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

The metabolic effects of adenosine on regionally ischemic myocardium were investigated in an open-chest rabbit model by means of phosphorus 31 nuclear magnetic resonance (NMR) spectroscopy. Sixteen anesthetized New Zealand white rabbits were subjected to thoracotomy; a reversible snare occluder was placed around a large branch of the left circumflex coronary artery, and an NMR surface coil was positioned adjacent to the myocardium perfused by this vessel. The animals were placed in a 2.0 T CSI spectrometer (GE Medical Systems, Fremont, Calif.), and baseline spectra were acquired. Eight animals were treated with intravenous adenosine (25 mg/kg), and eight rabbits served as control subjects. All animals were subjected to a 10-minute period of ischemia followed by a period of reperfusion. NMR spectra were acquired during both intervals. During the occlusion period, expected increases in inorganic phosphate levels and decreases in phosphocreatine levels were observed in both groups; however, inorganic phosphate increased less in adenosine-treated animals (adenosine: 33 +/- 2.8% total spectral area during occlusion vs control: 41 +/- 3.1%) and phosphocreatine diminished less with adenosine (adenosine: 26 +/- 3% vs control: 13 +/- 1.2%; p < 0.002). No significant differences were seen in beta-adenosine triphosphate levels. In both groups the metabolite levels during reperfusion recovered to near baseline values, although phosphocreatine remained slightly higher in the treated group during early reperfusion. An apparent cardioprotective effect of adenosine on relative phosphocreatine and inorganic phosphate levels can be observed in intact rabbits by means of phosphorus 31 NMR spectroscopy.
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PMID:Metabolic effects of adenosine on regional myocardial ischemia by phosphorus 31 nuclear magnetic resonance spectroscopy. 144 87

Angina is characterized by brief periods of ischemia followed by reperfusion; the cumulative effect of these episodes on energetics of the myocardium has not been fully elucidated. This study used an in vivo feline model for the assessment of high-energy phosphate compounds during brief sequential periods of ischemia and reperfusion. Nine adult, open-chest, anesthetized cats were prepared with a reversible occluder around the proximal left anterior descending artery and a 1.2-cm-inside diameter coil sutured on the myocardial surface in the distribution of the left anterior descending coronary artery. Levels of PCr, Pi, and ATP (beta-phosphate signal) were measured by 31P MRS in a GE CSI 2-T NMR spectrometer/imager. Measurements were obtained during a control period and during three successive occlusion-deocclusion periods of roughly 12 and 20 min' duration, respectively. The last deocclusion period was observed for 60 min. Electron microscopy was performed in two animals. PCr declined (P less than 0.01) rapidly following each occlusion to 51 +/- 5.2% (occlusion 1), 53 +/- 5.8% (occlusion 2), and 48 +/- 5.7% (occlusion 3) of the control value by 6 min. Pi rose (P less than 0.01) with the three sequential occlusions to 253 +/- 46, 288 +/- 57, and 277 +/- 46%, respectively. PCr and Pi returned to baseline promptly with reperfusion, while ATP showed a gradual decline throughout the experiment, decreasing to 77 +/- 7.2% of control at the end of the last reperfusion (P less than 0.05). Although PCr returned to baseline during reperfusion, ATP did not, suggesting a reduction in the nucleotide pool. These findings indicate that the repeated episodes of ischemia, which are insufficient to produce necrosis, can have an effect on myocardial high-energy phosphate metabolism as evidenced by mild depletion of ATP.
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PMID:Effect of repetitive brief episodes of cardiac ischemia on 31P magnetic resonance spectroscopy in the cat. 237 1

Chemical shifts were extracted from in vivo 3-dimensional 31P NMR CSI data and pH images were constructed. The images could spatially resolve tissue pH ranging from 5.8 to 7.2 (with uncertainty of 0.11-0.17 pH unit) in an ischemia-reperfusion model of diabetic rat calf muscles.
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PMID:pH mapping in living tissues: an application of in vivo 31P NMR chemical shift imaging. 842 90

A two turn saddle shaped surface coil receiver was developed that allowed high resolution magnetic resonance imaging of the rat spinal cord. This is particularly important in laboratory animals where central nervous system regions of interest are relatively small. A continuous copper wire 1.5 mm in diameter was wound into two turns 28 mm in diameter. The saddle shape of the second turn improved the homogeneity of the signal within the region of interest and maintained sufficient field of view and depth of penetration. The quality factor (Q) for the surface coil was Q = 199 unloaded, and Q = 60 loaded. Using this surface coil with a GE CSI II 2.0 Tesla small bore magnet, spin echo T1 (TR = 500 msec, TE = 25 msec) and T2 (TR = 2000 msec, TE = 100 msec) weighted images were obtained in cross section, using 2 mm slice thickness with 2 excitations per phase encoding step. A sagittal gradient echo (rapid scan, TR = 85 msec, TE = 10 msec) was used to document reestablishment of vascular flow following ischemia. Spinal cord ischemia was induced by 14 minute temporary occlusion of spinal cord blood supply. MRI was performed at 18 hours following ischemia. There was a 1.4 fold increase in T2 image intensity in ischemic rat spinal cord (n = 4), consistent with edema formation, compared to normal rat spinal cord (n = 4). Preliminary studies show that similar high resolution images can be performed on the rat brain. This technique uses standard MRI equipment and the surface coil is made from inexpensive readily available materials. There are various animal models of cerebral and spinal cord injury that would benefit from improved high resolution MRI. This coil design may have application in larger animal models and the clinical setting.
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PMID:High resolution magnetic resonance imaging of the rat spinal cord. 891 65

This study tests the hypothesis that increased levels of plasma lipids can accelerate accumulation of myocardial triacylglycerols in post-ischemic but viable myocardium. Two groups of dogs underwent 90 min of left anterior descending coronary artery (LAD) occlusion followed by 240 min of reperfusion. The first group of saline-treated dogs (n = 7) had physiological levels of plasma lipids during reperfusion: a second group treated with Liposyn and heparin (n = 5) experienced increased plasma lipids during reperfusion. The transmural content of triacylglycerols was determined during ischemia and reperfusion using 1H NMR one-dimensional chemical shift imaging (1D CSI), and at the end of reperfusion using Oil Red-O staining and chemical assay. TTC staining was used to identify the extent of irreversibly injured myocardium. Subepicardial and plasma triacylglycerol content, measured both by 1D CSI and chemically, did not change during reperfusion in saline-treated dogs. Infusing dogs with Liposyn and heparin for 90 min during reperfusion transiently elevated their plasma triacylglycerols, which returned to normal levels following Liposyn wash-out. During Liposyn wash-out, myocardial triacylglycerols measured by 1D CSI preferentially increased in the subepicardium of area-at-risk myocardium (P < 0.05). Triacylglycerol content, measured chemically, also increased in area-at-risk compared to non-ischemic subepicardium (P < 0.001). Significant endocardial damage occurred in both groups, but elevated levels of plasma lipids did not increase the size of the area-at-risk. Therefore, elevated plasma lipids caused a preferential accumulation of triacylglycerols in area-at-risk myocardium during reperfusion without exacerbating irreversible ischemic injury. These results are consistent with either inhibited fatty acid oxidation or mis-matched fatty acid extraction and oxidation in area-at-risk myocardium.
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PMID:1H NMR measurement of triacylglycerol accumulation in the post-ischemic canine heart after transient increase of plasma lipids. 914 Aug 7

MR spectroscopy opens a window to the non-invasive evaluation of various aspects of cardiac metabolism. Experimentally, the method has extensively been used since 1970's. 31P-MR allows the registration of cardiac high-energy phosphate metabolism to non-invasively estimate the energetic state of the heart: ATP, phosphocreatine, inorganic phosphate, monophosphate esters and intracellular pH can all be quantitated. In conjunction with extracellular shift reagents such as [DyTTHA]3- or [TmDOTP]5-, 23Na- and 39K-MR allow the measurement of intra- and extra-cellular cation pools. 1H-MR spectroscopy allows the detection of a large number of metabolites such as, e.g. creatine, lactate, or carnitine. Human cardiac spectrocsopy has so far been confined to the 31P nucleus. Localization techniques (DRESS, ISIS, 3D-CSI etc.) are required to confine the acquired signal to the heart region. Relative quantification is straightforward (phosphocreatine/ATP ratio), absolute quantification (mM) is under development. Cardiac 31P-MR spectroscopy has research application in at least three clinical areas: (1) Coronary artery disease: A biochemical stress test for non-invasive ischemia detection (decrease of phosphocreatine with exercise) and viability assessment via quantification of ATP may become feasible. (2) Heart failure: The phosphocreatine/ATP ratio may provide an independent index for grading of heart failure, allow to monitor the longterm effects of different forms of drug therapy on cardiac energy metabolism in heart failure, and may also hold prognostic information on survival. (3) Valve disease: It is possible that the decrease of phosphocreatine/ATP can be used to guide the timing for the valve replacement. At the present time, no routine clinical applications can be defined for the use of human cardiac spectroscopy in patients with cardiac disease. However, the technique holds great potential for the future as a non-invasive approach to cardiac metabolism, and in coming years routine applications may become reality.
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PMID:Clinical cardiac magnetic resonance spectroscopy--present state and future directions. 974 38

Detection of lactate by in vivo 1H magnetic resonance spectroscopy may provide a means of identifying regions of metabolic stress in brain and other human tissue, potentially identifying regional ischemia in stroke or necrosis in tumors. At higher field strengths (3 and 4 T), which have recently become available for whole-body human studies, the chemical shift difference between the doublet from the methyl protons and the quartet from the methine proton becomes comparable to the available radiofrequency (RF) pulse bandwidth. In this case "anomalous" J modulation occurs in PRESS and STEAM because the coupling partner of the observed resonance may or may not be refocused by the RF pulses depending on the position of the molecule within the voxel and the size of the chemical shift misregistration artifact. These anomalies lead to signal cancellation for echo times near odd multiples of 1/J (often used to highlight the inverted lactate doublet against nearby lipid peaks) in single voxel studies, and spatial variation of the doublet lineshape in chemical shift imaging studies, producing erroneous determination of relative lactate concentrations. While increasing the band-width of the RF pulses can reduce this effect by reducing the signal cancellation, some cancellation will always remain. A means of eliminating this effect using BASING/ MEGA (Mescher M et al. Solvent suppression using selective echo dephasing J Magn Reson A 1996;123:226-229; Star-Lack J et al. Improved water and lipid suppression for 3D PRESS CSI using RF band selective inversion with gradient dephasing (BASING). Magn Reson Med 1997;38: 311-321) water suppression pulses will be described, along with some of its limitations.
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PMID:Lactate detection at 3T: compensating J coupling effects with BASING. 1033 71

To obtain the spatially resolved (31)P spectroscopic image from myocardium during an acute myocardium ischemia at a high signal-to-noise ratio (SNR) in a very limited time window, we have exploited the spatial variation of the radiofrequency (RF) field produced by a single loop transmit/receive (TR) RF coil along its axis for spatial discrimination. By incrementally lengthening the duration of a square RF excitation pulse, the positional information can be systematically encoded as harmonics of various orders in MR signal. In the in vivo open-chest animal experiment, this RF coil was surgically sutured onto the epicardial surface of the left ventricular (LV) wall over the region perfused by the left anterior descending coronary artery. Using only 17 encoding steps, we have obtained one-dimensional (31)P spectroscopic images from both a multiple-layer phosphor phantom and an in vivo LV myocardium. In the animal study, the cardiac gating is used with respiratory synchronization. The MR data were only collected during the end diastole phase of the cardiac cycle (cardiac and respiratory synchronized) with an effective sequence repetition time (TR) of 6 seconds (to ensure the complete relaxation of the phosphorous magnetization). The total acquisition time for a complete experiment is about 10 minutes. Prior to the CSI reconstruction process, the raw data matrix was zero-filled in the spatial dimension. The spatially resolved metabolite map exhibited all the metabolite peaks including creatine phosphate and adenosine triphosphate. At the layer of endocardium, two peaks corresponding to 2, 3-diphosphoglycerate, which is contained in the erythrocytes, were clearly seen in the LV wall. Also, the method allows compensation in both volume and coil sensitivity variations for the resulting spectra. All results have demonstrated that it is an efficient nuclear magnetic resonance method capable of obtaining high-quality (31)P spectroscopic images with both excellent spatial localization and SNR in the research of cardiac ischemia. J. Magn. Reson. Imaging 1999;10:892-898.
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PMID:An efficient MR phosphorous spectroscopic localization technique for studying ischemic heart. 1054 4