JP4441588B2 - Image creation device for determining myocardial infarction - Google Patents

Description

The present invention performs magnetic resonance imaging in the imaging delay phase by injecting a magnetic resonance contrast agent into the subject, the image obtained by the photographing, automatically determined by image processing infarct size in the myocardium, intramyocardial The present invention relates to an image creation device for determining myocardial infarction , which displays results reflecting the infarct range and myocardial viability as numerical values and images .

  Ischemic heart disease is the leading cause of death in the US and Europe, and 70,000 people die annually in Japan due to ischemic heart disease. Myocardial infarction is a disease in which the myocardium becomes necrotic due to occlusion or severe stenosis of the coronary artery that supplies oxygen to the myocardium. In cases of acute myocardial infarction, both the infarcted myocardial region that has undergone irreversible necrosis and the ischemic myocardial region that is alive but cannot contract due to severe blood flow decline show decreased myocardial wall motion. Even if the movement of the myocardial wall is observed by echocardiography or cardiovascular angiography, the two cannot be distinguished. Because the infarcted myocardial region has undergone irreversible necrosis, there is no therapeutic effect even if coronary revascularization is performed, but the ischemic myocardial region can be expected to improve the wall motion function by coronary revascularization, It is very important to accurately distinguish between the two in order to provide appropriate treatment.

  Thus, in the medical treatment of myocardial infarction patients, it is extremely important to accurately evaluate the position and spread of the infarcted myocardium. So far, nuclear medicine examinations have been mainly used as diagnostic imaging methods for myocardial infarction, and infarct lesions are recognized as defects in myocardial perfusion scintigraphy using thallium and technesium preparations. However, in the nuclear medicine technique, it is difficult to accurately evaluate the diagnosis of subintimal infarction and the extent of the infarct lesion in the wall due to the limitation of spatial resolution. Electrocardiogram-synchronized magnetic resonance imaging (MRI) of the heart is excellent in spatial resolution and can accurately predict the presence of myocardial infarction and the spread within the myocardial wall (see, for example, Non-Patent Document 1).

Hajime Sakuma, et al, `` Acute Myocardial Infarction: Myocardial Viability Assessment in Patients Early-Comparison of Contrast-enhanced MR Imaging with Resting TI SPECT '', Radiology, January 2003, Vol.226, Number1, pp138-144

  It has been well known since the 1980s that the infarcted myocardium shows a high signal in contrast-enhanced MRI, but the myocardial contrast-enhanced MRI based on the conventional ECG-synchronized spin echo method has insufficient image quality and accurately captures the distribution of the infarcted myocardium. I couldn't. Recently, delayed contrast MRI using the inversion recovery method has been developed, and the image quality of myocardial contrast MRI has been dramatically improved, so that normal and infarcted myocardium can be clearly distinguished (Patent Document 1). reference). In contrast-enhanced MRI, infarct lesions from the acute phase to the chronic phase are clearly depicted as high-signal areas, and intimal, papillary muscle infarction, and right ventricular infarction can be easily diagnosed.

Japanese Patent Laid-Open No. 2004-24637

  In the infarcted myocardium, the extracellular fluid fraction in which the magnetic resonance contrast contrast agent is distributed increases with the necrosis of the myocardial cells and the cell membrane damage, and approaches 100% in the complete necrotic region. As a result, the contrast agent concentration in the infarct region is several times that of normal myocardium, and a clear high signal is shown in delayed contrast MRI. Chronic infarction showing fibrosis also shows a high signal because the myocardial cell component decreases and the extracellular fluid component relatively increases.

  It has been shown that the high-signal area in delayed contrast is in good agreement with the distribution of pathological infarcted myocardium by TTC staining. Since MRI has high spatial resolution, the intima and outer membrane edges of the myocardium are clearly depicted, and it is possible to diagnose myocardial viability from the thickness of the surviving myocardium that does not show delayed angiography. However, since the time required for the test is short, it can be clinically used as a routine test method. Regarding the effectiveness of contrast-enhanced MRI in diagnosing the extent of myocardial infarction and myocardial viability, the accumulation of evidence has recently progressed considerably, and the ratio of infarcted myocardial volume to the total myocardial volume (infarct occupancy rate) determines the treatment strategy. It is considered to be a very useful index.

However, at present, the determination of the myocardial infarction region in contrast-enhanced MRI is performed by a visual evaluation by a doctor, and it takes time to evaluate the image, and there is a problem that the result of the determination doctor varies. Therefore, the development of an image creation device for determining myocardial infarction that can quantitatively analyze and display the infarcted myocardial region in myocardial contrast MRI has been strongly desired.

  So far, visual evaluation has been used in determining the extent of myocardial infarction by contrast-enhanced MRI and determining myocardial viability. Divide the myocardium into a number of segments and calculate the ratio (%) of the thickness of the infarcted myocardium showing the contrast effect to the total thickness of the infarcted myocardium showing the contrast effect and the surviving myocardium not showing the contrast effect. Judgment is visually made every time, and if this ratio exceeds 50%, no effect can be expected even if treatment is performed, and if this ratio is small, it is indicated that the treatment is indicated for coronary revascularization.

However, since the conventional method is based on visual judgment, it is strongly influenced by the judgment person's experience and skill, and the result may vary depending on the threshold (window level) setting when displaying the image. is there. Furthermore, it is difficult to obtain a quantitative index such as the ratio of the infarcted myocardium in the entire myocardium and the weight of the infarcted myocardium by the visual determination method. There are academic presentations in which a certain threshold value is set and a region where the signal intensity exceeds the threshold value is determined as an infarcted myocardial region. However, there is a drawback that the range of the infarct region varies greatly depending on the threshold value setting. In addition, an image creation device for determining myocardial infarction that can effectively and quantitatively display the range of the infarct region from the myocardial intima side to the adventitia side has not been developed so far.

In order to solve this problem, the present inventors have studied a myocardial image processing method and a quantitative evaluation method of myocardial infarction region and myocardial viability, and have come to invent the present myocardial infarction determination image creation device. . In this apparatus, each image for each myocardial slice of electrocardiogram-synchronized magnetic resonance imaging (MRI) using a magnetic resonance contrast agent is first subjected to a V-filter (Variance dependent filter) process, and then subjected to a differentiation process. Further, thinning processing is performed to create a myocardial infarction determination image. The infarction determination image created for each myocardial slice is further divided into myocardial segments, and the myocardial infarction region and myocardial viability are obtained for each segment.

In this myocardial infarction determination image creation device, the myocardial infarction region and the myocardial viability determined for each segment of the myocardium are displayed in polar coordinates. Specifically, the base of the heart is placed around the apex, and the myocardial infarction occupancy rate on the intima side and the epicardium side of the infarcted myocardium is displayed in polar coordinates in a concentric manner for each angle divided from the side wall. To do.

The image creation device for determining myocardial infarction according to the present invention can automatically set the range of myocardial infarction and the range of surviving myocardium by the device itself instead of setting a threshold based on the subjectivity of the observer. did. Furthermore, has a thickness of myocardial infarction with viable myocardium, they quantitatively measures the percentage of the myocardial wall thickness, effectively function to quantify displaying a range extending to the outer membrane side from intramyocardial film side of the infarct area Therefore , as an image creation apparatus for determining myocardial viability in patients with myocardial infarction, accuracy and objectivity can be greatly improved as compared with a conventional image creation apparatus.

  Embodiments of a quantitative evaluation method for myocardial infarction range and myocardial viability according to the present invention will be described below with reference to the drawings. By the way, in the quantitative evaluation method according to the present invention, a magnetic resonance contrast agent having a T1 shortening effect and distributed in the extracellular fluid is intravenously administered, and the contrast agent is sufficiently distributed to the extracellular fluid. It is intended for myocardial contrast-enhanced MRI obtained using a magnetic resonance imaging method having a T1 enhancement effect such as a recovery method or a saturation recovery method.

  First, a method for quantitatively analyzing the range of myocardial infarction in myocardial contrast-enhanced MRI will be described (see FIG. 1). In contrast-enhanced MRI, the intima and adventitia edges of the myocardial wall of the left or right ventricle are detected, and the region of interest (ROI) for the entire myocardial region is set. Next, in order to quantitatively automatically extract the boundary between the surviving myocardium and the infarcted myocardium showing a high signal, V-filter processing is performed.

  The V-filter is a filter that performs smoothing while preserving the boundary. As shown in FIG. 3, the neighborhood of the target pixel is divided into four regions, and the average and variance are calculated in each region. An area where the variance is minimized is selected, and the average value is assigned to the target pixel. Since the selection area is clearly switched on both sides of the boundary, a sharp boundary can be obtained. By performing V-filter processing, noise is removed, the boundary is emphasized, and contour extraction becomes easy. Further, the V-filter processing has a feature that image change is reduced even if the threshold setting at the time of differentiation processing described later varies slightly.

  The image subjected to the V-filter processing is subjected to differentiation processing in order to detect the boundary between the normal myocardium and the necrotic myocardium. The contour of the infarcted heart muscle and the normal heart muscle in contrast-enhanced MRI of the myocardium is a portion where the signal strength of the image changes, and a differential operation for extracting the signal change is used for contour extraction. In order to obtain the first derivative for the image, the differential values in the x direction and the y direction are calculated using the Sobel differential operator shown in equations 1 and 2.

Here the f _x differential value in the x direction, the f _y a differential value in the y direction. After obtaining the differential value in both directions, the differential value f _xy obtained by combining the x and y directions is calculated according to Equation 3. F _xy is calculated for each pixel of the image to create a differential image. The total differential operator is 0, and the output is 0 in a flat region. Therefore, an area with a signal change, that is, an outline area is drawn.

  Next, contour extraction is performed using a binary image by image threshold processing after differentiation. When performing contour extraction, since the obtained contour is not one pixel wide, a one pixel wide contour is created by thinning processing. If it matches any of the eight patterns shown in FIG. 4, the target pixel is deleted. By repeating this process until there are no more pixels that match the pattern in FIG. 3, the region having a plurality of pixel widths is deleted from the outside to create a one-pixel width contour.

  Next, the intramural distribution of the infarcted myocardium and the surviving myocardium determined by the above method is effectively displayed for the multi-slice contrast MRI covering the entire myocardium, and the myocardial infarction from the intima side to the adventitia side A method of depicting the spread of the image will be described with reference to FIG.

  The infarcted myocardium calculated by the above method for delayed contrast MRI can be displayed on one image by displaying polar coordinates. The polar coordinate display of the myocardial infarction has an advantage that not only the distribution of the myocardial infarction of the entire myocardium can be evaluated at a time but also the correspondence with the coronary artery is easy.

  The method of displaying myocardial infarction lesions as polar coordinates as a myocardial blood flow defect is used in nuclear medicine, but MRI has high spatial resolution, so that the infarct region in the myocardium on the intima side and epicardium side that was difficult with nuclear medicine Can be evaluated separately. Myocardial infarction tends to occur on the intima side and spreads toward the adventitia side as the infarct level increases. When the myocardial infarction has stopped below the intima, the epicardial myocardium is alive, so that improvement in cardiac function can be expected by treatment such as coronary revascularization.

  On the other hand, when the myocardial infarction spreads not only to the intima side but also to the adventitia side, since only a few surviving myocardium remains, a therapeutic effect such as coronary revascularization cannot be expected. For this reason, a display method that allows a clinician to accurately and easily recognize the range of the infarcted myocardium within the myocardial wall has a great advantage in the diagnosis of myocardial infarction. In addition, quantitatively displaying the total amount of infarcted myocardium and the total amount of surviving myocardium in myocardial infarction patients from contrast-enhanced MRI images is important information for predicting the improvement effect of the cardiac function of the entire left ventricle by treatment.

  The present inventors have invented a method for quantitatively and comprehensively displaying the distribution of myocardial infarction and the spread of the infarcted myocardium from the myocardial intima side to the outer membrane side. That is, after determining the infarct region using a V-filter, differential processing, and thinning processing, the side wall of the left ventricular myocardial region becomes 0 degree with the point set at the center of the left ventricular cavity of each slice as the center point. In this way, it is divided at an arbitrary angle (for example, every 10 °), the area in the infarct region with respect to the myocardial region at each angle is calculated, and the infarct occupation rate is calculated.

  This process is performed for each slice from the apex to the base, and the infarct occupancy in each myocardial region is displayed in polar coordinates. Next, scanning was performed radially from the center of the left ventricle, and each distance from the center to the intima and outer membrane ROIs was calculated at each angle, and the midpoint of both distances was obtained. After dividing the myocardium into endocardium and epicardium using the obtained midpoint of each angle, calculate the occupancy rate of each region, and display the polar coordinate display map of infarct occupancy rate on the endocardium and epicardium side create. Furthermore, the ratio (%) of the infarcted myocardium and the survival myocardium in the whole myocardium, and the ratio (%) of the infarct myocardium and the survival myocardium in the intima-side myocardium and the epicardial myocardium are displayed.

A delayed contrast-enhanced MRI was performed on a total of 14 cases of 9 males and 5 females for examination.
15 minutes or more after intravenous injection of Gd-DTPA (0.1-0.15 mmol / kg) using a 1.5T cardiac high-speed MR device (CV / i) manufactured by GE and a phased array coil for heart manufactured by GE as an MRI device After the lapse of time, imaging was performed while breathing was stopped. An inversion recovery method (TR = 5.3 msec, TE = 1.3 msec, TI = 200-250 ms) was used for the imaging sequence, and imaging was performed with a slice thickness of 10 mm and an effective field of view of 34 cm × 34 cm.

  After identifying the intima and epicardium edges of the left ventricular myocardium and setting the region of interest (ROI) in the myocardial region, V-filter processing is performed to automatically detect the margin of the infarct region, and further differentiation and fine lines The contour of the infarct region was detected by performing the conversion process (see FIG. 1). After determining the infarct area, the set ROI was divided every 10 °, the area in the infarct area with respect to the myocardial area at each angle was calculated, and the infarct occupancy was calculated (FIG. 2). This process was performed for each slice from the apex to the base, and the infarct occupancy rate in each myocardial region was displayed in polar coordinates. Further, a radial scan was performed from the center of the left ventricle, and each distance from the center to the intima and outer membrane ROI was calculated at each angle, and the midpoint of both distances was obtained. After dividing the myocardium into endocardium and epicardium using the obtained midpoint of each angle, calculate the occupancy rate of each region, and display the polar coordinate display map of infarct occupancy rate on the endocardium and epicardium side Created.

<Case 1>
FIG. 5 shows the output result of the myocardial infarction determination image creation apparatus according to the present invention for the case after the lower wall infarction / reperfusion treatment on day 6 after the onset . In the polar coordinate display map showing the infarct occupancy ratio for the whole myocardium, it is clearly recognized that the infarct region is distributed on the lower wall. The infarct occupancy was 13.9% in all myocardial regions, 20.9% on the endocardium side, and 7.9% on the epicardium side. Looking at the polar coordinate display map of the infarct occupancy rate on the endocardium and epicardium side, the infarct area of the lower wall is mainly distributed on the intima side, and the infarct occupancy rate on the epicardial side myocardium is relatively 7.9% It can be seen that the lower wall myocardial viability is relatively maintained.

  The influence of the conventional method (threshold method) and the present method (V-filter processing method) on obtaining the myocardial infarction occupancy rate from the MRI image will be described. As shown in FIG. 6, the present method can obtain the infarct occupancy rate almost without being affected by the set value of the threshold value and is excellent in accuracy compared with the conventional method (threshold method).

<Case 2>
FIG. 7 shows the output result of the myocardial infarction determination image creation device according to the present invention for the case of lower wall infarction on the 7th day after onset . The infarct occupancy rate in this case was 27.7% in the whole myocardial region, 30.7% on the endocardium side, and 24.7% on the epicardial side. This case has the same lower wall infarction as the case of FIG. 5, but in the polar coordinate display map of the infarct occupancy on the endocardium and epicardium side, the range of myocardial infarction extends to the epicardial side of the lower wall, It can be seen that the viability of the myocardium in the inferior wall has already been lost, and the effect of treatment such as coronary revascularization cannot be expected much.

  In other cases, by creating a local coordinate display map of infarct occupancy rate, the distribution of myocardial infarction and the spread within the wall are clearly shown, and this method is useful in diagnosing myocardial infarction patients and determining treatment strategies. Sex was confirmed.

<Summary>
In this method, if the margins on the intima side and the adventitia side of the myocardium are traced, the subsequent detection process of the infarcted myocardial region is automated. Therefore, the calculation of the infarcted myocardial range and the infarct occupancy rate can be performed quantitatively without depending on the interpreter as in the conventional visual diagnosis. In addition, by dividing the left ventricular myocardial region into endocardial and epicardial sides, it is possible to evaluate the distribution of the infarct region in more detail and present quantitative images that directly relate to the decision of the treatment policy. It became.

It is a figure which shows the flow of the process for the quantitative analysis of the infarction area | region in delayed contrast MRI. It is a figure which shows the infarction image and infarct range (infarct occupation rate) in each area | region of a myocardium. It is a figure which shows 4 area | regions near the attention pixel in V-filter process. It is a figure which shows 8 patterns which delete a focused pixel in thinning process. It is a figure which shows the infarction occupation rate in case 1. FIG. It is a figure which shows the comparison of this method (V-filter method) and the conventional method (threshold method) about the influence of the threshold value which acts on an infarction occupation rate. FIG. 4 is a diagram showing an infarct occupancy rate in case 2.

Claims (1)

Using gated magnetic resonance imaging (MRI) apparatus using a magnetic resonance imaging agent, an image operation NaruSo location for myocardial infarction determined to be subjected to determination of the myocardial infarction region and myocardial viability of myocardial,
A V-filter (Variance dependent filter) process is performed on the captured MRI myocardial image, a differential process is performed on the image after the V-filter process, and a thinning process is performed on the image after the differential process Through the process, an image for determining myocardial infarction is created,
Based on the myocardial infarction determination image, the myocardial infarction region and the myocardial survival rate are obtained for each segment of the myocardium,
The cardiac base is arranged on the outer periphery centered on the apex, and the occupancy rate of the myocardial infarction region on the intima side and the epicardial side of the myocardial infarction determination image is displayed in polar coordinates concentrically for each angle divided from the side wall. An image creation device for determining myocardial infarction as a feature.

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