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The subject matter described herein relates to systems and methods for analyzing carotid artery intima-media thickness (CIMT). More particularly, the subject matter relates to a system and method for automatically selecting end-diastolic ultrasound frames (EUFs) and determining regions of interest (ROIs) in ultrasound videos to screen for arterial pathology consistent with advanced atherosclerosis.
The CIMT technique is a noninvasive ultrasound test to investigate for sub-clinical atherosclerosis in patients for cardiovascular disease (CVD) risk assessment. CIMT is measured based on ROIs in the cardiac cycle timing at EUFs. In addition, increased CIMT may be an independent predictor of future cardiovascular events, including heart attacks, cardiac death, and stroke. In a CIMT exam, a high-resolution B-mode ultrasound transducer is applied on the patient's neck to image the common carotid artery (CCA). A sonographer manually selects the EUF of interest from the captured ultrasound video, and searches within each of the selected frames for the ROI where the combined thickness of intimal and medial layers of the CCA walls can be measured reliably. However, the manual selection of the EUFs and ROIs can be a tedious and time consuming process that demands specialized expertise and experience.
Published studies on CIMT measurements in animals and humans of varying ages have made it possible to develop a reference quartile range of progression of CIMT for “normal” and pathologic at different ages. Typically, the arterial intimal-medial thickness tends to increase with the age of the patient, and if present chronicity and intensity of risk factors for atherosclerosis. After the measurements are taken, the results are compared against the reference range and a report indicating the status of “vascular age” is generated. If the vascular age and quartile matches the chronological age or younger, then the patient is said to have no evidence of sub-clinical atherosclerosis and can be placed at a lower risk for the possibility of future cardiovascular events. However, if the vascular age and quartile is greater than the chronological age reference range values, the patient is said to have evidence of sub-clinical atherosclerosis and can be vulnerable to increased possibility of future CVDs and therefore precautionary measures should be taken.
As previously described, measurement of CIMT and estimation of vascular age can be a tedious task. The accuracy and speed of CIMT measurement and estimation often varies depending on the users' experience and level of expertise. In addition, inadequate familiarity can prolong the reading time of ultrasound videos, thus leading to increased human efforts and decreased performance.
Therefore, there is a need for systems and methods to automatically and/or semi-automatically select EUFs and determine ROIs in ultrasound videos to provide a more user-friendly and less time consuming solution to interpret CIMT measurements.
The present disclosure describes embodiments that overcome the aforementioned drawbacks by providing a system and method that reduces CIMT interpretation time by automatically selecting EUFs and determining ROIs in ultrasound videos. EUFs are selected based on the QRS complex of the electrocardiogram (ECG) signal associated with the ultrasound video, and the ROI is detected based on image intensity and curvature of the carotid artery bulb. Once an EUF is selected and its corresponding ROI is determined, the system measures CIMT using active contour models (i.e., the snake algorithm) extended with hard constraints by computing the average thickness and maximum thickness. The vascular age may then be calculated and a patient report may be generated.
In accordance with one aspect, a method for automatically selecting ultrasound frames and regions of interest of an artery of a subject includes acquiring an imaging data set from a portion of the subject including the artery. A look up table is generated to map a plurality of ultrasound frames to a location in an electrocardiogram (ECG) signal. The imaging dataset is processed to identify, using the look up table, the plurality of ultrasound frames. The regions of interest of the artery are detected by identifying a region of the artery defined by artery edges. Using an algorithm, a thickness of the artery is calculated using the identified plurality of ultrasound frames and regions of interest of the artery. A report is generated related to the thickness of the artery of the subject.
In accordance with another aspect, a system for automatically selecting ultrasound frames and regions of interest of an artery of a subject is provided. The system includes an imaging data set acquired from a portion of the subject including the artery. A look up table is provided to map a plurality of ultrasound frames to a location in an electrocardiogram (ECG) signal. A processor is configured to process the imaging dataset to identify, using the look up table, the plurality of ultrasound frames. The processor is further configured to detect the regions of interest of the artery by identifying a region of the artery defined by artery edges and calculate, using an algorithm, a thickness of the artery using the identified plurality of ultrasound frames and regions of interest of the artery to generate a report related to the thickness of the artery of the subject.
The foregoing and other aspects and advantages of the disclosure will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration one embodiment. Such embodiment does not necessarily represent the full scope of the disclosure, however, and reference is made therefore to the claims and herein for interpreting the scope of the disclosure.
Referring particularly to
The transmitter 13 drives the transducer array 11 such that the ultrasonic energy produced is directed, or steered, in a beam or pulse. A B-scan can therefore be performed by moving this beam through a set of angles from point-to-point rather than physically moving the transducer array 11. To accomplish this, the transmitter 13 imparts a time delay (Ti) to the respective pulses 20 that are applied to successive transducer elements 12. If the time delay is zero (Ti=0), all the transducer elements 12 are energized simultaneously and the resulting ultrasonic beam is directed along an axis 21 normal to the transducer face and originating from the center of the transducer array 11. As the time delay (Ti) is increased, the ultrasonic beam is directed downward from the central axis 21 by an angle θ. A sector scan is performed by progressively changing the time delays Ti in successive excitations. The angle θ is thus changed in increments to steer the transmitted beam in a succession of directions.
Referring still to
To simultaneously sum the electrical signals produced by the echoes from each transducer element 12, time delays are introduced into each separate transducer element channel of the receiver 14. In the case of the linear transducer array 11, the delay introduced in each channel may be divided into two components, one component is referred to as a beam steering time delay, and the other component is referred to as a beam focusing time delay. The beam steering and beam focusing time delays for reception are precisely the same delays (Ti) as the transmission delays described above. However, the focusing time delay component introduced into each receiver channel is continuously changing during reception of the echo to provide dynamic focusing of the received beam at the range R from which the echo signal emanates.
Under the direction of the digital controller 16, the receiver 14 provides delays during the scan such that the steering of the receiver 14 tracks with the direction of the beam steered by the transmitter 13 and it samples the echo signals at a succession of ranges and provides the proper delays to dynamically focus at points P along the beam. Thus, each emission of an ultrasonic pulse results in the acquisition of a series of data points that represent the amount of reflected sound from a corresponding series of points P located along the ultrasonic beam.
The display system 17 receives the series of data points produced by the receiver 14 and converts the data to a form producing the desired image. For example, if an A-scan is desired, the magnitude of the series of data points is merely graphed as a function of time. If a B-scan is desired, each data point in the series is used to control the brightness of a pixel in the image, and a scan comprised of a series of measurements at successive steering angles (θ) is performed to provide the data necessary for display of an image.
Referring particularly to
The beam forming section 101 of the receiver 14 includes separate receiver channels 110. Each receiver channel 110 receives the analog echo signal from one of the TGC amplifiers 105 at an input 111, and it produces a stream of digitized output values on an “I” bus 112 and a “Q” bus 113. Each of these I and Q values represents a sample of the echo signal envelope at a specific range (R). These samples have been delayed in the manner described above such that when they are summed at summing points 114 and 115 with the I and Q samples from each of the other receiver channels 110, they indicate the magnitude and phase of the echo signal reflected from a point P located at range R on the steered beam (θ).
Referring still to
For example, a conventional ultrasound image may be produced by a detection processor 120 that calculates the magnitude M of the echo signal from its I and Q components:
M=√{square root over (I2+Q2)}. (1)
The resulting magnitude values output at 121 to the display system 17 result in an image in which the magnitude of the reflected echo at each image pixel is indicated.
This embodiment is implemented by a mechanical property processor 122 that forms part of the mid-processor 102. As will be explained in detail below, this processor 102 receives the I and Q beam samples acquired during a sequence of measurements of the subject tissue (i.e., artery) and calculates a mechanical property (i.e., thickness) of the tissue.
Referring now to
At process block 304, EUFs are detected automatically from the acquired ultrasound video at process block 302 for CIMT measurement and analysis. The EUF detection may be based on an electrocardiogram, for example. Typically, the ultrasound test for CIMT is performed with electrocardiography. To establish correspondences between imaging and electrocardiography data, a user interface 400, as shown in
The LUT may be generated by subtracting every two consecutive ultrasound frames 402 and indexing a resultant edge segment with the corresponding frame number. Given two frames 402 captured at time t and t+1, the subtraction image contains a small curvelet from the ECG signal 404, which had been masked out by the cardiac cycle indicator 406 in the frame at time t. The location of each curvelet and the corresponding frame number t may be stored in the lookup table. Repeating this procedure for all consecutive frames results in a number of curvelets, which are further concatenated to form a reconstructed ECG signal 500, as shown in
Returning to
The ROI 408 detected at process block 310 encompasses the segment where the CIMT is to be measured, for example. In one non-limiting example, the ROI 408 may form a rectangle having a length of about 1 cm and a height of about 0.65 cm corresponding to 92 pixels by 60 pixels. The ROI 408 may be identified automatically within the chosen EUF, and include the far wall of the distal 1 cm, for example, of the CCA where the plaques normally develop. As shown in
Still referring to
The user interface 400 shown in
Returning again to
Thus, the image may be preprocessed by median and Gaussian filtering, for example, and applying canny edge detection techniques to generate an edge map 422, as shown in
Referring to
In some embodiments, the CIMT measurement may performed after the EUF and ROI are determined. The measurement involves Carotid intima-media border detection, CIMT mean, minimum and maximum measurements and vascular age calculation. The work for border detection is a variant of the snake model with hard constraints. The hard constraint mechanisms force the snake model to pass through certain positions or take certain shapes, so that anatomic intricacies can be clearly measured and delineated with simple user interactions. This enables the user to easily adjust the border based on experience and judgment. As previously described, the length of the ROI may be 1 cm, which comprises 92 pixels. The intima-media thickness is the perpendicular distance between the (two borders of the wall) media-adventitia border and the lumen-intima border within the ROI, thereby obtaining 92 lengths corresponding to the 92 pixel points. The mean, maximum and the minimum CIMT from these lengths are then calculated.
Referring once again to
Thus, the above described system and method allows for automatic EUF and ROI detection in an ultrasound video for CIMT measurement. The EUFs are selected based on the QRS complex of the ECG signal associated with the ultrasound video, and the ROIs are detected based on image intensity and curvature of the carotid artery bulb. The method for automatic ROI and EUF detection has proven to be fast, reliable, and easy to use. The method is interactive and enables the user to modify the obtained detections. The system and method also reduce user-dependency by automating the CIMT measurement process. Thus, the system and method saves a significant amount of reading time in the process for CIMT measurement, thereby decreasing human efforts when incorporated into ultrasound systems by reducing the effective reading time and user dependency.
The present disclosure has been described in terms of one or more exemplary embodiments, and it should be appreciated that many equivalents, alternatives, variations, and modifications, aside from those expressly stated, are possible and within the scope of the disclosure.
This application claims the benefit of the filing date of U.S. provisional patent application Ser. No. 61/954,386 entitled “SYSTEM AND METHOD FOR MEASURING ARTERY THICKNESS USING ULTRASOUND IMAGING” filed Mar. 17, 2014, the entire contents of which are incorporated by reference herein for all purposes.
Filing Document | Filing Date | Country | Kind |
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PCT/US2015/020908 | 3/17/2015 | WO | 00 |
Number | Date | Country | |
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61954386 | Mar 2014 | US |