AU1197002A - Low density microspheres - Google Patents

Description

S&F Ref: 251910D4

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

0 0 Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: ImaRx Pharmaceutical Corp.

1635 E. 18th Street Tucson Arizona 85719 United States of America Evan C. Unger Spruson Ferguson St Martins Tower,Level 31 Market Street Sydney NSW 2000 (CCN 3710000177) Low Density Microspheres

G

The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c 1 Low Density Microspheres BACKGROUND OF THE INVENTION Computed tomography (CT) is a widespread diagnostic imaging method which measures, in its imaging process, the radiodensity (electron density) of matter, This radiodensity is depicted using CT in terms of Hounsefield Units Hounsefield Units, named after the inventor of the first CT scanner, reflect the relative absorption of CT X-rays by matter, the absorption being directly proportional to the electron density of that matter. -Water, for example, has a value of 0 HU, air a value of 1000 HU, and dense cortical bone a value of 15 1000 HU. Because of the similarity in density of various tissues in the body, however, contrast agents have been sought to change the relative density of different tissues, and improve the overall diagnostic efficacy of this imaging method.

20 In the search for contrast agents for CT, researchers have generally sought to develop agents that will increase electron density in certain areas of a region of the body (positive contrast agents). Barium and "iodine compounds, for example, have been developed for this purpose. For the gastrointestinal tract, barium sulfate is used extensively to increase the radiodensity of the bowel lumen on CT scans. Iodinated water soluble contrast media are also used to increase density within the gastro- intestinal tract, but are not used as commonly as the barium compounds, primarily because the iodine preparations are more expensive than barium and prove less 2 effective in increasing radiodensity within this region of the body.

Despite their widespread use, however, barium and iodine compounds are suboptimally effective as gastrointestinal contrast agents for CT. For example, if the concentration is too low, there is little contrast.

Conversely, if the concentration is too high, then these radiodense contrast agents cause beam hardening artifacts which are seen as streaks on the CT images. It is also difficult to visualize the bowel mucosa with either the barium or iodine contrast agents.

In an attempt to improve upon the efficacy of contrast agents for the gastrointestinal tract, lipid emulsions that are capable of decreasing electron density 15 (negative contrast agents) have been developed. Because :.lipids have a lower electron density than water, lipids provide a negative density on CT (a negative RU value).

While these lipid emulsions appear to be more effective than the barium and iodine agents at improving visual- 20 ization of the mucosa of the bowel, these contrast agents have limitations. First, there is a limitation to the concentration of lipid which a patient can tolerably drink, which puts a limit on the change in density (or HU) 0. 0.which the lipid based CT contrast agent can provide.

Lipid emulsions are also frequently expensive.

Furthermore, these lipid formulations are generally Sperishable, which provides for packaging and storage 0 ooproblems.

New and/or better contrast agents for computed tomography imaging are needed. The present invention is directed toward this important end.

SUMMARY OF THE INVENTION The present invention is directed to pomputed tomography imaging, and more particularly to the use of a contrast medium comprising a substantially homogeneous aqueous suspension of low density microspheres to image the gastrointestinal region and other body cavities of a patient. In one embodiment, the low density microspheres are gas-filled.

Specifically, the present invention pertains to methods of providing an image of the gastrointentional region or other body cavities of a patient comprising administering to the patient the aforementioned contrast medium, and (ii) scanning the patient using computed tomography imaging to obtain visible images of the gastrointestinal region or other body cavities.

The present invention is further directed to methods for diagnosing the presence of diseased tissue in the gastrointestinal region or other body cavities of a patient comprising administering to the patient the aforementioned contrast medium, and (ii) scanning the patient using computed tomography imaging to obtain visible images of any diseased tissue in the patient.

The present invention also provides diagnostic kits for computed tomography imaging of the gastro-intestinal region or other body cavities which include the subject i 15 contrast medium.

S"Thus, according to the first aspect of this invention there is provided a contrast medium for computed tomography imaging of the gastrointestinal region or other body S cavities comprising a substantially homogeneous aqueous suspension of low density gasfilled microspheres having an internal void volume of at least about 75% of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon.

I According to the second aspect of this invention there is provided a contrast medium for diagnostic imaging comprising a substantially homogeneous aqueous suspension of low density gas-filled microspheres having an internal void volume of at least about 75% of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon.

According to the third aspect of this invention there is provided a substantially homogeneous aqueous suspension of low density gas-filled microspheres having an internal void volume of at least about 75% of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon.

According to the fourth aspect of this invention there is provided a kit for computed tomography imaging of the gastrointestinal region or other body cavities of a patient comprising low density gas-filled microspheres having an internal void volume of at least about 75% of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon, in combination with a thickening or suspending agent.

fI:\DayLib\LIBUU]42753.doc:MCN According to the fifth aspect of this invention there is provided a kit for diagnostic imaging of patient comprising low density gas-filled microspheres having an internal void volume of at least about 75% of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon, in combination with a thickening or suspending agent.

According to the sixth aspect of this invention there is provided a method of providing an image of the gastrointestinal region and other body cavities of a patient comprising: administering to the patient a contrast medium comprising a substantially homogeneous aqueous suspension of low density gas-filled microspheres having an internal void volume of at least about 75% of the total volume of the microsphere, 1o wherein said gas comprises a perfluorocarbon, and scanning the patient using computed tomography imaging to obtain visible images of the gastrointestinal region or o ther body cavities.

According to the seventh aspect of this invention there is provided a method of providing an image of a region of a patient comprising administering to the patient a S° is contrast medium comprising a substantially homogeneous aqueous suspension of low oooi density gas-filled microspheres having an internal void volume of at least about 75% of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon, and scanning the patient using diagnostic imaging to obtain visible images of the region of a patient.

According to the eighth aspect of this invention there is provided a method for diagnosing the presence of diseased tissue in the gastrointestinal region or other body

C

cavities of a patient comprising administering to the patient a contrast medium comprising a substantially homogeneous aqueous suspension of low density gas-filled microspheres having an internal void volume of at least about 75% of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon, and scanning the patient using computed tomography imaging to obtain visible images of any diseased tissue in the patient.

According to the ninth aspect of this invention there is provided a method for diagnosing the presence of diseased tissue in a patient comprising administering to the patient a contrast medium comprising a substantially homogeneous aqueous suspension of low density gas-filled microspheres having an internal void volume of at least about of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon, and scanning the patient using diagnostic imaging to obtain visible images of any diseased tissue in the patient.

[i\DayLib\LIBUU42753.doc:MCN According to the tenth aspect of this invention there is provided a contrast medium for computed tomography imaging of the gastrointestinal region or other body cavities comprising an aqueous suspension of a biocompatible polymer, a perfluorocarbon gas, and a thickening or suspending agent, wherein in said suspension said biocompatible polymer associates with said perfluorocarbon gas to form one or more gas-filled microspheres.

According to the eleventh aspect of this invention there is provided a contrast medium for diagnostic imaging comprising an aqueous suspension of a biocompatible polymer, a perfluorocarbon gas, and a thickening or suspending agent, wherein in said suspension said biocompatible polymer associates with said perfluorocarbon gas to form one or more gas-filled microspheres.

According to the twelfth aspect of this invention there is provided an aqueous .suspension comprising a biocompatible polymer, a perfluorocarbon gas, and a thickening or suspending agent, wherein in said suspension said biocompatible polymer associates s5 with said perfluorocarbon gas to form one or more gas-filled microspheres.

According to the thirteenth aspect of this invention there is provided a kit for computed tomography imaging of the gastrointestinal region or other body cavities of a patient comprising a biocompatible polymer, a perfluorocarbon gas, and a thickening or suspending agent, wherein in said suspension said biocompatible polymer associates with said perfluorocarbon gas to form one or more gas-filled microspheres.

~According to the fourteenth aspect of this invention there is provided a kit for diagnostic imaging of a patient comprising a biocompatible polymer, a perfluorocarbon gas, and a thickening or suspending agent, wherein in said suspension said biocompatible polymer associates with said perfluorocarbon gas to form one or more gas-filled microspheres.

According to the fifteenth aspect of this invention there is provided a method of providing an image of the gastrointestinal region and other body cavities of a patient comprising administering to the patient a contrast medium comprising an aqueous suspension of a biocompatible polymer, a perfluorocarbon gas, and a thickening or suspending agent, wherein in said suspension said biocompatible polymer associates with said perfluorocarbon gas to form one or more gas-filled microspheres, and scanning the patient using computed tomography imaging to obtain visible images of the gastrointestinal region or other body cavities.

According to the sixteenth aspect of this invention there is provided a method of providing an image of a region of a patient comprising administering to the patient a [I:\DayLib\LIBUU42753.doc:MCN contrast medium comprising an aqueous suspension of a biocompatible polymer, a perfluorocarbon gas, and a thickening or suspending agent, wherein in said suspension said biocompatible polymer associates with said perfluorocarbon gas to form one or more gas-filled microspheres, and scanning the patient using diagnostic imaging to obtain visible images of the region of a patient.

According to the seventeenth aspect of this invention there is provided a method for diagnosing the presence of diseased tissue in the gastrointestinal region or other body cavities of a patient comprising administering to the patient a contrast medium comprising an aqueous suspension of a biocompatible polymer, a perfluorocarbon gas, o0 and a thickening or suspending agent, wherein in said suspension said biocompatible polymer associates with said perfluorocarbon gas to form one or more gas-filled D microspheres, and scanning the patient using computed tomography imaging to obtain visible images of any diseased tissue in the patient.

According to the eighteenth aspect of this invention there is provided a method for s15 diagnosing the presence of diseased tissue in a patient comprising administering to the patient a contrast medium comprising an aqueous suspension of a biocompatible polymer, a perfluorocarbon gas, and a thickening or suspending agent, wherein in said suspension said biocompatible polymer associates with said perfluorocarbon gas to form one or more gas-filled microspheres, and scanning the patient using diagnostic imaging to obtain visible images of any diseased tissue in the patient.

According to the nineteenth aspect of this invention there is provided a low density gas-filled microsphere having an internal void volume of at least about 75% of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon.

Detailed Description of the Invention A wide variety of different low density microspheres may be utilized in the present invention. Preferably, the microspheres (which are small spheres having a central void or cavity), are composed of biocompatible synthetic polymers or copolymers prepared from monomers such as acrylic acid, methacrylic acid, ethyleneimine, crotonic acid, acrylamide, ethyl acrylate, methyl methacrylate, 2-hydroxyethyl methacrylate (HEMA), lactic acid, glycolic acid, e-caprolactone, acrolein, cyanoacrylate, bisphenol A, epichlorhydrin, hydroxyalkylacrylates, siloxane, dimethylsiloxane, ethylene oxide, ethylene glycol, hydroxyalkyl-methacrylates, N-substituted acrylamides, N-substituted methacrylamides, N-vinyl-2-pyrrolidone, 2,4-pentadiene-1- [I:\DayLib\LBUU]42753.doc:MCN ol, vinyl acetate, acrylonitrile, styrene, p-aminostyrene, p-axino-benzyl -styrene, sodium styrene sul fonate, sodium 2 -sul foxyethylmethacrylate -vinyl pyridine, aminoethyl. lethacrylates, 2 -methacryloyloxytrimethyammoiu chloride, and POlyvinylidene, as well polyfunctional cross linking. monomers such as N,NIm ethyl eneb isacrylamide, ethylene glycol dimethacrylates, 2, 2 (p-phenylenedioxy) -diethyl dimethacrylate, divinylbenzene, triallylamine and methylenebis- (4-phenyl-* iSocyanate), including combinations thereof. Preferable polymers include polyacryl ic ai, polyethyl eneimine, Polymethacrylic acid, polymethylmethacrylate, polysiloxane, polydimethylsiloxane, polylac tic acid, poly(c-caprolactone), epoxy resin, p oly (ethylene oxide), poly (ethylene glycol) and polyamide (nylon). Preferable copolymers include the following: polyvinylidene..

pOlyaCrylonitrije, poyinlidn-placyontilpo lymethylmethacryl ate, and polystyrene -polyacryl on it r ii1 e.

A most preferred copolymer is polyvinylidene-.

polyacrylonitrile. The term biocompatible, as used herein ain conjunction with the terms monomer or polymer, is employed in its conventional sense, that is, to denote polymers that do not substantially interact with the tissues, fluids and other components of.-the body in a *a 25 adverse fashion in the particular application of interest, such as the aforementioned monomers and polymers. other suitable biocompatible monomers and polymers will be a.readily apparent to those skilled in the art, once armed. with the present disclosure.

The microspheres of the present invention are low density. By low density, it is meant that the microspheres of the invention have an internal void (cavity) volume which is at least about 75 %6 of the total volume of the microsphere. Preferably, the microspheres have a void volume of at least about 80 more preferably at least about 85 even More preferably at least about of the total volume of the microspheres.

8 The microspheres may be of varying size, provided they are low density. Suitable size microspheres include those ranging from between about 1 and about 1o00 microns in outside diameter, preferably between about 5 and about 70 microns in outside diameter. Most preferably, the microspheres are about 50 microns in outside diameter.

The microspheres of the invention may be prepared by various processes, as will be readily apparent to those skilled in the art, once armed with the present disclosure, such as by interfacial polymerization, phase separation and coacervation, multiorifice centrifugal preparation, and solvent evaporation. Suitable procedures which, may be employed or modified in accordance with the present disclosure to prepare microspheres within the 15 scope of the invention include those procedures disclosed in Garner et al., U.S. Patent No. 4,179,546, Garner,

U.S.

Patent No. 3,945,956, Cohrs et al., U.S. Patent No.

4,108,806, Japan Kokai Tokkyo Koho 62 286534, British Patent No. 1,044,680, Kenaga et al., U.S. Patent No. 3,293,114, Morehouse et al., U.S. Patent No. 3,401,475, Walters, U.S. Patent No.

3,479,811, Walters et al., U.S. Patent No. 3,488,714, Morehouse et al., U.S. Patent No. 3,615,972, Baker et al., U.S. Patent No. 4,549,892, Sands et al., U.S. Patent No.

25 4,540,629, Sands et al., U.S. Patent No. 4,421,562, Sands, U.S. Patent No. 4,420,442, Mathiowitz et al., U.S. Patent No. 4,898,734, Lencki et al., U.S. Patent No. 4,822,534, a *Herbig et al., U.S. Patent No. 3,732,172, Himmel et al., U.S. Patent No. 3,594,326, Sommerville et al., U.S. Patent No. 3,015,128, Deasy, Microencapsulation and Related Drug Processes, Vol. 20, Chs. 9 and 10, pp. 195-240 (Marcel Dekker, Inc., 1984), Chang et al., Canadian J. of Physiology and Pharmacology, Vol 44, pp. 115-129 (1966), and Chang, Science, Vol. 146, pp. 524-525 (1964), the disclosures of each of which are incorporated herein by reference in their entirety.

In accordance with the preferable synthesis protocol, the microspheres are prepared using a heat expansion process such as is described in Garner et al., U.S. Patent No. 4,179,546, Garner, U.S. Patent No.

3,945,956, Cohrs et al., U.S. Patent No. 4,108,806, British Patent No. 1,044,680, and Japan Kokai Tokkyo Koho 62 286534. In general terms, the heat expansion process is carried out by preparing microspheres of an expandable polymer or copolymer which contain in their void (cavity) a volatile liquid. The microsphere is then heated, plasticising the microsphere and volatilizing the gas, causing the microsphere to expand to up to about several times its original size. When the heat is removed, the thermoplastic polymer retains at least some of its 15 expanded shape. Microspheres produced by this process tend to be of particularly low density, and are thus preferred. The foregoing described process is well known in the art, and is referred to herein as the heat expansion process for preparing low density microspheres.

20 Polymers useful in the heat expansion process will be readily apparent to those skilled in the art and include thermoplastic polymers or copolymers, including polymers or copolymers of many of the monomers described above. Preferable of the polymers and copolymers described above include the following copolymers: polyvinylidene-polyacrylonitrile, polyvinylidenepolyacrylonitrile-polymethylmethacrylate, and polystyrenepolyacrylonitrile. A most preferred copolymer is polyvinylidene-polyacrylonitrile.

Volatile liquids useful in the heat expansion process will also be well known to those skilled in the art and include: aliphatic hydrocarbons such as ethane, ethylene, propane, propene, butane, isobutane, neopentane, acetylene, hexane, heptane; chlorofluorocarbons such as CC1 3 F, CC1 2 Fz, CC1F 3 CC1F,-CCIF 2 CF-CC1F and CF 2 -CC1F I 1 I I

CF

2

-CF

2

CF

2 -CC1F tetraalkyl silanes such as tetramethyl silane, trimethylethyl silane, trimethylisopropyl silane, and trimethyl n-propyl silane; as well as perfluorocarbons such as those having between 1 and about 9 carbon atoms and between about 4 and about 20 fluorine atoms, especially

C

4 In general, it is important that the volatile liquid not be a solvent for the microsphere polymer or copolymer. The volatile liquid should also have a boiling point that is below the softening point of the microsphere polymer or co-polymer. Boiling points of various volatile liquids and softening points of various polymers and copolymers will be readily ascertainable to one skilled in the art, and suitable combinations of polymers or copolymers and volatile liquids will be easily 15 apparent to the skilled artisan. By way of guidance, and as one skilled in the art would recognize, generally as the length of the carbon chain of the volatile liquid increases, the boiling point of that liquid increases.

Also, by mildly preheating the microspheres in water in 20 the presence of hydrogen peroxide prior to definitive heating and expansion may pre-soften the microsphere to allow expansion to occur more readily.

For example, to produce microspheres of the present invention, vinylidene and acrylonitrile may be copolymerized in a medium of isobutane liquid using one or more of the foregoing modified or unmodified literature procedures, such that isobutane becomes entrapped within the microspheres. When such microspheres are then heatedto between about 80'C and about 120*C, the isobutane gas expands, which in turn expands the microspheres. After heat is removed, the expanded polyvinylidene and acrylonitrile copolymer microspheres remain substantially fixed in their expanded position. The resulting low density microspheres are extremely stable both dry and suspended in an aqueous media. Isobutane is utilized merely as an illustrative liquid, with the understanding that other liquids which undergo liquid/gas transitions at 11 temperatures useful for the synthesis of these microspheres and formation of the very low density microspheres upon heating can be substituted for isobutane. Similarly, monomers other than vinylidene and acrylonitrile may be employed in preparing the microsphere.

Most preferably, the low density microspheres employed are those commercially available from Expancel, Nobel Industries, Sundsvall, Sweden, such as the EXPANCEL 551 DE microspheres. The EXPANCEL 551 DE T microspheres are composed of a copolymer of vinylidene and acrylonitrile which have encapsulated therein isobutane liquid.

Such. microspheres are sold as a dry composition and are approximately 50 microns in size. The EXPANCEL 551 DET 15 microspheres have a specific gravity of only 0.02 to 0.05, which is between one-fiftieth and one-twentieth the density of water.

In one embodiment, the microspheres of the present invention are gas-filled. By gas-filled, it is 20 meant that at least part of the void volume inside the microspheres is occupied by the gas. Preferably, substantially all of the void volume inside the microspheres is occupied by the gas. The gas may be any type of gas, such as, for example, carbon dioxide, oxygen, nitrogen, xenon, argon, neon, helium and air. Preferably, the gas is carbon dioxide, oxygen, nitrogen, xenon, argon, neon and helium. Most preferably, the gas is inert, that is, a gas that is substantially resistant to chemical or physical action. The gas-filled low density microspheres may be synthesized under pressure such that gases are solubilized in the liquid employed in microsphere synthesis. When the pressure is removed, the gas comes out of solution to fill the microsphere void. Such microspheres can further be subjected to a heat expansion process, as described above.

For example, to produce the gas-filled microspheres of the invention, one may copolymerize vinylidene and acrylonitrile using one or more of the foregoing procedures, such as phase separation/coacervation techniques in a pressurized and/or low temperature environment at about 300 psi, and/or at about O'C) with a high concentration of dissolved gas dissolved nitrogen) in solution, to form a large microsphere containing the dissolved gas.

When the pressure is removed and/or the temperature raised, the gas bubbles come out of solution, forming gas filled microspheres. Such microspheres can further be subjected to a heat expansion process, as described above.

It is preferable that the microspheres be relatively stable in the gastrointestinal tract or other body cavities during the length of time necessary for 15 completing an imaging examination. Low density microspheres prepared from the aforementioned monomer and polymer compositions will provide such stable microspheres.

In order for these microspheres to serve as 20 effective CT contrast agents, it is necessary for the microspheres to be mixed in solution in a substantially homogeneous suspension. This can be accomplished by using thickening and suspending agents. A wide variety of thickening and suspending agents may be used to a prepare the substantially homogeneous suspensions of the microspheres. Suitable thickening and suspending agents, for example, include any and all biocompatible agents known in the art to act as thickening and suspending agents. Particularly useful are the natural thickening and suspending agents alginates, xanthan gum, guar, pectin, tragacanth, bassorin, karaya, gum arabic, casein, gelatin, cellulose, sodium carboxymethylcellulose, methylcellulose, methylhydroxycellulose, bentonite, colloidal silicic acid, and carrageenin, and the synthetic thickening and suspending agents polyethylene glycol, polypropylene glycol, and .polyvinylpyrrolidone. As those skilled in the art would recognize, once armed with the 13 present disclosure, the suspending agents may be formulated, if desired, to be either less dense than water or of neutral density, so as to not subtract from the density lowering capabilities of the microspheres. -For example, a cellulose suspension may have a somewhat lower density than water, a 2 weight cellulose solution with 0.25 weight xanthan gum has a density of 0.95. The thickening and suspending agents may be employed in varying amounts, as those skilled in the art would recognize, but preferably are employed in amounts of about 0.25 to about 10 weight preferably about 0.5 to about weight of the contrast medium.

The substantially homogeneous, aqueous suspension of low density microspheres of the invention are useful as 15 CT contrast agents. These agents are capable of producing negative contrast in the gastrointestinal tract or in other body cavities, providing effective contrast enhancement and improved visualization in these areas of the body. Specifically, the present invention is directed to a method of providing an image of or detecting diseased tissue in the gastrointestinal region and other body cavities of a patient, the method comprising administering to the patient a contrast medium comprising a substantially homogeneous aqueous solution of low density microspheres, and scanning the patient using computed S. tomography imaging to obtain visible images of the gastrointestinal region or other body cavities or of diseased tissue in these areas of the body. The phrase gastrointestinal region or gastrointestinal tract, as used herein, includes the region of a patient defined by the esophagus, stomach, small and large intestines, and rectum. The phrase other body cavities, as used herein, includes any region of the patient, other than the gastrointestinal region, having an open passage, either directly or indirectly, to the external environment, such regions including the sinus tracts, the fallopian tubes, the bladder, etc. The patient can be any type of mammal, but most preferably is a human. As one skilled in the art would recognize, administration of the contrast medium to the patient may be carried out in various fashions, such as orally, rectally, or by injection. When the region to be scanned is the gastrointestinl~ region, administration of the contrast medium of the invention is preferably carried out orally or rectally. -When other body cavities such as the fallopian tubes or sinus tracts are to be scanned, administration is preferably by injection. As would also be recognized by one skilled in the art, wide variations in -the amounts of the gas filled microspheres can be employed in the methods and kits of the invention, with the precise amounts varying depending upon such factors as the mode of administration oral, rectal, is1 by injection), and the specific body cavity and portion C thereof for which an image is sought the stomach of Cthe gastrointestinl~ ta). Typically, dosage is initiated, at lower levels and increased until the desired contrast enhancement is achieved.

For CT imaging, it is generally desirable t decrease the density of the lumen of the gastrointestinal Stract or other body cavities to at least about -30 HU, the C maximum decrease being limited by the practical amount of the microspheres which may be suspended in the aqueous media and ingested by the patient. In general, a decrease in HU to between about -30 HU and'about -150 RU is .sufficient tomark the inside of the bowel or other body 0 cavity. By way of general guidance, and as a rough -rule of thumb, to decrease the density of the luicrosphere aqueous suspension to about -150 HU, the luicrospheres must Occupy about 15 1 of the total volume of the aqueous suspension. To achieve a density of about -50 HU, the microspheres must occupy about 5 of 'the total volume of the solution. The volume of contrast agent administered to the patient is typically between about 50 to about 1000 cc. *Using the EXPAJICEL 551 DE' microspheres as a model, it has been found that about 0.6 grams of the dry micron spheres in 100 cc of aqueous suspension is sufficient to decrease the density of the suspension to nearly -150 HU.

It should be noted that smaller microspheres are generally more stable in suspension, but usually have higher specific gravity than larger microspheres.

Therefore, for CT, the size and particular microspheres, as well as the suspending media (thickening and suspending agents) should selected to minimize specific gravity, while maximizing the stability of the suspension.

The contrast medium utilized of the present invention may also be employed with other conventional additives suitable for use in the applications contemplated for the subject invention.

15 Where gastrointestinal applications are concerned, such additives include conventional biocompatible anti-gas agents, osmolality raising agents, gastrointestinal transit agents (the later agents serving to decrease the gastrointestinal transit time and increase 20 the rate of gastrointestinal emptying) and, in some instances, gas-forming agents.

As used herein the term anti-gas agent is a compound that serves to minimize or decrease gas s* formation, dispersion and/or adsorption. A number of such agents are available, including antacids, antiflatulents, antifoaming agents, and surfactants. Such antacids and antiflatulents include, for example, activated charcoal, aluminum carbonate, aluminum hydroxide, aluminum phosphate, calcium carbonate, dihydroxyaluminum sodium carbonate, magaldrate magnesium oxide, magnesium trisilicate, simethicone, sodium carbonate, loperamide hydrochloride, diphenoxylate, hydrochloride with atropine sulfate, Kaopectate m (kaolin) and bismuth salts. Suitable antifoaming agents useful as anti-gas agents include simethicone, protected simethicone, siloxyalkylene polymers, siloxane glycol polymers, polyoxypropylenepolyoxyethylene copolymers, polyoxyalkylene amines and 16 imines, branched polyamines, mixed oxyalkylated alcohols, finely divided silica either alone or mixed with dimethyl polysiloxane, sucroglycamides (celynols), polyoxylalkylated natural oils, halogenated siliconcontaining cyclic acetals, lauryl sulfates, 2-lactylic acid esters of unicarboxylic acids, triglyceride oils.

Particles of polyvinyl chloride or silica may also function as anti-foaming agents in the subject invention.

Suitable surfactants include perfluorocarbon surfactants such as, for example, DuPont Zonyl T perfluoroalkyl surfactants known as ZonylT RP or ZonylT NF, available from DuPont, Chemicals and Pigments Division, Jackson ~Laboratory, Deepwater, NJ 08023. Of course, as those skilled in the art will recognize, any anti-gas agents 15 employed must be suitable for use within the particular biological system of the patient in which it is to be used. The concentration of such anti-gas agents may vary widely, as desired, as will be readily apparent to those skilled in the art. Typically, however, such agents are S 20 employed in concentrations of between about 20 and about 2000 ppm, most preferably in concentrations between about and about 1000 ppm.

uitable osmolality raising agents include polyols and sugars, for example, mannitol, sorbitol arabitol, xylitol, glucose, sucrose, fructose, dextrose, and saccharine, with mannitol and sorbitol being most preferred. The concentration of such osmolality raising agents may vary, as desired, however, generally a range of about 5 to about 70 g/l, preferably about 30 to about g/l of the contrast medium. Such compounds may also serve as sweeteners for the ultimate formulation, if desired.

Gastrointestinal transit agents include algin, as well as many of the compounds listed above as thickening and suspending agents, with algin being most preferred.

The amount of such agents will, of course, vary as those skilled' in the art will recognize, but generally will be employed in an amount of between about 5 and about In some applications, it may be helpful to incorporate gas-forming agents into the contrast medium.

Gas-forming agents include sodium bicarbonate, calcium carbonate, aminomalonate, and the like, which will form gas, for example, upon introduction into the gastrointestinal tract. Such gas-forming agents will ser-ve to distend the gastrointestinal tract and create a form of "double contrast" between the gas and the low density microspheres.

Kits useful for computed tomography imaging of the gastrointestinal region or other body cavities in accordance with the prese nt invention comprise low den sity microspheres, and a thickening or suspending agent, in addition to conventional computed tomography imaging kit components. Such conventional computed tomography kit components will be readily apparent to those skilled in the art, once armed with the present disclosure.

Where imaging of the gastrointestinal region is *6 contemplated, such computed tomography kit components may include, for example, anti -gas agents, osmolality raising agents, gastrointestinal transit agents and, in some instances, gas-forming agents.

The computed tomography imaging principles and techniques which are employed are conventional and are described, for example, in Computed Body Tomography, Lee, 0* Sagel, and Stanley, eds., Ch. 1, pp.- 1-7 (Raven Press, NY 1933). Any of the various types of computed tomography imaging devices can be used in the practice of the invention, the particular type or model of the device not being critical to the method of the invention.

The present invention is further described in the following Examples. Examples 1-7 are prophetic examples based at least in part on the teachings of Garner,

U.S.

Patent No. 3,945,956, and describe the preparation of microspheres by a heat expansion process. Examples 8-9 are actual examples that describe the preparation of contrast media of the invention. The following Examples are not to be construed as limiting the scope of the appended Claims.

Examples Example 1 A vessel is filled with 50 parts by weight of deionized water and 6 parts by weight of a 25 percent by weight aqueous colloidal silica dispersion. A mixture of 0.3 parts by weight of a 10 weight percent solution of diethylamine-adipic acid copolymer is added to the above.

A condensation reaction occurs creating a mixture having a viscosity of about 95 centipoise at a temperature of about 15 27" C. Potassium dichromate (0.05 parts by weight) is added to the aqueous phase as a water phase polymerization inhibitor. Sodium chloride (1 part by weight) is also present in the water phase; hydrochloric acid is used to adjust the pH of the aqueous phase to 4.0. Styrene 20 parts by weight), acrylonitrile (10 parts by weight), a mixture of diethylbenzene and divinylbenzene (0.21 parts by weight comprising a 55:45 percent mixture of each respectively), 6.25 parts by weight of isobutane and 0.07 parts by weight of secondary butyl peroxydicarbonate. The oil phase is added to the water phase with violent agitation created by a shearing blade rotating at 10,000 RPM employing a mixing blender. After the material has reacted for about 30 minutes, the mixture is poured into a citrate bottle and capped. The material is maintained at about 50*C in the citrate bath for about 24 hours and agitated throughout this time. At the end of 24 hours, the reaction bottle is cooled and the material is removed, washed and dried. A portion of the microspheres are set aside and the remainder are heated in an air oven for a period of about 30 minutes at about 150*C. A sample of the dry unexpanded and dry expanded microspheres are then studied by a Coulter Counter. The dry unexpanded 19 microspheres have a size of about 2 to 12 microns. About half of the microspheres exposed to the heating process show expansion.

Example 2 The procedures of Example 1 are substantially repeated with the exception that 1 part by weight of methanol is added to the reaction mixture. The dry unexpanded and dry heat expanded microspheres are then studied by Coulter Counter. The dry unexpanded microspheres measure about 8 to 10 microns in size.

Essentially all the microspheres exposed to heat expand.

es°e. Example 3 The procedures of Example 2 are substantially repeated except that after synthesis of the microspheres, o0 15 a slurry of the microspheres is added to an aqueous o solution containing 35 weight percent hydrogen peroxide.

This slurry is heated to a temperature of about 506C for about 3.5 hours and subsequently cooled and air-dried.

A

portion of the microspheres is then added to water and S. 0 0• 20 heated to a temperature of about 75"c with vigorous 6••e stirring for about 30 seconds. Study with Coulter Counter shows that pretreatment with hydrogen peroxide enables a 0" lower temperature and briefer period of heating to be used for definitive heating and expansion.

Example 4 The procedures of Example 1 are substantially repeated with the exception that 5 parts by weight of ethanol are included in the reaction mixture forming the microspheres. Coulter Counter shows that the dry unexpanded particles have diameters of about 24 to 28 microns. When heated, essentially all of the microspheres expand.

Example The procedures of Example 1 are substantially repeated with the exception that in place of methanol, 1 part by weight of normal butanol is used. The diameter of the dry unexpanded microspheres is about I0 to 12 microns and on heating, essentially all of the microspheres expand.

Example 6 The procedures of Example 1 are substantially repeated with the exception that the volatile liquid isobutane is replaced with perfluorocarbon liquid (C 4

F,

0 The remainder of the process is similar. The resulting microspheres are filled with perfluorocarbon liquid rather than isobutane.

Example 7 The procedures of Example 1 are substantially repeated with the exception that the reaction is conducted in a pressurized vessel enabling pressurization with gas and simultaneous agitation (agitation accomplished with either sonication or shearing blades within the device).

As the microspheres are formed within the device, the vessel is pressurized to about 300 psi with nitrogen gas.

The vessel is then depressurized, allowing the gas to come out of solution. The microspheres are then subjected to 20 heat as substantially described in Example 1.

Example 8 A suspension of 2 of 22 micron fiber length cellulose in 0.25 xanthan gum in water was prepared.

S. Scans by CT showed a CT density of about -45 HU for the cellulose suspension. EXPANCEL 551 DEm polyvinylidenepolyacrylonitrile microspheres, 50 microns in size, were then suspended in the aqueous cellulose suspension at a concentration of 0.4 grams of microspheres per 100 ml of cellulose suspension using vigorous shaking. The resulting suspension remained substantially homogeneous for about 10 minutes. The suspension was again shaken vigorously to render it substantially homogeneous and scanned immediately by CT. The resulting CT density as measured by the scanner was about -96 HU.

Example 9 A suspension of 1 algin was prepared. EXPANCEL 551 DET

M

microspheres were added to the algin suspension in an amount of about 0.2 grams of microspheres per deciliter of algin suspension, using vigorous shaking, to form a substantially homogeneous suspension. The resulting suspension was found to have much greater stability than the cellulose/microsphere suspension of Example 1. The algin/microsphere suspension was then scanned by CT, with the density as measured by the scanner being about

HU.

Various modifications of the invention in addition to those shown and described herein will be apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended Claims.

o

Claims (104)

1. A contrast medium for computed tomography imaging of the gastrointestinal region or other body cavities comprising a substantially homogeneous aqueous suspension of low density gas- filled microspheres having an internal void volume of at least about 75% of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon.

2. A contrast medium according to Claim 1 wherein said microspheres comprise polyvinylidene-polyacrylonitrile copolymer.

3. A contrast medium according to Claim 1 wherein said microspheres comprise a polyoxypropylene-polyoxyethylene copolymer.

4. A contrast medium according to any one of Claims 1 to 3 wherein said perfluorocarbon gas is selected from the group consisting of perfluorocarbons having between 1 and about 9 carbon atoms and between about 4 and about 20 fluorine atoms. A contrast medium according to Claim 4 wherein said perfluorocarbon gas is selected from the group consisting of perfluorocarbons having less than about 4 carbon atoms and less than 15 about 10 fluorine atoms. A contrast medium according to Claim 4 wherein said perfluorocarbon gas is C 3 F 8

7. A contrast medium according to Claim 4 wherein said perfluorocarbon gas is C 4 F 10

8. A contrast medium according to Claim 4 wherein said perfluorocarbon gas is C 5 F 12

9. A contrast medium according to Claim 4 wherein said perfluorocarbon gas is C 6 F 14 S. 20 10. A contrast medium according to any one of Claims 1 to 9 further comprising a thickening or suspending agent.

11. A contrast medium according to Claim 10 wherein said thickening or suspending agent S:0":i is selected from the group consisting of cellulose, carboxymethylcellulose, methylcellulose and methylhydroxycellulose.

12. A contrast medium according to Claim 11 wherein said thickening or suspending agent is methylcellulose.

13. A contrast medium according to any one of Claims 1 to 12 further comprising a compound selected from the group of antacids, antiflatulents, antifoaming agents, and surfactants.

14. A contrast medium according to Claim 13 wherein said compound selected from the group of antacids, antiflatulents, antifoaming agents, and surfactants, comprises a polymeric siloxane. A contrast medium according to Claim 14 wherein said polymeric siloxane is dimethylpolysiloxane.

16. A contrast medium according to Claim 15 wherein said dimethylpolysiloxane is simethicone. [I:\DayLib\LIBVV]00491 .doc:MCN

17. A contrast medium according to Claim 1 wherein said microspheres comprise a polyoxypropylene-polyoxyethylene copolymer, and said perfluorocarbon gas comprises C 5 F 1 2, and wherein said contrast medium further comprises methylcellulose and simethicone.

18. A contrast medium for diagnostic imaging comprising a substantially homogeneous aqueous suspension of low density gas-filled microspheres having an internal void volume of at least about 75% of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon.

19. A contrast medium according to Claim 18 wherein said microspheres comprise synthetic polymers or copolymers prepared from the group of monomers consisting of acrylic acid, methacrylic acid, ethyleneimine, crotonic acid, acrylamide, ethyl acrylate, methyl methacrylate, 2-hydroxyethyl methacrylate, lactic acid, glycolic acid, e-caprolactone, acrolein, dyanoacrylate, bisphenol A, epichlorhydrin, hydroxyalkylacrylates, siloxane, dimethylsiloxane, ethylene oxide, ethylene glycol, hydroxyalkyl-methacrylates, N-substituted acrylamides, N-substituted methacrylamides, N-vinyl-2- pyrrolidone, 2,4-pentadiene-1-ol, vinyl acetate, acrylonitrile, styrene, p-amino-styrene, p-amino- benzyl-styrene, sodium styrene sulfonate, sodium 2-sulfoxyethylmethacrylate, vinyl pyridine, 15 aminoethyl methacrylates, 2-methacryloyloxy-trimethylammonium chloride, N,N'- methylenebisacrylamide, ethylene glycol dimethacrylates, 2,2'-(p-phenylenedioxy)-diethyl dimethacrylate, divinylbenzene, triallylamine, and methylenebis-(4-phenylisocyanate). A contrast medium according to Claim 19 wherein said microspheres comprise synthetic polymers or copolymers prepared from the group of monomers consisting of acrylic acid, methacrylic acid, ethyleneimine, crotonic acid, acrylamide, ethyl acrylate, methyl methacrylate, 2-hydroxyethyl methacrylate, lactic acid, glycolic acid, e-caprolactone, acrolein, cyanoacrylate, bisphenol A, epichlorhydrin, hydroxyalkylacrylates, siloxane, dimethylsiloxane, ethylene oxide, ethylene glycol, hydroxyalkyl-methacrylates, N-substituted acrylamides, N-substituted methacrylamides, N-vinyl-2- pyrrolidone, 2,4-pentadiene-1-ol, vinyl acetate, acrylonitrile, styrene, p-amino-styrene, p-amino- benzyl-styrene, sodium styrene sulfonate, sodium 2-sulfoxyethylmethacrylate, vinyl pyridine, aminoethyl methacrylates, and 2-methacryloyloxy-trimethylammonium chloride.

21. A contrast medium according to Claim 18 wherein said microspheres comprise synthetic polymers or copolymers selected from the group consisting of polyacrylic acid, polyethyleneimine, polymethacrylic acid, polymethylmethacrylate, polysiloxane, polydimethylsiloxane, polylactic acid, poly(-caprolactone), epoxy resin, poly(ethylene oxide), poly(ethylene glycol), polyamide, polyvinylidene-polyacrylonitrile, polyvinylidene-polyacrylonitrile-polymethylmethacrylate, and polystyrene-polyacrylonitrile.

22. A contrast medium according to Claim 18 wherein said microspheres comprise a polyvinylidene-polyacrylonitrile copolymer.

23. A contrast medium according to Claim 18 wherein said microspheres comprise a polyoxypropylene-polyoxyethylene copolymer. [1:\DayLib\LIBVV00491 .doc:MCN

24. A contrast medium according to any one of Claims 18 to 23 wherein said microspheres are prepared by a heat expansion process. A contrast medium according to any one of Claims 18 to 24 wherein said perfluorocarbon gas is selected from the group consisting of perfluorocarbons having between 1 and about 9 carbon atoms and between about 4 and about 20 fluorine atoms.

26. A contrast medium according to Claim 25 wherein said perfluorocarbon gas is selected from the group consisting of perfluorocarbons having less than about 4 carbon atoms and less than about 10 fluorine atoms.

27. A contrast medium according to Claim 25 wherein said perfluorocarbon gas is C 3 F 8

28. A contrast medium according to Claim 25 wherein said perfluorocarbon gas is C 4 F 1 0

29. A contrast medium according to Claim 25 wherein said perfluorocarbon gas is C 5 F 12 A contrast medium according to Claim 25 wherein said perfluorocarbon gas is C 6 F 14

31. A contrast medium according to any one of Claims 18 to 30 further comprising a thickening or suspending agent. 15 32. A contrast medium according to Claim 31 wherein said thickening or suspending agent is selected from the group consisting of cellulose, carboxymethylcellulose, methylcellulose, and methylhydroxycellulose.

33. A contrast medium according to Claim 32 wherein said thickening or suspending agent is methylcellulose. 20 34. A contrast medium according to any one of Claims 18 to 33 further comprising a compound selected from the group of antacids, antiflatulents, antifoaming agents, and surfactants. A contrast medium according to Claim 34 wherein said compound selected from the group of antacids, antiflatulents, antifoaming agents, and surfactants, comprises a polymeric siloxane.

36. A contrast medium according to Claim 35 wherein said polymeric siloxane is dimethylpolysiloxane.

37. A contrast medium according to Claim 36 wherein said dimethylpolysiloxane is simethicone.

38. A contrast medium according to Claim 18 wherein said microspheres comprise a polyoxypropylene-polyoxyethylene copolymer, and said perfluorocarbon gas comprises C 5 F 12 and wherein said contrast medium further comprises methylcellulose and simethicone.

39. A substantially homogeneous aqueous suspension of low density gas-filled microspheres having an internal void volume of at least about 75% of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon. An aqueous suspension of microspheres according to Claim 39 wherein said microspheres comprise synthetic polymers or copolymers prepared from the group of monomers consisting of acrylic acid, methacrylic acid, ethyleneimine, crotonic acid, acrylamide, ethyl acrylate, [I:\DayLib\LIBVV]00491 .doc:MCN methyl methacrylate, 2-hydroxyethyl methacrylate, lactic acid, glycolic acid, e-caprolactone, acrolein, cyanoacrylate, bisphenol A, epichlorhydrin, hydroxyalkylacrylates, siloxane, dimethylsiloxane, ethylene oxide, ethylene glycol, hydroxyalkyl-methacrylates, N-substituted acrylamides, N-substituted methacrylamides, N-vinyl-2-pyrrolidone, 2,4-pentadiene-1-ol, vinyl acetate, acrylonitrile, styrene, p- amino-styrene, p-amino-benzyl-styrene, sodium styrene sulfonate, sodium 2- sulfoxyethylmethacrylate, vinyl pyridine, aminoethyl methacrylates, 2-methacryloyloxy- trimethylammonium chloride, N,N'-methylenebisacrylamide, ethylene glycol dimethacrylates, phenylenedioxy)-diethyl dimethacrylate, divinylbenzene, triallylamine, and methylenebis-(4- phenylisocyanate).

41. An aqueous suspension of microspheres according to Claim 40 wherein said microspheres comprise synthetic polymers or copolymers prepared from the group of monomers consisting of acrylic acid, methacrylic acid, ethyleneimine, crotonic acid, acrylamide, ethyl acrylate, methyl methacrylate, 2-hydroxyethyl methacrylate, lactic acid, glycolic acid, e-caprolactone, acrolein, S cyanoacrylate, bisphenol A, epichlorhydrin, hydroxyalkylacrylates, siloxane, dimethylsiloxane, I15 ethylene oxide, ethylene glycol, hydroxyalkyl-methacrylates, N-substituted acrylamides, N-substituted methacrylamides, N-vinyl-2-pyrrolidone, 2,4-pentadiene-1-ol, vinyl acetate, acrylonitrile, styrene, p- amino-styrene, p-amino-benzyl-styrene, sodium styrene sulfonate, sodium 2- sulfoxyethylmethacrylate, vinyl pyridine, aminoethyl methacrylates, and 2-methacryloyloxy- trimethylammonium chloride.

42. An aqueous suspension of microspheres according to Claim 39 wherein said microspheres comprise synthetic polymers or copolymers selected from the group consisting of polyacrylic acid, polyethyleneimine, polymethacrylic acid, polymethylmethacrylate, polysiloxane, polydimethylsiloxane, polylactic acid, poly(s-caprolactone), epoxy resin, poly(ethylene oxide), poly(ethylene glycol), polyamide, polyvinylidene-polyacrylon itrile, polyvinylidene-polyacrylonitrile- polymethylmethacrylate, and polystyrene-polyacrylonitrile.

43. An aqueous suspension of microspheres according to Claim 39 wherein said microspheres comprise a polyvinylidene-polyacrylonitrile copolymer.

44. An aqueous suspension of microspheres according to Claim 39 wherein said microspheres comprise a polyoxypropylenepolyoxyethylene copolymer.

45. An aqueous suspension of microspheres according to any one of Claims 39 to 44 wherein said microspheres are prepared by a heat expansion process.

46. An aqueous suspension of microspheres according to any one of Claims 39 to wherein said perfluorocarbon gas is selected from the group consisting of perfluorocarbons having between 1 and about 9 carbon atoms and between about 4 and about 20 fluorine atoms. [I:\DayLib\LIBVVIOO491 .doc:MCN

47. An aqueous suspension of microspheres according to Claim 46 wherein said perfluorocarbon gas is selected from the group consisting of perfluorocarbons having less than about 4 carbon atoms and less than about 10 fluorine atoms.

48. An aqueous suspension of microspheres according to Claim 46 wherein said perfluorocarbon gas is C 3 F 8

49. An aqueous suspension of microspheres according to Claim 46 wherein said perfluorocarbon gas is C 4 F 10 An aqueous suspension of microspheres according to Claim 46 wherein said perfluorocarbon gas is C 5 F 12

51. An aqueous suspension of microspheres according to Claim 46 wherein said perfluorocarbon gas is C 6 F 14

52. An aqueous suspension according to Claim 39 wherein said microspheres comprise a polyoxypropylenepolyoxyethylene copolymer, and said perfluorocarbon gas comprises C 5 F 1 2, and wherein said aqueous suspension further comprises methylcellulose and simethicone. 15 53. A kit for computed tomography imaging of the gastrointestinal region or other body cavities of a patient comprising low density gas-filled microspheres having an internal void volume of at least about 75% of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon, in combination with a thickening or suspending agent.

54. A kit for diagnostic imaging of patient comprising low density gas-filled microspheres 20 having an internal void volume of at least about 75% of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon, in combination with a thickening or suspending agent. A method of providing an image of the gastrointestinal region and other body cavities of a patient comprising administering to the patient a contrast medium comprising a substantially homogeneous aqueous suspension of low density gas-filled microspheres having an internal void volume of at least .0 about 75% of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon, and scanning the patient using computed tomography imaging to obtain visible images of the gastrointestinal region or other body cavities.

56. A method of providing an image of a region of a patient comprising administering to the patient a contrast medium comprising a substantially homogeneous aqueous suspension of low density gas-filled microspheres having an internal void volume of at least about 75% of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon, and scanning the patient using diagnostic imaging to obtain visible images of the region of a patient. [I:\DayLib\LIBVV00491.doc:MCN

57. A method for diagnosing the presence of diseased tissue in the gastrointestinal region or other body cavities of a patient comprising administering to the patient a contrast medium comprising a substantially homogeneous aqueous suspension of low density gas-filled microspheres having an internal void volume of at least about 75% of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon, and scanning the patient using computed tomography imaging to obtain visible images of any diseased tissue in the patient.

58. A method for diagnosing the presence of diseased tissue in a patient comprising administering to the patient a contrast medium comprising a substantially homogeneous aqueous suspension of low density gas-filled microspheres having an internal void volume of at least about 75% of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon, and scanning the patient using diagnostic imaging to obtain visible images of any diseased 15 tissue in the patient.

59. A contrast medium for computed tomography imaging of the gastrointestinal region or other body cavities comprising an aqueous suspension of a biocompatible polymer, a perfluorocarbon gas, and a thickening or suspending agent, wherein in said suspension said biocompatible polymer associates with said perfluorocarbon gas to form one or more gas-filled microspheres. 20 60. A contrast medium for diagnostic imaging comprising an aqueous suspension of a biocompatib!e polymer, a perfluorocarbon gas, and a thickening or suspending agent, wherein in said suspension said biocompatible polymer associates with said perfluorocarbon gas to form one or more gas-filled microspheres.

61. A contrast medium according to Claim 59 or 60 wherein said biocompatible polymer comprises synthetic polymers or copolymers prepared from the group of monomers consisting of acrylic acid, methacrylic acid, ethyleneimine, crotonic acid, acrylamide, ethyl acrylate, methyl methacrylate, 2-hydroxyethyl methacrylate, lactic acid, glycolic acid, e-caprolactone, acrolein, cyanoacrylate, bisphenol A, epichlorhydrin, hydroxyalkylacrylates, siloxane, dimethylsiloxane, ethylene oxide, ethylene glycol, hydroxyalkyl-methacrylates, N-substituted acrylamides, N-substituted methacrylamides, N-vinyl-2-pyrrolidone, 2,4-pentadiene-l-ol, vinyl acetate, acrylonitrile, styrene, p- amino-styrene, p-amino-benzyl-styrene, sodium styrene sulfonate, sodium 2- sulfoxyethylmethacrylate, vinyl pyridine, aminoethyl methacrylates, 2-methacryloyloxy- trimethylammonium chloride, N,N'-methylenebisacrylamide, ethylene glycol dimethacrylates, phenylenedioxy)-diethyl dimethacrylate, divinylbenzene, triallylamine, and methylenebis-(4- phenylisocyanate). [I:\DayLib\LIBVVOO491 .doc:MCN

62. A contrast medium according to Claim 61 wherein said biocompatible polymer comprises synthetic polymers or copolymers prepared from the group of monomers consisting of acrylic acid, methacrylic acid, ethyleneimine, crotonic acid, acrylamide, ethyl acrylate, methyl methacrylate, 2- hydroxyethyl methacrylate, lactic acid, glycolic acid, e-caprolactone, acrolein, cyanoacrylate, bisphenol A, epichlorhydrin, hydroxyalkylacrylates, siloxane, dimethylsiloxane, ethylene oxide, ethylene glycol, hydroxyalkyl-methacrylates, N-substituted acrylamides, N-substituted methacrylamides, N-vinyl-2-pyrrolidone, 2,4-pentadiene-l-ol, vinyl acetate, acrylonitrile, styrene, p- amino-styrene, p-amino-benzyl-styrene, sodium styrene sulfonate, sodium 2- sulfoxyethylmethacrylate, vinyl pyridine, aminoethyl methacrylates, and 2-methacryloyloxy- trimethylammonium chloride.

63. A contrast medium according to Claim 59 or 60 wherein said biocompatible polymer comprises synthetic polymers or copolymers selected from the group consisting of polyacrylic acid, polyethyleneimine, polymethacrylic acid, polymethylmethacrylate, polysiloxane, polydimethylsiloxane, polylactic acid, poly(s-caprolactone), epoxy resin, poly(ethylene oxide), poly(ethylene glycol), 15 polyamide, polyvinylidene-polyacrylonitrile, polyvinylidene-polyacrylonitrile-polymethylmethacrylate, and polystyrene-polyacrylonitrile.

64. A contrast medium according to Claim 59 or 60 wherein said biocompatible polymer comprises a polyvinylidene-polyacrylonitrile copolymer. A contrast medium according to Claim 59 or 60 wherein said biocompatible polymer 20 comprises a polyoxypropylene-polyoxyethylene copolymer.

66. A contrast medium according to any one of Claims 59 to 65 wherein said perfluorocarbon gas is selected from the group consisting of perfluorocarbons having between 1 and about 9 carbon atoms and between 4 and about 20 fluorine atoms.

67. A contrast medium according to Claim 66 wherein said perfluorocarbon gas is selected from the group consisting of perfluorocarbons having less than about 4 carbon atoms and less than S: about 10 fluorine atoms.

68. A contrast medium according to Claim 66 wherein said perfluorocarbon gas is C 3 F 8

69. A contrast medium according to Claim 66 wherein said perfluorocarbon gas is C 4 F 10 A contrast medium according to Claim 66 wherein said perfluorocarbon gas is C 5 F 12

71. A contrast medium according to any one of Claims 59 to 70 wherein said thickening or suspending agent is selected from the group consisting of alginates, xanthan gum, guar, pectin, tragacanth, bassorin, karaya, gum arabic, casein, gelatin, cellulose, carboxymethylcellulose, methylcellulose, methylhydroxycellulose, bentonite, colloidal silicic acid, carrageenan, polyethylene glycol, polypropylene glycol, and polyvinylpyrrolidone. [I:\DayLib\LIBVV00491 .doc:MCN

72. A contrast medium according to Claim 71 wherein said thickening or suspending agent is selected from the group consisting of cellulose, carboxymethylcellulose, methylcellulose, and methylhydroxycellulose.

73. A contrast medium according to Claim 72 wherein said thickening or suspending agent is methylcellulose.

74. A contrast medium according to any one of Claims 59 to 73 further comprising a compound selected from the group of antacids, antiflatulents, antifoaming agents, and surfactants. A contrast medium according to Claim 74 wherein said compound selected from the group of antacids, antiflatulents, antifoaming agents, and surfactants, comprises a polymeric siloxane.

76. A contrast medium according to Claim 75 wherein said polymeric siloxane is dimethylpolysiloxane.

77. A contrast medium according to Claim 76 wherein said dimethylpolysiloxane is simethicone.

78. A contrast medium according to Claim 59 or 60 wherein said biocompatible polymer is a 15 polyoxypropylene-polyoxyethylene copolymer, said perfluorocarbon gas is C 5 F 12 and said thickening or suspending agent is methylcellulose, and further comprising simethicone.

79. An aqueous suspension comprising a biocompatible polymer, a perfluorocarbon gas, Sand a thickening or suspending agent, wherein in said suspension said biocompatible polymer associates with said perfluorocarbon gas to form one or more gas-filled microspheres. 20 80. An aqueous suspension according to Claim 79 wherein said biocompatible polymer S. comprises synthetic polymers or copolymers prepared from the group of monomers consisting of acrylic acid, methacrylic acid, ethyleneimine, crotonic acid, acrylamide, ethyl acrylate, methyl methacrylate, 2-hydroxyethyl methacrylate, lactic acid, glycolic acid, e-caprolactone, acrolein, cyanoacrylate, bisphenol A, epichlorhydrin, hydroxyalkylacrylates, siloxane, dimethylsiloxane, 25 ethylene oxide, ethylene glycol, hydroxyalkyl-methacrylates, N-substituted acrylamides, N-substituted *o*o* methacrylamides, N-vinyl-2-pyrrolidone, 2,4-pentadiene-l-ol, vinyl acetate, acrylonitrile, styrene, p- amino-styrene, p-amino-benzyl-styrene, sodium styrene sulfonate, sodium 2- sulfoxyethylmethacrylate, vinyl pyridine, aminoethyl methacrylates, 2-methacryloyloxy- trimethylammonium chloride, N,N'-methylenebisacrylamide, ethylene glycol dimethacrylates, phenylenedioxy)-diethyl dimethacrylate, divinylbenzene, triallylamine, and methylenebis-(4- phenylisocyanate).

81. An aqueous suspension according to Claim 80 wherein said biocompatible polymer comprises synthetic polymers or copolymers prepared from the group of monomers consisting of acrylic acid, methacrylic acid, ethyleneimine, crotonic acid, acrylamide, ethyl acrylate, methyl methacrylate, 2-hydroxyethyl methacrylate, lactic acid, glycolic acid, e-caprolactone, acrolein, cyanoacrylate, bisphenol A, epichlorhydrin, hydroxyalkylacrylates, siloxane, dimethylsiloxane, [I:\DayLib\LIBVV]00491 .doc:MCN ethylene oxide, ethylene glycol, hydroxyalkyl-methacrylates, N-substituted acrylamides, N-substituted methacrylamides, N-vinyl-2-pyrrolidone, 2,4-pentadiene-l-ol, vinyl acetate, acrylonitrile, styrene, p- amino-styrene, p-amino-benzyl-styrene, sodium styrene sulfonate, sodium 2- sulfoxyethylmethacrylate, vinyl pyridine, aminoethyl methacrylates, and 2-methacryloyloxy- trimethylammonium chloride.

82. An aqueous suspension according to Claim 79 wherein said biocompatible polymer comprises synthetic polymers or copolymers selected from the group consisting of polyacrylic acid, polyethyleneimine, polymethacrylic acid, polymethylmethacrylate, polysiloxane, polydimethylsiloxane, polylactic acid, poly(e-caprolactone), epoxy resin, poly(ethylene oxide), poly(ethylene glycol), polyamide, polyvinylidene-polyacrylonitrile, polyvinylidene-polyacrylonitrile-polymethylmethacrylate, and polystyrene-polyacrylonitrile.

83. An aqueous suspension according to Claim 80 wherein said biocompatible polymer comprises a polyvinylidene-polyacrylonitrile copolymer.

84. An aqueous suspension according to Claim 79 wherein said biocompatible polymer .15 comprises a polyoxypropylene-polyoxyethylene copolymer.

85. An aqueous suspension according to any one of Claims 79 to 84 wherein said Sperfluorocarbon gas is selected from the group consisting of perfluorocarbons having between 1 and about 9 carbon atoms and between about 4 and about 20 fluorine atoms.

86. An aqueous suspension according to Claim 85 wherein said perfluorocarbon gas is 20 selected from the group consisting of perfluorocarbons having less than about 4 carbon atoms and less than about 10 fluorine atoms.

87. An aqueous suspension according to Claim 85 wherein said perfluorocarbon gas is C 3 F 8

88. An aqueous suspension according to Claim 85 wherein said perfluorocarbon gas is C 4 F 10

89. An aqueous suspension according to Claim 85 wherein said perfluorocarbon gas is C 5 F 12 An aqueous suspension according to any one of Claims 79 to 89 wherein said thickening or suspending agent is selected from the group consisting of alginates, xanthan gum, guar, pectin, tragacanth, bassorin, karaya, gum arabic, casein, gelatin, cellulose, carboxymethylcellulose, methylcellulose, methylhydroxycellulose, bentonite, colloidal silicic acid, carrageenan, polyethylene glycol, propylene glycol, and polyvinylpyrrolidone.

91. An aqueous suspension according to Claim 90 wherein said thickening or suspending agent is selected from the group consisting of cellulose, carboxymethylcellulose, methylcellulose, and methylhydroxycellulose. [I:\DayLib\LIBVV00491 .doc:MCN

92. An aqueous suspension according to Claim 91 wherein said thickening or suspending agent is methylcellulose.

93. An aqueous suspension according to Claim 91 or 92 further comprising a compound selected from the group of antacids, antiflatulents, antifoaming agents, and surfactants.

94. An aqueous suspension according to Claim 93 wherein said compound selected from the group of antacids, antiflatulents, antifoaming agents, and surfactants, comprises a polymeric siloxane. An aqueous suspension according to Claim 94 wherein said polymeric siloxane is dimethylpolysiloxane.

96. An aqueous suspension according to Claim 95 wherein said dimethylpolysiloxane is simethicone.

97. An aqueous suspension according to Claim 79 wherein said biocompatible polymer is a polyoxypropylene-polyoxyethylene copolymer, said perfluorocarbon gas is C 5 F 12 and said thickening agent or suspending agent is methylcellulose, and further comprising simethicone. 15 98. A kit for computed tomography imaging of the gastrointestinal region or other body cavities of a patient comprising a biocompatible polymer, a perfluorocarbon gas, and a thickening or suspending agent, wherein in said suspension said biocompatible polymer associates with said perfluorocarbon gas to form one or more gas-filled microspheres.

99. A kit for diagnostic imaging of a patient comprising a biocompatible polymer, a 20 perfluorocarbon gas, and a thickening or suspending agent, wherein in said suspension said biocompatible polymer associates with said perfluorocarbon gas to form one or more gas-filled microspheres.

100. A method of providing an image of the gastrointestinal region and other body cavities of a patient comprising S 25 administering to the patient a contrast medium comprising an aqueous suspension of a biocompatible polymer, a perfluorocarbon gas, and a thickening or suspending agent, wherein in said suspension said biocompatible polymer associates with said perfluorocarbon gas to form one or more gas-filled microspheres, and scanning the patient using computed tomography imaging to obtain visible images of the gastrointestinal region or other body cavities.

101. A method of providing an image of a region of a patient comprising administering to the patient a contrast medium comprising an aqueous suspension of a biocompatible polymer, a perfluorocarbon gas, and a thickening or suspending agent, wherein in said suspension said biocompatible polymer associates with said perfluorocarbon gas to form one or more gas-filled microspheres, and [I:\DayLib\LIBVV]00491 .doc:MCN scanning the patient using diagnostic imaging to obtain visible images of the region of a patient.

102. A method for diagnosing the presence of diseased tissue in the gastrointestinal region or other body cavities of a patient comprising administering to the patient a contrast medium comprising an aqueous suspension of a biocompatible polymer, a perfluorocarbon gas, and a thickening or suspending agent, wherein in said suspension said biocompatible polymer associates with said perfluorocarbon gas to form one or more gas-filled microspheres, and scanning the patient using computed tomography imaging to obtain visible images of any diseased tissue in the patient.

103. A method for diagnosing the presence of diseased tissue in a patient comprising administering to the patient a contrast medium comprising an aqueous suspension of a biocompatible polymer, a perfluorocarbon gas, and a thickening or suspending agent, wherein in said suspension said biocompatible polymer associates with said perfluorocarbon gas to form one or more S**o 15 gas-filled microspheres, and scanning the patient using diagnostic imaging to obtain visible images of any diseased tissue in the patient.

104. A low density gas-filled microsphere having an internal void volume of at least about of the total volume of the microsphere, wherein said gas comprises a perfluorocarbon. 20 105. A microsphere according to claim 104, wherein said microspheres comprise synthetic polymers or copolymers prepared from the group of monomers consisting of acrylic acid, methacrylic acid, ethyleneimine, crotonic acid, acrylamide, ethyl acrylate, methyl methacrylate, 2-hydroxyethyl S* methacrylate, lactic acid, glycolic acid, e-caprolactone, acrolein, cyanoacrylate, bisphenol A, epichlorhydrin, hydroxyalkylacrylates, siloxane, dimethylsiloxane, ethylene oxide, ethylene glycol, hydroxyalkyl-methacrylates, N-substituted acrylamides, N-substituted methacrylamides, N-vinyl-2- pyrrolidone, 2,4-pentadiene-l-ol, vinyl acetate, acrylonitrile, styrene, p-amino-styrene, p-amino- benzyl-styrene, sodium styrene sulfonate, sodium 2-sulfoxyethyl methacrylate, vinyl pyridine, aminoethyl methacrylates, 2-methactyloyloxy-triethylammonium chloride, N,N'- methylenebisacrylamide, ethylene glycol dimethacrylates, 2,2'-(p-phenylenedioxy)-diethyl dimethacrylate, divinylbenzene, triallylamine, and methylenebis-(4-phenyl-isocyanate).

106. A microsphere according to claim 105 wherein said microsphere comprises synthetic polymers or copolymers prepared from the group of monomers consisting of acrylic acid, methacrylic acid, ethyleneimine, crotonic acid, acrylamide, ethyl acrylate, methyl methacrylate, 2-hydroxyethyl methacrylate, lactic acid, glycolic acid, e-caprolactone, acrolein, cyanoacrylate, bisphenol A, epichlorhydrin, hydroxyalkylacrylates, siloxane, dimethylsiloxane, ethylene oxide, ethylene glycol, hydroxyalkyl-methacrylates, N-substituted acrylamides, N-substituted methacrylamides, N-vinyl-2- [I:\DayLib\LIBVV]00491.doc:MCN pyrrolidone, 2,4-pentadiene-l-ol, vinyl acetate, acrylonitrile, styrene, p-amino-styrene, p-amino- benzyl-styrene, sodium styrene sulfonate, sodium 2-sulfoxyethyl methacrylate, vinyl pyridine, aminoethyl methacrylates, 2-methacryloyloxy-triethylammonium chloride.

107. A microsphere according to Claim 104 wherein said microsphere comprises synthetic polymers or copolymers selected from the group consisting of polyacrylic acid, polyethyleneimine, polymethacrylic acid, polymethylmethacrylate, polysiloxane, polydimethylsiloxane, polylactic acid, poly(s-capro-lactone), epoxy resin, poly(ethylene oxide), poly(ethylene glycol), polyamide, polyvinylidene-polyacrylonitrile, polyvinylidene-polyacrylonitrile-polymethylmethacrylate, and polystyrene-polyacrylonitrile.

108. A microsphere according to Claim 104 wherein said microsphere comprises a polyvinylidene-polyacrylonitrile copolymer.

109. A microsphere according to Claim 104 wherein said microsphere comprises a polyoxypropylene-polyoxyethylene copolymer.

110. A microsphere according to any one of claims 104 to 109 wherein said microsphere is 15 prepared by a heat expansion process.

111. A microsphere according to any one of claims 104 to 110 wherein said perfluorcarbon gas is selected from the group consisting of perfluorcarbons having between 1 and 9 carbon atoms 6666** and between about 4 and about 20 fluorine atoms.

112. A microsphere according to Claim 111 wherein said perfluorocarbon gas is selected from *Oo 20 the group consisting of perfluorocarbons having less than about 4 carbon atoms and less than about 10 fluorine atoms.

113. A microsphere according to Claim 111 wherein said perfluorocarbon gas is C 3 F 8 6 114. A microsphere according to Claim 111 wherein said perfluorocarbon gas is C 4 F 1 0

115. A microsphere according to Claim 111 wherein said perfluorocarbon gas is C5F12.

116. A microsphere according to Claim 111 wherein said perfluorocarbon gas is CsFl4. 0

117. A microsphere according to Claim 104 wherein said microsphere comprises polyoxypropylene-polyoxyethylene copolymer, and said perfluorocarbon gas comprises C5F1 2

118. A microsphere according to Claim 104 wherein said microsphere comprises a polymer.

119. A microsphere according to Claim 118 wherein said polymer is prepared from a polyfunctional crosslinking monomer.

120. A microsphere according to Claim 105 wherein said polymer comprises an acrylate.

121. A microsphere according to Claim 105 wherein said polymer comprises a methacrylate.

122. A microsphere according to claim 105 wherein said polymer comprises a cyanoacrylate.

123. A microsphere according to any one of claims 104 to 122 wherein the outside diameter of said microsphere is from about 1 to about 1000 microns. [I:\DayLib\LIBVV10491 .doc:MCN

124. A microsphere according to Claim 123 wherein the outside diameter of said microsphere is from about 1 to about 70 microns.

125. A contrast medium for computed tomography imaging of the gastrointestinal region or other body cavities, said medium substantially as hereinbefore described with reference to any one of the examples.

126. A low density gas-filled microsphere as set out in claim 104, substantially as hereinbefore described with reference to any one of the examples.

127. A process for producing a low density gas-filled microsphere as set out in claim 104, substantially as hereinbefore described with reference to any one of the examples.

128. A low density gas-filled microsphere prepared by the process according to claim 127. Dated 18 January, 2002 ImaRx Pharmaceutical Corp. Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON e O0•0 [I:\DayLib\LBVV]00491 .doc:MCN