USE OF PARTICULATE CONTRAST AGENTS IN DIAGNOSTIC IMAGING FOR STUDYING PHYSIOLOGICAL PARAMETERS

Abstract: The present invention relates to a method of imaging of an animate human or non-human animal body, which method comprises: administering parenterally to said body a particulate material comprising a matrix or membrane material and at least one contrast generating species, which matrix or membrane material is responsive to a pre-selected physiological parameter whereby to alter the contrast efficacy of said species in response to a change in the value of said parameters; generating image data of at least part of said body in which said species is present; and generating therefrom a signal indicative of the value or variation of said parameter in said part of said body. The invention also relates to contrast media for imaging a physiological parameter.

Description: USE OF PARTICULATE CONTRAST AGENTS IN DIAGNOSΗC IMAGING FOR STUDYING PHYSIOLOGICAL PARAMETERS This invention relates to the use of particulate contrast agents m diagnostic imaging procedures for studying physiological parameters of the subject under investigation . In diagnostic imaging procedures, e.g. X-ray, MRI, ultrasound, light imaging and nuclear imaging, it has long been known to use contrast agents to facilitate visualization of particular organs or tissues or to identify diseased or malfunctioning regions, le. generating morphological images. The present invention is concerned with the use of parenterally administered particulate contrast agents for the quantitative or qualitative study of physiological parameters within the human or non-animal (e.g. mammalian, avian or reptilian, but preferably mammalian) body. Such parameters include for example pH, temperature, pressure, oxygen tension, carbon dioxide tension, ion tension/concentration the presence or concentration of other body metabolites or enzymes and cell surface properties, e.g. the presence or absence of various cell surface receptors. Parameters such as these may be indicative of the normal or abnormal functioning of the body as a whole or of a particular localized region, e.g. an organ which may or may not be tumorous, infected or otherwise malfunctioning. Likewise variations in such parameters may occur in response to drugs or other treatments administered to the body, e.g. hyperthermic treatment. As a result, quantitative, semi -quantitative or even qualitative determination of such parameters may be used to assess the need for a particular treatment or to monitor the success of a particular treatment. pH and temperature are particularly important as - 2 - indicators of abnormality or malfunction. Several m vivo methods, both imaging techniques and non imaging techniques, can be used to study physiological parameters, e g to diagnose disease Typical non- imaging techniques include simple blood pressure measurements, electrocardiography or electrocephalography for detection of electric currents m the heart muscle and brain, respectively, and other simple tests performed in doctors' offices or hospitals. Today, a variety of imaging techniques are also used. The most frequently used methods include various X-ray based techniques, MRI, ultrasound and diagnostic methods based on radioactive materials (e.g. scmtigraphy, PET and SPECT) Other diagnostic imaging methods include light imaging modalities, Overhauser MR (OMRI) , oxygen imaging (OXI) which is based on OMRI, magnetic source imaging (MSI) , applied potential tomography (APT) and imaging methods based on microwaves. The images obtained in X-ray techniques reflect the different densities of structures/organs/tissues m the patient's body. Contrast agents are today used to improve the image contrast m soft tissue examinations. Examples of such contrast agents include gas (negative contrast effect relative to tissue) ; barium sulphate suspensions; and lodmated agents including ionic monomeπc agents, non- ionic monomers, ionic dimers and non- ionic dimers. Typical examples of commercial X-ray contrast agents are Omnipaque and Visipaque 0 . MRI is an imaging method generally based on interactions between radiowaves and body tissue water protons m a magnetic field. The contrast parameter or signal intensity is dependent on several factors including proton density, spin lattice (T and spin spin (T ) relaxation times of water protons. Typical commercial MRI contrast agents include Omniscan ® , Magnevist ® and ProHance ® . Ultrasound is another valuable modality in - 3 - diagnostic imaging as it does not involve the use of ionizing radiation. In ultrasound examinations the patient is generally exposed to sound waves m the frequency of 1-10 MHz. These sound waves (or ultrasound waves) penetrate through or are reflected from the tissue. The transmitted or reflected sound waves are detected by a "microphone" and form the basis for development of a ultrasound image. Ultrasound imaging is a method of choice m pregnancy checks and birth control and diagnosis of cardiovascular and liver diseases . Although ultrasound contrast agents have been approved, there is as yet no general use of these agents. The main reason for this is the poor efficacy of the "first generation" agents. The ultrasound contrast agents currently under development are based on encapsulated gas because the reflection of sound from the liquid-gas interface is extremely efficient. Typical ultrasound contrast agents are gas encapsulated m a sugar matrix, m a shell of denaturated albumm/or partly denaturated albumin, m polymers, and m surfactants including phospholipids . A typical ultrasound contrast agent with high contrast efficacy consists of a fluonnated gas bubble (for example SF D or a perfluorcarbon such as perfluoropropane or perfluorobutane) coated with a mono or multilayer phospholipid membrane. The particle size will generally be around 4 micrometer with very few particles larger than 10 micrometer m diameter. The main indications for such a typical product m the future may be cardiac imaging (cardiac perfusion examinations) and liver imaging . Nuclear medicine imaging modalities are based upon administration of radioactive isotopes followed by detection of the isotopes, e.g. using gamma camera or positron emission tomography (PET) . The most frequently used examination is gamma camera detection of 99- - 4 - technetium m the form of a chelate, for example a technetium phosphonate chelate for bone scmtigraphy . Light imaging methods are performed using contrast agents that absorb and/or emit light (generally near infrared light) MSI methods may be performed without contrast agents; however, contrast agents based on magnetic materials improve this technique substantially. APT based methods can also be performed (like for example thallium scans) without use of contrast agents; again however, contrast agents based on physiologically acceptable ions or other agents with effect on conductivity improve the diagnostic utility of APT. All these different modalities complement each other with regard to diagnosis based on morphology/anatomy. However, there has been a great interest in measurement and quantification of various physiological parameters. (See for example J. Magn . Reson. Imaging 1997, 2, 82-90 for a review on physiologic measurements by contrast enhanced MR imaging) . Various methods for measurements of physiologically important parameters have been described m the scientific literature: tissue pH has been measured using near infrared reflectance spectroscopy (J. Clin. Monit . 1996, 12, 387-95); mtratumor pH has been measured using 1 F magnetic resonance spectroscopy ( Invest . Radiol . 1996, 3 . 1, 680-9); 6 -fluoropyridoxal polymer conjugates have been suggested as lή F pH indicators for magnetic resonance spectroscopy (Biocomug. Chem. 1996, 2, 536- 40) ; spectral imaging microscopy has been used for simultaneous measurements of intracellular pH and Ca 1 m insulin-secreting cells (Am. J. Phys ol . 1996, 270 , 1438-46), fluorescence ratio imaging has been used for measurement of interstitial pH m solid tumors (Br. J. Cancer 1996, 74., 1206-15); a fluorinated pH probe for "F magnetic resonance spectroscopy has been used for jL_n vivo pH measurement after hyperthermic treatment of tumors m mice (Acta Radiol . 1996, 2, 5363-4) ; P-NMR has been used for analysis of intracellular free magnesium and pH m erythrocytes (J. Soc. Gγnecol . Investig . 1996, 2, 66-70); intracellular pH has been estimated m developing rodent embryos using computer imaging techniques (Teratology, 1995, 72 , 160-8); biscarboxyethyl carboxyfluorescem has been evaluated as m vivo fluorescent pH indicator (J. Photochem. Photobiol. B. 1995, 227 , 302-8); the effect of blood flow modification on ultra- and extracellular pH has been measured by '"P magnetic resonance spectroscopy m murine tumors (Br. J. Cancer, 1995, 22, 905-11) ; intracellular Ca , pH and mitochondrial function m cultures of rabbit corneal tissue have been studied by digitized fluorescence imaging (In Vitro Cell Biol. Anim. 1995, 21, 499-507); a dual-emission fluorophore has been evaluated for fluorescence spectroscopy of pH m vivo (J. Photochem. Photobiol. B. 1995, 2.8, 19-23) ; nuclear magnetic resonance spectroscopy has been used to study lactate efflux and intracellular pH during hypoxia m rat cerebral cortex (Neurosci . Lett. 1994, 178 , 111- 4) ; 'P NMR spectroscopy has been used for imaging of phosphoenergetic state and intracellular pH m human calf muscles after exercise (Magn. Reson. Imaging 1994, 12 , 1121-6) ; multinuclear NMR spectroscopy has been used for studies of regulation of intracellular pH in neuronal and glial tumour cells (NMR Biomed. 1994, 1_, 157-166), 5 , 6-carboxyfluorescem has been used as a pH sensitive fluorescent probe for in vivo pH measurement (Photochem. Photobiol. 1994, 60., 274-9); a fluorinated pH-probe has been used for non-invasive in vivo pH measurements (Invest. Radiol. 1994, 29., 220-2); fluorescence ratio imaging microscopy has been used for non- invasive measurement of interstitial pH profiles in normal and neoplastic tissue (Cancer Res. 1994, 54 , 5670-4); 6-fluoro-pyridoxol has been used as probe of - 6 - cellular pH using F NMR spectroscopy (FEBS Lett. 1994, 349 , 234-8) , lactate and pH have been mapped m calf muscles of rats during ischemia/reperfusion assessed by in vivo proton and phosphorus magnetic resonance chemical shift imaging (Invest. Radiol. 1994, 2J9, 217- 23), nuclear magnetic resonance spectroscopy has been used for measurement of m vivo and ex vivo pH (Eur. J. Lab. Med. 1996, 4., 143-156); semmaphthofluorescein- calcein has been tested as fluorescent probe for determination of intracellular pH by simultaneous dual -emission imaging laser scanning confocal microscopy (J. Cell Physiol. 1995, 164 , 9-16) ; ampholytic dyes have been proposed for spectroscopic determination of pH m electrofocusmg (J. Chromatogr. A 1995, 695, 113-122); EPR spectroscopy has been used for direct and continuous determination of pH values m nontransparent water-moil systems (Eur. J. Pharm. Sci. 1995, 2, 21-6); intracellular Ca and pH have been imaged simultaneously glomerular epithelial cells (Am. J. Physiol. Cell Physiol . 1993, 4_6, 216-230); fluorinated macromolecular probes have been evaluated for non- invasive assessment of pH by magnetic resonance spectroscopy (Bioorg. Med. Chem. Lett. 1993, 2, 187-192); pH has been mapped m living tissue by application of vivo n P NMR chemical shift imaging (Magn. Res. Med. 1993, 29., 249-251); fluorescence spectroscopy has been used to measure temperature dependent aggregation of pH-sensitive phosphatidyl ethanolamme oleic acid-cholesterol liposomes (Anal. Biochem. 1992, 207. 109-113); 1J C NMR spectroscopy has been used to determine intracellular pH (Am. J. Physiol. Cell. Physiol. 1993, 264, C755-C760) ; P NMR chemical shift imaging has been used for pH mapping of living tissue (Magn. Reson. Med. 1993, 29 , 249-251) ; fluorescent probe and ' P NMR spectroscopy have been compared for measurement of the intracellular pH of propionibacterium acnes (Can. J. Microbiol. 1993, 39 , 180-6) ; panoramic imaging of brain pH and CBF has been performed during penicillin and metrazole induced status epilepticus (Epilepsy Res 1992, 12, 49-58); nuclear magnetic resonance spectroscopy has been used to study energy metabolism, intracellular pH and free Mg concentration the brain of transgenic mice (J. Neuroche . 1992, 22, 831-6; , the pH dependence of 5- fluorouracil uptake has been observed by vivo P and F nuclear magnetic spectroscopy (Cancer Res. 1991, 51 , 5770-3), P magnetic resonance spectroscopy has been used to study tumor pH and response to chemotherapy non-Hodkm's lymphoma (Br. J. Radiol. 1991, .64., 923-8); P magnetic resonance spectroscopy and microelectrodes have been used to evaluate dose-dependent thermal response of tumor pH and energy metabolism (Radiat Res. 1991, 127 , 177-183); hepatic intracellular pH has been studied m vivo by '"F NMR spectroscopy (Magn. Reson. Med. 1991, 19 . , 386-392); the relationship between vertebral traosseous pressure, pH, pO , pCO and magnetic imaging signal mhomogeneity has been evaluated a patient with back pain (Spine 1991, 16., 239-242); the effect of hypoxia on phosphorus metabolites and intracellular pH m the fetal rat brain have been studied by P NMR spectroscopy (J. Physiol. 1990, 430 , 98P) ; brain pH in head injury has been evaluated using image-guided 31 P magnetic resonance spectroscopy (Ann. Neurol . 1990, 2 . 8, 661-7); Se-labeled tertiary amines have been prepared and evaluated as brain pH imaging agents (Nucl . Med. Biol. Int. J. Radiat. Appl. Instrum. Part B 1990, 12, 601-7); 'H, P and 13 C nuclear magnetic resonance spectroscopy have been used to study cerebral energy metabolism and intracellular pH during severe hypoxia and recovery m the guinea pig cerebral cortex m vitro (J. Radiat. Appl. Instrum. Part B 1990, 26 , 356-369) ; development of a pH-sensitive contrast agent for H NMR imaging has been reported (Magn. Reson. Med. 1987, 5 , 302-5); and there have been other references to 'P NMR studies of pH, see for example Biomed. Res. (Japan 1989 10, Suppl. 3, 587-597, J. Cereb. Blood Flow Metab. 1990, 10, 221-6, Br. J. Radiol. 1990, 22, 120-4, Pediatr. Res. 1989, 22, 440-4, Radiology 1989, 170 , 873- 8, Cereb. Blood Flow Metab. 1988, 8 , 816-821, J Neuro . Chem. 1988, U51U, 1501-9 abd Am. Heart J 1988, 116 701-8. W098/41241 of Nihon Schermg discusses MRI techniques which utilise polymers the monitoring of pH. One important physiological parameter of great medical interest has been temperature; temperature has been measured by electron paramagnetic resonance spectroscopy (J. Biomech. En . 1996, 118 , 193-200), an ytterbium chelate has been used as a temperature sensitive probe for MR spectroscopy (Magn. Res. Med. 1996, 22, 648-651), fast imaging techniques have been evaluated m MRI for temperature imaging (J. Magn. Reson. B, 1996, 112 , 86-90), 31 P and l E magnetic resonance spectroscopy has been used to study relationship between bram temperature and energy utilization rate m vivo (Pediatr. Res. 1995, 22, 919- 925), local bram temperature has been estimated in vivo by H NMR spectroscopy (J. Neurochem. 1995, 38 , 1995 , 1224-30) , magnetic resonance has been used to follow temperature changes during interstitial microwave heating (Med. Phys. 1997, 24., 269-277), the temperature dependence of canine bram tissue diffusion coefficient has been measured vivo using magnetic resonance echoplanar imaging (Int. J. Hyperthermia 1995, 11 , 73-86), temperature dependent ultrasound colour flow Doppler imaging has been carried out of experimental tumours in rabbits (Ultrasound Med. Biol. 1993, 19 , 221-9), electrical impedance tomography has been proposed for temperature measurement (Trans ASME J. Biochem. Eng. 1996, 118 , 193-200), temperature measurement has been carried out m vivo using a temperature-sensitive lanthanide complex and H magnetic resonance spectroscopy (Magn. Res. Med. 1996, 35. 364-9) , body temperature imaging by impedance CT has been carried out (Med. Imag. Tech. (Japan) 1995, 13 , 696-702) , temperature imaging has been carried out inside the human body using microwaves (Med. Imag. Techn . (Japan) 1995, 22, 691-5), m vivo oxygen tension and temperature have been determined simultaneously using F NMR spectroscopy of perfluorocarbon (Mag. Res. Med. 1993, 22, 296-302), measurement of m vivo pH normal and tumor tissue has been carried out by localized spectroscopy using a fluorescent marker (Optical Eng. 1993, 22, 239-43), microwave temperature imaging has been proposed (IEEE Trans. Med. Imag. (USA) 1992, 4_, 457-69), non-invasive temperature mapping during hyperthermia has been carried out by MR imaging of molecular diffusion (Proceedings of the Annual International Conference of the IEEE 1988, 342-343) . There have been other reports of non- invasive and minimally invasive methods for the early detection of disease states by MRI, positron emission tomography, EEG imaging, MEG imaging, SPECT, electrical impedance tomography (APT) , ECG imaging and optical diffusion tomography, see for example Proceedings of the SPIE - The International Society for Optical Engineering (USA) 1887 (1993) . The following, predominantly MRI based, techniques have also been reported in the measurement of temperature and temperature changes; Med . Phys 1997, 24 (2) , 269-277, Int. J. Hyperthermia 1995, 11 (5) . 409- 424, Int. J. Hyperthermia 1992, 8(2), 253-262, Int. J. Hyperthermia (1994), 10 (3) , 389-394, Radiologe 1998, 22, 200-209, Med Phys 1997, 24 (12) , 1899-1906, JMRI 1998, 8 , 128-135, JMRI , 1998, 8 , 160-164, JMRI 1998, 2, 165-174, MRM 1995, 2J., 359-367, MRM 1995, 22, 729-731, MRM 1995, 22, 74-81, Radiology 1998, 208. 789-794, JMRI 1996, 2, 226-229, JMRI 1997, 188-196, JMRI 1998, 2, 197-202, JMRI 1998, 2, 31-39, JMRI 1998, 2, 121-127, JMRI 1998, 8 , 493-502, Int. J. Radiation Oncology Biol. Phys. 1998, - 1 0 - 40(4) , 815-822, Int. J Hyperthermia 1998, 1 (5) , 479- 493, Radiology 1995, 196, 725-733, Advances Radiation Therapy 1998 Eds. Mittal, Purdy and Ang, Kluver Academic Publishers, Chapter 10, pp. 213-245. Several patents and patent applications which relate to physiological imaging have been published: use of macrocyclic metal complexes as temperature probes for the determination of body temperature using spectroscopic methods with reduced background signals ( 094/27977 ) ; new fluorine containing macrocyclic metal complexes from tetraazadodecane derivatives useful for measuring tissue temperature from NMR chemical shift values, and as contrast agents for X-ray or NMR diagnosis ( 094/27978) ; determining and imaging of temperature change m human body using diffusion coefficients obtained by NMR to determine absolute temperature for individual points of body and temperature differences ( O90/02321) ; thermographic imaging using a temperature dependent paramagnetic material m an ESR enhanced magnetic resonance imaging apparatus ( O90/02343 ) ; fluorosubstituted benzene derivatives useful as agents for m vivo NMR diagnosis, e.g. for measurement of tissue specific pH temperature, redox potentials, etc. (EP-A-368429) ; a magnetic resonance pulsed heat system for selectively heating a region of a subject that uses pulsed heat from focussed ultrasound equipment to destroy tumor tissue and MRI to provide fast scan images to monitor tissue and temperature with a diffusion sensitive pulse sequence (US-A-5247935) ; a magnetic resonance pulsed heat system for selectively heating tissue - surgery is performed using localised heating of tissue guided by and monitored by temperature sensitive magnetic resonance imaging and body tissue is heated using a magnetic resonance imaging system having a source and a probe containing a magnetic imaging coil and heating imaging rf source (US-A- 5323778) ; apparatus for hyperthermia - 1 1 - treatment of cancer comprising a combined hyperthermia and MRI probe to simultaneously heat a malignant area and monitor temperature, with a filter to isolate signals (WO91/07132 ) ; and a temperature measurement method using tomographic techniques of magnetic resonance imaging to measure the temperature of a region indirectly from an intensity change of magnetic resonance signal (US-A-5207222 ) . The present invention however is based on the understanding that particulate contrast agents may be produced which the matrix or membrane material for the particles is responsive to a particular physiological parameter resulting a change m the contrast efficacy of the contrast agent which may be correlated to that physiological parameter. Thus viewed from one aspect the invention provides a method of imaging of an animate human or non-human animal body, which method comprises: administering parenterally to said body a particulate material comprising a matrix or membrane material and at least one contrast generating species, which matrix or membrane material is responsive to a pre-selected physiological parameter whereby to alter the contrast efficacy of said species response to a change in the value of said parameter; generating image data of at least part of said body m which said species is present; and generating therefrom a signal indicative of the value or variation of said parameter m said part of said body. Viewed from a further aspect the invention provides a parenterally admmistrable contrast medium for imaging of a physiological parameter, said medium comprising a particulate material the particles whereof comprise a matrix or membrane material and at least one contrast generating species, said matrix or membrane material being responsive to said physiological parameter to cause the contrast efficacy of said contrast generating species to vary in response to said parameter In a particularly preferred emoodiment , the matrix or membrane material comprises a lipid or lipid mixture having a Tc value between 35 and 80 ϋ C, preferably between 37 and 45°C, more preferably between 38 and 43°C (Tc is defined as the gel - to-liquid crystalline phase temperature) . In a further preferred embodiment, the matrix or membrane material comprises peptides or one or more polymers . Viewed from a still further aspect the invention provides the use of a contrast generating species for the manufacture of a particulate contrast medium for use m a method of diagnosis comprising generating a signal indicative of the value of said physiological parameter, the particles of said contrast medium comprising a matrix or membrane material and at least one contrast generating species, said matrix or membrane material being responsive to said physiological parameter to cause the contrast efficacy of said contrast generating species to vary in response to said parameter. In the method of the invention, the image data generated may if desired be presented as a two or more dimensional spatial image, alternatively they may be presented as a temporal image, again in two or more dimensions. However m the extreme the data may simply provide one or more image values (e.g. numerical values) which either directly or indirectly may be used to provide quantitative or qualitative information (a signal) indicative of the value of the parameter under study. The image data may if desired be presented visualizable form but alternatively they may simply be a set of data points which are collected and operated on to produce the signal without a visible image actually being generated. The signal indicative of the value of the parameter under study may likewise be generated m the form of a visible image, e.g. a map of the parameter value within the body, or a chart showing variation of - 13 - the parameter value with time, or it may simply be a calculated numerical value for the parameter or an indication that the parameter is below or above a particular threshold value. Desirably, however, the signal provides a quantitative or at least semi- quantitative value for the parameter, e.g. either a region of interest or a plurality of regions of interest m the body, for example providing a spatial and/or temporal map of the parameter within at least a portion of the body. Data relating to a physiological parameter may not necessarily also contain information relating to the anatomy of the animal body and thus, a further aspect of the invention relates to the combination of traditional anatomical imaging with physiological imaging to obtain two images, one containing information about a physiological parameter and the other containing anatomical information. The two images may be combined to give one image with both anatomical and physiological information . Thus, according to a further aspect is provided a method of imaging of an animate human or non-human animal body, which method comprises: administering parenterally to said body at least one contrast generating species the contrast efficacy whereof is responsive to a change m value of a preselected physiological parameter; generating image data of at least part of said body m which said species is present; and generating therefrom a signal indicative of the value or variation of said parameter m said part of said body and also generating an anatomical image of the same part of the animal body. The additional use of anatomical information may aid interpretation of the physiological data. An image generated response to a physiological parametr, a 'physiological image', may be formed using any of the - 14 - imaging methods and or contrast media described herein This physiological image can be combined with a conventional image obtained with or without a contrast agent . Suitable contrast agents for use with traditional anatomical imaging are well known m the art for all types of imaging techniques, MRI, X-ray, ultrasound, light and nuclear imaging etc. and many suitable contrast agents for anatomical imaging are discussed herein. The imaging technique used to obtain physiological data may be the same or different to the imaging technique used to obtain the anatomical image. In a preferred embodiment the imaging technique will be the same, MRI being particularly suitable. Two separate contrast agents may be used, one for physiological imaging and one for traditional imaging. The two agents can be injected sequentially and the body scanned sequentially with respect to the appropriate imaging techniques and optionally the two images which are generated are then combined. In an alternative embodiment, a single multi-functional contrast agent may be used which is capable of providing both physiological and anatomical information. A multi-functional MRI contrast agent may be used, wherein one of its functions responds to a physiological parameter while a second function provides anatomical information. Although a single contrast agent is applied, the body may be scanned twice and the resulting two images combined. In a further alternative embodiment a multifunctional contrast agent may be used wherein the components of the agent function as contrast agents for different imaging techniques. Thus, the contrast agent may contain microbubbles to provide contrast in ultrasound imaging and paramagnetic complexes for MRI, one of these components being responsive to a physiological parameter. Again, the images obtained by scanning according to the two imaging techniques may be - 15 - comb i ned . By way of a further example, MRI with hyperpolarised substances will tend to provide good physiological information relating to e.g. pH, temperature or pressure but little or no anatomical information. Thus, the hyperpolarised MR image is advantageously combined with an anatomical image, e.g. by superimposing the images. The two images may be generated separately or at the same time. The combination of physiological and anatomical imaging may be used to investigate all parts of the human or non-human animal body and any of the physiological parameters discussed herein, particularly pH and temperature. Where the physiological parameter is temperature, changes m the value of the parameter, i.e. temperature changes, may be caused by intrinsic or extrinsic means. Intrinsic means will include cancer, cardiovascular disease and inflammation while extrinsic means include hyperthermia (external heating) treatment. Thus, the physiological contrast agent may be a contrast agent for hyperthermia. The imaging technique used in the method of the invention may be any technique capable of use m conjunction with contrast agents, e.g. X-ray (e.g. CT scanning), MRI, MRS, MR microscopy, ESR imaging, ESR spectroscopy, Mόssbauer imaging, ultrasound, light imaging, nuclear imaging (e.g. scintigraphy, PET or SPECT) , MSI, APT, etc. In magnetic resonance techniques, signal strength or chemical shift or both may typically be studied. Preferably, the technique used will be an X-ray, MRI, ultrasound, light imaging or nuclear imaging technique (e.g. scintigraphy), in particular an MRI or ultrasound technique. The particulate contrast agent used will accordingly be or contain a material capable of havmg a contrast or signal generating effect m the particular imaging modality selected, e.g. a gas or gas precursor, a - 16 - paramagnetic, ferromagnetic, ferrimagnetic or superparamagnetic material or a precursor therefor, hyperpolarized nmr active (le. non zero nuclear spin) nuclei (e.g noble gas or C nuclei), a radionuclide , a chromophore, (which term is used to include fluorescent and phosphorescent materials as well as light absorbers) or a precursor therefor, an ionic species, etc. The physiological parameter studied using the method of the invention may be any physiochemical parameter capable of affecting the matrix or membrane material of the contrast agent, e.g. pressure, temperature, pH, oxygen tension, carbon dioxide tension, enzyme activity, metabolite concentration, tissue electrical activity, tissue diffusion, ion concentration, particularly Mg , Ca and Zn " , etc. Preferably however it will be selected from blood parameters, e.g. pressure, temperature and pH, m particular in the vasculature rather than the chambers of the heart. Where temperature is being measured, changes may be due to intrinsic factors such as disease or because of external factors, i.e. hyperthermia. It is not envisaged that the parameter be one which does not affect the membrane or matrix, for example flow rate or perfusion density. A key part of the present invention is that the contrast agent particles should comprise a membrane or matrix material which is responsive to the physiological parameter under investigation so as to alter the contrast efficacy of the contrast agent. The manner which the membrane or matrix responds will depend on the particular combination of imaging modality, physiological parameter and contrast generating material selected. Typically however the response might involve a change in membrane or matrix permeability to one or more species (e.g. water or gases), chemical or physical breakdown of the membrane or matrix material, generation of a contrast generating material, cleavage of - 1 7 - functional groups from a contrast generating material thereby changing its contrast generating ability, alteration of oxidation state m a contrast generating material thereby changing its contrast generating ability, etc. Such a response may thus for example involve release from the particulate contrast agent of water-soluble contrast generating moieties that are capable of being taken up into the extracellular fluid outside the vasculature. Particular examples of physiological parameter responsive particulate contrast agents will be described in greater detail below. Thus one embodiment of the invention relates to thermosensitive paramagnetic particulate compositions for temperature MRI -mapping of the human body. Another embodiment of the invention relates to the use of thermosensitive particulate gas compositions as an ultrasound-based in vivo thermometer. Yet another embodiment of the invention relates to radioactive compositions for temperature mapping in the human body. Another embodiment of the present invention relates to thermosensitive particulate compositions containing water-soluble X-ray contrast agents for mapping of temperature in the human body. Still another aspect of the present invention relates to particulate compositions containing near infrared dyes for light imaging based temperature mapping in the body. Another aspect of the present invention is to use one or more of the thermosensitive particulate compositions for temperature mapping in imaging guided hyperthermia treatment . Another embodiment of the present invention relates to pH sensitive particulate compositions for determination of pH m the body. By way of example the active contrast agent (or indicator or probe) may be a paramagnetic, magnetic or fluorinated compound detectable by MRI . The active contrast agent (or indicator or prooe) may be a gas or a gas generating substance for detection by ultrasound, it may be a radioactive substance for detection by scintigraphy, SPECT or PET, or it may be a fluorescent dye, a near infrared dye, a UV dye or another dye that can be detected vivo m light imaging or light detection methods Yet another embodiment of the invention relates to particulate compositions as contrast agents or as m vivo indicators or probes for detection of oxygen concentration/tension m the tissue using modalities such as ultrasound, MRI, Overhauser MRI and ESR. Another embodiment of the present invention relates to particulate compositions as contrast agents or as in vivo indicators or probes for detecting pressure, turbulence, viscosity, enzyme activity, ion concentrations, metabolite diffusion coefficients, elasticity and flexibility. Another aspect of the present invention relates to particulate compositions as contrast agents or as in vivo indicators or probes m combination with a targeting ligand, wherein said targeting ligand targets cells or receptors selected from the group consisting of myocardial cells, endothelial cells, epithelial cells, tumor cells, bram cells, and the glycoprotem GPIIb/IIIa receptor, for detection of changes in physiological parameters and/or quantification/ semiquantification of physiological parameters relevant for diagnosis of disease. Further examples of targeting ligands which can be used are : I) Antibodies, which can be used as vectors for a very wide range of targets, and which have advantageous properties such as very high specificity, high affinity (if desired), the possiblity of modifying affinity according to need etc. Whether or not antibodies will be bioactive will depend on the specific vector/target - 1 9 combination Both conventional and genetically engineered antibodies may be employed, the latter permitting engineering of antibodies to particular needs, e.g. as regards affinity and specificity. The use of human antibodies may be preferred to avoid possible immune reactions against the vector molecule. A further useful class of antibodies comprises so- called bispecific antibodies, i.e. antibodies havmg specificity for two different target molecules m one antibody molecule. Such antibodies may, for example, be useful m promoting formation of bubble clusters and may also be used for various therapeutic purposes, e.g. for carrying toxic moieties to the target. Various aspects of bispecific antibodies are described by McGu ness, B.T. et al . m Na t . Biotechnol . (1996) 14, 1149-1154; by George, A.J. et al . m J. Immunol . (1994) 152, 1802- 1811; by Bonardi et al . m Cancer Res . (1993) 53, 3015- 3021; and by French, R.R. et al . m Cancer Res . (1991) 51, 2353-2361. li ) Cell adhesion molecules, their receptors, cytokmes, growth factors, peptide hormones and pieces thereof. Such vectors/targeting ligands rely on normal biological protem-protem interactions with target molecule receptors, and so m many cases will generate a biological response on binding with the targets and thus be bioactive; this may be a relatively insignificant concern with vectors which target proteoglycans . m) Non-peptide agonists/antagonists or non- bioactive binders of receptors for cell adhesion molecules, cytokmes, growth factors and peptide hormones. This category may include non-bioactive vectors which will be neither agonists nor antagonist but which may nonetheless exhibit valuable targeting ability. IV) Oligonucleotides and modified oligonucleotides which bind DNA or RNA through Watson-Crick or other types of base-pairing. DNA is usually only present m 2 0 extracelluar space as a consequence of cell damage, so that such oligonucleotides, which will usually be non- bioactive, may be useful m, for example, targeting of necrotic regions, which are associated with many different pathological conditions Oligonucleotides may also be designed to bind to specific DNA- 01 RNA-bmdmg proteins, for example transcription factors which are very often highly overexpressed or activated m tumour cells or m activated immune or endothelial cells. Combinatorial libraries may be used to select oligonucleotides which bind specifically to possible target molecules (from proteins to caffeine) and which therefore may be employed as vectors for targeting v) DNA-b dmg drugs may behave similarly to oligonuclotides , but may exhibit biological acitvity and/or toxic effects if taken up by cells. vi ) Various small molecules, including bioactive compounds known to bind to biological receptors of various kinds. Such vectors or their targets may be used to generate non-bioactive compounds binding to the same targets. vn) Targeting ligands may be selected from combinatorial libraries without necessarily knowing the exact molecular target, by functionally selecting (in vitro, ex vivo or m vivo) for molecules binding to the region/structure to be imaged. IX) Proteins or peptides which bind to glucosammo-glycan side chains e.g. heparan sulphate, including glucosammoglycan-bind g portions of larger molecules, since binding to such glucosammoglycans side chains does not result a biological response. Proteoglycans are not found on red blood cells, thus eliminating undesirable adsorption to these cells. The particulate contrast agent may thus be used for quantiflcation/semi-quantification of a physiological parameter which is relevant for diagnosis of disease. The particulate contrast agent may be triggered into - 2 1 - giving a measurable signal difference either by the target parameter itself (e.g the local temperature, pH or pressure or by binding to the particular cell surface receptors of interest) or by a chemical or biological response of the target parameter (e g release of enzymes oi local variation pH or temperature due to cellular reactions) The particulate agent may thus respond to, identify and/or quantitatively or semi- quantitatively determine bacteria, viruses, antibodies, enzymes, drugs, toxins, etc. Another aspect of the present invention relates to intravenous particulate compositions as contrast agents or as m vivo indicators or probes with long vascular half life (reduced liver uptake) for detection of changes m physiological parameters and/or quantiflcation/semiquantification of physiological parameters relevant for diagnosis of disease. The particulate contrast agent used according to the invention may be a solid material, a porous material, a liquid crystal material, a gel, a plastic material, a material havmg one or more walls or membranes or liquid particles, e.g. emulsion droplets or gas based particles, e.g. micro bubbles. The particles can also be thermodynamically stabilised, e.g. micro emulsion droplets or surfactant micelles. The chemical composition of the particulate material can be one simple chemical compound or a mixture of two or more chemical compounds. Generally it will comprise two or more different chemical entities, at least one of which is a matrix or membrane forming material and at least one other of which is a contrast generating species. The composition can consist of solid material (s) only or it may be a mixture of different solids/liquids/gases . The particulate will generally have a mean particle size (e.g. as determined by particle size analyzers such as laser light scattering apparatus or Coulter counters) m the range 0.001 to 20μm, more preferably 0.01 to 10 μm, 22 - especially 0.05 to 7 μm Such particles are often described m the literature as particles, colloids, emulsions, droplets, icrocrystals , nanocrystals , microparticles , nanoparticles , vesicles, liposomes, bubbles, microspheres , microbubbles , coated particles, microballons and the like The term "polymer" as used herein refers to any chemical compound with more than 10 repeating units A polymer can be naturally occurring, synthetic, or semisynthetic. Semisynthetic polymers are polymers that are produced by synthetic modification of naturally occurring polymers. Compounds with 2 to 10 repeating units are herein generally referred to as "oligomers" and likewise may be natural, synthetic or semisynthetic The term "surface active compound" or "surfactant" is used herein to refer to any chemical compound havmg at least one hydrophilic functional group and at least one hydrophobic (lipophilic) group. In a multiphase system, surface active compounds will commonly accumulate at the interface. The term "lipid" is used herein to refer to naturally-occurring compounds, synthetic compounds and semisynthetic compounds which are surface active compounds and have structures similar to fatty acids, waxes, mono-, di- or tri-glycerides , glycolipids, phospholipids , higher (C ι0 or greater) aliphatic alcohols, terpenes and steroids. The term "gas" is used herein to refer to any compound or a mixture of compounds with sufficiently high vapor pressure to be at least partly m the gas phase at 37°C. When the imaging modality used according to the invention is ultrasound, the contrast generating species m the contrast agent will preferably consist of one or more encapsulated gases and/or one or more encapsulated gas precursors. This contrast generating species is able to interact with the surroundings so that the - 23 - contrast agent gives information about one or more physiological parameters generally as a result of an interaction between the surroundings and the encapsulation material, if necessary followed by changes related to the gas/gas-precursor. However gaseous contrast generating species may be used m other imaging modalities, such as MRI and X-ray for example. Typical examples of gas types that change contrast property as a result of the physiological parameters m the surrounding tissue include: gases that are generated from a precursor as a result for example of pH, temperature or pressure changes, e.g. as a result of a chemical reaction, as a result of the boiling point of the gas, or as a result of a change of solubility; gases that compete with blood gases for absorption or adsorption sites within the matrix or membrane material; gases that change properties (e.g. lose hyperpolarization or change other magnetic properties) upon contact with body fluids or components, including dissolved components, thereof; gas molecules sensitive to pH; gases that change properties/volume with temperature; gases that change volume as a result of surrounding gas (e.g. oxygen tension); etc. Preferred gases include hydrogen, oxygen, nitrogen, noble gases (including hyperpolarized gases) , carbon dioxide, fluorinated gases (e.g. sulphur hexafluoride, fluorohydrocarbons , perfluorocarbons and other fluorinated halogenated organic compounds in gas phase) , and low molecular weight hydrocarbons . Preferred gases also include any pharmaceutically acceptable gas mixture like for example air and air/perfluorocarbon mixtures. Preferably, the perfluorocarbon gas is selected from perfluoromethane , perfluoroethane , perfluoropropanes and perfluorobutanes . Any physiologically acceptable gas precursor can be used. Among suitable gas precursors are compounds that form a gas as a result of a chemical reaction (for example compounds sensitive to pH, for 24 - example carbonic acid, ammomalonic acid or other acceptable pH sensitive gas generating substances) . Other suitable gas precursors are compounds that form a gas as a result of other physiological conditions like foi example temperature, oxygen, enzymes or other physiological parameters/compounds relevant for body tissue (whether the normal or diseased state) or which are activated to a gas forming state as a result of an interaction with an external stimulus (e.g. photo- activation, sono-activation etc.). The encapsulation material can be any material such as for example lipids, phospholipids, surfactants, proteins, oligomers and polymers. Such materials may be chosen to dissolve, melt, collapse, weaken, increase porosity, or otherwise break down, change phase or change size (e.g. by aggregation due to change in surface charge, for example m response to local Ca 21 and/or Mg 1 concentration) response to the physiological parameter, e.g. to allow release of the contrast generating species into the surrounding fluid, or to allow body fluid or components thereof to come into contact with the contrast generating species, or to raise contrast agent species local concentration above the detection limit, etc. In this way the contrast generating effect of the contrast generating species may be dispersed (e.g. into the extracellular fluid space), switched on or increased (e.g. by generation of a contrast generating species such as a gas or by increasing water contact (for a positive (Tj effect) MR contrast agent such as a gadolinium chelate) ) , or switched off or decreased (e.g. by destruction of the compartmentalization required for a negative (T, effect) MR contrast agent such as a dysprosium chelate, or by quenching of a radical or depolarization of a hyperpolarized nucleus or dissolution of a blood soluble gas) . Moreover a porous solid matrix, e.g. a zeolite, may be impregnated with the contrast generating species - 25 - with the pore mouths then being closed off totally or partially using a material which breaks down, melts or dissolves when the relevant physiological parameter (e.g. pH, temperature, enzyme concentration) m the surrounding body fluid is above or below a pre-set value . The particulate contrast agent used according to the invention may respond to physiological parameters m several different ways. In one aspect, the particulate contrast agent may respond to physiological parameters by accumulation in the area where a certain value for a particular parameter is fulfilled, compared to areas where it is not. In another aspect of the invention, the particulate contrast agent responds by accumulation m areas where the physiological parameter value is not fulfilled. In yet another aspect of the invention, the particulate contrast agent responds to a given parameter by disintegration, the disintegration being dissolution or chemical breakdown. Especially advantageous is a response to a physiological parameter by leakage or other transport means m/out of the particles. The opposite situation where the response to a physiological parameter is to prevent dissolution/leakage by attaining an increase m stability/reduction in membrane transport compared to particles in areas where a threshold value for a given parameter is not fulfilled, is also a preferred aspect of the present invention. This type of response is advantageous since a time course may lead to a reduction m contrast by elimination from the organ m areas where the threshold value for the parameter is not fulfilled, while the contrast remains the area of interest . When a particulate composition responds by disintegration or transport, changes in contrast effect may be achieved by exposing otherwise invisible/shielded contrast agents, altering the distribution of contrast agents or, when the contrast agent is the particle - 2 6 itself ιas ultrasound contrast agents), destroying the contrast giving property Especially advantageous are paiticulate compositions where the contrast effect is gained by interaction with the environment In this case, both ransport of the contrast agent and transport of the actual environmental component may be utilized for detection of physiological parameters. An example is MRI contrast agents where an increased degree of water access/transport to the contrast agent leads to the measured contrast enhancement In this case, response to a physiological parameter may be an increased rate of water transport m/out of the particulate . The leakage or an increased transport rate of solutes m/out of a particulate may be accomplished m a variety of ways. All kinds of phase transitions may be utilized to induce leakage/transport. For instance, a solid particle/membrane may become leaky when it is melted, the process being sensitive to temperature. Phase transitions involving a gas phase may be used to respond to pressure as a physiological parameter. An especially useful aspect of the present invention is particles comprising liquid crystalline material as for example liposomes, niosomes or other vesicles. Liquid crystalline materials may undergo several different phase changes which may induce leakage and/or increase the transport rate of solutes or even breakdown of the particle. For example, the gel to liquid crystalline phase transition of phospholipids may increase the liposome permeability and increase the transport rate or induce leakage of solutes on heating and hence temperature sensitivity. The lamellar to reversed hexagonal phase transition will also induce leakage since the liposomes require lipids m lamellar, gel or other layered phase structure. The lamellar to reversed hexagonal phase transition may be induced by pH, electrolytes, and changes m the chemical environment - 27 - such as targeting, enzymes, antibodies etc Tne suitable parameter to respond to may be tuned by selection of the membrane composition and processing. Other phase transitions such as lamellar to cubic phases, lamellar to microemulsion phases or lamellar to normal hexagonal phase may also be used to introduce leakage . Gel based particles or gel -surrounding particles (e g. particles made by coacervation) may respond to a physiological parameter by, for example, a lowering of the viscosity of the gel . Such viscosity lowering may for example be obtained by temperature, pH or electrolytes such as Ca or Mg and the particles are thus sensitive to these parameters. Such parameters may also induce phase separation m the gel particles, leading to leakage of liquid and phase separation of the polymer which comprises the gel . These mechanisms may m turn influence a parameter such as water leakage and exposure of, e.g. paramagnetic chelates to water and hence lead to a change m MRI contrast. Particles or membranes composed of solid polymer may also respond to physiological parameters. For instance temperature may change the glass transition temperature of the polymer, and hence induce phase transitions m the polymer membrane, which m turn may influence a parameter such as water transport which influences the contrast efficacy of the contrast agent. Particles which at least m part are composed of or stabilised by water soluble polymers e.g. peptides, may respond to physiological parameters by alternation in the peptide conformation. For instance peptides may undergo an - helix to β - sheet transition or vice versa and hence influence a parameter which m turn effects contrast. Also transitions to/from - helix or β - sheet to random coil may influence a parameter such as membrane permeability, particle stability against aggregation/flocculation or even fusion, or particle - 28 - dissolution or precipitation which in turn alters the contrast efficacy of the contrast agent. Also of use as contrast agents when the imaging modality is ultrasounds are temperature and pressure sensitive emulsions and fluids. Leakage may also be controlled by entities forming channels or other transport routes through the membrane of a particle. These channels may control the transport of molecules in/out of the particle, and be quite selective for, e.g., ions. For instance the protein tubulin which forms microtubules in absence of Ca 21 may induce a higher leakage in presence of Ca ~ " than in absence of Ca and hence be Ca" sensitive. Other proteins/enzymes which may control the transport of substance in/out of a vesicle, include erythrocyte anion transporter, erythrocyte glucose transporter, Na + -Kfc ATPase (Na + /Kfc pump) , Ca 2 " - ATPase (Ca 2' pump) and Bacteriorhodopsin (H + - pump) . Also biosurfactants such as iturins, esperine, bacillomycins , mycosubtilin, surfactin and similar substances may be used as membrane components to induce/prevent leakage by response to external parameters since these molecules may respond by changes in secondary and tertiary structure as well as self-assembly properties on influence from extrinsic parameters . The contrast generating species in MR contrast agents used according to the invention will generally be a paramagnetic, superparamagnetic , ferrimagnetic or ferromagnetic compound and/or a compound containing other non zero spin nuclei than hydrogen, e.g. 19 F, 13 C, ' ;" N, ;<, Si, i! P and certain noble gases, such as 129 Xe or Ηe. Preferred as paramagnetic compounds are stable free radicals, and compounds (especially chelates) of transition metal or lanthanide metals, e.g. manganese compounds, gadolinium chelates, ytterbium chelates and dysprosium chelates. Preferred magnetic (e.g. - 2 9 - superparamagnetic) compounds are γ-Fe O , Fe C and other iron/metal oxides with high magnetic susceptibility. Preferred fluorinated compounds are compounds with relative short F T -relaxation times. Other preferred fluorinated compounds according to the present: invention are fluorinated pH-probes, such as compounds described m EP-0447013 of Scheπng A.G. and ZK-150471 described by Y. Aoki m Invest. Radiol 1996, 21, 680-689. Examples of MR contrast effective materials are well known from the patent literature, see for example the patent publications of Nycomed, Salutar, Sterling Wmthrop, Schermg, Squibb, Mallmckrodt, Guerbet and Bracco . In general, there are two types of contrast generating species useful m MR contrast agents for use according to the invention: species that change contrast property as a result of the physiological parameters m the surrounding tissue; and species that are inert to physiology but change contrast properties as a result of an interaction between coating material/encapsulation material and physiology. Typical examples here will be GdDTPA, GdDTPA-BMA, GdDOTA, GdHPD03A, PrD03A-derιvatives and Tm chelates thermosensitive liposomes or m pH-sensitive vesicles. Typical examples of species that change contrast property as a result of the physiological parameters in the surrounding tissue include: paramagnetic chelates that change relaxation properties and/or change chemical shift as a result of temperature, paramagnetic chelates that change coordination number and thereby relaxation properties and/or shift properties as a function of pH, paramagnetic compounds, for example manganese compounds (Mn (2+) /Mn (3+) ) , europium compounds (Eu(2+), Eu(3+)) and free radicals (radical, no radical) that change relaxation properties and/or shift properties as a result of oxygen tension/concentration or as a result of redox potential the surrounding tissue, paramagnetic - 3 0 - and magnetic compounds that change relaxation/shift properties as a result of enzymic activity (for example with enzymatic cleavage of paramagnetic chelates from macromolecules conjugated thereto causing a change in correlation time and/or water coordination) and paramagnetic chelates that change properties as a result of concentration of ions in the tissue, e.g. due to changes m water coordination. Paramagnetic compounds have, according to the present invention, either an effect on the relaxation times (T or T ) or an effect on chemical shift. Typical compounds that change relaxation times are gadolilmum chelates, manganese compounds and superparamagnetic iron oxides. Europium chelates, on the other hand, are well- known chemical shift compounds. The effect on chemical shift is related to temperature. Based on this, macrocyclic paramagnetic chelates like 2 -methoxyethyl substituted PrD03A and 1 , 4 , 7 , 10-tetraazacyclododecane- 1 , 4 , 7 , 10-tetrakιs (methylene phosphonate thulium complex) have been suggested as temperature probes (see WO 94/27977 (Platzek, Schermg) and C.S. Zuo et al . m J. Magn. Res. 133 53-60 (1998)) . All these paramagnetic compounds can be used according to the present invention. The contrast generating species m X-ray contrast agents for use according to the invention will generally be a gas or gas generator or a water-soluble compound containing heavy atoms (e.g. atomic number of 37 or greater), e.g. metal chelates, metal clusters, metal cluster chelates and lodmated compounds. Preferred contrast generating species include ionic and non-ionic lodmated organic aromatic compounds, m particular tπiodophenyl compounds. Most preferred are approved iodine based contrast agents such as salts, e.g. sodium or meglumme salts, of lodamide, lothalamate, diatrizoate, loxaglate and metrizoate, and non-ionics such as metπzamide (see DE-A-2031724) , lopamidol (see BE-A-635355) , lohexol (see GB A 1548594) , lotrolan (see EP-A 33426), lodecimol (see EP-A-49745), lodixanol (see EP-A 108638) , loglucol (see US-A-4314055 ) , loglucomide (see BE-A-846657) , loglumde (see DE-A-2456685 ) , logulamide (see BE-A-882309) , lopromide (see DE-A-2909439) , losacol (see DE-A- 3407473 ) , losimide (see DE-A-3001292) , lotasul (see EP-A-22056), loversol (see EP-A-83964) and loxilan (see W087/00757) . Such contrast generating species may be incorporated into matrices or coatings that are sensitive to one or more physiological parameter. The contrast generating species m nuclear medicine contrast agents for use according to the invention may be any radioactive compound of the type in diagnostic nuclear medicine, for example known compounds useful for scintigraphy, SPECT and PET. Typical compounds include radioiodmated compounds, Indium labelled materials and Tc labelled compounds (for example ^"TcDTPA, qi1 "TcHIDA and ' ,,η Tc labelled polyphophonates) and 5l CrEDTA. Such contrast generating species may be incorporated into matrices or coatings that are sensitive to one or more physiological parameter. Contrast agents can be prepared for other imaging modalities such as light imaging, Overhauser MRI, oxygen imaging, magnetic source imaging and applied potential tomography, by encapsulation of the contrast generating species, e.g. a chromophore or fluorophore (preferably having an absorption or emission maximum m the range 600 to 1300nm, especially 700 to 1200nm) , a stable free radical, a superparamagnetic particle or an ionic (preferably polyionic) species, for the respective modality into a physiologically sensitive matrix or coating . In vivo temperature measurements have been of great interest because temperature is an important physiological parameter related to several indications including cancer, cardiovascular diseases and - 32 - inflammation. Local monitoring of temperature will also be of great value during hyperthermia treatment. Contrast generating species can be released from the matrix/encapsulation material as a result of increased temperature and thereby change their contrast property or distribute to other tissues than the particulate product Alternatively for an MR active temperature sensitive agent, a change contrast efficacy may occur due to an increased permeability of the matrix/encapsulation material, and, hence, to an increased rate of water transport across the matrix/encapsulation material, even if the agent itself does not leave the matrix/encapsulation material. Typical examples of temperature sensitive particulate materials are temperature sensitive liposomes, these being especially suitable for use with MRI . These liposomes take advantage of the fact that the membrane permeability is markedly increased at the gel- to-liquid crystal phase transition temperature (TJ of their membrane lipids. Also, possibly depending upon the membrane properties and the nature of the MR active agent, leakage of the agent may occur. Liposomes made from specific phospholip ds or a specific blend of phospholipids may be stable up to 37°C but exhibit an increased water permeability or/and leak as they pass through an area of the body which the temperature is raised, e.g. to 40 to 45°C, as a result of a disease process or an external heating. Table 1 below shows the transition temperature of various saturated phosphatidylcholmes . Table 1 Phosphatidylcholmes (PC) Transition temperature Tc (°C) 33 12 : 0 -1 13 :0 14 14 : 0 23 15 : 0 33 16 :0 41 17 : 0 48 18 :0 55 19:0 60 20 : 0 66 21 :0 72 22 : 0 75 23 :0 79 24 :0 80 Table 2 below shows the phase transition of various unsaturated phosphatidylcholmes . 34 Table 2 Phosphat ldvlcholines (PC) Transition temperature Tc (°C) 12 1 36 18 lc9 20 18 lt9 12 18 lc6 1 18 2 53 18 3 60 18 4 70 Table 3 below shows the phase transition temperature of various asymmetric phosphatidylcholmes. Table 3 Phosphatidylcholmes (PC) Transition temperature Tc (°C) 14 0-16 0 35 14 0-18 0 40 16 0-14 0 27 16 0-18 0 49 16 0-18 1 -2 16 0-22 6 -27 16 0-14 0 30 18 0-16 0 44 18 0-18 1 6 18 1-16 0 -9 18 1-18-0 9 Table 4 below shows the phase transition temperature for various saturated symmetric phosphatidylglycerols (PG) m the form of their sodium salts. 3 5 Table 4 Phosphatidylglycerols (PG) Transition temperature Tc (°C) 12 0 3 14 0 23 16 0 41 18 0 55 Tables 1-4 are based on information from the product catalogue of Avanti Polar Lipid Inc., USA. Accordingly, phospholipids or blends of phospholipids may be selected to give products with the correct Tc for thermosensitive liposomes for diagnostic use Typical blends for preparation of thermosensitive liposomes for diagnostic use are mixtures of dipalmitoylphosphatidylcholme (DPPC) and dipalmitoylphosphatidyl glycerol (DPPG) and distearylphosphatidylchol e (DSPC) . Particulate contrast agents may also respond to temperature by utilizing the conformational temperature sensitivity of certain polymer systems. An example is poly (N-isopropyl acrylamide) which phase separates at 37°C. Hence particles comprising contrast agents will become leaky dependent on temperature (see Hoffmann et al . Macromol . Symp . 118: 553-563 (1997)). Other examples of temperature sensitive matrices/coatings are lipid suspensions/emulsions containing the contrast generating species or other particulate or particulate like formulations that release the contrast generating species or change properties as a result of changes m temperature. If the parameter under study is capable of manipulation, e.g. by treatment with drugs, external application of heat etc., it may be used to study the efficacy of such treatment or localized such treatment may be used to cause a change in contrast efficacy which - 3 6 m turn may be used to measure parameters such as organ perfusion Thus for example external application of heat at, near or upstream of an organ of interest may be used to cause release from the particles of a contrast agent which may diffuse into the organ and so to detect blood perfusion (or lack of perfusion) m that organ. In this context one might administer a thermally sensitive particulate agent in connection with an external heating to follow the heat transport m parts of the body. Heat transport m vivo is directly connected to blood flow through the bioheat equation (J. Appl Physiol. vol. 1, (1948), 93-122) — r,C 7 W h c h (T - T„ ) - k 2 T + (Q +QJ where r (kg/m ) is the density of tissue, C (J/kg°C) is the specific heat of tissue, t (s) is the time, T (°C) is the temperature, w π (kg/m s) is the blood perfusion, c (J/kg °C) is the specific heat of blood, T a (°C) is the arterial temperature, k (W/m °C) is the thermal conductivity of tissue, Q (W/m ) is the power deposition and Q„ (W/m 1 ) is the local metabolic rate. Hence, the thermosensitive particulate compositions may, after a controlled, localized external heating, give a measure of blood perfusion m an organ. The temperature response of thermosensitive MR- liposomes can m general be divided into three distinct regions : a) 'low relaxivity' region; r x = r^"; T< T,; where r is a constant with temperature (T) ; b) 'temperature active' region' r, (T) = f (T) , T <T<T , and c) 'high relaxivity' region; r, = r ' 114 ; T>T, ; where r '' is a constant with T (ideally, r ' 19 ' >> r ' ') . It is possible to quantify the local temperature in the temperature active region of the liposomes, provided - 37 - three criteria are met : 1 A well defined relationship exists around T between liposomal relaxivity and temperature; i.e. r (T) = f (T) ; T <T<T ; where T ; T is a clinically relevant temperature range. Ideally r should be a linear function of T over the range T ;T . 2. The temperature active region covers a large enough temperature range . 3. The Gd concentration in tissue [Gd] is known. If [Gd] is not known, even a qualitative assessment of temperature changes may prove difficult, since regions with different [Gd] would have a different degree of enhancement, even if the temperature were the same. Furthermore, it would be impossible to say whether lack of enhancement after heating was due to a low local temperature or the absence of the liposomes that region. However the local [Gd] in vivo can be estimated, based on the relaxation effects of the liposomes m the 'low relaxivity' state, by the following method: 1. Acquire quantitative R, and/or R 2 /R_* images (R ι, =l/T 1/ _) before contrast administration and after contrast administration but before hyperthermia is initiated. R, and R 2 /R 2 * images can be routinely acquired on most state-of-the-art clinical MR systems . 2. Measure the fractional change in R λ and/or R 2 /R 2 * , ΔR 1 =R 1 '" :,L -R 1 pre m the region of interest. 3. The local Gd concentration is then given by: [Gd] = ΔRj/ri. 4. If r, is not known, the ratio of the Gd concentration between two regions is given by: [Gd, ] / [Gd ] =)R1 /ΔR1 . Alternatively, R or R * images can be used to obtain the same Gd ratio. In general therefore, the absolute [Gd] can not be determined, unless the liposomal relaxivity m the tissue is known. However this may be fairly well approximated for the r relaxivity, but not the r * relaxivity, since this depends on tissue geometry. Nonetheless, the [Gd] m one region relative to another can be estimated as described above The relative [Gd] is valuable information that can be used to adjust the signal enhancement m the image so that it reflects actual temperature changes. In order for this to be possible, one need to assume that a 'core region' exists where the temperature is above T . It is likely a clinical situation that such a core region exists where the heating is most efficient surrounded by a 'penumbra' where heating is less efficient and the temperature distribution is less well defined. Now, by knowing the relative [Gd] m the core versus the penumbra, the image intensity can be adjusted to compensate for any difference m [Gd] m the two regions. It is possible to estimate [Gd,] / [Gd 2 ] using a strongly T -weighted sequence m which case change m signal intensity is almost linearly related to change m Rπ and hence [Gd] . This requires TR << Tj of the target tissue. Similarly, strongly T or T* -weighted sequences can be used to estimate [Gd / [Gd ] . Thus, when a Gd compound is encapsulated in liposomes, the resulting relaxivity (r 1 ,r 2 ) is small due to restricted water access to the paramagnetic centre. However, given that a very Tj-sensitive sequence is used, it is still possible to detect a change in T, due to the presence of the liposomes prior to heating (i.e. at temperatures well below T ) . Consequently, by acquiring quantitative R λ - or T -maps of the area of interest before and after contrast injection (prior to hyperthermia treatment) , the change in R : or T, enables the local Gd concentration [Gd] to be determined. After heating, regional variations m [Gd] can thus be accounted for; variations contrast enhancement due to temperature differences can therefore be distinguished from variations in contrast enhancement due to - 3 9 - concentration variations. The longitudinal relaxation rate R after contrast administration is given by: R = R + [Gd] *r ; Where R is the relaxation rate prior to contrast administration. The change in R, due to the contrast agent is therefore: ΔR = Rj-R = [Gd] *r ; After hyperthermia, a new R. - or T -map is generated . In conclusion, therefore, given that the T, effect of the liposomes is detectable below T ς , it is possible to map the local Gd concentration and consequently compensate for differences in contrast enhancement after heating due to local variations in Gd concentration. The R, or R, ' effect of the liposomes can also be used for this purpose. In vivo pH measurements have been of great interest because pH is an important physiological parameter associated to several severe diseases. The pH value is usually reduced during cancer diseases, cardiovascular diseases like for example stroke, osteoporosis, inflammations and autoimmune diseases. One type of pH sensitive encapsulation for diagnostic agents involves the use of pH sensitive liposomes. The general strategy is to employ pH- sensitive groups in the liposomal membrane. Such typical groups have pKa values between 4 and 5.5. Phospholipids useful for preparation of pH-sensitive diagnostic agents include diheptadecanoyl phosphatidylcholine (DHPC) in admixture with DPPC and N- palmitoyl homocystein (PHC) in different ratios (see Eur. J. Pharm. Biopharm. 1993, 3_9, 97-101 for a general review on temperature and pH-sensitive liposomes) . Another type of pH-sensitive encapsulation of contrast generating species involves the use of pH- sensitive surfactants like for example N-dodecyl-2- - 4 0 - imidazole propionate (DIP) which has pKa of 6.8 (see for example Pharm Res . 1993, 12, 404) This means that DIP at pH 7.3-7.4 (physiological) is in the non-ionized (non/low surfactant activity) form (80%) while at for example lysosomal pH (5.2) over 97% will be m the charged form Another means of pH-sensitive encapsulation of contrast generating species involves the use of matrix materials and/or coating materials with pKa values m the range of 4.5-7.0 so that the material is soluble or partly soluble m the charged form and insoluble or partly insoluble the non-charged form. Such compounds can be physiologically acceptable low molecular weight compounds or physiologically acceptable polymers . Still another means of pH-sensitive encapsulation involves the use of compounds that are chemically cleaved as a result of pH, for example polyorthoesters or polyacetals/ketals which are cleaved under acidic conditions . Liposomes comprising phosphatidyl ethanolamines (PE) as the central component are another example of liposomes which can undergo a phase transition and become leaky when pH is reduced. pH sensitive liposomes can also be achieved by incorporation of fatty acids into phospholipid membranes. In principle any charged particulate system where the charge is pH dependent and influences the packing of the membrane material can be used. Access to oxygen is critical for all types of cells, and diagnostic agents for determination of oxygen concentration/tension in tissue will be of great importance m diagnosis of diseases like cancer, cardiovascular diseases, autoimmune diseases and several diseases m the central nervous system. One type of oxygen or redox sensitive encapsulation/coating material is a material that has different solubility/diffusion properties dependent on the oxygen level or the redox status; for example compounds containing a nitro-group that is reduced m vivo to an ammo-group which improves solubilization of the material m reductive/low oxygen surroundings. Determination of concentration of physiologically important ions m tissue is important for several diseases . Types of ion concentration sensitive encapsulation materials that may be used in this regard include phospholipids, surfactants and other ion chelatmg materials Negatively charged liposomes will for example bind Ca(2+) and the membrane will change its diffusion properties and become more stiff. An example of Ca /Mg sensitive particulate compositions are liposomes enriched with the dimeric phospholipid cardiolipm. A cardiolipm containing membrane may undergo a lamellar to reversed hexagonal phase transition upon addition of the divalent cations since these ions bind to the cardiolipm di -phosphatidyl group . Ca or Mg ,+ sensitivity may be obtained by using charge stabilised particles, e.g. solid particles, liquid particles e.g. emulsion droplets, gas particles e.g. microbubble dispersions or liposomes. Ca or Mg'" may thus induce aggregation or flocculation among the particles and by this means alter contrast effect. Ca 2+ or Mg sensitivity may also be obtained by using stabilising moieties for the particles which are chemically or physically influenced by Ca + or Mg , for instance using surfactants which form water insoluble species when exposed to Ca or Mg ' and thus precipitate. Some particles or stabilising membranes surrounding particles may also respond with a phase transition when exposed to Ca or Mg . An example are liquid crystalline based particles e.g. liposomes, which may respond by a lamellar to reversed hexagonal phase - 42 - transition upon addition of Ca or Mg Also gel particles may respond easily to Ca or Mg by a significant lowering of viscosity or even phase separation of the polymer which forms basis for the gel on exposure to Ca or Mg . This viscosity reduction or phase separation may induce a change m contrast effect. Types of enzyme sensitive encapsulation material include matrices or coatings that are degraded by enzymes, for example simple esters of low molecular weight compounds or polyesters like polyacetic acid and others . Various metabolites may also change the properties of coating materials. Particulates can be made sensitive to for example antibodies based on enhanced leakaged due to a phase transition induced by the chemical binding between membrane molecules and the antibody. As an example, liposomes comprising N- (dinitrophenylammo-e-caproyl) - phosphatidyl ethanolamme (DNP-cap-PE) become leaky due to a lamellar to reversed hexagonal phase transition when binding to anti-DNP. Another example includes liposomes comprising human glycophorm A dioleoyl phosphatidyl ethanolamme membranes. These liposomes become leaky when immobilized antibodies are added. A further aspect of the present invention is to use one of the above described particulate diagnostic agents together with another compound that has the potential to change the physiological parameter of interest or together with use of an external energy source to change the parameter of interest . Thus one example is to administer thermosensitive diagnostic agents m connection with an external heating and to follow the heating effect in parts of the body. Another example is to administer compounds that change pH m connection with a pH-sensitive particulate diagnostic agent to follow the pH-profile m the area of interest . - 43 - Still another example is to cause the subject under study to inhale oxygen, after administration of an oxygen sensitive diagnostic agent, to follow oxygen uptake tissue. Early diagnosis is very important to obtain good therapeutic results In most disease processes changes physiological parameters take place before changes m morphology All existing contrast agents diagnose morphology The new types of contrast agent according to the invention are able to detect diseases at a very early stage m the disease process and thereby improve the therapeutic outcome for the patient. Where the particulate diagnostic agent or a component thereof carries an overall charge, it will conveniently be used m the form of a salt with a physiologically acceptable counterion, for example an ammonium, substituted ammonium, alkali metal or alkaline earth metal cation or an anion deriving from an inorganic or organic acid. In this regard, meglumme salts are particularly preferred. The diagnostic agents of the present invention may be formulated in conventional pharmaceutical or veterinary parenteral administration forms, e.g. suspensions, dispersions, etc., for example m an aqueous vehicle such as water for injections. Such compositions may further contain pharmaceutically acceptable diluents and excipients and formulation aids, for example stabilizers, antioxidants , osmolality adjusting agents, buffers, pH adjusting agents, etc. Where the agent is formulated in a ready-to-use form for parenteral administration, the carrier medium is preferably lsotonic or somewhat hypertonic . Where the particulate agent comprises a chelate or salt of an otherwise toxic metal species, e.g. a heavy metal ion, it may be desirable to include within the formulation a slight excess of a chelat g agent, e.g. - 44 - as discussed by Schermg m DE-A- 3640708 , or πore preferably a slight excess of the calcium salt of such a chelatmg agent. The dosage of the diagnostic agents of the invention will depend upon the imaging modality, the contrast generating species and the means by which contrast enhancement occurs (e.g. with switching on or off of contrast, with dispersion of contrast out of the vascular space, etc) . In general however dosages will be between 1/10 and 10 times the dosage conventionally used for the selected contrast generating species or analogous species m the same imaging modality. Even lower doses may also be used. While the present invention is particularly suitable for methods involving parenteral administration of the particulate material, e.g. into the vasculature or directly into an organ or muscle tissue, intravenous administration being especially preferred, it is also applicable where administration is not via a parenteral route, e.g. where administration is transdermal, nasal, sub-lingual or is into an externally vodmg body cavity, e.g. the gi tract, the bladder, the uterus or the vagina. The present invention is deemed to extend to cover such administration. The disclosures of all the documents mentioned herein are incorporated by reference. The present invention will now be illustrated further by reference to the following non- limiting Examples . Example 1 Preparation of Temperature Sensitive Paramagnetic Liposomes Liposomes containing GdHPD03A (ProHance , Bracco Spa, Milan, Italy) and GdDTPA-BMA (Omniscan , Nycomed Amersham Imaging AS, Oslo, Norway) were prepared by the - 45 - thin film hydration method. Two different saturated phospholipid blends were used; one consisting of hydrogenated phosphatidyl cholme (HPC) (Lipoid GmbH, Ludwigshafen, German) and hydrogenated phosphatidylser e-sodium (HPS) (NOF Corporation, Amagasaki , Japan) ,- the other composed of DPPC and DPPG- sodium (Sygena Ltd, Liestal , Switzerland) . The phospholipid mixtures contained 5% or 10% (w/w) of the negatively charged HPS and DPPG components. The phospholipid mixtures were dissolved m a chloroform/ methanol mixture and the organic solution was evaporated to dryness under reduced pressure. DPPC/DPPG liposomes were formed by hydratmg the lipid film with a preheated (55°C) aqueous solution (pH 7.4) of 250 mM GdDTPA-BMA or 250 mM Gd HPD03A. The HPC/HPS liposomes were prepared analogously but with a lipid hydration temperature of 70°C. The DPPC/DPPG and HPC/HPS liposomes where allowed to swell for 2 hours at 55 and 70°C respectively. The total lipid concentration was 50 mg/ml. The liposomes were subjected to 3 freeze-thaw cycles liquid nitrogen. Differently sized liposomes were produced by sequential extrusion (Lipex Extruder^, Lipex Biomembranes Inc., Vancouver, Canada) through polycarbonate filters of various pore diameters. The extrusion temperature was 55 and 70°C for the DPPC/DPPG and HPC/HPS liposomes respectively. Untrapped metal chelate was removed by gel filtration or dialysis against lsoosmotic and isoprotic glucose solution. Physiochemical Properties The mean hydrodynamic diameter of the liposomes varied from 103 nm to 276 nm, as measured by photon correlation spectroscopy (ZetaSizer IV, Malvern Instruments Ltd., Malvern, England); the zeta potential was negative in the order of -25 mV, as determined by laser Doppler velocimetry at 25°C (ZetaSizer IV, Malvern Instruments Ltd., Malvern, England). The mean - 46 - gel - to-liquid crystalline phase transition temperature (Tc) of the HPC/HPS and DPPC/DPPG preparations was 50 and 42°C, respectively, as determined by differential scanning calorimetry (DSC4, Perkin Elmer Inc., Norwalk, CT) . Temperature Response of In Vi tro MR Contrast Efficacy Figure 1 of the accompanying drawings and Table 5 below show the temperature sensitivity of m vitro T relaxivity (r ) for liposome encapsulated GdDTPA-BMA and GdHPD03A, respectively (0.47T). Figure 2 of the accompanying drawings shows the temperature response of the m vitro MR signal intensity for liposome encapsulated GdDTPA-BMA. Figure 3 of the accompanying drawings shows a series of T x -w GRE images prior to and after heating of a gel phantom containing inserts of liposome encapsulated GdDTPA-BMA. Table 5 Temperature (°C) r (s ] mM ') DPPC/DPPG HPC/HPS Control ' 103 nm 130 nm 20 0.16 0.06 4.53 25 0.23 0.08 4.27 30 0.31 0.12 3.94 37 0.69 0.21 3.75 45 3.30 0.53 3.07 55 3.10 3.00 2.82 60 - 2.96 2.54 non- liposomal GdHPD03A Example 2 GdDTPA-BMA encapsulated within DSPC/DPPC/DPPG liposomes DSPC/DPPC/DPPG (weight ratio; 28.5/66.5/5) - 47 - liposomes were prepared by the thin film hydration method. The phospholipids (500 mg) were dissolved a chloroform/methanol mixture and the organic solution was evaporated to dryness under reduced pressure . Liposomes were formed by hydratmg the lipid film with a preheated (57 C) aqueous solution (pH 1 7) of 250 mM GdDTPA- BMA (10 ml) . The liposomes were subjected to 3 freeze- thaw cycles and allowed to swell for one and a half hours at 65 C. The liposome dispersion was extruded at 65 C through polycarbonate filters of various pore diameters. The liposome size (z-average) after extrusion was 167 nm. Untrapped GdDTPA-BMA was removed by dialysis against lsoosmotic and isoprotic glucose solution . Table 6 shows the temperature sensitivity of the in vi tro r (0.235T) m glucose 5% solution for liposome encapsulated GdDTPA-BMA. Table 6 Temperature r λ m glucose 5% ( l C) (s^rnM -1 ) 30 0.098 35 0.13 38 0.22 40 0.27 41 0.31 43 1.10 45 2.92 Example 3 GdDTPA-BMA encapsulated withm DPPC/DPPG/DPPE-PEG-2000 liposomes DPPC/DPPG/DPPE-PEG-2000 (weight ratio; 90/5/5) liposomes were prepared by the thin film hydration method. The phospholipids (500 mg) were dissolved in a chloroform/methanol mixture and the organic solution was - 48 - evaporated to dryness under reduced pressure . Liposomes were formed by hydrating the lipid film with a preheated (57 C) aqueous solution (pH 1 7) of 250 mM GdDTPA- BMA (10 ml) . The liposomes were subjected to 3 freeze- thaw cycles and allowed to swell for one and a half hours at 65 'C . The liposome dispersion was extruded at 65 ' C through polycarbonate filters of various pore diameters. The liposome size (z-average) after extrusion was 132 nm. Untrapped GdDTPA-BMA was removed by dialysis against isoosmotic and isoprotic glucose solution. Tabl e 7 shows the temperature sensitivity of the in vi tro r (0.235T) in glucose 5% solution for liposome encapsulated GdDTPA-BMA. Table 7 Temperature r, in glucose 5% ( (, c) (s^mM "1 ) 35 0.32 37 0.46 38 0.56 39.2 2.53 40 4.16 42 5.65 Example 4 GdDTPA-BMA encapsulated within DSPC/DPPC/DPPG liposomes DSPC/DPPC/DPPG (weight ratio; 43/52/5) liposomes were prepared by the thin film hydration method. The phospholipids (500 mg) were dissolved in a chloroform/methanol mixture and the organic solution was evaporated to dryness under reduced pressure. Liposomes were formed by hydrating the lipid film with a preheated (63"C) aqueous solution (pH 1 7) of 250 mM GdDTPA- BMA (10 ml) . The liposomes were subjected to 3 freeze- thaw cycles and allowed to swell for one and a half - 4 9 - hours at 64 C. The liposome dispersion was extruded at 65 C through polycarbonate filters of various pore diameters. The liposome size (z-average) was 145 nm. Untrapped metal chelate was removed by dialysis against lsoosmotic and isoprotic glucose solution. Table 8 shows the temperature sensitivity of the in vi tro r (0.235T) m both glucose 5% solution and human serum for liposome encapsulated GdDTPA-BMA. Table 8 Temperature r glucose 5% r m serum ( C) (s mM " ') (s ' -inM -1 ) 35 0.12 0.14 40 0.22 0.25 42 0.29 0.44 44 0.88 1.91 46 4.47 4.51 48 4.40 4.51 50 4.40 4.35 Example 5 GdDTPA-BMA encapsulated within DPPC/DPPG liposomes DPPC/DPPG (weight ratio; 95/5) liposomes were prepared by the thin film hydration method. The phospholipids (500 mg) were dissolved in a chloroform/methanol mixture and the organic solution was evaporated to dryness under reduced pressure. Liposomes were formed by hydrating the lipid film with a preheated (52 U C) aqueous solution (pH 1 7) of 250 mM GdDTPA- BMA (10 ml) . The liposomes were subjected to 3 freeze- thaw cycles and allowed to swell for one and a half hours at 55°C. The liposome dispersion was extruded at 62 'C through polycarbonate filters of various pore diameters. The liposome size (z-average) after extrusion was 148 nm. Untrapped metal chelate was removed by dialysis against isoosmotic and isoprotic glucose 50 sol ut ion . Table 9 shows the temperature sensitivity of the in vi tro r (0.235 T) in both glucose 5% solution and human serum for liposome encapsulated GdDTPA-BMA. Table 9 Temperature r glucose 5% r in serum rc) (s^mM " ') (s "' πι " ') 35 0.331 0.389 38 0.753 0.810 39 1.47 1.20 40 3.75 3.31 41 4.88 5.05 42 4.80 4.99 44 4.80 4.78 48 4.77 4.88 Example 6 "Double transition" with a mixture of DSPC/DPPC/DPPG and DPPC/DPPG liposomes, containing both GdDTPA-BMA 1.5 ml liposomes from Example 4 were mixed with 1.5 ml DPPC/DPPG liposomes prepared as Example 5. The mixture was diluted to 40 ml with glucose 5% solution. Table 10 shows the temperature sensitivity of the in vi tro Rj (0.235 T) in glucose 5% solution for the liposome mixture. 5 1 Table 10 Temperature R in glucose 5% CO (s- ) 35 2.46 38 2.61 39 2.83 40 3.87 41 7.11 42 7.17 44 10.9 46 14.0 48 14.0 - 52 - Example 7 Perfluorobutane bubbles stabilised by 5mg/ml DSPC/DPPC/DPPG DSPC/DPPC/DPPG (weight ratio; 28.5/66.5/5) perfluorobutane gas bubbles were prepared by the thin film hydration method. The phospholipids (500 mg) were dissolved m a chloroform/methanol mixture and the organic solution was evaporated to dryness under reduced pressure. The lipid film was hydrated for 1 hour at 60 C after addition of 100 ml 1.5 % propylene glycol water. The final dispersion contained 5 mg lipids/ml . Five 2 ml vials were filled with 1 ml of the dispersion. The headspace was flushed with perfluorobutane gas. The vials were shaken on a CapMixer for 45 seconds and left on a roller table over night. The content of the five vials were collected and centrifuged for 5 minutes at 2000 rpm. The mfranatant was removed and replaced by the same volume water. The microbubbles were reconstituted by gentle handshaking after flushing the headspace with perfluorobutane gas. The washing procedure was repeated three times. The sample of perfluorobutane bubbles was characterized using Coulter Multisizer II fitted with an aperture of 50 μm and Nycomed m-house equipment for measuring acoustic attenuation. The dispersion showed a size distribution of volume median diameter of about 3 μm. The bubbles showed a nice attenuation spectrum in the range 3.5-8.0 MHz and were tested for pressure stability at an over-pressure of 150 mm Hg m the temperature range 22-47°C using the acoustic technique. The acoustic measurements showed that the gas bubbles disrupted at an over-pressure of 150 mm Hg at 47°C, whereas they remained stable at 40°C. This indicates that the gas microbubbles can be used m ultrasound imaging for m vivo mapping of physiological pressure. - 53 - Example 8 Imaging studies lr rats with GdDTPA-BMA encapsulated within DPPC/DPPG liposomes a) Intramuscular injection in the left thigh Liposomes were injected intramuscularly at a dosage of 0.02 mmol/kg Tne left thigh muscle was heated with focused ultrasounα whereas the right thigh muscle served as a control . Figures 4-5 show axial T -w SE images of the thigh before and after liposome injection, respectively. Figures 6-8 are T -w SE images after 2, 5, and 9 minutes of heating, respectively. At that timepomt, heating was terminated, the rat was removed from the MRI scanner and the temperature of the muscle was measured to be 47°C. Figure 9 represents the final image 15 minutes after termination of heating. For comparative purposes, the syringe containing the liposomal dispersion (identical to that injected) was included . The results indicate that the signal intensity of the left thigh muscle increases substantially after heating, as compared to the right thigh muscle and syringe . b) Intravenous injection Liposomes were injected intravenously into a rat (upper position) at a dosage of 0.10 mmol/kg. The rat m the lower position served as control (e.g. no injection nor heating) . Figure 10 is the axial T -w SE image of the liver 7 minutes after liposome injection. At 15 minutes post injection , the liver was heated by focused ultrasound (Figure 11) . Figures 12-13 are T -w SE images 16 and 21 minutes after initiation of heating, respectively. 54 After termination of heating, the measured temperature m the liver was 51 ϋ C. The results indicate that the liver signal intensity increases substantially after heating as compared to the control liver Example 9 Preparation of pH-sensitive paramagnetic liposomes Liposomes composed of DPPE/PA (4:1 mol/mol) containing GdDTPA-BMA were prepared by the thin film hydration method. The total lipid concentration was 25 mg/ml. Briefly, a chloroform/methanol (10:1) solution of the lipids was rotary evaporated to dryness and the resulting film was further dried under vacuum over night. The lipids were hydrated with 250 mM GdDTPA-BMA m 0.05 M Tris-HCl buffer (pH = 8.4) at 75 °C. The liposomes were subjected to 3 freeze-thaw cycles m MeOH/CO,(s) . The liposomes were sized down by sequential extrusion (Lipex Extruder"', Lipex Biomembranes Inc., Vancouver, Canada) through polycarbonate filters with various pore diameters . Untrapped metal chelate was removed by dialysis against isoosmotic glucose solution (pH=8.4) . Physicochemical properties The mean hydrodynamic diameter of the liposomes was measured to 165 nm by photon correlation spectroscopy (ZetaSizer IV, Malvern Instruments Ltd., Malvern, England) . The in vi tro T 1 -relaxation times of the paramagnetic liposomes were measured (0.235 T, Mmispec PC-llOb, Bruker GmbH, Rhemstetten, Germany) m different isoosmotic buffer solutions (0.05 M citrate- phosphate buffer and 0.05 M Tris-HCl buffer). The investigated pH range was 4-8.5 The buffered liposome dispersions were incubated at 37°C for 15 minutes. Table 11 shows the pH sensitivity of m vi tro rj- relaxivity for liposome encapsulated GdDTPA-BMA. 55 Table 11 pH dependency of the r (37 C, 0.235 T) for liposomal GdDTPA-BMA pH r (s " mM "1 ) 3.91 1.32 4.30 1.26 4.70 1.31 5.15 1.17 5.59 1.10 5.95 1.03 6.40 1.00 6.71 0.50 7.33 0.32 7.69 0.29 8.02 0.28 8.34 0.29 8.54 0.31 Example 10 DyDTPA-BMA encapsulated within DPPC/DPPG liposomes DPPC/DPPG (weight ratio; 95/5) liposomes were prepared by the thin film hydration method. The phospholipids (500mg) were dissolved in a chloroform/methanol mixture and the organic solution was evaporated to dryness under reduced pressure . Liposomes were formed by hydrating the lipid film at 50°C with an aqueous solution (pH 2 7) of 250 mM DyDTPA-BMA (sprodiamide, Nycomed Imaging AS, Oslo, Norway) (10ml) . The liposomes were subjected to 3 freeze-thaw cycles and allowed to swell for one hour at 59°C. The liposome dispersion was extruded at 65C through polycarbonate filters of various pore diameters. The liposome size (z-average) after extrusion was 153 nm. Untrapped DyDTPA-BMA was removed by dialysis against isoosmotic and isoprotic glucose solution. The temperature sensitivity of the MR contrast effect may be investigated. - 56 - Example 11 GdDTPA-dextran encapsulated withm DPPC/DPPG liposomes DPPC/DPPG (weight ratio; 95/5) liposomes were prepared by the thin film hydration method. The phospholipids (500 mg) were dissolved m a chloroform/methanol mixture and the organic solution was evaporated to dryness under reduced pressure. The liposomes were formed by hydrating the lipid film at 48 C with an aqueous solution of 50 mM GdDTPA-dextran (MW 156 kD) , whose synthesis is described m: P Rongved et al . , Carbohydr . Res . , 287 (1996) 77 - 89 . The liposome dispersion was sonicated at 46 C using a sonicator tip. The liposome size (z-average) after sonication was 70 nm. Untrapped GdDTPA-dextran is removed by gel filtration or dialysis against isoosmotic and isoprotic glucose solution. The temperature sensitivity of the MR contrast effect may be investigated. Example 12 GdDTPA-BMA encapsulated within dibehenoyl-PC liposomes Dibehenoyl-PC (22:0) (Table 1) liposomes may be prepared by the thin film hydration method. The phospholipids (500 mg) are dissolved m a chloroform/methanol mixture and the organic solution is evaporated to dryness under reduced pressure. Liposomes are formed by hydrating the lipid film at 80°C with an aqueous solution (pH 1 7) of 250 mM GdDTPA-BMA (10 ml) . The liposomes are subjected to 3 freeze-thaw cycles and allowed to swell for one and half -hours at 80°C. The liposome dispersion is extruded at 80°C through polycarbonate filters of various pore diameters. Untrapped GdDTPA-BMA is removed by gel filtration or dialysis against isoosmotic and isoprotic glucose solution. The temperature sensitivity of the MR contrast effect may be investigated. - 57 - Example 13 Superparamagnetic iron oxides (SPIOs) encapsulated within HPC/HPS liposomes HPC/HPS (weight ratio, 90/10) liposomes were prepared by a modified thin film hydration method. Liposomes were formed by adding a homogeneous mixture of phospholipids (700 mg) to 10 ml of a pre-heated (55 C) aqueous dispersion of PEGylated SPIOs (6.10 mg iron/ml) . The liposomes were allowed to swell for 30 minutes at 65 C The liposome dispersion was extruded at 66 C through polycarbonate filters of various pore diameters. Untrapped SPIOs are removed by gel filtration or dialysis. The temperature sensitivity of the MR contrast effect may be investigated. Example 14 Ultrasmall superparamagnetic iron oxides (USPIOs) encapsulated within HPC/HPS liposomes HPC/HPS (weight ratio; 90/10) liposomes were prepared by a modified thin film hydration method. Liposomes were formed by adding a homogeneous mixture of phospholipids (700 mg) to 10 ml of a pre-heated (70 U C) aqueous dispersion of USPIOs (3.63 mg iron/ml) . The liposomes were allowed to swell for 90 minutes at 70°C. The liposome dispersion was extruded at 70°C through polycarbonate filters of various pore diameters. Untrapped USPIOs are removed by gel filtration or dialysis. The temperature sensitivity of the MR contrast effect may be investigated. Example 15 Superparamagnetic iron oxides (SPIOs) or ultrasmall - SPIOs encapsulated within pH-sensitive liposomes SPIOs or USPIOs encapsulated within pH-sensitive liposomes may be prepared m a manner analogous to that used m Example 9. Untrapped superparamagnetic material is removed by gel filtration or dialysis. The pH- sensitivity of the MR contrast effect may be investigated . Example 16 GdDTPA-BMA encapsulated within DSPC/DMPG/cholesteroI liposomes DSPC/DMPG/cholesterol liposomes (molar ratio; 49:5:20) were prepared by a modified thm film hydration method. Liposomes were formed by adding a freeze-dπed mixture of phospholipids (60 g) to a pre-heated (59 C) aqueous solution (pH 2 6.3) of 250 mM GdDTPA-BMA/300 mM sucrose/lOmM phosphate (300 ml) . The liposomes were allowed to swell for 30 minutes at 59°C. The liposome dispersion was homogenized and extruded at high pressure through polycarbonate filters with a pore size of 400 nm. Untrapped GdDTPA-BMA was removed by ultraflltration with a 300 mM sucrose/10 mM phosphate solution. The liposome size (z-average) after ultraflltration was 110 nm. Liposomes were also lyophilized (2ml per vial) and reconstituted by addition of 2 ml of deionized water. The liposome size (z-average) after reconstitution was 119 nm. Table 12 summarizes the temperature sensitivity of the in vi tro R, (0.235 T) for liposome encapsulated GdDTPA- BMA a 300 mM sucrose/10 mM phosphate solution. The influence of lyophilization on the R, -temperature sensitivity of the reconstituted liposomes is also shown in Table 12. 59 Table 12 T Relaxation Time (ms) 35 C 40°C 55°C Before 930 750 350 lyophilisation After 670 590 340 lyophilisation Example 17 Commercially available Gd compounds/Gd compounds m development phase encapsulated within temperature- or pH-sensitive liposomes Liposomes containing the following contrast agents: GdBOPTA (Bracco spa, Italy) , GdDTPA (Sheπng AG, Berlin) , GdDOTA (Guerbet SA, Aulnay-sous-Bois) , Gadomer (Shenng AG, Berlin) MS-325 and protein bound MS-325 (Epix Medical Inc, USA) may be prepared m a manner analogous to that used m Examples 1-5, 9 and 12. Untrapped Gd compound is removed by gel filtration or dialysis. The temperature sensitivity of the MR contrast effect may be investigated. Example 18 Temperature sensitivity of m vi tro r z m blood for liposome encapsulated GdDTPA-BMA DPPC/DPPG/DPPE-PEG-2000 and DPPC/DPPG liposomes containing GdDTPA-BMA were prepared in a manner analogous to that used in Examples 3 and 5, respectively. Table 13 summarizes the temperature evolution of the m vi tro r (0.235 T) m rat blood for both liposome formulations. 60 Table 13 Temperature r (s^mM "1 ) r 1 (s^mM "1 ) (°C) DPPC/DPPG DPPC/DPPG/DPPE- 120 nm PEG 121 nm 35 0.260 0.244 37 0.479 0.391 39 0.659 0.588 40 1.18 0.823 41 2.45 1.26 42 4.06 2.87 43 5.18 3.65 44 4.57 4.06 Example 19 Pilot biodistribution and relaxometric studies of liposomal GdDTPA-BMA m male rats a) Intramuscular injection DPPC/DPPC liposomes containing GdDTPA-BMA (prepared in Example 18) were injected intramuscularly (im) into Sprague Dawley rats at a dosage of 20 :mol/kg. Table 14 shows the T, relaxation times (37°C, 0.235 T) of excised tissues and blood one and three hours after im injection of DPPC/DPPG liposomes (n= 2x3) . Table 15 shows the temperature response of the T, m muscle. All results are given as mean values. 61 Table 14 Time post Inj ection T x relaxation time (min) (ms) 0 500 833 248 60 451 950 249 180 440 833 243 Table 15 Time post Muscle T j Inj ection (ms) (min) 0 500 340 60 451 341 180 440 383 Despite large interindividual variations, the results show the temperature dependence of the muscle T j after im administration of liposome encapsulated GdDTPA- BMA. b) Intravenous injection DPPC/DPPG/DPPE-PEG-2000 and DPPC/DPPG liposomes containing GdDTPA-BMA (prepared in Example 18) were injected intravenously (iv) into Sprague Dawley rats at a dosage of 100 :mol/kg. Tables 16 and 17 show the T relaxation times (37"C, - 62 - 0 235 T) of excised tissues and blood, 5 minutes (n=3) , one (n=2) and three (n=3) hours after iv injection of DPPC/DPPG and DPPC/DPPG/DPPE-PEG-2000 liposomes, respectively. Also shown, is the Gd uptake m tissue, expressed as the percentage tissue uptake of the administered Gd dosage. Tables 18 and 19 summarize the temperature response of the blood T after iv injection of DPPC/DPPG and DPPC/DPPG/DPPE-PEG-2000 liposomes, respectively. A more detailed investigation of the temperature response was performed m blood withdrawn one hour after iv administration (n=3) of DPPC/DPPG liposomes, as shown m Table 20. All results are given as mean values . Table 16 Time post T relaxation time (ms) injection Tissue uptake (% of adm. Gd dosage) (mm) Liver Blood Spleen Lungs 0 248 833 510 613 5 212 533 357 547 11.6 60.0 1.9 0.88 60 223 589 315 520 13.7 25.9 4.3 0.48 180 227 823 353 557 7.9 1.3 2.0 0.06 63 Table 17 Time post T relaxation time (ms) inj ection Tissue uptake (% Df adm. Gd dosage) (min) Liver Blood Spleen Lungs 0 248 833 510 613 5 224 540 417 580 5.7 64.3 1.4 0.85 180 202 500 298 563 8.8 27.7 6.5 0.56 Table 18 Time post Blood Tj (ms) Injection (min) 37°C 43°C 0 833 880 5 533 151 60 589 273 180 823 797 6< * Table 19 Time post Blood T (ms) Inj ection (mm) 37°C 43°C 0 833 880 60 540 135 180 500 244 Table 20 Blood T (ms) 37°C 40°C 41°C 43°C 520 247 232 210 The results show the potential of both non-PEGylated and, especially, PEGylated liposomal GdDTPA-BMA as blood pool agents. The T -temperature sensitivity of the liposomes was also demonstrated blood. Example 20 In Vi tro Imaging Studies with GdDTPA-BMA encapsulated within DSPC/DPPC/DPPG liposomes DSPC/DPPC/DPPG liposomes containing GdDTPA-BMA were prepared analogously to Example 2. The liposome size (z-average) was 129 nm. MR imaging was performed at 2.0 T (Bruker Medspec) on a concentric spherical phantom m which the inner chamber contained liposomal GdDTPA-BMA diluted with an isotonic medium composed of glucose and 6.25% polyvmylpyrrolidone (cone. 0.8 mM Gd) , whilst the outer compartment was filled with saline. Microwave heating was performed at 434 MHz with a linear radio - 65 - frequency antenna placed in the outer chamber The microwave irradiation was applied simultaneously with the image acquisition. Blocks consisting of 10 diffusion-weighted spin-echo single shot EPI (DW-SE-EPI) images (b-factor from 3 to 864 s/mm ) , a set of SE-EPI images with inversion-recovery preparation (IR-SE-EPI) and gradient echo T -weighted (TTW-GE) images were repeated until the temperature of the liposome sample reached 48 C (m appr 110 mm) . T W-GE images were acquired with TE/TR/flip: 5ms/30ms/50 . T -maps were calculated from the set of 13 IR-SE-EPI images, measured with inversion times varying from 14.4 ms to 16 s. Plots of l/T (R ) versus temperature were generated from a fixed region-of -interest within the phantom. The sample temperature was measured by a thermocouple immediately after acquisition of each block. The temperature distribution within the imaged slice was evaluated from ADC-maps . The temperature evolution of the measured R λ for liposomal GdDTPA-BMA is summarized Figure 14. A linear correlation was obtained between R and temperature m the "transition region" 40.4-43.7°C (regression coefficient of 0.995) . Figure 15 shows selected Tj-W GE images of the phantom (a) before heating, (b) during heating; signal intensity distribution observed within liposome sample, and (c) after heating; homogeneous signal intensity distribution. Figure 16 shows the corresponding Tj-maps at the same time points as for Figure 15. By use of the linear correlation between R x and temperature, a corresponding temperature map could be derived from the Tj-map at timepo t (b) , as seen on Figure 17. The temperature map demonstrates the thermosensitivity of liposomal GdDTPA-BMA. (NB The temperature scale is only valid for the inner chamber containing liposomes) . - 66 Example 21 In vitro MR imaging studies with GdDTPA-BMA encapsulated within DPPC/DPPG liposomes - Determination of Gd concentration. A static in vi tro phantom, composed of twelve glass vials (10 mm dia.) placed m a rectangular plastic container, was used for this study. The plastic container was filled with a viscous isotonic medium composed of glucose/25% (w/w) polyvmyl -pyrrolidone (PVP) and doped with GdDTPA-BMA to give a Tj of about 430 ms at 1.5 T. Three of the vials contained a marker solution with a known T value (about 630 ms) . The remaining nine vials were filled with DPPC/DPPG-based GdDTPA-BMA liposomes (prepared m Example 18) dispersed varying amounts of isotonic 10% PVP/glucose solution. The Gd concentration [Gd] m the liposome samples ranged from 0 to 5.2 mM Gd as determined by inductively coupled plasma atomic emission spectrophotometry . The phantom was imaged at room temperature m a quadrature knee coil at 1.5 T on a Philips NT system. The following imaging sequences were used: 1. T T -FFE (spoiled gradient echo) TR/TE/flip: 15ms/2ms/30°. 2. TMIX (quantitative Tj/T sequence) 3. Dual TE FFE (T_* mapping) (TE1/TE2 : 4ms/50 ms) All three sequences were repeated after heating of the phantom, the latter achieved by placing the phantom m a warm (>60°C) water bath. The temporal effect of heating was not investigated, only the end-effect (i.e T >> T ) . A linear correlation was obtained between [Gd] and matrix corrected R (ΔR)) prior to heating (measured from TMIX sequence), with a regression coefficient of 0.996. The calculated liposomal r was 0.11 mM ^ s "1 . - 67 - Analogously, a liposomal r of 0.55 mM " s was determined from the R vs [Gd] curve (regression coefficient = 0.997) ; the r /r ratio being equal to 5. After liposome heating, the r and r were 3.23 and 3.75, respectively, giving an r /r ratio of 1.16. Figure 18 shows, prior to heating, a linear correlation beween [Gd] and the ratio of the signal intensities of liposome sample and PVP gel (SI ,. ,,/SI ,„-, ) using the T : -FFE sequence. Figure 19 shows the plot of the ) R 1 / ) R7' " ratio vs the [Gd] / [Gd'" rt ] ratio; here [Gd :;a: ] = 5.2 mM. The results demonstrated that prior to heating, the ) R j ratio accurately reflected the [Gd] ratio. Similar results were also obtained when the )R ratio was employed. The findings suggest that the T : - (and T -) effect of liposome encapsulated GdDTPA-BMA prior to heating is significant enough to enable a relative assessment of liposomal Gd concentration. Example 22 In vi tro MR imaging studies with GdDTPA-BMA encapsulated within DPPE/PA liposomes DPPE/PA liposomes containing GdDTPA-BMA were prepared analogously to Example 9. The mean hydrodynamic diameter of the liposomes was measured to 158 nm by photon correlation spectroscopy (Malvern PS/MW 4700, Malvern Instruments Ltd., Malvern, England). An in vi tro phantom, composed of thirteen glass vials (11 mm diameter) placed in a circular glass reactor, was used for this study. The glass reactor was filled with an agar gel (2 % w/v) doped with GdDTPA-BMA to give a Tj of about 900 ms at 1.5 T. The glass vials were filled with isoosmotic buffer solutions with pHs ranging from 4.8 to 8.2. The phantom was constantly held at a temperature of 37°C by circulating heated water through the shell of the reactor with a circulating water pump. Liposomes were added successively to each vial with a - 68 - time interval of 1 minute. The imaging was started 25 minutes after addition of liposomes to the first vial. The phantom was imaged at 1.5 T on a Philips NT system. The following imaging parameters were used: sequence: MIX-TSE; TR (ms): 800.0; TE (ms): 12.5; TI (ms): 500.0; flip (deg) : 90; slice thickness (mm) : 7.0; FoV (freq*phase, mm): 230.0*230.0. The scan cycles were repeated every minute for 20 minutes. Figure 20 shows the phantom 25 minutes after addition of liposomes to the first vial. The signal intensity increases with decreasing pH . Example 23 Particles from polymer made from ethylidene bis (16- hydroxyhexadecanoate) and adipoyl chloride Air filled particles of the polymer ethylidene bis (16-hydroxyhexadecanoate) and adipoyl chloride were made as described m Example 3f of WO 96/07434. Change of gas The dry powder was exposed to 20 mmHg vacuum for ca . 15 minutes, followed by inlet of perfluorobutane gas. The powder of polymer particles containing perfluorobutane gas were then redispersed to 10 mg/ml dry material in MilliQ water by shaking on a laboratory shaker for 12-16 hours. Examination by light microscopy indicated formation of a particle dispersion with irregular shaped particles. The particles floated readily, as expected for gas-contammg particles. Heating of the polymer particles 10 ml of the polymer dispersion was heated on a water bath to 65 °C in one minute while using magnet stirring. At this temperature the polymer melted. Microscopic evaluation indicated that the irregular particles changed to spherical, smooth particles, - 69 - indicating that the polymer capsule melted. Characterization The acoustic effect of the suspension prepared above was obtained by measuring the ultrasonic transmission through a dispersion in an aqueous carrier liquid, using a 3.5 MHz broadband transducer m a pulse- reflection technique. The aqueous carrier liquid was used as reference. Table 21 contains the observed acoustic attenuation compared to non-heated particle dispersion at the same concentrations, indicating that heat treatment removes most of the acoustic attenuation. The gas content was measured by density measurements before and after destruction of the microcapsules using high-energetic ultrasound. The results show that the gas content is conserved. The results show that by melting the polymer capsules, the gas filled microcapsules become almost invisible to ultrasound, probably due to the stiff polymer shell now surrounding the gas phase . Table 21. Characteristics of perfluorobutane containing polymer particles treated by heating the dispersions to 65°C. Description Gas content Acoustic attenuation [% v/v (rel. [dB/cm] sample vol . ) ] Reference 1.398 6.42 65°C, 1 mm 1.227 0.63 Example 24 The particles from example 23 above are studied by acoustic characterisation m vitro by measuring the ultrasonic transmission through a dispersion in an aqueous carrier liquid, using a 3.5 MHz broadband - 70 - transducer m a pulse-reflection technique. The aqueous carrier liquid is used as reference. The acoustic characterisation is started at room temperature where the acoustic attenuation is low as shown m Table 21 above. The temperature is raised and acoustic characterisations are done at different temperature intervals. When the temperature passes 48.6°C, the melting point of the polymer (see example 23 above) , the acoustic attenuation increases sharply, indicating a temperature sensitive contrast agent. A similar experiment could be done using a polymer with melting point around 37-40 G C, and hence closer to body temperature . Example 25 A spatula edge of micronised kaolin is added to 2 ml perfluorodimethylcyclobutane (b.p. 45°C) and dispersed using 0.2 ml Fluorad™ FC-171 surfactant. A milky white dispersion is obtained by vigorously stirring . 1 ml of a dispersion of 1 , 2 -distearoyl -phosphatidyl glycerol and (0,5 mg/ml) and distearoylphosphatidyl- choline (4,5 mg/ml) purified water is placed in a 2 ml vial to which is added 100 μl of the kaolin in perfluorodimethylcyclobutane dispersion described above. The vial is closed and then shaken for 75 seconds using an Espe CapMix ® to yield a kaolin in perfluorodimethylcyclobutane in water emulsion. An acoustic apparatus is mounted in which the acoustic effect of the suspension prepared above can be obtained by measuring the ultrasonic transmission through a dispersion in an aqueous carrier liquid, using a 3.5 MHz broadband transducer in a pulse-reflection technique. The aqueous carrier liquid can be used as reference. The sample is injected in a termostatted cell, where an overpressure or an underpressure can be applied by a pump. The emulsion is transformed to the acoustic cell and diluted with 50 ml water, keeping the temperature constant at 37°C. The first measurement is done at atmospheric pressure showing weak acoustic attenuation due to the presence of liquid emulsion droplets and no gas bubbles m the cell. The pressure is then gradually reduced at intervals, and the acoustic measurement is done at each interval. When the pressure reach 580 mmHg (i.e. 180 mmHg below atmospheric pressure), the acoustic attenuation increases sharply and significantly, demonstrating that the microdroplets now boil and turn to acoustic effective microbubbles. This experiment demonstrate how an emulsion with a disperse phase of boiling point slightly above body temperature can be used to map underpressure m vivo, for instance the underpressure which will occur below an embolisation of a blood vessel. Example 26 GdDTPA-BMA encapsulated withm Mg sensitive liposomes Beef -heart cardiolipm - cesium salt, dipalmitoylphosphatidylcholme (DPPC) and dipalmitoylphosphatidylglycerol - potassium salt (DPPG) are added to a round bottom flask m 40/55/5 mol ratio (totally 500 mg) and dissolved using chloroform. The chloroform is removed by evaporation under reduced pressure using a rotavapor. Liposomes are formed by hydrating the lipid film with a pre-heated (52°C) aqueous solution of 250 mM GdDTPA-BMA (10 ml) . The liposomes are subjected to 3 freeze-thaw cycles and allowed to swell for one and half -hour at 55 υ C. The liposome dispersion is extruded at 62 C through polycarbonate filters of various pore diameters. Untrapped GdDTPA-BMA is removed by dialysis against isoosmotic and isoprotic glucose solution. - 72 - The liposome dispersion is diluted ten times with water and transformed to an NMR tube. The r relaxivity at 0.235 Tesla is measured using a Mmispec NMR instrument at 37"C. The rl relaxivitiy is low. The sample is then titrated by a 0,6 M MgCl solution. When the Mg to caridolipin ratio increases, the lamellar to H phase transition is induced as described m F. Reiss- Husson, J. Mol . Biol . , 25, 363, (1967). The break-down of the liposomal structure leads to contact between the GdDTPA-BMA and water, inducing a significant increase in the rl relaxtivitiy . This experiment will demonstrate a Mg * sensitive MRI contrast agent. Example 27 GdDTPA-BMA encapsulated within Ca" sensitive liposomes The experiment as described in Example 26 above is repeated, but the MgCl solution is replaced by a CaCl ^ solution. Observations of a similar increase in relaxivity at a sufficiently high Ca ~J concentration demonstrate a Ca sensitive MRI contrast agent. Example 28 Perfluorobutane microbubbles stabilised by Phosphatidylserine as example of a Ca 2"1 sensitive ultrasound contrast agent Preparation Hydrogenated phosphatidylserine (5 mg/ml in a 1% w/w solution of propylene glycol in purified water) and perfluorobutane gas were homogenised by an Ystral ® rotor-stator at 7800 rpm and ca . 40°C to yield a creamy- white microbubble dispersion. The dispersion was fractionated to substantially remove undersized microbubbles (<2 μm) and the volume of the dispersion was adjusted to the desired microbubble concentration by adding aqueous sucrose to give a sucrose concentration - 73 - of 92 mg/ml 2 ml portions of the resulting dispersion were filled into 10 ml flat-bottomed vials specially designed for lyophilisation, and the contents were lyophilised to give a white porous cake. The lyophilisation chamber was then filled with perfluorobutane and the vials were sealed. Prior to use, water was added to a vial and the contents were gently hand-shaken for several seconds to give a perfluorobutane microbubble dispersion. Mi croscopi c inves tiga tion One drop of the microbubble dispersion was placed on an object glass for microscopy investigation. The sample was covered with a cover glass and placed under a microscope Droplets of a 50 mg/ml calcium chloride solution m water were added to the edge of the cover glass so that the solution penetrated into the microbubble dispersion. The behaviour of the microbubble dispersion as the calcium chloride solution front moved was recorded on videotape. Microbubble aggregates with larger dimensions than the initial microbubbles were observed to form, demonstrating that microbubbles with potential to have different ultrasound properties were generated. Example 29 TcDTPA encapsulated within DPPC/DPPG liposomes TcDTPA is prepared from sodium pertechnetate and a commercial kit containing SnCl and DTPA. TcDTPA is encapsulated m liposomes similar to Example 10 above. The product is a temperature sensitive contrast agent for sc tigraphic studies. - 74 - Example 30 Gadolinium DTPA labelled starch microspheres Gadolinium DTPA starch particles were prepared according to P. Rongved et al . m Carbohydrate Research 214 (1991) 325-330 substrate 9 to 12. The particles were suspended m 0.9 % NaCl solution before administration. The product can be used to diagnose diseases related to abnormal enzyme activity ( -amylase and esterase) ; for example. Example 31 lodixanol -containing liposomes A diagnostic composition comprising: lodixanol (total amount) 400 mg/ml Iodine encapsulated 80 mg/ml Sorbitol 20 mg/ml Trometamol (TRIS) 0.097 mg/ml EDTANa,Ca 0.1 mg/ml Hydrogenated phosphatidylcholine 51.2 mg/ml Hydrogenated phosphatidylserine 5.1 mg/ml Water for injection ad 1 ml (approx 0.9 ml) was prepared by dissolving the phospholipid m choloroform/methanol/water (4:1:0.025, volume) and evaporating the solvent (rotary evaporation) . An isotonic solution of lodixanol and sorbitol was made and heated to 60-70°C and this temperature was maintained during the remainder of the process. The phospholipid mixture was added with stirring, and the liposomes were formed. To control the size of the liposomes the preparation was homogenized (Rotor/Stator homogenizer) . The liposomes were then extruded through 7 polycarbonate filters placed in series (pore diameter 1 μm) . The - 75 - product was diluted with an isotonic solution of lodixanol and sorbitol, and trometamol adnEDTA were added. The product was filled into glass vials and autoclaved (121 U C, 15 minutes) . Tc = 49 "C. The product can be used to monitor temperature during hypertermia treatment with focused ultrasound. Example 32 Gas containing microbubbles of DPPC/PPG/DPPE-PEG "doped' with vector with affinity for angiogenesis Various products can be prepared using the technology described m WO 98/18500. The products can be used as tumor specific markers for hyperthermia treatment .

Claims: Cl a ims 1. A method of imaging of an animate human or non- human animal body, which method comprises: administering parenterally to said body a particulate material comprising a matrix or membrane material and at least one contrast generating species, which matrix or membrane material is responsive to a pre-selected physiological parameter whereby to alter the contrast efficacy of said species m response to a change m the value of said parameter; generating image data of at least part of said body in which said species is present; and generating therefrom a signal indicative of the value or variation of said parameter m said part of said body. 2. A method as claimed m claim 1 wherein the physiological parameter is pH, temperature, pressure, carbon dioxide tension, enzyme activity, tissue electrical activity, tissue diffusion or ion concentration . 3. A method as claimed m claim 2 wherein the physiological parameter is pH, temperature or pressure. 4. A method as claimed m any one of claims 1 to 3 wherein the response of the matrix or membrane material to a change in the value of the pre-selected physiological parameter is a change m matrix or membrane permeability or chemical or physical breakdown of the matrix or membrane material . 5. A method as claimed m any one of claims 1 to 4 wherein the imaging technique is MRI, scintigraphy or ultrasound or X-ray imaging. - 77 - 6 A method of MRI as claimed in claim 5 wherein the contrast generating species is a paramagnetic and/or superparamagnetic compound and/or an iron oxide or a gadolinium or dysprosium compound. 7 A method of ultrasound imaging as claimed claim 5 wherein the contrast generating species is an encapsulated gas selected from air, a fluorohydrocarbon, sulphur hexafluoπde and a perfluorocarbon. 8. A method of ultrasound imaging as claimed claim 5 wherein the particulate material comprises a temperature, pressure or pH sensitive emulsion or suspension . 9. A method as claimed claim 1 wherein said particulate material is in combination with a targeting ligand for a cell or receptor of interest. 10. A method as claimed m claim 1 wherein the membrane material forms a vesicle. 11. A method as claimed claim 1 wherein the matrix or membrane material is selected from a phospholipid and a physiologically acceptable polymer. 12. A method as claimed m claim 10 or 11 wherein the membrane material forms a temperature or pH sensitive liposome . 13. A method as claimed m claim 12 wherein the liposome is stable at normal body temperature but exhibits increased water permeability or leakage at temperatures greater than normal body temperature . 14. A method as claimed m claim 1 wherein the contrast efficacy is altered by interaction between the contrast generating species and the environment the part of the animal body where the matrix or membrane material has responded to a change the value of the physiological parameter. 15. A method as claimed m any one of the preceding claims wherein the physiological parameter is temperature and wherein the change m the value of said parameter is related to cancer, cardiovascular disease or inflammation or results from the treatment of hyperthermia the animal body. 16. A method as claimed m any one of claims 1 to 14 wherein the physiological parameter is pH and wherein the change the value of said parameter is caused by cancer, cardiovascular disease, osteoporosis, inflammations or autoimmune diseases. 17. A method as claimed any one of claims 1 to 16 wherein m addition to the generation of a signal indicative of the value or variation of a pre-determmed physiological parameter m a part of the animal body m which the contrast generating species is present, an anatomical image of the same part of the animal body is generated . 18. A method as claimed in claim 17 wherein no contrast agent is used to generate the anatomical image. 19. A method as claimed m claim 17 wherein a contrast agent is used in the generation of the anatomical image. 20. A method as claimed m claim 19 wherein the same contrast agent is used to generate a signal relating to the pre-selected physiological parameter and the anatomical image. - 7 9 - 21 A contrast medium for imaging of a physiological parameter, said medium comprising a particulate material the particles whereof comprise a matrix or membrane material and at least one contrast generating species, said matrix or membrane material being responsive to said physiological parameter to cause the contrast efficacy of said contrast generating species to vary m response to said parameter. 22. The use of a contrast generating species for the manufacture of a particulate contrast medium for use m a method of diagnosis comprising generating a signal indicative of the value of said physiological parameter, the particles of said contrast medium comprising a matrix or membrane material and at least one contrast generating species, said matrix or membrane material being responsive to said physiological parameter to cause the contrast efficacy of said contrast generating species to vary response to said parameter. 23. A method of imaging of an animate human or non- human animal body, which method comprises: administering parenterally to said body at least one contrast generating species the contrast efficacy whereof is responsive to a change m value of a preselected physiological parameter; generating image data of at least part of said body m which said species is present; and generating therefrom a signal indicative of the value or variation of said parameter in said part of said body and also generating an anatomical image of the same part of the animal body.

Inventors: BJOERNERUD ATLE, FOSSHEIM SIGRID LISE, GOLMAN KLAES, KLAVENESS JO, RONGVED PAL, SKURTVEIT ROALD, BJOERNERUD, ATLE, FOSSHEIM, SIGRID, LISE, GOLMAN, KLAES, KLAVENESS, JO, RONGVED, PAL, SKURTVEIT, ROALD
Applicants: BJOERNERUD ATLE, COCKBAIN JULIAN, FOSSHEIM SIGRID LISE, GOLMAN KLAES, KLAVENESS JO, NYCOMED IMAGING AS, RONGVED PAL, SKURTVEIT ROALD, BJOERNERUD, ATLE, COCKBAIN, JULIAN, FOSSHEIM, SIGRID, LISE, GOLMAN, KLAES, KLAVENESS, JO, NYCOMED IMAGING A.S., RONGVED, PAL, SKURTVEIT, ROALD
Application year: 1999
Main classification: A61K9
IPC codes: A61B5, A61B8, A61K49