Markus von Kienlin

Absolute concentrations of high-energy phosphate metabolites in normal, hypertrophied, and failing human myocardium measured noninvasively with 31P-SLOOP magnetic resonance spectroscopy☆

OBJECTIVEnThe purpose of the present study was to measure absolute concentrations of phosphocreatine (PCr) and adenosine triphosphate (ATP) in normal, hypertrophied, and failing human heart.nnnBACKGROUNDnConflicting evidence exists on the extent of changes of high-energy phosphate metabolites in hypertrophied and failing human heart. Previous reports using phosphorus-31 magnetic resonance spectroscopy ((31)P-MRS) have quantified metabolites in relative terms only. However, this analysis cannot detect simultaneous reductions.nnnMETHODSnFour groups of subjects (n = 10 each), were studied: volunteers and patients with hypertensive heart disease (HHD), aortic stenosis, and dilated cardiomyopathy (DCM). Left ventricular (LV) function and mass were measured by cine magnetic resonance imaging. Absolute and relative concentrations of PCr and ATP were determined by (31)P-MRS with spatial localization with optimum point spread function.nnnRESULTSnLeft ventricular ejection fraction remained normal in HHD and aortic stenosis, but was severely reduced to 18% in DCM; LV mass was increased by 55%, 79%, and 68% respectively. In volunteers, PCr and ATP concentrations were 8.82 +/- 1.30 mmol/kg wet weight and 5.69 +/- 1.02 mmol/kg wet weight, and the PCr/ATP ratio was 1.59 +/- 0.33. High-energy phosphate levels were unaltered in HHD. In aortic stenosis, PCr was decreased by 28%, whereas ATP remained constant. In DCM, PCr was reduced by 51%, ATP by 35%, and reduction of the PCr/ATP ratio by 25% was of borderline significance (p = 0.06). Significant correlations were observed among energetic and functional variables, with the closest relations for PCr.nnnCONCLUSIONSnIn human heart failure due to DCM, both PCr and ATP are significantly reduced. Ratios of PCr to ATP underestimate changes of high-energy phosphate levels.

Rapid recording of solvent-suppressed 2D COSY spectra with inherent quadrature detection using pulsed field gradients

Multidimensional NMR experiments have drawn much attention, particularly due to their ability to elucidate the structure of complex mo lecules. One of the ma jor drawbacks of many mu ltidimensional experiments is the long time required to record a dataset. In many cases, the m inimal experimental time is not lim ited by sensitivity, but rather by the number of repetitions needed to complete a phase-cycl ing protocol. Phase cycling may be necessary to select the desired coherence pathway ( 2 ) , to obtain absorptive l ineshapes (2-4, and to eliminate undesired signals such as axial peaks or quadrature artifacts (5). In order to reduce experimental time, efforts have been undertaken to design reduced phase-cycl ing schemes (6, 7). Spectral artifacts may also appear if the spin system is not in a constant state at the beginning of each pulse sequence, for example, in the case of a fast repetition rate. This problem may be solved by the use of a saturation-recovery sequence (8). Coherence pathways can also be selected in a single scan with the application of field gradients (9-11). Sotak et al. ( 12) have applied this principle to obtain in vivo 2D double-quantum spectra, and Hurd recently reported gradient-enhanced doublequantum-fi ltered COSY and gradient-enhanced TOCSY ( 13). In this contribution, we discuss how standard COSY spectra can be recorded without phase cycling if pulsed field gradients are available. Furthermore, it will be shown that quadrature detection in thef; doma in is attained inherently. F inally, solvent suppression is accomplished by using an alternative pulse sequence, and an improved deconvolut ion method for postprocessing. A similar approach, applied to in vivo 2D spectroscopy, has independently been reported by Z iegler et al. ( 14). F igure 1 a shows the two-pulse sequence for the basic COSY experiment (IS). Using the product-operator formalism to describe the evolution of a weakly coupled twospin system, the observable terms of the density operator after the second 90” pulse at the beginning of the detection period t2 are (16)

Spectral localization with optimal pointspread function

Abstract The SLIM experiment ( X. Hu, D. N. Levin, P. C. Lauterbur, and T. Spraggins, spectral localization by imaging, Magn. Reson. Med. 8, 314, 1988 ) promises to be an efficient technique for localized spectroscopy in vivo, allowing simultaneous acquisition of regional spectra from several, arbitrarily shaped compartments. In the present contribution, we evaluate how sensitivity is affected in this experiment, and we identify a source of localization errors stemming from inhomogeneities within the compartments. We present SLOOP (“spectral localization with optimal pointspread function”) as an extension of the SLIM technique. SLOOP optimizes sensitivity and minimizes localization errors by choosing an optimal set of phase-encoding gradients that matches the pointspread function to the shape of the volumes of interest. Experimental results obtained in vitro on a rabbit kidney are shown. SLOOP is also compared to Fourier series localization techniques and to spectroscopic imaging and is presented as a generalization of both of these that samples k space in a nonuniform fashion.

NMR probeheads for In Vivo applications

The NMR probehead is a key element of the receiving chain of an NMR spectrometer. To optimize the signal-to-noise ratio the probehead must be adapted for the specific application. This article describes the basic physics and characteristics of NMR probeheads for in vivo applications in small animals and plants as well as quality control procedures on the workbench and in the NMR spectrometer. Various probeheads including volume coils, surface coils, double tuned coils, and microscopy coils are presented and illustrated by results of specific in vivo applications.xa0© 2000 John Wiley & Sons, Inc.xa0Concepts Magn Reson 12: 361–388, 2000

Proton spectroscopic imaging of human brain

Abstract Signals from water and fat can cause artifacts in proton spectroscopic imaging in the human brain. The major problem is variation of the B0 field over a range of several ppm within the sensitive volume of the standard whole-head coil. Here, the coherence-pathway formalism is used to describe and evaluate the origin of artifacts in a double spin-echo (PRESS) sequence. The attenuation of unwanted coherences using pulsed field gradients is described for homogeneous and inhomogeneous B0 fields. The effect of the following parameters on the quality of the spectroscopic images is analyzed: (a) directional order of plane selection, (b) positioning of phase-encode gradients in the sequence, (c) postprocessing spatial windowing, and (d) motion. It is shown that, for a typical echo time of 272 ms, it is not necessary to first select a region of interest within the brain borders when sufficient phase-encode steps are used. Examples of 2D proton spectroscopic images with a nominal voxel volume of 0.85 ml are given for a healthy volunteer and a patient with a low-grade glioma.

Homonuclear J refocusing in echo spectroscopy

Abstract A simple pulse scheme is given for obtaining echoes with both chemical shift and homonuclear scalar coupling refocused. The procedure is illustrated for some biologically important nuclei, namely 31 P in ATP and 1 H in lactate. The refocusing of the scalar coupling J is perfect for AX systems, but incomplete for multiply coupled spins. However, for the latter, a gain in in-phase intensity is still obtained at relatively long echo times ( J ). Theory, in terms of the operator formalism, and experiment are presented for AX n systems and are in good agreement. Strategies to remove spectral artifacts resulting from pulse angle deviations are given.

Detection of myocardial viability based on measurement of sodium content : A 23Na-NMR study

MRI of total sodium (Na) content may allow assessment of myocardial viability, but information on Na content in normal myocardium, necrotic/scar tissue, and stunned or hibernating myocardium is lacking. Thus, the aims of the study were to: 1) quantify the temporal changes in myocardial Na content post‐myocardial infarction (MI) in a rat model (Protocol 1); 2) compare Na in normally perfused, hibernating, and stunned canine myocardium (Protocol 2); and 3) determine whether, in buffer‐perfused rat hearts, infarct scar can be differentiated from intact myocardium by 23Na‐MRI (Protocol 3). In Protocol 1, rats were subjected to LAD ligation. Infarct/scar tissue was excised at control and 1, 3, 7, 28, 56, and 128 days post‐MI (N = 6–8 each), Na content was determined by 23Na‐NMR spectroscopy (MRS) and ion chromatography. Na content was persistently increased at all time points post‐MI averaging 306*–160*% of control values (*P < 0.0083 vs. control). In Protocol 2, 23Na‐MRS of control (baseline), stunned and hibernating samples revealed no difference in Na. In Protocol 3, 23Na‐MRI revealed a mean increase in signal intensity, to 142 ± 6% of control values, in scar tissue. A threshold of 2 standard deviations of the image intensity allowed determination of infarct size, correlating with histologically determined infarct size (r = 0.91, P < 0.0001). Magn Reson Med 45:756–764, 2001.

Age and gender dependence of human cardiac phosphorus metabolites determined by SLOOP 31P MR spectroscopy.

The aim of this study was to apply 31P magnetic resonance spectroscopy (MRS) using spatial localization with optimal point spread function (SLOOP) to investigate possible age and gender dependencies of the energy metabolite concentrations in the human heart. Thirty healthy volunteers (18 males and 12 females, 21–67 years old, mean = 40.7 years) were examined with the use of 31P‐MRS on a 1.5 T scanner. Intra‐ and interobserver variability measures (determined in eight of the volunteers) were both 3.8% for phosphocreatine (PCr), and 4.7% and 8.3%, respectively, for adenosine triphosphate (ATP). High‐energy phosphate (HEP) concentrations in mmol/kg wet weight were 9.7 ± 2.4 (age < 40 years, N = 16) and 7.7 ± 2.5 (age ≥ 40 years, N = 14) for PCr, and 5.1 ± 1.0 (age < 40 years) and 4.1 ± 0.8 (age ≥ 40 years) for ATP, respectively. Separated by gender, PCr concentrations of 9.2 ± 2.4 (men, N = 18) and 8.0 ± 2.8 (women, N = 12) and ATP concentrations of 4.9 ± 1.0 (men) and 4.2 ± 0.9 (women) were measured. A significant decrease of PCr and ATP was found for volunteers older than 40 years (P < 0.05), but the differences in metabolic concentrations between both sexes were not significant. In conclusion, age has a minor but still significant impact on cardiac energy metabolism, and no significant gender differences were detected. Magn Reson Med, 2006.

Myocardial Na+ content after infarction during scar development.

Cardiac sodium content can be measured by 23NaN M R techniques. Judd et al. [1] have recently shown that total sodium content increases several-fold immediately after myocardial infarction. However, changes of sodium content during scar development are unknown. I f 23Na-NMR imaging is suitable for discrimination of viable and non-viable myocardium, total Na + content of scar and intact myocardial tissue must be different. Thus, we investigated myocardial sodium content up to 4 weeks after myocardial infarction. scans, 8 min 27 s). Absolute concentrations were determined by comparing to a Na ÷ reference dissolved in 10 mM D y T T H A (shift reagent).

Use of 23Na MRS to discriminate viable from non viable tissue: experimental studies.

3. ConclusionIn experimental models, the use of23Na MRI is an appropriate tool for the determination of infarct size as well as extra- and intracellular23Na content. As stunned and hibernating myocardium show no increased23Na content, the method could be used for discrimination of viable from non-viable myocardium.