WO1998023295A1

WO1998023295A1 - Method of imaging

Info

Publication number: WO1998023295A1
Application number: PCT/GB1997/003204
Authority: WO
Inventors: Gregory Lynn Mcintire; David Lee Ladd; Edward Richard Bacon; John Luke Toner; George Chao Na
Original assignee: Nycomed Imaging As; Cockbain, Julian
Priority date: 1996-11-28
Filing date: 1997-11-21
Publication date: 1998-06-04
Also published as: GB9624822D0; AU5062198A; EP0941126A1; JPH10158197A

Abstract

The invention provides a method for contrast enhanced imaging of at least part of the lymphatic system of a human or animal body which comprises administering a diagnostically effective contrast agent to said body and generating a contrast enhanced image of at least part of the lymphatic system of said body, characterised in that said agent is a water-soluble polymeric material having a molecular weight of at least 1kD and is administered indirectly but parenterally.

Description

Method of Imaging

The invention relates to a method of contrast enhanced imaging, in particular MR and X-ray imaging of the lymphatic system, and to contrast agent compositions useful therefor.

The status of the lymphatic system of the human body is often critical to the management of therapy in cancer patients. Accordingly it is highly desirable to be able to carry out diagnostic imaging of the lymphatic system in order to detect the existence or development of abnormalities therein.

Water-soluble contrast agents of the type routinely used in diagnostic imaging modalities, eg. iohexol and GdDTPA-BMA, do not accumulate adequately in the lymphatic system to provide contrast enhancement thereof either by intravenous or submucosal injection.

Accordingly, at present, available diagnostic imaging techniques are quite limited in their efficacy for lymphatic system imaging.

Ethiodol, an iodinated oily ethyl fatty acid ester present in poppyseed oil, is currently in use in X-ray lymphography (ie. lymphangiography) . This agent however has severe drawbacks in that it requires cannulation and direct injection into the lymph vessels, an invasive and painful procedure, and in that it requires a very long period before it is cleared from the lymphatic system. Furthermore, lodging of the oil agent in the lung can result in pulmonary embolism and decreased pulmonary function. More recently it has been found that subcutaneously administered nanocrystalline suspensions of substantially insoluble radiopaque materials can be used to provide contrast in X-ray imaging of the lymphatic system. Such nanocrystalline materials however also have potential drawbacks. Thus the particulate agent clears only slowly from the imaging site, is difficult to manufacture with uniform particle size and has to be formulated with a surfactant in order to stabilize the suspension. The inclusion of further materials, such as surfactants, in a contrast medium of course raises the risk of toxicity problems and ensures that additional hurdles have to be overcome before official approval for a product can be obtained.

However, it has now been surprisingly found that subcutaneously administered water-soluble polymeric contrast agents are efficacious at providing image contrast of the lymphatic system.

Thus viewed from one aspect the invention provides a method for contrast enhanced imaging of at least part of the lymphatic system of a human or animal (preferably mammalian) body which comprises administering a diagnostically effective contrast agent to said body and generating a contrast enhanced image of at least part of the lymphatic system of said body, characterised in that said agent is a water-soluble polymeric material having a molecular weight of at least 1 kD (preferably at least 10 kD, especially preferably at least 20 kD, eg. up to 2 mD, preferably up to 100 kD) and is indirectly administered parenterally, preferably in solution.

Viewed from a further aspect the invention provides the use of a diagnostically effective contrast agent which is a physiologically tolerable, water-soluble polymer having a molecular weight of at least 1 kD (preferably at least 10 kD, etc., as above), for the manufacture of an indirectly but parenterally administerable diagnostic imaging contrast medium for use in a method of diagnosis which involves indirect parenteral administration of said contrast medium and subsequent generation of a contrast enhanced image of at least part of the lymphatic system.

The contrast agent, in order to be capable of functioning as such, will contain at least one diagnostically effective moiety.

Viewed from a still further aspect the invention provides an indirectly but parenterally administrable diagnostic contrast agent composition, preferably an aqueous solution, for use in lymphography comprising a physiologically tolerable, diagnostically effective water-soluble polymer having a molecular weight of at least 1 kD (preferbly at least 10 kD, etc., as above), together with at least one pharmaceutically acceptable carrier or excipien .

Indirect parenteral administration according to the invention involves administration into tissue beneath the skin or mucosal membranes, eg. by injection, infusion or depot placement. Administration may thus be subcutaneous, intramuscular, peritumoral, intraperitoneal, and submucosal (ie. intratracheal, intracervical, etc.), or by pulmonary deposition. Subcutaneous administration is preferred. Thus administration according to the invention is differentiated from direct lymphographic techniques which involve administration of the contrast medium directly into the lymph vessels or nodes and from intravenous or intraarterial administration which involves locating a major blood vessel and administering the contrast medium into that. However, direct injection into the lymphatic system may also be effective using the water-soluble contrast agents of the invention .

By diagnostically effective, it is meant that the polymeric contrast agent incorporates at least one component (a label) which is effective at generating contrast in the selected imaging modality. Suitable imaging modalities include X-ray (eg. CT) , MRI, light imaging, scintigraphy, magnetotomography, SPECT, PET, electrical impedance tomography etc., preferably X-ray, MRI or scintigraphy. The contrast agents may if desired be diagnostically effective in more than one imaging modality; thus for example a soluble polymer may carry paramagnetic or heavy metal ions detectable in MRI or X- ray imaging as well as a dye detectable in light imaging .

For MRI, suitable labels include non-proton atoms which have non-zero nuclear spin or, more preferably, metal ions or metal cluster ions which are paramagnetic, eg. transition metals such as Mn, Fe or Cr or lanthanides such as Gd and Dy. Other suitable paramagnetic metal ions are well known from the patent literature relating to MR contrast media including the patent publications referred to herein. MR imaging will preferably be T_x- weighted imaging, however in the case of T₂ or T₂* agents (eg. dysprosium labelled materials) T₂-weighted imaging will also be useful.

For X-ray, the label will conveniently be a heavy atom (eg. having atomic number 37 or higher), conveniently iodine or a metal from period 5 or higher, eg. Bi, Pb, Ba or W. Again suitable heavy atoms are well known from the patent literature, including publications concerned with heavy metal cluster ions. Metals useful as MR imaging agents may also be useful for X-ray, albeit at lower efficiency than the heavy metals mentioned above. For light imaging, the label will be a chromophore or fluorophore, eg. a triphenylmethane or cyanine or a fluorescent metal ion (eg. europium) . For intraoperative uses, the label may be any of the currently used analytical labels (eg. fluorescein and analogs thereof, or a dansyl group) as well as the visibly coloured dye groups.

For scintigraphy, PET and SPECT, the label will be a radiolabel conveniently a metal radionuclide such as a Sc, Fe, Pb, Ga, Y, Bi, Mn, Cu, Cr, Zn, Ge, Mo, Tc, Ru, In, Sm, Sn, Sb, W, Re, Po, Ta or Tl radionuclide, eg. ⁴⁴Sc, ⁶⁴Cu, ⁶⁷Cu, ^luIn, ²¹²Pb, ⁶⁸Ga, ⁹⁰Y, ²¹²Bi, ⁵²Fe, ³Sc or ⁵Co.

Where the label is a metal, this will conveniently be incorporated into the polymeric agent by inclusion in the polymer structure of metal chelating groups (eg. groups such as EDTA, DTPA, DOTA, D03A, TMT, etc.) and metallating such chelant groups with ions of the metal. These chelant groups may form part of the polymer backbone or additionally or alternatively may be present in pendant side chains. Alternatively non-metal labels may be covalently attached to the end groups of linear, branched or dendrimeric polymers.

Where the label is a non-metal, eg. iodine or an organic chromophore, this may again be included in the backbone polymer repeat units (eg. as iodophenyl chain components) or again may additionally or alternatively be present in pendant side chains. Moreover, non-metal labels may be covalently attached onto or into the polymer backbone, eg. by covalent attachment to the end groups of a linear, branched or dendrimeric polymer.

To ensure water-solubility, the polymer agents of the invention will preferably incorporate hydrophilic groups (such as polyhydroxyalkyl or polyalkyleneoxy groups) , within the polymer backbone or additionally or alternatively in pendant side chains.

The polymer structure of the agents used according to the invention may be linear, branched or highly branched (eg. dendritic) . Linear polymers and dendrimeric polymers will however be preferred.

Thus by way of example the polymeric agent may contain repeat units of formula

- PB -

(SC)_n

where PB, the polymer backbone repeat unit, may incorporate a label (eg. iodine atoms or a metallated chelate group) and/or a hydrophilic backbone segment (eg. a polyalkyleneoxy linker group) , n is zero or a positive integer, and SC (the side chain) may incorporate a label (eg. iodine atoms or a metallated chelate group) and/or a hydrophilic segment (eg. a hydroxy poly (alkyleneoxy) group) .

Polyiodinated polymeric agents for use according to the invention may for example include compounds having repeat units of formula

where a and b are integers having values of from 1 to 4 ; c is zero or an integer having a value of 1 to 4; X is a first linker group providing a zero, 1, 2, 3 or 4 atom chain between iodophenyl groups; and L is a second hydrophilic linker group providing a chain of molecular weight up to 5000 between iodophenyl groups, preferably having pendant hydroxyl groups and incorporating ether oxygens within the chain, eg. as in polyalkyleneoxy residues. The phenyl :X or phenyl :L linkages may particularly conveniently be carbonyl groups or oxygen atoms, eg. in amide or ether functionalities.

Thus by way of example such compounds may be of formula

where a is 1, 2, 3 or 4 , preferably 2 or 3 ; b is 1, 2, 3 or 4, preferably 2 or 3 ; c is 0, 1, 2, 3 or 4, preferably 0 or 1 ;

R is H, alkyl, aryl, acyl, aroyl or aralkyl (eg. containing up to 20 carbons, preferably up to 6 carbons) optionally substituted with hydroxy groups;

R' is an optionally substituted (eg. with hydroxy or hydroxyalkyl) alkylene, preferably C₂_₂₀ alkylene, optionally interrupted by one or more oxygen or sulphur atoms ;

X is a linker providing a chain of 0 , 1, 2 or 3 atoms, eg. a bond, oxygen, carbonyl, SO, S0₂, CH_2; C(CH₃)₂ or a 2 or 3 atom chain made up or such components; and

R" is hydroxy, H, NHAc, or another hydrophilic group .

Such compounds may be prepared by iodination of mono or oligo phenyl alcohols (eg. bisphenol-A,

HO ~ζ^ ~{ ^~~θ }—OH, HO-C^"~~θ) 0 -< 0 -0H,

UO-( θ )—Cθ{ θ)—OH, H0-{^~0^~—OH or

1,3,5 trihydroxybenzene) followed by treatment with an^'

epoxide introducing agent (eg. BrCH₂CHCH₂) and polymer formation with a diamine (eg. H₂N (CH₂) ₂0 (CH₂) ₂NH₂) . Treatment of the polymer with acetic anhydride will convert any amine hydrogens to CH₃CO and base treatment will hydrolyse any unwanted esters that are formed.

Alternatively one may start from iodinated mono or oligophenyl dicarboxylic acids, activate the carboxyl groups (eg. with S0C1₂) , react with a diamine (eg. as above or an alkylenediamine such as NH₂ (CH₂) ₂NH₂) before polymerizing using an <*,ω chlorocarbonyl polyalkylene oxide or <*,ω bis epoxy compound (eg. CH₂CH-CH₂ 0 (CH₂) ₄OCH₂CHCH₂)

V V

Examples of other appropriate polymeric structures and chelating groups are described in WO94/08624, W094/ 08629, W095/26754, WO92/08494, EP-A-288256, W093/21957, WO90/12050, WO91/05762, WO93/06868 and EP-A-430863 and the documents cited therein.

The polymeric agent used according to the invention will preferably have a molecular weight in the range 1 to 2000 kD, eg. 3 to 70 kD, especially 10 to 50 kD. In the method of the invention, the contrast agent is conveniently injected or infused, preferably in aqueous solution or less preferably as an aqueous suspension, eg. at one or more injection sites in the hand, arm, foot, leg, crotch, chest or neck, preferably relatively close to and upstream of the lymph nodes or vessels of particular interest. For specific disease-draining lymph nodes, administration may be by peri-lesional injection. Furthermore, injection sites analogous to those used for ^99mτc sulphur colloids may be used, eg. peri-rectal, peri-lesional, peri-tumoral and classic injection sites such as the interdigital webbed spaces between the fingers or toes.

Dosages will preferably be relatively small volume, eg. 0.05 to 50 mL, preferably 2.0 to 10 mL for humans, the larger volumes conveniently being administered as a series of smaller injections, eg. 5 x 2 mL or 10 x 1 mL. Imaging can be effected immediately or after a delay of from minutes up to several days . Preferably however imaging is effected at from 30 minutes to 2 days, especially from 1 hour to 18 hours post injection. As is known in the art, massage and/or application of heat to the injection site may promote transport of the contrast agent into the lymphatic system, so permitting imaging to be effected more rapidly.

Generally dosages of from 0.0001 to 5.0 mmoles of chelated diagnostically effective metal is effective to achieve adequate contrast enhancement . For most MRI applications preferred dosages of imaging metal ion will be in the range from 0.02 to 1.2 mmoles/kg bodyweight (eg. at concentrations of 5 to 200 mM paramagnetic metal, eg. 20 to 100 mM) while for X-ray applications dosages of from 0.5 to 2.0 mmoles/kg are generally effective to achieve X-ray attenuation. Preferred dosages for most X-ray applications are from 0.8 to 1.5 mmoles of the metal/kg bodyweight . Where the agent is iodinated dosages of from 10 to 400 mgl/kg will generally be used. For scintigraphic applications dosages of from 0.0001 to 4 mmoles radionuclide/kg bodyweight will generally be used.

The polymeric contrast agents of the present invention may be formulated with conventional pharmaceutical or veterinary aids, for example emulsifiers, fatty acid esters, gelling agents, stabilizers, antioxidants, osmolality adjusting agents, buffers, pH adjusting agents, etc., and may be in a form suitable for subcutaneous administration, or for pre-use formulation for injection or infusion. Thus the polymeric compounds may be in conventional pharmaceutical administration forms such as powders, solutions, suspensions, dispersions, etc.; however, solutions in physiologically acceptable carrier media, for example water for injections, will generally be preferred.

The polymeric compounds may be formulated for administration using physiologically acceptable carriers or excipients in a manner fully within the skill of the art. For example, the compounds, optionally with the addition of pharmaceutically acceptable excipients, may be suspended or dissolved in an aqueous medium, with the resulting solution or suspension then being sterilized. Suitable additives include, for example, physiologically biocompatible buffers (as for example, tromethamine hydrochloride) , additions (eg. 0.01 to 10 mole percent relative to a chelated diagnostically effective metal) of chelants (such as, for example, DTPA, DTPA-bisamide or non-complexed polychelant) or calcium chelate complexes (as for example calcium DTPA, CaNaDTPA- bisamide, calcium polychelant or CaNa salts of polychelants) , or, optionally, additions (eg. 1 to 50 mole percent) of calcium or sodium salts (for example, calcium chloride, calcium ascorbate, calcium gluconate or calcium lactate) .

Parenterally administrable forms, eg. suspensions and solutions, should be sterile and free from physiologically unacceptable agents, and should have osmolality equal or nearly equal to that of plasma, eg. in the range 100 to 400 mOsm/kg, to minimize irritation or other adverse effects upon administration, and thus the contrast medium should preferably be isotonic or slightly hypertonic. In extreme cases, hypotonic solutions may be used efficaciously at small injection volumes . Suitable vehicles include aqueous vehicles customarily used for administering parenteral solutions such as Sodium Chloride Injection, Ringer's Injection, Dextrose Injection, Dextrose and Sodium Chloride Injection, Lactated Ringer's Injection and other solutions such as are described in Remington's Pharmaceutical Sciences, 15th ed., Easton: Mack Publishing Co., pp. 1405-1412 and 1461-1487 (1975) and The National Formulary XIV, 14th ed. Washington: American Pharmaceutical Association (1975) . The solutions can contain preservatives, antimicrobial agents, buffers and antioxidants conventionally used for parenteral solutions, excipients and other additives which are compatible with the chelates and which will not interfere with the manufacture, storage or use of products.

The various polymeric agents herein described as diagnostic imaging agents for the lymphatic system can be modified for delivery of. therapeutically active moieties to the lymph system. For example, therapeutic moieties can be attached to or otherwise incorporated within the structure of the water soluble polymer, in the same fasion as iodinated agents . Any therapeutic agent can be used, including peptides, proteins, and nucleic acids, as well as more conventional pharmaceutical molecules. Oncologies for metastatic disease, anti-inflammatories, antiviral agents as used against HIV and other viruses, antibiotics and radiotherapeutic agents are preferred.

The various documents referred to herein are hereby incorporated by reference .

The invention will now be described further by the following non-limiting Examples:

Example 1

NC 66368 Synthesis;

NC 66368 Synthesis:

SOC1,

HOCH2CH₂(OCH₂CH₂)3₂θH C1CH₂CH2(0CH2CH₂)32C1

PhCH₃ (1) (2)

C1CH2CH2(0CH₂CH₂)32C1 NaN /KI N₃CH2CH2(OCH2CH2)3₂N₃

DMF (2) (3)

H₂, Pd/C

N₃CH2CH₂(OCH₂CH2)3₂N3 NH₂CH2CH2(OCH2CH₂)3₂NH₂ 1N HC1 (3) (4)

NH₂CH2

GdCl₃

NC 66368 Polyoxyethylene bis (chloride) (2)

To a solution of polyethylene glycol [(1), average mol. weight 1.45K] (1000 g, 0.69 mol) in 1.5 L of toluene (60-80°C) was added S0C1₂ (200 mL, 2.76 mol) and DMF (10 mL) dropwise over 10 min. The reaction mixture was heated on a steam bath for 1 hr. An analysis by TLC (CH₂Cl₂:Me0H; 6:1) indicated very small amount of starting material still remained. An additional 20 mL of SOCl₂ was added to the reaction and it was heated on the steam bath for another 20 min to drive the reaction to completion. After cooling the reaction to 0°C with an ice bath, IN NaOH (2.5L) was carefully introduced to neutralize the solution and the layers were separated. The aqueous layer was washed with CH₂C1₂ (3 x IL) and the combined CH₂C1₂ layers were washed with water (2 x IL) and dried with MgS0₄. It was filtered and concentrated under reduced pressure to give a light yellow oil . The product was precipitated by adding TBME (2L) to the residue with cooling and stirring. The filtered product was dried in the oven under vacuum overnight to yield 941 g (94%) of the titled compound as a white solid. Anal. Calcd for C₆₄H₁₂₈0₃₁C1₂ : C, 52.49; H, 8.81; Cl, 4.84. Found: C, 51.94; H, 8.43; Cl, 5.00.

Polyoxyethylene bis(azide) (3)

To a suspension of polyoxyethylene bis (chloride) ((2), 500 g, 0.336 mol) and KI (139 g, 0.841 mol) in 1500 mL of DMF was added NaN₃ (109 g, 1.68 mol) . The suspension was heated on a steam bath at 70°C for 12 hr to give a yellowish solution. After cooling the reaction to room temperature, 2.5L of water was added and the solution was extracted with CH₂C1₂ (3 x IL) . The combined CH₂C1₂ layers were washed with water (3 x IL) , dried over MgS0₄, filtered and concentrated under reduced pressure to give a light yellow oil. The product was precipitated out by adding TBME (IL) to the residue with cooling and stirring. The filtered product was dried in the oven under vacuum overnight at room temperature to yield 452 g (90%) of the PEG diazide as a white solid. Anal. Calcd for C₆₄H₁₂₈0₃₁N₆ : C, 52.09; H, 8.73; N, 5.69. Found: C, 52.50; H, 8.58; N, 5.11.

Polyoxyethylene bi (amine) (4)

To a solution of polyoxyethylene bis(azide) ((3), 176 g, 0.117 mol) in IL of IN HC1 was added Pd/C (17.6 g) . The suspension was hydrogenated at 45 PSI for 15 hr. An aliquot withdrawn from the reaction indicated no more starting material by TLC (CH₂C1₂ :MeOH; 4:1) and the catalyst was removed by carefully filtering through a short plug of Celite. The filtrate was neutralized with 10% NaOH to pH=5-6 and extracted with CH₂C1₂ (3 x 600 mL) to remove the impurities . The aqueous solution was neutralized with 35% NaOH to pH>10 and extracted with CH₂C1₂ (2 x 500 mL) . The CH₂C1₂ layer was washed with water (500 mL) , brine (500 mL) and dried over MgS0₄. The filtrate was concentrated under reduced pressure to give a light yellow oil . The product was precipitated by adding TBME (IL) to the residue with cooling and stirring. The filtered product was dried in the oven under vacuum at room temperature overnight to give 138 g (81% yield) of the titled compound as a white solid. Anal. Calcd for C₆₄H₁₃₂0₃₁N₂ : C, 53.92; H, 9.33; N, 1.96. Found: C, 53.24; H, 9.35; N, 1.66.

NC 66368

To a solution of polyoxyethylene bis (amine) ((4), 550 g, 0.380 mol) in 5500 mL of water was added triethylamine (159 mL, 1.14 mol) and DTPA-dianhydride ((5), 149 g, 0.418 mol) . The suspension was stirred at room temperature and gave a clear solution after 10 min. The reaction was stirred for an additional 50 min and a solution of GdCl₃-6H₂0 (156 g, 0.418 mol) in 2000 mL of water was added. The reaction mixture was checked with PAR reagent to be sure only a slightly excess of GdCl₃"6H₂0 was added. The complexed solution (pH=2) was neutralized to pH~5 with 10% NaOH and then diafiltered using a Pellicon diafiltration unit with a 10 cutoff filter for 10 turnovers. A 10% NaCl (USP grade) solution (filtered through a 0.22 micron filter) was used for the first four turnovers and water was used for the remaining 6 turnovers. At the end of the diafiltration, the solution was concentrated to half of its original volume (pH=7) , filtered through a 0.22 micron filter and then lyophilized for 3 days leaving (532 g, 80%) of a sponge like product of Mw = 20,200 (SEC-HPLC analysis employing polyethylene glycol Mw standards) containing 7.09% w/w Gd by ICP analysis. Anal. Calcd for [C₈₀H₁₅₂GdN₅0_4o]_x : C, 48.50; H, 7.73; N, 3.53. Found (corrected for H₂0) : C, 48.14; H, 7.91; N, 3.29.

Example 2

NC 22181 Synthesis:

Et₃N DMSO

GdCl₃

NC 22181

To a solution of hexamethylene diamine ((7), 200 g, 1.72 mol) in 4L of DMSO was added triethylamine (810 mL, 5.52 mol) and DTPA-dianhydride ((5), 664 g, 1.84 mol). The suspension was stirred at room temperature for 45 h and a light yellow solution was obtained. 4L of EtOAc was added to the solution and product was precipitated as an oil . Solvent was decanted and the oil product was further washed with EtOAc (2 x 2L) . After the oil product was dried under vacuum for 1 hr, it was dissolved in 4L of water and GdCl₃'6H₂0 (312 g) was added. The solution was neutralized to pH^~5 with NaOH and filtered through a 0.45 micron filter. The filtered solution was diafiltered using a Pellicon diafiltration unit with a 10K cutoff filter for 10 turnovers. A 10% NaCl (USP grade) solution (filtered through a 0.22 micron filter) was used for the first five turnovers and water was used for the remaining 5 turnovers .

At the end of the diafiltration, the solution was concentrated to half of its original volume (pH=7) , filtered through a 0.22 micron filter and then lyophilized for 3 days leaving (203 g) of a sponge like product of Mw =18,900 (SEC-HPLC analysis employing polyethylene glycol Mw standards) containing 22.00% w/w Gd by ICP analysis. Elemental analysis : Anal. Calcd for [C₂₀H₃₂GdN₅O₈]_x (corrected for H₂0 and NaCl): C, 33.54; H, 5.70; N, 9.78. Found: C, 33.44; H, 5.77; N, 9.63; Na, 0.69; Cl, 0.98.

Example 3

Composition

NC 66368 (Example 1) was aseptically dissolved in physiological saline with the addition of enough TRIS buffer to make the solution 20 mM in buffer. The resulting solution was passed through a sterile 0.2 μm filter and packaged in 10 ml glass vials with teflon faced stoppers and conventional metal crimp tops . The vials were sealed and heat sterilized at 121°C for 15 minutes. The final composition of the solution was: NC 66368 80 mM Gd

NaCl 0.4% by weight

TRIS (pH8.0) 20 mM

Tϋ-vjπnpl e 4

Composition

600 mg of NC 22181 (Example 2) was aseptically dissolved in physiological saline (10 ML) with the addition of enough TRIS buffer to make the solution 10 mM in buffer. The resulting solution was passed through a sterile 0.2 μm filter and packaged in 10 ml glass vials with teflon faced stoppers and conventional metal crimp tops . The vials were sealed and heat sterilized at 121°C for 15 minutes. The final composition of the solution was:

[Gd] = 80 mM

NaCl = 0.9%

TriS = 10 mM

ahhi t- imaging

A rabbit was injected subcutaneously in the right front paw with 2 x 0.25 mL of the composition of Example 3 and imaged using MRI at 1.5T 24 hours after injection. Figure 1 of the accompanying drawings shows one MR image generated showing substantial contrast enhancement in the right axillary node (magnified in the box) as compared, by way of control, with the left axillary node (arrowed) .

PaKh-it Imaσing

NC 66368 was administered subcutaneously in the paw to New Zealand white rabbits at dosages of 0.064 and 0.128 mmole Gd/kg bodyweight (1 and 2 mL injections) . T₂- weighted MR imaging was carried out at 0, 0.16, 0.33, 0.5, 2 and 24 hours post injection and the detected enhancement of the popliteal was as set out in Table 1 below:

Table 1

* - immediately post-injection

Example 7

Imaging of NC 22181 in Rabbits

A solution of NC 22181 (Example 4) in saline was injected subcutaneously in the paws of New Zealand white rabbits at dosages of 0.1 ml, and 2.0 ml (approximately 0.006, 0.015, 0.064, and 0.128 mM Gd/kg body weight). TL weighted MR imaging was carried out at 24 hours post injection with the following % enhancements noted. Dose % enhancement

0.1 30

0.25 50

1.0 220

2.0 400

Clearly, this solution is efficacious at enhancement of lymph nodes after subcutaneous injection even at very low doses .

Claims

Claims :

1. A method for contrast enhanced imaging of at least part of the lymphatic system of a human or animal body which comprises administering a diagnostically effective contrast agent to said body and generating a contrast enhanced image of at least part of the lymphatic system of said body, characterised in that said agent is a water-soluble polymeric material having a molecular weight of at least 1 kD and is administered indirectly but parenterally.

2. A method as claimed in claim 1 wherein said contrast agent comprises a chromophore or fluorophore detectable in a light imaging technique.

3. A method as claimed in claim 1 or claim 2 wherein said contrast agent comprises a chelated metal ion or polyatomic ion detectable in a nuclear imaging, X-ray imaging or magnetic resonance imaging technique.

4. A method as claimed in any one of claims 1 to 3 wherein said contrast agent contains a diagnostically effective moiety bound covalently to or into the polymeric structure of the contrast agent .

5. A method as claimed in any one of claims 1 to 4 wherein said polymeric material is an iodinated polymer.

6. A method as claimed in claim 5 wherein said contrast agent contains polymer repeat units comprising iodinated phenyl groups .

7. A method as claimed in claim 6 wherein said polymeric material comprises repeat units of formula

where a and b are integers having values of from 1 to 4 ; c is zero or an integer having a value of 1 to 4; X is a first linker group providing a zero, 1, 2, 3 or 4 atom chain between iodophenyl groups; and L is a second hydrophilic linker group providing a chain of molecular weight up to 5000 between iodophenyl groups.

8. A method as claimed in claim 7 wherein said repeat units comprise an amide or ether functionality.

9. A method as claimed in claim 6 wherein said repeat units are of one of the following formulae

where a is 1, 2, 3 or 4 ; b is 1, 2, 3 or 4 ; c is 0, 1, 2, 3 or 4;

R is H, alkyl, aryl, acyl, aroyl or aralkyl optionally substituted with hydroxy groups;

R' is an optionally substituted alkylene, optionally interrupted by one or more oxygen or sulphur atoms;

X is a linker providing a chain of 0, 1, 2 or 3 atoms ; and

R" is hydroxy, H, NHAc, or another hydrophilic group .

10. A method as claimed in any one of claims 1 to 9 wherein said contrast agent has a molecular weight of from 10 to 50 kD.

11. A method as claimed in any one of claims 1 to 10 wherein said contrast agent further comprises a therapeutically effective moiety.

12. A method as claimed in any one of claims 1 to 11 wherein said contrast agent is administered by peri- rectal, peri-lesional or peri-tumoral injection or by injection into an interdigital web.

13. The use of a diagnostically effective contrast agent which is a physiologically tolerable, water- soluble polymer having a molecular weight of at least 1 kD for the manufacture of a subcutaneously administrable diagnostic imaging contrast medium for use in a method of diagnosis which involves indirect but parenteral administration of said contrast medium and subsequent generation of a contrast enhanced image of at least part of the lymphatic system.

14. Use as claimed in claim 13 of a polymeric material as defined in any one of claims 2 to 11.

15. An indirectly but parenterally administrable diagnostic contrast agent composition for use in lymphography comprising a physiologically tolerable, diagnostically effective water-soluble polymer having a molecular weight of at least 1 kD together with at least one pharmaceutically acceptable carrier or excipient .

16. A composition as claimed in claim 11 comprising as a contrast agent polymeric material as defined in any one of claims 2 to 11.