1. Field of the Invention
The invention concerns methods of determining tissue injury using non-invasive in vivo determination of intracellular and extracellular sodium and potassium ions by nuclear magnetic resonance procedures.
2. Description of Related Art
Proper therapy for numerous clinical conditions depends on early detection of metabolic abnormalities in a tissue. Perfused tissue and animal studies indicate that intracellular sodium may provide a sensitive and specific indication of the injury; however, measurement of intracellular sodium is neither simple nor quickly performed under currently available protocols. A simple, rapid and noninvasive method of detecting intracellular sodium in a target tissue has yet to be developed.
The sodium ion gradient across the cell membrane is critically important to many cell functions and is sensitive to disease; consequently, there is a continuing interest in methods which differentiate sodium in various tissue compartments. Although nuclear magnetic resonance (NMR) is a convenient, relatively sensitive, nondestructive method for detecting sodium in biological tissue, the usual one-pulse measurement suffers from the fact that .sup.23 Na or .sup.39 K resonances from various tissue compartments are isochronous and hence ion concentration gradients and ion fluxes cannot be monitored.
Likewise, potassium ion gradients, if disrupted, may adversely affect transport across the cell membrane. Transport processes are driven by ATP hydrolysis to generate electrochemical gradients across the membrane. In vivo differences between extra and intracellular potassium ion concentrations may possibly be an indicator of metabolic injury; however, as with sodium ion, NMR methods have not provided an effective means to measure and monitor potassium ion concentrations in the different compartments.
At least three NMR methods have been proposed to solve this problem: (i) methods based on relaxation time differences Lee, H. J., Labadie, C. & Springer, C. S. (1992) Abstr. 11th Mtg. SMRM, 2214 ; (ii) multiple quantum filters (MFQ's) Lyon, R. C., Pekar, J., Moonen, C. T. W. & McGlaughlin, A. L. (1991) Magn. Reson. Med. 18, 80-92 ; and (iii) the use of anionic paramagnetic shift reagents (SRs) Bansal, N., Germann, M. J., Lazar, I., Malloy, C. R. & Sherry, A. D. (1992) J. Magn. Reson. Imaging, 2, 385-391. Each approach has disadvantages, especially for in vivo applications. It is now clear that the methods based on relaxation time differences and MQF's do not accurately filter intra- versus extracellular signals Hutchison, R. B., Malhotra, D., Hendrick, R. E., Chan, L. & Shapiro, J. L. (1990) J. Biol. Chem 265, 15506-15510. In addition, the time required for data collection with these techniques limits their utility Lee, H. J., Labadie, C. & Springer, C. S. (1992) Abstr. 11th Mtg. SMRM, 2214. The primary disadvantage of paramagnetic SRs concerns possible acute toxicity Boulanger, Y., Fleser, A., Amarouche, R., Ammann, H., Bergeron, M. & Vinay, P. (1992) NMR Biomed. 5, 1-10. Since most SRs for biological cations are by necessity anionic and bind competitively with all biological cations, they could unknowingly compromise the physiology of an organ by disrupting normal Ca.sup.2+,Mg.sup.2+,Na.sup.+ or K.sup.+ ion gradients. Despite this disadvantage, SRs do allow simultaneous measurement of .sup.23 Na signals from multiple tissue compartments so that relative changes in Na.sup.+ ion concentrations can be detected in various compartments with excellent temporal resolution.
A number of different SRs have been successfully used to monitor intracellular sodium in isolated cells and perfused tissue Buster, D. C., Castro, M. M. C. A., Geraldes, C. F. G. C., Malloy, C. R., Sherry, A. D. & Siemers, T. C. (1990) Magn. Reson. Med. 15, 25-32 but only dysprosium(III) triethylenetetraminehexaacetate (DyTTHA.sup.2-) Blum, H., Osbakken, M. D. & Johnson, R. G. (1991) Magn. Reson. Med. 18, 348-357 and thulium(III) 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis (methylene phosphonate) (TmDOTP.sup.5-) Bansal, N., Germann, M. J., Lazar, I., Malloy, C. R. & Sherry, A. D. (1991) J. Magn. Reson. Imaging, 2, 385-391 have been used in vivo. Previously, TmDOTP.sup.5- aided .sup.23 Na chemical shift imaging has been used in combination with .sup.23 Na and .sup.1 H imaging to monitor Na.sup.+ in successive 1 mm slices in the rat brain in vivo. Like various relaxation agents used in MRI, the shift reagent (SR) does not cross the blood brain barrier Bansal, N., Germann, M. J., Lazar, I., Malloy, C. R. & Sherry, A. D. (1992) J. Magn. Reson. Imaging, 2, 385-391.
Major trauma frequently leads to multiple organ failure and death. Trauma centers throughout the country deal with serious injury arising from multiple fractures, ischemic injury or burn victims. Initial treatment is concerned with immediate control of overt damage such as bleeding, but must also be concerned with the cascade effects which may manifest several hours or even days after the initial trauma.
Damage to any of the major organs is a grave concern; however determination of liver damage is of particular interest because malfunction of this organ is considered to be a bellwether of multisystem failure. Unfortunately, many of the conventional methods of determining liver function do not necessarily reflect function of the organ but may be the result of remote physiological or physical damage.
Liver function is conventionally determined by measuring prothrombin times, selected enzyme activities such as SGOT, SGOT or bilirubin or albumin levels. Such tests do however require a blood sample to be drawn and time to run the tests. And there appears to be no particular parameter that is related to predicting liver function, i.e. whether or not the liver has itself been irreversibly damaged or whether abnormal enzyme levels are merely a manifestation of skeletal damage.