Radiographic imaging apparatus, radiographic imaging method, and storage medium

Abstract

A radiation imaging apparatus includes an image obtaining unit configured to obtain image data corresponding to incident radiation, and an image processing unit configured to perform a first bone density measurement based on image data obtained by the image obtaining unit with a first exposure field, and perform a second bone density measurement based on image data obtained by the image obtaining unit with a second exposure field narrower than the first exposure field.

Description

Technical Field

[0001] This invention relates to radiographic imaging apparatus, radiographic imaging methods, and procedures, and more particularly to radiographic imaging techniques applicable to the measurement of bone density. Background Technology

[0002] The number of people suffering from osteoporosis has increased with age. As a technique for diagnosing osteoporosis, bone density measurement based on dual-energy X-ray absorptiometry (hereinafter referred to as DXA) using X-rays with two different energies is known.

[0003] Typical DXA devices are generally designed to perform measurements by switching and scanning X-ray fan beams of different energies at high speeds. Recently, techniques have been developed for performing bone density measurements using DXA by using a flat panel detector (hereinafter referred to as FPD) formed by stacking two X-ray detection layers to perform cone-beam imaging operations, and for performing bone density measurements using DXA by performing two imaging operations with X-rays of different energies using a single-layer FPD.

[0004] Patent document 1 discloses a technique for measuring bone density by correcting the scattered lines of a wide-range X-ray image using a narrow-range X-ray image.

[0005] Citation List

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2011-245117 Summary of the Invention

[0008] Technical issues

[0009] Bone density measurements are often performed by measuring both the lumbar spine, which is susceptible to changes over time, and the proximal femur, which is prone to severe damage in the event of a fracture. Although the use of a flat panel detector and a cone beam of X-rays allows for simultaneous imaging of the lumbar spine and proximal femur in a short period of time, the use of a wide exposure field can reduce measurement accuracy due to scattered radiation.

[0010] The technology disclosed in Patent Document 1 has the following problems: since four imaging operations are required when changing the exposure range and X-ray exposure conditions, the inspection efficiency is reduced and the dose to the subject is increased.

[0011] The present invention has taken into account the above-mentioned problems and aims to provide a radiographic imaging technique that can improve examination efficiency and measurement accuracy while reducing the dose to the subject.

[0012] Solution to the problem

[0013] A radiation imaging apparatus according to one aspect of the present invention includes the following arrangement: The radiation imaging apparatus includes an image acquisition unit and an image processing unit, the image acquisition unit being configured to acquire image data corresponding to incident radiation, and the image processing unit being configured to perform a first bone density measurement based on the image data acquired by the image acquisition unit using a first exposure field, and to perform a second bone density measurement based on the image data acquired by the image acquisition unit using a second exposure field narrower than the first exposure field.

[0014] Beneficial effects of the invention

[0015] This invention provides a radiographic imaging technique that can improve examination efficiency and measurement accuracy while reducing the dose to the subject. Attached Figure Description

[0016] Figure 1 This is a diagram illustrating an example of the arrangement of a radiation imaging system according to the first embodiment;

[0017] Figure 2 This is a flowchart for explaining the processing procedure in the image processing unit according to the first embodiment;

[0018] Figure 3 This is a conceptual diagram showing high-energy images, low-energy images, and skeletal images;

[0019] Figure 4 This is a diagram used to explain the extraction of skeletal regions;

[0020] Figure 5 It is a diagram used to interpret the calculations for the baseline region and calibration curve;

[0021] Figure 6 This is an illustration used to explain an example of the setting of the exposure field range according to the first embodiment;

[0022] Figure 7 This is a flowchart for explaining the processing procedure in the image processing unit according to the second embodiment;

[0023] Figure 8 This is a flowchart explaining the processing procedure in the image processing unit according to the third embodiment; and

[0024] Figure 9 This is an illustration used to explain an example of setting the exposure field range according to the third embodiment. Detailed Implementation

[0025] In the following, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments are not intended to limit the scope of the claimed invention. Several features are described in the embodiments, but the invention is not limited to requiring all such features, and multiple such features can be suitably combined. Furthermore, in the drawings, the same reference numerals are given to the same or similar configurations, and repeated descriptions thereof are omitted.

[0026] (First Embodiment)

[0027] Figure 1 This is a diagram illustrating an example arrangement of a radiation imaging system 100 according to a first embodiment of the present invention. The radiation imaging system 100 includes a radiation generator 104, a radiation source 101, a radiation exposure field aperture 1001, a radiation grid 1002, an FPD 102 (radiation flat panel detector), and an information processing device 120. Note that the arrangement of the radiation imaging system 100 is also simply referred to as a radiation imaging apparatus. The information processing device 120 processes information based on radiation images obtained by imaging a subject.

[0028] The radiation generator 104 (generating unit) causes the radiation source 101 to generate radiation by supplying a high-voltage pulse to the radiation source 101 when the exposure switch is pressed. The radiation source 101 irradiates the subject 103 with the radiation. At this time, the radiation exposure field aperture 1001 prevents the radiation from irradiating areas outside the region of interest of the subject 103 by limiting the irradiation range of the radiation. This makes it possible to reduce unnecessary exposure and also reduce the scattered radiation generated from the subject 103. As the radiation grid 1002, a cross grid is preferably used. A cross grid is a grid with slits formed in a grid pattern in both the longitudinal and transverse directions. This grid can reduce scattered radiation more effectively and evenly than a general grid. This makes it possible to perform imaging using a conical beam, thus eliminating the need for long imaging times such as those using a fan beam or slit scanning. Although there are no particular restrictions on the type of radiation to be used, X-rays are generally used.

[0029] When the subject 103 is irradiated with radiation from the radiation source 101, the FPD 102 acts as an image acquisition unit and acquires image data based on the incident radiation. The FPD 102 acquires the radiation image by accumulating charge based on the image signal. The FPD 102 transmits the radiation image to the information processing device 120.

[0030] FPD 102 includes a radiation detection unit (not shown) comprising a pixel array for creating a signal corresponding to the radiation. The radiation detection unit detects radiation transmitted through the subject 103 and detects an image signal corresponding to the detected radiation. In the radiation detection unit, each of the pixels arranged in an array pattern (two-dimensional region) is provided with, for example, a phosphor (scintillator) that converts incident radiation into light and a photoelectric conversion element that outputs a signal corresponding to the converted light. The photoelectric conversion element of each pixel converts the radiation, which is converted into visible light by the phosphor, into an electrical signal and outputs it as an image signal (radiation image).

[0031] The control unit 105 includes an image processing unit 109 that processes radiographic images obtained from the FPD 102, and a storage unit 108 that stores the results of image processing and various types of programs. The storage unit 108 can store radiographic images output from the control unit 105, images processed by the image processing unit 109, and bone density calculation results.

[0032] As a functional configuration, the image processing unit 109 includes a difference image creation unit 110, a bone region extraction unit 111, a bone density calculation unit 112, a bone density determination unit 113, and an exposure field setting unit 114. The functions of these configurations are each implemented using, for example, one or more CPUs (Central Processing Units) and programs read from the storage unit 108. The configuration of each unit of the image processing unit 109 can be implemented by integrated circuits or the like, as long as similar functions are achieved. Furthermore, the internal configuration of the information processing device 120 may include a graphics control unit such as a GPU (Graphics Processing Unit), a communication unit such as a network card, a keyboard, and an input / output control unit such as a display or touch panel.

[0033] Monitor 106 displays a radiographic image (digital image) obtained by control unit 105 from FPD 102 or an image processed by image processing unit 109. Control unit 105 can control the display on monitor 106. Operation unit 107 can input commands to image processing unit 109 and FPD 102 and accept command input via user interface (not shown).

[0034] The control unit 105 obtains an image (bone image) indicating the distribution of skeletal parts of the subject by processing multiple radiation images with different energies of radiation irradiating the subject using an energy subtraction method. DXA requires at least two radiation images obtained by imaging with different radiation energies to create a subtractive image. To obtain different radiation energies, different voltage pulses can be supplied to the radiation source 101. The subject 103 can be irradiated with radiation of different energies from the radiation source 101.

[0035] As FPD 102, an FPD with stacked radiation detection units (not shown) can be used. The multilayer FPD 102 detects low-energy radiation by passing through the radiation detection unit of the upper layer, and detects high-energy radiation at the radiation detection unit of the lower layer after the radiation quality of the radiation that has passed through the upper layer radiation detection unit is hardened. This makes it possible to obtain low-energy radiation images at the upper radiation detection unit and high-energy radiation images at the lower radiation detection unit. Imaging performed by the multilayer FPD 102 can be accomplished with a single irradiation of radiation, which is advantageous in that it is unaffected by the body movement of the subject 103. Note that even a single-layer FPD 102 can obtain both low-energy radiation images (low-energy radiation images) and high-energy radiation images (high-energy radiation images) with a single irradiation of radiation by performing multiple samplings during a single irradiation. Imaging performed by the FPD 102 can be still image imaging or moving image imaging.

[0036] Reference Figure 2 The flowchart shown details the processing in the image processing unit 109 according to the first embodiment. Execution Figure 2 Each processing unit (difference image creation unit 110, bone region extraction unit 111, bone density calculation unit 112, and exposure field setting unit 114) in steps S202 to S205 shown in the diagram serves as a first bone density measurement unit. This first bone density measurement unit performs a bone density measurement (first bone density measurement) based on image data obtained by the FPD 102 (image acquisition unit) using a first exposure field. Each processing unit (control unit 105, difference image creation unit 110, bone region extraction unit 111, and bone density calculation unit 112) in steps S208 to S211 serves as a second bone density measurement unit. This second bone density measurement unit performs a bone density measurement (second bone density measurement) based on image data obtained by the FPD 102 (image acquisition unit) using a second exposure field that is narrower than the first exposure field. The second bone density measurement unit can measure bone density using a second exposure field based on the bone density measurement value obtained by the first bone density measurement unit and a predetermined threshold.

[0037] (S201: Follow-up examination)

[0038] In step S201, the control unit 105 uses the subject information input through the operation unit 107 to determine whether the measurement of the same subject is the first measurement, the second measurement, or a subsequent measurement (i.e., follow-up). The control unit 105 can perform this determination synchronously with the hospital information system (HIS) and the radiology information system (RIS), or it can be determined using information stored in the storage unit 108.

[0039] When the process has moved to bone density measurement performed by the second bone density measurement unit in previous measurements on the same subject (S208 to S211), the control unit 105 executes control over bone density measurement of the same subject starting from the bone density measurement performed by the second bone density measurement unit. When the second bone density measurement unit has performed bone density measurement (S208 to S211), it can be determined that osteoporosis is suspected in the subject. Therefore, the control unit 205 determines that the current examination is for follow-up or to determine the effect of the drug and proceeds the process to step S207 to perform the second bone density measurement. In this case, the control unit 105 executes control to start the measurement from the bone density measurement performed by the second bone density measurement unit without performing the bone density measurement performed by the first bone density measurement unit (S202 to S205). In contrast, if the current examination is the first examination, the control unit 205 proceeds the process to step S202 to perform the bone density measurement performed by the first bone density measurement unit (S202 to S205: first bone density measurement). The second bone density measurement unit can perform bone density measurement using a second exposure field based on the bone density measurement result obtained by the first bone density measurement unit. The second bone density measurement unit performs bone density measurement using a second exposure field based on the bone density measurement value obtained by the first bone density measurement unit and a predetermined threshold. The second bone density measurement unit can determine whether to omit the bone density measurement using the first exposure field, and perform the bone density measurement using the second exposure field according to the determination result.

[0040] (S202: First Imaging)

[0041] In the first imaging step S202, the exposure field setting unit 114 sets the radiation exposure field aperture 1001 to a first exposure field that enables imaging of multiple regions of the subject 103 (e.g., L1 to L4 of the lumbar spine and the hip joint 401 of the proximal femur). The control unit 105 controls the radiation imaging apparatus to perform imaging using the set first exposure field. The control unit 105 causes the radiation generator 104 to generate radiation by supplying a high-voltage pulse (pulse signal) to the radiation source 101 when the exposure switch is pressed. The radiation generator 104 causes the radiation source 101 to generate a cone-shaped beam of radiation by supplying a pulse signal based on the tube voltage to the radiation source 101. The radiation source 101 irradiates the subject 103 with the cone-shaped beam of radiation based on the pulse signal from the radiation generator 104. Radiation source 101 irradiates subject 103 with X-rays once at a high voltage V1 (first tube voltage, e.g., 140 kV) and once at a low voltage V2 (second tube voltage, e.g., 80 kV). Note that 140 kV, as an example of high voltage V1, and 80 kV, as an example of low voltage V2, are merely exemplary values. The invention is not limited to these examples, and voltages other than those shown can be used. For example, the voltage can be arbitrarily set according to the target measurement area, the image the user intends to see, the physique of subject 103, etc.

[0042] When irradiating with X-rays from radiation source 101, it is preferable to attach an additional filter (not shown) to the radiation exposure field aperture 1001. As an additional filter, for example, a copper plate with a thickness of 0.5 mm can be attached to the radiation exposure field aperture 1001. If the X-ray spectrum includes low-energy components, radiation-induced sclerosis is more likely to occur in the body of the subject 103. This can also be a factor contributing to a decrease in the accuracy of bone density calculations. However, attaching an additional filter will cut off the low-energy side of the X-ray spectrum, thereby improving the energy resolution between high-voltage and low-voltage X-rays.

[0043] FPD 102 creates high-voltage imaging based on high-voltage V1 by Figure 3 The high-energy image indicated by 3A, and created by low-voltage imaging based on low voltage V2. Figure 3 The low-energy image indicated by 3B.

[0044] In the first measurement, the radiation exposure field aperture 1001 is set to ensure a sufficiently wide exposure field (imaging range) for simultaneous imaging of the lumbar spine and proximal femur, as described by... Figure 3 As indicated by 3A and 3B. This allows for the simultaneous measurement of bone density in clinically important lumbar vertebrae and the proximal femur in a single measurement. This increases examination throughput and reduces the patient's workload by 10³.

[0045] As described above, the FPD 102, which uses stacked radiation detection units (not shown), can obtain radiation from the upper radiation detection unit by means of a single irradiation with X-rays, for example, by... Figure 3 The low-energy image indicated by 3B and obtained from the lower-level radiation detection unit, for example, by... Figure 3 The high-energy image indicated by 3A is a high-energy image. When the radiation source 101 emits X-rays using a high voltage V1 (e.g., 140 kV), the aforementioned additional filter is not required because the upper radiation detection unit has less leeway for hardening the radiation lines, resulting in a decrease in energy resolution. The image obtained by imaging using X-rays based on high voltage V1 is called a high-energy image, and the image obtained by imaging using X-rays based on low voltage V2 is called a low-energy image.

[0046] (S203: Creation of the skeletal image)

[0047] In step S203, the difference image creation unit 110 calculates the difference image obtained through the imaging in step S202. Figure 3 The high-energy images indicated by 3A and by Figure 3 The logarithmic difference between low-energy images indicated by 3B is used to create the image. Figure 3 The skeletal image 303 is indicated by 3C. The processing performed by the difference image creation unit 110 will be described in detail below. First, the high-energy image and the low-energy image can be represented by equations (1) and (2) given below.

[0048] -lnI H =-lnI H0 +μ HA σ A +μ HB σ B …(1)

[0049] -lnI L =-lnI L0 +μ LA σ A +μ LB σ B …(2)

[0050] In this case, I H Indicates by Figure 3 The high-energy image indicated by 3A, and I L Indicates by Figure 3 The low-energy image indicated by 3B. The high-energy and low-energy images obtained through imaging indicate the two-dimensional distribution of pixel values.

[0051] In addition, IH0 and I L0 These represent high-energy and low-energy images, respectively, in the absence of the subject 103. In this case, the suffix "H" indicates high energy, and the suffix "L" indicates low energy. The suffix "A" indicates soft tissue, and the suffix "B" indicates bone (skeletal region). Furthermore, μ HA and μ LA μ represents the mass decay coefficient of soft tissue at high and low energies, respectively. HB and μ LB σ represents the mass decay coefficient of bone at high and low energy levels, respectively. A σ represents the areal density of soft tissue. B This represents the surface density of bone. The unit of mass decay coefficient is cm². 2 / g, and the unit of area density is g / cm³. 2 .

[0052] In this case, the difference image creation unit 110 multiplies equation (1) by μ. LA / μ HA And by subtracting this product from equation (2), the skeletal image indicated by equation (3) given below is created. Figure 3 (3C).

[0053]

[0054] (S204: Skeletal Region Extraction)

[0055] In step S204, the bone region extraction unit 111 extracts bone regions (ROIs) subject to bone density calculation from a bone image indicating the distribution of skeletal parts in the subject 103. The simplest bone region extraction method allows the user to select a bone region on a user interface. However, requiring the user to extract bone regions using a mouse or similar device is cumbersome and time-consuming. Furthermore, the repeatability of bone density calculation accuracy decreases when different users extract different bone regions even for the same subject, or when the bone regions extracted by even the same user vary each time.

[0056] Therefore, it is preferable to automatically extract the skeletal regions using image processing-based segmentation. The skeletal region extraction unit 111 can extract the skeletal regions subjected to bone density calculation from the skeletal image indicating the distribution of skeletal parts in the subject 103 using known segmentation techniques such as watershed, graphcut, and grabcut. Furthermore, the skeletal region extraction unit 111 can extract the skeletal regions from the skeletal image using machine learning techniques such as Unet or PSPnet instead of the aforementioned segmentation techniques.

[0057] The skeletal region extraction unit 111 sets the skeletal region (analysis region) from the skeletal image to undergo skeletal density calculation. Figure 4 This is a diagram illustrating an example of skeletal region extraction. Figure 4 In the example of skeletal region extraction, L1 to L4 are extracted as the lumbar spine analysis region, and hip joint 401 is extracted as the analysis region of the proximal femur.

[0058] (S205: Bone density calculation)

[0059] In step S205, the bone density calculation unit 112 calculates the bone region (ROI) extracted by the bone region extraction unit 111 in step S204. Figure 4 The bone density calculation unit 112 sets the soft tissue region near the bone region and corrects the pixel values ​​of the bone region based on the pixel values ​​of the soft tissue region. The bone density calculation unit 112 then calculates the bone density of the bone region based on the corrected pixel values ​​of the bone region.

[0060] When calculating bone density, the bone density calculation unit 112 is set to the bone region undergoing the bone density calculation (e.g., in the case of the lumbar spine, with...). Figure 4 The soft tissue region near L1 to L4 (corresponding to L4 in the model). This soft tissue region will also be referred to as the baseline region below. (As shown by...) Figure 5 As indicated by 5A, the bone density calculation unit 112 sets baseline regions 501 and 502 at locations near the bone region undergoing bone density calculation so as to include only soft tissue and not any bone region. High-energy images in baseline regions 501 and 502 ( Figure 3 Pixel values ​​of 3A and low-energy images ( Figure 3 The pixel values ​​of 3B can be expressed by equations (4) and (5) given below, respectively. Since the baseline regions 501 and 502 are set to exclude any bone regions, equations (4) and (5) can be expressed by high-energy images (I) in soft tissue (suffix "A"). HA ,I H0 ), low-energy images (I LA ,I L0 ), mass decay coefficient (μ) HA ,μ LA ) and surface density (σ A )express.

[0061] -lnI HA -lnI H0 +μ HA σ A …(4)

[0062] -lnI LA -lnI L0 +μ LA σ A …(5)

[0063] In this case, the bone density calculation unit 112 calculates by multiplying equation (4) by μ. LA / μ HA And by subtracting the product from equation (5), we obtain equation (6) below, which gives the difference between high-energy and low-energy images in baseline regions 501 and 502 (soft tissue).

[0064]

[0065] Furthermore, the bone density calculation unit 112 obtains the following equation (7) by subtracting equation (3) from equation (6).

[0066]

[0067] The high-energy image I, which is the unknown in equation (7), in the absence of subject 103. H0 and low-energy images I L0 Removed. The left side of equation (7) is related to bone density σ. B Proportional, as indicated on the right. Equation (7) will be referred to as the baseline-corrected skeletal image.

[0068] Bone density calculation unit 112 from Figure 5 The calibration phantom 503 indicated by 5B is calculated. Figure 5 The calibration curve 507 indicated by 5C is used to convert the baseline-corrected bone image into bone density g / cm³. 2 Specifically, this operation is performed as follows.

[0069] The calibration phantom 503 includes a first calibration section 504, a second calibration section 505, and a third calibration section 506. The first calibration section 504, the second calibration section 505, and the third calibration section 506 of the calibration phantom 503 each have a strength of 0.5 g / cm³. 2 1.0g / cm 2 and 1.5g / cm 2 Bone density. (From) Figure 5 The calibration phantom 503 indicated by 5B is imaged under the same conditions as for the subject 103 to create a baseline-corrected skeletal image as expressed by equation (7). This makes it possible to obtain, for example, a skeletal image obtained by... Figure 5 The calibration curve 507 is indicated by 5C. Figure 5The calibration curve 507 indicated by 5C represents the relationship between bone density (vertical axis) and the pixel values ​​(horizontal axis) of the baseline-corrected bone image.

[0070] Finally, the bone density calculation unit 112 converts the pixel values ​​of the baseline-corrected bone image created based on the imaging of the subject 103 into bone density g / cm³ using the calibration curve 507. 2 Note that it is preferably made by Figure 5 The calibration phantom 503 indicated by 5B is imaged and the calibration curve 507 is preferably obtained before the day's examination.

[0071] (S206: Confirmation of suspicion of osteoporosis)

[0072] In step S206, the bone density determination unit 113 determines the bone density based on the values ​​calculated in step S205. Figure 4 Osteoporosis is determined by comparing the mean bone mineral density (YAM) of the L1 to L4 lumbar vertebrae and the bone mineral density of the hip joint 401 in the proximal femur. For example, the bone mineral density determination unit 113 performs the osteoporosis diagnosis by comparing the YAM value with the diagnostic criteria for primary osteoporosis. In this case, the YAM value is the average bone mineral density of young adults (20 to 44 years old). According to the diagnostic criteria for primary osteoporosis, if the subject's bone mineral density is 70% to 80% of the YAM value, then a diagnosis of reduced bone mass is made, and if the bone mineral density is less than or equal to 70% of the YAM value, then a diagnosis of primary osteoporosis is made. The bone mineral density determination unit 113 determines osteoporosis by comparing the YAM value with the mean bone mineral density of the L1 to L4 lumbar vertebrae and the bone mineral density of the hip joint 401 in the proximal femur based on the diagnostic criteria for primary osteoporosis.

[0073] If the bone density determination unit 113 determines in step S206 that the bone density of each region of the subject 103 is less than 80% of the YAM value (S206: Yes), then the control unit 105 causes the processing to proceed to step S207 (exposure field change) and transfers to step S208 for preparation of the second imaging. The control unit 105 controls the bone density measurements performed by the first bone density measurement unit (S202 to S205) and the bone density measurements performed by the second bone density measurement unit (S208 to S210). If the bone density measurement value obtained by the first bone density measurement unit is lower than a predetermined value, then the control unit 105 transfers the processing to perform the bone density measurement performed by the second bone density measurement unit. If the bone density measurement value of each of the multiple regions obtained by the first bone density measurement unit is lower than a predetermined value, then the control unit 105 performs a bone density measurement for each region using the second bone density measurement unit.

[0074] If the bone density determination unit 113 determines in step S206 that the bone density of each region of the subject 103 is equal to or greater than the YAM value (S206: No), then the control unit 105 determines that the probability of osteoporosis is low based on the determination result (discrimination result) and terminates the examination.

[0075] (S207: Exposure field changed)

[0076] In step S206 above, the exposure field setting unit 114 sets a second exposure field based on the bone density measurement result obtained by the first bone density measurement unit for the measurement performed by the second bone density measurement unit (S206: Yes). That is, if the bone density determination unit 113 determines that osteoporosis is suspected, the exposure field setting unit 114 changes the exposure field by limiting the aperture 1001 of the scaling X-ray exposure field. In the measurement performed by the first bone density measurement unit (S202 to S205), the exposure field setting unit 114 sets a first exposure field that enables imaging of multiple regions of the subject. In the measurement performed by the second bone density measurement unit (S208 to S210), the exposure field setting unit 114 sets a second exposure field that enables imaging of at least some of the multiple regions. In this case, the first exposure field includes the lumbar spine and proximal femur as multiple regions of the subject 103, and the second exposure field includes the lumbar spine or proximal femur as some of the multiple regions. Since the area outside the second exposure field is not irradiated by radiation, the increase in dose to the subject 103 can be suppressed.

[0077] In the first imaging in step S202, the exposure field setting unit 114 sets a first exposure field in the radiation exposure field aperture 1001 to enable imaging of multiple regions of the subject 103 (e.g., L1 to L4 of the lumbar spine and the hip joint 401 of the proximal femur). In contrast, in step S202, the exposure field setting unit 114 sets a second exposure field in the radiation exposure field aperture 1001 that is narrower than the first exposure field and enables imaging of at least some of the multiple regions.

[0078] The exposure field setting unit 114 can set the second exposure field by using a learning model associated with the setting of the exposure field corresponding to the area being measured by the second bone density measurement unit.

[0079] If the bone density determining unit 113 determines in step S206 that the average bone density of the L1 to L4 lumbar vertebrae indicates a decrease in bone density, then if... Figure 6As indicated in 6A, in this step, the exposure field setting unit 114 narrows the exposure field to include at least some of the multiple regions (L1 to L4 of the lumbar vertebrae and the hip joint 401 of the proximal femur). That is, the exposure field setting unit 114 changes the setting of the radiation exposure field aperture 1001 to narrow the exposure field to a second exposure field that is narrower than the first exposure field.

[0080] If the bone density determination unit determines in step S206 that a decrease in bone density has occurred in the hip joint 401 of the proximal femur, then as by Figure 6 As indicated by 6B, the exposure field is limited to include only the hip joint 401. In step S206, as by Figure 6 As indicated by 6B, the exposure field setting unit 114 restricts the exposure field to include the hip joint 401 as at least some of a plurality of regions (L1 to L4 of the lumbar spine and the hip joint 401 of the proximal femur). That is, as in the case of the lumbar spine, the exposure field setting unit 114 changes the setting of the radiation exposure field aperture 1001 to restrict the exposure field to a second exposure field that is narrower than the first exposure field.

[0081] If the radiation exposure field aperture 1001 can be electrically controlled synchronously with the radiation imaging system 100, then the exposure field can be automatically limited using the bone region extraction results in step S204. Alternatively, in the case of manually changing the exposure field settings, the control unit 105 can also perform display control to display instructions for limiting the exposure field according to the region to the user on the monitor 106.

[0082] (S208: Second Imaging)

[0083] In step S208, the control unit 105 controls the radiation imaging apparatus to generate radiation by supplying a pulse signal from the radiation generator 104 to the radiation source 101 when the exposure switch is pressed. In the second imaging in step S208, imaging is performed using a second exposure field set and changed in step S207. The second exposure field is narrower than the first exposure field used in the first imaging (S202), and the exposure field is limited to image at least some of a plurality of regions. Figure 6 As indicated by 6A and 6B, except that the exposure field is narrowed and a region is set as the imaging target region, the second imaging process is the same as the first imaging in step S202, so a detailed description of the imaging will be omitted.

[0084] (S209: Skeletal Image Creation)

[0085] In step S209, the difference image creation unit 110 creates a skeletal image by calculating the logarithmic difference between the high-energy image and the low-energy image obtained through imaging in step S208. (As shown by...) Figure 6 As indicated by 6A and 6B, except that the exposure field is narrowed and a region is set as the imaging target region, the image difference processing in step S209 is the same as the image difference processing in step S203, so a detailed description of the image difference processing will be omitted.

[0086] (S210: Skeletal Region Extraction)

[0087] In step S210, the bone region extraction unit 111 extracts the bone regions (ROIs) subjected to bone density calculation from the bone image. The bone region extraction process in this step is the same as that in step S204. Therefore, the bone region extraction unit 111 can use the results obtained in step S204 without extracting any bone regions and without any changes. That is, the bone region extraction unit 111 can apply the extraction results of the bone regions extracted by the first bone density measurement unit to the extraction of bone regions in the measurement performed by the second bone density measurement unit. Using the same bone regions as those extracted in step S204 allows for a more accurate grasp of the differences (changes) between the first bone density measurement in the first imaging and the second bone density measurement in the second imaging.

[0088] On the other hand, in some cases, the body of the subject 103 has moved between the first and second bone density measurements. In this case, the bone region can be extracted again.

[0089] According to this embodiment, in screening examinations such as initial medical visits or physical examinations, a first bone density measurement based on a first image is first performed to simultaneously measure the bone density of multiple regions of the subject (e.g., the lumbar spine and proximal femur). If osteoporosis is suspected in the first bone density measurement, then in a second bone density measurement based on a second image, the exposure field is narrowed to a specific area to perform a precise bone density measurement with reduced scattering. This can shorten the examination time in bone density measurements for many subjects, such as in screening examinations, and reduce the burden on subjects and users by increasing throughput.

[0090] (Second Embodiment)

[0091] The first embodiment illustrates a case where the first and second bone density measurement units perform imaging using two tube voltages (V1 and V2). The second embodiment will illustrate an arrangement where the first bone density measurement unit performs bone density measurement based on image data obtained from the FPD 102 (image acquisition unit) using radiation generated by a single tube voltage. Note that the radiation imaging system 100 ( Figure 1 The arrangement is the same as in the first embodiment.

[0092] Reference Figure 7 The flowchart shown describes the processing in the image processing unit 109 according to the second embodiment. This processing is different from the processing performed by the image processing unit 109 according to the first embodiment. Figure 2 The difference lies in the processing in steps S702 and S705, so only the different parts of the processing will be described.

[0093] (S702: First Measurement)

[0094] In the first imaging step S702, the control unit 105 performs imaging using a set first exposure field by controlling the radiation imaging apparatus. The control unit 105 causes the radiation source 101 to generate radiation by supplying a high-voltage pulse (pulse signal) from the radiation generator 104 to the radiation source 101 when the exposure switch is pressed. The radiation source 101 irradiates the subject 103 with X-rays based on the pulse signal from the radiation generator 104. The radiation source 101 irradiates the subject 103 with X-rays based on a single tube voltage (e.g., 140 kV). The tube voltage (e.g., 140 kV) corresponds to the high voltage V1 described in the first embodiment. The FPD 102 obtains a high-energy image based on the tube voltage (high voltage V1). Furthermore, bone density measurement is performed approximately using the technique described in step S705 below.

[0095] Therefore, in the first bone density measurement based on the first image, imaging is performed using a single tube voltage (high voltage V1), which facilitates control of the radiation generator 104. This makes it possible to perform bone density measurement, for example, while performing fluoroscopic imaging for positioning.

[0096] (S705: Bone density calculation)

[0097] In the first measurement (S702) according to the second embodiment, since imaging is performed using a single tube voltage, the bone density calculation unit 112 calculates the bone region (ROI) extracted by the bone region extraction unit 111 in step S204 using the following approximation method. Figure 4 Bone density.

[0098] As described in the first embodiment, the skeletal region in the high-energy image ( Figure 4 The pixel value of ) can be represented by the equation (8) given below.

[0099]

[0100] Baseline regions 501 and 502 formed by soft tissue Figure 5 The pixel value of 5A can be represented by the equation (9) given below.

[0101]

[0102] In this case, the area density σ is obtained by multiplying the volume density ρ by the tissue thickness d. Therefore, if the baseline region and the skeletal region can be approximated as having the same thickness, then the approximation of equation (10) given below holds.

[0103]

[0104] In this case, the superscript "b" represents the baseline region, the subscript "A" represents soft tissue, and the subscript "B" represents bone. When the baseline region is near the bone region in the human body, the approximation of equation (10) holds.

[0105] Therefore, the bone density calculation unit 112 can obtain formula (11) by substituting equation (10) into equation (9), subtracting the result from equation (8), and rearranging the result.

[0106]

[0107] High-energy image I in the absence of the unknown quantity in equation (8) and subject 103. HO The bone is removed, and a near-baseline corrected image of the skeleton can be obtained. The actual bone density (g / cm³) is then calculated. 2 The conversion is the same as in the first embodiment, and the bone density calculation unit 112 uses a method derived from... Figure 5 The calibration phantom 503 indicated by 5B and by Figure 5 The calibration curve 507 indicated by 5C is used to convert the pixel values ​​of the baseline-corrected bone image into bone density (g / cm³). 2 .

[0108] According to this embodiment, an approximate bone density measurement can be performed by using a single tube voltage to perform a first bone density measurement. For areas suspected of having osteoporosis identified by the first bone density measurement, a precise bone density measurement is performed by using two or more tube voltages for a second bone density measurement through the processing in steps S207 to S211. This allows for a seamless transition to a precise second bone density measurement by simultaneously observing bone density using a diagnostic device capable of mobile imaging, such as X-ray TV, while positioning the bone.

[0109] Note that in the bone density measurement (S207 to S211) performed by the second bone density measurement unit, the second bone density measurement unit performs the bone density measurement based on image data obtained by the FPD 102 (image acquisition unit) according to radiation emitted using multiple tube voltages including a single tube voltage. That is, the second bone density measurement unit performs the bone density measurement by using image data obtained from the bone density measurement performed by the first bone density measurement unit and image data obtained by the FPD 102 (image acquisition unit) using tube voltages different from the single tube voltage. Using the image data obtained from the bone density measurement performed by the first bone density measurement unit for the bone density measurement performed by the second bone density measurement unit can suppress the increase of dose to the subject 103 and accurately perform the bone density measurement by using image data from multiple tube voltages.

[0110] (Third Embodiment)

[0111] The first embodiment illustrates an arrangement in which a first bone density measurement based on a first imaging is performed to simultaneously measure the bone density of multiple regions of the subject 103, and when osteoporosis is suspected in the first bone density measurement, the exposure field in a second bone density measurement based on a second imaging is narrowed to a specific region to perform a precise bone density measurement with reduced scattering. The third embodiment will illustrate an arrangement in which the exposure field setting unit 114 sets multiple exposure fields when the second bone density measurement unit performs a second bone density measurement based on a second imaging. Note that the arrangement of the radiographic imaging system 100 ( Figure 1 The arrangement is the same as in the first embodiment.

[0112] Reference Figure 8 The flowchart shown describes the processing in the image processing unit 109 according to the third embodiment. This processing is different from the processing performed by the image processing unit 109 according to the first embodiment. Figure 2 The difference lies in the processing in step S807, so only the different parts of the processing will be described.

[0113] If the bone density determination unit 113 determines in step S206 of the first bone density measurement that there is suspicion of osteoporosis (S206: Yes), then the exposure field setting unit 114 changes the exposure field by limiting the scaling X-ray exposure field aperture 1001 (S207). The exposure field setting unit 114 sets multiple exposure fields. The bone density measurement unit according to this embodiment performs bone density measurement based on image data obtained by the FPD 102 (image acquisition unit) using the multiple exposure fields set by the exposure field setting unit 114.

[0114] Multiple exposure fields were used to cover each region of the subject undergoing bone density measurement, and areas outside the multiple exposure fields were not irradiated with radiation.

[0115] In this case, the first exposure field set in the first imaging (S202) is a single exposure field that ensures the imaging range to allow simultaneous imaging of multiple regions. In this step, the exposure field setting unit 114 changes the setting of the radiation exposure field aperture 1001 to divide the single first exposure field into multiple exposure fields, which correspond to the positions of multiple regions of the subject 103 (e.g., L1 to L4 of the lumbar spine and the hip joint 401 of the proximal femur). Figure 9 This is a diagram illustrating an example of the exposure field setup in the third embodiment. For example... Figure 9 As shown, the exposure field setting unit 114 divides the first exposure field (single exposure field) into an exposure field 901 corresponding to the lumbar vertebrae (L1 to L4) and an exposure field 902 corresponding to the hip joint 401 of the proximal femur by changing the setting of the radiation exposure field aperture 1001.

[0116] In step S208, imaging is performed using the second exposure field set and changed in step S207. The control unit 105 controls the radiation imaging device to generate radiation from the radiation source 101 by supplying a pulse signal from the radiation generator 104 to the radiation source 101 when the exposure switch is pressed, thereby simultaneously imaging the hip joint 401 of the lumbar spine (L1 to L4) and the proximal portion of the femur.

[0117] In step S211, the bone density calculation unit 112 simultaneously calculates multiple bone regions (ROIs) extracted by the bone region extraction unit 111 in step S210. Figure 4 Bone density.

[0118] According to this embodiment, setting multiple exposure fields in a second bone density measurement based on a second imaging technique enables accurate bone density measurements with reduced scattering to be performed simultaneously on multiple regions. For example, the multiple regions include the lumbar spine, which allows for easy determination of drug efficacy, and the proximal femur, which is an area where the subject is easily bedridden in the event of injury. That is, these regions are clinically important, and therefore this embodiment is effective in performing accurate bone density measurements with reduced scattering while simultaneously measuring two regions.

[0119] <Other Embodiments>

[0120] This invention can be implemented by supplying a program for implementing one or more functions of the above embodiments to a system or device via a network or storage medium, and causing one or more processors in the computer of the system or device to read and execute the program. This invention can also be implemented by a circuit (e.g., an ASIC) for implementing one or more functions.

[0121] This invention is not limited to the embodiments described above, and various changes and modifications can be made within the spirit and scope of this invention. Therefore, in order to inform the public of the scope of this invention, the following claims are made.

[0122] This application claims priority to Japanese Patent Application No. 2021-019226, filed on February 9, 2021, which is hereby incorporated herein by reference.

[0123] Reference Symbol List

[0124] 10: Radiation imaging system (radiation imaging device), 101: Radiation source, 102: FPD (radiation flat panel detector), 104: Radiation generator, 105: Control unit, 106: Monitor (display device), 108: Storage unit, 110: Differential image creation unit, 111: Bone region extraction unit, 112: Bone density calculation unit, 113: Bone density determination unit, 114: Exposure field setting unit, 116: Display control unit, 120: Information processing device.

Claims

1. A radiation imaging apparatus comprising: an image obtaining unit configured to obtain image data corresponding to incident radiation; and an image processing unit configured to perform a first bone density measurement based on image data obtained by the image obtaining unit with a first exposure field, and to perform a second bone density measurement based on image data obtained by the image obtaining unit with a second exposure field narrower than the first exposure field.

2. The radiation imaging apparatus according to claim 1, further comprising: a generating unit configured to generate radiation; and an exposure field setting unit configured to set an exposure field of radiation, wherein the exposure field setting unit sets the first exposure field and sets the second exposure field, the first exposure field enabling imaging of a plurality of regions of a subject in the first bone density measurement, the second exposure field enabling imaging of at least some of the plurality of regions with an exposure field narrower than the first exposure field in the second bone density measurement.

3. The radiographic imaging apparatus according to claim 2, wherein The first exposure field includes a lumbar vertebra and a proximal femur portion as the plurality of regions, and the second exposure field includes one of the lumbar vertebra and the proximal femur portion as some of the regions.

4. The radiographic imaging apparatus according to claim 2, wherein The exposure field setting unit sets the second exposure field by using a learned model associated with a setting of an exposure field corresponding to a region subjected to the second bone density measurement.

5. The radiographic imaging apparatus according to claim 2, wherein The exposure field setting unit sets the second exposure field based on a result obtained by the first bone density measurement.

6. The radiographic imaging apparatus according to claim 2, wherein Radiation is not applied to a region other than the second exposure field.

7. The radiation imaging apparatus according to claim 2, further comprising a control unit configured to control the image processing unit so as to perform the first bone density measurement and the second bone density measurement.

8. The radiographic imaging apparatus according to claim 7, wherein The control unit shifts a process to perform the second bone density measurement when a measurement value obtained by the first bone density measurement is lower than a predetermined value.

9. The radiographic imaging apparatus according to claim 1, wherein, The image processing unit performs the second bone density measurement with the second exposure field based on a result obtained by the first bone density measurement.

10. The radiographic imaging apparatus according to claim 1, wherein, The image processing unit performs the second bone density measurement with the second exposure field based on a measurement value obtained by the first bone density measurement and a predetermined threshold value.

11. The radiographic imaging apparatus of claim 8, wherein, The image processing unit discriminates whether to omit the first bone density measurement with the first exposure field and performs the second bone density measurement with the second exposure field in accordance with a discrimination result.

12. The radiographic imaging apparatus of claim 2, wherein, The generating unit generates cone beam radiation by supplying a pulse signal based on a tube voltage to a radiation source.

13. The radiographic imaging apparatus of claim 2, wherein, The generating unit generates radiation based on a first tube voltage and radiation based on a second tube voltage lower than the first tube voltage.

14. The radiographic imaging apparatus of claim 11, wherein, The image processing unit includes a creation unit configured to create a bone image indicating a bone distribution based on a difference between image data corresponding to radiation based on a first tube voltage and image data corresponding to radiation based on a second tube voltage, an extraction unit configured to extract a bone region subjected to a bone density measurement from the bone image, and a calculation unit configured to calculate a bone density of the bone region, and The calculation unit sets a soft tissue region near the bone region, corrects a pixel value of the bone region based on a pixel value of the soft tissue region, and calculates a bone density of the bone region based on the corrected pixel value of the bone region.

15. The radiographic imaging apparatus of claim 14, wherein, The extraction unit applies an extraction result of a bone region extracted in the first bone density measurement to extraction of a bone region in the second bone density measurement.

16. The radiographic imaging apparatus of claim 2, wherein, In the first bone density measurement, the first bone density measurement is performed based on image data obtained by the image obtaining unit from radiation generated using a single tube voltage, and In the second bone density measurement, the second bone density measurement is performed based on image data obtained by the image obtaining unit from radiation generated using a plurality of tube voltages including the single tube voltage.

17. The radiographic imaging apparatus of claim 14, wherein, In the second bone density measurement, the second bone density measurement is performed by using image data obtained in the first bone density measurement and image data obtained by the image obtaining unit using a tube voltage different from the single tube voltage.

18. An image processing apparatus including an image processing unit configured to perform a first bone density measurement based on a first radiation image and perform a second bone density measurement based on a second radiation image, the first radiation image corresponding to a first exposure field, the second radiation image corresponding to a second exposure field narrower than the first exposure field.

19. A radiation imaging method for a radiation imaging apparatus including an image obtaining unit configured to obtain image data corresponding to incident radiation, the method comprising: a first step of performing a first bone density measurement based on image data obtained by the image obtaining unit using a first exposure field; and a second step of performing a second bone density measurement based on image data obtained by the image obtaining unit using a second exposure field narrower than the first exposure field.

20. A non-transitory computer-readable storage medium storing a program for causing a computer to execute the method according to claim 19.

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