A new type of spectral CT implementation and correction method

Abstract

The present invention discloses a new type of energy spectrum CT implementation and correction method, including an anode target and a photon counting detector unit channel, the anode target is composed of two different materials distributed periodically in an angular direction along the rotation center of the anode target, the two anode target materials can respectively excite two types of X-rays with large energy spectrum differences under the bombardment of electrons, and at each collection time interval, the two types of X-rays with large energy spectrum differences are mixed through different energy spectrum mixing ratios, thereby outputting different energy spectrum rays, and can realize the collection of different energy rays at two or several adjacent collection time intervals. The photon counting detector unit channel is used as a reference channel to realize energy spectrum correction. The present invention uses a specially designed anode target, does not require a flying focus mode, and does not require two sets of reconstruction geometry to realize energy spectrum CT. At the same time, the designed anode target can quantitatively change the energy ratio of the ray energy spectrum by setting the position of the focus in the Y direction.

Description

Technical Field

[0001] The present invention relates to the field of medical imaging technology, and more specifically to an implementation mode and correction method of a novel energy spectrum CT. Background Art

[0002] Dual-energy computed tomography (CT) has a very high clinical application value and is currently a hot research topic in the field of CT. Dual-energy CT can provide richer material information than conventional CT by using the different attenuation coefficients of materials in X-rays of different energies, thereby improving image quality.

[0003] The current dual energy provision methods mainly include:

[0004] 1) Double-layer detectors. Double-layer detectors are usually made by attaching two types of detectors on both sides of a circuit board. 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 board can absorb the remaining high-energy X-rays. The two layers of detectors can be synthesized and decomposed to generate spectral CT images.

[0005] 2) Single tube high and low voltage switching. A high voltage generator that can switch the tube KV instantly is used. One KV value is used for each odd-numbered sample and another KV value is used for each even-numbered sample. The energy spectrum CT image is generated by synthesizing and decomposing the data corresponding to the two KVs.

[0006] 3) Dual tubes use different KVs. Two tubes 90 degrees apart use different KV values ​​to expose simultaneously, and the two detectors corresponding to the tubes receive data simultaneously. The data from the two detectors are reconstructed to generate spectral CT imaging.

[0007] 4) Photon counting detector: It can count X-ray photons in different X-ray energy intervals to generate sampling data in different energy intervals, and further reconstruct energy spectrum CT images.

[0008] 5) Change the X-ray filtering method to change the energy spectrum. By changing the X-ray filtering method to change the energy spectrum, sampling data corresponding to different energy spectra are obtained at different sampling times.

[0009] 6) Two half-circle CT scanning methods. Two half-circle scans are performed using two different KVs.

[0010] 7) Anode targets made of multiple materials. The anode target is composed of several different materials according to a certain design. The electron beam bombards different materials corresponding to different positions, generating X-rays with different energy spectra.

[0011] Among the above methods, the detection efficiency of method 1 is relatively low. The manufacturing costs of methods 2, 3 and 4 are high. The usual way to change the filter in method 5 is to set different filters on different X-ray beams at the flying focus, and realize dual energy through the flying focus. Method 6 is easily affected by motion artifacts. Method 7 requires a specially designed anode target, which is currently a non-mainstream method. The realization of dual energy is generally similar to method 5, and is also generated by controlling the flying focus. Methods 5 and 7 generally require the cooperation of the flying focus function to realize the generation of multi-energy rays, and the flying focus requires different reconstruction geometry. Some dual-energy reconstruction methods require that the reconstruction geometric positions of the two sets of energy rays should not be too different.

[0012] For example, patent CN109787494B proposes a voltage switching circuit and dual-energy CT, which realizes the output of dual-energy rays by increasing the voltage switching speed; patent CN101346034A proposes a dual-energy or multi-energy electrostatic field electron acceleration device and method that can be realized in a tube, which designs two cathode focusing rings in the tube, and generates rays of different energies through different cathode excitation. The high-voltage generator or tube containing dual cathode focusing rings required by the above two patents has high manufacturing costs.

[0013] Patent CN205508764U designs a multi-anode X-ray source, each of which is composed of a fan-shaped block. The fan-shaped blocks of multiple anode targets are complementary and nested into a combined anode target. The direction of the electron beam is changed by controlling the control circuit so that the electron beam is irradiated to each anode in turn, thereby realizing the generation of multi-energy rays.

[0014] Patent CN101175440A designs an anode target with different materials distributed in layers in the Z direction. Its dual energy realization form is to switch the focus position in the Z direction at high speed and continuously through the flying focus, and its focus position corresponds to the position of one material, thereby realizing dual energy emission.

[0015] Patent CN110477943A proposes a device that realizes dual-energy CT using a flying focus method. This patent realizes the dual-energy ray output of the flying focus by setting an X-ray filter on any X-ray beam of the flying focus. Patent CN110974275A proposes a device and method for realizing dual-energy scanning by flying focus switching and X-ray filter, wherein the X-ray filter is provided with periodically distributed slits, and through the flying focus mode, the rays emitted from different focal points pass through the slits and filters of the X-ray filter respectively, thereby achieving the purpose of dual-energy CT scanning. Both of the above patents realize dual-energy scanning by setting different filters in the ray beam lines corresponding to the two focal points through the flying focus mode. Summary of the invention

[0016] In view of the deficiencies in the prior art, the present invention provides a novel implementation method and correction method for spectral CT. Through a specially designed anode target, there is no need for a flying focus mode and two sets of reconstruction geometries for the implementation method of spectral CT. At the same time, the designed anode target can quantitatively change the energy proportion of the ray energy spectrum by setting the position of the focus in the Y direction.

[0017] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a new implementation mode and correction method of energy spectrum CT, including an anode target and a photon counting detector unit channel, the anode target is composed of two different materials and is periodically distributed in an angular direction along the rotation center of the anode target, the anode target is used to collect two different energy spectrum rays at intervals in the collection time sequence, the two anode target materials can respectively excite two X-rays with large energy spectrum differences under the bombardment of electrons, at each collection time interval, the two X-rays with large energy spectrum differences are mixed through different energy spectrum mixing ratios, thereby outputting different energy spectrum rays, which can realize the collection of different energy rays at two or more adjacent collection time intervals, the photon counting detector unit channel is used as a reference channel, and the energy mixing ratio of the mixed energy spectrum rays collected each time is calculated, thereby realizing energy spectrum correction.

[0018] Within one period of the anode target in the angular direction, the shape distribution of the two materials is not specified and can be fan-shaped, triangular, square, circular, or prismatic.

[0019] The photon counting detector unit channel is installed at a position where it can receive exposure radiation, such as the edge of a conventional energy integrating detector, the edge of a collimator opening, or inside a tube.

[0020] A special dedicated filter is set on the optical path of the photon counting detector unit channel receiving the ray to weaken the signal collected by the reference channel and avoid saturation of the collected signal data.

[0021] The special dedicated filter for the reference channel of the photon counting detector can be installed at any position on the optical path of the reference channel receiving the radiation, such as directly on the photon counting detector channel.

[0022] The correction method using real-time calculation of mixed energy ratio is as follows:

[0023] During clinical scanning, the reference channel of the photon counting detector records the energy spectrum curve of each acquisition time interval t in real time. , and the energy spectrum curve for A one-dimensional vector with the following relationship: ,

[0024] in, is the energy spectrum at the reference channel position at the acquisition time interval t The energy ratio, is the energy spectrum at the reference channel position at the acquisition time interval t The energy ratio of

[0025] The mixed energy ratio at the collection time interval t is calculated by solving the equation group by linear fitting. and , then the overall mixed energy spectrum for the current acquisition time interval t can be calculated by : .

[0026] The correction method using the advance calculation of the mixed energy ratio is as follows:

[0027] Before the clinical scan, the gantry enters the rotation state in advance and performs several pre-scans with a lower dose exposure. After the scan, the gantry continues to rotate, and the rotation sequence of the gantry is recorded from the first pre-scan, and the clinical scan phase begins at the same time;

[0028] During the above-mentioned pre-scanning, the reference channel of the photon counting detector collects the corresponding energy spectrum curve data. Then, according to the process of the above calibration method 1, the mixed energy ratio of each acquisition time interval t in the pre-scanning of several circles is calculated. and ;

[0029] Since the two anode materials are distributed periodically in the anode target in the angular direction, and The acquisition time interval sequence t also shows periodic changes;

[0030] Through several laps of pre-scanning, record and The periodic variation curve on the acquisition time interval sequence t is then obtained according to the periodic variation curve and , and the recorded gantry rotation sequence, to deduce the mixed energy ratio at each acquisition time interval during the clinical scanning phase , And the overall mixed energy spectrum .

[0031] In summary, compared with the prior art, the present invention has the following characteristics:

[0032] 1. Through the specially designed anode target, there is no need for flying focus mode and two sets of reconstruction geometry, and the implementation method of spectral CT is designed accordingly;

[0033] 2. It includes a photon counting detector channel unit for energy spectrum correction, and its manufacturing cost is lower than that of a detector composed entirely of photon counting detectors;

[0034] 3. The energy ratio of the ray energy spectrum can be quantitatively changed by setting the position of the focus in the Y direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a new type of energy spectrum CT that generates rays of different energies;

[0036] Figure 2 An embodiment of the distribution of two anode materials in an anode target;

[0037] Figure 3 This is a schematic diagram of the expansion along the angular direction of the first embodiment of the anode target distribution. DETAILED DESCRIPTION

[0038] Reference Figures 1 to 3 The specific implementation methods of a novel energy spectrum CT and a correction method of the present invention are further described.

[0039] 1. Special anode target design.

[0040] The anode target in a conventional CT tube is generally truncated cone-shaped and is made of one anode material. The specially designed anode target of the present invention is also truncated cone-shaped and is made of two different materials, which are distributed periodically in the angular direction along the rotation center of the anode target. Under the bombardment of electrons, the two anode target materials can respectively excite two types of X-rays with greatly different energy spectra. At each acquisition time interval, the two types of X-rays with greatly different energy spectra are mixed through different energy spectrum mixing ratios, thereby outputting rays with different energy spectra.

[0041] Within one period of the anode target in the angular direction, the shape distribution of the two materials is not specified and can be fan-shaped, triangular, square, circular, prism-shaped, etc.

[0042] 2. Application of reference channel of photon counting detector

[0043] Traditional spectral CT uses two different energy spectrum rays for clinical scanning, and the energy spectrum curves of the two different energy spectrum rays are usually fixed and acquired in advance. During the exposure scanning of the new energy spectrum CT proposed in the present invention, the energy spectrum of the exposure ray is mixed by the energy spectrum generated by the two anode materials, and the energy spectrum mixing ratio changes at each acquisition moment.

[0044] Therefore, compared with the traditional CT, the new energy spectrum CT proposed in this patent adds a photon counting detector unit channel as a reference channel, whose function is to collect energy spectrum information data of the ray at multiple consecutive collection moments. This collected energy spectrum information will be used to correct the mixed energy ratio of the energy spectrum ray.

[0045] The photon counting detector unit channel is installed at a position where it can receive exposure radiation, such as the edge of a conventional energy integrating detector; the edge of a collimator opening; or even inside a tube.

[0046] In addition, a special dedicated filter can be set on the optical path of the photon counting detector reference channel receiving rays to weaken the signal collected by the reference channel and avoid saturation of the collected signal data.

[0047] This special dedicated filter for the reference channel of the photon counting detector can be installed at any position on the optical path of the reference channel receiving radiation, such as directly installed on the photon counting detector channel.

[0048] The generation method of new energy spectrum CT energy rays:

[0049] Based on the special design of the anode target mentioned above, this patent proposes a new dual-energy data acquisition mode for spectral CT, which is achieved by collecting two different energy spectrum rays at intervals in the acquisition time series.

[0050] In the data collection of two consecutive collection time intervals, the generation method of different energy rays is used Figure 1 It means that the angular periodic distribution of the two anode materials is spread out at the focal position along the angular direction of the anode target rotation. Figure 1 In , n represents the nth pair of two consecutive acquisition time intervals in the acquisition time series; and It means that in two consecutive acquisition time intervals of the nth pair, the ray projection signals of energy spectrum 1 and energy spectrum 2 are collected respectively. Figure 1 It can be seen that in the data collection of two consecutive collection time intervals, the energy spectrum mixing ratios of the energy rays collected twice are quite different, thereby realizing the collection of energy rays with two different energy spectra at two consecutive collection time intervals.

[0051] A correction method corresponding to the above-mentioned new energy spectrum CT implementation method:

[0052] First, the two energy spectrum rays of the two anode materials under cathode electron bombardment pass through the corresponding filters to obtain the corresponding two energy spectrum curves, which need to be obtained in advance. These two energy spectrum curves can generally be expressed by two one-dimensional vectors through theoretical calculations, which are recorded as and .

[0053] In addition, when the rays excited by the two anode materials are filtered and collected in the optical path of the reference channel of the above-mentioned photon counting detector, the energy spectrum curves of the two kinds of rays after filtering in the reference channel are recorded as and , which is used to calculate the mixed energy ratio at each acquisition time interval. The energy spectrum curves after these two filters are and , also needs to be acquired in advance, which can be obtained in advance through experiments. The experimental method is: pre-set the focus position in the area with only a single anode material (anode material 1 or anode material 2); expose and scan to collect the received signal of the reference channel of the photon counting detector; the energy spectrum information of the signal collected by the reference channel of the photon counting detector is the energy spectrum curve of the reference channel corresponding to the anode material ( or ). and Available The one-dimensional vector representation of is the number of energy spectrum bins in the photon counting detector. The value on each bin corresponds to the photon count at that energy.

[0054] According to the parameters obtained above , , or , one of the following two correction methods can be used to calculate the mixed energy ratio at each acquisition time interval.

[0055] 1. Correction method for real-time calculation of mixed energy ratio

[0056] During clinical scanning, the reference channel of the photon counting detector records the energy spectrum curve of each acquisition time interval t in real time. . And the energy spectrum curve Likewise A one-dimensional vector with the following relationship:

[0057]

[0058] in, is the energy spectrum at the reference channel position at the acquisition time interval t The energy ratio, is the energy spectrum at the reference channel position at the acquisition time interval t energy ratio.

[0059] The mixed energy ratio at the collection time interval t is calculated by solving the equation group by linear fitting. and , then the overall mixed energy spectrum for the current acquisition time interval t can be calculated by :

[0060]

[0061] 2. Correction method for calculating the mixed energy ratio in advance

[0062] Before the clinical scan, the gantry enters the rotation state in advance and performs several pre-scans with a lower dose exposure. After the scan, the gantry continues to rotate, and the rotation sequence of the gantry is recorded from the first pre-scan, and the clinical scan phase begins at the same time.

[0063] During the above-mentioned pre-scanning, the reference channel of the photon counting detector collects the corresponding energy spectrum curve data. Then, according to the process of the above calibration method 1, the mixed energy ratio of each acquisition time interval t in the pre-scan is calculated. and .

[0064] Since the two anode materials are distributed periodically in the anode target in the angular direction, and The acquisition time interval sequence t also presents periodic changes.

[0065] Through several laps of pre-scanning, record and The periodic variation curve on the acquisition time interval sequence t is then obtained according to the periodic variation curve and , and the recorded gantry rotation sequence, to deduce the mixed energy ratio at each acquisition time interval during the clinical scanning phase , And the overall mixed energy spectrum .

[0066] From the implementation of the new energy spectrum CT described above, it can be seen that for two consecutive acquisition time intervals t and t+1, the mixed energy ratio of the two acquisitions is , and , The two correction methods proposed in the present invention can be used to calculate the different mixed energy spectra corresponding to the two consecutive acquisition time intervals. and , thereby realizing the new energy spectrum CT exposure imaging proposed in the present invention.

[0067] Anode target example solution:

[0068] In addition, according to the above design requirements, an example of the distribution of two anode materials in an anode target is proposed below: Example 1: Figure 2 The feature of Example 1 is that, while meeting the design requirements of the above-mentioned special anode target, Example 1 can also adjust the ratio of the two energy spectrum rays corresponding to the two anode materials by setting the focus point position in the Y direction, such as Figure 3 As shown, the anode target is composed of two anode materials, (A – C) are perspective views, (B, E) are front views, and (C, F) are side views. Figure 3 It can be seen that by setting the focus position 1 and position 2 in the Y direction, within a period of the anode target angular distribution, the distribution ratio of the two anode materials changes with the focus position in the Y direction. Therefore, this design can adjust the distribution ratio of the two energy spectrum rays corresponding to the two anode materials by setting the focus point position in the Y direction.

[0069] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A novel implementation and correction method of spectral CT, characterized in that: The invention comprises an anode target and a photon counting detector unit channel. The anode target is made of two different materials and is periodically distributed in an angular direction along the rotation center of the anode target. The anode target is used to collect two different energy spectrum rays at intervals in a collection time sequence. The two anode target materials can respectively excite two X-rays with large energy spectrum differences under the bombardment of electrons. At each collection time interval, the two X-rays with large energy spectrum differences are mixed through different energy spectrum mixing ratios, thereby outputting different energy spectrum rays, and can realize the collection of different energy rays at several adjacent collection time intervals. The photon counting detector unit channel is used as a reference channel to calculate the energy mixing ratio of the mixed energy spectrum rays collected each time, thereby realizing energy spectrum correction.

2. The implementation and correction method of the new energy spectrum CT according to claim 1, characterized in that: Within one period of the anode target in the angular direction, the shape distribution of the two materials is not specified and can be fan-shaped, triangular, square, circular, or prismatic.

3. The implementation and correction method of the new energy spectrum CT according to claim 1 is characterized in that: The photon counting detector unit channel is installed at a position where it can receive exposure radiation.

4. The implementation and correction method of the new energy spectrum CT according to claim 3 is characterized by: The photon counting detector unit channel is mounted on the edge of a conventional energy integrating detector, the edge of a collimator opening, or inside a tube.

5. The implementation and correction method of the new energy spectrum CT according to claim 1 is characterized in that: A special dedicated filter is set on the optical path of the photon counting detector unit channel receiving the ray to weaken the signal collected by the reference channel and avoid saturation of the collected signal data.

6. The implementation and correction method of the new energy spectrum CT according to claim 5 is characterized by: Special dedicated filters for the reference channel of a photon counting detector can be installed anywhere in the optical path of the reference channel receiving radiation.

7. The implementation and correction method of the new energy spectrum CT according to claim 6 is characterized by: Special dedicated filtering for the reference channel of a photon counting detector is installed directly on the photon counting detector channel.

8. The implementation and correction method of the new energy spectrum CT according to claim 1 is characterized in that: The correction method using real-time calculation of mixed energy ratio is as follows: During clinical scanning, the reference channel of the photon counting detector records the energy spectrum curve of each acquisition time interval t in real time. , and the energy spectrum curve Likewise A one-dimensional vector with the following relationship: , in, is the energy spectrum at the reference channel position at the acquisition time interval t The mixing energy ratio, is the energy spectrum at the reference channel position at the acquisition time interval t The mixing energy ratio; The mixed energy ratio at the collection time interval t is calculated by solving the equation group by linear fitting. and , then the overall mixed energy spectrum for the current acquisition time interval t can be calculated by , the calculation formula is as follows: .

9. The implementation and correction method of the new energy spectrum CT according to claim 1, characterized in that: The correction method using the advance calculation of the mixed energy ratio is as follows: Before the clinical scan, the gantry enters the rotating state in advance and performs several pre-scans with a lower dose exposure. After the scan, the gantry continues to rotate and the rotation sequence of the gantry is recorded from the first pre-scan, and the clinical scan phase begins at the same time. During the above-mentioned pre-scanning, the reference channel of the photon counting detector collects the corresponding energy spectrum curve data. Then, according to the above correction method, the mixed energy ratio of each acquisition time interval t in the pre-scan is calculated. and ; Since the two anode materials are distributed periodically in the anode target in the angular direction, and The acquisition time interval sequence t also shows periodic changes; Through several laps of pre-scanning, record and The periodic variation curve on the acquisition time interval sequence t is then obtained according to the periodic variation curve and , and the recorded gantry rotation sequence, to deduce the mixed energy ratio at each acquisition time interval during the clinical scanning phase , And the overall mixed energy spectrum .

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