly arranging a detector unit in each detector module.

[0003] In the prior art, the main methods of spectral CT include 1) double-layer detectors: double-layer detectors are usually two types of detectors attached to both sides of a circuit substrate. The layer close to the X-ray focus can absorb low-energy X-rays, but not high-energy X-rays. The other layer of detectors on the circuit substrate can absorb the remaining high-energy X-rays. The two layers of detectors can be synthesized and decomposed to generate spectral CT images. 2) Single tube high and low voltage switching: a high-voltage generator that can instantly and quickly switch the tube KV is used, using one KV value for each odd sampling and another KV value for the even sampling. The spectral CT image is generated by synthesizing and decomposing the data corresponding to the two KVs. 3) Dual tubes using different KVs: two tubes 90 degrees apart are exposed simultaneously using different KV values, and the two detectors corresponding to the tubes receive data simultaneously. The data of the two detectors are reconstructed to generate spectral CT imaging. 4) Photon counting detector: it can count X-ray photons in different X-ray energy intervals to generate sampling data of different energy intervals, and further reconstruct to generate spectral CT images. 5) Changing the X-ray filtering method to change the energy spectrum: By changing the X-ray filtering method to mechanically change the energy spectrum, different sampling times can be used to obtain sampling data corresponding to different energy spectra. 6) Two half-circle CT scanning methods: Two half-circle scans are performed using two different KVs.

[0004] In the above-mentioned various energy spectrum CT methods, in actual image reconstruction, the projection data obtained by high and low energy scanning are generally converted into a combination of Compton scattering and photoelectric effect, or into a combination of two base substances such as water and iodine or water and calcium. In the existing calculation formula, after a series of conversions and corrections, the calculation formula is obtained as follows:

[0005]

[0006]

[0007] The polynomial coefficient C nm and D nm One method to obtain these coefficients is to input the spectrum of the X-ray source, the energy spectrum response curve of the detector, and the energy spectrum responses of various filters on the ray path into the physical model, and add various length combinations of water and iodine substances to the scanning path for simulation. The absorption (P water，j , P iodine，j ), j=1,2... can be obtained, and then the coefficients Cnm and Dnm are obtained by fitting the above formula. However, there is a problem with this decomposition method. When the scanned object is pure water, due to D nm The existence of fitting errors cannot guarantee that the calculated iodine absorption P iodine After beam hardening, the P1 and P2 of pure water are equal, and C nm The fitting error will inevitably lead to That is, the calculated water absorption is not equal to the actual water absorption. In addition, when the density of the scanned object is small and close to the air density, the existence of fitting error will cause P water and P iodine These are numbers with opposite signs and close absolute values.

[0008] In summary, the technical problem actually solved by the present invention is that the prior art uses unconstrained polynomial fitting in dual-energy CT-based material decomposition. Due to the measurement and fitting deviation, it cannot guarantee that the iodine content of pure water material is completely zero, and therefore, it cannot guarantee the accuracy of the water material itself when scanning pure water. Summary of the invention

[0009] In order to overcome the above technical defects, the object of the present invention is to provide a dual-energy CT image reconstruction method, system and computer-readable storage medium. In the case of a pure water phantom, P1 and P2 are equal, so P iodine is zero, and P water =P1=P2.

[0010] The present invention discloses a dual-energy CT image reconstruction method, comprising the steps of:

[0011] S100: Based on the CT imaging system, the light signal Iair received by the detector when scanning the air and scanning the patient is obtained when the tube voltage value is KV1 and KV2 respectively. kv1 、Iair kv2 and I kv1 ,I kv2;

[0012] S200: According to Iair kv1 、Iair kv2 and I kv1 ,I kv2 Calculate the patient's absorption value P at tube voltage values ​​KV1 and KV2 kv1 and P kv2 ;

[0013]

[0014]

[0015] S300: P kv1 and P kv2 Corrected to monochromatic light P1 and P2;

[0016] P kv1 and P kv2 The calculation formula corrected for monochromatic light P1 and P2 is:

[0017]

[0018]

[0019] Among them A n and B n are the polynomial coefficients obtained after correction.

[0020] S400: After polynomial decomposition of P1 and P2, the absorption values ​​P of the two base substances water and iodine are obtained respectively. water and P iodine ;

[0021] S500: According to P water and P iodine Reconstruct the base material map and calculate the required energy spectrum image based on the base material map.

[0022] Preferably, the absorption values ​​P of the two base substances water and iodine are obtained respectively according to P1 and P2 through polynomials. water and P iodine The calculation formula is:

[0023]

[0024]

[0025] Preferably, the power exponents a, b and the orders of fitting n, m and the coefficients Fnm and Gnm in the calculation formula are determined according to the principle of minimum fitting deviation.

[0026] Preferably, according to P water and Piodine When reconstructing the base material graph, an approximate reconstruction algorithm or an analytical reconstruction algorithm of FBP and / or FDK is used.

[0027] Preferably, according to P water and P iodine When reconstructing the base material map, the base material map can also be reconstructed through an iterative reconstruction algorithm.

[0028] In view of this, a second object of the present invention is to provide a dual-spectrum image reconstruction system, comprising a processor and a memory connected to the processor.

[0029] The memory stores a dual-energy spectrum image reconstruction program, and when the dual-energy spectrum image reconstruction is executed by the processor, the dual-energy CT image reconstruction method described above is implemented.

[0030] In view of this, a third object of the present invention is to provide a computer-readable storage medium, which stores a computer program, and when the computer program is executed by a processor, it implements the dual-energy CT image reconstruction method as described above.

[0031] After adopting the above technical solution, compared with the prior art, the beneficial effect of the present invention is that the operation constraint is increased during the energy spectrum decomposition to reduce the fitting deviation; in the case of the pure water phantom, P1 and P2 are equal, thus ensuring P iodine is zero, and P water =P1=P2, and can ensure P water ≥0, when a material with a density close to that of air is scanned, there is no cancellation of the positive and negative absorption of water and iodine. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic diagram of a dual-energy CT image reconstruction method of the present invention;

[0033] Figure 2 The figure is a schematic diagram of the layout of a CT system for a dual-energy CT image reconstruction method of the present invention. DETAILED DESCRIPTION

[0034] The advantages of the present invention are further described below in conjunction with the accompanying drawings and specific embodiments.

[0035] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present disclosure. Instead, they are merely examples of devices and methods consistent with some aspects of the present disclosure as detailed in the appended claims.

[0036] The terms used in this disclosure are for the purpose of describing specific embodiments only and are not intended to limit the disclosure. The singular forms of "a", "said" and "the" used in this disclosure and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0037] It should be understood that although the terms first, second, third, etc. may be used in the present disclosure to describe various information, such information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the present disclosure, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0038] In the description of the present invention, it is necessary to understand that the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0039] In the description of the present invention, unless otherwise specified and limited, it should be noted that the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal connection between two components. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances.

[0040] In the following description, the suffixes such as "module", "component" or "unit" used to represent elements are only used to facilitate the description of the present invention, and have no specific meanings. Therefore, "module" and "component" can be used interchangeably.

[0041] See also Figure 1 As shown, this embodiment provides a dual-energy CT image reconstruction method, comprising the steps of:

[0042] S100: Based on the CT imaging system, the light signal Iair received by the detector when scanning the air and scanning the patient is obtained when the tube voltage value is KV1 and KV2 respectively. kv1 、Iair kv2 and I kv1 ,Ikv2 ;

[0043] S200: According to Iair kv1 、Iair kv2 and I kv1 ,I kv2 Calculate the patient's absorption value P at tube voltage values ​​KV1 and KV2 kv1 and P kv2 ;

[0044] S300: P kv1 and P kv2 Corrected to monochromatic light P1 and P2;

[0045] S400: After polynomial decomposition of P1 and P2, the absorption values ​​P of the two base substances water and iodine are obtained respectively. water and P iodine ;

[0046] S500: According to P water and P iodine Reconstruct the base material map and calculate the required energy spectrum image based on the base material map.

[0047] It should be noted that in the above step S100, Iair kv1 、Iair kv2 They represent the light signal amounts obtained when scanning the air with tube voltage values ​​KV1 and KV2, respectively. Figure 2 As shown in the figure, when the tube emits X-rays, it passes through the beam limiter to form a cone beam, penetrates the air and irradiates the detector. The detector will receive a signal. When the tube voltage value of the tube is KV1, the light signal received by the detector after the X-rays pass through the air is Iair kv1 When the tube voltage of the tube is KV2, the amount of light signal received by the detector after the X-ray passes through the air is Iair kv2 I kv1 ,I kv2 They represent the amount of light signal obtained when scanning a patient with tube voltage values ​​KV1 and KV2, respectively. Figure 2 As shown in the figure, when the tube emits X-rays, it passes through the beam limiter to form a cone beam, penetrates the patient and irradiates the detector. The detector will receive a signal. When the tube voltage value of the tube is KV1, the light signal received by the detector after the X-ray passes through the patient is I kv1 When the tube voltage of the tube is KV2, the amount of light signal received by the detector after the X-ray passes through the patient is I kv2 .

[0048] It should be noted that in the above step S200, according to Iair kv1 、Iair kv2 and Ikv1 ,I kv2 Calculate the patient's absorption value P at tube voltage values ​​KV1 and KV2 kv1 and P kv2 , the calculation formula is:

[0049]

[0050]

[0051] It should be noted that in the above step S300, since the X-rays emitted by the tube are not monochromatic light, but a combination of X-rays composed of several wavelengths, beam hardening occurs when scanning under tube voltage values ​​KV1 and KV2. Therefore, the calculated absorption P kv1 and P kv2 The absorption values ​​P1 and P2 corrected for beam hardening are calculated as follows:

[0052]

[0053]

[0054] It should be noted that the calculation of A in formulas (5) and (6) is n B n are the polynomial coefficients obtained after calibration.

[0055] It should be noted that in the above step S400, the absorption values ​​P of the two base substances water and iodine are obtained respectively after polynomial decomposition of P1 and P2. water and P iodine The calculation formula is:

[0056]

[0057]

[0058] It should be noted that a and b in the above calculation formulas (7) and (8) can take different values ​​according to the exact length of the fitting. nm and G nm It can be fitted by theoretical simulation or experimental measurement. For example, in a special case, a = 1, b = 1 can be taken, and the calculation formula can ensure that P water ≥0, when a material with a density close to that of air is scanned, there is no cancellation of the positive and negative absorption of water and iodine.

[0059] It should be noted that the power exponents a, b and the orders of fitting n, m in formulas (7) and (8) are determined based on the principle that the power exponents a, b and the orders of fitting n, m are minimized under the premise of minimizing the fitting deviation.

[0060] It should be noted that in the above step S500, according to P water and P iodine When reconstructing the base material graph, the base material graph is calculated using an approximate reconstruction algorithm or an analytical reconstruction algorithm based on FBP and / or FDK, or through an iterative reconstruction algorithm.

[0061] When implemented, the details are as follows:

[0062] The coefficients of the energy spectrum decomposition formula are calculated by theoretical simulation method and calculation formulas (7) and (8) to obtain F nm and G nm ;

[0063] The absorption P under two energy spectra can be obtained by any of the two CT scanning methods using a double-layer detector and two more than half-circle CT scanning methods. kv1 and P kv2 ;

[0064] Beam hardening correction is performed by calculating equations (5) and (6) to obtain P1 and P2;

[0065] After energy spectrum decomposition by using equations (7) and (8), we can get P water and P iodine ;

[0066] The base material map is reconstructed using an approximate reconstruction algorithm based on FBP, FDK, an analytical reconstruction algorithm, or an iterative reconstruction algorithm, and the required energy spectrum image is calculated based on the base material map.

[0067] It should be noted that the embodiments of the present invention have better practicability and do not impose any form of limitation on the present invention. Any technician familiar with the field may use the technical content disclosed above to change or modify it into an equivalent effective embodiment. However, any modification or equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A dual-energy CT image reconstruction method, characterized in that: Includes steps: S100: Based on the CT imaging system, the light signal Iair received by the detector when scanning the air and scanning the patient is obtained when the tube voltage value is KV1 and KV2 respectively. kv1 、Iair kv2 and I kv1 ,I kv2 ; S2 00: According to the Iair kv1 、Iair kv2 and I kv1 ,I kv2 Calculate the patient's absorption values ​​Pkv1 and Pkv2 at tube voltage values ​​KV1 and KV2 kv2 ; S300: The P kv1 and P kv2 Corrected to monochromatic light P1 and P2; S400: Obtaining absorption values ​​P of two base substances, water and iodine, respectively, after polynomial decomposition of P1 and P2 water and P iodine ; S500: According to the P water and P iodine Reconstructing a base material map, and calculating a required energy spectrum image according to the base material map; According to Iair kv1 、Iair kv2 and I kv1 ,I kv2 Calculate the patient's absorption value P at tube voltage values ​​KV1 and KV2 kv1 and P kv2 The calculation formula is: The P kv1 and P kv2 The calculation formula corrected for monochromatic light P1 and P2 is: According to P1 and P2, the absorption values ​​P of the two base substances water and iodine are obtained through polynomial calculation. water and P iodine The calculation formula is:

2. The dual-energy CT image reconstruction method according to claim 1, characterized in that: The power exponents a and b in the calculation formula and the orders of fitting n and m are determined by the principle of minimum fitting deviation.

3. The dual-energy CT image reconstruction method according to claim 1, characterized in that: According to the P water and P iodine When reconstructing the base material graph, an approximate reconstruction algorithm or an analytical reconstruction algorithm of FBP and / or FDK is used.

4. The dual-energy CT image reconstruction method according to claim 1, characterized in that: According to the P water and P iodine When reconstructing the base material graph, the base material graph is reconstructed through an iterative reconstruction algorithm.

5. A dual-energy image reconstruction system, characterized in that: comprising a processor, and a memory connected to the processor, The memory stores a dual-energy image reconstruction program, and when the dual-energy image reconstruction is executed by the processor, the dual-energy CT image reconstruction method according to any one of claims 1 to 4 is implemented.

6. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the dual-energy CT image reconstruction method according to any one of claims 1 to 4 is implemented.

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