Biomedical subjects

K Straubinger

Publications and source records attributed to K Straubinger.

9 recordsLinked to original sources

PubMed2007

The Luebeck interview for psychosocial screening in patients with inflammatory bowel disease.

BACKGROUND: Psychosocial factors play an important role in the course of inflammatory bowel disease (IBD). However, a simple, valid psychosocial screening instrument that is suitable for short patient-physician contacts does not exist. Therefore, the Luebeck semistructured Interview for Psychosocial Screening was developed as a rating tool for psychosocial stress in IBD patients (LIPS-IBD). METHOD: The entire interview requires approximately 10 minutes. Interrater reliability was tested. Depression, anxiety, social support, impact of the disease, global level of psychosocial stress, and demand for psychosocial support were rated in 92 patients with IBD on 5 point Likert scales. Patients from the in- and out-patient clinic for gastroenterology were included. In addition, patients filled out self-report questionnaires regarding depression, anxiety, social support, and impact of the disease. Indices of disease activity (Colitis Activity Index, Crohn's Disease Activity Index) were recorded. RESULTS: Both patients and physicians found the interview feasible. Reliability was good, with interrater reliability ranging from .76 to .94. Convergence with self-report instruments was also high (r = .5-.6). Ratings of depression and impact of the disease were correlated with indices of disease activity. DISCUSSION: LIPS helps to identify patients with high levels of psychosocial stress and provide them with more detailed psychologic assessments. It was found to be a suitable instrument for daily clinical routine. It is potentially a valuable screening tool to obtain reliable, valid, and useful information in daily practice in IBD treatment settings.

Adult↗

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↗

PubMed1996

Phosphorus J coupling constants of ATP in human myocardium and calf muscle.

Proton-decoupled 31P NMR spectroscopy of the heart and calf muscle of healthy volunteers was performed with a 1.5 T whole-body imager. By use of two-dimensional chemical-shift imaging in combination with slice-selective excitation, well-resolved localized spectra (elements of 38 ml) were obtained within 20 to 35 min from which the homonuclear J coupling constants of ATP could be determined. In myocardium, J gamma beta = 16.03 +/- 0.17 Hz and J alpha beta = 15.82 +/- 0.23 Hz were obtained, while the values in calf muscle were J gamma beta = 17.16 +/- 0.12 Hz and J alpha beta = 16.04 +/- 0.09 Hz. The difference in J gamma beta was significant. According to the literature, a possible reason for greater ATP J coupling constants is a smaller fraction of ATP complexed to magnesium. However, the chemical-shift difference between alpha- and beta-ATP, which is also a measure for the fraction of ATP complexed to magnesium, showed only a small difference in ATP complexation: 88% in myocardium and 90% in calf muscle. This small difference cannot account for the observed difference in J gamma beta.

Adenosine Triphosphate↗

PubMed1996

Sequence parameters of double spin-echo sequences affect quantification of citrate.

Quantification of citrate by localized 1H spectroscopy is usually performed using the water signal as reference, but the signal behavior of the J-coupled AB spin system of citrate after multipulse excitation is not as trivial as for uncoupled substances. The influence of the timing scheme of double spin-echo sequences and of the spatial flip angle distribution of (nonideal) refocusing pulses was analyzed systematically for the citrate resonances. Both single echo times of the double spin-echo sequence were varied between 20 ms and 250 ms in theoretical and experimental approaches. Relatively long total echo times (TE > 120 ms) provide high selectivity to citrate signals, since signals from triglycerides at 2.6 ppm are markedly reduced. Asymmetrical timing schemes of the double spin-echo sequence with one short single echo time of 20 ms and one longer single echo time of about 120 ms result in high integral signal from the central lines of citrate, whereas symmetrical timing leads to high sensitivity for total echo times TE near 100 ms. The integral citrate signals in spectra with relatively long echo times (TE > 120 ms) were found to depend markedly on the type of the refocusing pulses, affecting quantitative citrate measurements in vitro and in vivo.

Citric Acid↗

PubMed1995

Computer-algebra calculations and measurements on AB spin systems for double-spin-echo sequences.

The time evolution of the density operator of an AB spin system during a double-spin-echo pulse sequence is evaluated analytically by a computer-algebra system. The computer-algebra system allows one to generate the extensive formulas describing the density operator and yields an expression for the integral of the spectral signals. The simulation of spectra for arbitrary sequence timings can be easily performed by this new tool without risking errors that might occur in conventional calculations. The computer-algebra method can be extended straightforward to other pulse angles and types of sequences. The double-spin-echo pulse sequence is used in the point-resolved spectroscopy (PRESS) method which is often applied for volume selective examinations in vivo. For verification of the results generated by the computer-algebra system, 1H spectra from a half-liter spherical sample with an aqueous solution that was 0.1 M in sodium citrate and 0.1 M in sodium acetate were recorded after 90 degrees-180 degrees-180 degrees double-spin-echo pulse sequences on a 1.5-T whole-body unit. The measured behavior of the citrate AB spin system corresponds very well with the theoretical predictions. Thus, the theory provides the basis for optimization of sequence timings for double-spin-echo measurements with high signal gain from AB systems as, for example, citrate. In addition, the theoretically predicted signal modulations could be fitted to the experimental data, providing the transverse relaxation time of the AB-coupled protons.

Computer Simulation↗

PubMed1994

Spin-echo methods for the determination of 31P transverse relaxation times of the ATP NMR signals in vivo.

31P magnetic resonance spectroscopy (MRS) examinations of the calf muscles of healthy volunteers were performed to determine T2 of the coupled ATP signals by use of the Hahn spin-echo and the frequency-selective spin-echo method. Additional measurements with the J-coupling refocused double echo are presented. The most reliable determination of T2 relaxation times is possible with the frequency-selective spin echo. The other methods yield substantially wrong results. Theoretical explanations are given how J-coupling and pulse-angle deviations affect the signals and therefore the T2 determinations. The calculations for a weakly coupled homonuclear AX spin system are shown because they demonstrate most of the relevant facts. In addition, some important results for a homonuclear AMX spin system, which the ATP is considered to be, are given.

Adenosine Triphosphate↗

PubMed1993

A pitfall associated with determination of transverse relaxation times of the 31P NMR signals of ATP using the Hahn spin-echo.

T2 measurements of 31P NMR signals of ATP using the Hahn 90 degrees-180 degrees spin-echo sequence imply difficulties whenever the 180 degrees pulse angle is not completely perfect. The reason for this finding is the crucial influence of the J-couplings of the ATP signals which result in intensity modulations and consequently in false T2 values even when the echo times are chosen to TE = n/J. Examinations on the calf muscles of healthy volunteers were performed to demonstrate this effect and its influence on in vivo T2 determinations. The T2 relaxation times evaluated with the Hahn spin-echo in combination with a Helmholtz coil are far shorter than the true T2 values.

Adenosine Triphosphate↗

PubMed1993

31P transverse relaxation times of ATP in human brain in vivo.

31P MRS examinations of the brain of 10 healthy volunteers were performed to determine T2 of the coupled ATP signals by use of the localized 90 degrees-TE/2-2662-TE/2-acq frequency selective spin echo sequence for elimination of phase and intensity distortions. The T2 relaxation times obtained are much longer than usually assumed: gamma-ATP: 89 +/- 9 ms; alpha-ATP: 84 +/- 6 ms; beta-ATP: 62 +/- 3 ms.

Adenosine Triphosphate↗

PubMed1992

31P transverse relaxation times of the ATP NMR signals of human skeletal muscle in vivo.

31P MRS examinations of the calf muscles of 12 healthy volunteers were performed to determine T2 of the coupled ATP signals by using the 90 degrees-TE/2-2662-TE/2-acq selective spin-echo sequence for elimination of phase and intensity distortions. The T2 relaxation times obtained are much longer than those usually assumed: gamma-ATP, 93 ms; alpha-ATP, 74 ms; beta-ATP, 75 ms.

Adenosine Triphosphate↗