Speed variable TDS operation in x-ray imaging systems

Abstract

The invention relates to speed variable TDS operation in an X-ray imaging system. TDS (time delay summation) acquisition systems and methods may be used within various imaging devices and systems (10), such as density determination systems with a highly pixelated 2-D detector (26) and a compact x-ray fan beam (34) that scans a patient across a patient axis in a rasterized pattern. An improved system and method for extending the availability of TDS data on each lateral sweep of a scan by collecting data while the scan speed is variable is described. In this approach, the TDS shift strobe signal is no longer a constant periodic function. Instead, the time between the strobes depends on the scanning speed, and a strobe sequence is generated to provide a constant sampling distance between the strobes. Thus, the TDS shift sequence ensures a constant image pixel size (1106, 1108), enabling undistorted images despite the occurrence of variable speeds during signal summing.

Description

Background Art

[0001] The subject matter disclosed herein relates generally to medical diagnostic imaging systems, and more particularly to systems and methods for acquiring images of a patient for use in determining the patient's body composition, bone mineral density (BMD), and combinations thereof.

[0002] A dual energy imaging system, such as a body composition system and / or a bone densitometer, includes an x-ray source that emits a collimated beam of dual energy x-rays to image a patient. An x-ray detector is positioned relative to the x-ray source to receive x-rays that pass through the patient. The x-ray detector generates an electrical signal in response to the received x-rays. The electrical signal is converted into a digital signal that is utilized by the imaging system to generate an image of the patient.

[0003] Measurement of x-ray absorption of an object at two different x-ray energies can reveal information about the composition of the object as broken down into two selected elementary substances. In the medical field, the selected elementary substances are often bone and soft tissue. The ability to distinguish bone from surrounding soft tissue allows x-ray images to obtain quantitative information about body composition and / or bone density in the body for diagnosis of osteoporosis and other bone diseases.

[0004] Current bone densitometers use a frame-based data acquisition method to scan patients. In this mode, a large amount of data is generated using a highly pixelated 2-D detector, typically with low x-ray statistics per pixel, complicating image reconstruction. Therefore, there is a need for an improved system and method for acquiring body composition and / or bone density information.

[0005] TDI (Time Delay Integration) is well known in scanning applications as a method to improve the x-ray statistics of each pixel in a 2-D x-ray detector. The detector pixels integrate the absorbed x-ray charge during short time intervals and store it in a charge storage well on a solid-state ASIC. The collected charge of each pixel is shifted to the storage well of an adjacent pixel in synchronization with the beam motion so that features in the scanned object remain on the x-ray line between a single point in the detection plane and the focal spot of the source. At the end of the pixel row, the charge collection corresponding to that point is complete, the integrated charge is digitized, and ultimately transferred to a computing device for image calculations.

[0006] A similar approach called TDS (Time Delayed Sum) or DTDI (Digital TDI) performs x-ray (or photon) counting instead of charge integration. TDS causes each detector pixel to measure the charge from the absorbed x-rays and instantly differentiate them into different energy windows (e.g., low energy window and high energy window) during short time intervals. The x-ray count for this pixel is incremented for the appropriate energy window in the ASIC memory. The incremental sum of x-rays is shifted to the memory register of the adjacent pixel in synchronization with the beam motion so that features in the scanned object remain on the x-ray line between a single point in the detection plane and the focal spot of the source.

[0007] In both the TDI and TDS methods, this shift synchronization depends on the magnification of the feature, the detector pixel spacing and the scanning speed. In conventional applications, the scanning speed and the shift frequency are constant, and therefore the size of each image pixel in the scanning direction is also constant. In the detector plane, this size is usually equal to the detector pixel width. After readout, the image data consists of continuous columns or "rows" of image pixels with uniform size and count summation time. This is advantageous for simplifying analysis because the beam intensity comparison and image formation between pixels is simple.

[0008] Transverse scanning in DXA utilizes a raster scan across the patient axis and necessarily requires the x-ray source to rapidly accelerate and decelerate to a constant scan speed. Current body composition systems, densitometers, and TDS technologies only acquire data when the x-ray source is traveling at a constant speed. Not acquiring data during the acceleration and / or deceleration phases results in unused dose to the patient, so a common approach is to minimize motion ramp times. This approach means operating at the highest feasible acceleration and is ultimately limited by the limited motion motor torque. In addition, faster acceleration and deceleration times are more likely to introduce undesirable mechanical vibrations in the scanner arm, degrading image quality, or require additional travel distance to ensure vibrations are suppressed before imaging the region of interest.

[0009] Therefore, it is desirable to develop a system and method for capturing data during the acceleration and deceleration period of an x-ray source that does not require extremely high speeds during the acceleration and deceleration phases of the scanning device / x-ray source. In addition, the ability to acquire and use data in a variable speed region will enable less wasted dose to the patient and shorter scan times because the lateral travel distance can be shortened. Summary of the invention

[0010] The present invention recognizes that a TDS (Time Delayed Sum) acquisition method can be used within a body composition and / or density determination system having a highly pixelated 2-D detector and a compact x-ray fan beam that scans a patient across the patient axis in a rasterized pattern. A method is described for extending the availability of TDS data on each lateral sweep of a scan by acquiring data while the scan speed is variable. In this method, the TDS shift strobe signal is no longer a constant periodic function. Instead, the time between strobes depends on the scan speed, and a strobe sequence is generated to provide a constant sampling distance between strobes. Thus, the TDS shift sequence ensures a constant image pixel size, thereby enabling a distortion-free image despite the variable speed that occurs during signal summation.

[0011] In standard constant speed TDS operation, a constant time for signal summation occurs between each shift. This means that no normalization of elapsed time is required between image pixels, so the signal strength between each image pixel can be directly compared. For variable speed TDS, this assumption is no longer valid, and the time elapsed for each row of image pixels during the entire shift sequence must be recorded. The inverse of this time integral is then used to normalize the signals of all image pixels. The TDS shift strobe is generated by a motion controller that coordinates the scanning motion and issues each strobe to ensure that a constant distance is traveled during the sampling time. The motion controller can calculate the distance traveled according to a predetermined motion program or sequence. Alternatively, the controller can estimate the distance traveled by monitoring the motion encoding signal from the motor and / or motion controller that provides the motion of the x-ray source. At the same time, the data acquisition controller that is performing the TDS operation records the time elapsed by the image pixels during the entire shift sequence. Before image generation, the raw signal summation of each pixel must be normalized according to the elapsed time and corrected for any acquisition dead time. At this point, image generation and quantitative signal analysis can be performed as in constant speed TDS operation.

[0012] An additional advantage of variable speed TDS operation in DXA is that a significant portion of the raster scan is spent on acceleration (and deceleration) of the source / detector along the lateral path. For faster scan speeds, particularly those used for whole body DXA scans, the distance required for acceleration is greater due to the limited power and torque of the translation motor. Without incorporating data from the acceleration region, the scan field must be extended, resulting in longer scan times. For whole body scans, the entire width of the body must be scanned, and this sloped buffer necessarily requires a wider patient table, which increases the cost and technical design challenges of the gantry. Ultimately, the additional buffer requirement limits the maximum lateral scan speed and, therefore, the minimum scan time. Reducing scan time is an important goal because it improves patient comfort, improves scan quality by reducing the chance of patient movement, and increases the overall patient throughput of the scanning facility.

[0013] To reduce the ramp buffer width, the current implementation will ramp at the maximum acceleration of the motor, which affects the maximum pulse of the scanner arm. This can cause undesirable jerkiness and vibration, which can reduce image quality and quantitative measurements. Using data in the ramp region enables a smoother acceleration profile or program that takes longer to achieve maximum scan speed than a constant maximum acceleration. The smoother profile will apply a lower pulse to the scanner arm, reducing jerkiness and potentially reducing vibration.

[0014] Another advantage of variable speed TDS operation is that it enables TDS operation under conditions where it is desirable to adjust the scan speed in response to external signal strength. For example, when scanning dense areas, the signal strength may decrease, and therefore the scan speed may need to be dynamically reduced to increase the x-ray statistics per image pixel. Conversely, when the signal strength is high, increasing the scan speed will reduce the patient dose without any relative loss in the statistical quality of the image pixels.

[0015] According to an embodiment of the present technology, an imaging device includes: an X-ray source, which operates to transmit X-rays through an object, wherein the X-ray source is collimated to produce a divergent radiation beam; a detector, which operates to receive the X-ray energy of the X-ray after the X-ray passes through the object; a processing system, which is operably connected to the X-ray source and the detector, and the processing system is programmed to control the movement of the X-ray source and the detector relative to the object, and to perform a time delay summation (TDS) process to generate an image based on the X-ray energy received by the detector; and an electronic storage, which is operably connected to the processing system and stores instructions for operating the processing system in performing an imaging process, wherein the processing system is configured to determine a time delay summation (TDS) shift frequency that varies with the speed of the X-ray source and the detector, and perform a scan of the object based on the speed variable TDS shift frequency.

[0016] According to another embodiment of the present technology, a method for performing time delay summation (TDS) during imaging of an object includes the following steps: providing an imaging device, the imaging device having: an X-ray source, the X-ray source operating to transmit X-rays through the object, wherein the X-ray source is collimated to produce a divergent radiation beam; a detector, the detector operating to receive the X-ray energy of the X-ray after the X-ray passes through the object; a processing system, the processing system operably connected to the X-ray source and the detector, the processing system being programmed to control the movement of the X-ray source and the detector relative to the object, and performing a time delay summation (TDS) process to generate an image based on the X-ray energy received by the detector; and an electronic memory, the electronic memory being operably connected to the processing system and storing instructions for operating the processing system during imaging; determining a time delay summation (TDS) shift frequency that varies with the speed of the X-ray source and the detector; performing a scan of the object based on the speed variable TDS shift frequency; and based on the scan, generating an image of the object based on the X-ray energy signal detected at the detector.

[0017] According to another embodiment of the present technology, a medical imaging system having a multi-energy X-ray source operating to transmit X-rays through a patient is provided. The X-ray source is collimated to produce a divergent radiation beam. The medical imaging system also includes: a detector operating to receive the X-ray energy of the X-ray after the X-ray has passed through the patient; and a processing system. The detector includes detector pixels arranged in at least one row. The processing system is programmed to perform a scan of the patient based on a variable speed time delay sum (TDS) frequency and generate at least two images of the patient's bones corresponding to multiple energy levels of the multi-energy X-ray source. The processing system is further programmed to determine at least one of the patient's body composition, bone mineral density (BMD), and a combination thereof based on the at least two images. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] These and other features, aspects and advantages of the present invention will be better understood when the following detailed description is read with reference to the accompanying drawings, in which like characters refer to like parts throughout the several views, and in which:

[0019] Figure 1 is a schematic diagram illustrating a dual-energy x-ray imaging system for whole body scanning according to an embodiment of the present technology;

[0020] Figure 2 According to the implementation scheme of the present technology Figure 1 Schematic diagram of the detector and associated circuitry used in;

[0021] Figure 3 is a schematic diagram of a prior art time delay sum (TDS) technique;

[0022] Figure 4 is a schematic diagram depicting a TDS imaging sequence of a patient's bone according to an embodiment of the present technology;

[0023] Figure 5 is a schematic diagram depicting the increase in x-ray counts in an image pixel 400 with each shift when illuminated with a constant intensity beam in a prior art TDS imaging sequence, depicting the effect of variable speed on the prior art TDS imaging process, in accordance with an embodiment of the present technology.

[0024] Figure 6 is a schematic diagram depicting the effect of variable source velocity on a prior art TDS imaging process;

[0025] Figure 7 illustrates graphs of various parameters versus time for an example of a nominal flat field image of one sweep of a lateral scan performed with a 32-column detector at a slow source speed using standard prior art TDS operation (ie, constant time shift);

[0026] Figure 8 illustrates graphs of various parameters versus time for an example of a nominal flat field image of one sweep of a lateral scan performed with a 32-column detector at high source speed using standard prior art TDS operation (ie, constant time shift);

[0027] Fig. 9 illustrates graphs of various parameters versus time for an example of a nominal flat field image of one sweep of a lateral scan performed with a 32-column detector at high source speed using improved variable speed TDS operation (i.e., constant sampling distance TDS shift) in accordance with embodiments of the present technology;

[0028] Fig.10 is a flow chart illustrating a method of operating with a variable speed TDS according to an embodiment of the present technology;

[0029] Fig.11 is a schematic diagram depicting the effect of variable source velocity on a variable velocity TDS imaging process in accordance with an embodiment of the present technology.

[0030] Fig.12 is a schematic diagram depicting the operation of a normalized clock within a variable speed TDS imaging process according to an embodiment of the present technology; and

[0031] Fig.13 is a schematic diagram depicting the signal-to-noise ratio (SNR) enhancement in regions with slower motion within a variable speed TDS imaging process and the normalization process of the raw signal per pixel divided by the integration time per pixel in accordance with an embodiment of the present technology. DETAILED DESCRIPTION

[0032] One or more specific embodiments will be described below. In order to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be understood that in the development of any such actual implementation, as in any engineering or design project, many implementation-specific decisions must be made to achieve the developer's specific goals, such as complying with system-related and business-related constraints that may vary from implementation to implementation. In addition, it should be understood that such development efforts may be complex and time-consuming, but are still routine tasks for design, fabrication, and manufacturing for ordinary technicians who benefit from this disclosure.

[0033] When introducing elements of various embodiments of the present invention, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive, and mean that there may be additional elements in addition to the listed elements. Furthermore, any numerical examples in the following discussion are intended to be non-limiting, and thus the additional numerical values, ranges, and percentages are within the scope of the disclosed embodiments.

[0034] Exemplary embodiments of dual energy x-ray systems and methods for collecting, for example, bone and tissue information are described in detail below. Specifically, a detailed description of an exemplary dual energy x-ray system will first be provided, followed by a detailed description of various embodiments of methods and systems for generating patient anatomical images that can be used to diagnose medical conditions such as, for example, osteoporosis. In one embodiment, the system and method can be used to collect and measure bone mineral density, bone tissue information, and other bone-related information from a patient's bone image. In another embodiment, the system and method can be used to determine body composition that distinguishes between lean tissue and adipose tissue in areas that do not contain bone.

[0035] At least one technical effect of various embodiments of the systems and methods described herein is to acquire accurate patient anatomy, such as bone images, using a dual-energy x-ray imaging system. In some embodiments, a single dual-energy x-ray scan, and more specifically a single body scan, is used to acquire image information of multiple different bones, from which bone lengths are determined.

[0036] Figure 1 Schematic diagram of an exemplary dual-energy x-ray device or system, illustrated as a dual x-ray absorptiometry (DEXA or DXA) device or system 10, such as the device or system disclosed in U.S. Patent Application Publication No. US2023 / 0136752, entitled "System and Method For Imaging A Subject" by Wear et al., the entire contents of which are expressly incorporated herein by reference for all purposes, and the device or system is also referred to as a dual-energy bone densitometer system capable of performing bone density determination. The device or system 10 constructed according to various embodiments is configured to measure at least the area of ​​the bone, the length of the bone, the bone mineral content (BMC), the bone mineral density (BMD), and the thickness or density of the tissue. BMD is calculated by dividing the BMC by the area of ​​the bone. During operation, an x-ray beam with a broadband energy level is used to scan a subject, for example, a human subject is scanned to image the bone of the human subject. The images of the bones collected are used to diagnose medical conditions, such as osteoporosis. These images can be generated in part by determining the bone density information collected during the dual-energy x-ray scan.

[0037] The apparatus or system 10 includes a patient table 12 that provides a horizontal surface for supporting a subject, such as a patient 14, in a supine or lateral position along a longitudinal axis 16. The system 10 also includes a support member, such as a C-arm 18. The C-arm 18 has a lower end 20 positioned below the patient table 12 to support an x-ray source 22. The C-arm 18 has an upper end 24 positioned above the patient table 12 to support an x-ray detector 26. Optionally, the x-ray detector may be coupled to the lower end 20, and the x-ray source 22 is coupled to the upper end 24. The x-ray detector 26 may be manufactured, for example, as a multi-element or pixelated cadmium telluride (CdTe) detector that provides energy discrimination. The x-ray source 22 and the x-ray detector 26 may be moved in a raster pattern 28 to track a series of lateral scans 30 of the patient 14, during which dual-energy x-ray data is collected by the x-ray detector 26. The transverse scanning process generates a single image or 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. Scanning the patient using transverse motion is advantageous in minimizing the time between acquisitions 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 for more accurate merging of images.

[0038] The lateral scanning motion is generated by an actuator and / or motor 35, which is operably connected to the C-arm 18 and is under the control of the motion or translation controller 32. During operation, the x-ray source 22 generates a fan beam 34 having a plane parallel to the longitudinal axis 16. Optionally, the fan beam 34 may have a plane perpendicular to the longitudinal axis 16. The raster pattern 28 is adjusted so that there is some overlap (e.g., a slight overlap of 10%) between consecutive scan lines of the fan beam 34. The x-ray source 22, the x-ray detector 26, and the motion or translation controller 32 are in communication with and under the control of a computer 40, which may include both dedicated circuitry and one or more processors capable of executing a stored program (such as stored in an electronic memory 41 operably connected to the computer 40).

[0039] Reference again Figure 1, the computer 40 communicates with a terminal 42, which includes a display 44, a keyboard 46 and a cursor control device such as a mouse 48, thereby allowing an operator to input and output text and images to the operator. In some embodiments, the computer 40 is located away from the workstation 42. Optionally, the computer 40 may form a part of the workstation 42. The computer is adapted to perform one or more processing operations. Upon receiving the data, the acquired bone and tissue information (e.g., image and density information) may be processed and displayed in real time during the scanning session. Additionally or alternatively, the data may be temporarily stored in a memory device on the computer 40 during the scanning session, and then processed and displayed in an offline operation. The information may also be stored in a long-term storage device (e.g., a hard drive or a server) for later access such as during a follow-up scan of the same patient, and may be used to monitor, for example, changes in bone and tissue density over a period of time. The display 44 includes one or more monitors that present patient information including scanned images and bone length images to the operator for diagnosis and analysis. The displayed image may be modified, and the display settings of the display 44 are also manually adjusted using a keyboard 46, a mouse 48, or a touch screen icon on the display itself.

[0040] During operation, the device or 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 22 emits x-rays with a narrowband energy of a few keV and within a diagnostic imaging range of approximately 20keV to 150keV. In the dual-energy mode, the x-ray source 22 emits radiation with two or more energy bands emitted simultaneously or in rapid succession. The x-ray source 22 may also be configured to emit a single broadband energy exceeding a few keV within the diagnostic imaging range. The system 10 may 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 22. The system may also be switched between the dual-energy mode and the single-energy mode by removing or adding a K-edge filter. It should be noted that the x-ray source 22 may emit x-rays of different energies or energy ranges.

[0041] The x-ray source 22 may be configured to output a fan-shaped beam 34 of x-rays, such as Figure 1As shown. In some embodiments, the computer 40 controls the system 10 to operate in a single energy mode or a dual energy mode to determine at least some of the bone or tissue information of the scanned body. The single energy mode generally enables the generation of higher resolution images. Then, the acquired images can be used to measure, for example, bone density or other bone and tissue characteristics or content. As described above, the dual energy x-ray scan can be a linear scan of the entire patient's body, which can 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 can be collected, and the image includes image information related to the bones and tissues in the body. The whole body or whole body scan of the whole body can be performed as a single scan operation, which can be a low dose mode scan. In some embodiments, instead of a whole body or whole body scan, each rectangular area of ​​the body can be performed, which can be a single scan scan. Once the scan of the patient or a part thereof is completed, the dual energy signal provided by the detector 26 is decomposed into images of two basic substances such as bones and soft tissues. The high energy signal and the low energy signal can be combined to provide a single energy mode with an excellent signal-to-noise ratio for imaging purposes.

[0042] Figure 1 The detector 26 shown may be embodied as a linear array of detector elements, a lateral linear array of detector elements or pixels, the detector comprising two laterally separated rows of detector elements, or a stacked array detector, wherein the detector elements are stacked along the propagation direction of the radiation and are selectively sensitive to low and high energy spectra, respectively.

[0043] Figure 2 Depicted in Figure 1 Schematic diagram 100 of a detector and associated circuitry used in a system. Generally speaking, schematic diagram 100 shows a detector that can be used as Figure 11. The detector 102 of the detector 26 of the embodiment of the present invention. The detector 102 includes an array of detector pixels 104 having n rows and m columns. Each of these detector pixels is connected to a charge amplifier 106, one or more comparators 108, and a counter 110. When an x-ray beam 112 strikes a particular detector pixel (e.g., pixel (n, m)) after passing through a subject or patient, the detector pixel (n, m) converts the x-ray energy into a charge that is amplified by the charge amplifier 106. It should be noted that if the x-ray beam strikes the boundary of two detector pixels, the two detector pixels may receive the x-ray energy that will be converted into two charges. The output of the charge amplifier 106 is passed to the comparator 108, which identifies the charge as different energy windows (e.g., a low energy window and a high energy window) and provides a corresponding output to the counter 110. The counter 110 then updates (increments) the corresponding low energy or high energy count based on the output from the comparator 108. The contents of the counter 110 (or the x-ray energy count) are typically stored in a memory register of the corresponding detector pixel. It should be noted that if there is no charge from the x-ray detector pixel, i.e., when no x-ray beam falls on the detector pixel, the counter 110 will not be updated. After a certain duration (e.g., the recording period duration), the x-ray energy counts of the counter 110 are provided to a processor such as a computer 40. Based on the number of counts from the multiple counters, the processor ultimately determines a patient image that may be a bone image or a patient tissue image.

[0044] In this technique, the time delay sum (TDS) technique is used instead of Figure 2 Embodiment shown. TDS technology is the process of adding together multiple exposures of the same object as it passes through the detector. TDS technology allows images to be taken of moving objects. In TDS technology, the increasing sum of x-ray energy counts is shifted to the memory registers of adjacent detector pixels in synchronization with the movement of the x-ray beam, so that the object (e.g., bone) in the scanned subject (e.g., patient) is kept on the x-ray line between a single point in the detector plane and the focal spot of the source. In the TDS method, this shift synchronization depends on the magnification of the object, the detector pixel spacing, and the scanning speed. It is worth noting that objects at heights other than the optimal height for time delay synchronization will be blurred because the signal passing through the object will be distributed across multiple points in the detector plane.

[0045] Figure 3 2 is a schematic diagram 200 illustrating a TDS method according to an embodiment of the present technology. Schematic diagram 200 shows a detector 202 having an array of n rows and m columns of detector pixels. Figure 2 , after recording the duration of the period, the x-ray energy counts of the detector pixel counters are provided to the processor 40, Figure 3 In the embodiment, the x-ray energy count of the detector pixel counter is shifted to the adjacent detector pixel counter after the TDS shift duration. For example, in one embodiment, the TDS shift duration can be 0.56 milliseconds, and the total number of shifts can be 60 for one acquisition, while Figure 2 The recording period duration in may be 6 milliseconds, ie the recording period duration may be longer than the TDS shift duration.The shifting of x-ray energy counts from one counter to the next is done for all detector pixel counters synchronously with the x-ray beam motion.

[0046] For example, if an x-ray scanner is swept across the patient, and if the scan direction 204 of the x-ray beam is from right to left, then the x-ray energy count shift direction 206 is from left to right, ie, opposite to the scan direction. Figure 3 The pulse diagram 210 at the bottom shows a TDS shift strobe or pulse 212 with a TDS shift frequency f. The TDS shift frequency f translates into a TDS shift duration Δt0=1 / f between two pulses. Therefore, each time a TDS shift pulse is received, the counter contents of the corresponding detector pixel are shifted to an adjacent counter. For example, if the TDS shift duration between two pulses 212 is 1 millisecond (f=1 khz), the contents of the counter of detector pixel (i, j) are shifted to the right counter of detector pixel (i, j+1) after every 1 millisecond, where i and j correspond to the number of rows and columns, respectively. In other words, the contents of all detector pixel counters corresponding to row i are shifted to their corresponding right columns. In addition, the contents of the last column N are shifted to the main detector memory buffer 208 and then finally to the processor for generating an image of the object. In general, by shifting the contents of the counters to adjacent counters and then adding them together, multiple x-rays passing through the patient's bone are integrated as they pass through the bone within a given duration. The TDS shift frequency f depends on a number of parameters, such as the velocity v of the x-ray source motion, and will be explained in more detail in subsequent paragraphs.

[0047] Figure 4300 is a schematic diagram depicting a TDS imaging sequence of a patient's bone. The schematic diagram 300 shows three steps 302, 304, 306 of the TDS imaging sequence corresponding to three positions of an X-ray beam 308 at three different time instances. The schematic diagram 300 shows an object, e.g., a bone 310, in a patient 312 lying on a table 314. For all three steps 302, 304, 306, the corresponding positions 316, 318, 320 of a detector 322 are also shown in the schematic diagram 300. The detector 322 includes N detector pixel columns, each pixel having a size a. Due to the synchronization of the speed and TDS shift, although the signal integrated by the pixel is received from an area of ​​width Na, the total detector width d remains a.

[0048] As the x-ray scanner sweeps across the patient, step 302 is a first time instance when the x-ray beam 308 passes through the bone 310. In the illustrated embodiment, the x-ray scanner moves from the left to the right with reference to the bone 310 at a speed v. Thus, at step 302, the rays of the x-ray beam 308 that pass through the bone 310 are at an acute angle relative to the tabletop 314 to start from there. The attenuated x-ray beam 324 (i.e., the x-ray beam 308) then strikes the first detector pixel of the detector 322 after passing through the bone 310, as seen in the detector position 316. Step 304 refers to a second time instance when the rays of the x-ray beam 308 that pass through the bone 310 are at a right angle relative to the tabletop 314. As seen in the detector position 318, the attenuated x-ray beam 324 then strikes the middle detector pixel of the detector 322. Step 306 corresponds to a third time instance when the rays of the x-ray beam 308 that pass through the bone 310 are at an obtuse angle relative to the tabletop 314. In this example, attenuated x-ray beam 324 strikes the last detector pixel as seen in detector position 320 .

[0049] If the TDS method is not used, the charge accumulated at the detector pixels corresponding to the bone imaging at positions 316, 318 and 320 will remain at the same detector pixel, i.e., the first detector pixel, the middle detector pixel and the last detector pixel. This will cause the bone image to be distributed across the entire detector, and therefore the final bone image will be blurred. Alternatively, the frame rate can be increased to reduce blurring, at the expense of increased data volume and re-registration of frames in image reconstruction. However, in the TDS method, the contents of the detector pixels are continuously shifted to adjacent pixel counters at the TDS shift frequency until the bone is fully imaged, and finally the charge corresponding to the bone image at positions 316, 318 and 320 is accumulated in the last detector pixel. The contents of the last detector pixel are then read out by the processor to generate the bone image. In other words, the bone image charge at all detector positions is integrated in one detector pixel, rather than distributed across the entire detector, resulting in a less blurred or sharper image of the bone.

[0050] exist Figure 4 In one exemplary embodiment of the case where TDS is used to image features on the object plane SOD, the TDS shift frequency is selected according to the following formula:

[0051]

[0052] where v is the constant scanning velocity achieved after acceleration at the beginning of the sweep, a is the detector pixel size in the shift direction, and M O is the magnification of the object plane or object (i.e., the bone). O Depends on the distance of the bone from the source. At this optimal TDS frequency, the scanned feature in the object plane remains on the x-ray line between a single point in the detection plane and the focal spot of the source. In image 302, the scanning fan beam will be obscured by the feature in the object plane SOD, and its image is projected on the rightmost pixel in the detector array. In image 304, the detector scan to the left has progressed to a position where the feature is located in the center of the fan beam, and its image is projected onto the center pixel of the detector. Between these two points in time, the contents of all memory registers move to the left at the same speed as the feature image at each time interval Δt, while the detector and beam move to the right. This causes the "shadow" of the feature to be tracked synchronously on the face of the detector. When the fan beam passes completely over the feature, as in image 306, the x-rays corresponding to the feature have been almost completely aggregated into a single image pixel. The memory register of the last exposed pixel in the detector contains the complete sum of the low energy counts and high energy counts of the feature image from all N pixels in the detector, but only for area a / M O One characteristic of TDS is the accumulation of signal within an image pixel due to a shift in count summation.

[0053] Figure 5 Similar to Figure 3 4 shows how the x-ray count in image pixel 400 increases with each shift 402 when illuminated with a constant intensity beam. Image pixel 400 has its final amplitude by the time it reaches the last Nth column 404 of detector 406. Since there is a constant beam intensity and temporal sampling, all image pixels 400 in the middle of a flat field scan will have the same amplitude.

[0054] As previously described, the transverse scan utilizes a raster scan across the patient axis, generating an independent image for each sweep across the patient. In the case of DXA, this image is an image of the bone. Quantification of bone mineral density is performed by basis set decomposition, which is well known in the literature and prior art. Basis set decomposition relies on mapping the intensities of the low energy (LE) and high energy (HE) portions of the x-ray beam to calibration surface fits of LE and HE x-ray counts, which are acquired by basis set materials at a predetermined beam intensity. Therefore, the detector pixel size and sampling time are well known and reliable signal scaling is critical. In a standard implementation of a bone densitometer with a one-dimensional or two-dimensional detector array, data frames are collected only during the constant speed portion of the transverse scan. Each pixel of the detector counts the incident LE and HE x-rays independently and simultaneously during the constant sampling time, which corresponds to a regular and constant pixel area scanned out for each image pixel due to the constant motion speed of the source 22 and the detector 26. These regular data frames are transmitted to the control computer 40 for image reconstruction and analysis to derive bone mineral density or other appropriately calibrated materials. However, in these prior art TDS scanning methods previously described, data is discarded or not collected at all within the acceleration / deceleration ramp region. In order to limit the width of this ignored ramp region, in the prior art, the acceleration is constant and maximized to achieve the desired constant scanning speed of the source 22 and detector 26 as fast as possible. Typically, the maximum acceleration is limited by the torque capability of the motor and / or the mechanical constraints of the structure of the source 22 and detector 26 to minimize vibration, so the scan path or length needs to be extended to accommodate the acceleration and deceleration / ramp regions.

[0055] As a result of these ramping periods or regions 502, at the very beginning of the scanning sweep 504, the sum across all pixels is initially zero (or unknown), and at Figure 6In the case of such initial accumulation in the first column 508 of the sweep illustrated in , the first N image pixels 506 will have only a partial sum of the beam sensing signals before their detector pixel sums are shifted to memory. These first N columns 508 must be discarded because their previous contents are unknown. In conventional lateral scanning, data is collected or saved only when the source 22 and detector 26 are traveling at a constant scan speed / within a constant speed region 510, because outside the constant scan speed region 510, the distance of each sampling is not uniform. For the prior art TDS, once a constant speed is achieved / the constant speed region 510 is reached, additional N columns 508, which may be the same or different in number than the columns 508 in the ramp region 506, must also be discarded due to the inclusion of summation during the earlier ramp cycle 502. At low scan speeds, this unusable region of the scan 504 is acceptably small, but at high speeds with constrained acceleration, this may become a significant portion of the total distance of the scan sweep 504.

[0056] Reference now Figure 7 and Figure 8 , illustrates examples of nominal flat field images of one sweep 702, 802 of a lateral scan using a 32-column detector using standard prior art TDS operation (i.e., constant time shift). In both figures, the acceleration and deceleration of the source 22 and detector 26 are shown to be constant at 1200 mm / s 2 And an example with a full sweep width of 200mm. Figure 7 A constant scan speed of 50 mm / s is shown for the TDS sweep 702, which is a typical and moderate scan speed for anterior / posterior (AP) spine scans. Figure 8 , the constant scan speed achieved for the TDS sweep 802 is 300 mm / s, which is a desired speed for scanning a body composition scan of the entire patient. In both examples, the sweeps 702, 802 have a short TDS buffer build-up 704, 804 after the ramp or acceleration region or zone 706, 806 ends. When acceleration occurs in the opposite direction in the deceleration region or zone 706, symmetrically positioned TDS buffers 704, 804 are required in subsequent sweeps 702, 802. The scanning regions 708, 808 occur where there is a constant speed and after the initial TDS build-up has occurred at a constant speed.

[0057] exist Figure 7, the three graphs above show the acceleration, velocity and distance travel curves when the scanning speed is 50mm / s. The entire 200m sweep 702 requires about 4.1 seconds. The ramp area / area 706 occurs during the acceleration and deceleration phases of the motion and is only 0.042 seconds (about 1mm), which is about 2% of the entire sweep time. In standard TDS operation, the first 32 columns of data after the acceleration zone 706 ends and reaches a constant speed are also excluded from data analysis. This excludes another 0.053 seconds of data, which is an additional 1.25% of the sweep time. This 3.25% exclusion exposure time and a scanning distance of 7mm (which is essentially a wasted dose) are considered acceptable in bone density determination. Figure 7 The bottom graph of shows the image pixel signal per mm in the case of constant time sampling of a flat radiation field. The signal per mm is normalized by the value in the central region / scan region 708 of the graph where the velocity is constant. Note that in the acceleration and deceleration regions / zones 706, there is a significant increase in the signal per mm, in this example as much as 20 to 30 times the x-rays per mm. In addition, on the left side of the graph, the TDS accumulation region 704 at the end of the acceleration region 706 shows some non-constant signal per mm behavior.

[0058] At higher speeds, such as Figure 8 The diagram shows that Figure 7 Similar curve, but where the desired scan speed is 300 mm / s, the ramp region / acceleration zone 806 takes 6 times as long (about 0.25 seconds), and the distance until constant speed is achieved is now about 37.5 mm. With the additional TDS accumulation 804 distance of 2.7 mm after reaching full speed and taking into account the subsequent TDS buffer / accumulation 804 and deceleration region 806, about 80 mm of scan distance will be discarded. Since a body composition scan requires a sweep width of about 600 mm, extending the table width by 80 mm represents an additional widening of about 13%, thereby increasing the cost and requirements for the gantry supporting the patient. Figure 8 The bottom graph of shows the image pixel signal per mm in the case of constant time sampling of a flat radiation field. The signal per mm is normalized by the values ​​in the central region / scan region 808 of the graph, where the speed is constant. At higher terminal speeds relative to the acceleration rate, an extended region of non-constant signal per mm is evident, which is why quantitative DXA with conventional TDS operation typically ignores data from this region.

[0059] exist Figure 1 and Figures 9 to 13An alternative and improved method of prior art TDS sampling provided by the variable speed TDS system and method of the present disclosure is shown in FIG. The motion controller 32 (including the microprocessor 33) uses a motion program or curve 1002, such as stored in the memory 41 of the computer 40, to generate a signal to the motor 35 to drive the lateral movement of the detector 26 in a prescribed manner. With knowledge of the distance that the source 22 and the detector 26 always travel during the execution of the sweep 902, such as via a suitable sensor 1020 disposed on the C-arm 18 and / or the motor 35, the microprocessor 33 simultaneously generates each TDS shift strobe 1004, 1104 to the detector 26, so that the distance traveled by the detector 26 between the shift strobes 1004, 1104 is always constant, i.e., a constant sampling distance TDS shift frequency, even during the variable speed period occurring during the acceleration and deceleration zones 906 at each end of the sweep 902, except for the TDS buffer or accumulation zone 904 at each end of the sweep 902, greatly increasing the effective length of the scanning area 908. Thus, the image pixel 1110 produced after N strobes 1004, 1104 consists of the sum of x-rays from N constant-area sub-pixels 1108 and maintains the advantageous property of TDS, namely that its signal integration occurs along a substantially straight line between the source 22 and the point of interest 310 in the imaged object 312.

[0060] In the constant speed region during the sweep 902, i.e., in the scanning region 908, the strobes 1004, 1104 are emitted at regular time intervals as in a standard TDS acquisition. In the acceleration or deceleration region (ramp region 906), the strobes 1004, 1104 may no longer be emitted at regular time intervals due to the different times required to move the detector 26 a constant distance by acceleration or deceleration of the motor 35 in the ramp zone 906 defined by the program 1002 (again, constant sampling distance shift frequency). This means that the recorded signal of each image pixel 1106, 1108 will have a different signal integration duration. Therefore, each image pixel 1106, 1108 requires time normalization 1018 so that the signal intensity between pixels can be quantitatively compared. As Figures 10 to 12As best shown in , such normalized time measurement that may be performed in the detector 26 is performed by a free running clock signal / normalized clock 1010, 1202 having a frequency much higher than the highest expected frequency of the TDS shift strobe 1004, 1104. Cycles 1012 of the normalized clock 1010, 1202 are counted in a register and similarly shifted at 1206 as the TDS signal sum is shifted between sub-pixels 1108. After the TDS strobe 1004, 1104 is issued across the entire sweep 902, the number or count 1214 of clock cycles 1012, 1212 that occurred during the entire shift sequence / sweep 902 is recorded with each image pixel data line 1106. This clock cycle count 1214 serves as an estimate of the absolute time of the signal integration 1016, 1116 of the pixel data line 1106. The raw signal 1014 for each sub-pixel 1108 along line 1106 is then corrected by dividing by its corresponding time estimate 1216. This normalization 1018 using cycle counts 1214 may occur in the detector 26 or upstream of the data acquisition control computer 40. Once time normalized, each image pixel 1316 now has a constant width, and their count rate can be quantitatively compared to all other image pixels 1316, regardless of their location within the entire sweep 908.

[0061] During TDS operation, when register contents are shifted to adjacent pixel registers, there are insensitive periods during which no x-ray counts can be made. The duration of this insensitivity (or dead time) must be accounted for in time normalization 1018. If the time measurement is performed independently of the x-ray counts, for example by a clock and counter external to the detector 26, then dead time correction can be accomplished by subtracting a known dead time for each shift or strobe 1004, 1104, which is typically a constant time. Preferably, the clock cycles 1112 are counted in the same manner as the x-rays / strobes 1004, 1104, and therefore experience the same dead time. In this case, no explicit dead time correction is required for the time measurement, and the signal normalization is simply the ratio of the measured counts 1114 and the measured clock strobes 1004, 1104. This is an important simplification because it reduces the need for additional electronics and reduces the risk of the time counting pixels being out of sync with the image pixels.

[0062] Reference now Fig. 9 , for a vehicle with constant acceleration / deceleration and with Figure 8 The high scanning speed sweep shown shows a similar Figure 7 and Figure 8920 and graphs of signal / mm, time / pixel, and time-normalized count rate, but are affected by the variable sampling TDS and constant distance sampling with time normalization employed by the detector 26 and computer 40 when performing the scanning sweep 902, as previously described with respect to Figure 1 and Figures 9 to 13 The top graph 920 shows the raw signal per image pixel versus time before time normalization during a single sweep 902. Fig.11 The constant sampling distance shift frequency employed in the illustrated exemplary embodiment of the variable sampling TDS process in is equivalent to the image pixel size, although the method can be employed with alternative distance values ​​for the sampling employed, assuming an arbitrary but constant x-ray throughput. The middle graph 930 shows the time elapsed per image pixel, which has the same curve as the per pixel signal distribution in graph 920. The bottom graph 940 shows the final image pixel contrast time after time normalization using the count 1114 of the signal from the normalization clock 1010 over the time of the sweep 902, which is exactly the upper distribution in graph 920 divided by the middle distribution in graph 930. The original signal distribution in graph 920 has a 750% change from the edge of the sweep 902 (i.e., the point of the sweep 902 where TDS accumulation has been achieved) to the center of the sweep 902 (where the speed is constant). The time-normalized signal profile in graph 940 is reduced to 0.3% in this example and only in the TDS accumulation region 904, greatly enhancing the length of the sweep 902 over which image data can be collected and used in the imaging process. In addition, the longer counting time of the pixels in the accelerated region results in higher x-ray counts per pixel, which means higher statistical accuracy in the count rate measurement because the variance of the signal is proportional to sqrt(N), where N is the number of x-rays per image pixel. This reduced variance is equivalent to illustrating that the signal-to-noise ratio (SNR) is enhanced in these slower motion regions 1320.

[0063] An alternative implementation of the variable time sampling TDS system and method described herein is used to dynamically modulate the scan speed during a patient scan. The system and method of the variable speed TDS operation disclosed herein enables TDS operation under conditions where it is desired to adjust the scan speed in response to an external signal strength. For example, when scanning denser areas of the object 310, 312, the signal strength will decrease, so it is necessary to dynamically reduce the scan speed to increase the x-ray statistics of each image pixel. Conversely, when the signal strength is high, increasing the scan speed will reduce the patient dose without causing relative damage to the statistical quality of the image pixels. In an exemplary embodiment, when the x-ray rate (i.e., external signal strength) transmitted during scanning through thicker or high attenuation materials in the object 310, 312 decreases, as sensed by the detector 26 and / or the computer 40, the computer 40 operates the motion controller 32 and the motor 35 to slow down the movement of the C-arm 18 (i.e., the source 22 and the detector 26) to increase the throughput of each imaging pixel. When TDS is used for scanned data acquisition, a constant signal-to-noise ratio can be achieved while maintaining a constant size of imaging pixels by employing the variable time sampling TDS system described previously.

[0064] In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.

[0065] Reference is made to the technology presented and claimed herein and applied to physical and specific examples of a practical nature that clearly improves upon the present state of the art and, therefore, is not abstract, intangible, or purely theoretical. In addition, if any claim appended to the end of this specification contains one or more elements designated as "means for [performing] the function of ..." or "steps for [performing] the function of ...," it is intended that such elements be interpreted under 35 U.S.C. § 112(f). However, for any claim containing elements designated in any other manner, it is not intended that such elements be interpreted under 35 U.S.C. § 112(f).

[0066] This written description uses examples to disclose the subject matter, including the best mode, and also to enable those skilled in the art to practice the subject matter, including making and using any devices or systems and performing any included methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be 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 method for performing time delay summation (TDS) during imaging of an object (14), the method comprising the following steps: An imaging device (10) is provided, the imaging device comprising: an x-ray source (22) operative to transmit x-rays (34) through the subject (14), wherein the x-ray source (22) is collimated to produce a divergent radiation beam (34); a detector (26) operative to receive X-ray energy of the X-ray (34) after the X-ray (34) passes through the object (14); a processing system (33) operably connected to the X-ray source (22) and the detector (26), the processing system (33) being programmed to control movement of the X-ray source (22) and the detector (26) relative to the object (14) and to perform a time delay sum (TDS) process to generate an image based on the X-ray energy received by the detector; and electronic memory (41) operably connected to the processing system (33) and storing instructions for operating the processing system (33) in performing an imaging process; determining a time delay sum (TDS) shift frequency that varies with the speed of the X-ray source (22) and the detector (26); performing a scan of the object (14) based on the variable speed TDS shift frequency; and Based on the scanning, an image (1106, 1108) of the object (14) is generated based on the X-ray energy signals detected at the detector (26).

2. The method of claim 1, wherein the step of determining the variable speed TDS shift frequency comprises determining a constant sampling distance TDS shift frequency.

3. The method of claim 1, wherein the imaging device (10) further comprises a normalized clock (1010, 1202) for generating a clock signal (1012, 1212) recorded in conjunction with the variable speed TDS shift frequency.

4. The method of claim 1 , wherein the electronic memory (41) includes instructions for sweeping (902) the X-ray source (22) and the detector (26) over the object (14) when performing the scan, the sweep including an acceleration zone (906), a constant velocity zone (908), and a deceleration zone (906), and wherein the step of performing the scan of the object (14) includes applying the speed variable TDS shift frequency in each of the acceleration zone (906), the constant velocity zone (908), and the deceleration zone (906).

5. The method of claim 4, wherein the step of determining the variable speed TDS shift frequency comprises determining a constant sampling distance TDS shift frequency.

6. The method of claim 5, wherein the imaging device (10) further comprises a normalization clock (1010, 1202) for generating a clock signal (1012, 1212) recorded in conjunction with the constant sampling distance TDS shift frequency, and wherein the method further comprises the step of time normalizing the detected X-ray energy signal using the recorded clock signal (1010, 1212).

7. The method of claim 4, wherein, based on the scan, the step of generating an image (1106, 1108) of the object (14) based on the detected X-ray energy signal comprises generating the image (1106, 1108) based on the X-ray energy signal detected during each of the acceleration zone (906), the constant speed zone (908), and the deceleration zone (906).

8. The method of claim 1 , wherein the electronic memory includes parameters for a scan speed related to an intensity of the detected X-ray energy signal, and wherein the step of performing the scan of the object includes adjusting the speed of the scan and the speed variable TDS shift frequency.

9. The method of claim 8, wherein the step of determining the variable speed TDS shift frequency comprises determining a constant sampling distance TDS shift frequency.

10. The method of claim 9, wherein the imaging device (10) further comprises a normalization clock (1010, 1202) for generating a clock signal (1012, 1212) recorded in conjunction with the constant sampling distance TDS shift frequency, and wherein the method further comprises the step of time normalizing the detected X-ray energy signal using the recorded clock signal (1012, 1212).

11. The method of claim 1, wherein the step of performing a scan of the object based on the speed variable TDS shift frequency comprises performing a dual X-ray absorptiometry scan (14) of the object.

12. The method of claim 1, wherein the step of performing a scan of the subject based on the variable speed TDS shift frequency comprises performing a bone mineral density scan of the subject (14), a body composition scan of the subject (14), or a combination thereof.

13. An imaging device (10), comprising: an X-ray source (22) operative to transmit X-rays (34) through the subject (14), wherein the X-ray source (22) is collimated to produce a divergent beam of radiation; a detector (26) operative to receive X-ray energy of the X-ray (34) after the X-ray (34) passes through the object (14); a processing system (33) operably connected to the X-ray source (22) and the detector (26), the processing system (33) being programmed to control movement of the X-ray source (22) and the detector (26) relative to the object (14) and to perform a time delay sum (TDS) process to generate an image (1106, 1108) based on the X-ray energy received by the detector (26); and electronic memory (41) operably connected to the processing system (33) and storing instructions for operating the processing system (33) in performing an imaging process; The processing system (33) is configured to determine a time delay sum (TDS) shift frequency that varies with the speed of the X-ray source (22) and the detector (26), and perform a scan of the object (14) based on the speed variable TDS shift frequency.

14. The imaging device of claim 13, wherein the electronic memory (14) includes instructions for sweeping (902) the X-ray source (22) and the detector (26) over the object (14) when performing the scan, the sweep (902) including an acceleration zone (906), a constant velocity zone (908), and a deceleration zone (906), and wherein the processing system (33) is configured to adjust the speed variable TDS shift frequency in each of the acceleration zone (906), the constant velocity zone (908), and the deceleration zone (906).

15. A medical imaging system (10), comprising: a multi-energy X-ray source (22) operative to transmit X-rays (34) through a patient (14), the X-ray source (22) being collimated to produce a divergent beam of radiation; a detector (26) comprising a plurality of pixels (1106, 1108) arranged in at least one row and operative to receive X-ray energy of the X-ray (34) after the X-ray (34) passes through the patient (14); and A processing system (33) is programmed to perform a scan of the patient (14) based on a variable speed time delay sum (TDS) frequency to generate at least two images (1106, 1108) of the patient's bones (310, 312) corresponding to multiple energy levels of the multi-energy X-ray source, and determine at least one of the patient's body composition, bone mineral density (BMD), and a combination thereof based on the at least two images (310, 312).

Images