CN105326524B - The medical imaging procedure and device of the artifact in image can be reduced - Google Patents

Abstract

The present invention discloses a medical imaging method and device capable of reducing artifacts in an image, and relates to a medical imaging method, in which, images including a background portion and a high attenuation portion are scanned along one or more different scanning directions The object is scanned to generate a plurality of projection images. The following operations are performed on each projected image: the projected image is filtered to generate an original filtered image; the pixels close to the border in the high attenuation part of the projected image are moved towards the high attenuation part along the scanning direction or the opposite direction of the scanning direction Shrink the inside, and fill the gray value of the pixel close to the adjacent background part in the original area where the high attenuation part shrunk to the inside, so as to generate a shrunk image; filter the shrunk image to generate shrunk filter an image; fusing the original filtered image and the shrunk filtered image to produce a filtered image with reduced undershoot. The undershoot-reduced filtered image is back projected to obtain a reconstructed image. Furthermore, the invention also relates to a medical imaging device for carrying out the method.

Description

Medical imaging method and apparatus capable of reducing artifacts in images

technical field

The present invention relates to a medical imaging method and device, in particular to a medical imaging method and device capable of reducing artifacts in images.

Background technique

Medical imaging technology can obtain images of the internal structure of patients or objects to be observed without physically penetrating the skin, so it is widely used clinically. Projection radiography is a commonly used medical imaging technology, which uses X-rays to generate two-dimensional images based on the characteristics of X-rays (ie, different materials have different absorption rates). For example, tomosynthesis is such a projection radiography technology, which uses different physical principles, such as differential transmission when X-rays pass through the target object, to obtain image data and construct tomographic images (e.g., a three-dimensional rendering of the interior of a human body or other structure to be imaged).

Certain limitations or limitations of tomography techniques may lead to artifacts or other imperfections in the reconstructed images, e.g., highly attenuating parts in or on the patient with high X-ray absorption, such as metallic material parts (e.g. prostheses, implants, etc.). objects, screws, needles, etc.) can cause artifacts during tomography. For example, during tomography with backprojection as the reconstruction algorithm, objects with high X-ray absorption, such as metals, can cause artifacts that look like duplicates of the metal on different reconstruction planes , ie, ripple artifacts. Artifacts can seriously degrade the quality of the final image, and sometimes even make the image unusable for diagnosis, so it is very important to reduce the artifacts in the image.

Contents of the invention

An aspect of embodiments of the invention relates to a method of medical imaging. In this method, an object is scanned along one or more different scan directions to generate a plurality of projection images, wherein the object includes a background portion and a high attenuation portion. Perform the following operations on each projected image: filter the projected image to generate an original filtered image; move pixels close to the boundary between the high attenuation part and the background part in the high attenuation part of the projected image along the scanning direction or the scanning direction The reverse direction of the direction shrinks toward the interior of the high-attenuation part, and replaces the gray value of the pixel in the original high-attenuation part area where the high-attenuation part shrinks inward is replaced by a pixel whose gray value is close to the pixel gray value of its adjacent background part grayscale values to generate a shrunk image; filtering the shrunk image to generate a shrunk filtered image; and fusing the original filtered image and the shrunk filtered image to generate a filtered image with reduced undershoot. and back-projecting the plurality of filtered images with reduced undershoot generated by the plurality of projected images to obtain a reconstructed image.

Another aspect of embodiments of the invention relates to a medical imaging apparatus for imaging a subject. The device includes a ray source and a ray detector, a data acquisition system, a processor and a display device. The ray detector is used to receive the ray emitted by the ray source and passes through the object to be scanned, and the ray source and the ray detector are used to scan the radiation including the background part and the high attenuation part along one or more different scanning directions. Objects are scanned. The data acquisition system is used to receive data from the radiation detector when scanning an object, so as to generate corresponding projection data. The processor is used for receiving projection data from the data acquisition system to generate a projection image for reconstructing the image of the object. The processor includes a contraction module, a filter module, a fusion module and a back projection module, wherein the contraction module is used to convert pixels close to the boundary between the high attenuation part and the background part in the projection image along the The scanning direction or the opposite direction of the scanning direction shrinks toward the interior of the high attenuation part, and replaces the gray value of the pixel in the original high attenuation part area where the high attenuation part shrinks inward is replaced by the pixel gray value of the adjacent background part Values are close to the pixel gray value to generate a contracted image; the filtering module is used to filter the projected image to generate an original filtered image, and the contracted image is filtered to generate a contracted filtered image; the fusion module is used to fusing the original filtered image and the shrunk filtered image to generate a filtered image with reduced undershoot; a back-projection module configured to back-project the filtered image with reduced undershoot to obtain a reconstructed image. The display device displays the obtained image in response to the processor.

Description of drawings

By describing the embodiments of the present invention in conjunction with the accompanying drawings, the present invention can be better understood. In the accompanying drawings:

Figure 1 is a perspective block diagram of a digital tomography system equipped with a table in an exemplary embodiment.

Figure 2 is a perspective block diagram of a digital tomography system in an exemplary embodiment equipped with a wall.

Figure 3A shows a filtering kernel in the spatial domain in one embodiment, Figure 3B shows the spatial pixel gray value curve, and Figure 3C shows the filtering kernel shown in Figure 3A applied to the curve shown in Figure 3B The curve obtained after filtering.

FIG. 4 shows a flowchart of an imaging method according to an embodiment of the present invention.

5A and 5B respectively show a set of corresponding original projected images and projected images after the high attenuation part is shrunk inward and the shrunk area is filled with the pixel gray value of the approximate background part in one embodiment.

The thinner solid line and dotted line in Fig. 6 represent the pixel gray value curve near the boundary of the high attenuation part and the background part of a group of corresponding original filter image I originalal and contraction filter image I _fshrunken in one _embodiment , relatively The thick solid line represents the pixel gray value curve of the filtered image I _USfree near the boundary obtained by _{fusing I original and I fshrunken in} a certain way and eliminating undershoot artifacts.

Figures 7A and 7B show a corresponding set of raw filtered images and filtered images with undershoot artifacts removed, respectively, in one embodiment.

Figure 8 schematically shows backprojection of a metal-containing guest in one embodiment.

FIG. 9 shows a flowchart of an imaging method according to another embodiment of the present invention.

Figures 10A and 10B show a corresponding set of raw filtered images and filtered images with ripple artifacts removed, respectively, in one embodiment.

Detailed ways

Specific examples of the present invention will be described below. Unless otherwise defined, the technical terms or scientific terms used in the claims and the description shall have the ordinary meanings understood by those skilled in the technical field to which the present invention belongs. "First", "second" and similar words used in the patent application specification and claims of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "A" or "one" and similar words do not indicate a limitation of number, but mean that there is at least one. "Or" means to include any one or all of the listed elements or items. Words such as "comprises" or "comprises" and similar terms mean that the elements or items listed before "comprises" or "comprises" include the elements or items listed after "comprises" or "comprises" and their equivalent elements, and do not exclude other components or objects. Words like "connected" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. Approximate language used herein may be used in quantitative terms, indicating that certain variations in quantities are permissible without changing essential function. Accordingly, values modified by language such as "about", "approximately" and the like are not limited to the exact value itself. In some cases, the language of approximation may relate to the precision of the measuring instrument.

An embodiment of the present invention provides an imaging method, which can obtain a medical image of a target object through a tomographic imaging system. In this method, algorithms such as back-projection algorithm and filtered back-projection algorithm can be used to reconstruct the tomographic image, and the method of moving inward and filling the boundary can be used to reduce or eliminate undershooting and overshooting during the filtering process. In-plane artifacts such as overshooting can be reduced or eliminated by applying different weights to different pixels during the back projection process. By these methods, the reconstruction image can be reduced or eliminated. Artifact defects due to the presence of highly attenuating objects such as metals.

The method described here is broadly applicable to various tomographic reconstruction systems. Since these methods are particularly applicable to various X-ray tomography techniques, such as radiation tomography or digital object tomosynthesis (rad or digital object tomosynthesis), for the convenience of description, this paper will mainly combine a method such as the applicant in The tomographic imaging system described in the US patent application US 2009/0003679 entitled "System and method for a digital x-ray radiographic tomosynthesis userinterface" filed on September 10, 2007 exemplifies the method of the embodiment of the present invention discussed and described, but it should be understood that the method of the present invention is also applicable to other tomographic imaging systems or other tomographic reconstruction systems.

Figures 1 and 2 show examples of implementations of digital tomography systems 100, 200, respectively. The system 100 , 200 includes a digital tomography system 120 , 220 . FIG. 1 shows a structure with a platform, which includes an X-ray source 102 installed in a mechanism 160 , and an X-ray detector 104 located under a table 118 in a platform 116 . FIG. 2 shows a structure with a wall, which includes an X-ray source 202 installed in a mechanism 260 and an X-ray detector 204 arranged on a wall 216 . The patient to be examined is placed under the radiation of the X-ray beam 108, 208 emitted by the X-ray source 102, 202, and the X-ray beam 108, 208 impinges on the body of the patient 106, 206 to be examined, part of which The radiation travels through or around the patient to and strikes the detectors 104 , 204 .

In one embodiment, the X-ray source 102, 202 may be an X-ray tube, and the patient 106, 206 to be examined may be a human, an animal, a test phantom and/or other non-living body.

The patient 106 or 206 to be examined is placed between the x-ray source 102 , 202 and the detector 104 , 204 . During the tomography process, as shown in FIGS. 1 and 2, the X-ray source 102, 202 moves along the plane 110, 210, and also rotates to ensure that the X-ray beam 108, 208 is always aligned with the detection plane during the process. device 104,204. As previously mentioned, the x-ray source 102, 202 generally moves along a plane 110, 210 parallel to the plane 112, 212 of the detector 104, 204, although it may also move out of plane, but its substantially parallel to the detectors 104,204. The detector 104, 204 may remain in a fixed position while the radiograph is being taken. During the movement of the X-ray source 102, 202 along the plane 110, 210, a series of discrete projection radiographs (projection views) of the patient 106, 206 are obtained by the detector 104, 204 at discrete different positions. ). Projection image data can be obtained from the projection views for reconstructing slice images.

In the digital X-ray radiography tomography process, the X-ray sources 102, 202 are aligned with the fixed detectors 104, 204 through arc rotation or linear movement in a certain angle range 114, 214 (scanning angle ) includes a series of low dose exposures. The X-ray source 102, 202 emits multiple exposures during one scan from different projection angles. The scan angle 114, 214 refers to the angle from the first projection exposure to the last projection exposure. The scan angle 114, 214 is typically in the range of 20 to 60 degrees.

In one embodiment, the detectors 104, 204 may include a series of detection elements, typically corresponding to pixels, for sensing the intensity of X-rays passing through or around the patient and generating An electronic signal of the intensity of the incident X-ray beam. These acquired electronic signals are processed to reconstruct a three-dimensional volumetric image of the patient's anatomy. The intensity of the X-rays striking each detection element varies depending on the attenuation of the X-rays and the absorption rate of the intervening structures.

1 and 2 further schematically show a computer workstation 130, 230 connected to the digital tomography system 120, 220, which provides a user interface 140, 240 for digital radiography as described herein. The tomography procedure sets at least one reconstruction, dose and/or acquisition acquisition parameter.

The digital tomography system 120, 220 can be used to acquire and process projection image data, and reconstruct a volumetric or three-dimensional image of a patient. The digital tomography system 120, 220 is configured to acquire projection image data and process the data for viewing and analysis.

The computer workstation 130 , 230 includes at least one computer 132 , 232 having a controller 134 , 234 , a processor 136 , 236 , a memory 138 , 238 and a user interface 140 , 240 . The processor 136 , 236 is connectable to the controller 134 , 234 , the memory 138 , 238 and the user interface 140 , 240 . A user 150 , 250 controls the operation of the digital tomography system 100 , 200 through a computer workstation 130 , 230 . In one embodiment, the memory 138, 238 may be a storage device, memory board, data storage, and any other form of storage known in the art.

The digital tomosynthesis imaging systems 120, 220 are controlled by the controllers 134, 234, the controllers can not only provide energy, but also provide control signals of digital tomosynthesis examination sequences (digital tomosynthesis examination sequences), the signals include X The position of the radiation source relative to the patient and detector. The controllers 134 and 234 can obtain signals generated in the detector through instructions, and can also perform various signal processing and filtering functions, such as initial adjustment of the dynamic range, interleaving of digital image data, and the like. Generally, the controller 134, 234 operates the digital tomography system 120, 220 through instructions to execute an inspection scheme and process the acquired data. In one embodiment, the controller 134 , 234 receives instructions from the computer 132 , 232 . In one embodiment, the controller 134 , 234 may be part of the digital tomography system 120 , 220 instead of the computer workstation 130 , 230 . In one embodiment, the computer 132, 232 includes or is connected to the user interface 140, 240 for interacting with the user 150, 250 to select and/or change clinically relevant parameters, such as dosage , slice layout (reconstruction settings) and acquisition parameters, etc. In one embodiment, the digital tomography system 100 , 200 operates through the use of software or algorithms downloaded or integrated into the computer 132 , 232 .

In one embodiment, the user interface 140, 240 is a visual interface that may include a plurality of predefined tools that allow the user 150, 250 to view, select and edit reconstruction parameters (settings), view and select Dose parameters, and view, select and edit chromatography parameters. The user interface 140, 240 also allows the user 150, 250 to view the reconstructed image.

In one embodiment, the user interface 140 , 240 may include at least one input device for inputting and/or selecting information on the plurality of predefined tools displayed on the display of the user interface 140 , 240 . In one embodiment, the at least one input device may be a touch screen, a mouse, a keyboard, at least one button, or any other input device known in the art.

In use, the patient 106, 206 is positioned such that a projected view of a target object (e.g., a body part) can be obtained by the detector 104, 204, and after obtaining projected image data from the projected view, based on the projected The image data obtains a plurality of sliced images of the target object as a three-dimensional imaging representation of the object. In practice, the plurality of sliced images can be obtained through different reconstruction algorithms, including but not limited to back-projection algorithms and filtered back-projection algorithms.

In the process of imaging with the system, the object can be scanned along different scanning angles and directions to obtain projection images from different angles, and then the projection images can be reconstructed by different methods to obtain the required Reconstruct the image. In some embodiments, the guest includes a high attenuation portion and a background portion. Herein, a high attenuation portion refers to a portion in or on the object to be scanned that has high attenuation characteristics. The high-attenuation portion may have a much higher absorption rate of X-rays than the rest of the object, i.e. the background portion, for example, at least 2 or 3 times the absorption rate of X-rays by the high-attenuation portion at a distance of about 1 cm or, after absorbing X-rays, the pixel gray value of the high attenuation part is at least 20 or 10 smaller than the pixel gray value of its neighbors. Typically, the high attenuation portion involves high density materials such as metals, dental fillings, bone, and the like. In particular, said high attenuation part relates to components implanted in or mounted on a patient's body in clinical applications, such as components used to correct bones, which may broadly include various clinical applications involving metal objects, Such as screws and nails used to correct bones, and prosthetics such as teeth, spine, femur and knee. Whereas the background portion usually refers to the patient's tissue. In particular, the high attenuation part is metal and the background part is non-metal.

When the projection image of the object including the high attenuation part and the background part is reconstructed by the filtered back projection algorithm, undershoot or overshoot may occur at the boundary between the high attenuation part and the background part.

Filtered backprojection algorithms include filtering and backprojection. Typically, filtering is a differential operation that helps enhance the contrast and sharpness of an image. In general, filtering is a process of multiplying a ramp filter kernel with a window function:

Wherein, the filter kernel kernel(t) has a positive value at its center (at t=0), and a negative value at other positions. At strong boundaries (such as the boundary between an implanted metal component and body tissue), the difference between x(i) and x(i-1) or x(i+1) is large, in which In this case, although kernel(1) or kernel(-1) is much smaller than kernel(0), Xc(i) will still be greatly affected by x(i-1) or x(i+1), so that Undershoot or overshoot occurs.

For example, Figure 3A shows an example of a sloped filter kernel in the spatial domain, and Figure 3B shows the pixel gray value curve in the spatial domain, where the higher plateau stage represents the attenuation part of the metal contour, and the rest represent the background part. The filtering is typically a convolution process in the spatial domain, in which a kernel as shown in Figure 3A is applied to a curve as shown in Figure 3B. After filtering, a curve as shown in Fig. 3C is obtained. However, due to the high X-ray absorption of high attenuation parts such as metals, it may cause drastic intensity changes near their edges, which may cause problems with undershoot or overshoot after filtering, which will cause problems in the reconstruction Artifacts appear in the image. For example, as shown in Figure 7A, in the reconstructed image, artifacts due to undershoot or overshoot usually appear at some light-dark contrast boundaries near high-attenuation parts (such as implanted metal parts) and the junction of human tissue structures Defects (black border 701 as shown in the figure), the existence of artifacts hinders the observation of these joints. Since the projection image is usually filtered along the scan direction of the X-ray source, undershoot artifacts are generally produced along the scan direction.

In an embodiment of an aspect of the present invention, artifacts such as undershooting can be reduced through the following methods. As shown in FIG. 4, in step 41, after scanning the object including the background part and the high attenuation part along one or more different scanning directions to generate a plurality of projection images, based on the projection images, the filter back projection algorithm is used When the object is reconstructed, in step 42, the following operations are performed for each projected image: in step 421, the projected image (I _original ) is filtered to generate the original filtered image (I _original ); in step 422 In the projection image, the pixels close to the boundary in the high attenuation part in the projected image are shrunk toward the interior of the high attenuation part along the scanning direction or the opposite direction of the scanning direction, and in the area where the inwardly contracted high attenuation part is originally located, that is , filling the pixel gray value close to (equal or close to) the pixel gray value of its adjacent background part in the original high attenuation part area, to produce a shrink image (I _shrunken ); in step 423, the shrink image Filtering is performed to produce a shrunken filtered image (I _fshrunken ); in step 424, the original filtered image and the shrunk filtered image are fused to produce a filtered image with reduced undershoot (I _USfree ). In this way, a corresponding filtered image with reduced undershoot can be obtained for each projected image. In step 43, backprojection is performed based on the filtered images with reduced undershoot, so as to obtain a reconstructed image with reduced or eliminated undershoot. Compared with the original projected image, in the shrunken image, since the high attenuation part close to the boundary shrinks inward and fills it with the pixel gray value close to the background part, the boundary between the high attenuation part and the background part moves to the inside of the high attenuation part , so the undershoot defect in the contracted filtered image generated based on filtering the contracted image is also shifted to the interior of the high-attenuation part, and the undershoot no longer appears at the original boundary. Therefore, if the original filtered image is filtered in a certain way The image is fused with the shrinking filter image, so that the area near the boundary that produces undershoot artifacts in the original filter image is replaced by the corresponding area in the shrink filter image, which can not only eliminate the undershoot artifact but also retain the maximum The filtered image of the original structural features.

Based on the characteristics of the filter, in some specific embodiments, the width of the undershoot artifact area can be determined through the gradient strength, so as to determine the distance (shrinkage length) that each pixel point in the high attenuation part should shrink inward. Assuming that the scanning direction is the y-axis direction, the gradient of the image in the scanning direction can be represented by dy:

Among them, f _y is the input X-ray image. Then, the shrinkage length L(i,j) of the pixel point (i,j) can be calculated by the following equation:

L(i,j)=H(dy(i,j),kernel),

Among them, H is the function of the shrinkage length L(i,j) to the gradient dy(i,j), which is the function of the gradient dy(i,j) and the filter kernel kernel in the reconstruction process. The shrinkage length of a pixel with a larger gradient is larger. For pixels with small gradients, the shrinkage length is close to 0, and basically no shrinkage occurs. The gradient of the pixels in the strong boundary area is larger, and the shrinkage length is also larger.

In some specific embodiments, the pixel gray value filled in the area where the inwardly contracted high attenuation part was originally located (the original high attenuation part area) can be estimated by the pixel gray value of the adjacent background part . Particularly, in a specific embodiment, the pixel gray value filled in the original high attenuation part area is the average value of the pixel gray value of the adjacent background part.

Figures 5A and 5B show a corresponding set of original projected images (I _original ) and shrunken images (I _shrunken ), respectively, in one embodiment. It can be seen that compared with the original projected image, in the shrunk image, the high attenuation part (the black part in the figure) shrinks along the scanning direction A, that is, the size of the high attenuation part in the shrunk image in the scanning direction is smaller than that of the original projected image The size of the high attenuation part in the scan direction.

In some specific embodiments, the original filtered image I original and the shrinkage filtered image I _fshrunken can be fused by the following equation to generate the filtered image I _USfree with reduced _undershoot :

I _USfree ＝(1-mask)*I _fshrunken +mask*I _original ,

Wherein, mask ("mask") refers to a bitmap, in which a certain area is 1 and the rest of the area is 0, which can be used to multiply the target image to obtain a filtered image. In a specific embodiment, the value of the region corresponding to the pixel points from (i,j) to (i+/-C*L,j) in the scanning direction in the mask is 0, and the value of the remaining regions is 1, where L is the contraction length of the pixel point (i, j), and C is a constant parameter, which corresponds to the kernel used to filter the projected image and the contracted image. At pixel (i,j), within a small area in the scan direction, the minimum _{difference between I original and I fshrunken can} be found and used as the mask mask for pixel (i,j) The starting point of , the mask is 0 within the contraction length range from this point to the high attenuation part to the pixel point (i, j) along the scanning direction.

The thinner solid line 601 and dotted line 602 in Fig. 6 respectively represent the pixel gray value near the boundary _{between the high attenuation part and the background part of a group of corresponding original filter image I original and contraction filter image I fshrunken in} one embodiment Curve, the thicker solid line 603 represents the pixel gray value curve of the filter image I _USfree near the boundary obtained after the fusion of I _{original and I fshrunken by} the above equation, wherein the higher platform stage and the higher The low plateau stage respectively represents the high attenuation part and the background part, except for the part near the boundary between the high attenuation part and the background part, 601 , 602 and 603 roughly overlap. It can be seen that there is a downward overhang between the upper plateau stage and the lower plateau stage in 601 and 602, which represents the undershoot artifact at the boundary, while the obtained after fusion There is no undershoot artifact in the pixel gray value curve 603, so that the definition and sharpness of the boundary of the high attenuation part can be maintained.

Figures 7A and 7B show the original filtered image (I original ) and the filtered image with _reduced undershoot artifacts (I _USfree ) using the method described, respectively, in one embodiment. In the image shown in Figure 7A, there is a black border 701 at the boundary of the high attenuation part, that is, an undershoot artifact, but in the image shown in Figure 7B, there is no such artifact, so it can be displayed more clearly Organizational structures near boundaries.

On the other hand, due to the presence of high attenuation parts, ripple artifacts may also be generated during backprojection. Fig. 8 schematically shows the process of back-projecting the projected image of the object including the high attenuation part (metal is taken as an example below) and the background part. When performing back projection, the projection curves of various angles (such as L1 and L2) can be traced to obtain corresponding pixels on the detector, and superimposed at the reconstruction position. There are three regions in a three-dimensional space whose reconstructed slices are affected to different degrees by the metal in the object. The first of these is the metal area where the metal is located, and all projected views passing through this area carry the metal information; the second is the unaffected background area, that is, the non- The metal area, all projected views passing through this area do not contain metal information, and the pixels in this area have no artifacts; the third is the background area affected by metal, that is, in some projected views will be covered by metal blocking non-metallic areas. If this region is reconstructed based on the projected view including these projected views blocked by the metal, the information of the metal will be brought into this part of the background region, resulting in ripple artifacts. For example, as shown in FIG. 10A , ripples like metal artifacts overlapping with tissue appear in the image. The appearance of the moiré artifact reduces the contrast of the target structure, reduces the discernibility of subtle abnormal structures at the metal/structure interface, and may lead to misdiagnosis.

In another embodiment of the present invention, the ripple artifact can be reduced by the following method. As shown in FIG. 9 , in step 91 , scanning the object including the background portion and the high attenuation portion along one or more different scanning directions generates a plurality of projection images. In step 92, the following operations are performed on each projected image: in step 921, the projected image is filtered to generate a filtered image; in step 922, the weight of each pixel in the projected image is calculated to generate the weight image; in step 923, the filtered image is multiplied by a weighted image to generate a weighted filtered image. In step 93, the weighted filtered image generated by the plurality of projected images is back-projected to generate a temporarily reconstructed image. In step 94, the weighted images of the plurality of projected images are back-projected to generate weighted reconstructed images. In step 95, the gray value of each pixel in the temporarily reconstructed image is divided by the gray value of the corresponding pixel in the weighted reconstructed image to obtain the desired reconstructed image for output.

Figures 10A and 10B show the original filtered image and the filtered image with reduced ripple artifacts using the described method, respectively, in one embodiment. In the image shown in FIG. 10A , there are some ripple artifacts 901 around the high attenuation part, but there are no such artifacts in the image shown in FIG. 10B , so the tissue structure near the boundary can be displayed more clearly.

In some embodiments, the undershoot artifact and the ripple artifact can be simultaneously reduced by combining the above two methods, that is, in the filtering step, a weight is calculated for each pixel in the projection image I _originalal to generate weighted image, and multiplying the undershoot-reduced filtered image (I _USfree ) by the weighted image to produce an undershoot-reduced weighted filtered image; in the step of backprojecting, backprojecting the plurality of projections A weighted filtered image with reduced undershoot produced by the image to generate a temporarily reconstructed image; back-projecting the weighted images of the plurality of projection images to generate a weighted reconstructed image; dividing the gray value of each pixel in the temporarily reconstructed image The gray value of the corresponding pixel in the image is reconstructed with the weight to obtain the reconstructed image for output. The reconstructed image obtained by this method has no undershoot artifact and ripple artifact, and can clearly and accurately display the tissue structure of the scanned object.

In one embodiment, the weight image is Where e is the natural index, p is the gray value of the pixel point (i, j), t and s are parameters corresponding to one or more exposure parameters in the scanning step.

The method described in the previous embodiment can reduce the artifacts caused by the existence of high attenuation parts without reducing the image quality, and without introducing other artifacts or defects, so the method can restore more structures in the original artifact area Details and features that help improve resolution and thus improve diagnostic accuracy.

The present invention may be embodied in other specific forms without departing from the spirit or main characteristics of the invention. Therefore, no matter from which point of view, the above-mentioned embodiments of the present invention can only be considered as illustrations of the present invention and can not limit the present invention, and the scope of the present invention is defined by the claims, rather than by the above-mentioned delimitation, therefore, Any changes within the meaning and scope equivalent to the claims of the present invention should be considered to be included in the scope of the claims.

Claims (10)

1. a kind of medical imaging procedure comprising：

Object is scanned along one or more different scanning directions to generate a plurality of projected images, wherein the object Including background parts and highly attenuating part；

For projected image described in each：

Projected image is filtered, to generate original filtration image；

By the picture of the borderline region close to highly attenuating part and the boundary of background parts in the highly attenuating part in projected image Vegetarian refreshments is shunk along the negative direction of scanning direction or scanning direction towards highly attenuating partial interior, and will be in the borderline region Grey scale pixel value is substituted for the grey scale pixel value that background parts adjacent thereto are close, to generate contraction image, in the contraction In image, the boundary of highly attenuating part and background parts is moved to highly attenuating partial interior；

The contraction image is filtered, to generate contraction filtering image；And

It merges the original filtration image and shrinks filtering image to generate the filtering image of undershoot reduction；And

The filtering image of undershoot reduction caused by a plurality of projected images described in back projection, to obtain reconstruction image.

2. the method for claim 1, wherein

For projected image described in each, further comprise：

Weight is calculated for each pixel in the projected image, to generate weight image；And

The filtering image of the undershoot reduction and the weight image are multiplied to produce to the weighted filtering image of undershoot reduction；

The filtering image of undershoot reduction caused by a plurality of projected images described in back projection includes：

The weighted filtering image for the undershoot reduction that a plurality of projected images generate described in back projection temporarily rebuilds figure to generate Picture；

The weight image of a plurality of projected images described in back projection, to generate weight reconstruction image；And

By the gray value of corresponding pixel in the gray value of each pixel in temporary reconstruction image divided by weight reconstruction image, Obtain the reconstruction image for output.

3. a kind of medical imaging apparatus for being imaged to object comprising：

Radiographic source and ray detector, wherein the ray detector be used for receiving sent out by the radiographic source after pass through it is scanned Object ray, the radiographic source and ray detector are used for along one or more different scanning directions to including background portion Divide and the object of highly attenuating part is scanned；

Data collecting system is used for receiving the data from the ray detector when scanning object, to generate corresponding throw Shadow data；

Processor, it is described to rebuild to generate projected image for receiving the data for projection from the data collecting system The image of object comprising：

Module is shunk, is used for the side close to highly attenuating part and background parts in the highly attenuating part in the projected image The pixel of the borderline region on boundary is shunk along the negative direction of scanning direction or scanning direction towards highly attenuating partial interior, and will Grey scale pixel value in the borderline region is substituted for the grey scale pixel value that background parts adjacent thereto are close, and is shunk with generating Image, in the contraction image, the boundary of highly attenuating part and background parts is moved to highly attenuating partial interior；

Filter module carries out the contraction image for being filtered to the projected image to generate original filtration image Filtering is to generate contraction filtering image；

Fusion Module, for merging the original filtration image and shrinking filtering image to generate the filtering image of undershoot reduction； And

Back projection module is used for the filtering image of undershoot reduction described in back projection, to obtain reconstruction image；And

Display device shows the image of the acquisition by responding the processor.

4. device as claimed in claim 3, wherein the processor further comprises：

Weighting block is used for calculating weight for each pixel in the projected image, to generate weight image, and will be described The filtering image of undershoot reduction is multiplied to produce weighted filtering image with the weight image, and

The back projection module is used for：

The weighted filtering image for the undershoot reduction that projected image described in back projection generates, to generate temporary reconstruction image；

The weight image of projected image described in back projection, to generate weight reconstruction image；And

By the gray value of corresponding pixel in the gray value of each pixel in temporary reconstruction image divided by weight reconstruction image, Obtain the reconstruction image for output.

5. method as claimed in claim 2 or device as claimed in claim 4,

Wherein, the weight image isWherein e is natural Exponents, and p (i, j) is pixel The gray value of (i, j), t and s are the parameter of one or more of corresponding scanning step exposure parameter.

6. the method as described in claim 1 or device as claimed in claim 3, wherein the highly attenuating part includes Metal, the background parts include nonmetallic.

7. the method as described in claim 1 or device as claimed in claim 3, wherein the projected image and contraction Image is filtered by rebuilding kernel.

8. the method as described in claim 1 or device as claimed in claim 3, wherein in the highly attenuating part It is determined to the contracted length of each pixel of contract by its gradient intensity.

9. method as claimed in claim 8 or device, wherein the contracted length L (i, j) of pixel (i, j) is the side of passing through What formula L (i, j)=H (dy (i, j), kernel) was determined, wherein dy (i, j) is the ash of pixel (i, j) in a scanning direction Angle value gradient, H is one and is used for mapping the function that gradient dy (i, j) arrives contracted length L (i, j), and kernel is for described The reconstruction kernel that projected image and contraction image are filtered.

10. the method as described in claim 1 or device as claimed in claim 3, wherein the filtering of the undershoot reduction Image I_USfreeIt is the original filtration image I_foriginalWith contraction filtering image I_fshrunkenPass through equation I_USfree=(1- mask)*I_fshrunken+mask*I_foriginalIt is merged and generates, wherein mask is a kind of dot chart, in the dot chart From (i, j) to the value in the region of the pixel of (i+/- C*L, j) it is 0 on corresponding scanning direction, the value in remaining region is picture for 1, L The contracted length of vegetarian refreshments (i, j), C are constant parameter, correspond to and are used for being filtered the projected image and contraction image Reconstruction kernel.