Ultrasonic blood vessel measurement apparatus and method

• US 20040116808A1
• Filed: 10/09/2003
• Published: 06/17/2004
• Est. Priority Date: 11/06/2002
• Status: Active Grant

• Current Assignee: CIT Lending Services Corp. (Illinois) (CIT Group Incorporated), FUJIFILM SonoSite, Inc. (Fujifilm Holdings Corporation)
• Original Assignee: CIT Lending Services Corp. (Illinois) (CIT Group Incorporated)
• Inventors: Fritz, Helmuth, Fritz, Terry
• Granted Patent: US 6,835,177 B2
• Time in Patent Office: Days
• US Class Current: 600/437
• CPC Class Codes: A61B 5/02007 Evaluating blood vessel condition, e.g. elasticity, compliance
• CPC Class Codes: A61B 8/0858 involving measuring tissue layers, e.g. skin, interfaces
• CPC Class Codes: A61B 8/461 Displaying means of special interest
• CPC Class Codes: A61B 8/467 characterised by special input means
• CPC Class Codes: A61B 8/565 involving data transmission via a network
• CPC Class Codes: G06T 2207/30101 Blood vessel; Artery; Vein; Vascular
• CPC Class Codes: G06T 7/0012 Biomedical image inspection
• CPC Class Codes: G06T 7/60 Analysis of geometric attributes

Abstract

An apparatus and method for determining the apparent intima-media thickness (IMT) of arteries through acquisition and analysis of ultrasound images comprising an array of pixel intensities. An acquired image may be referenced, determining threshold values relating to the intensity of pixels forming images of portions of an artery wall, particularly the lumen, media, and adventitia. A datum, or datums, may be established across multiple columns of pixels bounding the portion of the image containing either the lumen/intima boundary, the media/adventitia boundary, or both. The datums may be approximate the shape of one more of the lumen, intima, media, and adventitia. Within a bounded portion of the image, a method may search for intensity gradients having characteristics indicating the gradients represent probable locations of the lumen/intima and media/adventitia boundaries. A valid gradient may be identified by its proximity to a characteristic point on a graph of pixel intensities or to a datum line, by an intensity above or below a threshold, or both. An IMT measurement is calculated based on the location of the lumen/intima and media/adventitia boundaries. An IMT measurement may be adjusted for sloping or tapering of an artery wall. Taper adjustment may be accomplished by normalizing an IMT measurement based on a compiled database of IMT measurements relating the amount of taper with respect to location to characteristic IMT values.

Claims

1. A method for characterizing a blood vessel, having adventitia, media, and intima regions surrounding a lumen, by measuring the apparent intima-media thickness, the method comprising:

providing an image of a blood vessel, the image having a longitudinal direction substantially corresponding to an axial direction of a blood vessel, a lateral direction substantially orthogonal thereto, and comprising pixels each having an intensity associated therewith;

selecting a series of longitudinal positions and finding for each longitudinal position thereof the brightest pixel, having the greatest value of intensity with respect to other pixels positioned laterally therefrom;

defining an adventitia datum by fitting a first curve to the lateral positions of the brightest pixels over a domain of the longitudinal positions;

defining a lumen datum by fitting a second curve to lateral locations of the lumen substantially closest toward the adventitia and corresponding to the longitudinal positions;

defining a media datum by fitting a third curve to pixels, a plurality of which correspond to the location of local minima distributed in a longitudinal direction and positioned between the lumen datum and the adventitia datum;

locating the lumen-intima boundary, extending along the longitudinal direction, as the lateral location of local steepest ascent of intensity in a traverse from the lumen datum toward the media datum;

locating the media-adventitia boundary, extending along the longitudinal direction, as the lateral location of local steepest ascent in intensity in a traverse from the media datum toward the adventitia datum; and

calculating the intima-media thickness as the lateral distance between the lumen-intima boundary and the media-adventitia boundary.

2. The method of claim 1, further comprising calibrating the image to provide a measure of distance longitudinally and laterally.

3. The method of claim 1, wherein defining the media datum further comprises fitting a third curve to additional pixels chosen due to location thereof at a distance limit from at least one of the adventitia datum and lumen datum.

4. The method of claim 3, wherein the distance limit is half the distance from the adventitia datum to the lumen datum.

5. The method of claim 1, wherein at least one of the first, second, and third curves is a piecewise fit curve.

6. The method of claim 5, wherein at least one of the first, second, and third curves is fit by a piecewise function selected from a polynomial, a trigonometric function, and an exponential function.

7. The method of claim 6, wherein the piecewise function is a polynomial of an order greater than one.

8. The method of claim 7, wherein the order is greater than two.

9. The method of claim 1, wherein the second curve is a translation of the first curve to a location laterally spaced from the adventitia and at which each pixel thereof has an intensity substantially corresponding to the intensity of the lumen in the image.

10. The method of claim 9, wherein the intensity of pixels corresponding to the lumen datum is a value selected to be above the value of the lowest level of intensity in the image, and above the value of intensity of substantially all pixels corresponding to the lumen proximate the lumen datum and located on a side thereof opposite the adventitia datum.

11. The method of claim 1, wherein the lumen datum corresponds to pixels, each bounded laterally opposite the adventitia by at least three adjacent pixels each having a value of intensity not greater than that of the pixel corresponding thereto in the lumen datum.

12. The method of claim 11, further comprising defining a lumen threshold value corresponding to the lowest value of intensity in the image plus a fraction of the difference of intensity between the highest value of intensity and the lowest value of intensity in the image.

13. The method of claim 1, wherein each pixel corresponding to the lumen datum has an intensity not greater than a lumen threshold value between the intensity of pixels corresponding to the minimum value of intensity in the image and the intensity of pixels corresponding to the maximum value of intensity in the image.

14. The method of claim 13, wherein the lumen threshold value corresponds to a preselected fraction of intensity difference, between that of the adventitia datum and the lumen datum, above the intensity corresponding to the lumen datum.

15. The method of claim 14, wherein the fraction is from about 5 percent to about 25 percent.

16. The method of claim 15, wherein the second curve is the first curve, translated laterally to a position substantially within the portion of the image corresponding to the lumen.

17. The method of claim 1, wherein the second curve has the same shape as the first curve, simply translated laterally to a location at which the intensity of each pixel corresponding thereto is substantially less than a value selected to correspond to an intensity of pixels in the portion of the image corresponding to the lumen.

18. The method of claim 1, wherein the second curve is fit to the lateral positions of pixels having a threshold value of intensity in the image and are bounded by adjacent pixels, on a side thereof opposite the adventitia datum, having substantially no greater value of intensity.

19. The method of claim 1, wherein the third curve comprises a fit of lateral positions of pixels each having a value of intensity representing a local minimum with respect to the lateral direction.

20. The method of claim 19, wherein the local minimum is bounded by a lumen threshold and an adventitia threshold.

21. The method of claim 19, wherein the lateral location of the local minimum is selected to correspond to a pixel found within half the distance from the adventitia datum to the lumen datum.

22. The method of claim 1, further comprising locating a lumen threshold representing a value of intensity proximate the intensity of the minimum value of intensity in a sampling region and an adventitia threshold proximate a value of intensity proximate the minimum value of intensity of pixels in a sampling region.

23. The method of claim 22, wherein the lumen threshold and adventitia threshold differ from the intensity of the minimum value of intensity and the maximum value of intensity, respectively, by a value corresponding to a fraction of the difference between the maximum value of intensity and the minimum value of intensity.

24. The method of claim 23, wherein the preselected value is from about 5 percent to about 25 percent.

25. The method of claim 24, wherein the preselected value is about 10 percent.

26. The method of claim 23, wherein the locations of steepest ascent of intensity are limited to a region of the image containing pixels having intensities between the lumen threshold and the adventitia threshold.

27. The method of claim 26, wherein the third curve is a curve fitted to lateral locations of pixels corresponding to local minimum values of intensity along the longitudinal direction.

28. The method of claim 27, wherein the media datum is adjusted to include only locations of pixels on the third curve or closer to the lumen datum, and each location of a pixel contributing to the third curve and lying between the third curve and the adventitia datum is replaced with the corresponding lateral location on the third curve.

29. A method for finding an intima-media thickness associated with a blood vessel, the method comprising:

providing an image having a longitudinal direction substantially corresponding to an axial direction of a blood vessel and a lateral direction across the axial direction;

the image further comprising locations distributed longitudinally and laterally, each location having an intensity associated therewith and positioned at a unique combination of lateral and longitudinal locations;

selecting a series of longitudinal positions along the longitudinal direction and determining for each such longitudinal position a lateral position at which the image has the greatest intensity;

defining an adventitia datum by fitting a first curve to a range of the lateral positions and a domain of the longitudinal positions;

determining the lateral location of the lumen by identifying for at least one of the longitudinal positions a position corresponding to the lumen;

locating the lumen-intima boundary, extending along the longitudinal direction, as the lateral location of local steepest ascent in intensity, proximate the lateral location of the lumen, in a traverse from the lateral location of the lumen toward the adventitia datum;

locating the media-adventitia boundary, at a plurality of the series of longitudinal positions, as the lateral location of local steepest ascent in intensity, proximate the adventitia datum, in a traverse from the lateral location of the lumen toward the adventitia datum;

calculating the intima-media thickness as the lateral distance between the lumen-intima boundary and the media-adventitia boundary.

30. The method of claim 29, wherein the lateral location of the lumen is determined by identifying the lateral location of at least one pixel having a value of intensity proximate the lowest value of intensity in the image, and being near the adventitia.

31. The method of claim 29, wherein the first curve is a piecewise fit curve.

32. The method of claim 31, wherein the piecewise element used to fit the first curve is selected from a polynomial, a trigonometric function, and an exponential function.

33. The method of claim 32, wherein the piecewise element is a polynomial of greater than first degree.

34. The method of claim 29, further comprising finding a locally high rate of change of intensity as a function of lateral position between the adventitia threshold and the lumen threshold.

35. The method of claim 29, further comprising defining a lumen threshold and adventitia threshold to limit a search for at least one of a local minimum, local maximum, and rate of change of intensity.

36. The method of claim 35, further comprising defining the adventitia threshold as corresponding to a first fraction of a difference between the maximum intensity and the minimum intensity of pixels lying in a portion of the image containing the media/adventitia and lumen/intima boundary

37. The method of claim 35, further comprising defining a lumen threshold corresponding to a second fraction of a distance laterally between the adventitia datum and the lumen datum.

38. The method of claim 29, wherein the second curve is the first curve, translated laterally.

39. The method of claim 38, wherein determining the lateral location of the lumen comprises defining a measurement region having a rectangular shape and surrounding a portion of a wall of an artery and identifying an edge of the measurement region lying in the lumen as the lateral location of the lumen.

40. A method for finding an intima-media thickness associated with a blood vessel, the method comprising:

providing an image having a longitudinal direction substantially corresponding to an axial direction of a blood vessel and a lateral direction across the axial direction, and comprising locations, distributed longitudinally and laterally, uniquely positioned, and each having an intensity associated therewith;

selecting a series of longitudinal positions along the longitudinal direction and determining for each such longitudinal position a lateral position at which the image has the greatest intensity;

defining an adventitia datum by fitting a first curve to a range of the lateral positions and a domain of the longitudinal positions;

determining the lateral location of the lumen with respect to the adventitia datum;

defining a lumen-intima boundary, and a media-adventitia boundary between the adventitia datum and the lumen;

calculating the intima-media thickness as the lateral distance between the lumen-intima boundary and the media-adventitia boundary.

41. A method for measuring the apparent intima-media thickness of an artery, the method comprising:

Providing an image of an artery wall having lumen, intima, media, and adventitia layers, the image comprising an array of pixels each having an intensity associated therewith and defining rows and columns of pixels with each column defining a longitudinal position and extending across lumen, intima, media, and adventitia layers and with each row defining a lateral position;

identifying an adventitia datum corresponding a curve fit to the lateral position of high intensity pixels in a plurality of columns;

identifying a bounding location, with portions of the lumen, intima, media bounded laterally between the bounding location and the adventitia datum;

identifying a first relatively large intensity gradient proximate the adventitia datum, in a plurality of columns, between the adventitia datum and the bounding location;

identifying a second relatively large intensity gradient proximate the bounding location, in a plurality of columns, between the adventitia datum and the bounding location;

calculating for each of a plurality of columns the lateral distance between the two intensity gradients; and

deriving from the lateral distances a value reflecting an intima-media thickness measurement.