JP2007216043A - X-ray ct apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray CT apparatus by which a plurality of cross section images at a phase of periodic motion of a scan object are effectively created. <P>SOLUTION: Data are collected from helical scan data. A phase of periodic motion of a scan object corresponding to a time point collecting the data and a position on a linear motion axis are acquired while corresponding each other. Images on a plurality of positions corresponding to a same phase on the axis are respectively created. Images positioned between a plurality of positions are created by arithmetic interpolation using the created images. Thereby, a plurality of cross section images at a phase of periodical motion of the scan object can be created only by several rotations of scanning. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image generation method, an image display method, and an X-ray CT (Computed Tomography) apparatus. More specifically, the present invention relates to one phase of periodic motion from data acquired by performing a helical scan on a periodically moving scan target. Image generation method for generating images in image, image display method for generating images in multiple phases of periodic motion from data collected by helical scanning of periodically moving scanning object, and displaying cine in order of phase, and these methods are suitable The present invention relates to an X-ray CT apparatus that can be implemented.

  Japanese Examined Patent Publication No. 2-6530 proposes an X-ray CT apparatus capable of collecting only data in one phase interval of the periodic motion of the heart. FIG. 24 shows a time chart of an operation of collecting only data in the diastole of the heart using the X-ray CT apparatus. (A) shows an electrocardiogram waveform, and the period h and phase of the heartbeat are detected from the R wave of the electrocardiogram waveform. (B) shows a delay time Td for determining the timing to start measurement and a measurement time Te for measuring data, and data measurement is performed at the beginning of the cardiac diastole by the delay time Td from the R wave of the electrocardiogram waveform. The data is measured only in the diastole of the heart by the measurement time Te. (C) shows the measurement angle θ. When all the views necessary for image generation are 0 ° to 360 °, the view data of 270 ° to 360 ° is measured at the first measurement, and the second measurement is performed. Measure the data of the view from 180 ° to 270 °, measure the data of the view of 90 ° to 180 ° at the third measurement, and measure the data of the view of 0 ° to 90 ° at the fourth measurement.

  (D) shows rotation scanning start timing times τ1 to τ4 for rotating the X-ray tube and the detector around the subject, and rotation times and stop times. 270 ° to 360 in the rotation time of the first rotation. Rotational scanning start timing time τ1 is determined so that the time corresponding to ゜ coincides with the measurement time of the first measurement, and the time corresponding to 180 ° to 270 ° in the rotation time of the second rotation and the second measurement time. The rotational scanning start timing time τ2 is determined so that the measurement time matches, and the rotational scanning is performed so that the time corresponding to 90 ° to 180 ° in the rotation time of the third rotation matches the measurement time of the third measurement. The start timing time τ3 is determined, and the rotational scanning start timing time τ4 is determined so that the time corresponding to 0 ° to 90 ° in the rotation time of the fourth rotation matches the measurement time of the fourth measurement. The rotation of the X-ray tube and the detector is stopped from the end of the first rotation to the start of the second rotation, and the rotation of the X-ray tube and the detector is stopped from the end of the second rotation to the start of the third rotation. The rotation of the X-ray tube and the detector is stopped from the end of the third rotation to the start of the fourth rotation.

  In the above-described conventional X-ray CT apparatus, scanning of a plurality of rotations is repeated in order to generate an image of one cross section of a scanning target (here, a heart). However, this is not efficient for generating a plurality of cross-sectional images, and is not practical. Accordingly, a first object of the present invention is to provide an image generation method capable of efficiently generating images of a plurality of cross sections in one phase of a periodic motion to be scanned. The second object of the present invention is to provide an image generation method capable of efficiently generating a projection image such as a 3D (dimension) image or an IP (intensity projection) image in one phase of the periodic motion of the scanning target. It is to provide. A third object of the present invention is to provide an image display method capable of displaying a periodic motion of a scanning target in a moving image.

  In a first aspect, the present invention is configured to linearly move an X-ray tube or detector and a scanning target along one axis relatively and rotate at least one of the X-ray tube or the detector around the scanning target. In an image generation method for collecting data (helical scan) and generating an image from the data, the position on the axis and the phase of the periodic motion of the scanning target corresponding to the time when the data was collected at that position are associated with each other And generating images at a plurality of positions corresponding to the same phase on the axis, and generating an image positioned between the plurality of positions by an interpolation operation using the generated images. An image generation method is provided. The image generated from the data collected by the helical scan has the strongest relationship with the phase of the periodic motion of the scanning target corresponding to the time when the data is collected at the position of the image. The reason is that all view data necessary to generate the image is calculated by interpolation using data collected at a position near the position, and the interpolation is collected at the position of the image. This is because the most weighted data is assigned. In the image generation method according to the first aspect, since the scanning target is helically scanned, images of cross-sections of the scanning target at a plurality of positions on the axis of linear movement can be obtained by performing a plurality of scans only once. Can be generated. However, since these images have the strongest relationship with the phase corresponding to the position of each image as described above, the phases are scattered. Therefore, if images are generated at a plurality of positions corresponding to the same phase, and an image positioned between the plurality of positions is generated by an interpolation operation using the generated images, a plurality of positions corresponding to the same phase is generated. It is possible to generate an image of a cross-section to be scanned at. That is, it is possible to efficiently generate images of a plurality of cross sections in one phase of the periodic motion to be scanned.

  In a second aspect, the present invention configures volume data from images at a plurality of positions corresponding to the same phase generated by the image generation method configured as described above, and passes through the volume data to each pixel on the projection plane. There is provided an image generation method characterized by generating a projection image by executing, for all pixels on a projection surface, obtaining a projection value of the pixel from the value of the volume data present on each projection line. As described above, in the image generation method according to the first aspect, it is possible to efficiently generate images of a plurality of cross sections in one phase of the periodic motion to be scanned. Therefore, if volume data is constructed from these cross-sectional images and a projection image is generated from the volume data, a projection image such as a 3D image or IP image in one phase of the periodic motion to be scanned can be efficiently generated. I can do it.

  In a third aspect, the present invention provides an image display characterized by generating projected images with different phases of the periodic motion of the scanning target by the image generating method configured as described above, and displaying the projected images in cine order in phase. Provide a method. As described above, in the image generation method according to the second aspect, it is possible to efficiently generate a projection image such as a 3D image or an IP image in one phase of the periodic motion to be scanned. Therefore, by generating projection images with different phases and displaying the projection images in cine order in the order of phase, it is possible to display the periodic motion of the scanning target in a moving image.

  In a fourth aspect, the present invention is configured to linearly move the X-ray tube or detector and the scanning target along one axis relatively and rotate at least one of the X-ray tube or the detector around the scanning target. Data collecting means for collecting data while performing data calculation means for calculating data of all views necessary for generating an image at a position on the axis from data in the vicinity of the position by interpolation calculation; In an X-ray CT apparatus provided with an image generation means for generating an image from view data, a movement detection means for detecting the period and phase of a periodic movement of a scanning target, a position on the axis, and data collected at that position Corresponding to the same phase on the axis by the position / phase associating means that obtains the phase of the periodic motion of the scanning object corresponding to the time point obtained in association with the data calculating means and the image generating means X-ray comprising: interpolated image generating means for generating images at a plurality of positions and generating images located between the plurality of positions by interpolation using the generated images. A CT apparatus is provided. According to the X-ray CT apparatus of the fourth aspect, the image generation method of the first aspect can be suitably implemented.

  In a fifth aspect, the present invention is configured to linearly move an X-ray tube or detector and a scanning target along one axis relatively and rotate at least one of the X-ray tube or the detector around the scanning target. Data collecting means for collecting data while performing data calculation means for calculating data of all views necessary for generating an image at a position on the axis from data in the vicinity of the position by interpolation calculation; In an X-ray CT apparatus provided with an image generation means for generating an image from view data, a movement detection means for detecting the period and phase of a periodic movement of a scanning target, a position on the axis, and data collected at that position A position / phase association unit that obtains the phase of the periodic motion of the scanning target corresponding to the time point, and images at a plurality of positions corresponding to the same phase on the axis by the data calculation unit Interpolation that calculates all view data necessary to generate each image, and then calculates all view data necessary to generate an image located between the plurality of positions by interpolation using the calculated data. An X-ray CT apparatus comprising an image data calculation unit is provided. The data of all views necessary to generate an image at one position on the axis of the linear movement has the strongest relationship with the phase of the periodic motion of the scanning target corresponding to the time when the data is collected at the position. . The reason is that the data of all the views is calculated by an interpolation calculation using data collected in the vicinity of the position, and the interpolation calculation gives the greatest weight to the data collected at the position. It is. In the X-ray CT apparatus according to the fifth aspect, since the scanning target is helically scanned, images of cross sections of the scanning target at a plurality of positions on the axis of linear movement can be obtained by performing a plurality of rotation scans only once. The data of all views for generating can be calculated. However, since the data of all the views has the strongest relationship with the phase corresponding to each position as described above, the phases are scattered. Therefore, all views for calculating data of all views at a plurality of positions corresponding to the same phase and generating an image positioned between the plurality of positions by interpolation using the calculated data of all views. If the above data is calculated, it is possible to generate a cross-sectional image to be scanned at a plurality of positions corresponding to the same phase from the data. That is, it is possible to efficiently generate images of a plurality of cross sections in one phase of the periodic motion to be scanned.

  In a sixth aspect, the present invention is configured to linearly move an X-ray tube or detector and a scanning target along one axis relatively and rotate at least one of the X-ray tube or the detector around the scanning target. Data collecting means for collecting data while performing data calculation means for calculating data of all views necessary for generating an image at a position on the axis from data in the vicinity of the position by interpolation calculation; In an X-ray CT apparatus provided with an image generation means for generating an image from view data, a movement detection means for detecting the period and phase of a periodic movement of a scanning target, a position on the axis, and data collected at that position A position / phase associating unit that obtains the phase of the periodic motion of the scanning target corresponding to the time point, and the data calculating unit and the image generating unit at a plurality of positions on the axis. A time-axis-enhanced image generating means for generating a time-axis-enhanced image at the plurality of positions by time-axis emphasis calculation using the generated image and a predetermined profile function after generating the images, and the time-axis emphasis An in-phase image selection means for selecting images at a plurality of positions corresponding to the same phase from the image, and an image positioned between the plurality of positions by interpolation using the selected time axis emphasized image An X-ray CT apparatus comprising an interpolation image generating means is provided. The X-ray CT apparatus according to the sixth aspect is basically the same as the X-ray CT apparatus according to the fourth aspect, but generates a plurality of images by the data calculation means and the image generation means, The difference is that the time axis emphasis calculation is performed using a plurality of generated images and a predetermined profile function, and images at a plurality of positions corresponding to the same phase are respectively selected from the generated time axis emphasizing images. Yes. As described in detail in the “Embodiments of the Invention”, when a plurality of images and a predetermined profile function are used, a phase having a narrower width than a phase having a strong relationship with the plurality of images has a strong relationship. It is possible to generate a possessed image, that is, a time axis enhanced image. Then, images at a plurality of positions corresponding to the same phase are respectively selected from the time axis emphasized images, and an image positioned between the plurality of positions is generated by an interpolation operation using the selected time axis emphasized images. For example, it is possible to generate cross-sectional images to be scanned at a plurality of positions corresponding to the same phase, and to improve the phase width. That is, it is possible to efficiently and accurately generate a plurality of cross-sectional images in one phase of the periodic motion to be scanned.

  In a seventh aspect, the present invention is configured to linearly move an X-ray tube or detector and a scanning target along one axis relatively and rotate at least one of the X-ray tube or the detector around the scanning target. Data collecting means for collecting data while performing data calculation means for calculating data of all views necessary for generating an image at a position on the axis from data in the vicinity of the position by interpolation calculation; In an X-ray CT apparatus provided with an image generation means for generating an image from view data, a movement detection means for detecting the period and phase of a periodic movement of a scanning target, a position on the axis, and data collected at that position The position / phase association means for obtaining the phase motion of the scanning target corresponding to the time point obtained in association with each other, and the data calculation means respectively generate images at a plurality of positions on the axis. Time axis enhancement data generation means for generating time axis enhancement data at the plurality of positions by calculating time axis enhancement using the calculated data and a predetermined kernel function after calculating all view data necessary for In-phase data selecting means for selecting data at a plurality of positions corresponding to the same phase from the time axis emphasizing data, and an image positioned between the plurality of positions by an interpolation calculation using the selected in-phase data An X-ray CT apparatus is provided, comprising: interpolated image data calculating means for calculating data of all views necessary to generate the image. The X-ray CT apparatus according to the seventh aspect is basically the same as the X-ray CT apparatus according to the fifth aspect, except that all views necessary for generating a plurality of images by the data calculating means are used. Calculate each data, perform time axis emphasis calculation using the data of all the calculated multiple views and a predetermined kernel function, and at a plurality of positions corresponding to the same phase from the generated time axis emphasis data The difference is that each data is selected. Similar to the case of the X-ray CT apparatus according to the sixth aspect, if data of a plurality of all views and a predetermined kernel function are used, the phase width has a strong relationship with the data of all the plurality of views. Data having a strong relationship with the width phase, that is, time axis emphasis data can be generated. Then, data at a plurality of positions corresponding to the same phase is selected from the time axis enhancement data, and an image located between the plurality of positions is generated by interpolation using the selected time axis enhancement data. If the data for this is calculated, the image of the cross section of the scanning object in the several position corresponding to the same phase can be produced | generated, and the width | variety of the phase can be improved. That is, it is possible to efficiently and accurately generate a plurality of cross-sectional images in one phase of the periodic motion to be scanned.

  In an eighth aspect, the present invention provides volume data from images at a plurality of positions corresponding to the same phase generated in the X-ray CT apparatus having the configuration described above, Projection image generating means for generating a projection image by executing the calculation of the projection value of the pixel from the value of the volume data present on each projection line that reaches the pixel for all the pixels on the projection surface, An X-ray CT apparatus is provided. According to the X-ray CT apparatus of the eighth aspect, the image generation method of the second aspect can be suitably implemented.

  In a ninth aspect, the present invention provides the X-ray CT apparatus having the above-described configuration, wherein the projection image generation unit generates projection images with different phases of the periodic motion of the scanning target, and then the projection images are cine-ordered in phase order. Provided is an X-ray CT apparatus further comprising a projected image cine display means for displaying. According to the X-ray CT apparatus of the ninth aspect, the image display method of the third aspect can be suitably implemented.

  In a tenth aspect, the present invention provides the X-ray CT apparatus having the above configuration, wherein the data calculation means has a plurality of interpolation calculation algorithms, and an interpolation calculation algorithm for selecting one of the interpolation calculation algorithms. An X-ray CT apparatus further comprising selection means is provided. Depending on the interpolation algorithm, the time resolution and the way in which artifacts occur are different. Therefore, if one of a plurality of interpolation calculation algorithms can be selected, an optimum interpolation calculation algorithm can be used according to the scanning conditions, the period of periodic movement, the scanning target, the purpose of diagnosis, and the like. .

  According to the image generation method and the X-ray CT apparatus of the present invention, it is possible to efficiently generate images of a plurality of cross sections in one phase of a periodic motion to be scanned by one helical scan. Further, it is possible to efficiently generate a projection image such as a 3D image or an IP image in one phase of the periodic motion to be scanned. In addition, according to the image display method and the X-ray CT apparatus of the present invention, it is possible to display the periodic motion to be scanned in a moving image.

  Hereinafter, the present invention will be described in more detail with reference to embodiments of the present invention shown in the drawings. Note that the present invention is not limited thereby.

-First embodiment-
FIG. 1 is a block diagram showing the configuration of an X-ray CT apparatus 100 according to the first embodiment of the present invention. The X-ray CT apparatus 100 includes an operation console 1, an imaging table 8, a scanning gantry 9, and an electrocardiograph 16. The operation console 1 exchanges control signals and the like with the imaging table 8 and the scanning gantry 9 with an input device 2 that receives instructions and information from an operator, a central processing unit 3 that executes image reconstruction processing, and the like. A control interface 4 for inputting an electrocardiogram waveform from the electrocardiograph 16, a data collection buffer 5 for collecting data acquired by the scanning gantry 9, a CRT 6 for displaying an image generated from the data, a program and data And a storage device 7 for storing. The imaging table 8 carries the subject and moves it in the body axis direction. The scanning gantry 9 is an X-ray controller 10, an X-ray tube 11, a collimator 12, a detector 13, a data collection unit 14, and a rotation that rotates the X-ray tube 11 and the like around the body axis of the subject. And a controller 15. Note that the X-ray tube 11 and the like can be continuously rotated by the slip ring. The electrocardiograph 16 outputs an electrocardiographic waveform of the subject.

  FIG. 2 is a flowchart of the helical scan and image generation processing by the X-ray CT apparatus 100. In step S1, the operator inputs scan parameters. The scan parameters include a scan condition such as an X-ray tube current and a beam width, a scan start position, a scan end position, a movement distance per rotation, and a rotation time. Here, as shown in FIG. 3, it is assumed that a scan start position Sp, a scan end position Ep, a movement distance d per rotation, and a rotation time τ are input. As a numerical example, d = 5 mm and τ = 1 s. In FIG. 3, V (P1) represents the aorta during expansion, and V (P6) represents the aorta during contraction. P1 and P6 represent phases P1 and P6 when one period h of the periodic motion of the aorta is equally divided into phases P1 to P10. The z axis represents an axis for moving the subject in a straight line (axis for moving the imaging table 8). A sine curve sin (θ) represents the vertical height of the X-ray tube 11 at each position on the z-axis. θ represents the rotation angle of the X-ray tube 11 at each position on the z-axis.

  Returning to FIG. 2, in step S <b> 2, the operator selects one interpolation calculation algorithm from 2-rotation linear interpolation, 1-rotation linear interpolation, 1-rotation nonlinear interpolation, half-rotation interpolation, and the like. As shown in FIG. 4A, the two-rotation linear interpolation is proportional to the distance from the position of φ = 2π when the data for generating the image at the position of φ = 2π is obtained by interpolation calculation. This is an interpolation calculation algorithm that decreases and weights φ = 0, φ = 4π to “0”. If this two-rotation linear interpolation is used, artifacts can be reduced. As shown in FIG. 4B, the one-rotation linear interpolation is proportional to the distance from the position of φ = π when obtaining data for generating an image at the position of φ = π by interpolation calculation. This is an interpolation calculation algorithm that decreases and weights φ = 0 and φ = 2π to “0”. As shown in FIG. 4C, the one-rotation non-linear interpolation gradually decreases in the vicinity of φ = π when obtaining data for generating an image at a position of φ = π by interpolation calculation. = Π / 2, an interpolation algorithm that weights rapidly in the vicinity of φ = 3π / 2, and thereafter gradually changes and weights to “0” when φ = 0 and φ = 2π. As shown in FIG. 4D, the half-rotation interpolation does not change in the vicinity of φ = π / 2 when data for generating an image at a position of φ = π / 2 is obtained by interpolation calculation. , Φ = π / 4 to 0, φ = 3π / 4 to π, the interpolation operation algorithm gives a weight which becomes linearly small and becomes “0” when φ = 0 and φ = π. When this half-rotation interpolation is used, the time resolution can be reduced.

  Returning to FIG. 2, in step S <b> 3, an electrocardiographic waveform is acquired from the electrocardiograph 16. Then, the period and phase of the heartbeat are detected from the R wave of the electrocardiogram waveform. In step S4, an interval (overlapping rate) e between positions for generating images is calculated from the heartbeat period h. For example, if one period h is equally divided into phases P1 to P10, e = (d / τ) · (h / 10). As a numerical example, if d = 5 mm, τ = 1 s, h = 1 s, e = 0.5 mm.

  In step S5, a helical scan is executed and data is collected. The helical scan need not be synchronized with the electrocardiogram waveform, but here, as shown in FIG. 5, it is assumed that the helical scan is performed in synchronization with the R wave of the electrocardiogram waveform ECG.

  Returning to FIG. 2, in step S6, high-speed overlapping / recon processing (FIG. 6) is executed to generate images at positions on the z-axis for each overlapping rate e. FIG. 6 is a flowchart showing high-speed overlapping / recon processing. This flowchart is shown by PAD (Problem Analysis Diagram). In step R1, step R2 is executed every time necessary data is collected. Here, the necessary data corresponds to data (for example, the first image) required to calculate a data set for generating a first image (first image) by image reconstruction calculation by interpolation calculation. (data for 1 rotation before and after the position on the z-axis, data for 1/2 rotation before and after, and data for 1/4 rotation before and after) or the previously generated image is weighted and subtracted to generate the second and subsequent images in order. Means the data needed to In step R2, it is determined whether or not the image to be generated is the first image. If it is the first image, steps R3 and R4 are executed. If it is after the second image, step R5 is executed. In step R3, data for one rotation before and after the position on the z-axis corresponding to the first image (during 2-rotation linear interpolation) or data for 1/2 rotation before and after (1 rotation linear interpolation or 1 rotation nonlinear interpolation) ) Or data of all the views at the position on the z-axis corresponding to the first image is calculated by interpolation calculation using data for 1/4 rotation in the front and rear direction (in the case of half rotation interpolation). In step R4, an image reconstruction operation is performed on the data of all views to obtain a first image. In step R5, a sequential generation calculation described below is performed to generate the second and subsequent images.

  Here, the sequential generation calculation will be described. 7 and 8 are explanatory diagrams of image generation. Each photographing position i is indicated by “01” to “12”. The cross-sectional structure of the subject H at each imaging position i “01” to “12” is indicated by matrices H (01) to H (12). The arrows around each of the matrices H (01) to H (12) indicate the view direction (scan direction). The data at each shooting position i is represented by matrices C (01) to C (12) in which the corresponding element in the view direction corresponds to the projection value and the other elements are “0”. For example, since the view corresponding to the matrix C (01) is in the direction from the upper left to the lower right, the projection value is 2 + 4 = 6. Therefore, the projection value “6” is the upper left element and the lower right element of the matrix C (01). Further, the lower left element and the upper right element are “0”.

  The linear interpolation operation uses the inverse proportion of the distance, that is, the data C of the shooting position i is multiplied by the interpolation weight W that becomes smaller as the distance between the position of the image and the shooting position i is larger, and the view of the position of the image is displayed. It can be considered to be data A. Therefore, assuming that the shooting position i “06” is the image position and the interpolation weight W is 1/6 for each unit distance, the view data A at the image position “06” is as shown in the matrix A01 to A11. For example, the matrix A01 is obtained by multiplying the matrix C (01) by the interpolation weight 1/6.

Here, as shown in FIG. 8, six views A′01 to A′06 are created from the 11 views A01 to A11 using the opposite view. For example, A′01 = A01 + A07 = C (01) × (1/6) + C (07) × (5/6)
It is.

  Since the image reconstruction calculation can be considered as the sum of the matrixes A01 to A11 of each view data or the sum of A′01 to A′06, the matrix D (06) of the image data at the position “06” of the image is D (06) = A01 + ... + A11 = A'01 + ... + A'06. When a display image I (06) is obtained by performing an image processing operation of I (06) = D (06) / 2-27 on the image data matrix D (06), the display image I (06) The value of the upper left element is “12”, the value of the lower left element is “15”, the value of the upper right element is “13”, and the value of the lower right element is “14”. When this display image I (06) is compared with the matrix H (06) of the cross-sectional structure of the subject H, it is found that the display image I (06) shows a cross section at the position “06” of the subject H. I understand.

  In general, when the number of views n = 2m−1 (m is a natural number) required for the image reconstruction calculation, the view data at the image position and the data for (m−1) views in front of the image position. And rear (m-1) view data may be used.

  9 and 10 are other explanatory views of image data generation. This is obtained by changing the image position = “06” in FIGS. 7 and 8 to the image position = “07”. 7 and 8 are compared with FIGS. 9 and 10, in FIGS. 7 and 8, the data C (01) to C (11) are used to generate the image data D (06). In FIG. 10, data C (02) to C (12) are used to generate image data D (07). That is, the data C (02) to C (11) are used redundantly. In this way, generating different image data by overlapping use of data obtained by helical scanning is called overlap recon.

  Although FIGS. 7 to 10 illustrate the interpolation method from the data corresponding to 1/2 rotation before and after the image positions “06” and “07”, the data corresponding to 1 rotation before and after the image position is sandwiched. The interpolation method from these sets is similar. FIGS. 11 to 14 show an interpolation method from a data set corresponding to one rotation before and after the position “12” of the image. 11 to 14, the number of views is n = 23 (in FIGS. 7 to 10, n = 11). Also, the interpolation weight difference Q between the positions separated by the unit distance is 1/12 (Q = 1/6 in FIGS. 7 to 10).

  As described with reference to FIGS. 7 and 8, the matrix D (06) of image data at the image position “06” is D (06) = A01 +... + A11 = A′01 +. is there. A01 to A11 are interpolation weights W = 1/6, 2/6, 3/6, 4/6, 5/6, 6/6, 5/6, 4 to C (01) to C (11). / 6, 3/6, 2/6, 1/6. Therefore, it can be written as:

  Also, as described with reference to FIGS. 9 and 10, the image data matrix D (07) at the image position “07” is D (07) = A01 +... + A11. A01 to A11 are obtained by multiplying C (02) to C (12) by the interpolation weight W. Therefore, it can be written as:

  If the equation (2) is subtracted from the equation (1), the following equation is obtained.

  If the equation (3) is modified, the following equation is obtained.

  Similar to equation (4), the following equation holds.

  The following general expression can be derived from (Expression 4) and (Expression 5).

  (Equation 6) is expressed as follows: view number n = 2m−1 (m is a natural number) required for the image reconstruction calculation, view data at the image position and (m−1) view portions in front of the image position. This is a general formula when an image is generated using the data of (m-1) views and data of the rear (m-1) views. The matrix D (06) in FIGS. 7 and 8 is an image at the first position (X = 1), and the matrix D (07) in FIGS. 9 and 10 is an image at the second position (X = 2). 7 to 10 correspond to the case where n = 11 (m = 6) and K = 6 in the equation (6). Equations (1) to (6) were derived on the assumption that data corresponding to 1/2 rotation before and after the position of the image as shown in FIGS. 7 to 10 is used. This general formula can also be applied to the case of using data corresponding to one rotation before and after the position of the image as shown in FIGS. That is, FIGS. 11 to 14 correspond to the case where n = 23 (m = 12) and K = 12 in the equation (6).

  The operation of ΔCx in the equation (6) is very important for the calculation speed. That is, in the case of ΔCx, C (X + K−2 + m) and C (X + K−2) do not calculate plus back projection and minus back projection, respectively, and first, data (projection value) C (X + K−2 + m) Taking the difference of C (X + K−2), the back projection is calculated for the obtained ΔCx. For example, in FIG. 7, when the third position (X = 3) is “08”, ΔC 3-6 calculates the difference between C (07) and C (01) = 24, and then calculates the back projection. I do. ΔC3 calculates the difference between C (13) and C (07), and then calculates the back projection.

  The difference between the positions of the first and second terms of ΔCx is m. Therefore, when data corresponding to 1/2 rotation before and after the position of the image is used, since the first term and the second term are in an opposing view relationship, ΔCx is the difference in the opposing view data (projection value). It makes sense to take On the other hand, when a data set corresponding to one rotation before and after the image position is used, since the first term and the second term are in the same phase view, ΔCx is the data (projection value) separated by 360 °. It makes sense to make a difference.

  As described above, the image at the first position needs to be generated by the interpolation calculation and the image reconstruction calculation corresponding to Expression (1), but the image at the Xth (≧ 2) position is It can be seen that it can be generated by the formula. In other words, the image at the Xth (≧ 2) position does not need to be subjected to interpolation calculation and image reconstruction calculation for all the views, and the (X−1) th image is used to It can be generated by simple addition and subtraction as shown in the equation and image reconstruction operation for only one view (ΔCx) for each of Ex-m and Ex (however, if Ex-m has already been calculated) No need to calculate).

  FIG. 15 represents an image I (m) at a position for each overlapping rate e on the z axis generated by the high-speed overlapping / recon processing.

  Returning to FIG. 2, in step S <b> 7, time axis enhancement processing is performed to generate an image x (m) corresponding to a phase having a narrower width than the phase width corresponding to the image I (m). That is, since the image I (m) is generated using data collected at positions before and after that position, the slice width is relatively thick as shown in FIG. This slice width corresponds to the width of the phase, and is 2 rotation linear interpolation> 1 rotation linear interpolation> 1 rotation nonlinear interpolation> half rotation interpolation. As shown in FIG. 16B, this is converted to an image x (m) having a relatively thin slice width, that is, an image x (m) having a relatively narrow phase width, in the time axis enhancement process.

  FIG. 17 shows the principle of time axis enhancement processing. FIG. 17A shows an image I (m).

  FIG. 17B shows an image I (m) and an image I (m + j) at a position before and after that position. FIG. 17C shows an image x (m) and an image x (m + j) at a position before and after that position. 17 (a) and FIG. 17 (c) are compared, if the image x (m) and the image x (m + j) at the positions before and after the position are combined with appropriate weights, the image I ( It can be seen that m) can be generated. Therefore, if this weight function is the profile function f (j) and the number of images at the front and rear positions is 2 · M, the following equation is established.

  FIG. 17D conceptually shows the profile function f (j). When the above equation (7) is solved using numerical analysis methods such as Gauss-Seidel method and Jacobi method, an image x (m) is generated as shown in FIG. it can. The profile function f (j) is obtained in advance by fitting the result of actual measurement using a phantom to the equation (7).

  Returning to FIG. 2, in step S8, the image x (m) is selected for each phase. That is, as shown in FIG. 18, the images x (m) corresponding to the phases P1,.

  Returning to FIG. 2, in step S9, an image located between the positions of the images x (m) having the same phase is generated by interpolation. That is, as shown in FIG. 19, an image (two-dot chain line) between the images (solid lines) corresponding to the phase P1 is generated by linear interpolation. Then, the process ends. As described above, it is possible to efficiently generate images of a plurality of cross sections in the phase P1, ..., P10 of the periodic motion to be scanned.

  FIG. 20 is a flowchart of 3D image display processing. In step D1, the operator inputs 3D parameters. Examples of 3D parameters include a projection direction and a data range. In step D2, the operator selects a display mode. The display mode includes a phase designation mode and a cine mode. If the phase designation mode is selected, the process proceeds to step D3, and if the cine mode is selected, the process proceeds to step D6. In step D3, the operator designates one phase. In step D4, a 3D image with the designated phase is generated. That is, the projection direction that constitutes volume data from the image x (m) of the designated phase among the images x (m) of each phase in FIG. 19 and passes through the volume data and reaches each pixel on the projection plane. All the pixels on the projection plane are determined by examining the value of the volume data present on each projection line of the image and setting the data included in the data range and closest to (or far from) the projection plane as the projection value of the pixel. To generate a 3D image. In step D5, a 3D image is displayed. Thereby, it is possible to overlook the entire scanning target in one phase of the periodic motion. Thereafter, the process is terminated.

  In step D6, a 3D image for each phase divided by one cycle is generated (the same processing as in step D3 is performed for each phase). In step D7, 3D images for each phase are displayed in cine order. As a result, the overall state in which the scanning target is periodically moving can be seen as a moving image. Thereafter, the process is terminated.

-Second Embodiment-
When selecting the image x (m) for each phase in step S8 in FIG. 2, images before and after the phase to be selected are also selected as a set as shown in FIG. 21, and images in the same phase are selected in step S9 in FIG. When interpolating and generating an image between positions x (m), when the distances are Z1 and Z2, as shown in FIG. 22, X1 = {x (a) + 2 · x (b) + 3 · x (c )} / 6 X2 = {3 · x (d) + 2 · x (e) + x (f)} / 6 x (g) = (Z2 · X1 + Z1 · X2) / (Z1 + Z2)
It is good. Thereby, the accuracy of interpolation can be improved.

-Third embodiment-
The order of step S6 and step S7 in FIG. 2 may be switched, and the time axis enhancement processing may be performed at the data level before generating the image. The principle of performing time axis enhancement processing at the data level is disclosed in, for example, Japanese Patent Publication No. 4-30300. That is, the data p (v, c) for all views for generating images at positions for each of the overlapping rates e on the z axis from the data collected by the helical scan in step S5 in FIG. Here, v represents the view number, and c represents the channel number of the detector. Next, assuming that the kernel function is h (m), equivalent view data q (v, c) at a certain position is calculated from Equation (8). The kernel function h (m) is obtained in advance from the aforementioned profile function f (j) by h (m) = F ′ {1 / F [f (j)]} (F is Fourier transform, F ′ Represents the inverse Fourier transform). FIG. 23 shows an example of the kernel function h (m).

  Next, an image x (m) is generated from the equivalent view data q (v, c), and step 8 and subsequent steps in FIG.

-Fourth Embodiment-
The time axis enhancement process in step S7 of FIG. 2 may be omitted. In particular, when half-rotation interpolation is selected as the interpolation calculation algorithm, the time resolution enhancement may be omitted because the time resolution is originally high.

-Fifth Embodiment-In the above description, as shown in FIG. 22, images of a plurality of phases P1,..., P10 are obtained substantially simultaneously, but only an image of one phase may be obtained. In this case, instead of step S6 in FIG. 2, images at positions corresponding to one phase are obtained by reconstruction calculation. Also, steps S7 and S8 in FIG. 2 are omitted.

1 is a configuration block diagram of an X-ray CT apparatus according to a first embodiment of the present invention. It is a flowchart of a helical scan and an image generation process. It is explanatory drawing of a scan parameter. It is explanatory drawing of the weighting method for every interpolation calculation algorithm. It is explanatory drawing of a data collection position and the phase of a heartbeat. It is a flowchart of a high-speed overlapping and recon process. It is explanatory drawing of the production | generation of the image by the data for 180 degrees before and behind. It is another explanatory drawing of the production | generation of the image by the data for 180 degrees before and behind. It is another explanatory drawing of the production | generation of the image by the data for 180 degrees before and behind. It is another explanatory drawing of the production | generation of the image by the data for 180 degrees before and behind. It is explanatory drawing of the production | generation of the image by the data for 360 degrees back and front. It is another explanatory drawing of the production | generation of the image by the data for 360 degrees back and front. It is another explanatory drawing of the production | generation of the image by the data for 360 degrees back and front. It is another explanatory drawing of the production | generation of the image by the data for 360 degrees back and front. It is explanatory drawing of the produced | generated image group. It is explanatory drawing of a time emphasis process. It is explanatory drawing of the principle of a time emphasis process. It is explanatory drawing of the image selected for every phase. It is explanatory drawing of the image group produced | generated by the interpolation calculation. It is a flowchart of a 3D image display process. It is another explanatory drawing of the image selected for every phase. It is explanatory drawing of the interpolation method using the image of FIG. It is explanatory drawing of a kernel function. It is a time chart of operation | movement of the conventional X-ray CT apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 X-ray CT apparatus 1 Operation console 2 Input device 3 Central processing unit 8 Imaging table 9 Scanning gantry 11 X-ray tube 12 Collimator 13 Detector 14 Data collection part

Claims (7)

Motion detection means for detecting the period and phase of the periodic motion in the scanning object;
A data collection means for collecting data while performing a helical scan by rotating the scanning object linearly along one axis and rotating at least an X-ray tube around the scanning object;
A position and phase associating means for acquiring the position on the axis and the phase of the periodic motion of the scanning target corresponding to the time when data is collected at the position;
Data calculation means for calculating all view data necessary for generating an image at a position on the axis from data in the vicinity of the position by interpolation calculation, wherein the data collection means is used for calculation by the interpolation calculation. A data calculation means for sequentially performing the interpolation calculation every time necessary data is collected;
Image generating means for generating an image from the data of all the views;
The position and phase association means, the data calculation means and the image generation means respectively generate images at a plurality of positions corresponding to the same phase on the axis, and then perform the interpolation operation using the generated images. An X-ray CT apparatus comprising: an interpolated image generating means for generating an image located between a plurality of positions. Motion detection means for detecting the period and phase of the periodic motion in the scanning object;
A data collection means for collecting data while performing a helical scan by rotating the scanning object linearly along one axis and rotating at least an X-ray tube around the scanning object;
A position and phase associating means for acquiring the position on the axis and the phase of the periodic motion of the scanning target corresponding to the time when data is collected at the position;
Data calculation means for calculating all view data necessary for generating an image at a position on the axis from data in the vicinity of the position by interpolation calculation, wherein the data collection means is used for calculation by the interpolation calculation. A data calculation means for sequentially performing the interpolation calculation every time necessary data is collected;
Image generating means for generating an image from the data of all the views;
After calculating the data of all views necessary for generating images at a plurality of positions corresponding to the same phase on the axis by the position and phase association unit and the data calculation unit, the calculated data is An X-ray CT apparatus comprising: interpolated image data calculating means for calculating data of all views necessary for generating an image positioned between the plurality of positions by the used interpolation calculation. Motion detection means for detecting the period and phase of the periodic motion in the scanning object;
A data collection means for collecting data while performing a helical scan by rotating the scanning object linearly along one axis and rotating at least an X-ray tube around the scanning object;
A position and phase associating means for acquiring the position on the axis and the phase of the periodic motion of the scanning target corresponding to the time when data is collected at the position;
Data calculation means for calculating all view data necessary for generating an image at a position on the axis from data in the vicinity of the position by interpolation calculation, wherein the data collection means is used for calculation by the interpolation calculation. A data calculation means for sequentially performing the interpolation calculation every time necessary data is collected;
Image generating means for generating an image from the data of all the views;
After the images at a plurality of positions on the axis are generated by the position and phase association unit, the data calculation unit, and the image generation unit, time axis enhancement using the generated image and a predetermined profile function A time axis emphasized image generating means for generating a time axis emphasized image at the plurality of positions by calculation;
In-phase image selection means for selecting images at a plurality of positions corresponding to the same phase from the time-axis enhanced image,
An X-ray CT apparatus comprising: an interpolation image generation unit configured to generate an image located between the plurality of positions by an interpolation calculation using the selected time axis emphasized image. Motion detection means for detecting the period and phase of the periodic motion in the scanning object;
A data collection means for collecting data while performing a helical scan by rotating the scanning object linearly along one axis and rotating at least an X-ray tube around the scanning object;
A position and phase associating means for acquiring the position on the axis and the phase of the periodic motion of the scanning target corresponding to the time when data is collected at the position;
Data calculation means for calculating all view data necessary for generating an image at a position on the axis from data in the vicinity of the position by interpolation calculation, wherein the data collection means is used for calculation by the interpolation calculation. A data calculation means for sequentially performing the interpolation calculation every time necessary data is collected;
Image generating means for generating an image from the data of all the views;
After calculating all view data necessary for generating images at a plurality of positions on the axis by the position and phase association unit and the data calculation unit, the calculated data and a predetermined kernel function, Time axis enhancement data generating means for generating time axis enhancement data at the plurality of positions by time axis enhancement calculation using
In-phase data selection means for selecting data at a plurality of positions corresponding to the same phase from the time axis enhancement data,
And interpolated image data calculating means for calculating data of all views necessary for generating an image positioned between the plurality of positions by interpolation using the selected in-phase data. X-ray CT system. The X-ray CT apparatus according to claim 1,
Volume data is constructed from the generated images at a plurality of positions corresponding to the same phase, and the projection of the pixel is performed from the value of the volume data existing on each projection line that passes through the volume data and reaches each pixel on the projection plane. An X-ray CT apparatus further comprising projection image generation means for generating a projection image by executing a value calculation for all pixels on the projection plane. The X-ray CT apparatus according to claim 5,
X-ray CT further comprising projection image cine display means for generating projection images at different phases of the periodic motion of the scanning object by the projection image generation means and then displaying the projection images in cine order in phase order. apparatus. The X-ray CT apparatus according to any one of claims 1 to 6,
The X-ray CT apparatus characterized in that the data calculation means has a plurality of interpolation algorithms, and further comprises an interpolation calculation algorithm selection means for selecting one of the interpolation calculation algorithms.

Images