System and method for cross calibration in dual energy x-ray absorptiometry

Abstract

The present invention provides methods and systems for cross-calibration between two or more dual-energy x-ray absorptiometry (DXA) systems. In one embodiment, a calibration phantom is scanned with a patient during a scanning sequence with a first system to obtain one or more coefficients that map pixel values ​​retrieved from a phantom image from the phantom scan to image pixel values ​​in a reconstructed patient image from the patient scan. The one or more coefficients can be used to adjust and / or compare BMD values ​​of the patient obtained when the patient is scanned with a phantom having similar composition and parameters as the calibration phantom and with a different system.

Description

Technical Field

[0001] Embodiments of the subject matter disclosed herein relate to medical imaging systems, and more particularly to calibration in dual-energy x-ray absorptiometry (DXA) systems. Background Art

[0002] Medical imaging modalities such as dual-energy x-ray absorptiometry (DXA) systems can be used to obtain bone mineral measurements. DXA involves scanning a patient at two different x-ray energy levels and using the resulting dual-energy scan data to determine bone mineral density (BMD). Bone measurements such as BMD and bone mineral content (BMC) can be obtained by DXA scans of the patient's entire body or specific body regions, while additional measurements such as fat mass (FM), lean soft tissue mass (LSTM), fat-free mass (FFM), soft tissue mass (STM), total body mass (TBM) require a full-body DXA scan.

[0003] Generally speaking, bone monitoring and / or whole body monitoring require long follow-up studies. However, due to the aging of DXA systems and the emergence of new technologies, old DXA systems can often be replaced with new systems from the same manufacturer or new systems from different manufacturers. In addition, in some cases, patients can change their preferred clinics and therefore may need to use different DXA systems to continue follow-up studies. In some cases, even when the same type (manufacturer and version) of system is used for follow-up studies, the age and / or operating conditions of the system may be different. In any scenario, whenever a DXA system changes, cross-calibration between different DXA systems can be performed to ensure that the scan data collected with the previous DXA system will be comparable to the scan data collected with the current DXA system.

[0004] However, the current cross-calibration process can be time-consuming, and its accuracy is sensitive to many external conditions. In addition, when a patient changes his clinic, a cross-calibration assessment may not be possible. Therefore, a new baseline for the patient may need to be established. Furthermore, when the elapsed time between BMD measurements is large, the current cross-calibration process may not be applicable due to the large changes in BMD values. In each case, BMD follow-up studies can be severely biased, ultimately reducing the confidence in the diagnosis.

[0005] For example, the current cross-calibration process recommends an in vivo study approach that involves scanning a patient on the same day with each (previous and current) system using standardized positioning, acquisition, and analysis parameters to assess the degree of system variability between the different systems. Such strict control of the cross-calibration is not always feasible, especially when patients change their clinical preferences. Even when such a controlled in vivo cross-calibration process is performed, if there is a large time gap between the previous scan (using the previous system) and the subsequent scan (using a different system), the accuracy of the assessment of the subsequent scan relative to the previous scan is greatly reduced despite reasonable agreement between the two different DXA systems. In addition, the current in vivo calibration process increases radiation exposure to patients because they need to be scanned with two systems at the same time. Summary of the invention

[0006] In one embodiment, a method includes: receiving a first data set from a first DXA system, the first data set including first scan data of a subject and second scan data of a phantom simultaneously obtained with the first DXA system; and a first conversion function based on the first scan data and the second scan data; receiving a second data set from a second DXA system, the second data set including third scan data of the subject and fourth scan data of a phantom simultaneously obtained with the second DXA system; and a second conversion function based on the third scan data and the fourth scan data; generating a first set of standardized BMD values ​​for the subject based on the first conversion function; generating a second set of standardized BMD values ​​for the subject based on the second conversion function; determining a correlation coefficient based on the second scan data of the phantom and the fourth scan data of the phantom; and correcting any one of the first set of standardized BMD values ​​and the second set of standardized BMD values ​​based on the correlation coefficient.

[0007] Thus, by scanning the phantom along with the patient, in addition to capturing the patient scan data, a snapshot of the physical effects of the system on the image (temperature, calibration, tube aging, detector efficiency, etc.) is captured. Thus, when it is desired to compare patient data between two systems, the BMD values ​​can be normalized relative to the corresponding phantom and corrected based on the correlation between the phantom scan data obtained from each system. Thus, the BMD values ​​measured by at least two systems can be automatically compared while achieving increased accuracy and repeatability.

[0008] It should be understood that the above brief description is provided to introduce in a simplified form selected concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is solely defined by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention will be better understood by reading the following description of non-limiting embodiments with reference to the accompanying drawings, in which:

[0010] Figure 1 is a schematic diagram of an exemplary x-ray imaging system for performing a bone density scan of a patient according to one embodiment of the present disclosure;

[0011] Figure 2 According to one embodiment of the present disclosure Figure 1 A block diagram of an x-ray imaging system;

[0012] Figure 3 A schematic diagram showing positioning of an exemplary phantom relative to an exemplary x-ray imaging system according to one embodiment of the present disclosure;

[0013] Figure 4 shows a schematic diagram of an exemplary phantom used during scanning with an exemplary x-ray imaging system according to one embodiment of the present disclosure;

[0014] Figure 5 A schematic diagram showing storage and accessing of scan data sets from different x-ray imaging systems according to one embodiment of the present disclosure is shown;

[0015] Figure 6 A general flow chart illustrating an exemplary method for quantifying bone mineral according to one embodiment of the present disclosure is shown;

[0016] Figure 7 A general flow chart illustrating an exemplary method for performing a cross calibration according to one embodiment of the present disclosure is shown;

[0017] Figure 8 A schematic flow chart illustrating another exemplary method for performing cross calibration according to an embodiment of the present disclosure is shown; and

[0018] Fig. 9 A high level flow chart illustrating an exemplary method for routine monitoring of an x-ray system is shown, according to one embodiment of the present disclosure. DETAILED DESCRIPTION

[0019] The following description relates to various embodiments of an x-ray imaging system. In particular, systems and methods for cross-calibration in a dual-energy x-ray absorptiometry (DXA) system are provided. An x-ray imaging system, such as Figure 1 to Figure 2 The depicted DXA imaging system can be used to assess bone health and is essential for the diagnosis of bone diseases such as osteoporosis. Specifically, patient scan data from a DXA system can be used to quantify bone mineral density (BMD) and bone mineral content (BMC), which are used to diagnose osteoporosis. In addition to determining BMD, DXA scan data can also be used for other application scenarios, such as fracture risk assessment, whole body composition analysis, etc. In general, DXA systems are essential for the diagnosis of bone diseases and the management of patients with such diseases. In addition, the management of bone diseases often requires follow-up scans to monitor BMD changes or drug efficacy. In order to maintain the high accuracy and repeatability of the DXA system, quality control (QC) can be performed on the BMD measurement results. The QC of the BMD measurement results includes daily calibration, wherein the average value of the BMD values ​​measured by the daily phantom is within the upper threshold and lower threshold of the baseline BMD value established for a given system. The QC of the BMD measurement results also includes cross-calibration, which can be performed when a previous DXA system is replaced with a different DXA system.

[0020] However, known cross-calibration methods are time consuming and require extensive scanning of a large number of subjects with both systems within a short period of time. Typically, the scan of each system may be repeated at least twice to achieve repeatability. Even with such extensive cross-calibration practices, it may be difficult to establish a baseline for each patient scanned with the previous system, especially after a long period of time. As a result, important patient scan information is lost, which results in reduced confidence in disease monitoring and diagnosis.

[0021] The present disclosure solves at least some of the above-mentioned problems and provides solutions for improving the cross-calibration process with higher accuracy and repeatability without losing critical patient information. Specifically, a method for a dual-energy x-ray system may include: scanning a calibration phantom simultaneously during each scan of a patient with an x-ray system; and obtaining patient scan data through the patient scan and the calibration data based on the phantom scan for each scan. The calibration data can be embedded with each item of patient scan data and can be stored in a reference space that can be accessed for calibration purposes. In addition to BMD measurement results for diagnosis and monitoring, exemplary positioning of a patient and a phantom for generating scan data that can be used for calibration is shown in FIG. Figure 3 An exemplary phantom that can be used for daily and / or cross-calibration procedures is shown in Figure 4In addition, an exemplary model for storing and accessing data in a reference space and from different DXA systems is shown in Figure 5 An exemplary method for generating scan data that can be used for quantification and cross-calibration is shown in Figure 6 An exemplary method for comparing BMD values ​​measured by two different DXA systems is shown in Figure 7 In addition, the current DXA system controller of the current DXA system may be configured to perform a cross-calibration between the previous system and the current system based on the plurality of patient scan data and the plurality of calibration data stored in the reference space, and based on the plurality of new scan data acquired by the current system, such as Figure 8 In addition, the scan data generated and stored as described herein can be used for daily calibration. An exemplary method for evaluating the DXA system management performance of a DXA system is described in Fig. 9 Shown in.

[0022] By scanning the calibration phantom along with the patient, each scan captures the operating state of the system during the scan. Therefore, calibration data can be obtained at any time and important patient information is preserved. In addition, by utilizing the calibration data, cross-calibration between two systems can be performed at a much faster rate because the need to scan the subject with a replacement system is reduced due to the immediate availability of the calibration data. In addition, the calibration data can be used for daily system monitoring and therefore such system problems can be quickly identified and corrected. Therefore, the scan quality and accuracy are improved, while also improving the calibration speed and precision.

[0023] The description herein relates to various embodiments of medical imaging systems. Specifically, methods and systems are provided that are used as, for example, a single energy x-ray absorptiometry (SXA) system for measuring breast density, or a dual energy x-ray absorptiometry (DXA) system for measuring bone mineral density. The example of DXA is used herein, but it should be recognized that in other embodiments, other modalities such as radiography and / or medical imaging may be used. For example, these may include, but are not limited to: PET, SPECT, C-arm angiography, mammography, ultrasound, etc. The discussion of DXA herein is provided as an example of a suitable application scenario.

[0024] See also Figure 1 and Figure 2An exemplary embodiment of the system 10 can be used to measure at least the area of ​​a bone, the length of a bone, the bone mineral content (BMC), the bone mineral density (BMD), or the thickness or density of a tissue. The BMD is calculated by dividing the BMC by the area of ​​the bone. During operation, an x-ray beam having a broadband energy level is used to scan an object, for example, a human patient is scanned to image the patient's bones. The acquired bone images are used to diagnose medical conditions, such as osteoporosis. These images can be generated in part by determining bone density information acquired during dual-energy x-ray scanning. As further described in detail herein, the position of the source 14, the detector 18, and / or the inspection table can be adjusted to achieve further desired imaging purposes, including but not limited to magnification, increased image resolution, or spatial resolution. For exemplary purposes, the imaging system 10 can be described as a dual-energy x-ray absorptiometry (DXA) system, but it should be appreciated that various other systems can also be implemented in a similar manner.

[0025] The imaging system 10 is shown to include a gantry 12. The gantry may be a substantially C-shaped or semicircular gantry or a C-arm gantry. The gantry 12 movably supports a source 14 and a detector 18 mounted on opposite ends relative to each other. In addition, a subject 22 is disposed between the source 14 and the detector 18.

[0026] The gantry 12 includes an x-ray source 14 that projects a beam of x-rays 16 toward a detector array 18. The gantry 12 illustratively includes a lower end 13 positioned below a subject 22 (such as a patient) and an upper end 15 positioned above the subject 22. The x-rays pass through the subject 22 to generate attenuated x-rays. Figure 1 As depicted, an x-ray source 14 may be secured to the upper end 15, and an x-ray detector 18 may be secured to the lower end 13. Figure 2 As depicted, detector 18 may be secured to upper end 15, and x-ray source 14 may be secured to lower end 13. Each detector element 20 is illustratively, but not limited to, a cadmium telluride (CdTe) detector element that produces an electrical signal representative of the intensity of the attenuated x-rays.

[0027] During a scan to acquire image data, the gantry 12 and / or components mounted on the gantry 12 can be moved relative to the subject 22 and / or the examination table 46. The examination table 46 may include a scanning surface on which the subject 22 can be positioned. For example, during the acquisition of image data, the gantry 12 can be moved to change the position and / or orientation of the source 14 and / or the detector 18 relative to the patient. In an exemplary embodiment, the gantry 12 can move the source 14 and the detector 18 in a lateral scanning path, a progressive overlapping scanning path, or a zigzag (e.g., raster) scanning path 24, such as Figure 1 and Figure 2As shown. It should be appreciated that other forms of image data acquisition may utilize other forms of scan paths, which may include, but are not limited to, rotation or tilting of the gantry 12. It should be appreciated that in other exemplary imaging systems within the present disclosure, one of the source or detector may remain in a fixed position while the other of the source or detector is capable of moving relative to the patient. In other exemplary embodiments as disclosed herein, the examination table configured to support the patient is further capable of moving to achieve the desired image acquisition.

[0028] The movement of the gantry 12 and the operation of the x-ray source 14 are governed by an imaging controller 26 of the imaging system 10. The imaging controller 26 includes an x-ray controller 28 that provides power and timing signals to the x-ray source 14. The x-ray controller 28 may also provide operating and / or control signals to the adjustable collimator 25 to shape the x-ray beam from the source 14 according to the imaging process to be performed. In some embodiments, the x-ray beam may be shaped (collimated) into a fan beam. In an exemplary embodiment, the fan beam 16 may be a narrow fan beam to limit the divergence between the x-rays in the beam, which has been shown to be beneficial in improving parallax and image overlap blur.

[0029] The imaging controller 26 also includes a gantry motor controller 30 that controls the motion, speed, and position of the gantry 12. In some embodiments, the gantry motor controller 30 can control the tilt angle of the gantry 12. The gantry motor controller 30 can also be operated to control the movable joint 50 between the detector 18 and the gantry 12. The gantry motor controller 30 can also be operated to control the movable joint 54, illustratively between the source 14 and the gantry 12. The inspection table motor controller 44 is operably connected to the inspection table 46 through the inspection table motor 70. Under the control signal from the inspection table motor controller 44, the inspection table motor 70 can be operated to translate, rotate and / or tilt the inspection table 46 in multiple degrees of freedom of movement. In one embodiment, the inspection table motor 70 is operable to move the inspection table 46 in three degrees of freedom (e.g., horizontal translation, vertical translation, and depth translation), while in another embodiment, the rotational degrees of freedom of movement (e.g., pitch, yaw, and roll) can be available. It should be appreciated that the table motor 70 may include one or more mechanical or electromechanical systems to perform these movements of the table 46, including but not limited to track and beam driven, screw driven, or chain driven actuators.

[0030] The x-ray source 14 and the x-ray detector 18 can be moved in a raster pattern 24 to track a series of transverse scans 27 of the subject 22, during which dual-energy x-ray data is collected by the x-ray detector 18. The transverse scanning process generates a single image or a quantitative data set, forming a plurality of scanned images acquired from the entire body of the patient, wherein the x-ray source 22 and the detector 26 are longitudinally aligned with the superior-inferior axis of the patient or transversely aligned from the left side to the right side of the patient. Using transverse motion to scan the patient is advantageous in minimizing the time between the acquisition of adjacent scanned images, because the transverse direction of the entire body of the patient is shorter than the longitudinal direction of the entire body of the patient. Therefore, transverse scanning can reduce the severity of patient motion artifacts between scanned images, thereby allowing more accurate merging of images.

[0031] The transverse scanning motion is produced by coordination between the motion control of the gantry 12, the x-ray source 14, and the x-ray detector 18 by the gantry motor controller 30, and the control of the table 46 by the table motor controller 44, which operates the table 46 via the table motor 70. During operation, the x-ray source 14 produces a fan beam 16 having a plane that is illustratively parallel to the longitudinal axis 48. Optionally, the fan beam 16 may have a plane that is perpendicular to the longitudinal axis 48. The raster pattern 24 is adjusted so that there is some overlap (e.g., 10% overlap) between consecutive scan lines of the fan beam 16.

[0032] The data acquisition system (DAS) 32 in the imaging controller 26 samples and digitizes the data from the detector elements 20 and converts the data into sampled and digitized data for subsequent processing. In some embodiments, the DAS 32 may be positioned adjacent to the detector array 18 on the gantry 12. The preprocessor 33 receives the sampled and digitized data from the DAS 32 to preprocess the sampled and digitized data. In one embodiment, the preprocessing includes, but is not limited to, bias correction, raw speed correction, reference channel correction, air calibration, and / or applying a negative logarithmic operation. As used herein, the term processor is not limited to those integrated circuits referred to as processors in the art, but refers broadly to controllers, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits, and any other programmable circuits, and these terms are used interchangeably herein. The preprocessor 33 preprocesses the sampled and digitized data to generate preprocessed data.

[0033] The image processor 34 receives the preprocessed data from the preprocessor 33 and performs image analysis, including image analysis of densitometry and / or absorption measurement through one or more image processing operations. The acquired bone and tissue information (e.g., image and density information) can be processed and displayed to the image processor 34 and / or the processing unit 36 ​​in real time through operation. The processing unit 36 ​​exemplarily operates to store the reconstructed image in a mass storage device 38, where, as non-limiting examples, the mass storage device 38 may include a hard disk drive, a floppy disk drive, a compact disk read / write (CD-R / W) drive, a digital versatile disk (DVD) drive, a flash drive, and / or a solid-state storage device. As used herein, the term computer is not limited to those integrated circuits referred to as computers in the art, but broadly refers to processors, microcontrollers, microcomputers, programmable logic controllers, application-specific integrated circuits, and any other programmable circuits, and these terms are used interchangeably herein. It should be appreciated that any one or more of the processors and / or controllers described herein may be performed by or in conjunction with processing unit 36, for example by executing computer-readable code stored on a computer-readable medium accessible and executable by processing unit 36.

[0034] The processing unit 36 ​​also receives commands and scanning parameters from a user (such as an operator) via a console 40, which includes a user interface device, such as a keyboard, a mouse, a voice-activated controller, a touch screen, or any other suitable input device. An associated display 42 allows a user (such as an operator) to observe images and densitometry data from the processing unit 36. The commands and scanning parameters are used by the processing unit 36 ​​to provide control signals and information to the imaging controller 26 (including the DAS 32, the x-ray controller 28, and the gantry motor controller 30). In addition, the processing unit 36 ​​can operate a table motor controller 44 (which is illustratively the imaging controller 26), which controls a movable subject support (which is illustratively a motorized table 46) to position the subject 22 within the gantry 12. Specifically, the table motor controller 44 adjusts the table 46 to move various portions of the subject 22.

[0035] During operation, the system 10 is configured to operate in a dual energy x-ray mode or a single energy x-ray mode. In the single energy mode, the x-ray source 14 emits x-rays with a narrow band energy of a few keV and emits x-rays in a diagnostic imaging range of about 20keV-150keV. In the dual energy mode, the x-ray source 14 emits radiation in two or more energy ranges emitted simultaneously or in rapid succession. The x-ray source 14 can also be configured to emit a single broadband energy of more than a few keV in the diagnostic imaging range. The system 10 can be switched between the dual energy mode and the single energy mode by increasing or decreasing the voltage and / or current of the x-ray source 14. The system 10 can also be switched between the dual energy mode and the single energy mode using a K-edge filter and an energy discriminating detector. It should be noted that the x-ray source 14 can emit x-rays of different energies or energy ranges.

[0036] The x-ray source 14 may be configured to output a fan beam 16 of x-rays. The x-ray source 14 may also be configured to output a pencil beam of x-rays (not shown), a cone beam of x-rays, or other configurations. In some embodiments, the processing unit 36 ​​controls the system 10 to operate in a single energy mode or a dual energy mode to determine at least some bone or tissue information of the scanned body. Generally speaking, the image resolution in the system 10 may be based on the detector element size, the source focal size, and the distance from the object to the detector. The acquired image may then be used to measure, for example, bone density or other bone and tissue properties or content. As described above, the dual energy x-ray scan may be a linear scan of the entire patient's body, which may be performed in a transverse type scanning sequence as described above. During the dual energy x-ray scan, an image of the entire body of the patient may be acquired, the image including image information related to the bones and tissues in the body. A circumferential or full body scan of the entire body may be performed as a single scan operation, which may be a low dose mode scan. In some embodiments, instead of a circumferential or full body scan, individual rectangular regions of the body may be scanned, which may be a single scan scan. Once the patient or a portion thereof is scanned, the dual energy signal provided by detector 18 is resolved into images of two basic substances such as bone and soft tissue. The high energy signal and the low energy signal can be combined to provide a single energy mode with excellent signal-to-noise ratio for imaging purposes.

[0037] In order to capture the operating status of the system and / or obtain calibration data, during each dual-energy x-ray scan of the subject 22, the phantom may be positioned along with the subject 22 so that the subject 22 and the phantom are scanned during a single scan sequence. An exemplary positioning of the phantom relative to the subject 22 is described below. Figure 3 middle.

[0038] Go to Figure 3 , which shows an exemplary DXA system (such as Figure 1 and Figure 2 Schematic diagram of a portion 300 of an imaging system 10 of an embodiment of the present invention, showing an exemplary positioning of a phantom relative to a patient during scanning with a DXA system. Specifically, during each scan with the DXA system, a phantom 314 is positioned on a DXA scanning table 302 along with a patient 316. The DXA scanning table 302 may include a scanning surface 303, which includes a patient scanning area 304 and a tube / detector parking area 310. In an exemplary embodiment, a patient 316 may be positioned on the patient scanning area 304, and the phantom 314 may be positioned within the parking area 310. The patient 316 and the phantom 314 may be scanned during a single scanning sequence. For example, in the illustrated embodiment, during a scanning sequence, radiation rays 312 from an x-ray source 308 may pass through the patient, and projection data of the patient 316 (also referred to herein as patient projection data) is obtained at the detector 306. After the patient is completely scanned, during the same scanning sequence, the phantom 314 may be scanned by the DXA system, and projection data (also referred to herein as phantom projection data) of the phantom 314 may be obtained at the detector 306. The starting position of the source 308 and detector 306 of the DXA system is shown at 320, and the final position of the source 308 and detector 306 of the DXA system is shown at 340. In this example, the source 308 and detector 306 may move relative to each other in the same direction indicated by arrow 307.

[0039] Thus, the entire body of the patient 316 and the phantom 314 can be scanned with the DXA system. Thus, after the scanning sequence is completed, patient projection data and phantom projection data are obtained. In one example, the patient projection data can be used for image reconstruction, while the phantom projection data can be reserved for later use, such as cross calibration, as described below in conjunction with Figures 6 to 8 In another example, the phantom projection data can be used to monitor system performance, as described below. Fig. 9 As described in.

[0040] The patient scan data may include patient projection data and patient reconstructed image data, while the phantom scan data may include phantom projection data, calibration data determined from the projection data, and additional calibration data. The phantom scan data may also include phantom image reconstruction data. The calibration data may include conversion ratios that map pixel values ​​retrieved from the phantom image to image pixel values ​​in the reconstructed patient image. The calibration data in the scan file may include image signal data corresponding to a calibration phantom (e.g., aluminum / synthetic resin phantom, QA phantom, etc.), detector status (e.g., bias, dead pixel, etc.), and other derived values ​​calculated from these phantom images. The additional calibration data may include one or more parameters indicating the physical effects of the DXA system on the reconstructed image. The one or more parameters may include acquisition parameters, including the temperature of the DXA system during the scan, exposure time, incident dose, tube current and tube voltage, and detector efficiency (e.g., signal-to-noise ratio). It may be noted that these acquisition parameters are not calibrated; however, these calibration data may be used to calculate the acquisition parameters.

[0041] The phantom scan data, including the calibration data and the additional calibration data, can be combined with the patient scan data and then transferred to the reference BMD space. For example, the DXA system controller can embed the patient scan data with the phantom scan data and transfer the combined patient and phantom scan data to the reference space.

[0042] Although this example shows a single phantom positioned below the patient on the DXA scanning table, other embodiments may include more than one phantom at different locations, such as beside the patient, above the patient, or to the side of the patient, in addition to or as an alternative to the bottom location shown herein. The phantom may also be positioned at a fixed position below the examination table. In addition, the following embodiments are also within the scope of the present disclosure: a single phantom is positioned on the examination table relative to the patient at any position in the scanning area on the scanning surface.

[0043] Thus, by scanning the phantom along with the patient during a scanning sequence, calibration data can be generated from the phantom scan data during each patient scan. The calibration data can capture the state of the system while the patient is being scanned and can be used to perform one or more types of calibration, as described below in conjunction with Figures 6 to 9 Further described.

[0044] Figure 4A schematic diagram of an exemplary phantom 400 that can be used to perform scans in conjunction with a patient is shown. During each scan, the phantom can be used to obtain calibration data in addition to the patient scan data. The phantom 400 may include a substrate 402 having a plurality of inserts 404 made of different materials, each insert having a different density. The substrate 402 may include a soft tissue-like background material, such as an artificial resin. Each material may include, for example, a combination of one or more of bone, soft tissue, and protein. The exemplary phantom 400 shows a plurality of inserts 404 made of different materials, having different densities and arranged in a matrix pattern. Other arrangements of the inserts are also within the scope of the present disclosure.

[0045] In an exemplary embodiment, the plurality of inserts may be different inserts of the target material, having different thicknesses and / or densities.

[0046] In another exemplary embodiment, each row of inserts may be made of a different material, and within each row, the inserts may be made of the same material with different densities and / or thicknesses, as shown.

[0047] In some exemplary embodiments, known standard phantoms may be used to obtain calibration data. Exemplary known phantoms may include, but are not limited to, various spinal phantoms.

[0048] In any case, the phantom characteristics (including insert composition) can be determined and stored with high accuracy and repeatability to enable phantom replication for calibration purposes.

[0049] Go to Figure 5 , which shows an exemplary block diagram showing a model 500 for storing, processing, and accessing multiple scan data from multiple DXA systems. Each of the multiple scan data may include patient scan data and phantom scan data acquired with each system.

[0050] Model 500 depicts a first set of scan data 502 obtained from a first system 510 (system A) and a second set of scan data 504 obtained from a second system 530 (system B). In one example, scan data 502 may be stored in a non-transitory memory of a processor of the first system 510, an edge device in communication with the processor of the first system 510, or any combination thereof. Similarly, scan data 504 may be stored in a non-transitory memory of a processor of the second system 530, an edge device in communication with the processor of the second system 530, or any combination thereof. In addition, each of the first system 510 and the second system 530 may be communicatively coupled to a reference space 520, as indicated by 508 and 506, respectively. Specifically, the processor of the first system 510 and the processor of the second system 530 may be communicatively coupled to a processor of the reference space 520. The reference space can be one or more of: a cloud-based reference space having a reference space controller and non-volatile memory, an edge device that communicates with the DXA system's processor and has a device controller and device non-volatile memory, a remote device that communicates with the DXA system and has a remote controller and non-volatile memory, or a combination thereof.

[0051] During each scan with each DXA system, a phantom (such as Figure 4 The phantom 400 in the image is imaged together with the patient to obtain patient scan data and phantom scan data. Thus, the first set of scan data 502 from the first system 510 may include: first scan data, including patient scan data 512 embedded with phantom scan data 513, the phantom scan data being obtained at a first time point during a first scan performed with the first system 510; second scan data, including patient scan data 514 embedded with phantom scan data 515, the phantom scan data being obtained at a second different time point during a second scan performed with the first system 510, and so on. Similarly, the second set of scan data 504 from the second system 530 may include: the first scan data of the second system, including patient scan data 532 embedded with phantom scan data 533, which was obtained at a first time point during the first scan with the second system 530; the second scan data of the second system, including patient scan data 534 embedded with phantom scan data 535, which was obtained at a second different time point during the second scan with the second system 530, and so on. In addition, the scan data from each system may include scan data of the same patient, scan data of different patients, or any combination thereof. In addition, the phantom used with the first system 510 may be of the same type or have highly similar properties (e.g., background material properties and insert properties) as the phantom used with the second system 530; and vice versa.

[0052] In an exemplary embodiment, a transformation may be applied to each patient scan data based on the corresponding phantom scan data. The transformation may produce a function having one or more coefficients that may be used to perform a regression analysis. Thus, in one example, the calibration data may include a polynomial function having one or more coefficients.

[0053] Each patient scan data along with the calibration data may be stored in reference space 520. Specifically, for each scan of each system, a corresponding scan transform is determined by retrieving specific pixel values ​​from the corresponding phantom scan data in one or more predetermined regions and mapping the patient image pixel values ​​to specific pixel values ​​in the phantom scan image. Each transform may produce a polynomial that may include, but is not limited to, a set of polynomial coefficients that transform the image pixel values ​​in the skeletal image of each scan to the reference space 520. Thus, in this example, the calibration information may include a set of polynomial coefficients, and the calibration information based on the phantom scan data is embedded into each patient DXA scan and captures not only the patient data, but also a snapshot of the physical effects of the system on the image (temperature, calibration status, tube aging, detector efficiency, etc.).

[0054] In addition, all scan data for each patient, including patient scan data and phantom scan data, can be stored in the BMD reference space 520 independent of system manufacturer / model. Standardized BMD values ​​(sBMD) can be evaluated in the reference space 520 and compared with any other system data that also provides cross-calibration information, provided that the corresponding phantoms are of the same type and / or have a high degree of repeatability. In other words, patients with scan data acquired from system A 510 and submitted to the new system B 530 for examination can have sBMD values ​​compared with greater accuracy and repeatability. An exemplary evaluation of sBMD values ​​in the reference space is described in Figure 7 middle.

[0055] The population data 505 with known embedded transformations can also be transformed into a reference BMD space and used as a diagnostic baseline. The population data can include: an average population BMD value for a population based on one or more of age and gender. In one example, the population data 505 can be used to determine one or more of a z-score and a T-score for a given patient.

[0056] Although this example shows two DXA systems, reference space 520 may store scan data from multiple DXA systems.

[0057] Figure 6A schematic flow chart illustrating an exemplary method 600 for quantifying bone mineral density in a patient according to one embodiment is shown. Specifically, the method 600 involves measuring bone mineral density based on patient scan data obtained by scanning the patient using a DXA system such as Figure 1 and Figure 2 The system described herein is obtained by scanning a patient. Figure 1 and Figure 2 Method 600 is described with reference to the depicted systems and components, but it should be understood that the method may be applied to other systems without departing from the scope of the present disclosure. Method 600 may be performed by processing unit 36 ​​and may be stored as executable instructions in a non-transitory memory of processing unit 36. Additionally or alternatively, method 600 may be performed by an edge device connected to the processing unit, a cloud in communication with the processing unit, or any suitable combination thereof.

[0058] Method 600 starts at 602. At 602, method 600 obtains desired scanning parameters from a user. The desired scanning parameters may include patient parameters (e.g., height, weight, etc.) and a scan volume (e.g., whole body, femoral neck, entire hip, lumbar spine). The desired parameters may include energy levels specified for scanning. In addition, the patient may be positioned before or after obtaining the desired scanning parameters. In any case, when the patient is positioned above the scanning area of ​​the DXA table, it may be determined whether the patient's positioning is suitable for scanning. For example, the controller may evaluate whether the patient is positioned within the desired scanning area of ​​the DXA table, and may further evaluate, based on the scan volume, whether the patient's portion of interest (e.g., hip) is properly positioned (e.g., within a certain angle relative to the longitudinal axis of the body) and in the scanning path of the DXA system. Based on the positioning assessment, the controller may provide indication information to the user. For example, if a patient positioning error is detected, the controller may provide an alarm indicating the error, and may provide suggestions for correcting the error.

[0059] Next, after obtaining the scan parameters and / or confirming patient positioning, method 600 may include adjusting the system based on the desired scan parameters. Adjusting the system may include: moving the detector and source to an initial position for scanning. In one example, the system adjustment may be automatic, where the controller may move the source and detector to the initial position after confirming one or more of: confirming the presence and position of the patient, and receiving the scan parameters. In another example, the system may be adjusted by a user.

[0060] Next, method 600 proceeds to 606 to determine whether the phantom is positioned within the scanning area. That is, before initiating the scan, the controller can determine whether the phantom is positioned within the scanning area. In addition, the controller can determine whether the phantom is positioned within the scanning path of the DXA system. In one example, the phantom can be positioned relative to the patient on the scanning surface of the DXA table and within the scanning area (e.g., along the longitudinal axis of the patient's body below the patient's feet). As described above in conjunction with Figure 3 As discussed, the phantom may be positioned at other locations on the scanning surface relative to the patient. Other locations on the scanner surface may include: along the longitudinal axis of the patient's body above the patient's head, along an axis parallel to the longitudinal axis (i.e., on one side of the patient), or anywhere on the scanner surface adjacent to the patient such that the patient and the phantom are scanned during a single scan. For example, based on information from a sensor coupled to the scanning surface, the controller may determine the presence of the phantom on the scanning surface. Furthermore, in some embodiments, more than one phantom may be used.

[0061] If the phantom is not detected, the answer at 606 is no, and the method 600 may proceed to 605. At 605, the method 600 includes prompting the user to position the phantom within the scanning area. The method 600 may then continue to monitor for the presence of the phantom. If the presence of the phantom is confirmed within the scanning area, the method 600 proceeds to 608. At 608, the method 600 includes scanning the patient and the phantom during a single scanning sequence. For example, when the phantom is positioned below the patient's feet, during a full-body scan, the scanner may initiate the scan at a first position above the patient's head and continue scanning until both the patient and the phantom are scanned. During a partial-body scan, the scanner may initiate the scan at a position above the patient's chest and continue scanning until the desired portions of both the patient and the phantom are scanned. In some embodiments, additional scans of the phantom may be performed separately before and / or after scanning the patient and the phantom. These additional scans may also be used for calibration purposes.

[0062] Next, at 610 , method 600 includes obtaining scan data at a detector, the scan data including patient scan data obtained by scanning the patient and phantom scan data obtained by scanning the phantom.

[0063] Next, the patient scan data and the phantom scan data can be used in one or more paths. In one path, at 624, the patient scan data and the phantom scan data can be used to generate a patient scan image and a phantom scan image. In addition, at 626, the method 600 includes quantifying patient bone mineral information, including patient bone mineral content and bone mineral density, based on one or more of the patient scan data, the patient scan image, the phantom scan data, and the phantom scan image.

[0064] Next, at 628, the patient scan image can be displayed to the user via the user interface. In addition, quantitative data including bone mineral content and bone mineral density can be displayed. In some embodiments, the following items can be indicated to the user: a T score indicating the amount of deviation from the average bone density of a healthy adult population, and a Z score indicating the amount of deviation from the average bone density of a healthy adult population of the same age and gender of the patient. In addition, additional measurements such as fat mass (FM), lean soft tissue mass (LSTM), fat-free mass (FFM), and soft tissue mass (STM) can be calculated based on the patient scan data and the phantom scan data. In one example, a phantom image can be displayed to the user. In some examples, if the phantom scan data is not obtained, the controller can provide an alert to the user via the interface that the phantom scan data is not obtained.

[0065] The patient scan data and phantom scan data obtained at 610 can also be used to calculate the standardized BMD value and cross-calibration formula. Therefore, at 612, in addition to generating patient scan images and quantifying BMD and BMC, method 600 also includes processing a reference space (such as Figure 5 At 614, processing the patient scan data and the phantom scan data for the reference space includes retrieving specific pixel values ​​of a plurality of predetermined regions on the phantom image reconstructed from the phantom scan data. In one example, the plurality of predetermined regions may include a plurality of calibration phantom inserts (such as, Figure 4 and multiple regions within the insert 404 of the calibration phantom base (such as Figure 4 One or more areas on a substrate 402).

[0066] Additionally, processing the patient scan data and the phantom scan data for calibration includes, at 616, determining a transformation to map pixel values ​​retrieved from the phantom image to image pixel values ​​in the reconstructed patient image.

[0067] Furthermore, at 618, additional calibration information may be obtained from the phantom scan data, including the effects of system temperature, indications of tube aging, detector efficiency, exposure time, incident dose, tube current, and tube voltage, etc. Furthermore, the phantom may include other objects inside the phantom in addition to the target material insert, thereby providing additional information, such as spatial resolution, pixel gain maps, etc. Furthermore, one or more patient parameters may be obtained, including patient information, such as height, weight, gender, etc.; system parameters, including system information, system temperature, output voltage, rated current, etc.; and environmental parameters, including ambient temperature, ambient pressure, and ambient humidity in the DXA system environment.

[0068] Continuing to 620, method 600 includes embedding all calibration data with the patient scan data. The all calibration data may include conversion coefficients that map the phantom data to the patient data and other additional calibration data as indicated above. Specifically, for each scan, patient scan data and phantom scan data are obtained, and each item of patient scan data is embedded with corresponding calibration data obtained from the phantom scan data of the calibration phantom scanned with the patient. In one example, the all calibration data may include a function that converts image pixel values ​​in the patient scan to phantom composition. For example, a conversion from image pixel values ​​to known material composition / thickness / density in each predetermined region of the phantom may be obtained. With the various predetermined regions, a regression may be performed to find a function that converts image pixel values ​​in the patient scan to phantom composition space.

[0069] Next, at 616, method 600 includes storing the embedded patient scan data in a reference space. The reference space can be one or more of: a cloud-based reference space having a reference space controller and non-transitory memory, an edge device in communication with a processor of the DXA system and having a device controller and device non-transitory memory, a remote device in communication with the DXA system and having a remote controller and non-transitory memory, or a combination thereof.

[0070] In one example, patient bone mineral quantification can be performed in a reference space, and the BMD value can be stored in the reference space. In other embodiments, the controller can calculate the BMD value, and the scan data and the BMD value can be converted and stored in the reference space. In addition to storing the embedded patient scan data in the reference space, the embedded patient scan data and the patient BMD value can be stored in a non-transitory memory of the processing unit.

[0071] Method 600 then ends when both paths are completed.

[0072] Thus, with each scan, calibration data indicating the overall systemic effect on bone mineral quantification can be obtained and stored in the reference space. The calibration information can be retrieved when needed and used for one or more of the following: automatic cross calibration, as described below in conjunction with Figure 7 Combined cross calibration, as described below Figure 8 as described; and system performance evaluation, such as combined Fig. 9 described.

[0073] Figure 7A schematic flow chart showing an exemplary method 700 for comparing BMD values ​​obtained between two different systems according to one embodiment is shown. Specifically, during scanning with each of the two different systems, a phantom can be scanned along with the patient to obtain patient scan data and phantom scan data for each system. The phantom scan data from each system can be used to obtain a standardized BMD value measured for the patient with each system, thereby enabling comparison of BMD values ​​between each system without the need to establish a baseline when using different systems. Reference will be made herein to Figures 1 to 5 Method 700 is described with reference to the systems and components depicted, but it should be understood that the method may be applied to other systems without departing from the scope of this disclosure. Method 700 may be performed by a reference space controller of a reference space (such as reference space 520) and may be stored as executable instructions in a non-transitory memory of reference space controller 520. Additionally or alternatively, method 700 may be performed by an edge device in communication with a reference space, a cloud in communication with a reference space, or any suitable combination thereof.

[0074] The method 700 starts at 702. At 702, the method 700 includes receiving, from a first system, first patient scan data of a first patient, and first phantom scan data of a first phantom scanned together with the first patient. After receiving the first patient scan data and the first phantom scan data, the method 700 proceeds to 704. At 704, the method 700 includes generating a first set of BMD values ​​based on the first patient scan data. The first set of BMD values ​​may include one or more of a first whole-body BMD; one or more BMDs of a region of interest (ROI BMD), including a first lumbar spine BMD, a first femoral neck BMD, and a first total hip BMD; and one or more local BMD values, such as, a first total arm BMD, a first spine BMD, a first trunk BMD, a first pelvis BMD, and a first leg BMD.

[0075] In one example, the first set of BMD values ​​can be obtained by: reconstructing a first scan image using first patient scan data; and quantifying BMD based on a high intensity attenuation value and a low intensity attenuation value of each pixel of the first scan image. As previously discussed, the high intensity value and the low intensity value can be obtained by performing a dual energy (high energy and low energy) scan using a DXA system.

[0076] In another example, a reconstructed image can be generated at an image processing controller of the first system, and thus, the first patient scan data can include first patient image reconstruction data. The first patient scan data including the first patient image reconstruction data can then be transmitted and stored in a non-transitory memory of the reference space controller. Thus, during the generation of the first set of BMD values, the reference space controller can calculate the first set of BMD values ​​using the reconstructed image data.

[0077] Next, method 700 includes receiving second patient scan data of the first patient and second phantom scan data of a second phantom obtained later from a different second system at 706. The different second system may be from a different manufacturer than the first system or from a different version of the same manufacturer as the first system. In addition, the second phantom and the first phantom may be similar in construction and design. Figure 4 After receiving the second patient scan data and the second phantom scan data, method 700 proceeds to 708. At 708, method 700 includes generating a second set of BMD values ​​using the second patient scan data. Similar to the first set of BMD values, the second set of BMD values ​​may include one or more of the following second whole body BMD, one or more local BMDs, and one or more ROI BMDs determined using the second patient scan data.

[0078] As discussed above for the first set of BMD values, the second set of BMD values ​​may be generated by using the second patient scan data to reconstruct a second scan image, and calculating BMD values ​​based on the second scan image. In another example, the second scan image may be reconstructed at an image processor of the second system, and the second reconstructed image data may be transmitted to the reference space together with the second patient scan data. Based on the second reconstructed image data and the second patient scan data received from the second system, the reference space controller may generate the second set of BMD values.

[0079] After generating the first set of BMD values ​​and the second set of BMD values, the method 700 proceeds to 710. At 710, the method 700 may include determining a correlation factor between the first phantom scan data and the second phantom scan data. Determining the correlation factor may include generating the first set of phantom BMD values ​​based on the first phantom scan data obtained with the first system; and generating the second set of phantom BMD values ​​based on the second phantom data obtained with the second system. Since phantoms having similar characteristics are used during scanning with each of the first system and the second system, the first set of phantom BMD values ​​and the second set of phantom BMD values ​​may be compared. For example, a regression analysis may be performed between the first set of phantom BMD values ​​and the second set of phantom BMD values, and the correlation factor may be determined based on the regression analysis. Depending on the complexity of the regression model, the regression analysis may be performed by any one of a univariate regression method and a multivariate regression method based on the distribution of the phantom scan data obtained with each system under comparison.

[0080] Although the exemplary method shows the generation of multiple sets of patient BMD values ​​and correlation factors in sequence, it should be understood that once the first scan data and the second scan data are obtained, the multiple sets of BMD values ​​and correlation factors can be calculated in any order. After the first set of BMD values ​​and the second set of BMD values ​​and correlation factors are obtained based on the first phantom scan data and the second phantom scan data, the method 700 proceeds to 712.

[0081] At 712, method 700 includes adjusting the second set of BMD based on the correlation factor to enable a direct comparison between the first set of BMD values ​​for the first patient (based on the first patient scan data obtained at the first earlier time using the first system) and the second set of adjusted BMD values ​​(based on the second patient scan data and the second phantom scan data obtained at the second later time using the second system and adjusted based on the first phantom scan data obtained using the first system). In some examples, the first set of BMD can be adjusted based on the correlation factor to enable a direct comparison between the first set of adjusted BMD values ​​for the first patient and the second set of adjusted BMD values. That is, adjustments of old measurements can be made to the new machine.

[0082] In this way, cross-calibration can be performed automatically and the BMD value can be automatically adjusted based on the calibration data from the phantom scan data.

[0083] In an exemplary embodiment, multiple patient scan data and multiple corresponding phantom scan data (i.e., phantom scan data obtained in each of multiple patient scans) stored in a reference space can be used for cross-calibration between two DXA systems. For example, a first DXA system can be replaced with a different second DXA system. In order to use the scan data and DXA measurement results from the first system (for example, as a reference for subsequent studies to monitor the patient's bone health over a period of time, monitor disease progression, monitor treatment effects, etc.), a cross-calibration between the first system and the second system is performed. During cross-calibration, calibration data from the multiple phantom scan data and patient scan data obtained with the first system can be retrieved from the reference space and used together with the patient scans and phantom data from the second system for regression analysis. Therefore, since the calibration data is available from the reference space, additional patient scans can be performed without the previous first system. Below in Figure 8 An exemplary method for performing cross calibration is discussed in .

[0084] Go to Figure 8 , which shows a general flow chart illustrating an exemplary method 800 for cross-calibrating between a first prior art system and a second prior art system. According to one embodiment, cross-calibration can be performed by utilizing multiple patient scans and multiple corresponding phantom scans from each system. Figures 1 to 5 Method 800 is described with reference to systems and components of the present invention, but it should be understood that the method can be applied to other systems without departing from the scope of this disclosure. Method 800 can be executed by processing unit 36 ​​and can be stored as executable instructions in a non-transitory memory of processing unit 36. In addition or alternatively, method 800 can be executed by the following: a reference space controller, an edge device connected to the processing unit, a cloud in communication with the processing unit, or any suitable combination thereof.

[0085] The method 800 begins at 802. At 802, the method 800 includes receiving user input. The user input may be received via a user interface of the DXA system (such as, Figure 2 40 in the user interface 40). Next, at 804, method 800 determines whether a cross calibration is required based on the user input. If the answer is yes, method 800 proceeds to perform a cross calibration, as discussed further below. If the answer at 804 is no, method 800 proceeds to adjust system parameters based on the desired operation indicated by the user. Method 800 then returns.

[0086] Returning to 804, if the answer is yes, method 800 proceeds to 807. At 807, method 800 includes receiving cross-calibration parameters. The cross-calibration parameters may include one or more indications of a plurality of systems to be cross-calibrated, including the number of systems to be cross-calibrated and the identities of the systems to be cross-calibrated. The cross-calibration parameters may also include a plurality of subjects whose scan data may be used for cross-calibration and a time period for obtaining scan data for cross-calibration (e.g., within 60 days from the date of cross-calibration).

[0087] After receiving the cross-calibration parameters, method 800 proceeds to performing a cross-calibration. Performing a cross-calibration includes, at 808, receiving, via a reference space, a plurality of prior patient scan data and corresponding prior calibration data obtained using a first prior system. As discussed above, during each scan, in addition to scanning the patient, one or more phantoms (e.g., calibration phantoms) may also be scanned. Thus, with each patient scan data, corresponding phantom scan data is obtained. The calibration data retrieved from the corresponding phantom scan data is embedded with the patient scan data and stored in the reference space. When a cross-calibration is required, such as in response to a system change, the patient scan data embedded with the corresponding calibration data may be retrieved from the reference space. In this way, a plurality of prior scan data embedded with the corresponding calibration data may be retrieved. In one example, the plurality of prior scan data may be based on a desired number of subjects. The desired number of subjects may be based on, for example, a cross-calibration parameter indicated by a user. Alternatively, the desired number of subjects may be automatically determined based on one or more systems and calibration types. Based on the desired number of subjects, a desired number of prior scan data and corresponding calibration data may be retrieved. Furthermore, additional parameters such as scan time may be considered as scan data for cross calibration. For example, the scan data may be selected from scans performed within 60 days prior to replacing the previous system.

[0088] Performing a cross calibration includes obtaining multiple current patient scan data and corresponding current calibration data at 812. Multiple current patient scan data can be obtained by scanning multiple subjects with the current system that is cross-calibrated with the previous system. The multiple subjects scanned with the current system can be multiple subjects whose scan data are retrieved from the previous system (at 808). Therefore, for the same multiple subjects, multiple previous scan data and corresponding calibration data are retrieved from the reference space, and multiple current scan data and corresponding current calibration data are obtained by scanning each of the multiple subjects with the current system. In this way, for the cross calibration between the two systems (the previous system and the current system), two sets of scan data for the multiple subjects are obtained, including multiple previous scan data and corresponding previous calibration data, and multiple current scan data and corresponding current calibration data. These two sets of scan data can be used for cross calibration between the previous system and the current system, as further discussed below.

[0089] By retrieving scan data including calibration data obtained from multiple subjects using a previous system, additional scans during cross-calibration of the two systems can be reduced, thereby reducing radiation exposure to the subject and reducing the time spent on cross-calibration.

[0090] Next, after retrieving the plurality of previous scan data from the previous system, the method 800 proceeds to 810. At 810, the method 800 includes generating a plurality of previous patient BMD values ​​and a plurality of phantom BMD values ​​based on the plurality of previous scan data of the subjects. In addition, the plurality of current patient data and the corresponding current calibration data may be used to generate the current BMD value. Thus, after obtaining the plurality of current scan data (from step 812), the method 800 includes generating a plurality of current patient BMD values ​​and a plurality of current phantom BMD values ​​based on the plurality of current scan data of the subjects.

[0091] After obtaining the plurality of previous patient BMD values ​​and phantom BMD values ​​and the plurality of current patient BMD values ​​and phantom BMD values, the method 800 proceeds to 816. At 816, the method 800 includes performing one or more of a regression analysis and a consistency analysis between: the plurality of previous BMD values ​​calculated by the previous system based on the plurality of previous scan data (from step 810); and the plurality of current BMD values ​​calculated by the current system using the plurality of current scan data (from step 814). Specifically, a first regression analysis may be performed between the plurality of previous patient BMD values ​​and the plurality of current patient BMD values; and a second regression analysis may be performed between the plurality of previous phantom BMD values ​​and the plurality of current phantom BMD values ​​to determine a correlation between the previous DXA system and the current DXA system. The first regression analysis may include a regression analysis between the following items: BMD values ​​measured by the previous system and the current system for the whole body, region of interest (ROI BMD) of the subject, including the subject's lumbar spine BMD, femoral neck BMD, and total hip BMD; and one or more local BMD values, such as the subject's total arm BMD, spine BMD, trunk BMD, pelvis BMD, and leg BMD values. The second regression analysis may include a regression analysis of multiple regions of interest (e.g., each region contains materials with different density ranges) between the previous calibration phantom and the current calibration phantom.

[0092] Additionally, a first consistency analysis between multiple previous patient BMD values ​​and multiple current patient BMD values; and a second consistency analysis between multiple previous phantom BMD values ​​and multiple current BMD values ​​may be performed to assess consistency between measurements from previous DXA systems and the current DXA system.

[0093] In one example, the first regression analysis and the second regression analysis can be performed using a linear regression model. Furthermore, it should be understood that other regression models including Deming regression and multiple regression can be utilized in addition or alternatively and are within the scope of the present disclosure.

[0094] Regarding consistency analysis, in one example, Bland and Altman analysis can be used to perform the first consistency analysis and the second consistency analysis. It should be understood that other consistency and / or correlation analysis methods including Pearson correlation analysis can be used additionally or alternatively, and these methods are within the scope of the present disclosure.

[0095] Continuing to 818, method 800 includes obtaining a set of correction factors for the current system based on the regression analysis and correlation analysis between the current system measurement results and the previous system measurement results. Specifically, obtaining the set of correction factors may include: obtaining a first set of calibration formulas (hereinafter referred to as in vivo calibration formulas) based on a first regression analysis between the previous patient BMD value and the current patient BMD value, each calibration formula corresponding to a regression analysis of BMD values ​​of different anatomical regions of the subject between the two systems; and obtaining a second set of calibration formulas (hereinafter referred to as in vitro calibration formulas) based on a second regression analysis between the previous phantom BMD value and the current phantom BMD value, each calibration formula corresponding to a regression analysis of BMD values ​​of different areas of interest between the previous phantom and the current phantom using the previous system and the current system, respectively.

[0096] Obtaining multiple sets of calibration factors, each calibration factor corresponding to a different part of the scanned subject's body (e.g., whole body, femoral neck, total hip, lumbar spine, other local ROIs, etc.) also includes adjusting the in vivo calibration formula based on the in vitro calibration formula; and obtaining a final set of calibration formulas, each final calibration formula corresponding to a different part of the subject's body. For example, a whole body in vivo calibration formula based on a regression analysis between a set of previous whole body BMD values ​​obtained with a previous system and a set of current whole body BMD values ​​obtained with a current system can be as follows:

[0097] Whole body BMD 先前 =α1*total BMD 当前 ,

[0098] where α1 is a whole-body correction factor determined based on a regression analysis between: whole-body BMD measurements obtained by a previous system; and whole-body BMD measurements obtained by the current system.

[0099] Furthermore, the in vitro calibration formula based on the regression analysis between a set of previous phantom BMD values ​​and a set of current phantom BMD values ​​may be as follows:

[0100] In vitro BMD 先前 =α2*BMD in vitro 当前

[0101] where α2 is a whole-body correction factor determined based on a regression analysis between: phantom BMD measurements obtained by a previous system; and phantom BMD measurements obtained by the current system.

[0102] The whole-body in vivo calibration formula and the corresponding in vitro calibration formula may be compared, and the whole-body in vivo calibration formula may be adjusted based on the in vitro calibration formula to obtain a final calibration formula, which may be as follows:

[0103] Final BMD 先前=β f (α1, α2)*Final BMD 当前 ,

[0104] where B is the final whole-body correction factor determined based on α1 and α2.

[0105] Similarly, final calibration formulas and correction factors for ROI BMD values ​​and local BMD values ​​can be obtained. In this way, a set of final correction factors can be obtained for the current system, which can be used to establish a baseline for patients scanned with the previous system. By utilizing scan data from the previous system and including embedded calibration data, additional scans performed with the previous system during cross-calibration to establish correction formulas and evaluate the consistency of the two systems can be reduced.

[0106] Although the above example shows the calibration formula and correction factor determination process for BMD values, calibration formulas and correction factors can also be obtained for any other measurement results using the DXA system, including BMC; visceral mass measurements, such as fat mass (FM), lean soft tissue mass (LSTM), fat free mass (FFM), and soft tissue mass (STM); protein quantification measurements; measurements using contrast agents, etc.

[0107] Furthermore, in addition to performing regression analysis and obtaining a calibration formula for the current system relative to the previous system, the consistency between the previous system and the current system may be employed by using one or more methods such as Bland and Altman analysis, Pearson correlation, and the like.

[0108] After obtaining a set of calibration factors for the current system, method 800 proceeds to 820. At 820, method 800 includes establishing a baseline in the current system for a plurality of patients scanned with a previous system based on the set of calibration factors. Method 800 then ends.

[0109] Fig. 9 A schematic flow chart illustrating an exemplary method 900 for evaluating DXA system performance according to one embodiment is shown. Figure 1 and Figure 2During operation of a DXA system (such as the one described above), routine calibration may be performed to ensure consistency and accuracy with system measurements, and also to assess whether there are changes in the measurements, such as due to system factors and environmental factors (including temperature and pressure). However, performing routine calibration every day can be time consuming. In some cases, changes in measurements due to system factors and environmental factors may occur during the scan cycle before the next routine calibration is performed, and will not be detected until the next calibration. By scanning a calibration phantom with a patient, in addition to BMD and other bone and mass measurements, the data from the scan can be used to monitor and evaluate system performance for each scan, and as discussed below, indicate when calibration is needed. In this way, the accuracy, consistency, and efficiency of the DXA system can be improved.

[0110] Will refer to Figures 1 to 5 Method 900 is described with reference to systems and components of, but it should be understood that the method can be applied to other systems without departing from the scope of this disclosure. Method 900 can be executed by processing unit 36 ​​or reference space controller and can be stored as executable instructions in non-transitory memory of processing unit 36 ​​or reference space controller or a combination thereof.

[0111] The method 900 begins at 902. At 902, the method 900 includes obtaining, during a scanning cycle, first scan data, second scan data, and so on, up to nth scan data. In one example, a scanning cycle may include a period between a first scan and a last scan performed in a day. In another example, a scanning cycle may be based on a number of scans, and thus, there may be one or more scanning cycles in a day based on the number of scans. In yet another example, a user may indicate a scanning cycle and / or initiate a system evaluation prior to calibration or at any time during system operation. Each scan performed with the DXA system may be performed with a calibration phantom (such as, Figure 4 Thus, each item of scan data may include patient scan data and calibration phantom data.

[0112] Next, the method 900 proceeds to 904. At 904, the method 900 includes obtaining a bone mineral quantification index for each item of phantom scan data obtained during the scanning cycle. In one example, a BMD value for each item of phantom data during a first scanning cycle may be obtained.

[0113] Next, at 906, method 900 includes determining bone mineral quantification consistency between at least two phantom scans during the scanning cycle. Bone mineral quantification consistency can be evaluated by using, for example, correlation and / or consistency analysis. In one example, a correlation and / or consistency analysis can be performed between phantom bone mineral quantification values ​​from two subsequent scans. In another example, a correlation and / or consistency analysis can be performed between bone mineral quantification values ​​obtained from any two scans during the scanning cycle. In yet another example, a reference scan can be obtained, for example, during a routine calibration, and a correlation and / or consistency analysis can be performed between the reference scan and each scan during the scanning cycle.

[0114] Correlation and / or consistency analysis may be performed by any of the Pearson correlation method, Bland-Altman analysis, etc. Additionally or alternatively, other methods such as linear regression may be used to assess the accuracy of bone mineral quantification between scans by the system.

[0115] Next, method 900 proceeds to 908. At 908, method 900 includes evaluating whether the correlation coefficient is greater than a threshold value. For example, based on the consistency analysis, a correlation coefficient indicating the degree of correlation / consistency between the phantom bone mineral quantifications between the two scans may be obtained.

[0116] If the correlation coefficient is not less than the threshold, the correlation of the phantom quantification values ​​is high, indicating that the phantom quantification differences between multiple scans are low. Therefore, if the answer at 908 is no, the method 900 proceeds to 912 to indicate that the DXA scan can continue without further calibration. However, if the correlation coefficient is less than the threshold, the method 900 proceeds to 910 to indicate that the correlation of the phantom values ​​is not high, and therefore a system calibration is required before further scanning.

[0117] A technical effect of the present disclosure is faster and more efficient cross-calibration between DXA systems. In addition, since calibration data is readily available to a DXA system, additional scans of a subject during cross-calibration of a DXA system with another DXA system can be reduced. Thus, radiation exposure to the subject is reduced. Another technical effect of the present disclosure is improved accuracy of subsequent studies of BMD. Yet another technical effect of the present disclosure is increased accuracy and repeatability of BMD quantification. Yet another technical effect of the present disclosure is increased accuracy of images generated by an imaging system.

[0118] An embodiment of a method includes: receiving a first data set from a first DXA system, the first data set including first scan data of a subject and second scan data of a phantom obtained simultaneously with the first DXA system; and a first conversion function based on the first scan data and the second scan data; receiving a second data set from a second DXA system, the second data set including third scan data of the subject and fourth scan data of a second phantom obtained simultaneously with the second DXA system; and a second conversion function based on the third scan data and the fourth scan data; generating a first set of standardized bone mineral quantification values ​​for the subject based on the first conversion function; generating a second set of standardized bone mineral quantification values ​​for the subject based on the second conversion function; determining a correlation coefficient based on the second scan data of the phantom and the fourth scan data of the second phantom; and correcting any one of the first set of standardized bone mineral quantification values ​​and the second set of standardized bone mineral quantification values ​​based on the correlation coefficient. The first embodiment of the method includes wherein determining the correlation coefficient includes: generating a first set of phantom bone mineral quantification values ​​based on the second scan data of the phantom; generating a second set of phantom bone mineral quantification values ​​based on the fourth scan data of the second phantom; and performing a regression analysis between the first set of phantom bone mineral quantification values ​​and the second set of phantom bone mineral quantification values. In a second embodiment of the method, it optionally includes the first embodiment, and further includes wherein the phantom and the second phantom have the same composition. In a third embodiment of the method, it optionally includes one or more of the first and second embodiments, the method further includes wherein the first data set from the first DXA system is obtained in a first time period, and the second data set from the second DXA system is obtained in a second time period, the second time period being later than the first time period. In a fourth embodiment of the method, it optionally includes one or more or each of the first to third embodiments, the method further includes: wherein the first set of standardized bone mineral quantification values ​​includes a first set of bone mineral density values ​​and a first set of bone mineral content values; and wherein the second set of standardized bone mineral quantification values ​​includes a second set of bone mineral density values ​​and a second set of bone mineral content values. In a fifth embodiment of the method, the method optionally includes one or more or each of the first to fourth embodiments, the method further includes generating a first set of standardized tissue mass values ​​for the subject based on the first conversion function; generating a second set of standardized tissue mass values ​​for the subject based on the second conversion function; determining a second correlation coefficient based on the second scan data of the phantom and the fourth scan data of the second phantom; and correcting any one of the first set of standardized tissue mass values ​​and the second set of standardized tissue mass values ​​based on the second correlation coefficient.In a sixth embodiment of the method, the method optionally includes one or more or each of the first to fifth embodiments, the method including generating a first set of standardized protein values ​​for the subject based on a first conversion function; generating a second set of standardized protein values ​​for the subject based on a second conversion function; determining a third correlation coefficient based on second scan data of a phantom and fourth scan data of a second phantom; and correcting any one of the first set of standardized protein values ​​and the second set of standardized protein values ​​based on the third correlation coefficient.

[0119] An embodiment for an x-ray system is provided. The x-ray system includes: a source configured to emit a radiation beam; a detector configured to detect the radiation beam and generate an electrical signal in response to the detected radiation; and a processor communicatively coupled to the detector and provided with instructions in a non-transitory memory, the instructions, when executed, causing the processor to: acquire current scan data of a subject and current scan data of a phantom with the detector; retrieve previous scan data of the subject and previous scan data of a second phantom, each acquired with a different detector in a different system from a reference space communicatively coupled to the system; calculate a correlation factor based on the current scan data of the phantom and the previous scan data of the second phantom; and calculate a current set of bone mineral quantification values ​​for the subject based on the current scan data of the subject, the current scan data of the phantom, and the correlation factor. In a first embodiment of the x-ray system, the phantom and the second phantom are each formed of a plurality of inserts partially embedded in a background material, the plurality of inserts being arranged in a matrix pattern, the matrix pattern comprising a plurality of rows and a plurality of columns; and wherein each of the plurality of rows is made of a different material having one or more of a different density and a different thickness. In a second embodiment of the x-ray system, which optionally includes the first embodiment, current scan data of the phantom is obtained after a current scan of the subject during a single scan sequence. In a third embodiment of the x-ray system, which optionally includes one or both of the first and second embodiments, a correlation factor is determined based on a regression analysis between the current scan data of the phantom and previous scan data of a second phantom. In a fourth embodiment of the x-ray system, which optionally includes one or more or each of the first to third embodiments, the processor is also equipped with instructions in a non-volatile memory, which instructions, when executed, cause the processor to determine a current set of bone mineral quantification values ​​for the phantom; perform a consistency analysis with a reference set of bone mineral quantification values ​​for the phantom; determine a correlation coefficient based on the consistency analysis; and in response to the correlation coefficient being below a threshold, indicate a calibration requirement for the current system; otherwise, indicate to continue operating the x-ray system without calibration. In a fifth embodiment of the x-ray system, which optionally includes one or more or each of the first to fourth embodiments, the processor is also provided with instructions in a non-volatile memory, which, when executed, causes the processor to obtain calibration data from the current scan data of the phantom; embed the calibration data with the current scan data of the subject, and transmit the embedded current scan data of the subject to a reference space controller that communicates with the processor.In a sixth embodiment of the x-ray system, which optionally includes one or more or each of the first to fifth embodiments, obtaining calibration data includes determining one or more conversion coefficients of a conversion function that maps a plurality of pixel values ​​from a phantom image reconstructed from current scan data of the phantom to a plurality of subject image pixel values, the subject image pixel values ​​being obtained from a subject image reconstructed from current scan data of the subject. In a seventh embodiment of the x-ray system, which optionally includes one or more or each of the first to sixth embodiments, the current set of bone mineral quantification values ​​includes a current set of bone mineral density values ​​and a current set of bone mineral content values. In an eighth embodiment of the x-ray system, which optionally includes one or more or each of the first to seventh embodiments, the source is a dual energy x-ray emitter.

[0120] One embodiment relates to a dual-energy x-ray absorptiometry system. The absorptiometry system includes a gantry, the gantry including a radiation source, the radiation source being configured to emit radiation and move along a scanning path; and a radiation detector, the radiation detector being configured to move along the scanning path to receive radiation, the radiation source and the radiation detector being coupled to opposite ends of the gantry; an inspection table disposed between the radiation source and the radiation detector, the inspection table including a scanning area for positioning a subject and a phantom; a processor, the processor being communicatively coupled to the radiation source and the radiation detector and having instructions in a non-volatile memory, the instructions, when executed, causing the processor to: receive a plurality of previous images from a reference space controller communicatively coupled to the processor; The invention provides a method for determining a plurality of subject scan data and a plurality of corresponding previous calibration data, wherein the plurality of previous subject scan data and the plurality of corresponding previous calibration data are obtained by scanning a plurality of subjects with different dual energy x-ray systems; obtaining a plurality of current subject scan data and a plurality of corresponding current calibration data by scanning the plurality of subjects with the dual energy x-ray system; performing a regression analysis between the plurality of previous calibration data and the plurality of current calibration data; obtaining a set of correction factors for the dual energy x-ray system based on the regression analysis; and establishing a baseline in the dual energy x-ray system for the plurality of subjects based on the set of correction factors, the plurality of subjects being scanned with the different dual energy x-ray systems. In a first embodiment of the absorptiometry system, the plurality of current calibration data are obtained by scanning a calibration object with a dual energy x-ray system together with each subject of the plurality of subjects; and wherein the plurality of previous calibration data are obtained by scanning a different calibration object with each subject of the plurality of subjects with a different dual energy x-ray system. In a second embodiment of the x-ray system, which optionally includes the first embodiment, the calibration object and the different calibration object are similar in structure and composition and are each composed of a plurality of inserts partially embedded in a background material, the plurality of inserts being arranged in a matrix pattern, the matrix pattern comprising a plurality of rows and a plurality of columns; and wherein each of the plurality of rows is made of a different material having a different density. In a third embodiment of the x-ray system, which optionally includes one or both of the first and second embodiments, the processor is further provided with instructions in a non-volatile memory, which instructions, when executed, cause the processor to: embed each of the plurality of current subject data with each of the corresponding calibration data; and transmit the embedded current subject data to a reference space controller.

[0121] As used herein, the elements or steps listed in the singular and beginning with the word "one" or "a kind of" should be understood as not excluding a plurality of the elements or steps, unless such exclusion is explicitly stated. In addition, the reference to "an embodiment" of the present invention is not intended to be interpreted as excluding the existence of additional embodiments that also include the cited features. In addition, unless explicitly stated to the contrary, the embodiment of "including", "comprising" or "having" an element or multiple elements with a specific characteristic may include additional such elements without the characteristic. The terms "including" and "in..." are used as the concise language equivalents of the corresponding terms "including" and "wherein". In addition, the terms "first", "second" and "third" etc. are only used as marks, and are not intended to impose numerical requirements or specific positional order on their objects.

[0122] This written description uses examples to disclose the invention, including the best mode, and also to enable a person of ordinary skill in the relevant art to practice the invention, including making and using any devices or systems and performing any included methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to a person of ordinary skill in the art. Such other examples are intended to fall within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insignificant differences from the literal language of the claims.

Claims

1. A dual-energy x-ray absorptiometry method comprising: receiving a first data set from a first DXA system, the first data set comprising first scan data of a subject and second scan data of a phantom simultaneously acquired with the first DXA system; and a first transfer function based on the first scan data and the second scan data; receiving a second data set from a second DXA system, the second data set comprising third scan data of the subject and fourth scan data of a second phantom simultaneously acquired with the second DXA system; and a second transfer function based on the third scan data and the fourth scan data; generating a first set of standardized bone mineral quantification values ​​for the subject based on the first conversion function; generating a second set of standardized bone mineral quantification values ​​for the subject based on the second conversion function; determining a correlation coefficient based on the second scan data of the phantom and the fourth scan data of the second phantom; as well as Based on the correlation coefficient, any one of the first set of standardized bone mineral quantification values ​​and the second set of standardized bone mineral quantification values ​​is corrected.

2. The method according to claim 1, wherein determining the correlation coefficient comprises generating a first set of phantom bone mineral quantification values ​​based on the second scan data of the phantom; generating a second set of phantom bone mineral quantification values ​​based on the fourth scan data of the second phantom; and performing a regression analysis between the first set of phantom bone mineral quantification values ​​and the second set of phantom bone mineral quantification values. 3 . The method of claim 1 , wherein the first data set from the first DXA system is obtained during a first time period and the second data set from the second DXA system is obtained during a second time period, the second time period being later than the first time period.

4. The method of claim 1, wherein the first set of standardized bone mineral quantification values ​​comprises a first set of bone mineral density values ​​and a first set of bone mineral content values; and wherein the second set of standardized bone mineral quantification values ​​comprises a second set of bone mineral density values ​​and a second set of bone mineral content values.

5. The method of claim 1 , further comprising generating a first set of standardized tissue mass values ​​for the subject based on the first transfer function; generating a second set of standardized tissue mass values ​​for the subject based on the second conversion function; determining a second correlation coefficient based on the second scan data of the phantom and the fourth scan data of the second phantom; And based on the second correlation coefficient, correcting any one of the first set of standardized organization quality values ​​and the second set of standardized organization quality values.

6. The method according to claim 1 further includes generating a first set of standardized protein values ​​for the subject based on the first conversion function; generating a second set of standardized protein values ​​for the subject based on the second conversion function; determining a third correlation coefficient based on second scanning data of the phantom and fourth scanning data of the second phantom; and correcting any one of the first set of standardized protein values ​​and the second set of standardized protein values ​​based on the third correlation coefficient.

7. An x-ray system comprising: a source configured to emit a radiation beam; a detector configured to detect the radiation beam and to generate an electrical signal in response to the detected radiation; as well as a processor communicatively coupled to the detector and having instructions in non-transitory memory that, when executed, cause the processor to: Using the detector, collecting current scan data of the subject and current scan data of the phantom; retrieving previously scanned data of the subject and previously scanned data of a second phantom, both acquired using different detectors in different systems from a reference space communicatively coupled to the system; calculating a correlation factor based on current scan data of the phantom and previous scan data of the second phantom; and A current set of bone mineral quantification values ​​for the subject is calculated based on the current scan data of the subject, the current scan data of the phantom, and the correlation factor.

8. The system of claim 7, wherein the phantom and the second phantom are each comprised of a plurality of inserts partially embedded in a background material, the plurality of inserts being arranged in a matrix pattern comprising a plurality of rows and a plurality of columns; and wherein each of the plurality of rows is made of a different material having one or more of a different density and a different thickness.

9. The system of claim 7, wherein the processor is further provided with instructions in a non-volatile memory, which, when executed, cause the processor to determine a current set of bone mineral quantification values ​​for the phantom; perform a consistency analysis using a reference set of bone mineral quantification values ​​for the phantom; determine a correlation coefficient based on the consistency analysis; and in response to the correlation coefficient being lower than a threshold, indicate a calibration requirement for the current system; otherwise, indicate continued operation of the x-ray system without calibration.

10. A system according to claim 7, wherein the processor is also equipped with instructions in the non-volatile memory, which, when executed, causes the processor to obtain calibration data from the current scan data of the phantom; embed the calibration data with the current scan data of the subject, and transmit the embedded current scan data of the subject to a reference space controller that communicates with the processor.

11. A system according to claim 10, wherein obtaining the calibration data includes determining one or more conversion coefficients of a conversion function, which maps a plurality of pixel values ​​from a phantom image reconstructed by current scan data of the phantom to a plurality of subject image pixel values, wherein the subject image pixel values ​​are obtained from a subject image reconstructed by current scan data of the subject.

12. A dual-energy x-ray absorptiometry system comprising: a gantry including a radiation source configured to emit radiation and move along a scanning path; and a radiation detector configured to move along the scanning path to receive the radiation, the radiation source and the radiation detector being coupled to opposite ends of the gantry; an inspection table disposed between the radiation source and the radiation detector, the inspection table comprising a scanning area for positioning a subject and a phantom; a processor communicatively coupled to the radiation source and the radiation detector and having instructions in non-transitory memory that, when executed, cause the processor to: receiving, from a reference space controller communicatively coupled to the processor, a plurality of previous subject scan data and a plurality of corresponding previous calibration data, the plurality of previous subject scan data and the plurality of corresponding previous calibration data being calibration data retrieved from the scan data of the plurality of corresponding first phantoms, the plurality of previous subject scan data and the plurality of corresponding previous calibration data being calibration data obtained by scanning a plurality of subjects and a plurality of corresponding first phantoms with different dual energy x-ray absorptiometry systems; obtaining a plurality of current subject scan data and a plurality of corresponding current calibration data by scanning the plurality of subjects and a plurality of corresponding second phantoms with the dual-energy x-ray absorptiometry system, the plurality of corresponding current calibration data being calibration data retrieved from the scan data of the plurality of corresponding second phantoms; performing a regression analysis between the plurality of previous calibration data and the plurality of current calibration data; Based on the regression analysis, a set of correction factors for the dual-energy x-ray absorptiometry system is obtained; and Based on the set of correction factors, baselines are established in the dual-energy x-ray absorptiometry system for the plurality of subjects, the plurality of subjects being scanned with the different dual-energy x-ray absorptiometry systems.

13. A system according to claim 12, wherein the multiple current calibration data are obtained by scanning a second phantom together with each subject in the multiple subjects with the dual-energy x-ray absorptiometry system; and wherein the multiple previous calibration data are obtained by scanning a first phantom together with each subject in the multiple subjects with the different dual-energy x-ray absorptiometry system.

14. The system of claim 12, wherein the second phantom and the first phantom are similar in structure and composition and are each comprised of a plurality of inserts partially embedded in a background material, the plurality of inserts being arranged in a matrix pattern comprising a plurality of rows and a plurality of columns; and wherein each of the plurality of rows is made of a different material having a different density.

15. The system of claim 12, wherein the processor is further provided with instructions in the non-transitory memory, the instructions when executed causing the processor to: embedding each of the plurality of current subject data with each of the corresponding calibration data; and The embedded current subject data is transmitted to the reference space controller.

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