Patent Application
20050267365
This invention relates generally to medical diagnostic systems. In particular, the present invention relates to methods and apparatus for acquiring and processing diagnostic data sets to identify the location of the transition between different types of tissue and between tissue and blood.
Coronary artery disease (CAD) has many known causes. The early detection and treatment of significant occlusive CAD before infarction is an important goal in reducing the downstream consequences of CAD. Many variables contribute to vascular health and may prove useful in the search for early markers of at-risk individuals. For example, echocardiography has the ability to measure one of the most important of the early markers, atherosclerotic burden. Atherosclerotic burden may be measured crudely during transesophageal echocardiography of the aorta. Further, as usually performed in clinical practice, the detection of plaque is qualitative at best, making it unlikely that robust data can be derived for early detection of preclinical artherosclerosis. Far more carefully studied is high resolution B-mode ultrasound scanning of the carotid arteries with measurement of intima-medial thickness (IMT). This test has been a mainstay of epidemiologic investigations of coronary and cerebrovascular disease for decades. Excellent data document the validity of using carotid findings to predict the state of the coronary circulation, and carotid IMT both detects patients with current disease as well as accurately predicting future cardiac and cerebrovascular events. Carotid IMT measurements have been proven to provide incremental data to traditional risk prediction based on clinical data. It is the only imaging test recommended by the American Heart Association for this purpose . Ultrasound imaging allows precise measurement of the total intima and media thickness of large- and medium-size peripheral arteries like the carotid, femoral, or radial arteries. The most common method to measure IMT is based on high-resolution B-mode imaging. Repeated and averaged manual measurement is relatively easy to perform, but is operator-dependent and of poor reproducibility. An accurate measurement with excellent reproducibility can be achieved only by using computer-assisted automatic methods.
Ultrasound imaging permits precise measurement of the total intima and media thickness of large and medium-size peripheral arteries, for example, the carotid, femoral, or radial arteries. At least some known methods to measure IMT are based on high-resolution B-mode imaging using repeated and averaged manual measurement. Manual measurement from B-mode images is relatively easy to perform, however, the results are operator-dependent and often of poor reproducibility. Other imaging modalities also may acquire vascular or cardiac images, but experience the same problems. In addition, it would be beneficial to more precisely identify and measure the interface between two types of tissue in other anatomy or masses of interest, such as the liver, heart, cysts and tumors.
In one embodiment, a method for measuring an anatomic structure based on at least one medical diagnostic image frame using an integrated ultrasound device is provided. The image frame includes a first axis that is substantially parallel to an intima-media and a second axis that is perpendicular to the first axis. The method includes identifying a first interface of the anatomic structure based on an intensity of the interface in an image frame, for a plurality of points on the first interface, identifying a corresponding point on a second interface of the anatomic structure using a predetermined threshold based on the intensity of the first interface, determining a distance difference between points of the first interface and a corresponding point of the second interface, and outputting at least one of the determined distance difference and the at least one image frame to a display.
In another embodiment, an integrated ultrasound device is provided. The device includes a transmitter for transmitting ultrasound signals into an area of interest, a receiver for receiving echo signals from transmitted ultrasound signals, a memory for storing at least one image frame including the echo signals, an electro-cardiograph gating (ECG) waveform and synchronization unit, a processor configured to process the at least one image frame to automatically identify at least one of a lumen-intima interface and a media adventia interface, and an output for outputting information based on an output of the processor.
In a further embodiment, a computer program embodied on a computer readable medium for controlling an integrated ultrasound device is provided. The program controls the integrated ultrasound device to measure an intima-media thickness (IMT) based on at least one medical diagnostic image frame that includes a first axis that is substantially parallel to the intima-media and a second axis that is perpendicular to the first axis. The program includes a code segment that prompts a user for at least one of the image frame and a selected region of interest, and then determines a first axis and second axis coordinate for a plurality of points on a media adventia interface, determines a first axis and second axis coordinate for a plurality of points on a lumen-intima interface, determines a distance difference between a point on the media adventia interface and a corresponding point on the lumen-intima interface, and outputs a statistical analysis of at least one of the plurality of points, the output includes at least one of an average IMT, an IMT standard deviation, an IMT maximal value, and an IMT minimal value.
Transducer 11 may be moved, such as along a linear or arcuate path, while scanning a region of interest (ROI). The scan planes 18 are stored in the memory 20, and then passed to a scan converter 42. Scan-converter 42 synchronizes the modules of ultrasound system 10. In some embodiments, the transducer 11 may obtain lines instead of the scan planes 18, and the memory 20 may store lines obtained by the transducer 11 rather than the scan planes 18. The scan converter 42 may store lines obtained by the transducer 11 rather than the scan planes 18. The scan converter 42 creates a data slice from a single scan plane 18. The data slice is stored in slice memory 44 and then passed to the video processor 50 and display 67. System 10 may facilitate measuring an anatomic structure within the region of interest in at least one of a real-time mode, a frame freeze mode, a cine-loop run mode, a VCR playback mode, and an ultrasound device internal archive single frame or loop frame playback mode.
An integral ECG waveform and synchronization unit 68 is coupled to a patient skin (not shown). ECG waveform and synchronization unit 68 uses a plurality of electrodes 70 to measure electrical current passing through a patient's body. The electrical current corresponds to the electrical activity of the patient's heart muscles, or the contraction and relaxation thereof. This current may be used to identify a cyclical portion of the heart's cycle, thus allowing blood-vessel data to be acquired during intervals that substantially correspond to a substantially similar portion of the heart's cycle when the blood vessel is in a substantially uniform position. A post-processor and intima-media thickness measurement calculator 72 may receive raw image data and/or scan converted data to identify structures of a blood vessel and automatically determine thicknesses of those structures. Post-processor and intima-media thickness measurement calculator 72 may also receive archive data from a data archive 74, such as a video cassette recorder (VCR) and/or a VCR play-back internal frame grabber unit, or other data storage device, which may be located locally to system 10, integral with system 10, or may be located remotely from system 10 and accessed over a data network (not shown). Post-processor and intima-media thickness measurement calculator 72 may transmit highlighting signals to display 67 to provide trace determined interfaces with a brighter pixel intensity and/or false color highlight of determined interfaces to aid an operator in determining accurate output.
The ultrasound system 100 also includes a signal processor 116 to process the acquired ultrasound information (i.e., RF signal data or IQ data pairs) and prepare frames of ultrasound information for display on display system 118. The signal processor 116 is adapted to perform one or more processing operations according to a plurality of selectable ultrasound modalities on the acquired ultrasound information. Acquired ultrasound information may be processed in real-time during a scanning session as the echo signals are received. Additionally, or alternatively, the ultrasound information may be stored temporarily in RF/IQ buffer 114 during a scanning session and processed in less than real-time in a live or off-line operation.
The ultrasound system 100 may continuously acquire ultrasound information at a frame rate that exceeds fifty frames per second, which is the approximate perception rate of the human eye. The acquired ultrasound information may be displayed on the display system 118 at a slower frame-rate. An image buffer 122 is included for storing processed frames of acquired ultrasound information that are not scheduled to be displayed immediately. The image buffer 122 may be of sufficient capacity to store at least several seconds worth of frames of ultrasound information. The frames of ultrasound information are stored in a manner to facilitate retrieval thereof according to its order or time of acquisition. The image buffer 122 may comprise any known data storage medium.
During a scan, a user may select a region of interest (ROI) 312 that includes a portion of an anterior wall 313 and/or a portion of a posterior wall 314 of a vessel, such as artery 300. A user may select a second ROI 316 that includes both a portion of anterior wall 313 and a portion of posterior wall 314 of the vessel, if the scan is to be performed using tissue motion synchronization. Tissue motion synchronization and electro-cardiograph gating (ECG) synchronization permits evaluation of frames captured at a fixed time relative to an oscillatory motion of a tissue, such as, a vein or artery wall, and heart wall, at a fixed time relative to a heart cycle. In the exemplary embodiment, the IMT measurement is performed at a selectable fixed point in time relative to the ECG waveform, for example, during end-diastole. System 10 can synchronize on any part of the ECG waveform received from the built-in ECG unit or from an external ECG waveform. The synchronization location is preselectable and automatic, but may be manually adjusted.
The synchronization discussed above may be selected by a user to be based on vessel-wall motion detection rather than on ECG waveform. The same IMT algorithm is used, in this case, to delineate both walls of artery 300 (anterior 313 and posterior 314). By measuring the distance between anterior wall 313 and posterior wall 314 as function of time, it is possible to follow the pulsatility of artery 300, and synchronize the frame-selection for an IMT measurement similarly to the synchronization to the ECG waveform.
System 10 may receive image data at a resolution greater than display is capable of displaying. For example system 10 may be able to obtain images with a 1200 pixel per inch resolution, but display 67 may only be capable of displaying 400 pixels per inch. System 10 may use the display resolution images to measure IMT and may selectably zoom display 67 to use the entire 1200 pixel per inch resolution available in the received image. Such a zoom feature facilitates an accurate IMT measurement. System 10 also configured to detect a zoom setting for each frame of image data, for example, live data, archived data, and frame grabbed data from a VCR playback. A user may retrieve image frame data from a plurality of image frame data sources, such as real-time data raw data, real-time data preprocessed data, frame freeze data, cine-loop data, and/or VCR playback data. When reviewing image frame data from various sources collected at widely varying timeframes, each image frame may be stored in different resolution setting with respect to each other image frame. Correlating image frames over time may be used while making a diagnosis, such that viewing image frames at different resolution settings may cause errors to be made. System 10 may selectably read the resolution setting and zoom setting of each image frame and automatically modify the resolution setting and/or zoom setting of each image frame to be consistent with respect to each other at a user-preferred selectable setting.
To facilitate imaging and the determination of the vessel IMT a contrast agent may be injected into the vessel prior to or during a scan. Generally, contrast is injected into the blood-stream passing through the vessel, such as artery 300, to facilitate enhancing visibility of the blood vessels and the vessel-borders delineation. The contrast agent also may enhance the visibility and delineation of “soft-plaque”, which may be non-reflective (i.e., has very dark gray shade) and may be difficult to distinguish from the surrounding blood filled lumen. The contrast agent facilitates sound reflection of the blood, such that the blood appears as a lighter gray shade and the relatively darker soft-plaque becomes more distinguishable and visible in the ultrasound image.
Method 400 includes calculating 402 an intensity histogram of an entire image frame or in a user selected region-of-interest (ROI). A user selected ROI should include a part of lumen 307 and adventitia 306 (shown in FIG. 3). Image frame intensity values may be normalized 404 based on the calculated histogram. Smoothing using, for example, a finite impulse response (FIR) filter is applied 406 laterally along the image in a direction of artery 300 (shown in
For each x-axis 407 coordinate, moving from the curve (adventitia 306) to lumen 307, the coordinates of media-adventitia interface 311 are determined 416 using a half-height of the correlated geometric pattern. For each x-axis 407 coordinate, an intensity vector along y-axis 411, for example, perpendicular to the determined adventitia, is determined from original ROI 312 or 316, starting from adventitia 306 and moving toward lumen 307. A second derivative of the vector is determined 420, and a threshold is applied to further delineate the interfaces. The value of the applied threshold is adjustable by the user as a sensitivity adjustment. Lumen-intima interface y-axis 411 coordinates at a second peak of the second derivation is determined 422. For the determined coordinates of lumen-intima interface 309 and media-adventitia interface 311, a median filter is applied 424 to remove singular noise. Best-fitting third order polynomial curves for the determined coordinates of lumen-intima interface 309 and media-adventitia interface 311 are determined, and the interface points are validated by removing 426 points that exceed a predetermined distance from the best fit curve.
For each x-axis 407 coordinate, if both lumen-intima interface 309 and media-adventitia interface 311 y-axis 411 coordinates are validated, the IMT is calculated as the difference between y-axis 411 coordinates of the lumen-intima interface point and media-adventitia interface point at that x-axis 407 coordinate. The difference may then be multiplied by an image-scaling factor. For each x-axis 407 coordinate, based on the polynomial fit of the adventitia interface, the slope angle of the adventitia with respect to lumen-intima interface 309 is determined 430 and the calculated IMT is corrected by multiplying by the cosine of the slope angle. Apply 432 standard statistical analysis to all validated points to determine, for example, but not limited to an average IMT, an IMT standard deviation, an IMT maximal value, and an IMT minimal value.
Method 400 may include injection of a contrast agent into the blood vessel to facilitate enhancing visibility and delineation of the vessel walls. When using a contrast agent, a plurality of initialization parameters may be modified or additional parameters set to indicate to the IMT algorithm that a contrast agent is being used and characteristic is relative to the particular contrast agent used.
A technical effect of various embodiments of the present invention is to automatically identify and measure an anatomical structure. Specifically, the system captures image frames of ultrasound data representing a region of interest. In one embodiment of the present invention, structures of a blood vessel are located, identified, and measured. Various methods of displaying the output of the structure and measurements are selectable to facilitate diagnosis.
While various embodiments the present invention have been described with reference to an integrated ultrasound scanner configured to automatically measure IMT in a blood vessel, numerous other applications are contemplated. It is contemplated that the method and systems of the present invention may be applied to other imaging modalities, such as MRI, and anatomic structure other than a blood vessel.
The above-described systems and methods of automatically measuring IMT in a blood vessel in an integrated ultrasound scanner are cost-effective and highly reliable for facilitating monitoring and diagnosing disease. More particularly, the methods and systems described herein facilitate identifying and determining a thickness of, for example, blood vessels in an integrated ultrasound scanner. As a result, the methods and systems described herein facilitate reducing healthcare costs in a cost-effective and reliable manner.
Exemplary embodiments of real-time integrated ultrasound systems and methods are described above in detail. However, the systems are not limited to the specific embodiments described herein, but rather, components of each system may be utilized independently and separately from other components described herein. Each system component also can be used in combination with other system components.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
