ROBOTIC IMAGE CONTROL SYSTEM

Abstract

This disclosure involves the use of X-ray markers that appear in fluoroscopic images and are detected by image processing software to partially or fully automate or assist in the performance of one or more of the steps of a percutaneous interventional procedure typically involving a catheter device.

Description

BACKGROUND OF THE INVENTION

Systems exist for the robotic feeding of percutaneous interventional devices such as guide wires and working catheters into guide catheters and procedures exist for the placement and seating of guide catheters such that their distal ends are adjacent the site of action for the intervention, typically a valve or chamber of the heart or a lesion in a blood vessel such as an artery. The guide catheter is typically placed by manual manipulation of medical personnel and its continued seating after placement assumed or determined by feel. The interventional devices such as guide wires and working catheters may be fed by the operation of robotic controls by medical personnel such as shown in U.S. Pat. No. 7,887,549.

SUMMARY OF THE INVENTION

The present invention involves the use of X-ray markers that appear in fluoroscopic images and are detected by image processing software to partially or fully automate or assist in the performance of one or more of the steps of a percutaneous interventional procedure typically involving a guide catheter.

The present invention also involves a process for mapping the three dimensional configuration of a blood vessel of a human subject by providing an elongated percutaneous device, a system for measuring advancement and retraction of the elongated percutaneous device and a fluoroscopic imaging system which provides a two dimensional image of a portion of the elongated percutaneous device in the blood vessel. A first fluoroscopic image is obtained when the portion of the elongated percutaneous device is at a first location within the blood vessel and a second fluoroscopic image is obtained when the portion of the elongated percutaneous device is at a second location within the blood vessel. A measurement is made of a first distance that the elongated percutaneous device has advanced or retracted when the first fluoroscopic image is taken and a measurement is made of a second distance that the elongated percutaneous device has advanced or retracted between the first fluoroscopic image and the second fluoroscopic image. The fluoroscopic images are correlated with the distance measurements to provide an indication of the travel of the elongated percutaneous device out of the plane of the fluoroscopic image.

The present invention further involves a process to optimize the plane of a fluoroscopic image used to monitor a percutaneous interventional procedure on a human subject involving a blood vessel by providing an elongated percutaneous device, a system for measuring advancement and retraction of the elongated percutaneous device and a fluoroscopic imaging system which provides a two dimensional image of a portion of the elongated percutaneous device in the blood vessel. The elongated percutaneous device is advanced into or retracted out of the blood vessel and a first fluoroscopic image is obtained when the portion of the elongated percutaneous device is at a first location within the blood vessel and a second fluoroscopic image is obtained when the portion of the elongated percutaneous device is at a second location within the blood vessel. A first distance that the elongated percutaneous device has advanced or retracted is measured when the first fluoroscopic image is taken and a second distance that the elongated percutaneous device has advanced or retracted between the first fluoroscopic image and the second fluoroscopic image is measured. The fluoroscopic images are correlated with the length measurements to provide an indication of the travel of the elongated percutaneous device out of the plane of the fluoroscopic image and the plane of the fluoroscopic image is adjusted to minimize the amount of travel of the elongated percutaneous device out of the plane of the fluoroscopic image.

The present invention additionally involves apparatus for mapping the three dimensional configuration of a blood vessel of a human subject which comprises a guide catheter configured to have its distal end positioned at the ostium of a blood vessel, a fluoroscopic imaging system which provides a two dimensional image of the blood vessel, a robotically driven guide wire carrying an X-ray marker, a measuring mechanism which reports the distance the guide wire has been advanced into the guide catheter, and a control mechanism which captures fluoroscopic images of the X-ray marker of the guide wire when the X-ray marker is at various distances from the distal end of the guide catheter and correlates them to the distances that the guide wire has been advanced into the guide catheter.

BRIEF DESCRIPTION OF THE DRAWINGS

This application will become more fully understood from the following detailed description, taken in conjunction with the accompanying figures, wherein like reference numerals refer to like elements in which:

FIG. 1 is a schematic of the environment in which percutaneous interventional procedures are robotically performed.

FIG. 2 is a schematic of the placement of a guide catheter and a guide wire in a human body.

FIG. 3 is a schematic of a guide wire carrying an X-ray marker.

FIG. 4 is a schematic of a guide catheter carrying X-ray markers.

FIG. 4 (a) and FIG. 4 (b) are schematics of various configurations of X-ray markers on a guide catheter.

FIG. 5A-5H are schematics of a procedure of placing an angioplasty balloon over a lesion using a guide catheter, a guide wire, a working catheter and X-ray markers.

FIG. 6 is a schematic of a guide catheter in relationship to the plane of a 2-D fluoroscopic image.

FIG. 7 is a flow diagram of creating a 3-D map of the path of a guide wire being fed into a guide catheter.

FIG. 8 is a flow diagram of the automated feeding of a guide wire into a guide catheter.

FIG. 9 is a flow diagram of the automated feeding of a guide wire into a guide catheter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Three Dimensional Roadmap

An embodiment involves mapping the path to be followed in deploying a percutaneous intervention device at its site of action. One approach involves deploying a guide catheter in the conventional manner, i.e. manually, and then feeding a guide wire through the guide catheter and measuring its apparent travel path in two-dimensional fluoroscopic images. This may be combined with measurements about the length of guide wire fed into the guide catheter and a general map of the artery system in which the guide catheter is deployed to render a three dimensional map of the path which includes travel in the z direction relative to the two dimensional fluoroscopic images.

A three dimensional relative height map of the artery system is built iteratively by comparing the length of the guide wire fed into the catheter guide to the measurement of the 2D motion of the distal end of the guide wire in the fluoroscopic image between two successive positions. The map can be sampled at a given incremental fixed length of guide wire by acquiring a fluoroscopic image every time a fixed length of wire is inserted and measuring the 2D motion of the wire along the path of the artery. Alternatively a fluoroscopic image can be acquired at regular time interval and a measurement of the length of the wire inserted and the 2D motion the wire along the path of the artery acquired. The measurement of the length of wire fed into the guide catheter and the measured path of the wire along the artery produce a relative height measurement between the initial and final position of the wire by using simple foreshortening geometry. This method only determines the magnitude of the differential height. The polarity of the displacement (up or down) must be inferred by anatomical observation of the arteries or by acquiring a second orthogonal fluoroscopic with a two plane system,

The measurement of the 2D motion of the wire in the artery can be facilitated by insertion of an easily detected fluoroscopic marker on the guide wire. The marker position can be easily be detecting by image processing of the fluoroscopic image.

An embodiment involves providing additional markers to determine the height at multiple positions along the guide wire or working catheter being fed into a guide catheter. The additional markers may be on the guide wire or working catheter being fed or both. Multiple, concurrent height measurements can be achieved along the guide wire or working catheter by simultaneously detecting all the makers and measuring their 2D motion individually. The marker positions can be easily be detecting by image processing of the fluoroscopic image or a plurality of fluoroscopic images.

One of the markers may be inserted at the tip of the wire.

The height map can be updated iteratively every time a guide wire is inserted or any other wire containing marker is inserted into the guide catheter. By changing the sampling time of the fluoroscopic images or the length or rate of insertion of the wire into the catheter guide, the measurement of the height will occur at different locations along the arteries and will fill up the height map.

The accuracy of the height map can be improved by estimating the 2D location of the markers more accurately. The successive 2D fluoroscopic images can be registered to each other by estimating the global 2D motion of each image with respect to a reference image. The estimation of the overall motion is represented by a unique 2D translation vector. The estimation of the overall motion is additionally represented by a unique 2D rotation angle. Once the 2D images are globally aligned, a secondary local alignment close to the marker can be performed for additional accuracy. The global and local alignment can be performed by normalized correlation of the current image and reference image or images or two other images to be aligned. The global and local alignment can be performed using the generalized Hough transform of the current image and reference image or images to be aligned.

Automatic Loading of a Guide Catheter

An embodiment involves robotically advancing a guide wire or working catheter (i.e. a catheter that carries a balloon, a stent or both) through a guide catheter until it is close to the end of the guide catheter adjacent to the site of action such as a blood vessel lesion or a chamber or valve of the heart. The tip of the guide wire or the distal end of the working catheter and the distal end of the guide catheter may both be provided with a marker visible in a fluoroscopic image.

An embodiment involves providing additional markers, possibly distinctive, to better monitor the progress of the guide wire or working catheter in the guide catheter. The additional markers may be on the guide catheter or the guide wire or working catheter being fed or both. Fluoroscopic images in which these markers appear may be combined with information about the length of guide wire or working catheter fed into the guide catheter to estimate the position of the tip of the guide wire or the end of the working catheter. The multiple markers on the guide catheter may also be used to estimate the effective velocity of the guide wire or working catheter as it is being fed through the guide catheter and this effective velocity may take account of the travel out of the plane of the fluoroscopic images.

The control mechanism of the drive feeding the guide wire or working catheter into the guide catheter causes the feeding to substantially slow or stop as the two markers approach each other. One approach involves taking fluoroscopic images of the progress of the guide wire or working catheter through the guide catheter and using image processing software to estimate the distance between the two markers. The feeding can then be slowed or stopped when the distance falls below a preset value. The X-ray exposure of the patient may be reduced by taking intermittent fluoroscopic images and the frame rate may be selected in accordance with the velocity of feeding of the guide wire or working catheter.

When multiple markers are used on either the guide wire or working catheter and the guide catheter, redundant detection of set of markers decreases the risk of overshooting the end of the guide catheter by imposing a stop if a maker or a set of marker preceding the last distal marker are not detected within a predefined length of guide wire or working catheter.

The use of multiple markers increase the accuracy of the velocity estimation by averaging multiple measurements individually affected by variable foreshortening due to the out of fluoroscopic plane wire incursion.

Additionally, accuracy of the velocity and tip position is increase by the use of a precomputed 3D map of the arteries that take into account foreshortening.

An embodiment involves providing proximal markers for greater safety. One approach is to provide additional markers on the guide catheter spaced proximally from its distal end and using these markers to better assure the control of the emergence of the guide wire or working catheter out of the distal end of the guide catheter.

Maintenance of Guide Catheter Seating

An embodiment involves determining whether the distal end of a guide catheter has become unseated after it was placed adjacent to the site of action, such as an arterial lesion or a chamber or valve of the heart, and taking corrective action to reseat it. In some cases when a working catheter carrying a stent, a balloon or both passes through a guide catheter toward its distal end seated near the site of action, it causes the guide catheter to move in the opposite direction causing the distal end to unseat. The corrective action may involve applying pressure to the guide catheter in the distal direction to cause it to reseat.

Monitoring to Determine if Guide Wire Well Seated

An embodiment involves monitoring the arterial pressure or the ST wave or an electrocardiogram of the patient undergoing the interventional procedure or observing the appearance of a cloud of contrast agent. A change in one of the first two parameters may be used as an indication that the guide catheter is becoming unseated. The appearance of the third may also be used as an indication that distal end of the guide catheter is not in its proper position when contrast agent is being fed through the guide catheter.

The contrast agent may be detected by means of image processing of the fluoroscopic images.

An embodiment involves comparing two registered fluoroscopic images by subtracting from each other and thresholding the resulting subtracted image and computing the size of the thresholded area. The two registered images are comprised of a reference image and the current image or the two registered images are comprised of two successive images.

Active Balloon Stabilization

An embodiment involves stabilizing an angioplasty or stent deployment balloon in its proper position for activation using a robotic feed mechanism. This may involve advancing or retracting the working catheter that is deploying the balloon. The positioning may be monitored by the examination of fluoroscopic images with image processing software and the software may then signal the needed amount of adjustment. For instance, if the balloon, with or without stent, is being deployed over a lesion, image processing software may monitor fluoroscopic images in which markers at both ends of the balloon and the lesion appear and signal the appropriate amount of advancement or retraction to assure that the balloon is in its proper position for inflation.

The system may use a pre-computed 3D height map to correct for foreshortening and compute the foreshortened adjusted length of catheter that needs to be fed. The adjusted length of catheter is provided to the robotic system to advance the catheter by that amount.

The system may measure the length of the balloon in the 2D fluoroscopic image and in infer the local 3D height at that location by comparing the 2D length of the balloon to the known length of the balloon using simple foreshortening trigonometry. The height information is then to compute the foreshortened adjusted length of catheter that needs to be fed. The adjusted length of catheter is provided to the robotic system to advance the catheter by that amount.

Guide Catheter Conduction of Ultrasound

An embodiment involves utilizing the guide catheter as an ultrasonic conduit to determine its position. The boundary conditions at the distal end of the conduit may be used to determine whether it is properly seated.

X-Ray Imaging of Different Areas

An embodiment involves using multiple images of different areas involved in a percutaneous interventional procedure. It may be advantageous to use multiple fields of view and to tailor the frequency of X-ray imaging to the particular field of view. For instance, one field of view may involve all or most of the path of percutaneous devices such as guide catheters, guide wires and/or working catheters and another to involve the immediate area of the site of action. It may be that more frequent imaging is appropriate for the latter field of view. The differential sampling rates may allow for reducing the overall X-ray exposure of the patient.

The position of the area of interest at the distal end of the catheter may be updated by using an estimation of the velocity of the catheter or guide write feed through the catheter guide to position the window prior to the next fluoroscopic acquisition. The velocity of the device being fed through the guide catheter may be estimated using X-ray markers as discussed above.

Optimization of the Plane of fluoroscopic Images

An embodiment involves adjustment of the plane of fluoroscopic images of the guide wire or working catheter as it advances through and out of the guide catheter. It may be advantageous to adjust the plane of the images to maximize the portion of the travel of the device that is in the plane of the fluoroscopic image. This may involve a comparison of the apparent travel path in two-dimensional fluoroscopic images with the length of the guide wire or working catheter that has been fed into the guide catheter.

FIG. 1 shows the environment in which the various embodiments of the present invention find particular utility. It shows a catheter laboratory 10 for robotically performing percutaneous interventional procedures. A patient 11 is supported on a table 14 and the procedure is observed with fluoroscopic X-ray equipment 12. A cassette 22 supported by a robotic arm 20 is used to automatically feed a guide wire 50 (shown in FIG. 2) into a guide catheter 40 seated in an artery 60 (shown in FIG. 5) of the patient 11. The cassette 22 is controlled from a remote station 24 in order to isolate the medical personnel conducting the procedure from exposure to the X-ray radiation used to monitor the procedure by use of fluoroscopic equipment. The station includes remote controls 26 for controlling the cassette 22 and a screen 28 with which to monitor the progress of the procedure. It displays the arterial system 29 being addressed by the procedure. U.S. Pat. No. 7,887,549, incorporated herein by reference, has a detailed disclosure of this environment.

FIG. 2 shows a guide catheter 40 that has been fed into the torso 30 of a patient 11 to reach the cardiac region 32. Within the guide catheter 40 is a guide wire 50 whose tip 52 has not yet passed out of the distal end 42 of the guide catheter 40. The X-ray equipment which is used to monitor the progress of the guide wire 50 as it passes through the guide catheter 40 and approaches its distal terminus 42 may be controlled such that it images the entire path until the guide wire tip enters the cardiac region 32 and then just images the cardiac region 32. It may also be controlled to take images at a more frequent rate once the tip 52 enters the region 32.

FIG. 3 shows a guide wire 50 which terminates at its distal end with a tip 50 that contains an X-ray marker which is readily apparent in a fluoroscopic image of the tip 52.

FIG. 4 shows a guide catheter 40 with a distal terminus 42 which has been provided with a distal X-ray marker 44, an intermediate X-ray marker 46 and a proximate X-ray marker 48. Also shown is the length 39 of the guide catheter 40 which extends from its proximal end to the intermediate X-ray marker 48 as well as the length 41 from there to the intermediate X-ray marker 46, the length 43 from that X-ray marker to the distal X-ray marker 44 and the length 45 from the distal X-ray marker 44 to the distal end of the guide catheter 42. These markers 44, 46 and 48 and theses lengths 39, 41, 43 and 45 may be used to control the movement of guide wire or working catheters being fed through the guide catheter 40. For instance, image-processing software may be used to analyze iteratively successive fluoroscopic images of the distal portion of the guide catheter and recognize when the X-ray marker in the guide wire tip 52 has first passed the markers 48, 46 and 44. This information can then be used to control the movement and speed of a guide wire 50 being fed to the guide catheter via its proximal end. In one embodiment the guide wire 50 can be quickly fed until its tip 52 until it reaches the marker 48 and then the feed speed can be reduced and then the automatic feed can be terminated when the tip 52 reaches the marker 46. In another approach when the tip 52 reaches the marker 46 the feed speed is reduced and the feed is terminated when the tip 52 reaches the marker 44. This two stage feeding procedure provides automatic feeding that ceases closer to the distal terminus 42 of the guide catheter 40 with reduced risk of overshooting the terminus 42. The distances 39,41, 43 and 45 may be used to set feeding velocities appropriate for the rate of taking fluoroscopic images and the latency time of the image processing software. Alternatively, these distances may be used to calculate the effective feeding velocity of the guide wire 50 and determine an appropriate time to terminate the automatic feeding such that the tip 52 does not emerge from the distal terminus 42.

FIG. 4 (a) shows an alternative in which just two markers 46 and 44 are used and the distance 43 is greater than distance 45. This supports an approach in which the feed is slowed when marker 46 is reached and stopped when marker 44 is reached.

FIG. 4 (b) show an alternative in which an X-ray marker 43 has been provided immediately adjacent to the terminus 42 and each of the markers 43, 44 and 46 has been given a distinctive character so that the image processing software will be aided in distinguishing them.

FIG. 5A-H show using X-ray markers and image processing software to control an interventional procedure from feeding a guide wire 50 to a guide catheter 40 to the secure placement of an angioplasty balloon 80 across a lesion 62 in an artery 60.

In FIG. 5A the guide wire 50 is being fed at an accelerated rate into a guide catheter 40 which is seated in an artery 60 with its distal end adjacent to a lesion 62. The tip 52 has yet to cross the intermediate marker 46.

In FIG. 5B the tip 52 has been detected as having passed the intermediate marker 46 by the image processing software which is analyzing iterative fluoroscopic images of the progress of the guide wire 50 and this software has caused a decrease in the feed velocity.

In FIG. 5C the image processing software has detected that the tip 52 has passed the distal X-ray marker 44 and has further slowed or stopped the feeding of the guide wire. In the latter case a signal has been sent indicating to the medical personnel conducting the procedure that manual advancement of the guide wire is needed.

In FIG. 5D the tip 52 has been advanced out of the distal terminus 42 of the guide catheter 40 and across the lesion 62. This could have been done manually or by image processing software that recognizes the lesion 62.

In FIG. 5E a working catheter 70 carrying an angioplasty balloon 80 at its distal end has been advanced over the guide wire 50 but has not yet reached the X-ray marker 46. The balloon 80 carries X-ray markers at both its distal end 82 and its proximal end 84.

In FIG. 5F the distal end 82 of the balloon 80 has passed marker 46 and thus the image processing software has slowed the feed rate of the working catheter 70.

In FIG. 5G the end 82 has passed marker 44. The image processing software has either signaled to the medical personnel conducting the procedure that manual advancement of the working catheter 70 is needed or it has slowed the advancement rate.

In FIG. 5H the balloon has been advanced across the lesion 62 either manually or under control of image processing software that can recognize the lesion 62. The balloon may carry a stent for deployment across the lesion.

FIG. 6 shows a guide catheter 40 following the path of an artery which is not illustrated. It has a portion 47 that has passed below the plane 90 of the fluoroscopic image into a lower plane 94 and it has a portion 49 that has passed above the plane 90 into a higher plane 92. iterative fluoroscopic images in plane 90 can be combined with measurements of the length of guide wire being fed into the guide catheter can be combined to yield an indication of the 3-D path of the guide catheter and therefore the artery itself.

FIG. 7 shows a procedure that may be followed to develop the indication of the 3-D path.

FIG. 8 describes a procedure for controlling the feeding of a guide wire 50 to a guide catheter 40 such that it does not emerge from the distal terminus 42 of the guide catheter using velocity measurements.

FIG. 9 describes a procedure for controlling the feeding of a guide wire 50 to a guide catheter 40 such that it does not emerge from the distal terminus 42 of the guide catheter using iterative fluoroscopic images.

While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the invention as claimed.

Claims

1. A process for mapping the three dimensional configuration of a blood vessel of a human subject comprising: providing an elongated percutaneous device;providing a system for measuring advancement and retraction of the elongated percutaneous device;providing a fluoroscopic imaging system which provides a two dimensional image of a portion of the elongated percutaneous device in the blood vessel;advancing or retracting the elongated percutaneous device within the blood vessel;obtaining a first fluoroscopic image when the portion of the elongated percutaneous device is at a first location within the blood vessel and a second fluoroscopic image when the portion of the elongated percutaneous device is at a second location within the blood vessel;measuring a first distance that the elongated percutaneous device has advanced or retracted when the first fluoroscopic image is taken;measuring a second distance that the elongated percutaneous device has advanced or retracted between the first fluoroscopic image and the second fluoroscopic image;correlating the fluoroscopic images with the distance measurements to provide an indication of the travel of the elongated percutaneous device out of the plane of the fluoroscopic image.

2. The process of claim 1 wherein the blood vessel is an artery.

3. The process of claim 2 wherein a general map of the artery system of which the blood vessel is part is used to aid in the correlation.

4. The process of claim 2 wherein anatomical observation is used to aid in the correlation.

5. The process of claim 1 wherein the elongated percutaneous device is a robotically driven guide wire with an X-ray marker located at its tip which has been advanced out of the distal end of a guide catheter which is positioned in the heart of the subject.

6. The process of claim 1 wherein the elongated percutaneous device is a guide wire with an X-ray marker located at its tip.

7. The process of claim 6 wherein a second set of fluoroscopic images of the X-ray marker of the guide wire taken in a plane orthogonal to the plane of the first set of fluoroscopic images is used to aid in the correlation.

8. The process of claim 6 wherein a fluoroscopic image is taken each time a predetermined length of guide wire is advanced into the guide catheter.

9. The process of claim 1 wherein a fluoroscopic image is taken at predetermined time intervals and a length measurement is made at the same time.

10. The process of claim 1 wherein the length measurement is taken after removing any slack in the elongated percutaneous device.

11. The process of claim 10 wherein the slack is removed by first advancing the elongated percutaneous device into the blood vessel and then partially withdrawing it.

12. The process of claim 1 wherein the three dimensional mapping is used to aid in the placement of a working catheter.

13. The process of claim 12 wherein the working catheter is being placed to deliver an interventional device to a lesion in the blood vessel.

14. The process of claim 13 wherein the device is one or more balloons or a stent.

15. A process to optimize the plane of a fluoroscopic image used to monitor a percutaneous interventional procedure on a human subject involving a blood vessel comprising: providing an elongated percutaneous device;providing a system for measuring advancement and retraction of the elongated percutaneous device;providing a fluoroscopic imaging system which provides a two dimensional image of a portion of the elongated percutaneous device in the blood vessel;advancing the elongated percutaneous device into or retracting the elongated percutaneous device out of the blood vessel;obtaining a first fluoroscopic image when the portion of the elongated percutaneous device is at a first location within the blood vessel and a second fluoroscopic image when the portion of the elongated percutaneous device is at a second location within the blood vessel;measuring a first distance that the elongated percutaneous device has advanced or retracted when the first fluoroscopic image is taken;measuring a second distance that the elongated percutaneous device has advanced or retracted between the first fluoroscopic image and the second fluoroscopic image;correlating the fluoroscopic images with the length measurements to provide an indication of the travel of the elongated percutaneous device out of the plane of the fluoroscopic image; andadjusting the plane of the fluoroscopic image to minimize the amount of travel of the elongated percutaneous device out of the plane of the fluoroscopic image.

16. The process of claim 15 wherein the elongated percutaneous device is a robotically driven guide wire with an X-ray marker located at its tip which has been advanced out of the distal end of a guide catheter which is positioned in the heart of the subject.

17. The process of claim 15 wherein a fluoroscopic image is taken either each time a predetermined length of the elongated percutaneous device is advanced into or retracted from the blood vessel or at predetermined time intervals and a length measurement is made at the same time.

18. An apparatus for mapping the three dimensional configuration of a blood vessel of a human subject comprising: a guide catheter configured to have its distal end positioned at the ostium of a blood vessel;a fluoroscopic imaging system which provides a two dimensional image of the blood vessel;a robotically driven guide wire carrying an X-ray marker;a measuring mechanism which reports the distance the guide wire has been advanced into the guide catheter; anda control mechanism which captures fluoroscopic images of the X-ray marker of the guide wire when the X-ray marker is at various distances from the distal end of the guide catheter and correlates them to the distances that the guide wire has been advanced into the guide catheter.

19. The apparatus of claim 18 wherein the blood vessel is an artery and the distal end of the guide catheter is positioned in the heart of the subject.

20. The apparatus of claim 18 wherein the control mechanism causes a fluoroscopic image to be taken either each time a predetermined length of guide wire is advanced into the guide catheter or at predetermined time intervals and causes a length measurement to be made at the same time.