Patent Application
20220074873
The present invention relates to radiographic image processing apparatus, a radiographic image processing method, and a radiographic image processing program.
As a radiographic image processing technique, for example, the following technique is known. In this technique, X-rays are emitted from an X-ray tube to a subject, and X-rays transmitted through the subject are detected by a flat-panel X-ray detector (hereinafter referred to as “FPD”), thereby acquiring a projected image. At this time, the first, second, and third cameras capture an optical image of a marker disposed on a monitoring plate to obtain the image. Then, a three-dimensional position calculation unit calculates the three-dimensional position of the X-ray tube and the FPD, based on the respective acquired images. A reconstruction calculation unit generates a tomographic image or the like based on the group of projected images and the measured three-dimensional positions (see, e.g., Patent Document 1).
There also is the following technique. In this technique, a series of radiographic images are captured in a state in which a marker is reflected together with a subject in the imaging field of view. Based on the marker images reflected in the respective radiographic images, it is possible to recognize how much the imaging system deviates from the ideal position. Based on this recognition, the image correction is performed (see, e.g., Patent Document 2).
For example, an X-ray tomographic plane examination apparatus using an X-ray Tomosynthesis detects an image of the tomographic plane by synthesizing a plurality of image data acquired by one imaging. At this time, when synthesizing a plurality of image data, the position of the X-ray tube emitting the X-rays needs to be calculated. As a premise, it is required to detect a metal marker embedded in a phantom to be reflected together with a subject.
However, in order to detect the metal marker from the captured radiographic image, it is required to scan the region of interest in the captured image to repeat the binarization, so that an enormous amount of processing and time are required. Further, in a case where the position of the metal marker is detected in the image, the X-ray tube position estimation result greatly changes with the accuracy of less than one pixel, so that the accuracy of detecting the marker position is also required.
In one aspect, the present invention provides a radiographic image processing technique capable of detecting a metal marker from a radiographic image at high speed and with a high degree of accuracy.
A radiographic image processing apparatus according to one aspect of the present invention, includes:
an acquisition unit configured to acquire a radiographic image reflecting a plurality of markers:
a generation unit configured to generate a low-resolution image in which a resolution of the radiographic image has been reduced;
a position identification unit configured to identify respective positions of the plurality of markers in the low-resolution image, based on a characteristic of the plurality of markers; and
a position estimation unit configured to estimate positions of the plurality of markers in the radiographic image, by searching for positions on the radiographic image corresponding to the respective positions of the plurality of markers in the low-resolution image.
The above-described radiographic image processing apparatus may further include:
a search unit configured to search for a region of interest reflecting the plurality of markers in the low-resolution image, based on the characteristic of the plurality of markers.
The above-described search unit may narrow down a scan region with respect to the low-resolution image in a stepwise manner, based on the characteristic of the plurality of markers.
The above-described search unit may identify a temporary region of interest including a region reflecting the plurality of markers in the low-resolution image and identifies the region of interest reflecting the plurality of markers from the temporary region of interest based on the characteristic of the plurality of markers.
The above-described position identification unit may identify respective barycentric coordinates of the plurality of markers included in the region of interest as the respective positions of the plurality of markers in the low-resolution image, based on the characteristic of the plurality of markers.
A radiographic image processing method to be performed by a radiographic image processing apparatus according to one aspect of the present invention, includes:
acquiring a radiographic image reflecting a plurality of markers;
generating a low-resolution image in which a resolution of the radiographic image has been reduced;
identifying respective positions of the plurality of markers in the low-resolution image, based on the characteristic of the plurality of markers; and
estimating positions of the plurality of markers in the radiographic image by searching for positions on the radiographic image corresponding to the respective positions of the plurality of markers in the low-resolution image.
A radiographic image processing program according to one aspect of the present invention is configured to making a computer execute processing, the processing including:
acquiring a radiographic image reflecting a plurality of markers;
generating a low-resolution image in which a resolution of the radiographic image has been reduced;
identifying respective positions of the plurality of markers in the low-resolution image, based on the characteristic of the plurality of markers; and
estimating positions of the plurality of markers in the radiographic image by searching for positions on the radiographic image corresponding to the respective positions of the plurality of markers in the low-resolution image.
According to one aspect of the present invention, a metal marker can be detected from a radiographic image at high speed and with a high degree of accuracy.
When a high voltage is applied based on the signal from the imaging control unit 7, the X-ray tube 2 generates radiation (X-rays) and emits the radiation toward the detector 4. The X-ray tube 2 is movably held by the position change mechanism 3. The position change mechanism 3 changes the position of the X-ray tube 2 based on the signal from the imaging control unit 7.
The detector 4 is a flat panel X-ray detector (Flat Panel Detector: FPD). This detector 4 is arranged to face the X-ray tube 2, and converts the captured image by the radiation emitted from the X-ray tube 2 into image data. That is, the detector 4 converts the radiation to an electric signal, reads the converted electric signal as a signal of the image, and outputs the signal of the image to the radiographic image processing apparatus 6. Note that the detector 4 is provided with a plurality of conversion elements (not shown) and pixel electrodes arranged on the plurality of conversion elements (not shown). Further, the plurality of conversion elements and pixel electrodes are arranged at a predetermined period (pixel pitch).
The phantom 5 is also referred to as a calibration phantom, and has a configuration in which metallic spheres are arranged at the center of a rectangular parallelepiped made of, for example, acrylic resin or the like. The phantom 5 is arranged between the X-ray tube 2 and the detector 4, and is imaged together with the subject T to estimate the position of the X-ray tube 2.
The radiographic image processing apparatus 6 is an apparatus for processing the signal of the image acquired by the detector 4. The configuration of the radiographic image processing apparatus 6 will be described later.
Hereinafter, the metal marker may be referred to as a “marker”. The metal markers (or markers) 11a, 11b, 11c, 11d, 12a, 12b, 12c, 12d are collectively referred to as metal markers (or markers) 10.
Here, the paired metal markers are arranged at least 70 mm apart from each other in the near and far direction. Further, the metal markers constituting the pair are arranged at positions that do not overlap when viewed in the near and far direction (when the phantom 5 is viewed in a plan).
The control unit 21 is, for example, a processor (not shown), such as, e.g., a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or an FPGA (Field-Programmable Gate Array) configured for image processing. The control unit 21 controls the entire operation of the radiographic image processing apparatus 6 and performs the image processing.
The storage unit 29 is a large-capacity storage device, such as, e.g., a hard disk drive and an SSD (Solid State Drive), and stores a radiographic image 30 acquired by the detector 4. The storage unit 29 stores the information on the detection condition 33 of the marker used in this embodiment. In the storage unit 29, an operating system (OS) and a program related to radiographic image processing (including a program associated with this embodiment) are installed.
The memory 30 is a working storage region used by the control unit 21 to perform predetermined processing or to display data on a screen. The memory 30 is a volatile storage device, such as, e.g., a RAM (Random Access Memory), but may be a non-volatile flash memory depending on the specification.
The input I/F 34 is, for example, an interface to which an input device (not shown), such as, e.g., a keyboard and a control panel, is connected. The detection condition 33 of the marker 10 can be set via the input device. The output I/F 35 is an interface to which, for example, a display device, such as, e.g., a touch panel, and/or an output device (not shown), such as, e.g., a printer, is connected. The communication I/F 36 is an interface for communicating with other devices, such as, e.g., the detector 4 and the imaging control unit 7.
Next, the processing performed by the control unit 21 will be described. The control unit 21 generally performs marker position estimation processing 22 and X-ray tube position estimation processing 28 in this embodiment. The marker position estimation processing 22 is processing for estimating the position of the reflected marker 10 from the captured radiographic image. When performing the marker position estimation processing 22, the control unit 21 reads out and executes the program of this embodiment stored in the storage unit 29. With this, the control unit 21 functions as an acquisition unit 23, a generation unit 24, a search unit 25, a position identification unit 26, and a position estimation unit 27. At this time, the control unit 21 reads out the detection condition 33 stored in the storage unit 29 and places it in the memory 30.
The acquisition unit 23 acquires a radiographic image 31 reflecting a plurality of markers 10 via the communication I/F 35 or stored in the storage unit 29, and places it in the memory 31.
The generation unit 24 generates a low-resolution image 32 in which the resolution of the radiographic image 31 has been reduced and arranges it in the memory 30.
The search unit 25 searches for a region of interest reflecting the plurality of markers 10 in the low-resolution image 32 based on the characteristic of the plurality of markers set in the detection condition 33. Here, the region of interest represents a predetermined region selected for the image analysis from the low-resolution image 32. The search unit 25 can narrow down the scan region with respect to the low-resolution image 32 in a stepwise manner based on the characteristic of the plurality of markers 10. Based on the characteristic of the plurality of markers, the search unit 25 may identify a temporary region of interest including a region reflecting the plurality of markers 10 in the low-resolution image 32, and may identify the region of the interest reflecting one or a plurality of markers from the temporary region of interest.
The position identification unit 26 identifies the respective positions of the plurality of markers 10 in the low-resolution image 32 based on the characteristic of the plurality of markers set in the detection condition 33. More specifically, the position identification unit 26 identifies the respective positions of the plurality of markers 10 included in the region of interest in the low-resolution image 32, based on the characteristic of the plurality of markers 10 set in the detection condition 33. Based on the characteristic of the plurality of markers 10, the position identification unit 26 identifies the respective barycentric coordinates of the plurality of markers 10 included in the region of interest as the respective positions of the plurality of markers 10 in the low-resolution image 32.
The position estimation unit 27 estimates the positions of the plurality of markers 10 in the radiographic image 31 by searching for positions on the radiographic image 31 corresponding to the respective positions of the plurality of markers 10 in the low-resolution image 32.
The X-ray tube position estimation processing 28 identifies the above-described pairs in the vertical direction in the phantom 5, based on the position and the area of the marker reflected in the radiographic image 31 estimated by the marker position estimation processing 22. The X-ray tube position estimation processing 28 estimates the position of the X-ray tube based on the position coordinate of the marker identified as a pair.
The program according to this embodiment may be executed not only by the radiographic image processing apparatus 6 but also by an information processing device, such as, e.g., a computer. The program in this embodiment may be installed on the computer from a telecommunication network or a recording medium.
A recording medium including such a program is configured by a removable media that is distributed separately from the device body to the user to provide the program to each user. The recording medium may also be configured by a recording medium or the like provided to each user in a condition in which it is incorporated in the device main body in advance.
In this specification, the step describing a program recorded in the recording medium includes processing performed in time series in the order. Further, this step includes the processing that is executed in parallel or individually, although not necessarily executed in chronological order.
Next, the control unit 21 performs X-ray tube position estimation processing (S2). In the X-ray tube position estimation processing (S2), the following processing is executed in order. The processing includes: binary image generation processing (S2-1); labeling processing (S2-2); area calculation processing (S2-3) of each region; far and near determination processing (S2-4) of a marker by an area; marker pair determination processing (S2-5); and X-ray tube coordinate estimation processing (S2-6).
In the binary image generation processing (S2-1), the control unit 21 generates a binarized radiographic image, based on the signal of the image detected by the detector 4.
In the labeling processing (S2-2), the control unit 21 labels each of the metal markers 11a-11d, 12a-12d for which the positions were estimated by the marker position estimation processing (S1) in the radiographic image to distinguish them from each other.
The area calculation processing (S2-3) of each region is processing in which the control unit 21 calculates the area of each of the plurality of metal markers 11a to 11d and 12a to 12d in the labeled radiographic image. Here, the control unit 21 also calculates the average value of the maximum value and the minimum value of the calculated areas.
In the far and near determination processing (S2-4) of the marker by an area, the control unit 21 determines that the metal markers 11a to 11d in the radiographic image having an area larger than the calculated average value as a threshold is relatively far from the detector 4 (positioned at the upper portion within the phantom 5 in
In the marker pair determination processing (S2-5), the control unit 21 classifies the plurality of metal markers 11a-11d, 12a-12d based on the relative position on the x-y coordinate plane of the plurality of metal markers 11a-11d, 12a-12d for each classified group. Then, the control unit 21 selects the metal markers 11a-11d of the first group and the metal markers 12a-12d of the second group, which match the relative position, as pairs.
Specifically, the control unit 21 selects, for example, one of the following pairs as the metal markers in which the relative position matches. That is, the control unit 21 selects one of the pair of the metal markers 11a and the metal marker 12a, the pair of the metal markers 11b and the metal marker 12b, the pair of the metal marker 11c and the metal marker 12c, and the pair of the metal marker 11d and the metal marker 12d.
Note that in the phantom 5, as a plurality of pairs of metal markers arranged in a distance in the near and far direction with respect to the detector 4, here, the four pairs are exemplified as the configurable number, but the present invention is not limited thereto. Even considering that some metal markers are not reflected in the captured image due to, for example, tilting of the phantom 5, in order to estimate the X-ray tube position, it is sufficient that at least two pairs of metal markers are provided. Further note that the marker is not limited to a metal one, and any material may be used as long as the absorption amount of X-rays is large.
In the X-ray tube coordinate estimation processing (S2-6), the control unit 21 estimates the position of the X-ray tube 2, based on the position coordinate of the paired and selected metal markers 11a-11d, 12a-12d. Now a three-dimensional space including the X-ray tube 2, the metal markers 11a, 12a, and the metal markers 11a, 12a in the radiographic image is assumed. At this time, the position coordinate of the position S of the X-ray tube 2 is defined as (x, y, Sd). Further, the position coordinate of the position of the metal marker 11a is defined as (Pa, Pb, Pd+Ps). The position coordinate of the position of the metal marker 12a is defined as (Pa, Pb, Pd). The position coordinate of the position of the metal marker 11a in the radiographic image is defined as (a1, b1, 0). The position coordinate of the position of the metal marker 12a in the radiographic image is defined as (a2, b2, 0).
Note that x is a coordinate of the X-ray tube 2 in the X-direction. Also, y is a coordinate of the X-ray tube 2 in the Y-direction. In addition, Pa is a coordinate of the metal marker 11a, 12a in the X-direction. Pb is a coordinate of the metal markers 51a and 52a in the Y-direction. Sd is a distance (SID: Source Image receptor Distance) in the Z-direction from the detector 4 to the X-ray tube 2. Further, Pd is a distance in the Z-direction from the detector 4 to the metal marker 12a. Further, Ps is a distance in the Z-direction between the metal markers 11a and 12a to each other.
The X-ray tube 2, the metal markers 11a and 12a, and the metal markers 11a and 12a in the radiographic image are in the relation of externally dividing points. Therefore, from this relation, the position coordinate of the position S of the X-ray tube 2 is derived from the following Expressions (1) and (2).
x={a1*(1−β)−a2*(1−α)}/(β−α) (1)
y={b1*(1−β)−b2*(1−α)}/(β−α) (2)
where,
α=(Pd+Ps)/(Pd+Ps−Sd)
β=Pd/(Pd−Sd)
With this, even if the radiographic image capturing apparatus 1 does not have a mechanism to measure the absolute position, it is possible to estimate the position of the X-ray tube by the positional relation of the plurality of markers in the radiographic image.
Next, the marker position estimation processing (S1) will be described in detail.
In S1, the control unit 21 reduces the processing time required to estimate the position of the marker by narrowing down the scan range of the radiographic image with the reduced resolution in a stepwise manner. Also, since the X-ray tube coordinate changes with the accuracy of less than one pixel, the coordinate of the final marker is estimated using the radiographic image of the original resolution. Note that it is assumed that the data of the captured image (radiographic image) reflecting the subject T and the phantom 5 acquired by the detector 4 has been stored in advance in the storage unit 29.
First, as the acquisition unit 23, the control unit 21 reads out the radiographic image 31 stored in the storage unit 29 and arranges it in the memory 30 (S11).
Next, as shown in
The degree of reduction in the resolution of the radiographic image 31 may be arbitrarily set by the operator by, for example, a control panel or the like, or may be set to a predetermined value in advance.
Next, as the search unit 25, the control unit 21 detects the rough position of the phantom (the region where a maker may be present, the region being referred to as a temporary phantom region) from the low-resolution image 32. Here, as shown in
When performing the labeling, the control unit 21 detects and labels the metal marker from the low-resolution image 32 based on the detection condition 33. The detection condition 33 defines the characteristic of the metal marker reflected in the low-resolution image 32, and is, for example, the circularity and/or the area of the marker in the low-resolution image 32. For example, when there exit the largest number of labeled objects whose circularity and/or area satisfy a predetermined condition (threshold value), the control unit 21 sets the region specified by the position 42 of the region of interest as a phantom region.
Then, as the search unit 25, the control unit 21 determines the phantom position to be estimated based on the temporary phantom region 42 (S14). That is, as shown in
Then, as the position identification unit 26, the control unit 21 estimates the rough coordinate of the markers in the range of the phantom region 52 (S15). Here, as shown in
As the position estimation unit 27, the control unit 21 makes a final determination of the coordinate of each marker on the original radiographic image 31 prior to the resolution reduction (S16). Here, as shown in
According to this embodiment, in the radiographic image reflecting the marker, the position of the phantom in which makers are embedded is temporarily identified from the radiographic image reduced in resolution. Then, the search range is narrowed down by using the region specified as the position of the temporary phantom as the region of interest, and the rough position of each marker is specified. This allows the estimation of the coordinate of the final marker in the original radiographic image prior to the resolution reduction. As a result, the processing time required for estimating the position of markers can be shortened by narrowing down the scan range of the radiographic image in which the resolution has been reduced in a stepwise manner. Also, since the estimation of the coordinate of the final marker is performed using the radiographic image of the original resolution, it is possible to cope with the change in the X-ray tube coordinate with the accuracy of less than one pixel.
Note that in the above, labeling is performed to detect labeled objects satisfying the detection condition 33 from labeled objects. However, the detection condition 33 may be set for each labeling, or may be the same extraction condition.
Note that, in the above-described embodiment, an image acquired by tomosynthesis has been described as an example as the radiographic image, but the present invention is not limited thereto, and an image acquired by tomography photographing, such as, e.g., CT (Computed Tomography), may be used. Alternatively, the image applied to this embodiment may be, for example, an MRI (magnetic resonance imaging) image or another medical image.
As described above, a radiographic image processing apparatus (for example, a radiographic image processing apparatus 6) includes:
an acquisition unit (e.g., the acquisition unit 23) configured to acquire a radiographic image (e.g., the radiographic image 31) reflecting a plurality of markers:
a generation unit (e.g., the generation unit 24) configured to generate a low-resolution image (e.g., the low-resolution image 32) in which a resolution of the radiographic image has been reduced;
a position identification unit (e.g., the position identification unit 26) configured to identify respective positions of the plurality of markers in the low-resolution image, based on a characteristic (e.g., the detection condition 33) of the plurality of markers; and
a position estimation unit (e.g., the position estimation unit 27) configured to estimate positions of the plurality of markers in the radiographic image, by searching for positions on the radiographic image corresponding to the respective positions of the plurality of markers in the low-resolution image.
With this configuration, it is possible to detect the metal markers from the radiographic image at high speed and with a high degree of accuracy. In other words, since the scan range of the radiographic image in which the resolution has been reduced can be narrowed down in a stepwise manner, the processing time required for estimating the positions of the markers can be shortened. Further, the X-ray tube coordinate changes with the accuracy of less than one pixel, but the final estimation of the coordinates of the markers is performed using the radiographic image of the original resolution. Therefore, it is possible to estimate the coordinates of the markers with a high degree of accuracy, and as a result, it is possible to estimate the X-ray tube coordinate with a high degree of accuracy.
The radiographic image processing apparatus (e.g., the radiographic image processing apparatus 6) is further provided with:
a search unit (e.g., the search unit 25) configured to search for a region of interest reflecting the plurality of markers in the low-resolution image, based on the characteristic of the plurality of markers.
With this configuration, a plurality of marker regions of interest in the low-resolution image can be searched.
The search unit (e.g., the search unit 25) narrows down a scan region with respect to the low-resolution image in a stepwise manner, based on the characteristic of the plurality of markers.
With this configuration, it is possible to narrow down the region in which the markers exist.
The search unit (e.g., the search unit 25) identifies a temporary region of interest (e.g., the temporary phantom region 42) including a region reflecting the plurality of markers in the low-resolution image and identifies the region of interest (e.g., the phantom region 52) reflecting the plurality of markers from the temporary region of interest based on the characteristic of the plurality of markers.
With this configuration, the position in which the phantom exists can be estimated from the rough phantom region.
The position identification unit (e.g., the position identification unit 26) identifies respective barycentric coordinates of the plurality of markers included in the region of interest as the respective positions of the plurality of markers in the low-resolution image, based on the characteristic of the plurality of markers.
With this configuration, although the X-ray tube coordinate changes with the accuracy of less than one pixel, the estimation of the coordinate of the final marker is performed using the radiographic image of the original resolution. Therefore, it is possible to estimate the coordinate of the marker with a high degree of accuracy, and as a result, it is possible to estimate the X-ray tube coordinate with a high degree of accuracy.
Further, a radiographic image processing method to be performed by a radiographic image processing apparatus according to this embodiment, includes:
acquiring a radiographic image (e.g., the radiographic image 31) reflecting a plurality of markers (e.g., S11 in
generating a low-resolution image (e.g., the low-resolution image 32) in which a resolution of the radiographic image has been reduced (e.g., S12 in
identifying respective positions of the plurality of markers in the low-resolution image, based on the characteristic (e.g., the detection condition 33) of the plurality of markers (e.g., S15 in
estimating positions of the plurality of markers in the radiographic image by searching for positions on the radiographic image corresponding to the respective positions of the plurality of markers in the low-resolution image (e.g., S16 in
With this configuration, the metal markers can be detected from the radiographic image at high speed and with a high degree of accuracy. In other words, since the scan range of the radiographic image in which the resolution has been reduced can be narrowed down in a stepwise manner, the processing time required for estimating the position of the markers can be shortened. In addition, although the X-ray tube coordinate changes with the accuracy of less than one pixel, the estimation of the coordinate of the final marker is performed using the radiographic image of the original resolution, so that the coordinate of the marker with a high degree of accuracy can be estimated, resulting in the estimation of the high-precision X-ray tube coordinate.
Further, the radiographic image processing program according to this embodiment makes a computer execute the processing comprising:
acquiring a radiographic image (e.g., the radiographic image 31) reflecting a plurality of markers (e.g., S11 in
generating a low-resolution image (e.g., the low-resolution image 32) in which a resolution of the radiographic image has been reduced (e.g., S12 in
identifying respective positions of the plurality of markers in the low-resolution image, based on the characteristic (e.g., the detection condition 33) of the plurality of markers (e.g., S15 in
estimating the positions of the plurality of markers in the radiographic image by searching for positions on the radiographic image corresponding to the respective positions of the plurality of markers in the low-resolution image (e.g., S16 in
With this configuration, the metal markers can be detected from the radiographic image at high speed and with a high degree of accuracy. In other words, since the scan range of the radiographic image in which the resolution has been reduced can be narrowed down in a stepwise manner, the processing time required for estimating the positions of the markers can be shortened. Although the X-ray tube coordinate changes with the accuracy of less than one pixel, but the final estimation of the coordinates of the marker is performed using the radiographic image of the original resolution. Therefore, it is possible to estimate the coordinates of the markers with a high degree of accuracy, and as a result, it is possible to estimate the X-ray tube coordinate with a high degree of accuracy.
Although the present embodiment has been described based on embodiments and modifications, the above-described embodiments are for facilitating the comprehension of the present embodiment, and are not intended to limit the embodiment. This aspect may be modified and improved without departing from the spirit and scope thereof, and the present aspect includes equivalents thereof. In addition, unless the technical feature is described as essential in this specification, the technical feature can be appropriately deleted.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-239838 | Dec 2018 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/041000 | 10/17/2019 | WO | 00 |
