Biomedical subjects

F Schick

Publications and source records attributed to F Schick.

At least 19 recordsLinked to original sources

PubMed1997

Highly selective water and fat imaging applying multislice sequences without sensitivity to B1 field inhomogeneities.

Improved selectivity to one chemical shift component was obtained using simultaneous slice-selective and chemical shift-selective excitation in sequences with usual spin-echo refocusing. The new type of sequences can be applied on modern whole-body units and permits multislice operation. Spatial-spectral excitation is based on prior research in this field, but the proposed improved version provides off-center slice excitation by the usual processing of the RF pulse envelopes. In addition, no irregular gradient shapes are necessary. The required B0 homogeneity of the new method is similar to conventional "fat-sat" techniques. In contrast to fat-sat methods, selectivity to water is not reduced by unavoidable misadjustments of the transmitter or B1 field inhomogeneities in the newly developed approach. Thus, the reported method has the potential to replace standard frequency selective fat-sat sequences for most applications.

Humans↗

PubMed1997

SPLICE: sub-second diffusion-sensitive MR imaging using a modified fast spin-echo acquisition mode.

Recent human studies for measuring of the apparent diffusion coefficient in tissue by magnetic resonance imaging have been conducted by time-consuming standard spin-echo acquisition sequences and phase correction with navigator echoes. Diffusion-weighted echo-planar sequences have been shown to be rapid alternatives for brain imaging. Both methods show inherent disadvantages in applications on thoracic or abdominal sites. A new approach combining single-shot diffusion-weighted imaging with a modified fast spin-echo acquisition mode is reported here. The modification is necessary, because normal fast spin-echo acquisition requires a particular phase relation between the magnetization and the refocusing pulses. Unfortunately, this phase relation is not provided after diffusion sensitive preparation. Therefore, the split echo acquisition mode was developed and is shown to be insensitive to the phase of the magnetization. The advantages of both fast spin-echo acquisition and diffusion weighting can be combined in the SPLICE sequence (split aqcuisition of fast spin-echo signals for diffusion imaging). The applicability of the new technique is shown by series of sub-second diffusion-weighted images from different parts of the body.

Adult↗

PubMed1997

Phase-contrast MR angiography for detection of arteriosclerotic renal artery stenosis.

PURPOSE: To compare the accuracy of 3-D phase-contrast (PC) MR imaging with a 2-D time-of-flight (TOF) technique in the detection of arteriosclerotic renal artery stenosis. MATERIAL AND METHODS: Twenty-two patients with 28 angiographically proven renal artery stenoses were examined in a prospective blinded fashion by using 2-D TOF MR angiography (MRA) with venous saturation (FLASH) and 3-D PC MRA. The renal arteries were subdivided into 3 segments and graded for the presence of stenoses on a scale of 0-4 by 3 radiologists in blind. RESULTS: The accuracy of TOF and PC imaging in detecting renal artery stenoses was 65% and 77% respectively. Both 2-D TOF and 3-D PC MRA depicted 84% of the stenoses of the proximal renal artery greater than 50% in diameter. Renal artery stenoses greater than 50% and more than 15 mm in distance from the aorta were detected in 40% of cases with the 2-D TOF sequence and in 76% with the 3-D PC technique (p < 0.05). The rate of false-negative results was 32%. CONCLUSION: PC MRA is better at visualizing stenoses in the middle segment of the renal arteries and supplements conventional TOF techniques with additional information. However, even when the two techniques are combined, the false-negative rate in the MR imaging of stenoses of the renal arteries still needs to be reduced.

Aged↗

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

Three-dimensional chemical shift-selective MRI of a ruptured intracranial dermoid cyst.

We report a man with a ruptured intracranial dermoid cyst, suffering from headache, nausea, vomiting and a generalised seizure. MRI was performed before and 2 weeks after surgical resection. On T1-weighted images the tumour gave high signal, as did fatty material in the frontal and parietal brain sulci. Identification of this hyper-intense material as lipids was possible by chemical-shift-selective 3D gradient-echo imaging, which provided excellent contrast between the subarachnoid lipids and the adjacent normal brain, with a good spatial resolution. Possible complications of subarachnoid and intraventricular lipid particles after dermoid cyst rupture are discussed and the diagnostic value of 3 D chemical-shift-selective additional to conventional T-1-weighted spin-echo images in identification of even small amounts of fat is emphasised.

Adult↗

PubMed1996

Assessment of the composition of bone marrow prior to and following autologous BMT and PBSCT by magnetic resonance.

Lumbar bone marrow was assessed by means of magnetic resonance (MR) in 23 examinations of eight patients who underwent autologous bone marrow transplantation (ABMT) or peripheral blood stem cell transplantation (PBSCT). Various imaging and spectroscopic techniques were applied for measurements carried out prior to conditioning for ABMT/PBSCT and in the course of reconstitution and correlated with clinical and blood chemistry data in these patients. The signal intensity from lumbar bone marrow was determined in T1-weighted and water- and fat-selective MR images. The distribution of the magnetic field was demonstrated by a field-mapping method. Localized proton spectroscopy was performed from volume elements of 2 ml located in the central region of vertebral bodies in order to evaluate the fraction of the water signals, the transverse relaxation times T2 of the signals from water and lipids, and the line widths of the spectral signals. Regions of bone marrow after inflammatory conditions or intensive irradiation are shown to be not involved in marrow reconstitution. Additional information about marrow composition was obtained by the magnetic field mapping and by the line widths in the spectra. Considerable alterations of the amount of paramagnetic hemosiderin were revealed following transplantation. Patients with low water signal and strong local inhomogeneities of the magnetic field in the marrow prior to transplantation had a delayed hematopoietic reconstitution compared with the patients lacking these MR features.

Adult↗

PubMed1996

Assessment of the magnetic field distribution in yellow and red bone marrow by the MAGSUS technique.

The MAGSUS imaging technique has been shown to provide insights into the distribution of the macroscopic and microscopic static magnetic field without requiring further data processing. Applications of the MAGSUS technique on bone marrow are reported in more detail in this article. Effects of the superposition of water and lipid signals and of considerable transverse relaxation on MAGSUS imaging are demonstrated, and adapted imaging parameters are presented. Examples of applications on marrow with different physiological and pathological compositions and different locations are shown. Appropriate adjustments for a reliable estimation of the trabecular density in peripheral yellow marrow and for an assessment of the field distribution in hemopoietic red marrow are reported. Osteoporotic peripheral marrow with reduced amount of trabecular structures and alterations due to osteodystrophia deformans can be simply revealed by this method. An estimation of the trabecular density can also be performed by MAGSUS in vertebral bodies of hematologically unaffected persons, but the interindividually differing amount of paramagnetic depositions in the marrow (e.g., hemosiderin) must be taken into account.

Adolescent↗

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↗

PubMed1996

Evaluation of K-space segmented cine sequences for fast functional cardiac imaging.

RATIONALE AND OBJECTIVES: In functional cardiac magnetic resonance imaging, reduction of measuring time is very important for many patients who are not able to rest motionless for long-lasting examinations. In this study, the image quality of sequences with k-space segmented data recording was compared with conventional gradient-echo sequences for cine imaging with flow compensation in applications on patients with normal and reduced ejection fractions. METHODS: Thirty-one subjects (4 volunteers and 27 patients with cardiac diseases) were examined using different techniques for cine imaging of the left and right ventricles. The ejection fraction in the patients was calculated based on images of a conventional two-dimensional gradient-echo technique using a biplane ellipsoid model. The results from k-space segmented methods (3 to 9 Fourier lines per cardiac cycle for each phase image) were compared with the conventional images of the same short-axis view separately for groups of subjects with normal and reduced ejection fraction. The contrast between blood and myocardium at several sites of the heart and the homogeneity of the blood signal in the ventricle were evaluated for several phases of the heart cycle. RESULTS: The segmentation in the acquisition of raw data allows reduction of measuring time to approximately 20% to 40% of the time required for conventional sequences in cine imaging of the heart. In patients with normal or only slightly reduced heart function (ejection fraction > or = 60%) the image quality of k-space segmented sequences was not significantly different from the conventionally recorded images. In contrast, patients with markedly lowered ejection fraction (< 60%) showed degraded results of the k-space segmented sequences compared with the conventional sequence (P < 0.001). The anterolateral border and the right ventricle especially were not sufficiently delineated by the k-space segmented sequences in these patients. CONCLUSION: The k-space segmentation for the reduction of examination time is suitable for measuring heart volumes and functional parameters of patients expected to have a nearly normal ejection fraction, whereas for patients with markedly reduced cardiac function further technical improvements of segmented techniques are necessary.

Adult↗

PubMed1996

Functional MR imaging of anomalies of the aorta.

Stenosis of a vessel is a well-known reason for increased resistance leading to lower flow rates. Other anomalies of the shape or additional blood influx are often considered to be less influential on flow dynamics inside the vessel. In this report, examples of irregular flow patterns in the human aorta are presented. The cases were selected from magnetic resonance examinations of 25 volunteers and more than 150 patients with dysfunctions of the heart or anomalies of the thoracic vessels. The protocol for magnetic resonance examinations included black blood imaging performed in the cine mode (with ECG triggering). Even minor modifications of the aortic shape are shown to result in marked disturbances of the laminar flow pattern in some patients. Effects of abnormal curvatures, additional blood influx, stenoses and dilatation of the aorta are demonstrated.

Adult↗

PubMed1995

Magnetization transfer in hemopoietic bone marrow examined by localized proton spectroscopy.

The sensitivity of hemopoietic bone marrow to magnetization transfer is analyzed in 15 healthy volunteers and seven patients with different hematological disorders (inflammation, plasmacytoma, hemopoietic reconstitution after bone marrow transplantation). To obtain sufficient signal-to-noise ratio, a 90 degrees - 180 degrees - 180 degrees double spin echo (PRESS) single voxel spectroscopic method was combined with pulsed magnetization transfer. Several spectra were recorded from each volume element inside the vertebral marrow, alternately with and without prepulses for magnetization transfer. Water signals from marrow with increased content of extracellular water due to inflammation or edema revealed less magnetization transfer effects than marrow with increased intracellular water content due to high cellularity. The preliminary results show magnetization transfer to be a promising tool for the clinically important characterization of the water composition in red bone marrow.

Adult↗

PubMed1995

The distribution of the magnetic field in the spine depends on the composition of bone marrow.

Although the composition of bone marrow with hemopoietic cells, fat cells, and extracellular fluid can be roughly assessed by standard MR-imaging techniques and especially water and lipid-selective chemical-shift-imaging methods, a new approach to the characterization of the magnetic properties of marrow was performed by special field-mapping techniques. The distribution of the magnetic field inside and outside vertebral bodies containing paramagnetic substances was systematically studied for phantoms and by measurements in vivo. Nineteen healthy volunteers and 26 patients with alterations of the bone marrow due to hematologic disease were examined. The amount of paramagnetic substances in the marrow was estimated by measuring steps of Larmor frequency of the water resonances at the transition between vertebral bodies and adjacent intervertebral disks. These frequency steps were exhibited by MAGSUS imaging on a 1.5 Tesla whole-body imager. Additional volume-localized 1H spectroscopy allowed a more quantitative assessment of the spectral components. The measured frequency steps of the water resonances ranged between 0 and 26 Hz for the healthy volunteers examined. In contrast, patients with pathologically altered marrow and high amount of paramagnetic substances revealed frequency steps of up to 85 Hz. The frequency steps in 8 patients after bone marrow transplantation (BMT) with slow reconstitution (mean 48.9 Hz, standard deviation (s.d.) 21.7 Hz) were significantly (p < 0.001) higher than in normal volunteers. Seven BMT patients with good reconstitution (frequency steps: mean 16.7 Hz, s.d. 13.9 Hz) were not clearly different from the healthy subjects. Six patients with acute leukemia showed significantly (p < 0.01) increasing frequency steps during initial cytotoxic treatment: The frequency steps increased from a mean of 4.7 Hz (s.d. 2.7 Hz) before treatment to a mean of 30.2 Hz (s.d. 14.6 Hz) after a few months of therapy.

Acute Disease↗

PubMed1995

Magnetic resonance imaging reveals a markedly inhomogeneous distribution of marrow cellularity in a patient with myelodysplasia.

A 47-year-old male patient with myelodysplasia showed increasing values of serum lactate dehydrogenase (up to 3500 units/l) and an increasing blast count. Several biopsies (taken from the posterior iliac crest) revealed marked hypocellularity. In contrast, magnetic resonance imaging of the marrow demonstrated an inhomogeneous distribution of marrow with hypocellular and also large hypercellular areas not detected by cytological and histological analysis. A location for biopsy of hypercellular marrow was provided by T1-weighted and water-selective magnetic resonance imaging. The findings in the patient were compared with those in a matched healthy volunteer.

Bone Marrow↗

PubMed1995

Magnetization transfer by simple sequences of rectangular pulses.

On-resonant radio frequency (RF) sequences composed of a train of short rectangular pulses of the same kind were optimized in order to obtain selective saturation of protons with short transverse relaxation times for magnetization transfer purposes. It is demonstrated that the sequences regarded allow a good adaptation to different requirements for magnetization transfer examinations on whole-body imagers. The sequences presented here provide relatively strong saturation of protons with very short transverse relaxation times T2 approximately less than 50 microseconds, whereas signals from protons with long T2 to be recorded are hardly influenced in a broad frequency range. The sequences are especially advantageous for applications in pulse files with limited numbers of support points.

Magnetic Resonance Imaging↗

PubMed1995

Adapted techniques for clinical MR imaging of tendons.

To determine whether the echo time of magnetic resonance gradient-echo and spin-echo imaging sequences may be important for the occurrence of high signal strength from tendon with pathological alterations, imaging sequences with sufficient spatial resolution and very short echo times were developed for whole-body imagers with standard gradient system. The sequences were applied on the Achilles tendons of five healthy volunteers and seven patients with achillodynia. Some affected regions inside tendon, probably corresponding with tissue with subtle edema in the collagen bundles were only revealed in images recorded with very short echo times TE < 5 ms, whereas stronger affections and protons in liquids between the fiber bundles were also shown in images with longer echo times TE > 10 ms. Gradient-echo methods allow shorter echo times than spin-echo techniques for a given gradient system of the imager and given spatial resolution. So minimum echo time gradient-echo sequences should be used for sensitive imaging of tendon alterations, because no considerable signal dephasing due to susceptibility effects were found in tendon.

Achilles Tendon↗

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↗

PubMed1995

Characterization of bone marrow after transplantation by means of magnetic resonance.

Magnetic resonance (MR) has become a new tool for noninvasive characterization of bone marrow in patients with hematological disorders in the past few years. Experiences gained from 1H MR imaging and spectroscopic investigations in 48 healthy volunteers and more than 130 patients with hematological disorders are reported and interpreted. Twenty-four of the patients underwent bone marrow transplantation (BMT) before the MR examinations. The findings in these studies provided noninvasive characterization and monitoring of vertebral marrow after BMT. Specifically, MR techniques were found to be suitable for studies of different aspects in physiological and pathological alterations of bone marrow: The water content within the marrow can be analyzed by chemical-shift selective-imaging techniques with good spatial resolution. Spectroscopic methods also allow more sensitive quantification of the signal fractions, as well as separate evaluation of the relaxation times of water and lipids. Relaxometry might be useful to characterize the cellular and extracellular portions of water molecules. Furthermore, the distribution of the magnetic field within small-volume elements of vertebral marrow can be measured. The field distribution is influenced by the trabecular density and the composition of the marrow. High amounts of hemosiderin in the marrow result in clearly broadened field distributions, demonstrated by increasing line widths in MR proton spectra. Magnetic resonance techniques can be used to assess not only the cellularity of the bone marrow, but also metabolic alterations in this compartment which result from cytotoxic treatment or immunological processes.

Bone Marrow↗

PubMed1995

Lactate quantification by means of press spectroscopy--influence of refocusing pulses and timing scheme.

The quantitative assessment of lactic acid in tissue is an important goal for in vivo volume-selective NMR spectroscopy to aid in the noninvasive diagnosis of oxygen deficiency of other metabolic disorders. PRESS localized 1H spectra provide comparatively high signal-to-noise ratio from small volume elements in a single acquisition mode. The quantification of lactate after multipulse excitation is not trivial due to the J-coupling characteristics which do not occur for the substances serving as references. The influence of the timing scheme and of the quality of the refocusing pulses was systematically evaluated for the lactate resonances by volume-selective measurements. Gaussian pulses, Hanning-filtered sinc pulses, and numerically optimized RE-BURP-pulses were applied for refocusing the magnetization in the PRESS sequence and the effects on the lactate AX3 spin system were compared. For these pulses, sequence parameters are presented providing high sensitivity to lactate signals. Timing schemes are shown which provide good quantification of lactate, even in cases with B1-inhomogeneities or slight misadjustment of the transmitter amplitude. The combination of both echo times in the double-echo sequences clearly influences the signal characteristics of lactate at overall echo times near TE = 145 and 290 ms, which may result in pure in-phase magnetization for this weakly coupled homonuclear system. Numerically optimized refocusing pulses (RE-BURP) provided up to 50% higher signal ratio of the methyl protons of lactate to uncoupled nuclei than the often used Hanning-filtered sinc pulses.

Acetates↗