JP2009254893A - X-ray computerized tomography apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To set scan conditions under consideration of time resolution of actual image data in accordance with the heart rate of an object in using helical scan in combination with electrocardiogram reconstruction. <P>SOLUTION: The X-ray computerized tomography apparatus conducts reconstruction of image data in an electrocardiogram reconstruction method based on data obtained by scanning the object by helical scan. It is provided with a scan expert system 43 to specify a combination of a helical pitch and scan speed in such a way that the time resolution of the image data is the highest based on the heart rate of the object, and construct a scan plan screen including the helical pitch and the scan speed predetermined, and the time resolution of the image data, and a display 38 to display the scan plan screen. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an X-ray computed tomography apparatus that scans a subject by a helical scan and reconstructs image data based on the obtained data under an electrocardiogram synchronous reconstruction method.

  An X-ray computed tomography apparatus provides information about a subject based on the intensity of X-rays that have passed through the subject, and includes many images including diagnosis, treatment, and surgical planning of diseases. It plays an important role in medical practice.

  Improvement of the temporal resolution of the image is one of the important issues particularly in the cardiac examination which is fast movement using the X-ray computed tomography apparatus. The main countermeasure for this problem is to increase the time per rotation of the X-ray tube, that is, to increase the scanning speed.

  There is a half reconstruction method as a method capable of realizing a time resolution higher than the scan speed. As is well known, as shown in FIG. 8, the half reconstruction method represents the specific phase of the heart motion specified by the operator, usually, the heart rate period from the P wave of the electrocardiogram to the next P wave as 100 as a percentage. The image data is reconstructed by supplementing projection data collected while the X-ray tube rotates within a range of 180 ° + α (α is a fan angle) centered on the position and the opposite data. In this half reconstruction method, the time required for the X-ray tube to rotate in the range of 180 ° + α is recognized as the time resolution of the image data.

  There is a segment reconstruction method as a technique for improving the temporal resolution of an image as compared with the half reconstruction method. As shown in FIG. 9, in the segment reconstruction method with 3 segments, projection data in the range of 60 ° + α / 3 is collected from three consecutive or discrete heartbeats, and the range of 180 ° + α is collected. It is characterized by aligning projection data. The ideal time resolution of this segment reconstruction method is given as the time required for the X-ray tube to rotate in the range of 60 ° + α / 3.

  This ideal time resolution is even under certain circumstances where the rotational period of the x-ray tube is ideally offset from the heartbeat period. In most cases where the deviation of the rotation period of the X-ray tube with respect to the heartbeat cycle is not ideal, the time resolution decreases with the deviation of the rotation period of the X-ray tube with respect to the heartbeat period. The worst case occurs when the rotation period of the X-ray tube and the heartbeat period are completely synchronized, and in that case, the number of segments automatically shifts to 1, that is, the half reconstruction method completely. Its time resolution matches that of the half reconstruction method.

  As described above, in the segment reconstruction method, the time resolution varies according to the shift of the rotation period of the X-ray tube with respect to the heartbeat period, so it is difficult to understand intuitively. When a helical scan is used in combination with the segment reconstruction method, it is difficult because of restrictions on the effective slice thickness.

JP-A-9-75338 JP 2000-342577 A

  An object of the present invention is an X-ray computed tomography apparatus that scans a subject by a helical scan and reconstructs image data based on the obtained data under an electrocardiogram synchronous reconstruction method. It is to realize setting of scanning conditions in consideration of time resolution of actual image data corresponding to the number.

  One aspect of the present invention is an X-ray computed tomography apparatus that scans a subject by a helical scan and reconstructs image data based on the obtained data under an electrocardiogram synchronous reconstruction method. Means for specifying a combination of a helical pitch and a scan speed so that the time resolution of the image data is highest based on the heart rate of the image data, and the time resolution of the image data together with the specified helical pitch and scan speed. And a means for constructing a scan plan screen including the above and a means for displaying the scan plan screen.

  According to the present invention, in an X-ray computed tomography apparatus that scans a subject by a helical scan and reconstructs image data based on the obtained data under an electrocardiogram synchronous reconstruction method, Scan conditions can be set in consideration of the time resolution of actual image data corresponding to the number.

It is a figure which shows the structure of the X-ray computed tomography apparatus by embodiment of this invention. It is a top view of the X-ray detector of FIG. It is a figure which shows the example of the time resolution profile currently hold | maintained at the time resolution data memory of FIG. It is a figure which shows the example of a scan plan screen constructed | assembled by the expert system of FIG. FIG. 5 is a diagram showing an example of a simple time resolution window popped up by clicking the “time resolution (simple) button” in FIG. 4. FIG. 6 is a diagram showing an example of a time resolution graph window popped up by clicking the “detail button” in FIG. 5. FIG. 5 is a diagram showing an example of a time resolution window popped up by clicking the “time resolution (detail) button” in FIG. 4. It is explanatory drawing of a half reconstruction method. It is explanatory drawing of the segment reconstruction method.

  Embodiments of an X-ray computed tomography apparatus (X-ray computed tomography apparatus) according to the present invention will be described below with reference to the drawings. In addition, the X-ray computed tomography apparatus has a rotation / rotation (ROTATE / ROTATE) type in which an X-ray tube and a radiation detector are rotated as one body, and a large number of detection elements are arrayed in a ring shape. There are various types such as a fixed / rotation (STATIONARY / ROTATE) type in which only the X-ray tube rotates around the subject, and the present invention can be applied to any type. Here, the rotation / rotation type that currently occupies the mainstream will be described. In addition, to reconstruct one slice of tomographic image data, projection data for about 360 ° around the periphery of the subject is required, and projection data for 180 ° + view angle is also required in the half scan method. . The present invention can be applied to any reconstruction method. Here, the half scan method will be described as an example. In addition, the mechanism for converting incident X-rays into electric charges is based on an indirect conversion type in which X-rays are converted into light by a phosphor such as a scintillator and the light is converted into electric charges by a photoelectric conversion element such as a photodiode, The generation of electron-hole pairs in semiconductors and their transfer to the electrode, that is, the direct conversion type utilizing a photoconductive phenomenon, is the mainstream. Any of these methods may be employed as the X-ray detection element, but here, the former indirect conversion type will be described. In recent years, the so-called multi-tube X-ray computed tomography apparatus in which a plurality of pairs of an X-ray tube and an X-ray detector are mounted on a rotating ring has been commercialized, and the development of peripheral technologies has progressed. Yes. The present invention can be applied to both a conventional single-tube X-ray computed tomography apparatus and a multi-tube X-ray computed tomography apparatus. Here, a single tube type will be described.

  FIG. 1 shows the configuration of an X-ray computed tomography apparatus according to this embodiment. This X-ray computed tomography apparatus has a gantry 1 configured to collect projection data relating to a subject. The gantry 1 includes an X-ray tube 10 and a multi-slice X-ray detector 23. The X-ray tube 10 and the multi-slice X-ray detector 23 are mounted on a ring-shaped rotating frame 12 that is rotationally driven by a gantry driving device 25. The central portion of the rotating frame 12 is opened, and the subject P placed on the top 2a of the bed 2 is inserted into the opening. In order to detect an electrocardiogram of the subject P, an electrocardiograph 22 is attached to the subject P.

  A tube voltage is applied between the cathode and anode of the X-ray tube 10 from the high voltage generator 21, and a filament current is supplied to the filament of the X-ray tube 10 from the high voltage generator 21. X-rays are generated by applying a tube voltage and supplying a filament current.

  As shown in FIG. 2, the multi-slice X-ray detector 23 includes a plurality of X-ray detection elements 26 having a square light receiving surface of 0.5 mm × 0.5 mm, for example. For example, 916 X-ray detection elements 26 are arranged in the channel direction. For example, 40 rows are juxtaposed in the slice direction.

  A data acquisition device 26 generally called a DAS (data acquisition system) converts a signal output from the detector 23 for each channel into a voltage signal, amplifies it, and converts it into a digital signal. This data (raw data) is supplied to the computer unit 3 outside the gantry.

  The preprocessing unit 34 of the computer unit 3 performs correction processing such as sensitivity correction on the data (raw data) output from the data collection device 26 and outputs projection data. This projection data is sent to the storage device 37 of the computer system 3 and stored together with the electrocardiogram data of the electrocardiograph 22.

  The computer system 3 includes a system controller 29, an input device 39, a display 38, a scan controller 30, a reconstruction unit 36, a scan expert system 43, a heart rate detector 41, time resolution data, as well as the preprocessing unit 34 and the storage device 37. The memory 35 and the time resolution generator 41 are included. The reconstruction unit 36 supports both half reconstruction processing and segment reconstruction processing. The heart rate detection unit 41 has a function of identifying, for example, a P wave cycle from the electrocardiogram data and measuring the heart rate of the subject P based on the cycle.

  The time resolution generator 41 has a function of accessing the time resolution data memory 35 in accordance with the request of the scan expert system 43. For example, when a request for provision of time resolution is supplied from the scan expert system 43 together with data relating to scan speed, helical pitch, and heart rate, the time resolution generation unit 41 sets the time corresponding to the scan speed, helical pitch, and heart rate. The resolution is specified and returned to the scan expert system 43.

  The time resolution data memory 35 holds data related to a plurality of time resolution profiles obtained by calculation or simulation in advance based on the scan speed and the helical pitch. FIG. 3 shows examples of four types of time resolution profiles corresponding to segment reconstruction. The time resolution profile represents a change in time resolution with respect to a change in heart rate. The time resolution represents an effective time resolution inherent to image data reconstructed by half reconstruction or segment reconstruction processing. In the case of half reconstruction processing, the scan speed representing the time required for one rotation of the X-ray tube 10 is simply given by a time obtained by multiplying (180 ° + α) / 360 °. On the other hand, in the segment reconstruction process, the time resolution is determined depending on the scan speed and the helical pitch in the scan conditions, and also the heart rate of the subject. The helical pitch is defined as an actual distance that the top plate 2a moves while the X-ray tube 10 makes one rotation, or an index obtained by dividing the distance by the detector width in the slice direction. I will explain it. The detector width is given by the total number of columns of the detector 23 or the length obtained by multiplying the number of columns used by the operator by the distance between the center points of adjacent columns. Data relating to a plurality of time resolution profiles having different combinations of scan speeds and helical pitches are stored in a time resolution data memory 35 such as a ROM. The time resolution data memory 35 reads time resolution profile data, and can read data related to time resolution corresponding to the scan speed, the helical pitch, and the heart rate as inputs, and also corresponds to the heart rate as an input. It is designed to be able to read data on scan speed, helical pitch and time resolution.

  The scan expert system 43 is provided to assist the operator in determining the scan plan, and has a function of determining recommended values of scan conditions such as a reconstruction mode, a helical pitch (HP), a scan speed (SS), Build a scan plan screen that includes the recommended scan condition recommendations, time resolution, and partial time resolution profile.

  FIG. 4 shows an example of a scan plan screen that is initially constructed by the scan expert system 43. The scan plan screen includes patient information, gantry information, and scanogram images, as well as scan conditions and reconstruction conditions planned by the scan expert system 43 according to the imaging region and examination plan designated or selected by the operator. And window conditions are displayed. For example, as scan conditions, a scan mode, a scan start position, a scan end position, “CTDI” (CT Dose Index) representing an exposure dose determined by the US Food and Drug Administration, a tube voltage “kV”, a tube current “mA”, Scan speed, number of slices (number of columns used), helical pitch, reconstruction mode are included. On the scan plan screen, a button labeled “time resolution (simple)” and a button labeled “time resolution (detail)” are arranged.

  When the operator clicks a button labeled “time resolution (simple)”, the scan expert system 43 activates a function for simply presenting the time resolution. In the scan expert system 43, the data regarding the planned helical pitch, the scan speed, and the heart rate of the subject detected immediately before the planning is sent to the time resolution generator 41, and the time resolution corresponding to them is requested. In response to the request, the time resolution generation unit 41 accesses the time resolution data memory 35 according to the received helical pitch, scan speed, and heart rate, and sets the time resolution corresponding to the helical pitch, scan speed, and heart rate. Acquired and returned to the scan expert system 43.

  As shown in FIG. 5, the scan expert system 43 scans the helical pitch, the scan speed, the heart rate, the time resolution obtained from the corresponding time resolution generator 41, and a simple time resolution including the reconstruction mode. A screen (here, called a window for distinguishing from FIG. 4) is constructed. This window is displayed in a pop-up on the scan plan screen in FIG. The window includes a button labeled “acquire heart rate” and a button labeled “details”.

  When the “acquire heart rate” button is clicked, the scan expert system 43 requests the heart rate detector 42 to provide data relating to the heart rate of the subject P. In response to this request, the heart rate detector 42 activates the electrocardiograph 22 and acquires the electrocardiogram data of the subject P over a predetermined period of, for example, 5 seconds. The heart rate detection unit 42 identifies a characteristic wave, for example, a P wave from the electrocardiogram data, calculates a heart rate for each P wave from the time width between the P wave and the P wave, that is, a heartbeat cycle, and scan expert system as data on the heart rate. 43.

  In practice, the heart rate of the subject is not constant but varies. In the scan expert system 43, the average heart rate (or median value) in 5 seconds is detected from the heart rate data. The scan expert system 43 requests the time resolution generator 41 to provide the detected average heart rate together with the data regarding the planned helical pitch and scan speed, and the corresponding time resolution. The time resolution generation unit 41 acquires the time resolution corresponding to the average heart rate, the planned helical pitch, and the scan speed from the time resolution data memory 35 and returns it to the scan expert system 43.

  The scan expert system 43 includes a planned helical pitch, scan speed, average heart rate, time resolution received from the time resolution generator 41 corresponding thereto, a reconstruction mode, and a graph representing a time change of the heart rate, A scan plan screen (here, referred to as a window to be distinguished from FIG. 4) is constructed. This window is displayed in a pop-up on the scan plan screen in FIG.

  When the button labeled “Detail” is clicked, the scan expert system 43 requests the time resolution generator 41 to provide data of a time resolution profile corresponding to the planned helical pitch and scan speed. The time resolution generation unit 41 reads out the data of the time resolution profile corresponding to the planned helical pitch and scan speed from the memory 35 and returns the data to the scan expert system 43. The scan expert system 43 cuts a partial time resolution profile having a predetermined width centered on the average heart rate from the received time resolution profile, and constructs the window of FIG. In the example of FIG. 6, a partial time resolution profile is generated with a width of 5 heartbeats around the average heart rate 67. This window includes a partial temporal resolution profile with a predetermined width centered on the average heart rate.

  As an actual work, the operator confirms the current planned helical pitch, scan speed, and time resolution corresponding to the average heart rate of the subject with numerical values or profiles. If the confirmed time resolution is lower than the desired time resolution, or if the confirmed time resolution is excessively higher than the desired time resolution, the screen returns to the scan condition setting screen of FIG. Change one. After the change, click the “Time resolution (simple)” button, and if necessary, click the “Get heart rate” button and the “Details” button, and updated according to the changed helical pitch and scan speed. The time resolution can be confirmed on the window of FIG. 5 or FIG. By repeating such an operation, it is possible to set a helical pitch and a scan speed that achieve a desired time resolution.

  Returning to FIG. 4, when the “time resolution (details)” button on the scan condition setting screen is clicked, the scan expert system 43 first sends data on the heart rate of the subject P to the heart rate detection unit 42. Request to provide In response to this request, the heart rate detection unit 42 activates the electrocardiograph 22 and sets the subject P over the predetermined period of the longest breath holding time designated by the operator for the subject to be examined, for example, 30 seconds. Obtain ECG data. This longest breath holding time is set as the upper limit of the scanning time of the helical scan. The heart rate detector 42 discretely calculates the heart rate for each P wave from the electrocardiogram data, and supplies it to the scan expert system 43 as data relating to the heart rate. The scan expert system 43 detects the lowest heart rate, the highest heart rate, and the average heart rate (or median value) in 30 seconds from the data relating to the heart rate.

  The scan expert system 43 time-resolves partial time resolution profiles ranging from the lowest detected heart rate to the highest heart rate for all helical pitch and scan speed combinations held in the memory 35. Obtained via the generator 41 or from the memory 35.

  For each acquired time resolution profile, the scan expert system 43 specifies a plurality of time resolutions corresponding to a plurality of heart rates discretely acquired within 30 seconds, and the sum or average of the specified time resolutions. Calculate Then, from among a plurality of time resolution profiles, a predetermined number, in this case, three time resolution profiles having the highest or the shortest total or average of the calculated time resolutions is selected. The scan expert system 43 constructs the window illustrated in FIG. 7 including the helical pitch and scan speed corresponding to the three selected time resolution profiles. In this window, the helical pitches and scan speeds corresponding to the three selected time resolution profiles are displayed in the order of higher time resolution along with the scan time (also referred to as the imaging time) obtained by dividing the imaging range by the helical pitch. To third candidates. The window further includes three parts where the longest breath holding time, average heart rate, minimum heart rate, and maximum heart rate are limited to the range of the minimum heart rate and maximum heart rate cut from the three selected time resolution profiles. A graph of a typical time resolution profile is included. From these three candidates, the operator can select a desired plan after confirming each time resolution. If necessary, by clicking the button labeled “Breath Trial”, the work from heart rate detection to the display in FIG. 7 can be repeated as many times as necessary to practice breath holding of the subject. .

  As described above, according to the present embodiment, it is possible to confirm the time resolution of actual image data according to the heart rate of the subject and set the scan conditions, here the scan speed and the helical pitch, and vice versa. In addition, a desired scan speed and helical pitch can be set from among candidates for scan speed and helical pitch with high temporal resolution.

(Modification)
The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention at the stage of implementation. Furthermore, the above embodiment includes various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, some constituent requirements may be deleted from all the constituent requirements shown in the embodiment.

  INDUSTRIAL APPLICABILITY The present invention can be used in the field of an X-ray computed tomography apparatus that scans a subject by a helical scan and reconstructs image data based on the obtained data under an electrocardiographic reconstruction method. .

DESCRIPTION OF SYMBOLS 1 ... Base, 2 ... Bed, 3 ... Electrocardiograph (ECG), 4 ... Contrast agent injector, 5 ... Base interface, 6 ... Bed interface, 7 ... Injector interface, 8 ... Electrocardiograph interface, 9 ... Data / control Bus 10, input device 11, scan expert system, 12 system control unit 13 reconfiguration processing unit 14 real prep processing unit 15 data storage unit 16 display unit 17 computer system

Claims (6)

In an X-ray computed tomography apparatus that scans a subject by a helical scan and reconstructs image data based on the obtained data under an electrocardiogram synchronous reconstruction method,
Based on the heart rate of the subject, means for specifying a combination of helical pitch and scan speed so that the time resolution of the image data is the highest,
Means for constructing a scan plan screen including a temporal resolution of the image data together with the identified helical pitch and scan speed;
An X-ray computed tomography apparatus comprising: means for displaying the scan plan screen. In an X-ray computed tomography apparatus that scans a subject by a helical scan and reconstructs image data based on the obtained data under an electrocardiogram synchronous reconstruction method,
Means for identifying a plurality of candidates for a combination of a helical pitch and a scanning speed at which the time resolution of the image data is highest based on the heart rate of the subject;
Means for constructing a scan plan screen including a temporal resolution of the image data corresponding to each of the plurality of specified candidates, together with a helical pitch and a scan speed of each of the plurality of specified candidates;
An X-ray computed tomography apparatus comprising: means for displaying the scan plan screen. The combination of the helical pitch and the scanning speed is specified such that the sum or average of a plurality of time resolutions corresponding to a plurality of heart rates discretely acquired from the subject is the highest. Item 2. The X-ray computed tomography apparatus according to Item 1. The plurality of candidates related to the combination of the helical pitch and the scan speed are specified such that the sum or average of the plurality of time resolutions corresponding to the plurality of heart rates discretely acquired from the subject is the highest. The X-ray computed tomography apparatus according to claim 2. 2. The X-ray computed tomography apparatus according to claim 1, wherein the combination of the helical pitch and the scan speed is specified so that the time resolution becomes the highest within the upper limit of the breath holding time of the subject. 3. The X-ray computer according to claim 2, wherein the plurality of candidates related to the combination of the helical pitch and the scanning speed are specified so as to have the highest time resolution within the upper limit of the breath holding time of the subject. Tomography equipment.

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