CN107884806B - Dual-energy CT imaging-oriented X-ray energy spectrum detection and reconstruction analysis method - Google Patents

Dual-energy CT imaging-oriented X-ray energy spectrum detection and reconstruction analysis method Download PDF

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CN107884806B
CN107884806B CN201710978864.4A CN201710978864A CN107884806B CN 107884806 B CN107884806 B CN 107884806B CN 201710978864 A CN201710978864 A CN 201710978864A CN 107884806 B CN107884806 B CN 107884806B
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史再峰
孟庆振
李杭原
黄泳嘉
李金卓
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Tianjin University
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Abstract

The invention relates to the field of X-ray energy spectrum detection and analysis by using a semiconductor detector, and provides an X-ray energy spectrum detection and reconstruction analysis method for dual-energy CT imaging. Therefore, the invention relates to an X-ray energy spectrum detection and reconstruction analysis method for dual-energy CT imaging, which comprises the following steps: step 1: defining a dynamic dual-energy window for scanning imaging; step 2: x-ray exposure and photo-generated charge collection and storage; step 3: grouping and accumulating the photogenerated charge information in the semiconductor; step 4: the projection results of a plurality of different high-low energy spectrum combinations are solved under the condition of one ray exposure and are used for imaging. The invention is mainly applied to X-ray energy spectrum detection occasions.

Description

Dual-energy CT imaging-oriented X-ray energy spectrum detection and reconstruction analysis method
Technical Field
The invention relates to the field of X-ray energy spectrum detection and analysis by using a semiconductor detector, in particular to the detection and analysis of medical dual-energy spectrum CT (Computed Tomography) X-ray energy spectrum.
Background
The key of the accurate imaging of the medical energy spectrum CT is to improve the distinguishing capability of the detector on X-ray photons with different energies and improve the accuracy of energy spectrum analysis calculation. The double-layer detector and the single-photon counting detector are two major X-ray energy spectrum detectors at present, the two X-ray energy spectrum detectors perform scanning projection in a mode of presetting an effective energy window (energy spectrum band), and image reconstruction of different objects is based on attenuation information of the same energy spectrum band. However, the imaging accuracy of objects to be measured with different thicknesses and compositions under different dual-energy combinations is different, the dynamic range of CT imaging is limited by fixed energy spectrum segmentation, and it is difficult to meet the requirement of obtaining projection data of variable energy spectrum under single radiation dose, thereby performing multi-energy dynamic combination imaging.
Generally, the photon energy of medical X-ray is 0 keV-120 keV, the linear attenuation coefficient of the photon in the object will decrease exponentially as the photon energy increases, and for the dual energy spectrum CT using two energy segments for imaging, it is shown that the low energy segment X-ray will be completely absorbed at the shallower part of the semiconductor and generate electron-hole pairs, and the higher energy X-ray completely absorbs and needs a thicker semiconductor. Most of the energy released when ray photons are absorbed in a silicon semiconductor is used for exciting and generating electron-hole pairs, and the number of photo-generated electrons and the energy of deposited photons have a good linear relation. The difference of the absorption positions of the X-ray photons with different energies in the semiconductor and the linear relation between the photon energy and the photo-generated charges provide a basis for X-ray energy spectrum detection and reconstruction analysis.
Disclosure of Invention
In order to overcome the defects of the prior art and overcome the defects in the detection and analysis of the energy spectrum CT ray, the invention aims to provide an X-ray energy spectrum detection and reconstruction analysis method for dual-energy CT imaging. Through one-time X-ray helical scanning, projection information of different energy sections can be obtained through analysis and used for image reconstruction by integrating photo-generated charges in semiconductors at different positions and depths, the radiation dose can be reduced, multi-energy dynamic combined imaging can be realized, and the dynamic range of CT system imaging is improved. Therefore, the technical scheme adopted by the invention is that the method for detecting, reconstructing and analyzing the X-ray energy spectrum for dual-energy CT imaging comprises the following steps:
step 1: defining a dynamic dual-energy window for scanning imaging, and dividing an energy spectrum to be analyzed after passing through a human body into two energy windows based on the data requirement of dual-energy CT imaging, wherein ElIs a low energy window with a fixed energy interval of 0keV-EMax；EhIs a high energy window with an energy range of Eb-EMax，EMaxThe highest energy of the spectrum of the radiation source, EbEnergy points are demarcated for high and low energy spectrums;
step 2: x-ray exposure and photo-generated charge collection and storage: x-rays are incident from the side edge of the silicon semiconductor, ray photons with different energies are completely absorbed in semiconductors with different depths to generate photo-generated charges, and photo-generated charge information generated at different positions is collected and respectively stored during exposure;
step 3: grouping and accumulating the photo-generated charge information in the semiconductor, analyzing and calculating the high-low energy spectrum projection, and dividing the photo-generated charge in the semiconductor into two groups for accumulation aiming at the selected double-energy window, wherein l0For the X-ray to be incident on the semiconductor starting position,/pAnd lhIs a theoretical value obtained according to the Lambert-beer law and respectively represents that the completely absorbed energy is EbAnd EMaxRequired thickness of the semiconductor for radiation photons,/pWith EbChange in (b);
and analyzing and calculating high-low energy spectrum projection according to the charge accumulation information, wherein for the dual-energy CT imaging, the projection of the variable high-low energy spectrum to be solved is represented as follows:
Figure DEST_PATH_IMAGE002
wherein
Figure BDA0001438838870000022
And
Figure BDA0001438838870000023
respectively representing the light intensity of the high-energy window and the low-energy window to be measured after penetrating through the human body,
Figure BDA0001438838870000024
and
Figure BDA0001438838870000025
the original light intensity of the high and low energy windows, Q (l)i) And Q' (l)i) Representing the number of photo-generated charges, Q, collected per unit thickness in a detector pixel under normal and empty scans, respectivelylowAnd Q'lowRespectively represent twoThe total number of photo-generated charges generated by the low-energy spectrum segment under the secondary scanning; energy less than EbWill be atpPreviously absorbed completely, QhighAnd Q'highThe total number of photo-generated charges generated by the high-energy spectrum section under two scans;
step 4: adjustment EbPosition, redefining high and low energy spectrum, and adjusting boundary E according to different detector pixels, scanning process and projection requirementsbChanging the width and average energy of the high energy spectrum, selecting EbAnd returning to Step2, solving the projection results of a plurality of different high-low energy spectrum combinations under the condition of one ray exposure and using the projection results for imaging.
In one example, EbTake 45keV, 68keV and 75keV as examples, and the corresponding three energy combinations are: (45-80,0-80keV), (68-80,0-80keV), (75-80,0-80keV), lpThe positions are respectively as follows: 3.9cm, 7.9cm and 9.0 cm.
The invention has the characteristics and beneficial effects that:
the invention provides an X-ray energy spectrum detection and reconstruction analysis method for dual-energy CT imaging. By integrating photo-generated charges in semiconductors at different depths and reconstructing an analytic equation, projection information of the same object under different energy combinations is obtained through one-time radiation, scanning time and ray dose are reduced, time and space resolution is improved, radiation dose is reduced, dynamic range of an imaging system is improved, and more specific and various projection information is provided for energy spectrum CT imaging.
Description of the drawings:
FIG. 1 is a flow chart of X-ray energy spectrum detection and reconstruction analysis.
FIG. 2 is a schematic diagram of a variable dual energy spectrum detection and reconstruction analysis. In the figure:
a, segmenting dynamic energy;
b charge accumulation in detector pixels.
Detailed Description
The invention provides an X-ray energy spectrum detection and reconstruction analysis method for dual-energy CT imaging, a flow chart is shown in figure 1, and the specific implementation scheme is as follows:
step 1: a dynamic dual energy window for scanning imaging is defined. Based on the data requirements of dual-energy CT imaging, as shown in FIG. 2(a), the energy spectrum to be resolved after passing through the human body is divided into two energy windows, where ElIs a low energy window with a fixed energy interval of 0keV-EMax；EhIs a high energy window with an energy range of Eb-EMax，EMaxThe highest energy of the spectrum of the radiation source, EbThe energy points are demarcated for high and low energy spectra.
Step 2: x-ray exposure and photo-generated charge collection and storage. As shown in fig. 2(b), taking a bulk silicon semiconductor as an example of a detector (but not limited to silicon), when X-rays are incident from the side edge of the silicon semiconductor, radiation photons with different energies will be completely absorbed in semiconductors with different depths and generate photo-generated charges, and information of the photo-generated charges generated at different positions is collected and stored when the radiation photons are exposed.
Step 3: and accumulating the photo-generated charge information in the semiconductor in groups, and analyzing and calculating the high-energy and low-energy spectrum projection. As shown in fig. 2(b), the photogenerated charge in the semiconductor is accumulated in two sets for selected dual energy windows. Wherein l0For the X-ray to be incident on the semiconductor starting position,/pAnd lhIs a theoretical value obtained according to the Lambert-beer law and respectively represents that the completely absorbed energy is EbAnd EMaxRequired thickness of the semiconductor for radiation photons,/pWith EbMay be varied.
And analyzing and calculating high-low energy spectrum projection according to the charge accumulation information. For dual-energy CT imaging, the projection of the variable high and low energy spectrum to be solved can be expressed as:
Figure 360989DEST_PATH_IMAGE002
wherein
Figure BDA0001438838870000032
And
Figure BDA0001438838870000033
respectively representing the light intensity of the high-energy window and the low-energy window to be measured after penetrating through the human body,
Figure BDA0001438838870000034
and
Figure BDA0001438838870000035
for high and low energy windows of original light intensity (null scan), Q (l)i) And Q' (l)i) Representing the number of photo-generated charges, Q, collected per unit thickness in a detector pixel under normal and empty scans, respectivelylowAnd Q'lowRespectively representing the total number of photo-generated charges generated by the low-energy spectrum segment under two scans; energy less than EbWill be atpPreviously absorbed completely, QhighAnd Q'highIs the total number of photo-generated charges generated in the high energy spectrum segment under two scans.
Step 4: adjustment EbAnd position, redefining the high-low energy spectrum. By adjusting the boundary E for different detector pixels, scanning processes and projection requirementsbThe width of the high energy spectrum and the average energy can be varied. Selected EbAnd returning to Step2, the projection results of a plurality of different high-low energy spectrum combinations can be solved under the condition of one ray exposure and used for imaging.
The present invention is further illustrated by the following examples, which are not intended to limit the invention thereto, and simple variations thereof, which may be made by persons skilled in the art in light of the teachings herein, should be considered to be within the scope of the invention as claimed. The following detailed description is made with reference to the accompanying drawings:
the X-ray source employed in the present invention is generated by GE Maxiray125, where the peak tube voltage and current are set to E, respectivelyMax80keV and 1mAs, the other parameters are set by default. The thickness l of each detector pixel is such that it completely absorbs radiation photons with a maximum energy of 80keVhAre all set to 9.6 cm. As shown in table 1, by adjusting the high and low energy spectrum cut-off point EbObtaining three different energy combinations, here denoted as EbAre respectively set to a value of 45keV,68keV and 75keV, for example, the corresponding three energy combinations are: (45-80,0-80keV), (68-80,0-80keV), (75-80,0-80keV), lpPosition (distance l)0) Respectively as follows: 3.9cm, 7.9cm and 9.0 cm.
TABLE 1
Figure BDA0001438838870000036
After one-time X-ray exposure, the photo-generated charge information in the semiconductor of each unit thickness is read, quantized and stored respectively, the photo-generated charges are accumulated in groups according to the mode, an analytical equation is reconstructed, and then projection information of different energy sections can be obtained through analysis and used for image reconstruction.

Claims (2)

1. An X-ray energy spectrum detection and reconstruction analysis method for dual-energy CT imaging is characterized by comprising the following steps:
step 1: defining a dynamic dual-energy window for scanning imaging, and dividing an energy spectrum to be analyzed after passing through a human body into two energy windows based on the data requirement of dual-energy CT imaging, wherein ElIs a low energy window with a fixed energy interval of 0keV-EMax；EhIs a high energy window with an energy range of Eb-EMax，EMaxThe highest energy of the spectrum of the radiation source, EbEnergy points are demarcated for high and low energy spectrums;
step 2: x-ray exposure and photo-generated charge collection and storage: x-rays are incident from the side edge of the silicon semiconductor, ray photons with different energies are completely absorbed in semiconductors with different depths to generate photo-generated charges, and photo-generated charge information generated at different positions is collected and respectively stored during exposure;
step 3: grouping and accumulating the photo-generated charge information in the semiconductor, analyzing and calculating the high-low energy spectrum projection, and dividing the photo-generated charge in the semiconductor into two groups for accumulation aiming at the selected double-energy window, wherein l0For the X-ray to be incident on the semiconductor starting position,/pAnd lhIs a theoretical value obtained according to the Lambert-beer law and respectively represents that the completely absorbed energy is EbAnd EMaxRequired thickness of the semiconductor for radiation photons,/pWith EbChange in (b);
and analyzing and calculating high-low energy spectrum projection according to the charge accumulation information, wherein for the dual-energy CT imaging, the projection of the variable high-low energy spectrum to be solved is represented as follows:
Figure FDA0002279361050000011
wherein
Figure FDA0002279361050000012
And
Figure FDA0002279361050000013
respectively representing the light intensity of the high-energy window and the low-energy window to be measured after penetrating through the human body,
Figure FDA0002279361050000014
and
Figure FDA0002279361050000015
the original light intensity of the high and low energy windows, Q (l)i) And Q' (l)i) Representing the number of photo-generated charges, Q, collected per unit thickness in a detector pixel under normal and empty scans, respectivelylowAnd Q'lowRespectively representing the total number of photo-generated charges generated by the low-energy spectrum segment under two scans; energy less than EbWill be atpPreviously absorbed completely, QhighAnd Q'highThe total number of photo-generated charges generated by the high-energy spectrum section under two scans;
step 4: adjustment EbPosition, redefining high and low energy spectrum, and adjusting boundary E according to different detector pixels, scanning process and projection requirementsbChanging the width and average energy of the high energy spectrum, selecting EbAnd returning to Step2, solving the projection results of a plurality of different high-low energy spectrum combinations under the condition of one ray exposure and using the projection results for imaging.
2. The dual-energy CT imaging-oriented X-ray energy spectrum detection and reconstruction analysis method as claimed in claim 1, wherein E isbTake 45keV, 68keV and 75keV as examples, and the corresponding three energy combinations are: (45-80,0-80keV), (68-80,0-80keV), (75-80,0-80keV), lpThe positions are respectively as follows: 3.9cm, 7.9cm and 9.0 cm.
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