Patent Application
20140100550
1. Field of the Invention
The present invention is directed to medical imaging and more particularly to a catheter discrimination and guidance system for an infrared detector and image display system to assist clinicians in performing intravenous and other vein access procedures.
2. Description of the Related Art
Intravenous (IV) catheters are used to access veins for blood draw, and for fluid delivery. There are very few techniques for assisting clinicians in verifying a positive cannulation of a vein. The standard technique for peripheral IV access involves using a tourniquet to engorge veins, followed by palpation to identify a suitable vein and finally insertion of the catheter needle. Clinicians must rely on “feel” when inserting the needle into a vein and on observing blood flashback to ascertain when the catheter has successfully cannulated the vein. Statistics indicate that this trial-and-error process requires an average of 2.4 attempts and up to 20 min for a clinician to successfully cannulate a vein. Aside from the increased pain and anxiety experienced by patients, there are real costs associated with IV care. Patient throughput, nurse time, consumables, and increased infection rates all contribute to increased medical care costs for hospitals and governments.
Systems have been developed for assisting in venous access and overcoming the disadvantages of traditional trial-and-error techniques. One such system is the VeinViewer® infrared detector and image projector manufactured and sold by Christie Medical Holdings, Inc., a division of Christie Digital Systems, Inc., which is described in U.S. Pat. No. 7,239,909, and U.S. Publication Nos. 2010051808, 20070158569 and 20060122515, the contents of which are incorporated herein by reference.
According to the VeinViewer® system, diffuse infrared light is used to image vasculature below the surface of the skin, and the image is then projected onto the skin to reveal the location of the vasculature. The vasculature image is projected in exactly the same anatomical location as the vasculature itself, and in its three-dimensional context (skin of patient) making it very easy to see the vessels. Also, since there is no transducer to hold, the clinician's hands are free to perform venous access.
Although the VeinViewer® system has been widely adopted by hospitals, its application has been somewhat limited by the fact that it cannot detect a successful cannulation event. Ultrasound is the only current visualization technology that can show if a successful cannulation has occurred. Ultrasound is commonly used for deep vein access such as PICC lines and CVC's, but is not typically used for peripheral veins.
Prior art relevant to the invention includes literature on the theory and mathematical modeling of the opto-characteristics of different materials, such as disclosed in:
Also relevant to the present invention are prior art needle guidance systems, such as disclosed in:
It is an object of an aspect of this specification to set forth a system for improving intravenous and other vein access procedures by guiding clinicians in achieving optimal intravenous (IV) placement while minimizing infiltration and extravasations effects.
According to the present invention, a catheter discrimination and guidance system is provided that detects the catheter and its related parameters from an acquired infrared image and uses these parameters to direct a clinician before and during the vein access procedure.
These together with other aspects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.
a is a schematic representation of the needle-tissue-vein interfaces and related physical parameters, and
a is a schematic diagram of pre-insertion catheter alignment aided by a projected series of dots.
b is a schematic diagram of pre-insertion catheter alignment aided by a projected compass line.
a is a schematic diagram of pixel analysis to locate the series of dots of
b is a schematic diagram of pixel analysis to locate the compass line of
Prior to describing the principles of the present invention, it is helpful to briefly review the theory behind optical vascular imaging. Photon scattering in soft tissue is dependent on photon wavelength and tissue composition. Projecting an incident beam of diffuse light on tissue results partly in backscattered light that is detectable at the surface of the tissue, and forward-scattered light that travels through the tissue. The forward scattered light interacts with scattering sites within the tissue and loses its intensity due to elastic and inelastic scattering phenomena. The inelastic phenomenon is also known as absorption. The intensity of the backscattered light is dependent on the type of tissue at the point of observation.
Turning to
According to the known Kubelka-Munk theory of reflectance, a relationship exists, specifically a paired differential equation, between the incident and backscattered light and the tissue thickness. Solutions to the equation exist for different boundary conditions.
In order to estimate the depth xv, under the skin, of a vein 100-3, three boundary conditions must be considered: (1) infinite tissue thickness, (2) tissue—vein boundary, and (3) needle—vein boundary.
Having regard to the first boundary condition, if the tissue is very thick (i.e. infinite tissue thickness), the incident beam 100-1 loses all of its intensity through scattering. Utilizing this condition, one can solve for all of the involved unknown parameters except for the scattering factor of the tissue.
At the tissue-vein boundary, almost all of the incident beam intensity is absorbed through elastic/inelastic scattering from blood within the vein, resulting in negligible reflectance. For a finite tissue thickness, there is no reflection at the exterior end medium (i.e. air). Using this condition, an equation can be arrived at for depth of the vein that is also irrespective of the tissue scattering parameter; however, it relies on the known thickness of the tissue where the total light absorption occurs.
Most light is absorbed within centimeters of the tissue thickness but this thickness value is unknown and its evaluation is not practical during performance of a clinical routine, due to various human tissue variants. This thickness dependency can be resolved using a predefined needle specific light reflectance over the skin and the measureable physical depth of the needle tip below the skin during the procedure. The needle depth can be measured for a standard catheter needle size through a procedure described in greater detail below.
This thickness dependency can also be resolved using the following methodology. The incident light intensity can be reduced to a level that substantially all photons are lost within a finite specific skin thickness. This skin thickness behaves like an infinite thickness under normal incident light application. In order to find this specific thickness, a vein contrast concept is used. Veins are discriminated within skin tissue due to the contrast resulting from significant light absorption in veins. Contrast is lost if the photons are not able to reach the vein surface due to lack of light intensity and the scattering/absorption effects only within skin tissue. Thus, light intensity is reduced to a level at which vein contrast is lost and, accordingly, photons annihilate right at the vein surface (the vein depth) and the skin thickness can be considered infinite in practical application. Measuring the related light intensity and reflection assists in resolving undefined tissue-related parameters.
In order to determine the needle-vein intersection (i.e. when the needle tip touches the vein surface, consecutive values of needle reflectance below the skin are registered during the catheter insertion process. It will be noted that, due to the high absorption of blood, the same needle reflectance values are expected to be detected at the needle tip (observed over the skin) while it is in the vein. Accordingly, needle-vein intersection occurs when the observed needle tip reflectance becomes equal to vein reflectance.
Turning to
The exemplary catheter system 210 depicted in
IR light 225 from IR imager/projector 200-5 illuminates the patient's soft tissue 215 with light in the range of 850 +/−40 nm, which is mainly absorbed by blood (haemoglobin) in the vein 220. The unabsorbed light 230 is reflected back and is detected by the IR imager/projector 200-5. The reflected image is processed by the image processing subunit 200-3, and then re-projected on the patient's skin in real-time to show the location of vein 220 beneath the patient's skin. The IR imager/projector 200-5 preferably includes a cut-off filter and a polarizer to differentiate reflected imaging light from background IR light in the environment.
With reference to
The catheter outline is detected and the device observed catheter length is determined at step 310. The catheter length is the observed distance between the catheter tip to the catheter housing, which are discriminated accordingly. The detected length value is used to calculate the insertion angle of the needle and locate the tip of the needle as it is inserted into the skin and as it penetrates the vein. Since the system 200 captures a two dimensional view of a scene, the actual length of the catheter 210-2 is different from its device observed value but is related to it by the angle it makes with the skin surface and can be determined using perpendicular projection, as described below. The maximum observed length is the actual length of the catheter and can be estimated according to a calibration process described below. Finally, the location of the catheter start and end points are determined (i.e. the point that connects the catheter to the catheter housing is the start point and the free end of the catheter is the end point), as discussed below.
Since catheters are gauged according to their expected usage and come in various sizes, the calibration process permits calculation of the length for various catheter sizes without requiring any external predefined input from the user. The actual length of the catheter 210 is closely related to the length value as observed by the IR imager/projector 200-5 by the angle it makes with the skin surface at the point of vein access. Therefore, in use the clinician first follows a calibration process by which the catheter is positioned under the IR imager/projector 200-5 of system 200 and is rotated through small positive and negative angles relative to the skin surface, passing through zero degrees, in order to register and measure the actual catheter length, illustrated schematically in
The system 200-4 must discriminate the catheter from its environment. The catheter discrimination process is slightly different depending on whether the catheter is translucent or opaque. In either case, multi-resolution analysis is performed to expedite the catheter and needle discrimination processes, whereby captured images are first reduced to a lower resolution and an initial analysis is performed. Later the remaining analyses (e.g. frequency filtering, length and angle measurements) are performed using the original-size images.
Translucent catheters are composed of material that is permeable to infrared light and accordingly not visible to the IR imager/projector 200-5. However, by using a physical polarizer with the IR imager/projector 200-5, the catheter appears as a solid black line of measurable thickness in the captured image (
An opaque catheter has different characteristics than a translucent catheter, and is visible in the infrared wavelength region. The opaque catheter covers the metallic needle and totally absorbs the infrared light. The detection process for opaque catheters is similar to the process for translucent catheters discussed above, but the seed point is chosen as the point having maximum intensity value (rather than minimum intensity value). A small length of the needle (about 1-2 mm) is uncovered at the tip of the catheter and its length is measured using the procedure described earlier for translucent catheters.
The image is later thresholded about the intensity of the seed point, thereby allowing a range of intensities. However, as a result of catheter positioning, angle, absorption and other factors involving scattering, it is not possible through the use of simple thresholding to obtain a solid line representing the catheter. Therefore, as shown in
As an alternative to catheter discrimination based on detecting the location of the catheter start point at the catheter housing 210-1, opto-genic catheters may be used. This alternative is especially useful with non-standard catheters whose length does not fit within the field of view of the system 200. Specifically, opto-genic catheters may be provided with optical markings that can be detected using image processing algorithms and used to estimate the visible length of the catheter (i.e. from the marking to the catheter tip). Opto-genic markings can be made using an etching process on the catheter to change its optical characteristics (e.g. specular reflection). The markings do not hamper the hygienic or normal clinical functionalities of the catheters.
Where opto-genic catheters are not available, a clip-on marker 210-4 may be provided, according to an additional aspect of the invention, to assist in discriminating different catheter types that are not compatible the preferred catheter discrimination and guidance system 200 (i.e. the Vein Viewer® system, discussed above). The marker 210-4 is attached to or removed from the catheter housing 210-1 by a simple clip-on arrangement. The length and end point features of the marker are identified using the image processing algorithms already set forth herein, followed by the angle measurement and calibration process set forth herein.
The marker 210-4 is designed so as not to hamper the normal functionality of the catheter 210. The markings can include security-enabled, manufacturer-specific features that can be identified using the image processing routines set forth herein.
With reference to
Although the marker set forth herein is described as being of added clip-on design, a person of skill in the art will understand that the marker can be molded in as part of the catheter housing.
Returning to
At this stage, the required catheter-related values (e.g. its length, angle and tip) have been determined and the IR imager/projector 200-5 then projects images and information onto the skin in order to assist the clinician in visualizing the catheter insertion process while the catheter is partly in the skin and out of view (step 340) and informs the user when the catheter and needle enter the vein (step 350), as discussed further below.
Finally, at step 360, the IR imager/projector 200-5 generates and projects a map (location and depth) of veins in close proximity to the vein access point, irrespective of the type and color of the skin. No tissue characteristic parameters have to be known a priori.
The critical vein depth value can be evaluated, as described previously, and the catheter positioning angle can be calculated from the catheter observed length based on perpendicular image acquisition and projection:
l′
c
=l
c.cos(θ) (1.1)
where l′c is the value observed at the IR imager/projector 200-5. At the start of the clinical procedure, the catheter tip is at the skin surface of the tissue at point a (the catheter—skin access point). When the tip penetrates the skin to the vein surface, it travels from point a to point b (the needle—vein access point) on the skin surface: Where point b can be calculated using the procedure explained earlier using the needle reflectance and its tip location.
Thus, at the vein surface:
|{right arrow over (b)}−{right arrow over (a)}|=|{right arrow over (ab)}|=xv.tan(θ) (1.1)
The 200-5 can be configured to reduce light intensity until vein contrast is lost in order to determine an estimate for the vein depth, xv, as discussed above. As tissue characteristics may influence vein depth, this can be performed as a short calibration process prior to step 340.
Thus, according to step 360, the system 200-4 causes IR imager/projector 200-5 to project the points a and b on the skin surface (e.g. using high intensity coloured dots) so that, the clinician is guided to adjust the direction of the catheter from the insertion point a in a straight line following the vein to point b, as shown in the inset portion at the top right of
Lateral targeting can also be provided for the catheter before the catheter tip penetrates the skin surface. The catheter discrimination and guidance system 200 can be configured to provide guidance to a clinician as to the location of a suitable vein and a suitable direction in which to insert the catheter prior to insertion.
a shows the catheter 210 over a skin surface 1100, onto which is projected a catheter direction line 1102 representative of the catheter 210 direction in the plane of projection. The catheter direction line 1102 can be determined as discussed above with respect to
Also projected is a vein path indicator for a vein 1104. In this embodiment, the vein path indicator includes a series of dots 1106. The dots 1106 are located along the vein's midline 1200, as shown in
The discrimination and guidance unit 200-4 is configured to determine the closest vein(s) to the catheter 210, and project the midline of each of such veins as a series of dots 1106. Signal conditioning for the exact locations of the points is performed to provide a consistent and nonvolatile presentation. That is, a filter can be applied to calculated point locations, so that visible jitter or insignificant positional fluctuation of the points is avoided.
Images captured for veins tend to be darkest at vein midlines, as more light is absorbed by a vein at its midline due to the midline typically being the thickest part of the vein. To generate the series of dots 1106, the discrimination and guidance unit 200-4 is configured to perform a process for points along a tracking line 1300 which is coincident with the catheter direction line 1102 and extends from the catheter tip 1103 and up to a predetermined length forward in the captured image, as shown in
The process includes analyzing image pixels of a series of spaced-apart lateral lines 1302 perpendicular to the tracking line 1300. The lateral lines 1302 symmetrically extend to both sides of the tracking line 1300 for a predetermined distance. The lateral lines 1302 may be evenly spaced at a predetermined interval. For each lateral line 1302, the discrimination and guidance unit 200-4 performs a search to find one or more sufficiently dark pixels 1304 and treats these pixels as vein midpoints. The process can determine that a pixel is sufficient dark when the pixel's intensity does not exceed a predetermined intensity. The acquired vein midpoints are then projected over the skin using a specific color as the series of dots 1106.
Pixel intensity analysis as discussed herein can include analyzing any suitable pixel characteristic, such as brightness, luminance, hue, saturation, and the like. Selecting a suitable characteristic for pixel intensity analysis may depend on characteristics of the source light, characteristics of captured light, and similar.
The process is repeated for each image frame captured, so that updates are made in real time and new veins are detected and have their midpoints projected as the series of dots 1106 while the catheter 210 is moved. The clinician can then reference the series of dots 1106 when selecting a suitable vein and then aligning the catheter 210 with the selected vein.
The discrimination and guidance unit 200-4 can further be configured to output feedback for aiding alignment of the catheter 210 with the series of dots 1106 indicating the selected vein. The feedback can be visual, audible, or a combination of such. For example, the color of the dots 1106 can be changed, an additional visual object can be projected, or the unit 200-4 can emit a sound via speaker 200-6. The feedback can be configured to change as the alignment of the catheter 210 with the series of dots 1106 approaches an optimal alignment. For example, a frequency of an audible tone changes as the alignment of the catheter 210 approaches optimal alignment. Alternatively or additionally, a visual indicator is added to the image when the alignment of the catheter 210 is within a threshold of the optimal alignment.
Alignment of the catheter 210 with the series of dots 1106 can be calculated using a linear regression calculation. Referring to
For continuous feedback, such as a tone of changing frequency, the feedback can be proportional to the calculated error. For thresholded feedback, such as a visual indicator added to the image, such feedback can be provided when the calculated error is below a threshold error.
The discrimination and guidance unit 200-4 can be configured to discriminate between veins by comparing vectors between the points 1304, in that positionally distant groups of points or groups of points following different paths are treated as different veins. Thus, the techniques described above can be limited to a group of points 1304 that is determined to be nearest the catheter tip 1103. For example, the error calculation may be configured to exclude points not belonging to the group nearest the catheter tip 1103, so that alignment feedback is not unduly influenced by a vein that is not intended to be selected.
In other embodiments, as shown in
As the clinician moves the catheter 210, as indicated by arrow M, the angle A between the catheter direction line 1102 and the compass line 1108 changes. As the angle A approaches zero, that is, as the catheter direction line 1102 and the compass line 1108 become closer, feedback may be provided, as discussed above. The clinician is thus guided to reduce the angle A and align the catheter direction line 1102 and the compass line 1108, so as to align the catheter direction line 1102 with the midline 1110 of the vein 1104.
The discrimination and guidance unit 200-4 is configured to provide the compass line 1108 according to a vein detected near the catheter tip 1103. If two or more veins are determined to be suitably near the catheter tip 1103, then the discrimination and guidance unit 200-4 selects the vein with the largest number of dark pixels.
The compass line 1108 can be configured to behave according to a conceptual center of gravity. That is, when the catheter 210 is distant to the vein 1104, the compass line 1108 points towards the nearest best (darkest) vein as if there is a gravity force present. Signal conditioning can be performed on the compass line 1108 to provide a consistent and nonvolatile presentation. A filter can be applied to a calculated angle of the compass line 1108, so that insignificant angular fluctuation is avoided.
Referring to
The image pixels in each sweep line 1308 are analyzed for intensity. The discrimination and guidance unit 200-4 selects the sweep line 1308 with the greatest number of pixels with the least overall intensity as the direction for the compass line 1108. Such pixels can be determined according to various methods, such as a count of pixels of intensity below a threshold intensity, a total intensity being a normalized sum of intensities for all pixels on the sweep line, and the like.
The present invention has been described with respect to the forgoing embodiments and variations. Other embodiments and variations are possible. For example, although the preferred embodiment is discussed in connection with an infrared detector and image projector system 200, such as the VeinViewer® system manufactured and sold by Christie Medical Holdings, Inc., the principles of catheter discrimination and guidance may be implemented in HUD (head's up display) or other types of vascular imaging systems.
The many features and advantages of the invention are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the invention that fall within the true spirit and scope of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the claims.
This application is a continuation-in-part of application Ser. No. 13/648,517, filed Oct. 10, 2012, the entirety of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13648517 | Oct 2012 | US |
| Child | 13865650 | US |
