Medical x-ray measuring device

Abstract

To suppress deterioration in accuracy due to a body motion as compared to a system in which scanning for measurement is performed after a deceleration start point is determined by preceding scanning or the like.SOLUTION: A control part 40 conveys a measurement system at a first speed until a scanning position of a measurement system consisting of an X-ray generator 26 and an X-ray detector 30 enters a region b of a subject from a region a1 outside the subject. The first speed is a speed higher than a second speed, which is a speed of scanning for measurement. During the scanning, when a detection value of the X-ray detector 30 becomes a predetermined threshold or lower, the control device 40 decelerates the speed of scanning for the measurement system to a second speed. The threshold is a predetermined value, which is lower than an X-ray detection value in the region a1, and an X-ray detection value or higher in a part of a soft tissue where a bone is not present in the region b1. A region where a lumbar spine and the like which are main measurement objects are present is measured by the scanning of the second speed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a medical X-ray measurement device, and more particularly to the control of scanning. [Background technology]

[0002] Known medical X-ray measurement devices include X-ray tissue diagnostic devices, X-ray photography devices, X-ray CT devices, etc. In the following, a bone densitometer, which is one type of X-ray tissue diagnostic device, will be described.

[0003] A bone densitometer is generally a device that measures and calculates the bone density of bones in a subject based on dual-energy X-ray absorptiometry (DEXA). In a bone densitometer, for example, a fan beam of X-rays that spreads radially two-dimensionally is mechanically scanned in a direction perpendicular to the plane of the fan, and X-rays that have passed through the subject are detected in parallel. More specifically, low-energy X-rays and high-energy X-rays are alternately irradiated while the beam is scanned, thereby obtaining low-energy X-ray detection values ​​and high-energy X-ray detection values ​​that are alternately arranged in the mechanical scanning direction.

[0004] The device disclosed in Patent Document 1 determines measurement conditions by pre-scanning a measurement space with weak X-rays, and measures bone density distribution by repeating scans of the measurement space with stronger X-rays for the main measurement according to the measurement conditions. The measurement conditions determined by the pre-scan include, for example, the speed of repeating scans and the area to be measured.

[0005] In the device disclosed in Patent Document 2, a pre-scan is performed on the subject using low-energy X-rays, thereby detecting the boundary of the tissue of interest within the subject. Scanning conditions for the main scan are determined based on the position of the boundary. In this case, an irradiation sequence is determined so that as many effective pixels as possible are set within the width of the tissue of interest. The irradiation sequence is composed of a run-up portion, an execution portion, and an overrun portion. The scanning speed, etc. are variably set in the run-up portion. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-19788 [Patent Document 2] JP 2015-93000 A Summary of the Invention [Problem to be solved by the invention]

[0007] There is a significant time lag between the advance scan or prescan for determining the measurement conditions, etc. and the scan for actually performing the measurement using those measurement conditions, etc. The possibility that the subject's body movement occurs during this time cannot be ignored, and this has an adverse effect on the accuracy of the measurement results. [Means for solving the problem]

[0008] A medical X-ray measurement device according to the present invention is a medical X-ray measurement device comprising: an irradiation unit that irradiates a subject with X-rays while scanning in a first direction; a detection unit that detects the intensity of the X-rays that have passed through the subject; and a control unit that causes the irradiation unit to start the scan from a position where the X-rays pass through the outside of the subject, sets the scanning speed to a first speed until the intensity detected by the detection unit becomes equal to or less than a first threshold value corresponding to the boundary where the X-rays enter the soft tissue of the subject from the outside, and reduces the scanning speed to a second speed at a deceleration start time determined based on the time when the intensity detected by the detection unit becomes equal to or less than the first threshold value.

[0009] In this invention, scanning is performed at a first speed, which is faster than a second speed, which is the scanning speed for measurement, until the scanning position moves from the outside of the subject into the soft tissue. Then, once it is determined that the subject has entered the soft tissue, the scanning speed is reduced to the second speed. This speed control is performed based on the X-ray detection values ​​during the scan for actual measurement. Methods that determine the boundary between the outside of the subject and the soft tissue in a preliminary scan have a problem in that there is a high risk of body movement occurring between the preliminary scan and the scan for measurement. However, this invention controls based on the detection values ​​during the scan for measurement, so there is less risk of body movement.

[0010] Here, the deceleration start time is, for example, the time when the intensity detected by the detection unit becomes equal to or less than the first threshold value. This first threshold value may be, for example, a predetermined value that is smaller than the X-ray intensity detected by the detection unit when the X-rays pass through only air and greater than the X-ray intensity detected by the detection unit when the X-rays pass through air and soft tissue.

[0011] In one embodiment, the deceleration start time may be a time delayed by a predetermined delay time determined according to the attributes of the subject from the time when the intensity detected by the detection unit becomes equal to or less than the first threshold. The attributes of the subject may be, for example, gender or age, and the subject's physique can be roughly determined from these attributes. For example, in the case of measuring the lumbar vertebrae, it is sufficient to obtain a measurement result of a region of interest of a predetermined width centered on the central axis of the spine, regardless of the subject's physique. A person with a large physique can have a longer delay from when the detected intensity becomes equal to or less than the first threshold to when deceleration starts than a person with a small physique.

[0012] The control unit may also control the scanning speed based on the intensity detected by the detection unit when low-energy X-rays are irradiated from two levels of X-rays, high and low, that are alternately irradiated in the DEXA method.

[0013] The irradiation unit may also be configured to irradiate an X-ray beam having a width in an orthogonal direction perpendicular to the first direction, the detection unit may detect the X-ray beam having a width in the orthogonal direction by a plurality of conversion devices arranged in a range of a predetermined width in the orthogonal direction or by mechanically scanning one conversion device over the range, and the control unit may control the scanning speed based on the intensity detected by the detection unit at the center of the range in the orthogonal direction.

[0014] Furthermore, after reducing the scanning speed to the second speed, the control unit may increase the scanning speed to the first speed when the intensity detected by the detection unit becomes equal to or greater than a second threshold corresponding to the boundary from the soft tissue to the outside. This shortens the time required for measurement and reduces the radiation dose to the soft tissue compared to when the speed is not increased.

[0015] Furthermore, the control unit may increase the scanning speed to the first speed when the scanning progresses a predetermined distance after the intensity detected by the detection unit decreases to an intensity corresponding to the bone of the subject and then becomes equal to or greater than a third threshold corresponding to the boundary between the bone and the soft tissue. Here, the predetermined distance corresponds to, for example, a distance corresponding to the width in the first direction of a region of interest including a bone to be measured, such as a lumbar vertebra. In particular, the predetermined distance corresponds to, for example, the distance from the position of the rear end of the bone to the position of the rear end of the region of interest in the first direction. In this aspect, accurate measurement is performed at the second speed up to a predetermined distance from the boundary between the bone and the soft tissue, and then the scanning speed is increased. This shortens the measurement time and reduces the radiation exposure dose.

[0016] Furthermore, the control unit may stop the irradiation of the X-rays from the irradiation unit when the intensity detected by the detection unit during the scan decreases to a level at which the X-rays have penetrated the bones of the subject, and then becomes equal to or greater than a third threshold corresponding to the boundary between the bones and the soft tissues, and the scan progresses a predetermined distance. In this aspect, for example, by stopping the irradiation of X-rays after an important portion for measurement is accurately measured at the second speed, the exposure dose of the soft tissues and the like behind that portion can be reduced.

[0017] In yet another aspect, the scanning is achieved by moving an X-ray generator included in the irradiation unit in the first direction, and the control unit stops the movement of the X-ray generator in the first direction after stopping the irradiation of the X-rays from the irradiation unit. According to this aspect, the measurement time is shortened by stopping the movement of the X-ray generator before scanning the entire width of the subject.

[0018] Here, the control unit may stop the movement of the X-ray generator in the first direction, and then move the X-ray generator to an initial position in a direction opposite to the first direction. By automatically returning the stopped X-ray generator to its initial position, the cycle until the start of the next measurement is shortened. [Effects of the Invention]

[0019] According to the present invention, the deceleration start point is determined based on the X-ray detection value during the measurement scan, which makes it possible to suppress deterioration of accuracy due to body movement compared to a method in which the deceleration start point is determined by a pre-scan or the like and then the measurement scan is performed. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a perspective view of the appearance of an X-ray measurement device. [Figure 2] FIG. 2 is a diagram schematically illustrating the internal configuration of the X-ray measurement device as seen from the side. [Figure 3] FIG. 10 is a diagram showing a conventional change pattern of conveying speed. [Figure 4] 10A and 10B are diagrams illustrating an example of a change pattern of a conveying speed according to an embodiment. [Figure 5] FIG. 2 is a diagram illustrating a control procedure according to an embodiment. [Figure 6] FIG. 10 is a diagram illustrating a control procedure according to a modified example. [Figure 7] FIG. 10 is a diagram showing an example of a change pattern of the conveying speed in another modified example. [Figure 8]FIG. 8 is a diagram illustrating a control procedure for realizing the change pattern of FIG. 7. [Figure 9] FIG. 10 is a diagram showing an example of a change pattern of the conveying speed in yet another modified example. [Figure 10] FIG. 10 is a diagram illustrating a control procedure for realizing the change pattern of FIG. 9. DETAILED DESCRIPTION OF THE INVENTION

[0021] <Example of device configuration> 1 shows a perspective view of an example of an X-ray measurement device 10 to which the control according to the present disclosure is applied and a Bucky table 18 used therewith. The X-ray measurement device 10 is an example of a medical X-ray measurement device according to the present invention.

[0022] The X-ray measurement device 10 includes a main body 12 that generates X-rays 20, an arm 14 that detects the X-rays 20, and a support 16 that supports the arm 14 above the main body 12. The space surrounded by the main body 12, the support 16, and the arm 14 forms a measurement space 22 in which a subject is placed. The subject is received in the measurement space 22 from the side where the support 16 is not present, toward the positive direction of the y-axis.

[0023] The X-ray measurement device 10 is placed so that the main body 12 fits under the table base of the Bucky table 18. In the measurement space 22, the subject lies on the Bucky table 18, leaving some space at the front side in FIG. 1. The X-ray measurement device 10 measures bone density, body fat percentage, muscle percentage (hereinafter, the measured quantity that combines the body fat percentage and muscle percentage will be referred to as the fat / muscle percentage), etc. based on the detection value of X-rays 20 that are emitted from the main body 12, pass through the subject, and are detected by the arm 14.

[0024] Here, an embodiment is described in which the X-ray measurement device 10 and the Bucky table 18 are separate entities, but the upper surface of the main body 12 of the X-ray measurement device 10 may serve as a Bucky table on which the subject lies, and the X-ray measurement device 10 and the Bucky table may be integrated into one configuration.

[0025] FIG. 2 shows a schematic side view of the X-ray measurement device 10. In FIG. 2, the up-down direction is the x-direction, the left-right direction is the y-direction, and the direction perpendicular to the paper surface is the z-direction. This figure shows the main internal configuration of the main body 12 and the arm 14. The X-ray measurement device 10 includes an X-ray generator 26 housed in a main body housing 24 and an X-ray detector 30 housed in an arm housing 28. The X-ray beam emitted by the X-ray generator 26 may have a planar beam shape with a width in the z-direction. For example, a planar beam shape parallel to the zx plane is one example. The beam shape may also be a fan-shaped beam whose width increases in the z-axis direction with increasing distance from the X-ray generator 26. The X-ray generator 26 is an example of an irradiation unit that irradiates an object with X-rays, and the X-ray detector 30 is an example of a detection unit that detects the intensity of X-rays that have passed through the object.

[0026] The X-ray generator 26 and the X-ray detector 30 are transported horizontally within the main body 12 and the arm 14 by a transport mechanism (not shown), while maintaining a mutually opposing positional relationship. This transport realizes X-ray beam scanning in the y direction. Therefore, the y direction is the transport direction in which the transport mechanism transports the measurement system, in other words, the direction of mechanical scanning by that transport. In the illustrated example, the X-ray generator 26 and the X-ray detector 30 (hereinafter, collectively referred to as the "measurement system") are transported from the rightmost end of the transport range to the left. During the y-direction scanning in response to this transport, the X-ray beam passes through an area a1 of only air (i.e., an area where the subject 32 is not present), then passes through an area b where the subject 32 is present, and then passes through an area a2 of only air again. The irradiation of the X-ray beam from the X-ray generator 26 begins when the scanning position of the measurement system is at the scan start position in the first region a1 of only air, and continues until the scanning position reaches the scan end position in region a2 after region b. The detection value obtained when the X-rays irradiated from the X-ray generator 26 are detected by the X-ray detector 30 while the scanning position of the measurement system is in region a1 is acquired as reference data for the DEXA method. The X-ray measurement device 10 obtains the distribution of the absorptance for the subject 32 based on the detection values ​​acquired by the X-ray detector 30 while scanning the region b and the above-mentioned reference data. Here, the distribution of the absorptance refers to the distribution in the horizontal plane (yz plane) of the absorptance for X-rays passing upward through the region b. The absorptance is defined as the value indicated by the reference data divided by the detection value of the X-rays detected by the X-ray detector 30. The smaller the detection value of the X-rays detected by the X-ray detector 30, the greater the absorptance. The distribution of the absorptance can also be said to be a distribution equivalent to the reciprocal of the detection value of the X-rays detected by the X-ray detector 30. The X-ray measurement device 10 obtains the distribution of the absorptance for each of two types of X-rays with different energies by the operation described below, and measures bone density, fat / muscle ratio, etc. from the distribution of each absorptance.

[0027] The specific configuration of the X-ray measurement apparatus 10 will be described. A control device 38 is connected to the X-ray measurement apparatus 10. The control device 38 includes a control unit 40, an operation panel 42, and a display 44. The operation panel 42 as an operation unit includes a keyboard, a mouse, a drag ball, a lever, etc. The control unit 40 is configured as a computer including a processor, memory, etc., and operates according to a pre-stored program. The control device 38 may be integrated with the X-ray measurement apparatus 10, or may be configured separately. The control unit 40 may also be configured as multiple computers interconnected via a network, etc. In this case, the multiple computers that make up the control unit 40 exchange data with each other and cooperate to execute the processing of the control unit 40, which will be described later.

[0028] An X-ray tube or the like that generates X-rays is used as the X-ray generator 26. The control unit 40 controls the tube voltage or tube current of the X-ray tube to change the energy, radiation amount (intensity), etc. of the generated X-rays. The top plate of the main body housing 24 is made of a material that is transparent to X-rays, and X-rays are emitted upward from the X-ray generator 26 through the top plate.

[0029] The bottom plate 58 of the arm housing 28 is formed from a material that transmits X-rays, and X-rays emitted from the main body 12 toward the arm 14 are detected by the X-ray detector 30 through the bottom plate 58.

[0030] The X-ray detector 30 uses a conversion device such as an electron tube that converts X-rays into electrical energy or a photodiode that operates at X-ray wavelengths. The X-ray detector 30 is configured, for example, by arranging a plurality of conversion devices in multiple rows, with the row direction being perpendicular to the transport direction and horizontal (positive direction of the z-axis), and outputting detection values ​​from the plurality of conversion devices. The X-ray detector 30 may also be configured to output detection values ​​at each detection point by mechanically linearly scanning one conversion device in the z-axis direction.

[0031] In this configuration, the X-ray generator 26 is housed in the main body housing 24 and the X-ray detector 30 is housed in the arm housing 28, but the X-ray measurement device 10 may also be configured such that the X-ray generator 26 is housed in the arm housing 28 and the X-ray detector 30 is housed in the main body housing 24.

[0032] <Scanning (transport) control> Many conventional devices of the same type as the X-ray measurement device 10 have multiple measurement modes. For example, some devices have three modes: high-speed mode, standard mode, and high-resolution mode. These modes are realized, for example, by changing the transport speed of the measurement system or the intensity of the irradiated X-rays. In other words, the transport speed of the measurement system is the speed of X-ray scanning in the y direction.

[0033] For example, in an example where three modes are realized by only changing the transport speed, the high-speed mode has a faster transport speed than the standard mode, and the high-resolution mode has a slower transport speed than the standard mode. Alternatively, multiple modes can be realized by combining transport speed and X-ray intensity. For example, the high-resolution mode and the standard mode have the same transport speed, but the high-resolution mode has a higher X-ray intensity, while the high-speed mode has the same X-ray intensity as the standard mode but a faster transport speed. The slower the transport speed, the more precise the measurement results will be and the higher the measurement accuracy will be, but the higher the radiation exposure and the longer the measurement time will be. Furthermore, the higher the X-ray intensity, the higher the measurement accuracy will be but the higher the radiation exposure. Taking these conditions into consideration, an operator such as a medical technician will make a decision based on the subject's body thickness, the purpose of the examination, etc. For example, if the subject's body thickness is thick, the high-resolution mode will be selected, and if the subject's body thickness is thin, the high-resolution mode or the standard mode will be selected. Furthermore, the high-resolution mode will be selected for measurements to evaluate drug efficacy, and the high-speed mode or the standard mode will be selected for health checkups.

[0034] The transport speed of the measurement system may also be rephrased as the scanning speed of the X-ray in the y direction.

[0035] In conventional devices, the measurement system is transported at a fixed, predetermined transport speed corresponding to the selected mode during measurement. Figure 3 shows an example of this conventional transport speed control for the measurement system. This example shows a case where two speeds, high and low, are selectable as the transport speed for the measurement system. "High speed" is used, for example, in the high-speed mode of the three modes mentioned above. "Low speed" is the speed used in the standard mode or high-resolution mode and may also be considered the standard speed. Hereinafter, "high speed" and "low speed" refer to specific transport speeds that can be achieved by the transport mechanism, and "high speed" is a specific speed faster than "low speed." Furthermore, "low speed" is a transport speed for measuring the area important for measurement (i.e., the ROI described below) with the desired measurement accuracy.

[0036] The upper part of FIG. 3 shows a change pattern 100 of the transport speed in the standard mode or the high-resolution mode, and the lower part shows a schematic representation of a bone density image 200 obtained as a result of the measurement.

[0037] In this example, the transport speed starts at 0 at the transport start position on the left side of the figure and accelerates at a constant rate until it reaches the scan start position set to the right of the transport start position. The scan start position is the position where X-ray detection scanning begins to generate a bone density image. The scan start position is set within the above-mentioned area a1. At the scan start position, the transport speed reaches a predetermined "low speed" corresponding to the standard mode or high-resolution mode. After this, the transport speed remains constant at "low speed" until it reaches the scan end position set near the right end of the transport range. From the scan end position to the transport end position further to the right, the transport speed decelerates at a constant rate, and becomes 0 at the transport end position.

[0038] X-ray detection scanning is performed from the scan start position to the scan end position, and a bone density image 200 is obtained by this scanning. Generally, bone density images, like regular X-ray images, are black and white images in which the brightness increases as the X-ray absorption rate increases. However, the bone density images 200 in FIG. 3 and FIG. 4 (described later) are shown inverted black and white to make the leading lines and other features more visible. This bone density image 200 is of a human lumbar spine. The bone density image 200 shows the upper part of the ilium 204 and the lumbar vertebrae 1 through 5 arranged above it. To avoid complexity, only the second, third, and fourth lumbar vertebrae L2, L3, and L4 are labeled in the figure. Bones such as the ilium 204 and lumbar vertebrae L2 through L4 have significantly higher X-ray absorption rates than the surrounding soft tissues 202, such as internal organs, muscles, and fat. Therefore, the bones and soft tissues 202 are clearly distinguished in the bone density image 200 by differences in brightness (or density). 3, which is shown with black and white reversed from a normal X-ray image, bones such as lumbar vertebrae L2 to L4 have a significantly higher black density than soft tissue 202. In addition, in bone density image 200, the portions outside the subject (i.e., outside soft tissue 202) correspond to regions a1 and a2 where X-rays pass only through air, and the density there is close to 0 (i.e., X-ray absorption is minimal).

[0039] FIG. 3 shows an example in which the measurement system is transported at a constant low speed, but similarly, in the case of transport at high speed, conventionally the transport speed was constant from the scanning start position to the scanning end position.

[0040] Now, transporting the measurement system at a constant speed like this is easy to control. Here, what is important in measuring bone density is the bone part of interest, such as the lumbar vertebrae L2 to L4, and the information on the X-ray detection values ​​of the surrounding area, especially the soft tissue, is not so important. However, when transporting the measurement system at a constant speed as described above, important and unimportant areas will receive the same amount of radiation exposure.

[0041] In contrast to this, in this embodiment, the transport speed is changed between the scan start position and the scan end position to reduce the radiation dose in unimportant parts. That is, the transport speed is increased in unimportant parts to reduce the radiation dose.

[0042] Here, it is conceivable to identify the positions of the soft tissues and bones by performing a preliminary scan or prescan, and then control the transport speed according to the identified positions of the soft tissues and bones during the return main scan (which measures bone density). However, with this method, there is a high risk of the subject moving during the interval between the preliminary scan or prescan and the main scan.

[0043] Therefore, in this embodiment, no preceding scan or prescan is performed, and the transport speed in the main scan for measuring bone density is controlled based on the detected value of X-rays in the main scan.

[0044] FIG. 4 illustrates a conveying speed change pattern 110 in this embodiment. This change pattern 110 is used in standard mode or high-resolution mode. In this change pattern 110, the conveying speed is accelerated from 0 to "high speed" from the conveying start position on the left edge to the scanning start position. In the illustrated example, the acceleration during this period is constant, but the acceleration does not necessarily have to be constant. This "high speed" is a speed higher than the conveying speed in standard mode or high-resolution mode, and an example of this is the conveying speed in high-speed mode. From the scanning start position to position A on the right side thereof, the conveying speed remains at "high speed."

[0045] Position A is the boundary position between an air-only region a1 and a region b where the subject exists, in the center of the z-direction scanning range of the X-ray detector 30. In terms of transporting the measurement system, i.e., scanning in the y-direction, the measurement system enters the soft tissue region from outside the subject at position A. During measurement, the subject is positioned on the Bucky table 18 so that the lumbar vertebrae L2 to L4, which are the target of interest, are located in the center. The control unit 40 determines that the measurement system has reached position A when the X-ray detection value at the center drops significantly from the previous value. For example, it is determined that position A has been reached when the X-ray detection value at the center becomes equal to or less than a predetermined first threshold.

[0046] When position A is reached, the transport speed begins to decelerate. This deceleration continues until the transport speed reaches "low speed." This deceleration ensures that the transport speed reaches "low speed" by the time the measurement system reaches the left end of the region of interest (hereinafter abbreviated as ROI, where ROI stands for Region of Interest). The ROI is the region of interest when analyzing bone density images. As an example, the range of the ROI along the z-axis is 6 cm to the left and right of the central axis of the spine, including lumbar vertebrae L2 to L4, and its width is 12 cm. For example, if the deceleration completion position is determined so that deceleration is completed by the left end of the ROI (i.e., 6 cm to the left of the central axis of the spine) even for the thinnest possible subject, deceleration can be completed before the scanning position enters the ROI, regardless of the subject being measured. Also, this is just one example, but the range of the ROI along the x-axis direction ranges from the intervertebral space between the first lumbar vertebra L1 (symbol omitted in the figure) and the second lumbar vertebra L2 to the intervertebral space between the fourth lumbar vertebra L4 and the fifth lumbar vertebra L5 (symbol omitted in the figure).

[0047] After the transport speed reaches "low speed," it remains constant at "low speed" until the measurement system reaches position B. Position B is the boundary position between region b, where the subject exists, and region a2, which is composed of only air, in the center of the scanning range of the X-ray detector 30 in the z direction. In other words, at position B, the measurement system leaves the subject region (particularly soft tissue) and exits the subject. The control unit 40 determines that the measurement system has reached position B when the detected X-ray value at the center significantly increases from the previous value. For example, it is determined that position B has been reached when the detected X-ray value at the center becomes equal to or greater than a predetermined second threshold.

[0048] When it is determined that position B has been reached, the transport speed begins to accelerate. The transport speed is accelerated to "high speed." After the transport speed reaches "high speed," that "high speed" is maintained until the measurement system reaches the scanning end position. Then, between the scanning end position and the transporting end position, the transport speed is decelerated to 0.

[0049] According to this change pattern 110, the measurement system is transported at a "low speed" in the area important for measurement, i.e., the ROI area, where high measurement accuracy can be obtained, while the measurement system is transported at a "high speed" in other areas. This makes it possible to shorten the time required for the entire scan while maintaining the same measurement accuracy in the ROI area, compared to the example in which the transport speed is kept constant at a "low speed" from the scan start position to the scan end position as shown in Figure 3. Furthermore, it is possible to reduce the radiation exposure dose in the "high speed" transport speed range.

[0050] Hereinafter, the mode in which the transport speed is controlled in accordance with this change pattern 110 will be referred to as the "time-saving mode" or "exposure reduction mode" (collectively referred to as the "time-saving mode" below). The following explanation will be given using the time-saving mode for the standard mode or high-resolution mode as an example. However, as can be easily understood by those skilled in the art, if the transport mechanism of the measurement system can achieve a transport speed faster than the conventional transport speed in the high-speed mode, a similar time-saving mode can also be defined for the high-speed mode.

[0051] An example of a speed control procedure according to this change pattern 110 is shown in FIG. 5. In this procedure, when a measurement sequence in the time-saving mode is started, the control unit 40 accelerates the transport speed of the measurement system to "high speed" (S10). This acceleration is performed until the position of the measurement system reaches the scan start position. When it detects that the measurement system has reached the scan start position (the judgment result in S12 is Yes), the control unit 40 starts X-ray scanning while maintaining the "high speed" transport speed (S14). By the time this scanning starts, the control unit 40 has already started up the X-ray generator 26 and the X-ray detector 30. From that point on, the control unit 40 starts recording the detection value of the X-ray detector 30 (or the bone mineral content or bone density value calculated from the detection value). At this time, the measurement system is located within region a1 (see FIG. 2), and the X-rays irradiated from the X-ray generator 26 pass only through air before reaching the X-ray detector 30. In this case, the X-rays are hardly absorbed, so the detection value of the X-ray detector 30 is high. After this scan start position, X-ray irradiation and detection continues until the measurement system reaches the scan end position.

[0052] Thereafter, the control unit 40 monitors the detected value of the X-ray detector 30, for example, periodically. This monitoring is performed when the detected value reaches the first threshold value T s1 This is repeated (S16) until the first threshold T s1 is a predetermined value that is lower than the detection value when X-rays pass through only air and greater than the detection value when X-rays pass through soft tissue. If the determination result in S16 is Yes, the control unit 40 starts decelerating the transport speed of the measurement system, and reduces the transport speed to "low speed" within a predetermined time, for example, from the start of the deceleration (S18). "Low speed" is the transport speed when measuring the ROI in this mode. Thus, in this procedure, the point when the determination result in S16 is Yes is the point when the transport speed starts to be decelerated.

[0053] In S16, the detection value of the X-ray detector 30 when low-energy X-rays are irradiated, out of the two levels of X-rays alternately irradiated in the DEXA method, is the object of judgment. This is because the difference in detection value between the case of air only and the case of soft tissue is more likely to become apparent with low-energy X-rays. The same applies to the detection value judgment steps in S20 and other flowcharts such as those in Figures 6 and 8.

[0054] Now, when the conveying speed is reduced to the "low speed", the detected value of the X-ray detector 30 becomes equal to or exceeds the second threshold value T s2 The measurement system is transported at this "low speed" until it is detected that the second threshold T s2 is a predetermined value that is higher than the detection value when the X-ray passes through soft tissue that does not include bones, and is equal to or lower than the detection value when the X-ray passes through only air. s2 is the first threshold T s1 It may be the same value as, or may be different from,

[0055] If the determination result of S20 for the detected value is Yes, the control unit 40 starts accelerating the conveying speed of the measurement system, and increases the conveying speed to "high speed" within, for example, a predetermined length of time from the start of acceleration (S22). Thereafter, the control unit 40 maintains the conveying speed at "high speed" until the measurement system reaches the scan end position, at which point it starts decelerating the conveying speed. Thereafter, the conveying speed is reduced to 0 by the time the measurement system reaches the transport end position (S26).

[0056] Next, the generation of an image from the detection values ​​of the X-ray detector 30 when the transport speed is changed according to the change pattern 110 shown in FIG. 4 will be described.

[0057] In the DEXA method, low-energy X-rays and high-energy X-rays are alternately emitted from the X-ray generator 26. As the measurement system is transported, the X-rays at two energy levels, high and low, are detected by the X-ray detector 30, and high-energy X-ray detection values ​​and low-energy X-ray detection values ​​are obtained, which are arranged alternately in the mechanical scanning direction (the y direction in Figure 2). These pairs of high- and low-level detection values ​​constitute one piece of detection data. The detection data is obtained from the X-ray detector 30 at equal time intervals. Here, with conventional transport speed control, the transport speed is constant from the scanning start position to the scanning end position, so that an undistorted image can be obtained by, for example, determining the value of one pixel from one piece of detection data.

[0058] However, in the change pattern shown in Figure 4, the transport speed changes during scanning. Whether the transport speed is "high" or "low," the energy of the X-rays emitted by the X-ray generator 26 is switched between high and low at equal intervals, so detection data is also acquired at equal intervals. Therefore, in a method that associates detection data with pixels one-to-one, the image in the "high" transport speed range is compressed in the y direction more than the image in the "low" transport speed range. This is because the transport distance per time interval for acquiring one detection data is longer at "high" speed than at "low" speed, so the number of detection data points in the same length in the y direction is smaller at "high" speed than at "low" speed. Furthermore, in the accelerating or decelerating range, the transport distance per detection data point changes over time, so the compression or elongation of the image changes along the y direction. Therefore, if detection data is associated one-to-one with pixels, an inaccurate image containing compressed or elongated areas along the y direction will be generated.

[0059] To address this issue, the control unit 40 of this embodiment varies the association between detection data and pixels in the y direction depending on the transport speed. For example, if "high speed" is twice as fast as "low speed," one pixel is generated from one detection data in the "low speed" transport speed section, while two pixels in the y direction are generated from one detection data in the "high speed" transport speed section. Furthermore, generalizing this to include acceleration and deceleration sections, the system calculates bone density for each test data item and maps the calculated bone density for each test data item to coordinates on the image corresponding to the location where the test data was acquired. The value of each pixel in the image is then calculated by interpolating the bone densities of the mapped bone densities surrounding the pixel.

[0060] (Variation 1) In the procedure of FIG. 5, the X-ray detection value is the first threshold T s1 However, the deceleration start time is determined when the X-ray detection value is below the first threshold T s1A delay may be set to a certain amount from the point in time when it is detected that the y-axis position of the measurement system has reached the soft tissue. The length of the delay (hereinafter referred to as the delay time) may be a fixed value. Alternatively, the delay time may be determined according to the subject's attributes. The subject's attributes here refer to a combination of gender, age, etc. For each of these attributes, the subject's physique, such as the width of the waist, is statistically known. As mentioned above, the ROI is a region with a fixed width of 6 cm on each side from the central axis of the spine. Therefore, subjects with a larger waist width have a larger distance from the left edge of the soft tissue to the left edge of the ROI than subjects with a smaller waist width. Since the deceleration from "high speed" to "low speed" only needs to be completed before the measurement system reaches the left edge of the ROI, the delay time can be longer for subjects with a larger waist width than for subjects with a smaller waist width. Increasing the delay time extends the "high speed" section, thereby shortening the measurement time and reducing the radiation exposure dose.

[0061] An example of control for delaying the deceleration start point by a delay time according to the attributes of the subject will be described with reference to Fig. 6. Among the procedures in Fig. 6, steps that are similar to steps in the procedures in Fig. 5 are given the same reference numerals, and duplicated explanations will be omitted.

[0062] In this example, delay time data that specifies the delay time for each attribute of the subject is registered in the control unit 40. This delay time data is, for example, a table that records the delay time corresponding to each combination of gender and age group (e.g., young, middle-aged, elderly). The delay time for each combination may be determined in advance based on statistical information on the waist width of people by age and gender.

[0063] In the procedure of FIG. 6, first, the control unit 40 searches the delay time data for a delay time corresponding to the subject's attribute information (e.g., gender, age) input by the operator (S30). Thereafter, the control unit 40 executes the processes of S10 to S16. If the determination result of S16 is Yes, the control unit 40 immediately starts slowing down the transport speed (S18) in the procedure of FIG. 5. However, in this example, the control unit 40 waits for the delay time retrieved in S30 to elapse from the point in time when the determination result of S16 is Yes (S32). Once the delay time has elapsed (the determination result of S32 is Yes), the control unit 40 starts slowing down the transport speed. Thereafter, the control unit 40 executes steps S18 to S26, similar to the procedure of FIG. 5.

[0064] (Variation 2) In the change pattern 110 shown in Figure 4, the measurement system scanned the area including the spine at a "low speed", and then accelerated the transport speed at position B where the soft tissue exited the subject (i.e., area a2 shown in Figure 2).

[0065] In contrast to this, in this modified example, acceleration starts shortly after the scanning position of the measurement system passes through the ROI, before it reaches position B.

[0066] 7 shows an example of a change pattern 112 of the transport speed in this modified example. In this change pattern 112, the transport speed starts to accelerate at position D. Position D is a position slightly to the right of the right end of the ROI and a position further to the left than position B.

[0067] Position D is determined, for example, based on position C of the right end of the lumbar vertebrae. For example, the point in time when the detection value at the center in the z direction of the X-ray detector 30 changes from a relatively low intensity value corresponding to bone to a relatively high intensity value corresponding to soft tissue during scanning is the point in time when the scanning position of the measurement system reaches position C of the right end of the lumbar vertebrae. A position a predetermined distance from this point (i.e., to the right) is determined to be position D. In this case, the predetermined distance is about half the width of the ROI (6 cm in the example dimensions described above). A position about half the width of the ROI from the right end of the lumbar vertebrae is slightly to the right of the right end of the ROI.

[0068] The change pattern 112 shown in FIG. 7 has an acceleration timing earlier than the change pattern 110 shown in FIG. 4, so the time required for measurement is shorter and the radiation dose is also smaller.

[0069] The processing procedure of the control unit 40 in this modified example is illustrated in Fig. 8. In Fig. 8, steps that are the same as steps in the procedure of Fig. 5 are given the same reference numerals, and duplicated explanations will be omitted.

[0070] Steps S10 to S18 in the procedure of Fig. 8 are the same as those in Fig. 5. In the procedure of Fig. 8, after S18, the detection value at the center of the X-ray detector 30 in the z direction is periodically monitored, and the detection value is compared with the threshold value T b1 It is determined whether the threshold T b1 is a predetermined value that is lower than the detection value of the X-ray detector 30 when the X-ray passes through only soft tissue that does not contain bones, and is equal to or higher than the detection value when the X-ray passes through bones.

[0071] The determination result of S40 being Yes means that the position in the y direction of the measurement system has reached the lumbar vertebrae. In this case, the control unit 40 continues to monitor the detection value of the central part of the X-ray detector 30 in the z direction, and determines whether the detection value is equal to or lower than the third threshold T b2 It is determined whether or not the third threshold T b2 is a predetermined value that is higher than the detection value when the X-ray passes through a bone portion and is equal to or lower than the detection value when the X-ray passes through a soft tissue that does not include a bone portion.

[0072] A Yes determination result in S42 means that the position of the measurement system in the y direction has entered the soft tissue region from the right end of the lumbar vertebrae. From the point at which the Yes determination result in S42 is obtained, the control unit 40 waits for the measurement system to advance a predetermined distance (S44). This predetermined distance is approximately half the width of the ROI. When the Yes determination result in S44 is obtained, the control unit 40 starts to decelerate the transport speed (S22). Thereafter, the control unit 40 executes S24 and S26.

[0073] (Variation 3) 9 illustrates a conveying speed change pattern 114 according to another modification. In the change pattern 112 shown in FIG. 7, the conveying speed is accelerated when the scanning position of the measurement system reaches position D. In contrast, in the change pattern 114 shown in FIG. 9, the conveying speed is decelerated when position D is reached, and the movement of the measurement system is finally stopped. Furthermore, when deceleration begins, the emission of X-rays from the X-ray generator 26 may be stopped.

[0074] When this change pattern 114 is used, no measurement is performed beyond position D (to the right in FIG. 9), and therefore no image can be obtained, but since images within the ROI are obtained, this does not hinder diagnosis.

[0075] The processing procedure of the control unit 40 in this modified example is illustrated in Fig. 10. Of the procedures shown in Fig. 10, steps that are the same as steps in the procedures shown in Fig. 8 are given the same reference numerals, and duplicated explanations will be omitted.

[0076] Steps S10 to S44 of the procedure in FIG. 10 are the same as those in FIG. 8. In the procedure in FIG. 10, if the determination result in S44 is Yes (i.e., the scanning position of the measuring device has reached position D), the control unit 40 causes the X-ray generator 26 to stop emitting X-rays (S50). This is because, since deceleration is about to occur, if X-ray irradiation were continued, the exposure dose to the soft tissue would increase as the transport speed decreases. After stopping the X-ray emission, the control unit 40 slows down the transport speed of the measurement system and finally stops the measurement system (S52). After this stop, the control unit 40 controls the transport mechanism to return the measurement system to the transport start position (S54). The control unit 40 then waits for an instruction for the next measurement.

[0077] The embodiments and modifications of the present invention have been described above. These embodiments and modifications are merely examples for the purpose of explanation. Various modifications and improvements are possible within the scope of the present invention. [Explanation of symbols]

[0078] 10 X-ray measuring device, 14 arm unit, 24 main body housing, 26 X-ray generator, 30 X-ray detector, 38 control device, 40 control unit, 42 operation panel, 44 display.

Claims

1. an irradiation unit that irradiates the subject with the X-rays while scanning in a first direction; a detection unit that detects the intensity of the X-rays that have passed through the subject; a control unit that causes the irradiation unit to start the scanning from a position where the X-rays pass through the outside of the subject, sets the scanning speed to a first speed until the intensity detected by the detection unit becomes equal to or less than a first threshold corresponding to a boundary where the X-rays enter soft tissue of the subject from the outside, and reduces the scanning speed to a second speed at a deceleration start time point determined based on the time point when the intensity detected by the detection unit becomes equal to or less than the first threshold; A medical X-ray measurement device comprising:

2. 2. The medical X-ray measurement device according to claim 1, wherein the deceleration start time is a time when the intensity detected by the detection unit becomes equal to or less than the first threshold value.

3. 2. The medical X-ray measurement device according to claim 1, wherein the deceleration start time is a time that is delayed by a predetermined delay time determined in accordance with an attribute of the subject from a time that the intensity detected by the detection unit becomes equal to or less than the first threshold value.

4. the irradiation unit repeatedly irradiates high-energy X-rays and low-energy X-rays alternately according to a DEXA method during the scanning in the first direction; the control unit controls the scanning speed based on the intensity detected by the detection unit when the low-energy X-ray is irradiated.

2. The medical X-ray measurement device according to claim 1.

5. the irradiation unit irradiates an X-ray beam having a width in an orthogonal direction orthogonal to the first direction, the detector detects the X-ray beam having a width in the orthogonal direction by using a plurality of conversion devices arranged in a range of a predetermined width in the orthogonal direction or by mechanically scanning one conversion device over the range; the control unit controls the scanning speed based on the intensity detected by the detection unit at the center of the range in the orthogonal direction.

2. The medical X-ray measurement device according to claim 1.

6. 2. The medical X-ray measurement device according to claim 1, wherein, after the control unit reduces the scanning speed to the second speed, when the intensity detected by the detection unit becomes equal to or greater than a second threshold corresponding to a boundary from the soft tissue to the outside, the control unit increases the scanning speed to the first speed.

7. 2. The medical X-ray measurement device according to claim 1, wherein the control unit increases the scanning speed to the first speed when, during the scanning, the intensity detected by the detection unit decreases to an intensity corresponding to a bone portion of the subject, and then becomes equal to or greater than a third threshold corresponding to a boundary between the bone portion and the soft tissue, and the scanning progresses a predetermined distance.

8. 2. The medical X-ray measurement device according to claim 1, wherein the control unit stops the emission of the X-rays from the irradiation unit when, during the scanning, the intensity detected by the detection unit decreases to a level at which the X-rays have passed through a bone part of the subject, and then becomes equal to or greater than a third threshold corresponding to a boundary between the bone part and the soft tissue, and the scanning progresses a predetermined distance.

9. the scanning is achieved by moving an X-ray generator included in the irradiation unit in the first direction; the control unit stops the movement of the X-ray generator in the first direction after stopping the emission of the X-rays from the emission unit.

9. The medical X-ray measurement device according to claim 8.

10. 10. The medical X-ray measurement device according to claim 9, wherein the control unit stops the movement of the X-ray generator in the first direction, and then moves the X-ray generator in a direction opposite to the first direction to an initial position.

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