Split-screen display system and standardized methods for ultrasound image acquisition and processing for improved measurements of vascular structures
A standardized acquisition methodology assists operators to accurately replicate high resolution B-mode ultrasound images obtained over several spaced-apart examinations. The methodology utilizes a split-screen display in which the arterial ultrasound image from an earlier examination is displayed on one side of the screen while a real-time “live” ultrasound image from a current examination is displayed next to the earlier image on the opposite side of the screen. A computerized echo edge recognition and tracking methodology automatically identifies ultrasound echo boundaries of the intima-media complex and automatically extracts IMT and arterial dimension measurements, without introducing human measurement error. Measurement accuracy is enhanced by use of sub-pixel resolution for echo edge boundary definition. Utilizing this methodology, measurement of vascular dimensions, such as carotid arterial IMT and diameter, the coefficient of variation is substantially reduced to values approximating from about 1.0% to about 1.25%. Dynamic material properties of arterial structures are measured in a standardized region in accordance with a standardized methodology in order to promote measurement repeatability.
1. A method for obtaining vascular anatomical structure measurements, the measurements taken in substantially the same location of carotid arterial wall structure in each of a plurality of time-spaced-apart examinations, the method comprising:
obtaining a first ultrasound image of a longitudinal section of a carotid artery, the image including a carotid bulb portion as a reference location;
storing the first ultrasound image as a prior examination image in a memory store;
obtaining a second ultrasound image of a longitudinal section of a carotid artery, the image including a carotid bulb portion as a reference location;
displaying the second image in a first half of a split-screen display;
retrieving the first image from the memory store;
displaying the first image in a second half of the split-screen display;
manipulating an ultrasound transducer until the second image visually matches the first image; and
performing a vascular anatomical structure measurement on an arterial wall portion of the carotid distal to the carotid bulb on the first ultrasound image.
2. The method according to claim 1 , wherein each ultrasound image includes anatomical landmarks, including a portion of a carotid artery bulb structure, each ultrasound image further including an image of at least a length of a far wall portion of the carotid artery distal to the carotid artery bulb portion.
3. The method according to claim 2 , wherein the vascular anatomical structure measurement is an intima media thickness (IMT) measurement.
4. The method according to claim 2 , wherein the vascular anatomical structure measurement is an arterial diametric measurement.
5. The method according to claim 2 , wherein the vascular anatomical structure measurement is an arterial elasticity measurement.
6. A method for developing vascular characteristic measurements from ultrasound images, the method comprising:
processing vascular ultrasound images taken during the course of an ultrasound examination procedure on a video recorder;
storing vascular ultrasound images taken during the course of a previous ultrasound examination procedure on a mass data storage memory unit;
providing a digitizing and image processing system;
providing a computer processing unit coupled to the video recorder, mass data storage memory unit, and digitizing system; and
displaying a digitized vascular ultrasound image retrieved from the memory storage unit on one side of a split-screen display and displaying a digitized vascular ultrasound image taken from the video recorder on the other side of the split-screen display.
7. The method according to claim 6 , wherein an analysis engine is hosted on the computer processing unit, the method further comprising:
establishing an approximate boundary location of a first interface region of a portion of an arterial wall structure;
establishing an approximate boundary location of a second interface region of said portion of the arterial wall structure;
establishing an actual interface edge, for the first and second interface regions, within a plane region centered about the corresponding approximate boundary location; and
performing a vascular characteristic measurement calculation made with respect to the actual interface edges of the first and second interface regions.
8. The method according to claim 7 , wherein each ultrasound image is acquired in accordance with a particular standardized acquisition methodology by which a vascular characteristic measurement calculation is made on a substantially similar characteristic region of the far wall of a carotid artery.
9. The method according to claim 8 , wherein the particular standardized acquisition methodology comprises:
orienting a patient position such that a first side of the neck is exposed and the head is counter-rotated about 45 degrees;
positioning an ultrasound transducer so as to develop a transverse image view through a neck section chosen to contain a visualization of a carotid artery and a jugular vein; displaying the transverse view on a split-screen display;
manipulating transducer position and angulation until the jugular vein and carotid artery are displayed in a substantially vertical stack orientation, the stack defining an approximate vertical image line through a center of the jugular and a center of the carotid; and
rotating the transducer through about 90 degrees around the approximate vertical axis, so as to develop a longitudinal image view along a length of the carotid artery, while maintaining the jugular vein and the carotid artery in the substantially stacked orientation.
10. The method according to claim 9 , further comprising the step of manipulating transducer position so as to bring the real-time longitudinal view into congruence with the retrieved longitudinal view by visual comparison of the images displayed in the first and second half portions of the split-screen display.
11. The method according to claim 10 , further comprising
acquiring an ECG trace in simultaneous fashion with the acquisition of the real-time longitudinal image, an ECG trace being acquired in substantially similar fashion for the retrieved previously obtained longitudinal image; and
displaying the corresponding ECG trace with the respective longitudinal image, each ECG trace defining a time index such that real-time and previous longitudinal images are displayed at substantially the same time during a cardiac cycle.
12. The method according to claim 11 , wherein each ultrasound image includes anatomical landmarks, including a portion of a carotid artery bulb structure, each ultrasound image further including an image of at least a length of a far wall portion of the carotid artery distal to the carotid artery bulb portion.
13. The method according to claim 12 , wherein the vascular anatomical structure measurement is an intima media thickness (IMT) measurement.
14. The method according to claim 12 , wherein the vascular anatomical structure measurement is an arterial diametric measurement.
15. The method according to claim 13 , wherein each actual interface edge, for the first and second interface regions is determined to within a pixel resolution of the display.
16. The method according to claim 15 , wherein each actual interface edge, for the first and second interface regions is determined to within a sub-pixel resolution of the display.
17. The method according to claim 16 , wherein the establishing an approximate boundary location of the first and second interface regions further comprises:
identifying a first brightness transition region corresponding to said first interface region;
marking a plurality of pixel locations corresponding to said first brightness transition region;
identifying a second brightness transition region corresponding to said second interface region; and
marking a plurality of pixel locations corresponding to said second brightness transition region.
18. The method according to claim 17 , further comprising:
(automatically) fitting the plurality of pixel locations corresponding to said first brightness transition region with a curve defining the edge of the first brightness transition region;
fitting the plurality of pixel locations corresponding to said second brightness transition region with a curve defining the edge of the second brightness transition region; and
defining pairs of pixel points corresponding to vertically opposed regions of the first and second brightness transition regions.
19. The method according to claim 18 , further comprising:
calculating a separation distance between each of the pairs of pixel points corresponding to vertically opposed regions of the first and second brightness transition regions; and
statistically processing the separation distances so as to define a mean separation corresponding to an intima-media thickness.
20. The method according to claim 19 , wherein each image resides on a frame of the video recorder, the boundary processing performed on a particular frame, the method further comprising:
performing the separation distance calculation on a first frame;
performing the separation distance calculation on a second frame, sequentially acquired with respect to the first frame; and
statistically averaging the results of the two separation distance calculations.
21. A computer processing system for developing vascular characteristic measurements from ultrasound images, the system comprising:
a video recorder, the recorder temporarily storing vascular ultrasound images taken during the course of an ultrasound examination procedure;
a mass data storage memory unit, the memory storage unit storing vascular ultrasound images taken during the course of a previous ultrasound examination procedure;
a digitizing and image processing system;
a computer processing unit coupled to the video recorder, mass data storage memory unit, and digitizing system; and
a split-screen display system coupled to the computer processing unit, wherein the processing unit displays a digitized vascular ultrasound image retrieved from the memory storage unit on one side of the split-screen display and displays a digitized vascular ultrasound image taken from the video recorder on the other side of the split-screen display.
22. The system according to claim 21 , further comprising an analysis engine hosted on the computer processing unit, the analysis engine including:
means for establishing an approximate boundary location of a first interface region of a portion of an arterial wall structure;
means for establishing an approximate boundary location of a second interface region of said portion of the arterial wall structure;
means for establishing an actual interface edge, for the first and second interface regions, within a plane region centered about the corresponding approximate boundary location; and
a vascular characteristic calculation engine, the vascular characteristic calculation engine returning vascular characteristic measurement calculation made with respect to the actual interface edges of the first and second interface regions.