One-dimensional Chemical Shift Imaging Research Articles

Multinuclear absolute magnetic resonance thermometry

Non-invasive measurement of absolute temperature is important for proper characterization of various pathologies and for evaluation of thermal dose during interventional procedures. The proton (hydrogen nucleus) magnetic resonance (MR) frequency shift method can be used to map relative temperature changes. However, spatiotemporal variations in the main magnetic field and the lack of local internal frequency reference challenge the determination of absolute temperature. Here, we introduce a multinuclear method for absolute MR thermometry, based on the fact that the hydrogen and sodium nuclei exhibit a unique and distinct characteristic frequency dependence with temperature and with electrolyte concentration. A one-to-one mapping between the precession frequency difference of the two nuclei and absolute temperature is demonstrated. Proof-of-concept experiments were conducted in aqueous solutions with different NaCl concentrations, in agarose gel samples, and in freshly excised ex vivo mouse tissues. One-dimensional chemical shift imaging experiments also demonstrated excellent agreement with infrared measurements.

Transmurally differentiated measurement of ATP hydrolysis rates in the in vivo porcine hearts.

Compare the transmural distribution of forward creatine kinase reaction (kf,CK ) and ATP hydrolysis rate (kr,ATPase ) in the myocardium of normal porcine heart. Rate constants were extracted from partially relaxed spectra by applying the T1nom method, effectively reducing data acquisition time by up to an order of magnitude. T1nom method for double saturation of PCr and Pi is introduced and validated through simulations. Bioenergetics was measured in vivo utilizing one-dimensional chemical shift imaging (1D-CSI) magnetic resonance (31) P spectroscopy. At basal conditions, there was no significant difference between subepicardial layers (EPI) vs. the subendocardial layers (ENDO) for both fluxf,CK and fluxr,ATPase . At high cardiac workload (HWL), where the rate pressure product increased 2.6-fold, PCr/ATP ratio and fluxf,CK showed no significant change in both EPI and ENDO layers, while fluxr,ATPase increased significantly (baseline: 1.11 ± 0.12 and 1.12 ± 0.13 μmol/g/s, EPI and ENDO, respectively; to HWL: 2.35 ± 0.27 and 2.21 ± 0.08 μmol/g/s, EPI and ENDO, respectively, each P < 0.01 vs. baseline). In the normal heart, increase of cardiac work state is accompanied by an increase in ATP hydrolysis rate with no changes in CK flux rate. There are no significant differences between EPI vs. ENDO concerning the ATP hydrolysis rate or CK flux rate in both baseline and high cardiac work states.

Saturation-transfer effects and longitudinal relaxation times of (31) P metabolites in fibroglandular breast tissue at 7T.

To investigate longitudinal relaxation times and saturation-transfer effects of phosphorous metabolites in breast fibroglandular tissue in vivo with (31) P MR spectroscopy at 7T. Progressive saturation with adiabatic half passage excitation was used to determine T1 values of (31) P metabolites in a group of six healthy volunteers. Saturation-transfer experiments were performed in seven healthy volunteers by saturating at 0 ppm and 10 ppm with sinc-Gaussian pulses (90 ms; 10-ms pulse interval; B1 = 17 μT) prior to excitation. Localization was performed by surface coils and one-dimensional chemical shift imaging. Data were analyzed via spectral fitting with the JMRUI software package, and T1 values were obtained by fitting the data to the signal equation. The determined longitudinal relaxation time values at 7T were as follows: phosphoethanolamine, 4.0 ± 0.2 s; phosphocholine, 1.8 ± 0.2 s; inorganic phosphate, 6.1 ± 0.1 s; phosphodiesters, glycerophosphatidylethanolamine plus glycerophosphocholine, 2.1 ± 0.1, and glycerophosphatidylethanolamine, 1.5 ± 0.1s; γ-ATP, 2.1 ± 0.1 s; and α-ATP, 2.0 ± 0.1 s. Saturation-transfer measurements with saturation pulses at 0 ppm showed a significant signal reduction in the phosphodiester 2-3 ppm range, whereas the γ-ATP signal at -2.5 ppm was not affected significantly. Longitudinal relaxation times of phosphorous metabolites in fibroglandular tissue revealed relatively low T1 values for phosphodiesters. Saturation-transfer measurements showed that the phosphodiester signals were the only signals that were affected significantly, possibly indicating the presence of mobile phospholipids. Magn Reson Med 76:402-407, 2016. © 2015 Wiley Periodicals, Inc.

Spatially and chemically resolved measurement of intra- and inter-particle molecular diffusion in a fixed-bed reactor

This work demonstrates for the first time the ability to spatially and chemically resolve inter- and intra-particle apparent diffusion coefficients in a packed bed during reaction using Nuclear Magnetic Resonance. The measurements were performed using a diffusion preconditioned one-dimensional chemical shift imaging pulse sequence; all the data are recorded within a single measurement. The reaction studied was the continuous liquid phase esterification of acetic acid and ethanol to form ethyl acetate and water over an ion-exchange resin at ambient temperature and pressure. Inter- and intra-particle apparent diffusivities of the hydrocarbons were resolved at four different spatial positions along the length of the catalyst bed. Absolute composition measurements were obtained of the liquid in the inter-particle space of the bed. Relative concentration measurements of the chemical species in the intra-particle space are also reported. The development of these measurement methods advances our ability to characterise mass transfer limitations in situ within a working fixed-bed reactor.

Chemical shift imaging (CSI) by precise object displacement

A mechanical device (NMR lift) has been built to displace vertically an object (typically an NMR sample tube) inside the NMR probe with an accuracy of 1 microm. A series of single pulse experiments are performed for incremented vertical positions of the sample. With a sufficiently spatially selective radio-frequency (r.f.) field, one obtains chemical shift information along the displacement direction (one-dimensional chemical shift imaging (CSI)). Knowing the vertical r.f. field profile (the amplitude of the r.f. field along the vertical direction), one can reconstruct the spectrum associated with all the slices corresponding to consecutive sample positions and improve the spatial resolution, which is simply related to the accuracy of the displacement device. Beside tests performed on phantoms, the method has been applied to solvent penetration in polymers and to benzene diffusion in a heterogeneous zeolite medium.

Abnormal cardiac energetics in patients carrying the A3243G mtDNA mutation measured in vivo using phosphorus MR spectroscopy

Cardiomyopathy is a frequent cause of morbidity and mortality in patients carrying the A3243G transition in the mitochondrial DNA (mtDNA) tRNALeu(UUR) gene, the most common heteroplasmic single mtDNA defect. We used phosphorus magnetic resonance spectroscopy ( 31P-MRS) to look for evidence of an in vivo bioenergetics defect in patients carrying the A3243G mtDNA mutation with and without echocardiographic signs of left ventricle hypertrophy (LVH). Eight patients, three with LVH, carrying the A3243G mtDNA mutation and 10 healthy subjects underwent one-dimensional chemical shift imaging 31P-MRS. In the patients, mean cardiac phosphocreatine to adenosine triphosphate ratio (PCr/ATP) (1.55±0.58) was significantly reduced compared to the control group (2.34±0.14; P<0.001). Cardiac PCr/ATP was within the normal range only in one case that showed normal echocardiography. Our results point to a central role of bioenergetics deficit in the development of cardiac hypertrophy in patients with the A3243G mtDNA mutation. Impaired cardiac energy metabolism in patients with normal echocardiography suggests that the enhancement of mitochondrial function may be beneficial not only to patients with cardiac hypertrophy but also to those patients carrying the mutation in the absence of signs of cardiac hypertrophy and/or dysfunction but with cardiac bioenergetics deficit.

Focal and lateralized subcortical abnormalities in unipolar major depressive disorder: an automated multivoxel proton magnetic resonance spectroscopy study

Background The results of prior proton magnetic resonance spectroscopy ( 1H-MRS) studies in unipolar major depressive disorder (MDD) evaluating choline (Cho)/creatine (Cr) and N-acetyl-L-aspartate (NAA)/Cr ratios are mixed. These single-voxel or one-dimensional chemical-shift imaging (CSI) nonautomated 1H-MRS studies has been unable to evaluate global or lateralized abnormalities in neuronal or membrane function. Using automated multivoxel two-dimensional CSI 1H-MRS techniques, we tested the hypothesis that patients with MDD have focal neuronal and membrane abnormalities localized in the subcortical region. Methods Whole brain and subcortical measures of Cho, NAA, Cr, and myo-inositol ( mI) were obtained in 18 patients with MDD and 20 control subjects using automated two-dimensional CSI 1H-MRS. Results Compared with control subjects, MDD patients had a significantly lower mean NAA/Cr amplitude in the caudate and a significantly higher mean Cho/Cr amplitude in the putamen, particularly on the right side. No differences were observed for global whole brain measurements. Conclusions The findings support reduced neuronal viability or function in the caudate and altered membrane phospholipid metabolism in the putamen for patients with MDD. Our results are consistent with prior magnetic resonance imaging, positron emission tomography, and postmortem reports of focal and lateralized abnormalities of the basal ganglia in MDD.

In situ magnetic resonance visualisation of the spatial variation of catalytic conversion within a fixed-bed reactor

We report the first application of magnetic resonance techniques to explore the spatial variation in chemical conversion of a catalysed reaction occurring within a fixed-bed reactor. The reaction studied is the liquid-phase esterification of methanol and acetic acid, catalysed by a proton exchange (Amberlyst 15 ion exchange resin) catalyst. This esterification is considered as a generic liquid-phase reaction, for which the extent of reaction is measured non-invasively, in situ, by monitoring the 1 H chemical shift of the hydroxyl resonance associated with fluid in the inter-particle space of the bed. The paper highlights the application of one-dimensional chemical shift imaging and volume selective magnetic resonance spectroscopy techniques to measure directly and quantitatively the spatial distribution of chemical conversion within a fixed-bed of catalyst particles. In the specific case study considered here it is shown that while conversion within the bed is homogeneous under batch reaction conditions, as expected, when reaction occurs under flowing conditions fractional variations in steady-state conversion of up to ∼20% exist within transverse sections through the bed, perpendicular to the direction of superficial flow. We suggest that magnetic resonance visualisation techniques are now able to provide a quantitative tool to aid in the integrated design of catalyst and reactor.

Distribution and dynamics of laser‐polarized 129Xe magnetization in vivo

The first magnetic resonance imaging studies of laser-polarized 129Xe, dissolved in the blood and tissue of the lungs and the heart of Sprague-Dawley rats, are described. 129Xe resonances at 0, 192, 199, and 210 ppm were observed and assigned to xenon in gas, fat, tissue, and blood, respectively. One-dimensional chemical-shift imaging (CSI) reveals xenon magnetization in the brain, kidney, and lungs. Coronal and axial two-dimensional CSI show 129Xe dissolved in blood and tissue in the thorax. Images of the blood resonance show xenon in the lungs and the heart ventricle. Images of the tissue resonance reveal xenon in lung parenchyma and myocardium. The 129Xe spectrum from a voxel located in the heart ventricle shows a single blood resonance. Time-resolved spectroscopy shows that the dynamics of the blood resonance match the dynamics of the gas resonance and demonstrates efficient diffusion of xenon gas to the lung parenchyma and then to pulmonary blood. These observations demonstrate the utility of laser-polarized 129Xe to detect exchange across the gas-blood barrier in the lungs and perfusion into myocardial tissue. Applications to measurement of lung function, kidney perfusion, myocardial perfusion, and regional cerebral blood flow are discussed. Magn Reson Med 42:1137–1145, 1999. © 1999 Wiley-Liss, Inc.

Distribution and dynamics of laser-polarized (129)Xe magnetization in vivo.

The first magnetic resonance imaging studies of laser-polarized (129)Xe, dissolved in the blood and tissue of the lungs and the heart of Sprague-Dawley rats, are described. (129)Xe resonances at 0, 192, 199, and 210 ppm were observed and assigned to xenon in gas, fat, tissue, and blood, respectively. One-dimensional chemical-shift imaging (CSI) reveals xenon magnetization in the brain, kidney, and lungs. Coronal and axial two-dimensional CSI show (129)Xe dissolved in blood and tissue in the thorax. Images of the blood resonance show xenon in the lungs and the heart ventricle. Images of the tissue resonance reveal xenon in lung parenchyma and myocardium. The (129)Xe spectrum from a voxel located in the heart ventricle shows a single blood resonance. Time-resolved spectroscopy shows that the dynamics of the blood resonance match the dynamics of the gas resonance and demonstrates efficient diffusion of xenon gas to the lung parenchyma and then to pulmonary blood. These observations demonstrate the utility of laser-polarized (129)Xe to detect exchange across the gas-blood barrier in the lungs and perfusion into myocardial tissue. Applications to measurement of lung function, kidney perfusion, myocardial perfusion, and regional cerebral blood flow are discussed. Magn Reson Med 42:1137-1145, 1999.

1H NMR Measurement of Triacylglycerol Accumulation in the Post-ischemic Canine Heart after Transient Increase of Plasma Lipids

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 tansmural content of triacylglycerols was determined during ischemia and reperfusion using1H 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.

Effect of ethanol and fructose on liver metabolism: A dynamic 31Phosphorus magnetic resonance spectroscopy study in normal volunteers

In vivo 31Phosphorus magnetic resonance spectroscopy ( 31P-MRS) permits evaluation of dynamic changes of individual phosphorus-containing metabolites in the liver parenchyma, such as phosphomonoester (PME), adenosine triphosphate, and inorganic phosphate (P i). Intravenous fructose load alters phosphorus metabolites and allows assessment of liver function by 31P-MRS. 31P-MRS data obtained in alcoholic liver disease are however inconclusive. To study the hypothesis that fructose load can be used to investigate metabolic effects of ethanol ingestion, the interaction of different metabolites-i.e., fructose and ethanol-were followed in vivo. Using a 1.5 Tesla magnetic resonance system, six healthy volunteers were examined in three sessions each: a session after administration of (a) fructose only (250 mg/kg) was compared with (b) fructose load after ethanol ingestion (0.8g/kg). A control experiment (c) was done after ethanol only. Spectra were acquired using one-dimensional chemical shift imaging with a temporal resolution of 5 min. Following a fructose load, the concomitant uptake of ethanol showed drastic changes of individual metabolic steps of the hepatic metabolism (averages ± standard deviation). While the velocity of the net formation of PME (relative increase 0.46 ± 0.11 without ethanol vs. 0.61 ± 0.25 with ethanol) and the use of adenosine triphosphate (−0.13 ± 0.03 vs. −0.16 ± 0.03) and P i (−0.022 ± 0.009 vs. −0.021 ± 0.004) were not significantly affected by ethanol uptake, a significant ( p < 0.01) reduction of PME degradation (31.3 ± 9.4 vs. 61.9 ± 16.9 relative total area) and absence of an overshoot for P i (10.5 ± 4.9 vs. −7.1 ± 5.3 relative area 13 min to 43 min) was observed after ethanol administration. Dynamic 31P-MRS allows the observation of individual steps of hepatic metabolism in situ; fructose metabolism in the human liver is slowed down by concomitant ethanol ingestion after the phosphorylation step of fructose. This could be explained by inhibition of aldolase rather than ethanol-induced changes of the hepatic redox state. Fructose load can be used to study effects of alcohol ingestion and might therefore be useful in patients with alcoholic liver disease.

Effect of 6-aminonicotinamide on the pentose phosphate pathway: 31P NMR and tumor growth delay studies.

6-aminonicotinamide (6AN) has been shown to enhance radiosensitivity in vitro, although previous in vivo studies failed to show an effect. 31P NMR spectra were obtained by using a one-dimensional chemical shift imaging technique on a first generation transplant of the CD8FI spontaneous mammary carcinoma tumor model. Spectra were obtained both before and 10 h after treatment with 6AN (20 mg/kg). Changes in pH, nucleoside triphosphate/inorganic phosphate, and phosphocreatine/ inorganic phosphate measured at 10 h post-6AN were not significant. A new peak was detected 10 h post-6AN, which was assigned to 6-phosphogluconate (6PG), indicating inhibition of the pentose phosphate pathway (PPP). Based on the spectral data demonstrating inhibition of the PPP at 10 h post-6AN, tumor-bearing mice were irradiated (15 Gy x 3 fractions) on Days 1, 10 or 11, and 21 10 h after administration of 6-aminonicotinamide (20 mg/kg). Tumor-bearing mice receiving 6AN alone (20 mg/kg x 3), radiation alone (15 Gy x 3), or saline were also studied. Tumor growth delay studies indicated that 6AN alone induced a small but significant tumor growth delay (4.3 +/- 0.8 days). Radiation alone induced a tumor growth delay of 34.5 +/- 2.7 days. Treatment with 6AN followed by radiation induced a tumor growth delay of 57.0 +/- 3.8 days. This was significantly greater than the TGD values for treatment with 6AN alone or radiation (P < 0.01). No complete regressions were noted after treatment with 6AN or radiation alone. Concomitant therapy with 6AN plus radiation yielded 6/28 complete regressions (21%), which was significantly greater than radiation (P < 0.05) or 6AN alone (P < 0.01) on this mammary carcinoma.

Phosphocreatine and creatine kinase in piglet cerebral gray and white matter in situ.

Rates of adenosine triphosphate (ATP) metabolism are higher in cerebral gray matter than in white matter. Like other excitable tissues, brain contains a phosphocreatine (PCr)/creatine kinase (CK)/ATP system including cytosolic (B-CK) and mitochondrial (Mi-CK) isozymes. High B-CK activity is present in white and gray matter while Mi-CK is mostly in gray matter. An in situ localizing 31P-NMR technique, one-dimensional chemical shift imaging (1D-CSI), has been used to study the PCr/CK/ATP system in these regions. In the metabolically mature 4-week-old piglet, the PCr/nucleoside triphosphate (NTP) ratio measured by the 1D-CSI technique is at least 50% higher in white than gray matter. Total creatine (Cr), ATP, and total NTP concentrations are the same in rapidly frozen rat white and gray matter, suggesting that PCr/Cr ratio is much higher in white matter. The PCr increases more in gray than white matter between 4 days and 4 weeks of age in piglet brain. The CK catalyzed reaction rate constant, measured by combining the saturation transfer experiment with the 1D-CSI, is also much higher in white than gray matter at both ages. The postnatal maturational increase in the CK rate constant is greater in gray matter. In summary, these differences in PCr concentration and CK reaction rates and isozymes characterize two physiologically different PCr/CK/ATP systems in gray and white matter.

31P nuclear magnetic resonance spectroscopic imaging of regions of remodeled myocardium in the infarcted rat heart.

The clinical course of a patient with a myocardial infarction (MI) depends largely on the ability of the noninfarcted region to remodel and compensate for the loss of the infarcted region. Previous studies have shown that the remaining viable myocardium remodels morphologically, functionally, and biochemically. The purpose of this study was to define the regional distribution of the biochemical remodeling that occurs after MI in rat hearts by use of a technique that could be applied noninvasively to human subjects. Infarcts of the left ventricular apex and anterolateral wall were induced by occluding a coronary artery. Eight to 10 weeks after infarction, one-dimensional chemical shift imaging (CSI) was used to obtain 31P nuclear magnetic resonance (NMR) spectra of eight 2.5-mm-thick cross-sectional slices along the long axis (from base to apex) of isolated buffer-perfused rat hearts. Regional ATP and phosphocreatine (PCr) contents were compared in remodeled versus normal (sham) myocardium. Spin-echo 1H MR images identified the mass of each slice, allowing calculations of metabolite amount per unit myocardium in each slice. 1H MR images identify the hypertrophy of remodeled myocardium but do not discriminate between scar and viable tissue. In contrast, 31P CSI does distinguish viable tissue. Compared with shams, there was less 31P signal in the slices distal to the occlusion containing mainly scar tissue and increased signal intensity in slices proximal to the occlusion because of myocyte hypertrophy. The ATP signal intensity changed in direct proportion to the viable tissue mass in the slice, suggesting that the amount of ATP per unit mass in viable remodeled myocardium is the same as that of the shams. In contrast, the amount of PCr per unit mass in remodeled myocardium decreased. This decrease is uniform across the slices, correlates with infarct size, and parallels a similar decrease in tissue creatine content. 31P CSI of post-MI hearts shows that (1) PCr decreases uniformly (ie, independent of the distance from the scar) in the noninfarcted remodeled myocardium, and its amount inversely correlates with infarct size; and (2) the ATP signal provides a profile of viable myocardium and is a biochemical marker of morphological remodeling and hypertrophy that has occurred in noninfarcted regions. Thus, 31P CSI provides both a marker that tissue injury has occurred (decreased PCr) and a marker of the extent of remodeling in response to injury (ATP distribution) in a single set of noninvasive measurements.

In vivo 19F-NMR spectroscopic study of halothane uptake in rabbit brain

Uptake of a fluorinated anesthetic, halothane, in rabbit brain and blood was studied using 19F-NMR spectroscopic techniques. Localized one-dimensional chemical shift imaging and non-localized one-pulse sequence were used to measure brain uptake kinetics in vivo. Halothane signal was found predominantly in the cerebral cortex. Uptake in the brain followed a first-order biexponential kinetics. The average half-lives were 4 min and 70 min, respectively, for the ‘fast’ and ‘slow’ phases of the uptake. Uptake in the arterial blood was also biexponential. However, equilibration of halothane in the brain considerably lagged behind that in arterial blood. This delay was ascribed to a ‘restricted diffusion’ of the anesthetic molecule into brain tissue.

Lateralized abnormality of high-energy phosphate and bilateral reduction of phosphomonoester measured by phosphorus-31 magnetic resonance spectroscopy of the frontal lobes in schizophrenia

Magnetic resonance spectroscopy (one-dimensional chemical shift imaging) was used to measure membrane phospholipid metabolism and high-energy phosphate metabolism in the left and right frontal lobes of 27 schizophrenic patients. In the schizophrenic patients, the phosphomonoester peak area was decreased in bilateral frontal lobes compared with that in age-matched normal subjects. On the other hand, the peak area of β-adenosine triphosphate was increased in the left frontal lobe in the schizophrenic group. The phosphocreatine peak area was increased in the left frontal lobe of schizophrenic patients with high scores on the Scale for the Assessment of Negative Symptoms (SANS).

Quantitative measurements of cardiac phosphorus metabolites in coronary artery disease by 31P magnetic resonance spectroscopy.

31P metabolite measurements in the human heart by magnetic resonance spectroscopy (MRS) have been reported previously. By use of a method in which metabolite content was quantified with reference to a standard located outside the chest, it has become possible to measure the content of phosphocreatine (PCr) and ATP in vivo in the human heart. In this study, PCr and ATP contents were measured by 31P MRS and compared in human myocardium with reversible ischemia or scar diagnosed by exercise thallium scintigraphy. Forty-one subjects with stenosis of the left anterior descending coronary artery (> 50%) and 11 healthy control subjects (C) composed the present study group. Patients were divided into two groups on the basis of exercise 201Tl scintigraphy: a reversible 201Tl defect group (RD[+], n = 29) who demonstrated redistribution at late image and a fixed 201Tl defect group (RD[-], n = 12). While the subjects lay supine within the magnet, 31P MR spectra were obtained from the anterior and apical regions of the left ventricle by slice-selected one-dimensional chemical shift imaging. For metabolite quantification, a standard was placed at the center of the surface coil. ANOVA revealed significant differences among the three groups with respect to the mean (+/- SD) PCr at rest (C, 12.14 +/- 4.25 > RD[+], 7.64 +/- 3.00 > RD[-], 3.94 +/- 2.21 mumol/g wet heart tissue, P < .05) as well as a significant decrease in ATP in the RD(-) group (C, 7.72 +/- 2.97; RD[+], 6.35 +/- 3.17 > RD[-], 4.35 +/- 1.52 mumol/g wet heart tissue, P < .05). Compared with healthy control subjects, PCr content decreased significantly in patients with both reversible and fixed 201Tl defects, and ATP content decreased significantly in subjects with fixed thallium defects. These results suggest that the measurement of ATP content in the human heart by 31P MRS is a clinically important method for the evaluation of myocardial viability.

Water‐Suppressed one‐dimensional 1h nmr chemical shift imaging of the heart before and after regional ischemia

This study tests the hypothesis that brief periods of ischemia result in an increase in myocardial lipids during early reperfusion. We conducted 1H NMR spectroscopy to serially measure myocardial lipids before and after regional ischemia. Localized 1H NMR spectra (spatial resolution of 1.25 mm) were obtained using a one-dimensional chemical shift imaging technique. Two regions, the subendocardium and the subepicardium, were estimated by summing spectral areas from three slices (3.75 mm). Two groups of dogs that underwent a 45 min ischemia and 4 h reperfusion were studied: a group in which the myocardium beneath the surface coil underwent ischemia and reperfusion; and a group in which the ischemic event was distant from the tissue under the surface coil. Microsphere measurements showed significant blood flow reductions in the subepicardium and subendocardium in the ischemic zones during coronary occlusion. Flow returned to baseline values during reperfusion. In the ischemic zone group, the subendocardium, the triglyceride resonance areas decreased by 24% (p < 0.05) during reperfusion. However, subepicardial triglyceride areas were unchanged. Subendocardial creatine areas were also unchanged. The non-ischemic zone group subendocardial triglycerides decreased by 33% (p < 0.05) following ischemia and reperfusion in the remote region. In contrast to the ischemic group, the subepicardial triglyceride resonance areas decreased by 42% (p < 0.05). Subendocardial creatine areas were unchanged. These data show that triglycerides of the ischemic-reperfused subendocardium do not increase during 4 h of reperfusion. Furthermore, they show that the triglycerides resonance areas of the non-ischemic region decrease following remote ischemia and reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

An assessment of artefacts in localized and non-localized 31P MRS studies of phosphate metabolites and pH in rat tumours.

UA hepatomas, GH3 prolactinomas and N-methyl-N-nitrosourea-induced mammary tumours, which were subcutaneously grown in rats, have been studied by 31P MRS using non-localized pulse-acquire, image selected in vivo spectroscopy (ISIS) and one-dimensional chemical shift imaging (1-D CSI) techniques. Comparisons have been made with measurements from acid extracts of these tumour types and surrounding tissues (i.e., muscle and skin). Since muscle containing high concentrations of phosphocreatine (PCr) is often found adjacent to the tumour, we have compared the ratio of the PCr to gamma-NTP peaks in the spectra with the same ratio calculated from the acid extract data, and have used deviations between the two sets of data to assess the discrimination of the MRS localization technique to signals from the tissue surrounding the tumour. Extract data showed an average NTP content of 1.25 mumol/g wet wt for all three tumour types. PCr (at 0.42 mumol/g wet wt), was significant only in the GH3 prolactinoma whereas it was negligible in the other tumour types (< 0.1 mumol/g wet wt). There was good agreement between the ISIS PCr/gamma-NTP ratio and the extract data for all tumours. However, the 1-D CSI data showed an unexpectedly large contamination of the tumour spectrum with PCr signals from the skin which was shown by subsequent phantom experiments to be due to the curved geometry of tumour and skin rather than Fourier bleed. In pH measurements by MRS it was found that biological variability was greater than the effects of artefacts (due to either the chemical shift artefact in the ISIS technique or partial volume effects) in the localization technique. An average pH of 7.2 was observed for all tumours. By initially comparing data from different localization schemes with that from chemical extracts potential sources of error have been highlighted and show that phantom studies alone are not sufficient to fully assess the accuracy of localized MRS data.