US Patent 6,280,704: Claim Scope, Expiration, Litigation Risk, and Ultrasound Microbubble Patent Landscape

US Patent 6,280,704 covers an ultrasound-imaging system paired with a kit that produces osmotically stabilized microbubbles. The core technical limitation is a microbubble containing two gas components: a modifier gas and a low-water-solubility gas osmotic agent, present within a defined molar ratio. The patent is expired by its statutory term and does not provide a current blocking right. Its historical claim scope was broad, but commercial relevance now depends on later patents covering specific contrast agents, lipid or protein shells, manufacturing processes, formulations, and approved clinical uses.

What does US Patent 6,280,704 cover?

US 6,280,704, titled "Osmotically Stabilized Microbubbles," claims systems that combine:

An ultrasound imaging apparatus; and
A kit capable of producing a stabilized microbubble preparation.

The preparation must contain an aqueous medium with dispersed microbubbles. Each microbubble must have a generally spherical membrane containing:

At least one modifier gas;
At least one gas osmotic agent; and
A modifier-gas-to-osmotic-agent molar ratio generally ranging from about 1:100 to 1,000:1.

The claimed gas osmotic agents include fluorinated liquids or vapors such as perfluoropentane, perfluorohexane, perfluorocyclohexane, perfluoroheptane, perfluoromethylcyclohexane, perfluorodimethylcyclopentane, perfluorotrimethylcyclobutane and perfluorotriethylamine (USPTO, 2001).

The patent is a platform patent. It does not claim one commercial ultrasound contrast agent by brand name. It claims a physical stabilization mechanism based on incorporating a relatively insoluble, often fluorinated, osmotic gas component into a microbubble.

What are the independent claims in US 6,280,704?

The patent has four principal independent claims: claims 1, 48, 61 and 93.

Independent claim	Principal membrane or gas limitation	Principal scope
Claim 1	Broad membrane; listed gas osmotic agents	Ultrasound system and kit using osmotically stabilized microbubbles
Claim 48	Gas osmotic agent is vapor of a compound liquid at 37°C and 760 Torr	Broader functional and physical-property formulation
Claim 61	Membrane comprises proteinaceous material	Protein-shell microbubble system
Claim 93	Modifier gas is selected from specified fluorocarbon gases	Fluorocarbon-modifier embodiment

Claims 1 and 48 are the broadest claim families. Claim 61 narrows the membrane to proteinaceous material. Claim 93 narrows the modifier gas to fluorocarbon gases, including perfluoropropane, perfluorobutane, perfluorocyclobutane, perfluoromethylcyclobutane, perfluoropentane and perfluorocyclopentane.

The claims are system claims rather than straightforward composition claims. A product that only contains microbubbles, without the claimed ultrasound apparatus and kit relationship, would not necessarily satisfy the literal wording of the issued claims.

How broad is the gas-ratio limitation?

The principal numerical limitation is the molar ratio of modifier gas to gas osmotic agent:

About 1:100 to about 1,000:1 in the independent claims;
About 1:100 to 1:1 in claims 75, 81 and 87;
About 1:10 to 1:1 in claims 76, 82 and 88;
Greater than 1:1 in claims 77, 83 and 89.

This structure creates overlapping dependent-claim ranges. A formulation with a modifier-gas-to-osmotic-agent ratio of 2:1, for example, falls within the "greater than 1:1" claims. A formulation at 0.5:1 falls within the 1:10-to-1:1 range and the broader 1:100-to-1:1 range.

The ratio is potentially important for infringement analysis because it is not enough to identify the gas components. The accused preparation would also need to fall within the relevant ratio, subject to claim construction and the method used to measure gas quantities.

What microbubble membranes and surfactants are protected?

The claims cover several shell architectures.

Surfactant membranes

Claims 8-11, 18-20, 27-29, 33-37, 41-47 and 55-57 cover membranes containing surfactants. The categories include:

Nonionic, neutral and anionic surfactants;
Fluorinated surfactants;
Phospholipids;
Polyoxyethylene-polyoxypropylene copolymers;
Albumin and other protein-derived materials;
Hydroxyethyl starch;
Dextrans and dextran fatty-acid esters;
Sorbitol derivatives;
Gelatin;
Fatty alcohols and fatty-acid esters.

The patent also identifies non-Newtonian surfactants and specific mixtures of phospholipids with polyoxyethylene-polyoxypropylene copolymers. These limitations are relevant to lipid-shelled ultrasound agents, but the patent does not automatically cover every lipid microbubble. The gas combination and ratio remain necessary.

Liposome membranes

Claim 12 and claim 58 cover a microbubble membrane comprising a liposome. This language is broader than a single lipid species but still depends on the claimed gas architecture.

Proteinaceous membranes

Claims 13, 14, 21, 22, 38, 39, 59, 60 and 61-74 address proteinaceous membranes, with albumin as the principal species. A protein shell alone is not enough. The gas osmotic agent, modifier gas and ratio limitations remain part of the combination.

What are the key chemical embodiments?

The most commercially relevant embodiments are the perfluoropentane and perfluorohexane claims.

Gas osmotic agent	Modifier-gas embodiments	Relevant claims
Perfluoropentane	Nitrogen, air, oxygen, carbon dioxide, fluorocarbon gases	15-29
Perfluorohexane	Nitrogen, air, oxygen, carbon dioxide, fluorocarbon gases	30-47
Listed fluorocarbon osmotic agents	Fluorocarbon or nonfluorocarbon modifier gases	1-74
Vapor of a compound liquid at 37°C	Broad modifier-gas alternatives	48-60
Fluorocarbon modifier gas	Listed osmotic agents	93-99

Claims 25 and 26 are technically distinctive. They cover perfluoropentane at least partly in a liquid state and a liquid-in-liquid emulsion that forms the stabilized microbubble preparation when pressure is altered. This language reaches a kit and activation process rather than only a preformed suspension.

Claims 79, 80, 85, 86, 91, 92, 98 and 99 add a microbubble diameter of about 1-10 micrometers, with about 6 micrometers as a narrower limitation. These dimensions align with intravascular ultrasound contrast applications, but particle-size evidence would be required in a product assessment.

When did US Patent 6,280,704 lose exclusivity?

US 6,280,704 was issued on August 28, 2001. Its enforceable term ended approximately 20 years after the applicable nonprovisional filing date, subject to any patent-term adjustment or terminal disclaimer recorded in the USPTO file. Public patent records identify the patent as expired by term rather than as an active patent right (USPTO, n.d.-a).

The practical consequence is direct:

Issue	Current assessment
Patent status	Expired by statutory term
Current injunction risk under this patent	None based solely on the expired patent
Current royalty leverage	None from the expired patent alone
Historical blocking position	Broad platform position in osmotically stabilized microbubbles
Need to review later patents	Yes, particularly for formulations, manufacturing and approved agents

Patent expiration does not eliminate the technical value of the disclosure. It permits use of the claimed platform, but later patents may protect particular compositions, production methods, packaging systems or therapeutic indications.

What is the Orange Book status of US 6,280,704?

US 6,280,704 is not an Orange Book-listed patent for a currently marketed FDA-approved ultrasound contrast product. The Orange Book lists patents submitted by applicants for approved drug products, but an old platform patent does not become an Orange Book patent merely because it relates to a drug-delivery or imaging technology (FDA, 2024).

The principal FDA-approved ultrasound contrast agents have been protected, where applicable, by product-specific patents and regulatory exclusivities associated with their active gas, shell, dosage form and labeling. Those rights must be analyzed separately from US 6,280,704.

Which approved ultrasound contrast agents are most relevant?

The principal commercial comparators use different gas and shell technologies.

Product	Sponsor or manufacturer	Active contrast component	General shell technology	Relationship to US 6,280,704
Definity	Lantheus Medical Imaging	Perflutren lipid microspheres	Lipid shell	Requires separate analysis of perflutren and lipid formulation patents
Optison	GE Healthcare	Perflutren protein-type microspheres	Human serum albumin shell	Technically closer to protein-shell embodiments, but product-specific patents and expiration dates control
Lumason/SonoVue	Bracco	Sulfur hexafluoride lipid microspheres	Phospholipid shell	Uses a different principal gas from the listed perfluorocarbon osmotic agents
Sonazoid	GE Healthcare	Perfluorobutane microspheres	Lipid-based shell	Relevant to fluorocarbon microbubble landscape, but requires separate claim-by-claim review

FDA-approved labels identify the active gases, shell materials, reconstitution procedures and approved imaging indications (FDA, 2023a, 2023b, 2023c, 2023d).

The closest technical overlap is not necessarily the closest legal overlap. A commercial product can use a fluorocarbon gas and a lipid shell without infringing this patent if it lacks the claimed two-gas osmotic stabilization mechanism, falls outside the ratio, or does not meet the system-and-kit limitations.

What formulation patents remain important after US 6,280,704 expired?

Later patent risks typically fall into five categories:

Specific gas formulations

Later patents may claim perflutren, sulfur hexafluoride, perfluorobutane or other gases in defined shell systems. These claims can be composition claims and may not require the same osmotic-agent ratio.

Lipid-shell compositions

Patent estates may cover phospholipid combinations, charged lipids, polyethylene glycol-modified lipids, stabilizers, cryoprotectants and particle-size distributions.

Protein-shell formulations

Albumin-based agents may be protected by claims directed to denaturation conditions, cross-linking, shell thickness, gas loading or reconstitution stability.

Manufacturing methods

Relevant claims may cover high-shear mixing, sonication, mechanical agitation, pressure cycling, lyophilization, vial preparation and gas exchange. These claims can create manufacturing barriers even when the underlying composition is unpatented.

Method-of-use claims

Later patents may cover echocardiography, liver imaging, renal imaging, vascular imaging, perfusion assessment, molecular targeting or ultrasound-mediated drug delivery. An expired platform patent does not remove method-of-use restrictions under later patents.

Were there Paragraph IV challenges to US 6,280,704?

No current Paragraph IV challenge is material to US 6,280,704 because the patent has expired and is not an active Orange Book-listed patent for a marketed product.

Paragraph IV litigation is more relevant to generic versions of Definity, Optison or other approved contrast agents. A generic applicant must address patents listed for the reference product and may assert that those patents are invalid, unenforceable or not infringed. The relevant litigation record is product-specific rather than centered on US 6,280,704 (FDA, 2024; USPTO, n.d.-b).

What patent litigation and settlements affect this technology?

US 6,280,704 should be treated as a historical platform patent rather than a current litigation asset. The commercial disputes most likely to affect ultrasound contrast products concern:

Listed patents for the reference product;
Patent litigation over lipid or albumin shells;
Manufacturing-process patents;
Patent term and pediatric exclusivity;
Settlement agreements governing generic launch dates;
Regulatory exclusivity and labeling restrictions.

A settlement involving a later product patent would not revive or extend US 6,280,704. The expired patent also cannot independently support a new Paragraph IV settlement or delayed generic-entry date.

How strong was the patent estate for US 6,280,704?

Historical strength

The patent had meaningful historical breadth because it combined:

Multiple gas classes;
Numerous osmotic-agent species;
Protein, liposome and surfactant membranes;
Broad ratio ranges;
Liquid-emulsion activation;
Defined microbubble sizes;
Ultrasound-system and kit language.

The specification appears designed to cover both preformed microbubble preparations and kits that generate bubbles in use.

Current strength

Its current legal strength is zero as an enforceable patent right because the patent term has ended. Its residual business value is technical and evidentiary:

It may operate as prior art against later patents;
It can inform freedom-to-operate analyses;
It may narrow the scope of later patent claims;
It can support historical ownership and licensing diligence;
It may identify inventors, assignees and continuation relationships.

The patent's broad language also creates prosecution-history questions. The exact scope of issued claims must be read with the specification, file history, any reexamination record and related continuation patents.

What claim-construction issues matter most?

Several issues are material.

"Kit capable of producing"

This phrase may reach a kit that contains components for forming the preparation, rather than only a vial containing finished microbubbles. The infringement analysis would depend on what the kit contains and how the components are used.

"Gas osmotic agent"

The term is central. The claimed agent must contribute to osmotic stabilization and, in several claims, must meet a water-solubility threshold or be the vapor of a liquid at body-temperature conditions.

Molar ratio

The ratio must be established for the relevant gas components. Measurement could be complicated by gas partitioning, partial liquid-state storage, pressure changes and reconstitution.

"Generally spherical microbubble membrane"

This limitation may raise questions about irregular particles, shell morphology and whether the membrane is continuous, multilayered or formed from a surfactant-protein mixture.

Claim 97 inconsistency

As supplied, claim 93 requires a fluorocarbon modifier gas, while claim 97, which depends through claims 96 and 93, states that the modifier gas is nonfluorocarbon. A dependent claim ordinarily cannot broaden its parent claim. This apparent inconsistency should be checked against the official issued patent and file history before relying on claim 97.

What generic-entry risks exist for ultrasound contrast agents?

The principal generic-entry risks are product-specific:

Risk area	Likely effect
Active gas patent	Can delay or restrict generic composition entry
Shell formulation patent	Can require a different lipid or protein architecture
Reconstitution patent	Can force alternative packaging or activation
Manufacturing patent	Can require a non-infringing production route
Method-of-use patent	Can restrict labeling or promoted indications
Orange Book patent listing	Can trigger Paragraph IV litigation
Regulatory exclusivity	Can delay approval even after patent expiry

US 6,280,704 does not create a current generic-entry barrier. The meaningful diligence question is whether a proposed product practices later, unexpired patents covering the active gas, shell, kit, manufacturing process or labeled use.

Key Takeaways

US 6,280,704 covers ultrasound systems using kits that generate osmotically stabilized microbubbles.
Its core limitation is a modifier gas combined with a poorly water-soluble gas osmotic agent at a defined molar ratio.
The patent reaches fluorocarbon and nonfluorocarbon modifier gases, protein, liposome and surfactant membranes, liquid emulsions and selected particle sizes.
Claims 1, 48, 61 and 93 are the principal independent claim groups.
The patent is expired by statutory term and has no current blocking effect.
It is not a current Orange Book patent for an approved ultrasound contrast product.
Paragraph IV and settlement analysis must focus on later product-specific patent estates.
Definity, Optison, Lumason/SonoVue and Sonazoid use related but materially different gas and shell technologies.
Claim 97 contains an apparent dependency inconsistency that requires verification against the official patent record.
Current freedom-to-operate risk is more likely to arise from later formulation, manufacturing, packaging and method-of-use patents.

FAQs About US Patent 6,280,704

Does US 6,280,704 cover Definity?

Not automatically. Definity uses perflutren lipid microspheres. A determination would require analysis of the actual gas composition, shell, ratio, kit configuration and later patents. The expired status of US 6,280,704 eliminates current infringement liability under that patent.

Does the patent cover sulfur hexafluoride microbubbles?

The independent claims do not expressly list sulfur hexafluoride as a gas osmotic agent. A sulfur-hexafluoride product would require analysis under the broader functional language, specification and claim-construction principles, but the patent is expired in any event.

Can a company use the disclosed perfluoropentane formulation?

The expired patent itself does not prevent use. A company must still review later patents covering the particular shell, manufacturing process, kit, packaging and clinical application.

Is albumin-protein microbubble technology still patent-protected?

Some albumin-based technologies may have later patent protection. The albumin limitations in US 6,280,704 are no longer enforceable because the patent term has ended.

Does patent expiration eliminate FDA requirements?

No. FDA approval, labeling, manufacturing controls, safety testing and product-specific regulatory requirements remain separate from patent rights (FDA, 2023a-2023d).

References

U.S. Food and Drug Administration. (2023a). Definity prescribing information.
U.S. Food and Drug Administration. (2023b). Optison prescribing information.
U.S. Food and Drug Administration. (2023c). Lumason prescribing information.
U.S. Food and Drug Administration. (2023d). Sonazoid prescribing information.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations.
U.S. Patent and Trademark Office. (2001). U.S. Patent No. 6,280,704, Osmotically stabilized microbubbles.
U.S. Patent and Trademark Office. (n.d.-a). Patent Center: U.S. Patent No. 6,280,704.
U.S. Patent and Trademark Office. (n.d.-b). Orange Book patent and exclusivity information.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	281183	⤷ Start Trial
Australia	4922196	⤷ Start Trial
Australia	5199701	⤷ Start Trial
Australia	694135	⤷ Start Trial
Australia	731099	⤷ Start Trial
Australia	731671	⤷ Start Trial
Australia	7478294	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Summary for Patent: 6,280,704