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O Lutz

Publications and source records attributed to O Lutz.

At least 19 recordsLinked to original sources
PubMed2001

Osteodensitometry of human heel bones by MR spin-echo imaging: comparison with MR gradient-echo imaging and quantitative computed tomography.

The aim of the study was to investigate whether quantitative magnetic resonance (MR) fast spin-echo (FSE) imaging with moderate spatial resolution enables osteodensitometry in peripheral yellow bone marrow. Signal intensities in T1-weighted FSE images from yellow bone marrow indicate the amount of adipose tissue per volume. The signal intensity in marrow regions with spongy bone was assessed and compared to signal intensity of pure fatty marrow (100%). Heel bones of 30 patients with suspected osteoporosis were analyzed and the FSE images were compared with results from parallel MR gradient-echo (GE) imaging and quantitative computed tomography (QCT) examinations. High correlation was found between FSE imaging and QCT [r = 0.91 in the dorsal region of interest (ROI); r = 0.86 in ventral ROI]. Linear correlation coefficients between GE imaging and QCT were slightly lower in the dorsal part (r = -0.86) and considerably lower in the ventral part (r = -0.68). Correlation between the two MR techniques amounted to r = -0.72/-0.61 (dorsal/ventral). The high correlation between FSE imaging and bone mineral density (BMD) allows possible clinical applications of FSE imaging for diagnosis of osteoporosis. Further improvements of the accuracy using reference phantoms might be possible.

Adult↗
PubMed2001

Reliable detection of macromolecules in single-volume 1H NMR spectra of the human brain.

In short echo time proton MR spectra of the brain, resonances from macromolecules are visible. The macromolecular resonances in the 0.5-2.0 ppm region can be affected by lipid contamination arising from fat-containing regions outside the selected volume of interest (VOI). This study demonstrates that considerable lipid contamination may remain in stimulated echo acquisition mode (STEAM) spectra even if the spoiling of unwanted coherences is sufficient and the VOI is placed 2 cm or more away from fat-containing regions. The observed contamination was attributed to residual remote out-of-volume excitation, although only very small out-of-slice ripples of less than 0.2% of the in-slice excitation were found in the calculated excitation profile of the RF pulses. Spatial presaturation of fat-containing regions led to a sufficient suppression of the contamination and enabled the detection of highly reproducible macromolecular resonances. Thus, in single-volume spectroscopy as well as in spectroscopic imaging (SI or CSI), the combination of volume selection and outer volume presaturation, each in three dimensions, is highly recommended to ensure accurate detection and reliable evaluation of even small pathological alterations in macromolecules, e.g., proteins or lipids, or other resonances in the 0.5-2.0 ppm region.

Artifacts↗
PubMed2001

Quantitative evaluation of the lactate signal loss and its spatial dependence in press localized (1)H NMR spectroscopy.

Localized (1)H NMR spectroscopy using the 90 degrees -t(1)-180 degrees -t(1)+t(2)-180 degrees -t(2)-Acq. PRESS sequence can lead to a signal loss for the lactate doublet compared with signals from uncoupled nuclei which is dependent on the choice of t(1) and t(2). The most striking signal loss of up to 78% of the total signal occurs with the symmetrical PRESS sequence (t(1)=t(2)) at an echo time of 2/J (approximately 290 ms). Calculations have shown that this signal loss is related to the pulse angle distributions produced by the two refocusing pulses which leads to the creation of single quantum polarization transfer (PT) as well as to not directly observable states (NDOS) of the lactate AX(3) spin system: zero- and multiple-quantum coherences, and longitudinal spin orders. In addition, the chemical shift dependent voxel displacement (VOD) leads to further signal loss. By calculating the density operator for various of the echo times TE=n/J, n=1, 2, 3,..., we calculated quantitatively the contributions of these effects to the signal loss as well as their spatial distribution. A maximum signal loss of 75% can be expected from theory for the symmetrical PRESS sequence and TE=2/J for Hamming filtered sinc pulses, whereby 47% are due to the creation of NDOS and up to 28% arise from PT. Taking also the VOD effect into account (2 mT/m slice selection gradients, 20-mm slices) leads to 54% signal loss from NDOS and up to 24% from PT, leading to a maximum signal loss of 78%. Using RE-BURP pulses with their more rectangular pulse angle distributions reduces the maximum signal loss to 44%. Experiments at 1.5 T using a lactate solution demonstrated a maximum lactate signal loss for sinc pulses of 82% (52% NDOS, 30% PT) at TE=290 ms using the symmetrical PRESS sequence. The great signal loss and its spatial distribution is of importance for investigations using a symmetrical PRESS sequence at TE=2/J.

Acetic Acid↗
PubMed2001

Unveiling extracellular inorganic phosphate signals from blood in human cardiac 31P NMR spectra.

31P NMR spectra of the human heart are usually contaminated by signals that originate from blood. The main blood signals are 2,3-diphosphoglycerate (2,3-DPG), which overlap and sometimes obscure the signal of myocardial inorganic phosphate used to calculate intracellular pH and to monitor metabolic changes in the heart. In this work we demonstrate, first, that even without proton decoupling the resolution of such spectra can be high enough to evaluate intracellular inorganic phosphate of myocardium in about 70% of the spectra and, second, that extracellular inorganic phosphate from blood contributes a signal in the chemical shift region of the 2-phosphate signal of 2,3-DPG.

2,3-Diphosphoglycerate↗
PubMed2001

Fast acceleration-encoded magnetic resonance imaging.

Direct acceleration imaging with high spatial resolution was implemented and tested. The well-known principle of phase encoding motion components was applied. Suitable gradient switching provides a signal phase shift proportional to the acceleration perpendicular to the slice in the first scan of the sequences. An additional scan serving as a reference was recorded for compensation of phase effects due to magnetic field inhomogeneities. The first scan compensated for phase shifts from undesired first- and second-order motions; the second scan was completely insensitive to velocity and acceleration in all directions. Advantages of the proposed two-step technique compared to former approaches with Fourier acceleration encoding (with several phase encoding steps) are relatively short echo times and short total measuring times. On the other hand, the new approach does not allow us to assess the velocity or acceleration spectrum simultaneously. The capabilities of the sequences were tested on a modern 1.5 T whole body MR unit providing relatively high gradient amplitudes (25 mT/m) and short rise times (600 micros to maximum amplitude). The results from a mechanical acceleration phantom showed a standard deviation of 0.3 m/s2 in sequences with an acceleration range between -12 and 12 m/s2. This range covers the expected maximum acceleration in the human aorta of 10 m/s2. Further tests were performed on a stenosis phantom with a variable volume flow rate to assess the flow characteristics and possible displacement artifacts of the sequences. Preliminary examinations of volunteers demonstrate the potential applicability of the technique in vivo.

Acceleration↗
PubMed2000

Artifacts in CSI-measurements caused by the drift of the static magnetic field.

In chemical shift resolved spectroscopic imaging (CSI) temporal changes in the static magnetic field (drift) can lead to distortions of the phase encoding process. This can result in localization artifacts. The extent of the artifact depends on the size of the drift, the number of acquisitions, as well as on the combination of the size of the field of view and the number of phase encoding gradient steps. Furthermore, it is affected by the succession of the phase encoding gradients. Precautions are described which allow substantial minimization of the artifact.

Humans↗
PubMed2000

An interleaved sampling strategy for MR spectroscopy in vivo: applications on human calf musculature.

Assessment of relaxation times, magnetization transfer rates, or apparent diffusion coefficients by volume selective (1)H MR spectroscopy requires data from several single spectra with variable sequence parameters. Unintentional movements during the examination lead to inaccuracies, especially if the spatial distribution of concentrations is inhomogeneous. Improved comparability of the single spectra in a series recorded in vivo were obtained using a modified spectroscopic technique with INTerleaved ACquisiTion of multiple SPECtra (INTACTSPEC). INTACTSPEC series of spectra from the tibialis anterior muscle (m. tib. ant.), soleus muscle (m. soleus), and tibial bone marrow of 20 healthy volunteers were analyzed. Transverse relaxation times T(2) of methylene signals in muscular lipid stores ranged from 77 ms (intramyocellular methylene component in m. tib. ant.) to 88 ms (intramyocellular methylene component in m. soleus) and were similar to those from yellow tibial bone marrow (T(2) = 84 ms). Echo time-dependent signal intensities of choline and creatine deviated markedly from a monoexponential behavior in m. tib. ant., but were nearly exponential in m. soleus. Results from water diffusion measurements parallel and perpendicular to the axis of the lower leg showed significant differences between m. tib. ant. and m. soleus, probably due to the spatial orientation of the muscle fibers. Apparent diffusion coefficients along the leg axis were found to be higher in m. tib. ant. (2.10 +/- 0.08 x 10(-3) mm(2)/s) compared to m. soleus (1.78 +/- 0.11 x 10(-3) mm(2)/s), but m. soleus showed less restricted diffusion in perpendicular orientation (1.59 +/- 0.19 x 10(-3) mm(2)/s versus 1.20 +/- 0.08 x 10(-3) mm(2)/s in m. tib. ant.). Magnetization transfer experiments with various RF preparation pulse amplitudes led to very similar results for m. tib. ant. and m. soleus.

Adult↗
PubMed2000

Magnetic resonance osteodensitometry in human heel bones: correlation with quantitative computed tomography using different measuring parameters.

RATIONALE AND OBJECTIVES: Density of trabecular bone structures in human heel bones was assessed by 3D magnetic resonance (MR) gradient echo imaging (GEI) with multiple echoes. Different spatial resolutions were applied to investigate the influence of the pixel size on signal characteristics in GEI and to find suitable measuring parameters for a maximum correlation between GEI and bone mineral density obtained by quantitative computed tomography (QCT). METHODS: Thirty-five patients aged 31 to 65 years with suspected osteoporosis underwent MR and QCT examinations of the heel bones. The MR protocol included 3D GEI with three echo times (TE1 = 9.3, TE2 = 27.9, and TE3 = 46.5 ms) and isotropic pixel sizes of (0.6 mm)3, (1.2 mm)3, and (2.4 mm)3. Several subregions in the heel bones were analyzed. For determination of signal reduction with increasing TE, signal intensity ratios were calculated pixelwise from images with TE2/TE1 and TE3/TE1. RESULTS: All examinations showed that the T2*-related signal decrease was more pronounced for lower spatial resolution. In the dorsal part of the heel bones, the correlation between signal ratios in GEI and QCT-based bone mineral density values was between r = -0.86 for a spatial resolution of (0.6 mm)3 and r = -0.73 for (2.4 mm)3. Areas with low trabecular density in the ventral part of the heel bones showed clearly lower correlation coefficients (-0.65 < r < -0.67). CONCLUSIONS: Spatial resolution in 3D GEI clearly influences the T2*-related signal characteristics. Despite measuring different physical properties of spongy bone by GEI and QCT, a relatively high correlation between GEI with small pixel sizes and QCT was obtained in the dorsal part of the heel bones, but not in the ventral part with partly thickened trabeculae and irregular distribution. However, standardized measuring protocols with preferably small pixel sizes (as low as [0.6 mm]3) should be applied, and correlation curves must be determined, dependent on the actual bone marrow site, before clinical routine MR osteodensitometry becomes possible.

Absorptiometry, Photon↗
PubMed1999

Potential pitfall in the determination of free [Mg2+] by 31P NMR when using the beta/alpha-ATP peak height ratio method.

Recently, Clarke et al. (Clarke K, Kashiwaya Y, King MT, Gates D, Keon CA, Cross HR, Radda GK, Veech RL. The beta/alpha peak height ratio of ATP. A measure of free [Mg2+(free)] using 31P NMR, J. Biol. Chem. 1996;271:21142 21150.) reported a new method to noninvasively determine the concentration of intracellular free magnesium ([Mg2+(free)]) based on the measurement of the peak height ratio h(beta/alpha) of the beta- and alpha-ATP signals in 31P NMR spectra. h(beta/alpha) varies with [Mg2+(free)], however, the study presented here shows that h(beta/alpha) also strongly depends on the homogeneity of the static magnetic field. For this reason, we performed at a magnetic field strength of 1.5 T 31P NMR measurements of solutions that mimic intracellular medium. The magnetic field homogeneity was varied by changing the currents in the shim coils, and the effect on hbeta/alpha is demonstrated with and without proton decoupling. In both cases, h(beta/alpha) strongly depends on the magnetic field homogeneity and can therefore lead to a pitfall in the determination of [Mg2+(free)].

Adenosine Triphosphate↗
PubMed1999

Elimination of residual lipid contamination in single volume proton MR spectra of human brain.

Short echo time 1H NMR spectra of the human brain reveal signals from various metabolites. In addition, resonances from macromolecules are present that may provide further useful information in several brain diseases. The detection of all these signals is possible if excellent volume selection is obtained; even small lipid contamination from surrounding fat tissue leads to strong spectral contamination. It affects the macromolecule resonances in the 0.5 to 2.0 ppm region and some adjacent metabolite signals and jeopardizes their quantitative analysis. This paper demonstrates how spatial contamination from insufficiently dephased signals can be recognized, analysed, and removed in localized STEAM spectroscopy of the brain.

Adipose Tissue↗
PubMed1998

31P NMR spectroscopy detects metabolic abnormalities in asymptomatic patients with hypertrophic cardiomyopathy.

BACKGROUND: Hypertrophic cardiomyopathy (HCM) often causes sudden, unexpected death in adolescents and young adults. Alterations in myocardial metabolism are considered to be causes for contractile dysfunction. We examined the question of whether metabolic abnormalities antedate the manifestation of symptoms in patients with HCM. METHODS AND RESULTS: Proton-decoupled 31P NMR spectroscopy of the anterior left ventricular wall of the heart of 14 young, asymptomatic patients with HCM was performed with a 1.5-T whole-body imager. Spectra of the phosphate metabolites were compared with those of normal control subjects. The patients exhibited a significantly reduced (P<0.02) ratio of phosphocreatine (PCr) to ATP of 1.98+/-0.37 (mean+/-SD), compared with 2.46+/-0.53 obtained in 11 normal control subjects. In addition, the group of patients with severe hypertrophy of the interventricular septum (n=8) showed a significantly increased (P<0.05) Pi-to-PCr ratio, with a Pi x 100/PCr of 20.0+/-8.3 versus 9.7+/-7.2 in control subjects. Both abnormalities are similar to those found in ischemic myocardium. This view is also supported by a significantly increased (P<0.01) phosphomonoester (PME)-to-PCr ratio, with a PME x 100/PCr of 20.7+/-11.2 compared with 8.4+/-6.7 in control subjects, indicating altered glucose metabolism. CONCLUSIONS: 31P NMR spectroscopy detects alterations of myocardial metabolism in asymptomatic patients with HCM. These alterations may contribute to the understanding of the pathophysiology and natural history of the disease.

Adolescent↗
PubMed1998

Detection of phosphomonoester signals in proton-decoupled 31P NMR spectra of the myocardium of patients with myocardial hypertrophy.

Proton-decoupled 31P NMR spectroscopy at 1.5 T of the anterior left ventricular myocardium was used to monitor myocardial phosphate metabolism in asymptomatic patients with hypertrophic cardiomyopathy (HCM, n = 14) and aortic stenosis (AS, n = 12). In addition to the well-known phosphorus signals a phosphomonoester (PME) signal was detected at about 6.9 ppm in 7 HCM and 2 AS patients. This signal was not observed in the spectra of normal controls (n = 11). We suggest that in spectra of patients with myocardial hypertrophy the presence of a PME signal reflects alterations in myocardial glucose metabolism.

2,3-Diphosphoglycerate↗
PubMed1998

Influence of pulse angle variations on stimulated echo acquisition mode proton nuclear magnetic resonance spectra of AB spin systems: theory and experiments with citrate.

The influence of pulse angle variations in the localization sequence stimulated echo acquisition mode (STEAM) on the signal of strongly coupled AB spin systems has been examined. Experimental 1H nuclear magnetic resonance (NMR) spectra of citrate were recorded on a 1.5 T whole-body imager. Theoretically calculated spectra were generated, with good correlation to experimental results. The dependence of the signal intensity on sequence timing and pulse angles was calculated analytically. For longer sequence timings, the ratio of the signal intensity from citrate to the signal intensity from uncoupled nuclei depends strongly on the applied flip angles. The shape of spectra also changes with varying flip angles. These effects are clearly less pronounced for STEAM than for point resolved spectroscopy (PRESS). The results have to be considered for quantitative measurements of citrate in spectroscopic investigations as, e.g. of prostate neoplasms.

Acetic Acid↗
PubMed1998

Proton spectroscopy of human brain with very short echo time using high gradient amplitudes.

In localized proton magnetic resonance spectroscopy very short echo times (TE) are achieved to diminish signal loss due to T2 relaxation and to avoid phase distortions due to J-coupling. A sequence for single volume spectroscopy in human brain is described with a TE as low as 5 ms. Examinations were performed on a 1.5 T whole-body imager with actively shielded gradients. A self-designed stimulated echo acquisition mode (STEAM) sequence with very high amplitude spoiling gradients of 24 mT/m was used to take advantage of the whole potential of the gradient system. Optimization of TE was carried out by controlling spectral quality and localization in both phantom and volunteer measurements. Proton spectra of human brain were acquired in 21 healthy volunteers. Spectra of occipital white matter, parieto-occipital grey/white matter, and cerebellum revealed none or only small eddy current distortions at a TE of 5 ms. The volume of interest was 8-12 ml, repetition time was 1.5 s, and mixing time was 5 ms. Peak ratios of major metabolites referring to creatine were estimated and the relative standard deviations were calculated to determine interindividual reproducibility. The relative standard deviation of myo-inositol ranged from 6% to 11% within these brain regions whereas for glutamine and glutamate 7% to 16% were found.

Adult↗
PubMed1998

31P/1H WALTZ-4 broadband decoupling at 1.5 T: different versions of the composite pulse and consequences when using a surface coil.

Two derivatives of the wideband alternating-phase low-power technique for zero-residual splitting (WALTZ)-4 decoupling sequence for broadband decoupling named WALTZ-4a and WALTZ-4b were compared for their proton decoupling performance in 31P nuclear magnetic resonance (NMR) spectroscopy using a Siemens Magnetom SP 1.5 T whole-body imager. Version WALTZ-4a originally implemented by the manufacturer doubles and triples the transmitter amplitude of the 90 degrees pulse to achieve the 180 degrees and 270 degrees flip angle required for one composite pulse R in the WALTZ sequence. WALTZ-4b follows the sequence reported from Shaka et al. and leaves the transmitter amplitude constant but increases the durations of the 180 degrees and 270 degrees pulses. The decoupling performance of WALTZ-4b is superior because it requires less transmitter power and, therefore, it is advantageous in all in vivo studies where a low specific absorption rate is desired. When WALTZ-4 is used in combination with a surface coil for transmission the theoretically required flip angles cannot be achieved in the entire sensitive volume of the coil. The decoupling performance was therefore investigated at lower and higher flip angles. Again, WALTZ-4b is advantageous and provides, in certain ranges that are off-resonant from the decoupling frequency, a good decoupling quality even for flip angles that are only 60% of the theoretically required.

Adenosine Triphosphate↗
PubMed1998

High-resolution cardiac imaging using an interleaved 3D double slab technique.

A three-dimensional (3D) gradient-echo sequence with interleaved double-slab excitation was developed and optimized for the requirements in pediatric cardiac imaging. For this purpose high contrast between blood and myocardium signal should be obtained without the use of contrast agents. An acceptable measuring time for a large region examined with high spatial resolution should be achieved as well, especially with regard to the small structures of the heart and vessels of infants. The presented approach works with gradient moment nulling and a short echo time of 5.5 ms resulting in generally high signal intensity and only minor signal losses due to turbulent flow. The sequence allows simultaneous ECG-gated recording of two separately excited slabs with small thickness (10 mm) and with a distance of several centimeters between them. Thus, common effects of presaturation in 3D imaging can be avoided, although a relatively short measuring time is achievable. In order to get a 3D data set with good signal homogeneity of blood and of the other structures across a large volume of interest several double-slab measurements with suitable positions must be performed. The latter aspect is especially important for postprocessing techniques as multiple planar reconstruction and maximum intensity projection. Examples of applications of the new technique and appropriately postprocessed images are presented allowing demonstration even of subtle cardiac malformations.

Artifacts↗