Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2002-02-07
2004-04-13
Imam, Ali M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06719699
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to the medical use of ultrasound acoustic energy for imaging, doppler based flow measurement, and therapy. In particular, the present invention pertains to the use of adhesive, acoustic self-coupling hydrogels to couple sound between ultrasound transducers and protective sheaths or covers.
BACKGROUND OF THE INVENTION
Ultrasound, as used for medical applications, utilizes high frequencies, typically between 1 and 30 MHz for imaging and flow measurements and between 0.050 and 1.00 MHz for therapy, all of which are poorly transmitted by air and require a medium similar in acoustic properties to tissue, commonly a thick fluid, gel or solid membrane, which displaces air and fills contours between the “eye” or transducer of an ultrasound instrument (such as a probe or scanhead), which converts energy between electrical and acoustic, and the body or object into which the sound is being directed. This medium, by nature of its physical and acoustic properties, serves as an ultrasound acoustic transmission “coupler” between the object of interest and the electronic transducer, thereby acoustically joining the two, so that the sound based information developed can freely pass back and forth between the body and the electronics. Because of the “coupling” effect, this media is commonly referred to as an ultrasound couplant, ultrasound transmission media or acoustic transmission media.
Hydrophilic membranes as coupling media is disclosed, for example, in U.S. Pat. No. 6,039,694 to Larson, et al., which teaches the use of hydrogel films composed of block co-polymers of polyurethane and polyacrylonitrile. The patent discloses application of these materials for ultrasound scanning in the form of shape-conforming films produced by dipping methods, flat membranes that can be stretched over the active surface of an ultrasound probe, scanning through a membrane that is placed in direct contact with skin, and imaging through a latex or other polymeric protective probe cover with such a membrane covering the active area of the transducer and portions of the transducer body. These self-coupling hydrogel films eliminate the requirement for gels and other liquid couplants, and can provide a microbial barrier between the patient and ultrasound probe.
However, by virtue of the composition and mechanical properties, use of films such as those of U.S. Pat. No. 6,039,694 is limited. The films are slippery and lack adhesive characteristics. Such characteristics, while desirable as a scanning surface, tend to allow the membrane to slip off non-horizontal surfaces and slide with the ultrasound probe as it is moved over the surface of the membrane. While the films of U.S. Pat. No. 6,039,694 have sufficient mechanical strength to permit conformal fit by stretching the film over the active face of an ultrasound probe, the absence of adhesive characteristics requires that the membrane be secured to the probe by some mechanical means such as a rubber band or strap.
U.S. Pat. No. 5,522,878 to Montecalvo et al. describes a solid, multipurpose, flexible, ultrasonic, biomedical couplant hydrogel in sheet form to facilitate transfer of ultrasound energy to and from a patient. Also described is a method of attaching the sheet to skin to hold the couplant gel in place during an exam, which constitutes a band of pressure sensitive adhesive bonded to plastic foam, such as foamed rubber, that is located along the outer perimeter of the sheet. The hydrogel sheet so described is not adhesive in and of itself, but depends on an unreliable potential that sufficient perspiration will be present to make the gel somewhat tacky in instances where the chemical composition is such that addition of moisture to the hydrogel will result in some degree of tack. The adhesive border, so described, is not acoustic self-coupling, therefore restricting ultrasound scanning to areas exclusive of those covered with adhesive covered foam.
U.S. Pat. No. 5,782,767 to Pretlow, III, describes a pad assembly for coupling ultrasound from a transducer probe into the human body, wherein a humectant, such as glycerin in combination with water, creates sufficient surface tension for a pad containing a mixture of water and a humectant, such as glycerin, to remain attached to the probe face by the weak forces of surface tension when the pad is extracted from the storage container and placed on skin. Since general scanning procedures normally require large volumes of couplant materials, and the transducer is moved over large areas, such as is done in fetal scanning, the device of U.S. Pat. No. 5,782,767 is limited to single site applications, such as is disclosed by Pretlow for monitoring bladder fullness, rather than as a device for general ultrasound scanning procedures, where its design for such use would not be practical. Use of this device for general scanning would rapidly deplete the glycerin and water mixture, and since the acoustic coupling and the weak forces of surface tension rely upon the presence of this mixture of liquids rather than an engineered adhesive, such general use would to a high degree lead to probable loss of acoustic coupling and separation of the couplant pad from the transducer face.
U.S. Pat. No. 5,394,877 to Orr et al. describes a contact medium structure attachable to externally applied medical diagnostic devices for providing self-adherence of a medical device to the skin of a patient thereby eliminating the need for retaining belts or similar means. A contact medium is described that is inherently adhesive, hydrophilic, skin compatible, ultrasonic compatible and pressure sensitive to facilitate self-adhesion of the medical device to the patient's skin. The device of Orr et al. discloses use as an ultrasound conductive medium, however such device provides only for the attachment of one side the adhesive membrane to the skin of a patient and the opposite adhesive side to a medical device such as a transducer for monitoring purposes, and as such, is limited to use on one site once properly placed. The design of the device of Orr et al. restricts use of medical devices to one area of the body and prevents free gliding motions of a medical device, such as an ultrasound transducer, over the body of a patient, as is necessary for medical imaging procedures. For example, ultrasound imaging over large external areas or imaging from within the body of a patient is inconsistent with its stated use or structural design.
The formulation, manufacture and use of adhesive hydrogels for products that form an interface with skin and tissue Is known to the artisan as is the formulation, preparation and use of adhesive hydrophilic compounds for wound treatment and electrically conductive devices. Adhesive hydrogels are commercially available from producers including 3M Corporation, Ludlow Technical Products and Lectec Corporation. For example, Ludlow Technical Products produces UV cured electrically conductive gels designated Series RG 63B, and E-Beam cured PEO and PVP under the descriptions of GKG-1 and GPPG-1 for wound care.
Adhesive materials can be generally described as being hydophobic or hydrophilic. Examples of hydrophobic adhesives include such familiar items as adhesive tape and bandages. Hydrophobic adhesive materials are most often produced from vinyl based monomers then coated on various flexible polymeric backings which provide for utility as devices to hold other materials such as gauze for maintaining wound dressings in place and in common household uses.
Pressure sensitive hydrophilic adhesives have been developed that provide for a broad range of applications where such materials come into contact with human skin and tissues. Such adhesive materials can be produced by various methods and formulations that provide physical and mechanical properties specific to intended applications. Examples include formulations that produce films and membranes by cross-linking hydrophilic polymers in combination with various humectants, tackifiers, photoinitiators and cross-linkers
Imam Ali M.
McDowell Robert L.
Sonotech, Inc.
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