USE OF ECHOGENIC COATING FOR ULTRASOUND IMAGING OF MEDICAL DEVICES IN DEEP TISSUE LAYERS

Abstract

A medical device to be inserted into a body at depths greater than 5 cm, includes an echogenic coating composition including: (i) a polymer matrix and (ii) an amount of ultrasound-reflective microparticles having a diameter that is at least 10 and at most 250 μm in size, with a defined relationship between the particle size, expressed as D 50, and the surface density. A method for ultrasound detection of a medical device at a scan depth greater than 5 cm includes providing the medical device with the echogenic coating composition. An echogenic assembly includes the medical device having the echogenic coating composition and a convex probe.

Claims

1. A medical device to be inserted into a body at depths greater than 5 cm, comprising: an echogenic coating composition comprising: (i) a polymer matrix and (ii) an amount of ultrasound-reflective microparticles having a diameter that is at least 10 and at most 250 μm in size, wherein the relationship between the particle size, expressed as D.sub.50, and the surface density is as follows: TABLE-US-00005 surface density (microparticles/mm.sup.2) Condition Particle size (μm) Lower limit Upper limit I 10 < D.sub.50 ≤ 22 362 2080 II 22 < D.sub.50 ≤ 27 478 1626 III 27 < D.sub.50 ≤ 32 467 1692 IV 32 < D.sub.50 ≤ 38 235 1636 V 38 < D.sub.50 ≤ 45 256 1459 VI 45 < D.sub.50 ≤ 53 218 1594

2. The medical device of claim 1, wherein the relationship between the particle size, expressed as D.sub.50, and the surface density is as follows: TABLE-US-00006 surface density (microparticles/mm.sup.2) Condition Particle size (μm) Lower limit Upper limit I 10 < D.sub.50 ≤ 22 856 2080 II 22 < D.sub.50 ≤ 27 1218 1626 III 27 < D.sub.50 ≤ 32 1074 1692 IV 32 < D.sub.50 ≤ 38 350 1636 V 38 < D.sub.50 ≤ 45 291 1459 VI 45 < D.sub.50 ≤ 53 318 1594

3. The medical device of claim 1, wherein the relationship between the particle size, expressed as D.sub.50, and the surface density is as follows: TABLE-US-00007 surface density (microparticles/mm.sup.2) Condition Particle size (μm) Lower limit Upper limit III 27 < D.sub.50 ≤ 32 1380 1692 IV 32 < D.sub.50 ≤ 38 1153 1636 V 38 < D.sub.50 ≤ 45 370 1459 VI 45 < D.sub.50 ≤ 53 370 1594

4. The medical device of claim 1, wherein the polymer material is selected from poly(ether sulfones), polyurethanes, polyacrylates, polymethacrylates, polyamides, polycarbonates, polyepoxides, polyethers, polyimides, polyesters, fluorinated polyolefins, polystyrenes and combinations thereof.

5. The medical device of claim 1, wherein the microparticles are spherical.

6. The medical device of claim 1, wherein the microparticles are made of glass.

7. A method for ultrasound detection of a medical device comprising: disposing the medical device at a scan depth greater than 5 cm, preferably greater than 10 cm, more preferably greater than 15 cm, ultrasonically detecting the medical device having the echogenic coating composition of claim 1.

8. The method of claim 7, further comprising: utilizing a linear or convex probe, preferably a convex probe.

9. The method of claim 8, further comprising: utilizing a convex probe with a radius of curvature between 5 and 80 mm.

10. The method of claim 8, further comprising: utilizing a convex probe operating with ultrasound waves with a frequency of between 2.5 and 7.5 MHz.

11. An echogenic assembly comprising: a medical device for use at scan depths greater than 5 cm, preferably greater than 10 cm, more preferably greater than 15 cm, comprising the echogenic coating composition defined in claim 1, and a convex probe.

12. A method comprising: utilizing the composition according to claim 1 in a non-surgical procedure.

13. The method according to claim 7, wherein the step of utilizing the device is a non-surgical procedure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is an ultrasound image of a polyurethane tube coated with spherical microparticles, microspheres, together with a measurement of the mean pixel intensity of the selected region of interest (the coated PU tube).

[0010] FIG. 2 is an ultrasound image of a polyurethane tube coated with spherical microparticles, microspheres, together with a measurement of the mean pixel intensity of the background.

[0011] FIG. 3 are ultrasound images of coated polyurethane tubes with different coatings.

DETAILED DESCRIPTION OF THE INVENTION

[0012] A “medical device” is defined herein as any kind of device that can be used in an animal or human body. The medical device can preferably be inserted or implanted in the body. Preferably, such medical device is an instrument used in surgery, treatment and/or diagnosis. Surgical instruments are well known in the art. Non-limiting examples of medical devices include (balloon) catheters, needles, stents, cannulas, tracheotomes, endoscopes, dilators, tubes, introducers, markers, stylets, snares, angioplasty devices, trocars, guidewires and forceps. A medical device according to the present invention is, therefore, preferably selected from the group consisting of cathethers, needles, stents, cannulas, tracheotomes, endoscopes, dilators, tubes, introducers, markers, stylets, snares, angioplasty devices, fiducials, trocars and forcepses.

[0013] Deep tissue is considered to be structures at a scan depth of at least 5 cm, preferably at least 10 cm, more preferably at least 15 cm. For instance, with obese patients it may be necessary to locate or visualize a device by ultrasonic imaging when the device is inserted at a depth of 10 to 15 cm into the body. Sonograms of deep tissue are often made with convex transducers operating at a depth range of 5-30 cm, as most linear transducers operate at depth ranges of 3-10 cm or even less.

[0014] As used herein, a coating for ultrasound detection comprises any coating that is tolerated by a human or animal body and that comprises microparticles that can be visualized, due to scattering of ultrasound waves. Typically, such coating comprises biocompatible materials that are non-toxic, hypoallergenic and stable.

[0015] An ultrasound wave (also called “an ultrasound signal” or “ultrasound”) is defined as a sound pressure wave with a frequency above the audible range of normal human hearing. Typically, ultrasound waves have a frequency above 20 kHz. For imaging of medical devices, ultrasound waves with a frequency between 2 MHz and 50MHz are preferably used.

[0016] As used herein, the term “ultrasound image” means any kind of visualization of an object using ultrasound waves. Typically, reflected ultrasound waves are converted into electrical pulses which are processed and transformed into digital images. Such images are embraced by the term ultrasound image.

[0017] A “microparticle” is defined herein as a particle with a size below 250 μm, as particles greater than 250 μm are too large for practical use (the adhesion becomes problematic and the coating may appear “rough” to the patient). Moreover, the microparticle has a size greater than 10 μm. Below this value, the microparticles have insufficient visibility for practical use. Microparticles can have any shape, such as a regular shape (for instance, spherical, oval or cubical) or an irregular shape. Preferred are microspheres, which are essentially spherical in shape. The term “essentially spherical” reflects the fact that the microparticles need not be perfectly spherical as long as the distances between the centre and any point at the surface do not differ more than 50%, more preferably no more than 30%, from each other in at least 70%, preferably at least 80%, most preferably at least 90% of the particles. Gas-filled microparticles may be used, but preferably the microparticles are solid.

[0018] Echogenic microparticles are defined herein as microparticles that are able to reflect an ultrasound wave.

[0019] A monolayer, also called a single layer, is defined herein as a one-particle thick layer of particles on the surface of a device, meaning that there is on average no more than one particle on an axis perpendicular to the surface of the device. Some variations in thickness of the layer are tolerated, as long as at least 70%, preferably at least 80%, most preferably at least 90% of the coated surface of a device is coated with a single layer of particles.

[0020] Median values are defined as the value where half of the population resides above this point, and half resides below this point. The D.sub.50 is the size in μm that splits the particle size distribution, based on volume distribution in half, with 50% of the microparticles having a particle size above and 50% below this diameter.

[0021] A microparticle with a diameter between a given range is defined herein as a microparticle of which the diameter lies within the recited range, including the upper value of the range. For instance, a microparticle with a diameter between 38 and 45 μm may have a diameter of greater than 38 μ, a diameter of 45 μ, or a diameter with a value anywhere within this range. The diameter of a non-spherical particle is defined as the diameter of the smallest sphere that can enclose the particle in its entirety.

[0022] Contrast measurements are a quantitative method to evaluate the ultrasound visibility of the medical device. The method compares the mean pixel intensity of the medical device, against the mean pixel intensity of the surrounding background image. Contrast values of the coated area are used to quantitatively assess ultrasound visibility of different coatings. Pixel intensity is measured using ImageJ, a Java-based image processing program developed at the National Institutes of Health and the Laboratory for Optical and Computational Instrumentation (LOCI, University of Wisconsin), or a similar image processing program. If the image quality or “contrast” is below 25, then the device is not visible enough for clinical use.

[0023] From the recorded images, the contrast is determined by comparing the mean pixel intensity of the coated objects to the mean pixel intensity obtained for the surrounding background, according to the following equation:

Contrast=P.sub.ROI−P.sub.bkg

where

P.sub.ROI=mean pixel intensity of the region of interest

P.sub.bkg=mean pixel intensity of the surrounding background

[0024] Examples of the obtained ultrasound images with contrast from 10 to 50 are shown in FIG. 3. As can be seen in FIG. 3, a minimum contrast of 25 is required in order to achieve good ultrasound visibility. Having a contrast of 30 or even 40 is preferred.

[0025] In order to locate or visualize a device by ultrasonic imaging when the device is inserted into the body, an ultrasound probe is used. In addition to linear ultrasound probes also convex (curved) type probes are known, as well as phased (sector) type probes. Convex probes find use in the diagnoses of organs, transvaginal and transrectal applications and abdominal application. A convex probe is therefore frequently used for examinations in deeper tissue structures, e.g., tissue at least 5 cm deep. The piezoelectric crystal arrangement is curvilinear and the beam is convex. The radius of curvature may vary from 5 to 80 mm. The convex probe makes use of lower frequencies, typically in the range of 2.5-7.5 MHz. The coating of the present invention, and medical devices comprising the new coating, can be accurately located using convex probes. The present invention therefore also includes a method for locating or visualizing a device that is inserted into deep tissue structures of a body by ultrasonic imaging with the use of an ultrasound probe, preferably a convex probe. Note that a linear ultrasound probe may be used as well.

[0026] The particle size distribution of the microparticles used in the present invention may be relatively broad, as long as the particles are at least 10 μm in diameter and at most 250 μm in diameter. The inventors found that there is a non-linear relationship between the diameter of the microparticles and the surface density (minimum and maximum). Below the lower limits of the surface density insufficient visibility is obtained which adversely affect the accuracy of localizing the coated medical device. Above the upper limits a range of problems occur, such as, over exposure causing the contours of the medical device to become blurred and less defined which will also adversely affect the accuracy of localizing the coated medical device. Above the upper limit there are problems related to adhesion of the coating to the medical device and abrasiveness of the coated medical device.

[0027] Within the limits provided above, it has been determined that for improved visibility in deep tissue structures the relationship between the particle size, expressed as D.sub.50, and the surface density is as follows (for a contrast of at least 25):

TABLE-US-00001 surface density (microparticles/mm.sup.2) Condition Particle size (μm) Lower limit Upper limit I 10 < D.sub.50 ≤ 22 362 2080 II 22 < D.sub.50 ≤ 27 478 1626 III 27 < D.sub.50 ≤ 32 467 1692 IV 32 < D.sub.50 ≤ 38 235 1636 V 38 < D.sub.50 ≤ 45 256 1459 VI 45 < D.sub.50 ≤ 53 218 1594

[0028] More preferably, the relationship between the diameter, expressed as D.sub.50, and the surface density is as follows (for a contrast of at least 30):

TABLE-US-00002 surface density (microparticles/mm.sup.2) Condition Particle size (μm) Lower limit Upper limit I 10 < D.sub.50 ≤ 22 856 2080 II 22 < D.sub.50 ≤ 27 1218 1626 III 27 < D.sub.50 ≤ 32 1074 1692 IV 32 < D.sub.50 ≤ 38 350 1636 V 38 < D.sub.50 ≤ 45 291 1459 VI 45 < D.sub.50 ≤ 53 318 1594

[0029] Still more preferably, the relationship between the diameter, expressed as D.sub.50, and the surface density is as follows (for a contrast of at least 40):

TABLE-US-00003 surface density (microparticles/mm.sup.2) Condition Particle size (μm) Lower limit Upper limit III 27 < D.sub.50 ≤ 32 1380 1692 IV 32 < D.sub.50 ≤ 38 1153 1636 V 38 < D.sub.50 ≤ 45 370 1459 VI 45 < D.sub.50 ≤ 53 370 1594

[0030] Each of the conditions concerns microparticles wherein 50% (by volume) of all microparticles have a diameter between the lower limit of 10 μm and the actual value of the Dso, whereas the remaining 50% of microparticles have a diameter between the actual value of the Dso and the upper limit of 250 μm. The distribution may therefore be relatively broad. Microparticles with a normal diameter distribution, preferably a narrow diameter distribution, wherein at least 60% (by volume) of all microparticles have a diameter of D.sub.50±5 μm may be very suitably be used. For instance, microparticles may be used with a very narrow diameter distribution, wherein at least 70% (by volume), preferably at least 80%, more preferably at least 90%, still more preferably at least 95% of all microparticles have a diameter of D.sub.50±5 μm. Alternatively, “gap-graded” or multimodal selections of microparticles may be used, whereby “ordinary” suitable grades of different conditions are mixed, thereby creating a more complex diameter distribution. These gap-graded or multimodal grades may be used at the surface density set out above for the D.sub.50 of these complex grades.

[0031] Surprisingly, the selection of the microparticles within the above subranges also provides for smooth coatings, whereby abrasion and adhesion problems, that are believed to be caused by the formation of bilayers of particles, is avoided. Moreover, a bilayer may appear “rough” to the patient and may impact the adhesion of the coating to the medical device. If a coating with a bilayer is bent, the coating will crack and come off, or if inserted into a body, the coating adhesion will be compromised and the coating will be abraded and flake off the surface of the device. This obviously needs to be avoided.

[0032] A medical device according to the present invention can be coated with various kinds of microparticles that are visible with ultrasound. Such microparticles are known in the art.

[0033] Typically, said microparticles comprise a material selected from the group consisting of ceramics, glasses, silicates, metals and any combination thereof. Such materials provide for optimal ultrasound response in common coating matrices.

[0034] Preferably, said microparticles are made from glass, more preferably from silica-based glass, most preferably from soda-lime glass. Such particles have a high acoustic impedance and therefore good ultrasound visibility in common coating matrices. Moreover, they are relatively easy to manufacture as compared to microparticles of other materials.

[0035] The above described microparticles need to be embedded in a coating matrix which adheres to both the medical device and the microparticles. In principle, any coating matrix capable of adhereing to both the microparticles and to a medical device can be used. The coating matrix should be suitable for in-vivo use. Such coating is preferably non-toxic, hypo-allergenic and stable. Preferably, the coating matrix comprises a polymer material.

[0036] As polymer material, various polymers and combinations of polymers may be used, which includes homopolymers, copolymers, terpolymers, and block copolymers. Preferably, the polymer material is selected from poly(ether sulfones), polyurethanes, polyacrylates, polymethacrylates, polyamides, polycarbonates, polyepoxides, polyethers, polyimides, polyesters, fluorinated polyolefins, polystyrenes and combinations thereof.

[0037] Preferably, said medical device is selected from the group consisting of cathethers, needles, stents, cannulas, tracheotomes, endoscopes, dilators, tubes, introducers, markers, stylets, snares, angioplasty devices, fiducials, trocars and forcepses. These medical devices may comprise a plastic or metallic surface.

[0038] Methods for providing echogenic coatings are well-known. A medical device may for instance be coated with the microparticles by dip coating, spray coating, pad printing, roller coating, printing, painting or inkjet printing. Reference is for instance made to U.S. Pat. Nos. 5,289,831, 5,921,933, and 6,506, 156, to international patent application WO 2007/089761 and to Ultrasound in Medicine and Biology, Vol. 32, No. 8, pp. 1247-1255, 2006, which describe methods for preparing echogenic particles and coatings. Such coating is preferably biocompatible, non-toxic, hypo-allergenic and stable.

[0039] The invention thus provides use of an echogenic coating composition on a medical device to be inserted into a body at depths deeper than 5 cm, comprising the new echogenic coating compositions. It also provides a medical device for use at scan depths greater than 5 cm, preferably greater than 10 cm, more preferably greater than 15 cm, comprising the new echogenic coating composition. Moreover, the present invention provides a method for ultrasound detection of a medical device at a scan depth greater than 5 cm, preferably greater than 10 cm, more preferably greater than 15 cm, by providing the medical device with the echogenic coating composition of the present invention. Particularly attractive is the method wherein use is made of a linear or convex probe, preferably a convex probe. The convex probe preferably has a radius of curvature between 5 and 80 mm, more preferably between 20 and 65 mm. Suitably, use is made of a convex probe operating with ultrasound waves with a frequency of between 2.5 and 7.5 MHz. The invention also provides an echogenic assembly comprising a medical device for use at scan depths greater than 5 cm, preferably greater than 10 cm, more preferably greater than 15 cm, comprising the echogenic coating composition of the present invention, and a convex probe. In the echogenic assembly the coating of the medical device is specifically adapted for localization by the convex probe.

[0040] The invention may be better understood with reference to the drawings.

[0041] FIGS. 1 and 2 show an example of the pixel intensity measurement. In FIG. 1 the pixel intensity measurement is performed of the region of interest (P.sub.roi). In FIG. 2 the pixel intensity measurement is performed of the background (P.sub.bkg). The visibility is determined by the contrast, based on the equation provided before, Contrast=P.sub.roi−P.sub.bkg, for a coated PU tube placed at 8 cm at 45° in an echogenic gel, whereby the ultrasound images of the coated tubes were obtained using an Esaote Mylab One touch with a linear probe. Scanning frequency was 10 MHz and the brightness gain 64%.

[0042] FIG. 3 shows ultrasound images of the coated area with measured contrast from 10-60. It is clear that images with higher contrast give better visibility. 25 is the minimum contrast needed for the clinician to be able to accurately localize the coated device.

[0043] Experimental

[0044] Contrast measurements have been performed on polyurethane tubes on which a thin film of coating containing microparticles has been applied using a dip coater. The surface density of microparticles on the PU tubes has been determined by counting the number of microparticles per mm.sup.2 under a microscope. The contrast measurements have been performed in an ultrasound phantom as a test medium, using a linear array ultrasound probe operating at 10 MHz. The tubes were inserted at an approximate angle of 45°, relative to the ultrasound probe. The distal end of the polyurethane tube was positioned at a depth of 8 cm inside the test medium.

[0045] A series of coated PU tubes were prepared with an increasing number of particles on the surface for each of the 6 particle size conditions. The ultrasound contrast of each coated PU tube was measured according to the method described above. The data are indicated in Table 1. In the table the surface density of microparticles per square millimetre is provided for a contrast of at least 25, at least 30 or even at least 40. Moreover, an upper limit is provided where monolayer is still visible, and an upper limit beyond which bilayer formation will occur. Since problems of adhesion and abrasiveness are to be avoided upper limits that are close to the upper limit known to have a monolayer are preferred.

TABLE-US-00004 TABLE 1 Con- Con- Con- Con- Particle size trast trast trast Maximum dition (μm) >25 >30 >40 monolayer Bilayer I 10 < D.sub.50 ≤ 22 362 856 n.a. 1980 2180 II 22 < D.sub.50 ≤ 27 478 1218 n.a. 1541 1712 III 27 < D.sub.50 ≤ 32 467 1074 1380 1552 1833 IV 32 < D.sub.50 ≤ 38 235 350 1153 1511 1762 V 38 < D.sub.50 ≤ 45 256 291 370 1373 1546 VI 45 < D.sub.50 ≤ 53 218 318 370 1478 1711