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Query: UMLS:C0022116 (ischemia)
 91,303 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Combined magnetic resonance imaging (MRI) and spectroscopy (MRS) allows unique experimental insights into the central nervous system (CNS) disorders. Clinical applications are forthcoming. In order to address the potential clinical uses of MRI/MRS, experimentally induced focal brain lesions were evaluated with this modality. Focal lesions more closely mirror clinical situations than do global insults, but have rarely been the focus of MRS studies. Fluid-percussion trauma in 48 rats, focal ischemia in 18 rats and in 16 mongrel dogs were produced, with various degrees of severity. A discrepancy between temporal evolution data of MRI and MRS was found: MRI always showed an increase in lesion extension over time while 31P and 1H MRS almost always showed improvement. The severity and evolution of these MRS findings was surprising, and differed from the results reported for global brain injuries. Besides possibly reflecting real improvement in the metabolic state, other explanations for the phenomena exist. Diffusion of inorganic phosphate out of the regional site of injury and its reincorporation for more prominent lactate build-up in regional injury are possible. Therefore the use of MRS to predict metabolic and clinical outcomes of regional brain injury requires methodologic caution, but its combination to MRI offers an unprecedented tool for studies of focal CNS pathology.
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PMID:Combined magnetic resonance imaging and spectroscopy in experimental regional injury of the brain. Ischemia and impact trauma. 298 Apr 91

In summary, then, the major strength of MRI in evaluating cerebral ischemia is in the sensitivity that this methodology provides for detection of the disease process. However, it must be realized that edema is a nonspecific event related to various insults affecting the brain. There is still an uncertain capability of MRI in separating acute hemorrhagic from acute ischemic events. The superior sensitivity of MRI should help in investigations aimed at evaluating various forms of intervention in acute ischemia. Because some of these acute changes are at the biochemical rather than morphologic level, proton MRI alone probably will be insufficient to explore numerous variables. For this reason, the potential offered by MRS in cerebral ischemia research and in clinical settings is important. Vascular imaging is relatively complex. Several techniques show promising results but at the present time have poor resolution in comparison to ultrasound and angiography. For the immediate future, they will remain investigational.
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PMID:Magnetic resonance imaging of cerebral ischemia and infarction. 307 44

Magnetic resonance spectroscopy is able to measure noninvasively a variety of important metabolites involved in cell energetics. These include phosphocreatine, ATP, inorganic phosphate, pH, and lactate. Anoxia, ischemia, and infarction produce rapid loss of high-energy phosphates and accumulation of hydrolysis products. Many animal studies have shown that MRS monitors metabolic changes in various models of human disease. The availability of large, high field magnets and the development of noninvasive localization techniques permits MRS to be performed on selected volumes within the body. It is now clear that MRS in humans will be immediately useful in several areas including studies of malignancy, ischemia, and infarction of various organs and metabolic disorders. It is expected that human MRS will be increasingly used for clinical investigation and eventually for medical diagnosis.
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PMID:NMR spectroscopy for clinical medicine. Animal models and clinical examples. 332 57

To investigate mechanisms of development in ischemic myocardial injury, intracellular pH and high energy phosphates in perfused guinea-pig hearts were monitored by 31P-MRS. Intracellular ATP content decreased to 1.2% and 26.4% of control during 60 minutes global ischemia, respectively with and without preischemic administration of isoproterenol. Intracellular pH declined to 6.48 and 6.03 respectively. Postischemic cardiac function was severely impaired by isoproterenol. ATP breakdown had little influence on intracellular pH in ischemic hearts. It was verified that inotropic agents can progress ischemic myocardial injury, and that contractile recovery is more correlated with the residual ATP level than intracellular pH.
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PMID:Determination of mechanisms of myocardial ischemic injury by 31P-MRS effect of catecholamine on ischemic hearts. 334 71

The ATP and creatine phosphate (PCr) contents in isolated guinea-pig hearts were determined by 31P-MRS measurement at 80.75 MHz using the Langendorff technique. Reperfusion of post-ischemic hearts with adenosine for 180 minutes increased ATP to 117.4% and decreased PCr to 59.8% of the preischemic value. Reperfusion without adenosine did not increase ATP and did not decrease PCr. The depressed cardiac function due to ischemia was remarkably improved in post-ischemic hearts by the increase in ATP due to adenosine. We found that the loss of ATP due to ischemia is not necessarily proportional to the extent of myocardial ischemic injury.
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PMID:31P-MRS study of bio-energy recovering phenomenon. 334 17

Perfused guinea-pig hearts, which were analyzed by 31P-MRS, were subjected to 30 and 60 minute ischemia and reperfused using two perfusates, one containing 200 microM inosine, and the other without inosine. After 4 hour reperfusion with inosine, ATP levels increased to 95.5% of preischemic value (30 minute ischemia) and 76.2% (60 minute ischemia). However, after 4 hour reperfusion without inosine, ATP levels increased only to 72.2% (30 minute ischemia) and to 48.2% (60 minute ischemia). In 60 minute ischemic hearts reperfused with inosine, left ventricular maximal positive dp/dt (LV dp/dt) was improved significantly to 82.4% after 6 hour reperfusion in contrast to hearts reperfused without inosine (43.1%). Administration of inosine was very useful for increasing myocardial gross energy product and improving cardiac performance.
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PMID:The effect of inosine on the post ischemic heart as bio-energy recovering factor in 31P-MRS. 335 62

Using 1H MRS continuous negative echo acquisition during steady-state frequency selective excitation (CASTLE) myocardial lactate accumulation was followed in a globally ischemic perfused rat heart model. 1H MRS CASTLE derived lactate determinations were verified biochemically and were measured during ischemia and reperfusion (both in the absence and in the presence of a known inhibitor of glycolysis). In addition, using the Bloch equations modified for the effect of diffusion in the presence of a magnetic field gradient the theoretical dependency of measurements made with CASTLE upon T1, T2 and the flip angle alpha were demonstrated. It was found that 1H MRS CASTLE allowed for rapid identification of the lactate -CH3 resonance in an isolated perfused heart with little shimming required, and excellent water and lipid suppression. Measurements of lactate using this technique reflected a true difference in myocardial lactate as evidenced by biochemical analysis and the expected changes in tissue lactate that accompanied reperfusion and ischemia in the presence of a glycolytic inhibitor. Theoretical calculation demonstrated that the dependency of the relative signal intensity obtained with 1H MRS CASTLE was a complex function of T1, T2, and alpha. These calculations also demonstrated the theoretical feasibility of applying 1H MRS CASTLE to localized spectroscopy using a surface coil.
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PMID:Very rapid lactate measurement in ischemic perfused hearts using 1H MRS continuous negative echo acquisition during steady-state frequency selective excitation. 338 23

We have proposed that tissue metabolic failure during hypoxia or ischemia is related to the microheterogeneous distribution of tissue oxygen and not to failure of the creatine kinase equilibrium. This theory is based on the concept that sharp oxygen gradients exist in rapidly metabolizing tissue and that shifts in these gradients can place specific cells at risk for metabolic death while relatively adjacent cells escape unharmed; cells that are unharmed meet the steady-state requirements (V less than Vmax), those at risk do not (V greater than Vmax). Though it would seem that confirmation of such a hypothesis would require metabolic delineation at a high resolution, we have shown how 31P MRS provides information supporting this hypothesis. This possible use of MR spectroscopy to define microheterogeneous events suggests further clinical possibilities for this instrument in defining the rate of cell loss and the response to therapeutic interventions.
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PMID:An approach to the problem of metabolic heterogeneity in brain: ischemia and reflow after ischemia. 343 6

Magnetic resonance spectroscopy can be used to characterize the bioenergetic state of the musculoskeletal system, and several marker compounds related to the tissue's biochemistry have been found to exist. Potential new techniques involving better spatial localization, spectral editing, and examination of nuclei other than phosphorus are in the developmental stage. Their development over the next few years will determine the extent to which MRS will become a universally used medical tool. However, the results with 31P alone guarantee a continued role in the study of muscular disease, peripheral vascular disease, and hypoxia and ischemia of the neonatal brain.
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PMID:Magnetic resonance spectroscopy of the musculoskeletal system. 345 10

To assess the applicability of phosphorus-31 magnetic resonance spectroscopy (31P-MRS) in the analysis of renal transplant viability and preservation techniques with respect to pre-transplant ischemia, we studied two rat groups. Twenty-five rat kidneys were subjected to various time increments of warm ischemia (Group A), and 31P-MRS was performed on each kidney at time intervals of up to 72 hours during simple hypothermic storage. We correlated findings of 31P-MRS with simultaneous findings of electron microscopic (EM) ultrastructural viability parameters (in Group A) and subsequent survival and renal function in 30 rats (Group B) subjected to similar amounts of variable ischemia. Intracellular phosphorus metabolite levels were nondestructively monitored by 31P-MRS via spectral peaks of NAD, sugar monophosphates (SP), and inorganic phosphate (Pi). We concluded: SP/Pi and NAD/Pi ratios decay in a time-dependent manner for both warm and cold ischemia, although this process is much slower during cold storage; EM viability parameters correlate with the development of acute tubular necrosis (irreversible damage) versus nonviability (gross cell death) on a qualitative basis only; and 31P-MRS enables a quantitative assessment of renal viability and ischemic renal damage and can predict the degree of acute tubular necrosis and post-ischemic renal function. 31P-MRS is potentially a noninvasive, nondestructive method of assessing viability during simple hypothermic storage of the rat kidney. Preliminary evidence shows that this MRS method can be applied to human kidney viability studies for clinical renal transplantation and urologic research concerning renal preservation.
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PMID:Assessment of renal viability by phosphorus-31 magnetic resonance spectroscopy. 351 65


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