WO2002032307A1

WO2002032307A1 - Method and system for measuring dimensions of an organ

Info

Publication number: WO2002032307A1
Application number: PCT/IL2001/000959
Authority: WO
Inventors: Rami Evron; Tsuriel Assis; Ran Carmeli
Original assignee: Paieon Inc.
Priority date: 2000-10-18
Filing date: 2001-10-18
Publication date: 2002-04-25
Also published as: AU2002212642A1

Abstract

A method and system for measuring a distance d between a first point and a second point in an organ. The method comprises generating a three-dimensional reconstruction of the organ and a three-dimensional reconstruction of a calibration device. The calibration device bears two markers separated by a distance x1 The distance x2 between the markers in the reconstruction of the calibration device and the distance d1 between the two points in the reconstruction of the organ are then determined. The distance d is obtained in a calculation involving the distances x1, x2, and d1.

Description

METHOD AND SYSTEM FOR MEASURING DIMENSIONS

OF AN ORGAN

FIELD OF THE INVENTION

This invention relates to methods and systems for analyzing a computer reconstruction of an organ.

BACKGROUND OF THE INVENTION A diseased artery is often treated by insertion of a prosthesis such as a stent into the artery. Improper stent selection or its positioning within the artery may significantly increase the chance for re-narrowing of the artery and may even result in total blockage. In order to determine the characteristics of the appropriate stent, the dimensions of the stenosis (its diameter, length and cross section) must first be determined. Thus, accurate assessment of the severity of arterial disease, such as arterial stenosis or aneurysm, is a prerequisite for optimal treatment.

Imaging of an organ, such as an artery or other blood vessel or a urethra, usually involves introducing a radio-opaque substance into the organ. In the case of a blood vessel, an angiographer releases a contrast material, such as an iodine solution, from the tip of a catheter introduced onto the artery. The contrast material is carried from the catheter tip by the blood flow and an X-ray image of the arterial anatomy is obtained in the vicinity of the catheter tip. The catheter may also be designed to function as a calibration device by bearing two radio-opaque markers separated by a known distance. The markers may be separated, for example, by the outer diameter of the catheter, or a selected distance along the catheter axis. The calibration device is imaged together with the arteries, and the distance between the markers in the image is used to determine actual distances between features in the arterial anatomy. The actual dimensions of a stenosis may thus be calculated from its dimensions in the image. However, in order for this calculation to be accurate, it is first necessary to determine the angle between the line of the markers and the plane of the image, as well as the angle between the artery and the plane of the image.

U.S. Patent No. 4,671,291, discloses a catheter tip having at least three unevenly spaced radio-opaque bands along its length. The catheter tip is introduced into an artery and imaged together with the artery. By counting the number of bands that are individually identifiable in the image, the angle between the catheter tip and the image plane (which is equal to the angle between the artery and the image plane) can be calculated. This method, however, can only be used for calculating distances in the artery containing the catheter tip, and cannot be used for measuring other arteries in the image.

SUMMARY OF THE INVENTION The present invention provides a method and system for measuring the dimensions of an organ such as an artery or other blood vessel, or a urethra. The method is particularly useful in measuring the dimensions of a blood vessel abnormality such as a stenosis or aneurysm.

In accordance with the invention a three dimensional reconstruction of the organ and a three dimensional reconstruction of a calibration device are obtained. The organ and calibration device may be reconstructed in the same reconstruction or in different reconstructions. The calibration device may be, for example, part of a catheter or guide wire bearing radio-opaque markers separated by a known distance xi (measured for example in millimeters). For example, two radio-opaque markers may be placed diametrically opposite to one another on the circumference of a catheter tip. Typically, but not necessarily, in order to measure the dimensions of an abnormal artery, the calibration device is introduced into another artery in the same arterial tree containing the abnormal artery and positioned near the artery. After the calibration device has been positioned, at least two images of the organ and the calibration device are obtained from different perspectives. These images are used to generate the three-dimensional reconstructions of the organ and the calibration device as is known in the art. In the case that the organ is an artery, the three-dimensional reconstructions may be generated, for example, as disclosed in Applicant's co-pending U.S. Patent Application Serial No. 09/662,325 entitled "System and Method for Three-Dimensional Reconstruction of an Artery ", filed on September 14, 2000. The reconstructed organ and the reconstructed calibration device may be displayed on a display device, for example, a computer monitor screen, from any desired perspective. The distance x₂ between the markers on the calibration device in the reconstruction (typically measured in pixels) is determined. The ratio xι/ ₂ between the two distances xi and x₂ is a scaling factor that is used to determine the actual distance between two points in the organ from the distance in pixels between the points in the reconstruction. Two points are selected in the organ and the distance di between them in the reconstruction is determined. The actual distance d between the two points in the organ may then be calculated by

The present invention further provides a method for measuring a distance d between a first point and a second point in an organ, comprising:

(i) generating a three-dimensional reconstruction of the organ; (ϋ) generating a three-dimensional reconstruction of a calibration device, the calibration device bearing two markers separated by a distance xi; (iii) determining in the reconstruction of the calibration device a distance x₂ between the markers; (iv) determining in the reconstruction of the organ a distance di between the first and second points; and (v) obtaining the distance d in a calculation involving the distances xi,

X2, and di. The present invention also provides a system for measuring a distance d between a first point and a second point in an organ, comprising: (i) a calibration device bearing at least two markers, the markers being separated by a distance i; (ii) an imaging system configured to image the organ and the calibration device from at least two perspectives. (iii) a processor configured to:

(a) generate a three-dimensional reconstruction of the organ from two or more images of the organ obtained from different perspectives;

(b) generate a three-dimensional reconstruction of the calibration device from two or more images of the calibration device obtained from different perspectives;

(c) determine in a reconstruction of the calibration device a distance x₂ between the markers;

(d) determine in a reconstruction of the organ a distance di between the first and second points;

(e) determine the distance d in a calculation involving the distances

The present invention also provides a program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform method steps for measuring a distance d between a first point and a second point in an organ, the method comprising:

(i) generating a three-dimensional reconstruction of the organ from two or more images of the organ obtained from different perspectives; (ii) generating a three-dimensional reconstruction of a calibration device from two or more images of the calibration device obtained from different perspectives, the calibration device bearing two markers separated by a distance xi; (iii) determining in the reconstruction of the calibration device a distance X₂ between the markers; (iv) determining in the reconstruction of the organ a distance di between the first and second points; and (v) obtaining the distance d in a calculation involving the distances xi, X2, and di. The present invention further provides a computer program product comprising a computer useable medium having computer readable program code embodied therein for measuring a distance d between a first point and a second point in a tubular organ, the computer program product comprising: computer readable program code for causing the computer to generate a three-dimensional reconstruction of the organ from two or more images of the organ obtained from different perspectives; computer readable program code for causing the computer to generate a three-dimensional reconstruction of a calibration device from two or more images of the calibration device obtained from different perspectives, the calibration device bearing two markers separated by a distance xi; computer readable program code for causing the computer to determine in the reconstruction of the calibration device a distance ₂ between the markers; computer readable program code for causing the computer to determine in the reconstruction of the organ a distance di between the first and second points; computer readable program code for causing the computer to obtain the distance d in a calculation involving the distances Xi, 2, and di.

BRIEF DESCRIPTION OF THE DRAWINGS In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Fig. 1 shows a system in accordance with one embodiment of the invention; and Fig. 2 shows a flowchart for carrying out the method of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 shows a system for measuring the dimensions of an organ such as an artery or other blood vessel, or a urethra in accordance with one embodiment of the invention. The system comprises a table 102 upon which a patient 103 lies. An X-ray source 104 is located under the table for projecting X-rays through the patient 103 to an X-ray camera 105 located above the table 102, diametrically opposite the X-ray source 104. The X-ray camera 105 generates video signals 108 representing an X-ray image. The video signals 108 are stored in a memory 110 of a processor 115. Images captured by the X-ray camera 105 may be viewed on a display 120 either in real-time or after being retrieved from the memory 110. An operator input 125, that may be, for example, a keyboard and/or computer mouse or computer joystick, are used to allow an operator to input instructions to the processor 115. In order to obtain X-ray images of the individual 103 from different perspectives, the operator changes the orientation of the X-ray source 104 and the X-ray camera 105 by an activating mechanism (not shown). The processor 115 is programmed to generate a three-dimensional reconstruction of a tubular organ and/or a calibration device from two or more images of the organ and/or calibration device obtained from different perspectives. The three-dimensional reconstruction(s) may be represented on display 120 using pseudo three-dimensional effects such as directional lighting and shading, or as a stereoscopic pair of images on the display 120 to be viewed by the operator using a stereoscopic viewer. Fig. 2 shows a flow chart of a method for measuring the distance d between two points of an organ such as an artery or other blood vessel, or a urethra, in accordance with one embodiment of the invention. The two points may be, for example, the end points of a diseased region of an artery in which case the distance between the two points corresponds to the length of the diseased region in the artery. In step 200, a three dimensional reconstruction of a calibration device and a three dimensional reconstruction of the organ are obtained. The calibration device bears at least two markers separated by a known distance xi. In step 210, the distance x∑ in pixels between the markers on the calibration device is determined in the reconstruction. In step 220, two points are selected in the reconstruction of the organ whose separation in the organ is to be determined. In step 230, the distance di in pixels between the two points is determined in the reconstruction. In step 240, the distance d between the two points in the artery is then obtained in a calculation involving the distances xi, x₂, and di. It will be understood that the system according to the invention may be a suitably programmed computer. Likewise, the invention contemplates a computer program being readable by a computer for executing the method of the invention. The invention further contemplates a machine-readable memory tangibly embodying a program of instructions executable by the machine for executing the method of the invention.

Claims

CLAIMS:

1. A method for measuring a distance d between a first point and a second point in an organ, comprising:

(i) generating a three-dimensional reconstruction of the organ; (ii) generating a three-dimensional reconstruction of a calibration device, the calibration device bearing two markers separated by a distance xi; (iii) determining in the reconstruction of the calibration device a distance x₂ between the markers; (iv) determining in the reconstruction of the organ a distance di between the first and second points; and (v) obtaining the distance d in a calculation involving the distances xi,

X2, and di.

2. The method according to Claim 1 wherein the distance d is obtained using the algebraic expression d=dιx₂/xι.

3. The method according to Claim lor 2 wherein the organ is a blood vessel or a urethra.

4. The method according to Claim 3 wherein the blood vessel is an artery.

5. A system for measuring a distance d between a first point and a second point in an organ, comprising:

(i) a calibration device bearing at least two markers, the markers being separated by a distance i; (ii) an imaging system configured to image the organ and the calibration device from at least two perspectives. (iii) a processor configured to:

(a) generate a three-dimensional reconstruction of the organ from two or more images of the organ obtained from different perspectives; (b) generate a three-dimensional reconstruction of the calibration device from two or more images of the calibration device obtained from different perspectives;

(c) determine in a reconstruction of the calibration device a distance X2 between the markers;

(e) determine the distance d in a calculation involving the distances xi, X2, and di.

6. The system according to Claim. 5 wherein the distance d is determined using the algebraic expression d=dι ₂/ ι.

7. The system according to Claim 5 or 6 wherein the organ is a blood vessel or a urethra.

8. The system according to Claim 7 wherein the blood vessel is an artery.

9. A program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform method steps for measuring a distance d between a first point and a second point in an organ, the method comprising:

(i) generating a three-dimensional reconstruction of the organ from two or more images of the organ obtained from different perspectives;

(ii) generating a three-dimensional reconstruction of a calibration device from two or more images of the calibration device obtained from different perspectives, the calibration device bearing two markers separated by a distance xi; (iii) determining in the reconstruction of the calibration device a distance

X₂ between the markers; (iv) determining in the reconstruction of the organ a distance di between the first and second points; and (v) obtaining the distance d in a calculation involving the distances xi, X2, and di.

10. A computer program product comprising a computer useable medium having computer readable program code embodied therein for measuring a distance d between a first point and a second point in a tubular organ, the computer program product comprising: computer readable program code for causing the computer to generate a three-dimensional reconstruction of the organ from two or more images of the organ obtained from different perspectives; computer readable program code for causing the computer to generate a three-dimensional reconstruction of a calibration device from two or more images of the calibration device obtained from different perspectives, the calibration device bearing two markers separated by a distance Xi; computer readable program code for causing the computer to determine in the reconstruction of the calibration device a distance x∑ between the markers; computer readable program code for causing the computer to determine in the reconstruction of the organ a distance di between the first and second points; computer readable program code for causing the computer to obtain the distance d in a calculation involving the distances xi, X2, and di.