Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-08-04
2003-08-26
Jaworski, Francis J. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06610016
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to echogenic coatings for biomedical devices, and methods of preparing them. The coatings include echogenic irregularities and dramatically improve the visibility of the devices when viewed using ultrasound imaging techniques.
2. Background Information
Ultrasonic imaging has many applications. This technology is especially valuable for medical imaging applications because diagnostic ultrasound procedures are safe, very acceptable to patients and less expensive than other digital imaging technologies such as CT or MRI. Also, instruments are widely available and images are produced in real time. However, currently the contrast resolution of ultrasound is not as good as the other technologies. Hence, improvements in image quality open the door to rapid growth of this technique.
A variety of ultrasound contrast agents are known. These include porous uniformly-sized non-aggregated particles as described in Violante and Parker, Ser. No. 08/384,193. Such contrast agents may enhance the visibility of target tissue into which they are injected, but they can not enhance the ultrasound visibility of insertable medical devices.
In many medical procedures, the ability to accurately place a device within a tissue or passageway, especially within a suspected lesion, such as an abscess, cyst, tumor, or in a specific organ such as kidney or liver, is very important to complete the diagnosis or therapy of a patient. Such devices include needles, catheters, stents, dilators, introducers, angiography and angioplasty devices, pacemakers, in-patient appliances such as pumps, and artificial joints. Fine needle biopsy, fluid drainage, catheter placement for angiography, angioplasty, amniocentesis, or drug delivery are a few examples of medical procedures requiring accurate placement of medical devices. Inaccurate device placement may create a need to repeat a procedure thereby adding to medical care costs and patient discomfort or may, in some cases, result in a false negative diagnosis for example if a biopsy needle missed a lesion. Worse, misplacement may harm a patient directly.
Most medical devices, including catheters, have an acoustic impedance similar to that of the tissue into which the device is inserted. Consequently visibility of the device is poor and accurate placement becomes extremely difficult if not impossible. Another problem affecting the visibility of devices is the scattering angle. For example, stainless steel needles have an acoustic impedance significantly different from tissue and are highly visible under ultrasound imaging when the needle is in the plane of the ultrasound beam, but if the needle is moved to some other angle off-axis, the ultrasound beam is scattered in a direction other than the transducer and the needle becomes less visible or even invisible under ultrasound imaging.
Both of the problems described above have been addressed by efforts to increase the scattering power of the device so that the device becomes visible even when it is not completely in the plane of the ultrasound beam. U.S. Pat. No. 4,401,124 describes enhancing the scattering power of a needle by means of grooves in the tip of the device. This approach improves the angle of echo scattering, but the intensity of the scattered signal is less than ideal, and at any angle other than the optimum, signals are lost into the background speckle.
Another approach to improve the echogenicity of devices is set forth in Bosley et al., U.S. Pat. No. 5,201,314. This patent describes a material having an acoustic impedance different from that of the surrounding medium, and improved scattering. The material may be the device itself or a thin interface layer including hard particles such as metal or glass. The presence of spherical indentations formed or embossed on the device surface is said to produce enhanced scattering.
One problem with this approach is that the interface layer is generated during the extrusion process for forming a plastic device, or by soldering, or ion beam deposition, which are inapplicable to many devices, and are expensive and difficult to control. Also the differences in acoustical properties between glass or metal and body cavities are not very large, so echogenicity is not greatly enhanced. Further, the described devices are not smooth since the echogenicity is produced either by indentations in the surface or the addition of metal or glass balls of diameter greater than the thickness of the interface layer. The presence of the particles complicates the manufacturing process, and may weaken the surface of the device which can lead to sloughing of particles, device failure, or instability of the desired effect. Such coatings have not found their way into the market.
SUMMARY OF THE INVENTION
This invention satisfies a long felt need for improving the ultrasound imaging of biomedical devices. The coatings of the invention provide highly echogenic devices which are readily recognized from surrounding tissue or fluid under ultrasound imaging.
The invention succeeds at providing a broadly applicable method of enhancing the ultrasound visibility of surfaces, an objective which previous efforts have failed to reach. The invention solves two problems of the prior art—providing the medical device with an acoustic impedance quite different from that of the animal or human tissue into which it is placed (high acoustic impedance differential), and increasing ultrasound scattering—by a simple, inexpensive, reproducible means of applying a polymer composite coating that has acoustical irregularities. The coatings of the invention are easily made by a variety of methods. They do not require solid particles or particle preparations and do not require machining or extrusion, elements employed in the prior art. Nonetheless, the coatings of the invention provide improved echogenicity.
An adherent, smooth coating employing acoustical irregularities to provide an increased acoustical impedance differential and increased ultrasound scattering differs from prior approaches, and was not previously known or suggested. Such a coating provides advantages that were not previously appreciated, such as broad applicability, the possibility of applying the coating after the device is manufactured, low cost, uniformity, and adaptability to be combined with other coating technologies such as lubricious coatings and coatings containing pharmaceutical agents.
A coated device prepared according to this invention is easily discernable under ultrasound imaging regardless of the angle to the transducer. Since the device is easily recognized against the background tissue or fluid, its exact location is easily identified. This positional certainty can greatly facilitate medical procedures such as biopsies, abscess drainage, chemotherapy placement, etc.
The coatings of the invention include echogenic features, such as discrete gas bubbles and pores, providing acoustically reflective interfaces between phases within or on the coated surface. These interfaces provide an acoustical impedance differential that is large, preferably several orders of magnitude. The shape of the bubbles or other gaseous spaces also improves scattering so that a device may be imaged at virtually any angle.
The advantages and objectives of the invention may be achieved by entrapping gas bubbles in a smooth, thin, biocompatible coating which can be applied to virtually any biomedical device. Gas bubbles are desirable to provide an acoustic impedance mismatch (acoustical impedance differential) much greater than can be obtained by previous inventions. Gas bubbles, especially of small diameter less than about 10 microns, are difficult to stabilize, and satisfactory methods for producing them are a further advantage of this invention. The presence of bubbles entrapped in a thin coating, preferably about 5 to about 50 microns thick, greatly enhances the echogenicity of the device while leaving the device surface very smooth so as to be virtually undetectable by the patient or phy
Lanzafame John F.
Lydon Margaret
Violante Michael R.
Whitbourne Richard J.
Gollin Michael A.
Jaworski Francis J.
STS Biopolymers, Inc.
Venable LLP
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