JP2010011980A - Image processor and image diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor and an image diagnostic apparatus which improves accuracy of diagnosis of intravascular constriction. <P>SOLUTION: A memory section 28 stores imaging volume data of imaged blood vessels of a subject and non-imaging volume data acquired when the blood vessel is not imaged. A calcified area specifying section 30 specifies a calcified area included in the non-imaging volume data on the basis of pixel values. A calcified area emphasizing section 32 emphasizes a calcified area included in the imaging volume data and corresponding to the specified calcified area. A three-dimensional image processing section 34 generates image data on the basis of the imaging volume data in which the calcified area is emphasized. A display section 38 displays the generated image. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image processing apparatus and an image diagnostic apparatus for diagnosing intravascular stenosis.

  There are image processing apparatuses and image diagnostic apparatuses for diagnosing intravascular stenosis. In the diagnosis of intravascular stenosis due to calcification of blood vessels, it is important to accurately identify the calcified region. At present, MDCT (Multi-Slice CT) has obtained the same high clinical evaluation as EBCT (Electron Beam Computed Tomography) regarding the identification of calcified areas in coronary arteries. (See Non-Patent Document 1 and Non-Patent Document 2).

  As a typical example of specifying the calcified region, there is an Agatston method (threshold method) (see Non-Patent Document 3). However, in the Agatston method, due to the influence of the partial volume effect or the like, the calcified region is extracted too much or too little. If the calcified region is not specified accurately, the diagnostic accuracy of intravascular stenosis is reduced.

As a method for identifying a calcified region in which the influence of the partial volume effect is reduced as compared with the Agatston method, there is a method based on a PVE statistical model (see Non-Patent Document 4). However, in the method based on the PVE statistical model, the accuracy of specifying the calcification region greatly depends on the accuracy of the constructed model. Also, building a model is very difficult.
Becker CR et al, “Current development of cardiac imaging with multidetector-row CT,” Eur. J Radiol, 36 (2), pp.97-103 (2000) Jun Horiguch etc., “Quantification of Coronary Artery Calcium Using Multidetector CT and a Retrospective ECG-Gating Reconstruction”, AJR: 177 (2001) ASAgatston etc., “Quantification of coronary artery calcium using ultrafast computed tomography,” J. Am. Coll. Cardiol., Vol.15, pp.827-832 (1990) Peter Santago etc., “Statistical Models of Partial Volume Effect,” IEEE Tran. On Image Processing. Vol.4, No.11, pp.1531-1540 (1995)

  An object of the present invention is to provide an image processing apparatus and an image diagnostic apparatus that can improve the diagnostic accuracy of intravascular stenosis.

  The image processing apparatus according to claim 1, a storage unit that stores first volume data relating to a contrasted blood vessel of a subject and second volume data relating to the blood vessel that is not contrasted; and the second volume data A specifying unit for specifying the calcified region included in the first volume data corresponding to the specified calcified region, the calcified region included in the first volume data corresponding to the specified calcified region, and the calcification A generating unit that generates image data based on the first volume data in which the region is emphasized; and a display unit that displays the generated image.

  The diagnostic imaging apparatus according to claim 4 includes an X-ray tube that generates X-rays, an X-ray detector that detects X-rays generated from the X-ray tube and transmitted through a subject, and the X-ray detector Based on output data, a volume data generating unit that generates first volume data related to the contrasted blood vessels of the subject and second volume data related to the blood vessels that are not contrasted; and the second volume data A specifying unit for specifying the calcified region included in the first volume data corresponding to the specified calcified region, the calcified region included in the first volume data corresponding to the specified calcified region, and the calcification An image generation unit that generates image data based on the first volume data in which the region is emphasized; and a display unit that displays the generated image.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the image processing apparatus and image diagnostic apparatus which implement | achieve the improvement of the diagnostic accuracy of intravascular stenosis.

  Hereinafter, an image processing apparatus and an image diagnostic apparatus according to embodiments of the present invention will be described with reference to the drawings. The image diagnostic apparatus and the image processing apparatus according to the present embodiment are used for diagnosis of stenosis due to blood vessel calcification in a region of interest (scan region). This embodiment can be implemented using any part of the subject as a region of interest. However, for specific explanation, the region of interest is a heart that is useful in clinical settings.

  In order to accurately diagnose vascular stenosis, it is necessary to accurately specify the position of the calcified region. By the way, the blood vessel is not displayed on the image if it is scanned as it is. In order to display, it is necessary to contrast the blood vessel with a contrast medium. However, since the contrast between the calcified region and the contrast agent deteriorates due to the partial volume effect, it is not possible to accurately identify the calcified region from the volume data regarding the contrasted blood vessels (hereinafter referred to as contrast volume data). Can not.

  The feature of this embodiment is that, in order to avoid the influence of the partial volume effect, the calcified region included in the contrast volume data is used by using volume data (hereinafter referred to as non-contrast volume data) related to the blood vessel that is not contrasted. , To identify.

  The diagnostic imaging apparatus according to the present embodiment is preferably an X-ray computed tomography apparatus (hereinafter referred to as an X-ray CT apparatus) or an X-ray angio apparatus capable of generating volume data. Hereinafter, for the sake of specific description, it is assumed that the diagnostic imaging apparatus according to the present embodiment is an X-ray CT apparatus.

  FIG. 1 is a diagram showing a configuration of an X-ray CT apparatus 1 according to the first embodiment. As shown in FIG. 1, the X-ray CT apparatus 1 includes a gantry 10 and a computer device 20. The gantry 10 rotatably supports an annular or disk-shaped rotating frame 11. The rotating frame 11 has an X-ray tube 13 and an X-ray detector 14 so as to face each other with the subject P interposed therebetween for scanning. The rotating frame 11 continuously rotates at a constant angular velocity. It is assumed that the subject P is placed in the imaging region so that the body axis (Z axis) substantially coincides with the long axis of the top 12.

  The X-ray tube 13 receives an application of a high voltage from the high voltage generator 15 and a supply of filament current to generate X-rays. X-rays generated from the X-ray tube 13 and transmitted through the subject P are detected by the X-ray detector 14.

  The computer device 20 includes a data collection unit 22, a preprocessing unit 24, a reconstruction processing unit 26, a storage unit 28, a calcified region specifying unit 30, a calcified region enhancing unit 32, a three-dimensional image processing unit 34, and a stenosis rate calculating unit. 36, a display unit 38, an input unit 40, and a control unit 42.

  The data collection unit 22 converts a signal corresponding to the intensity of transmitted X-rays output from each channel of the X-ray detector 14 into a digital signal. This digital signal is called projection data.

  The preprocessing unit 24 preprocesses the projection data from the data collection unit 22. Specifically, the pre-processing unit 24 removes quantum noise included in the projection data using the Weblet method. The weblet method is a known technique, for example, literature (Y. Yang, N. Nakamori, Y. Yoshida, “Improvement of CT Image Degraded by Quantum Mottle Using Singularity Detection,” IEICE Trans on Inf. & Syst. , Vol.E86-D, No.1, pp.123-130 (2003)).

  The reconstruction processing unit 26 reconstructs the projection data by electrocardiographic synchronization to generate contrast volume data and non-contrast volume data. The reconstruction processing algorithm may be any existing algorithm, for example, Feldkamp CT image reconstruction algorithm (LAFeldkamp etc., “Practical cone-beam reconstruction,” J.Opt.Soc.Am, A1, pp.612 -619 (1984)) and its extension method (G. Wang etc., “A general cone-beam reconstruction algorithm,” IEEE Trans. Med. Imaging, No. 12, pp. 486-496 (1993)) It is done.

  The storage unit 28 stores the generated contrast volume data and non-contrast volume data. It is assumed that the contrast volume data and the non-contrast volume data are aligned.

  The calcification region specifying unit 30 specifies the calcification region included in the non-contrast volume data based on the pixel value. In order to specify the calcified region, the calcified region specifying unit 30 includes a threshold processing unit 301 and a region expansion process 302. The threshold processing unit 301 specifies a candidate region for the calcification region included in the non-contrast volume data by threshold processing based on the CT value range of the calcification region. Hereinafter, a candidate area for a calcification area is referred to as a calcification candidate area. The CT value range is set to a range of CT values that the calcified region has. Further, the CT value range changes according to the spatial resolution and voxel size of the volume data. The region expansion processing unit 302 removes isolated points (noise) from the calcification candidate region by region expansion processing based on the CT value range of the calcification region, and specifies the calcification region.

  The calcified region emphasizing unit 32 emphasizes the calcified region included in the contrast volume data corresponding to the calcified region specified on the non-contrast volume data. More specifically, the coordinate value of the calcified region specified on the non-contrast volume data is specified, and the pixel value of the voxel on the contrast volume data having the specified coordinate value is replaced with the specific pixel value. Note that the voxel on the contrast volume data in which the pixel value is replaced may be a part of the calcified region (for example, a boundary part).

  The three-dimensional image processing unit 34 generates image data in which the calcified region is emphasized based on the contrast volume data in which the calcified region is emphasized.

  The stenosis rate calculating unit 36 calculates the stenosis rate of the vascular region based on the diameter or area of the vascular region on the generated image and the diameter or area of the calcified region in the vascular region.

  The display unit 38 displays the generated image and the calculated stenosis rate.

  The input unit 40 inputs various instructions from the user to the computer device 20. As the input unit 40, a pointing device such as a mouse or a trackball, a selection device such as a switch, or an input device such as a keyboard can be used as appropriate.

  The control unit 42 functions as the center of the X-ray CT apparatus 1 and controls each part constituting the X-ray CT apparatus 1. Moreover, the control part 42 performs the specification / display process of a calcification area | region by controlling each part.

  Hereinafter, the details of the specifying / displaying process of the calcification region according to the present embodiment will be described. First, the partial volume effect will be briefly described. The partial volume effect is that when a plurality of substances having different linear absorption coefficients are present in one voxel, the CT value of one voxel is an average of the CT values of the plurality of substances. According to the literature (M.Soret, SLBacharach etc., “Partial-Volume Effect in PET Tumor Imaging,” The Journal of Nuclear medicine, Vol.48, No, 6, pp.932-945 (2007)) The degree of influence of the volume effect is (1) size and shape of the attention area, (2) difference between the pixel value of the attention area and the surrounding area, (3) spatial resolution (spatial resolution), (4) Four factors of image pixel size (sampling interval) change in combination.

  Next, the difference in the influence of the partial volume effect on the calcified region in the blood vessel when blood contains a contrast agent and when it does not contain a contrast agent will be described. The difference between the CT value of the calcified region relating to the contrast volume data and the CT value of the blood region containing the contrast agent is calculated by comparing the CT value of the calcified region relating to the non-contrast volume data and the CT value of the blood region not containing the contrast agent. It is smaller than the difference. Hereinafter, a blood region that does not contain a contrast agent is simply referred to as a blood region. A blood region containing a contrast agent is referred to as a contrast agent region.

  On the other hand, the CT value of the calcified region varies depending on the difference in the concentration of calcium contained in the calcified region and individual differences. Therefore, the threshold for extracting the calcified region has a certain width.

  Due to the partial volume effect, the contrast between the calcified region and the contrast agent region and the contrast between the calcified region and the blood region are lowered. In particular, since the CT values of the calcified region and the contrast agent region are approximate, the extraction accuracy of the calcified region from the contrast volume data is very low. On the other hand, since the CT values of the calcification region and the contrast agent region are not approximated, the extraction accuracy of the calcification region does not change much even if the partial volume effect is applied. That is, it can be said that the contrast volume data is more influenced by the partial volume effect than the non-contrast volume data.

  In the calcified area specifying / displaying process according to the present embodiment, the calcified area is extracted with high accuracy in consideration of the difference in the influence of the partial volume effect between the contrast volume data and the non-contrast volume data.

  Hereinafter, the flow of the specifying / displaying process of the calcification region by the control unit 42 will be described. FIG. 2 is a diagram illustrating the flow of the specifying / displaying process of the calcified region. The control unit 42 reads the contrast volume data and the non-contrast volume data generated by the electrocardiogram synchronous reconstruction method from the storage unit 28 (step S1). Hereinafter, generation processing of contrast volume data and non-contrast volume data using an electrocardiogram synchronous scan and reconstruction method will be briefly described.

  In the electrocardiogram synchronous scan, the control unit 42 assumes that the RR interval (time interval between adjacent R waves) in the electrocardiogram data is substantially constant, and triggers the R wave (or R wave from the R wave for a predetermined time). The scan is performed for a certain period from (after) to a predetermined cardiac time phase. The scan is repeated for a certain period for each heartbeat. First, immediately after injecting the contrast agent, the control unit 42 repeatedly performs an electrocardiographic scan on the scan region including the heart. Immediately after the injection of the contrast agent, no contrast agent flows into the heart. That is, non-contrast volume data is generated by performing electrocardiographic synchronization reconstruction processing on projection data collected immediately after contrast agent injection. When contrast medium monitoring is performed after injection of the contrast medium and it is determined that the contrast medium is filled in the coronary arterial blood vessels of the heart, the control unit repeats the ECG scan repeatedly in the scan area. Contrast volume data is generated by performing electrocardiographic synchronization reconstruction processing on the projection data collected during this period.

  Thus, since the non-contrast volume data and the contrast volume data are imaged at the same subject position and scanning conditions, alignment is unnecessary. The non-contrast volume data and the contrast volume data are volume data relating to the same cardiac phase by electrocardiographic synchronization reconstruction.

  When the non-contrast volume data is read, the control unit 42 causes the calcified region specifying unit 30 to perform the calcified region specifying process.

  In the calcification region specifying process, the calcification region specifying unit 30 first causes the threshold processing unit 301 to perform threshold processing. In the threshold processing, the threshold processing unit 301 performs threshold processing on the non-contrast volume data within the CT value range for threshold processing, and extracts calcification candidate regions (step S2). The CT value range is determined according to the spatial resolution and voxel size of the non-contrast volume data. For example, when the spatial resolution is 1 mm, the CT value range of the calcified region is 120 HU to 700 HU. In this case, the threshold range is automatically set to 300 HU to 700 HU. When the spatial resolution is 0.5 mm, the CT value range of the calcified region is 221HU to 1134HU. The threshold range may be set by the user via the input unit 40.

When the threshold processing is performed, the calcification region specifying unit 30 causes the region expansion processing unit 302 to perform region expansion processing. In the region expansion processing, the region expansion processing unit 302 performs region expansion processing on the calcification candidate region using the CT value range for region expansion processing as an integration condition, and extracts a calcification region (step S3). Specifically, first, the region expansion processing unit 302 sets all voxels constituting the boundary portion of the calcification candidate region as seed points. The voxels in the vicinity of 26 from each seed point are searched, and the neighboring voxels satisfying the integration condition are integrated. The integration condition is set as shown in (1) based on the CT value p of the neighboring voxels and the maximum CT value pmax of the threshold range, for example.
p ≧ pmax / 2 (1)
The maximum CT value pmax in the threshold range in equation (1) is set to 700 HU when the spatial resolution is 1.0 mm. Therefore, p ≧ 350.

  When the voxel integration is finished, a plurality of regions are usually generated. Of the plurality of generated regions, a region that does not satisfy the continuity requirement is removed as an isolated point.

  By combining the above threshold processing and region expansion processing, the calcified region specifying unit 30 can specify the calcified region included in the non-contrast volume data with high accuracy.

  When the region expansion process is performed, the control unit 42 causes the calcified region enhancement unit 32 to perform the calcified region enhancement process (step S4). In the enhancement process of the calcification area, the calcification area enhancement unit 32 emphasizes the calcification area included in the contrast volume data based on the position of the calcification area extracted from the non-contrast volume data.

  FIG. 3 is a diagram illustrating a process of emphasizing the calcification region CCR included in the contrast volume data CV based on the calcification region NCR extracted from the non-contrast volume data NV. As illustrated in FIG. 3, the contrast volume data CV includes many regions FR that are overestimated as being calcified regions because they are not actually calcified regions due to the partial volume effect. The non-contrast volume data NV also includes an overestimated region due to the partial volume effect, but the size is sufficiently smaller than the size of the overestimated region NV included in the contrasted volume data CV. In the enhancement process, first, the coordinate value of the calcified region NCR is acquired. Then, a pixel value or color information indicating the calcified region NCR is assigned to a voxel having the same coordinate value as the acquired coordinate value. Note that only a part of the calcified region NCR included in the contrast volume data CV, for example, an edge portion may be emphasized.

  When the calcified region enhancement processing is performed, the control unit 42 causes the three-dimensional image processing unit 34 to perform image generation processing (step S5). In the image generation process, the three-dimensional image processing unit 34 generates image data in which the calcified region is emphasized based on the contrast volume data in which the calcified region is emphasized. For example, image data is generated from volume data by volume rendering or surface rendering.

When the image is generated, the control unit 42 causes the stenosis rate calculation unit 36 to perform a stenosis rate calculation process (step S6). In the stenosis rate calculation process, the stenosis rate calculation unit 36 calculates the stenosis rate of the vascular region based on the diameter or area of the vascular region on the generated image and the diameter or area of the calcified region in the vascular region. calculate. For example, the stenosis rate S is calculated by the following equation (2) based on the area S1 of the calcified region and the area S2 of the blood vessel region on the image.
S = ((S1-S2) / S1) × 100 (2)
Further, the stenosis ratio S may be calculated by changing the area S1 of the calcified region of the formula (2) to the diameter R1 of the calcified region and the area S2 of the calcified region to the diameter R2 of the calcified region.

  When the stenosis rate calculation processing is performed, the control unit 42 causes the display unit 38 to perform display processing (step S6). In the display process, the display unit 38 displays an image in which the calcified region is emphasized and the stenosis rate of the blood vessel. The calcified area on the image is displayed with emphasis according to the assigned pixel value and color information. When only the edge portion of the calcified region is emphasized, the edge portion is highlighted and displayed.

  This completes the calcification area specifying / displaying process.

  According to the present embodiment, the calcified region is specified on the non-contrast volume data with little influence of the partial volume effect, and the calcified region included in the contrast volume data is emphasized based on the position information of the specified calcified region. And display. Therefore, it is possible to extract the calcification region with higher accuracy compared to the conventional case where the calcification region is specified on the contrast volume data having a large influence of the partial volume effect. Moreover, the calculation accuracy of the stenosis rate of the blood vessel is improved with the improvement of the extraction accuracy of the calcified region. Thus, according to the present embodiment, it is possible to provide an image processing apparatus and an image diagnostic apparatus that can improve the diagnostic accuracy of intravascular stenosis.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage.

  For example, the identification / display processing of the calcified region of the present embodiment is performed by using the control unit 42 as a center, the storage unit 28, the calcified region specifying unit 30, the calcified region enhancing unit 32, the three-dimensional image processing unit 34, and the stenosis rate calculation. The image processing apparatus 50 including the unit 36, the display unit 38, and the input unit 40 can also be implemented.

  In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is a diagram showing a configuration of an image diagnostic apparatus (X-ray computed tomography apparatus) according to an embodiment of the present invention. The figure which shows the flow of the identification / extraction process of the calcification area | region by the control part of FIG. The figure which shows the process which emphasizes the calcification area | region contained in contrast volume data based on the calcification area | region extracted from the non-contrast volume data based on step S4 of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Diagnostic imaging apparatus, 10 ... Gantry, 11 ... Rotating frame, 12 ... Top plate, 13 ... X-ray tube, 14 ... X-ray detector, 15 ... High voltage generator, 20 ... Computer apparatus, 22 ... Data collection part , 24 ... Pre-processing unit, 26 ... Reconstruction processing unit, 28 ... Storage unit, 30 ... Calcified region specifying unit, 301 ... Threshold processing unit, 302 ... Region expansion processing unit, 32 ... Calcified region emphasizing unit, 34 ... 3D image processing unit, 36 ... stenosis rate calculation unit, 38 ... display unit, 40 ... input unit, 42 ... control unit.

Claims (5)

A storage unit for storing first volume data relating to a blood vessel in which a subject is contrasted and second volume data relating to the blood vessel not being contrasted;
A specifying unit that specifies a calcified region included in the second volume data based on a pixel value;
An emphasizing unit for emphasizing the calcified region included in the first volume data corresponding to the identified calcified region;
A generating unit for generating image data based on the first volume data in which the calcified region is emphasized;
A display unit for displaying the generated image;
An image processing apparatus comprising:   The image processing according to claim 1, further comprising a calculation unit that calculates a stenosis rate of the vascular region based on a diameter or area of the vascular region on the image and a diameter or area of the calcified region occupying the vascular region. apparatus. The specific part is:
A threshold processing unit that performs threshold processing on the second volume data and extracts candidate regions of the calcification region;
A region expansion processing unit that identifies the calcified region by performing region expansion processing on the extracted candidate region;
The image processing apparatus according to claim 1, further comprising: An X-ray tube that generates X-rays;
An X-ray detector for detecting X-rays generated from the X-ray tube and transmitted through the subject;
Based on output data from the X-ray detector, a volume data generating unit that generates first volume data relating to the contrasted blood vessels of the subject and second volume data relating to the blood vessels not contrasted; ,
A specifying unit that specifies a calcified region included in the second volume data based on a pixel value;
An emphasizing unit for emphasizing the calcified region included in the first volume data corresponding to the identified calcified region;
An image generating unit for generating image data based on the first volume data in which the calcified region is emphasized;
A display unit for displaying the generated image;
An image diagnostic apparatus comprising:   The diagnostic imaging apparatus according to claim 4, further comprising a preprocessing unit that removes quantum noise included in the output data.

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