[en] The purpose of this study was to evaluate in vivo the influence of inversion pulse slice selectivity on oxygen-enhanced magnetic resonance imaging (MRI). Thirteen healthy volunteers were studied with a two-dimensional cardiac- and respiratory-gated adiabatic inversion-recovery half-Fourier single-shot turbo spin-echo (HASTE) sequence with either slice-selective or non-slice-selective inversion recovery (IR) pulse at inversion times increasing from 300 to 1400 ms. The signal-to-noise ratio (SNR) at every inversion time (TI), real signal difference (ΔSI), and relative enhancement ratio of lung parenchyma at TI ≥800 ms were statistically compared for oxygen-enhanced and non-oxygen-enhanced MR images with slice-selective or non-slice-selective IR pulses. The SNRs of acquisitions with slice-selective IR pulses were significantly higher than those of non-sliceselective IR pulses (P<0.05). At TI 800 ms, the ΔSI of lung parenchyma on IR-HASTE images with slice-selective inversion pulse type was significantly higher than on that with the non-slice-selective type (P<0.05). Relative enhancement ratios of the slice-selective IR pulses were significantly lower than those of non-slice-selective IR pulses at TIs between 800 and 1400 ms (P<0.05). Slice selectivity of inversion pulse type affects oxygen-enhanced MRI in vivo. (author)

No abstract available

[en] Perfusion imaging in the central nervous system (CNS) is mostly performed using the first-pass dynamic susceptibility-weighted contrast-enhanced (DSC) MRI. The first-pass of a contrast bolus in brain tissue is monitored by a series of T2*-weighted MR images. The susceptibility effect of the paramagnetic contrast agent leads to a signal loss that can be converted, using the principles of the indicator dilution theory, into an increase of the contrast agent concentration. From these data, parameter maps of cerebral blood volume (CBV) and flow (CBF) can be derived. Regional CBF and CBV values can be obtained by region-of-interest analysis. This review article describes physical basics of DSC MRI and summarizes the literature of DSC MRI in neurooncological issues. Studies, all with relatively limited patient numbers, report that DSC MRI is useful in the preoperative diagnosis of gliomas, CNS-lymphomas, and solitary metastases, as well as in the differentiation of these neoplastic lesions from infections and tumor-like manifestations of demyelinating disease. Additionally, DSC MRI is suitable for determining glioma grade and regions of active tumor growth which should be the target of stereotactic biopsy. After therapy, DSC MRI helps better assessing the tumor response to therapy, residual tumor after therapy, and possible treatment failure and therapy-related complications, such as radiation necrosis. The preliminary results show that DSC MRI is a diagnostic tool depicting regional variations in microvasculature of normal and diseased brains. (orig.)

[en] The fission probabilities of ²³⁷U and ²³⁶Pa have been determined over the excitation energy range from the respective first to above the second chance fission thresholds using the ²³⁸U(d,tf) and ²³⁸U(d,αf) pickup reactions for the deuteron energy E_d = 24.85 MeV. (Author)

[en] Recently it has been shown that regional lung perfusion can be assessed using time-resolved contrast-enhanced magnetic resonance (MR) imaging. Quantification of the perfusion images has been attempted, based on definition of small regions of interest (ROIs). Use of complete lung segmentations instead of ROIs could possibly increase quantification accuracy. Due to the low signal-to-noise ratio, automatic segmentation algorithms cannot be applied. On the other hand, manual segmentation of the lung tissue is very time consuming and can become inaccurate, as the borders of the lung to adjacent tissues are not always clearly visible. We propose a new workflow for semi-automatic segmentation of the lung from additionally acquired morphological HASTE MR images. First the lung is delineated semi-automatically in the HASTE image. Next the HASTE image is automatically registered with the perfusion images. Finally, the transformation resulting from the registration is used to align the lung segmentation from the morphological dataset with the perfusion images. We evaluated rigid, affine and locally elastic transformations, suitable optimizers and different implementations of mutual information (MI) metrics to determine the best possible registration algorithm. We located the shortcomings of the registration procedure and under which conditions automatic registration will succeed or fail. Segmentation results were evaluated using overlap and distance measures. Integration of the new workflow reduces the time needed for post-processing of the data, simplifies the perfusion quantification and reduces interobserver variability in the segmentation process. In addition, the matched morphological data set can be used to identify morphologic changes as the source for the perfusion abnormalities

[en] The probability for non-radiative (n.r.) excitations in muonic ²⁰⁹Bi was determined from a (μ^-, γγ)-measurement by comparing the intensities of muonic X-ray transitions in single and coincidence spectra. The values of P_n.r.(3p→1s)=(17.9±2.0)% and P_n.r.(3d→1s)=(3.0±2.2)% were measured for the first time. The strength of the n.r. decay of the 2p-level was found to be (4.2±2.2)%. The n.r. transition probabilities of two subcomplexes of the (2p→1s)-transition leading to different mean excitation energies are (3.2±1.8)% and (5.0±2.0)%, respectively. (orig.)

[en] Purpose: Evaluation of lung perfusion by contrast-enhanced 3D MRI using partial parallel imaging techniques. Materials and Methods: Eight healthy volunteers were examined using a contrast-enhanced dynamic FLASH 3D sequence with partial parallel imaging technique at 1.5 T MRI with a TA of 1.5 sec. The whole lung was covered by 36 coronal slices. A ventral, middle and dorsal slice of each lung was manually segmented and signal-to-time curves were computed. For absolute quantification of blood flow through the right and left pulmonary artery, phase-contrast flow measurements were performed. Results: No significant difference was found between the signal intensity in the right (8.9±2.6) and left (8.0±3,5) lung, corresponding to a left-to-right signal intensity ratio of 0.9. A significantly higher signal intensity was found in the dorsal regions of the lungs (p=0.01) compared to the ventral regions. The time to peak of the signal intensity was significantly shorter in the dorsal (15.3 sec) and middle (15.7 sec) regions of the lungs (p=0.03 and p=0.04, respectively) than in the ventral regions (16.3 sec). The ratio between blood flow through the left (2.2 L/min) and right (2.7 L/min) lung was 0.84. Conclusion: Partial parallel image acquisition can assess the perfusion of the lungs at high temporal resolution. The perfusion is slightly higher on the right than on the left. The signal increases faster and has a higher peak in the dorsal lung regions. (orig.)

[en] The pionic X-ray of ¹⁸¹Ta, ^natRe, ^natPt, ¹⁹⁷Au, ²⁰⁸Pb, ²⁰⁹Bi and ²³⁷Np have been investigated to obtain data for a systematical study of the pionic 3d and 4f levels. In order to reduce background the experimental method has been improved by using an array of Compton suppression BGO-shields and neutron time-of-flight discrimination. The widths of the pionic 3d levels are observed to be narrower by a factor 1.5 than theoretical predictions obtained with standard optical potentials. A deviation is also found for the strong interaction quadrupole shift, ε₂, for both the 4f and 3d orbits. A possible explanation for the smaller width, Γ₀(3d), can be found by extending the parametrization of the optical potential with absorption terms. (orig.)

[en] The probability for delayed muon induced fission of ²⁰⁹Bi has been determined from a (μ^-, f₁f₂) measurement. The measured fission probability P_f=(4.2±0.7)x10^-5 is compared with theoretical predictions. The high fission threshold reaction seems well suited for studying the influence of two-body meson-exchange currents in nuclear muon capture. (orig.)

[en] Published in summary form only