New evidence for a subshell gap at N = 32

Abstract An 879.9(2) keV γ -ray transition has been identified following the β decay of 58 V and assigned as the 2 58 Cr 34 . A peak in the energies of the first excited 2 + states for the even-even chromium isotopes is now evident at 56 Cr 32 , providing empirical evidence for a significant subshell gap at N = 32. The appearance of this neutron subshell closure for neutron-rich nuclides may be attributed to the diminished π1f 7/2 -ν1f 5/2 monopole proton-neutron interaction as protons are removed from the 1f 7/2 single-particle orbital. 2001 Elsevier Science B.V. All rights reserved. PACS: 21.60.Cs; 23.20.Lv; 27.40.+z Trends in nuclear masses and binding energies have suggested nuclei associated with nucleon numbers expected to be maximum at midshell. However, the development of collectivity away from major closed shells may be inhibited by the presence of subshell closures, or minor shell gaps. In order to study such phenomena, experimental probes of quadrupole collectivity may be utilized. One measure of the extent of quadrupole collectivity in even-even nuclear systems is the energy of the first excited 2 + state, E(2 + 1 ). According to Grodzins [2

Hybrid MR-PET of brain tumours using amino acid PET and chemical exchange saturation transfer MRI

PURPOSE: PET using radiolabelled amino acids has become a promising tool in the diagnostics of gliomas and brain metastasis. Currently, amide proton transfer (APT) chemical exchange saturation transfer (CEST) MR imaging is evaluated for brain tumour imaging. In this hybrid MR-PET study, we compared in brain tumours with 3D data derived from APT-CEST MRI and amino acid PET using O-(2-18F-fluoroethyl)-L-tyrosine (18F-FET). METHODS: Eight patients with gliomas were investigated simultaneously with 18F-FET PET and APT-CEST MRI using a 3T MR-BrainPET scanner. CEST imaging was based on a steady-state approach using a B1 average power of 1μT. B0 field inhomogeneities were corrected and parametric images of magnetisation transfer ratio asymmetry (MTRasym) and differences to the extrapolated semi-solid magnetisation transfer reference method, APT# and nuclear Overhauser effect (NOE#), were calculated. Statistical analysis of the tumour-to-brain ratio of the CEST data was performed against PET data using the non-parametric Wilcoxon test. RESULTS: A tumour-to-brain ratio derived from APT# and 18F-FET presented no significant differences and no correlation was found between APT# and 18F-FET PET data. Distance between local hot spots APT# and 18F-FET were different (average 20 ± 13 mm, range 4 - 45 mm). CONCLUSION: For the first time CEST images were compared with 18F-FET in a simultaneous MR-PET measurement. Imaging findings derived from18F-FET PET and APT CEST MRI seems to provide different biological information. The validation of imaging findings by histological confirmation is necessary, ideally using stereotactic biopsy

Targeting murine heart and brain: visualisation conditions for multi-pinhole SPECT with 99mTc- and 123I-labelled probes

The study serves to optimise conditions for multi-pinhole SPECT small animal imaging of (123)I- and (99m)Tc-labelled radiopharmaceuticals with different distributions in murine heart and brain and to investigate detection and dose range thresholds for verification of differences in tracer uptake.A Triad 88/Trionix system with three 6-pinhole collimators was used for investigation of dose requirements for imaging of the dopamine D(2) receptor ligand [(123)I]IBZM and the cerebral perfusion tracer [(99m)Tc]HMPAO (1.2-0.4 MBq/g body weight) in healthy mice. The fatty acid [(123)I]IPPA (0.94 +/- 0.05 MBq/g body weight) and the perfusion tracer [(99m)Tc]sestamibi (3.8 +/- 0.45 MBq/g body weight) were applied to cardiomyopathic mice overexpressing the prostaglandin EP(3) receptor.In vivo imaging and in vitro data revealed 45 kBq total cerebral uptake and 201 kBq cardiac uptake as thresholds for visualisation of striatal [(123)I]IBZM and of cardiac [(99m)Tc]sestamibi using 100 and 150 s acquisition time, respectively. Alterations of maximal cerebral uptake of [(123)I]IBZM by >20% (116 kBq) were verified with the prerequisite of 50% striatal of total uptake. The labelling with [(99m)Tc]sestamibi revealed a 30% lower uptake in cardiomyopathic hearts compared to wild types. [(123)I]IPPA uptake could be visualised at activity doses of 0.8 MBq/g body weight.Multi-pinhole SPECT enables detection of alterations of the cerebral uptake of (123)I- and (99m)Tc-labelled tracers in an appropriate dose range in murine models targeting physiological processes in brain and heart. The thresholds of detection for differences in the tracer uptake determined under the conditions of our experiments well reflect distinctions in molar activity and uptake characteristics of the tracers

CHAPTER 4. Ultra-high Field Imaging

MR spectroscopy (MRS) reveals information about the molecular structures underlying the MR signal. Properties such as chemical shift and scalar coupling cause a characteristic splitting of the resonance frequencies and following the numerical fitting of the acquired data to the corresponding basis spectra, these shifts can be used to distinguish different kinds of molecules. For in vivo applications, spatial localisation techniques for signal acquisition, such as STEAM or PRESS, and water signal suppression, i.e. CHESS or MEGA, are required. Using non-proton nuclei as target nuclei allows MRI to investigate in vivo metabolic processes and pathology non-invasively. These so-called X-nuclei impose increased technological and methodological demands, as the sensitivity and abundance are significantly lower compared to protons and their spin dynamics might be more sophisticated and complex. Nevertheless, the potential benefit of acquiring such data is tremendous both clinically and in research. The most prominent X-nuclei in vivo are 2H, 7Li, 13C, 17O, 19F, 23Na, 31P, 35Cl and 39K and a subset are discussed here. One of the applications that constitutes a ‘perfect fit’ for ultra-high field imaging is the depiction of brain anatomy. The usual challenges of ultra-high field imaging pertain but once overcome anatomical imaging of the brain is able to produce in vivo images with unprecedented resolution and contrast. The chapter concludes with a brief excursion into ‘emerging applications’ and includes phase and susceptibility imaging, quantitative susceptibility imaging and CEST-based imaging at ultra-high field

Challenge by the murine brain: Multi-pinhole SPECT of 123I-labelled pharmaceuticals

This protocol presents an improved method for SPECT imaging based on multi-pinhole techniques, applied to the visualisation of neurotracers in small animal models. Three types of collimators with 6-pinhole apertures adapted to special requirements for the imaging of the brain of mice and rats and to full body imaging in mice are employed in the experiments. A conventional triple-headed TRIAD/Trionix SPECT system was upgraded with pyramidal supports and shieldings onto the multi-pinhole collimators were installed. The system was employed for the assessment of the uptake of [123I]FP-CIT and [123I]IBZM, well known tracers of dopamine transport and dopamine D2/D3 receptors, respectively. Requirements regarding the applied radioactivity are reported, as well as further conditions determining the effectiveness of the detection of the uptake of [123I]FP-CIT and [123I]IBZM. The measurements in mice required only 20-25% of the activity described in previous studies. Dynamic measurements are presented, with a time resolution as high as 10 min in the brain of rats. Due to the lower signal intensity obtained for mice, the time resolution was 42min for [123I]FP-CIT, with a ratio ROI/background of 5.4, and 17 min for [123I]IBZM, with the ratio ROI/background of 4.5 (1.6-7.4)

Magnetic field dependence of the distribution of NMR relaxation times in the living human brain

This study investigates the field dependence of the distribution of in vivo, whole-brain T1 values, and its usefulness for white matter/grey matter segmentation. Results on T1 values are presented on 12 healthy volunteers. T2 and T2* distributions and their field dependence have been measured on the same cohort of volunteers. In this paper, however, only the T2 and T2* results on a single volunteer are presented. The reported field dependence of T2 and T2* values should, therefore, be given less weight than that of T1 times.Relaxation times were measured in vivo on 12 healthy volunteers, using three nearly identical whole-body scanners, operating at field strengths of 1.5, 3, and 4 T and employing nearly identical software platforms and very similar hardware. T1 mapping was performed using TAPIR, a sequence based on the Look-Locker method. T2* mapping was performed with a multi-slice, multi-echo, gradient echo sequence. A multi-slice, multi-echo T2 mapping sequence based on the Carr-Purcell-Meiboom-Gill (CPMG) method was used to map T2. For each volunteer, the global distribution of T1 relaxation times was described as the superposition of three Gaussian distributions. The field and age-dependence of the centroids and widths of the three Gaussians was investigated. The segmentation of the brain in white and grey matter was performed separately for each field strength. Using the T1 segmentation and the fact that all maps were coregistered, we investigated the distribution of T2 and T*(2) values separately for the white and grey matter and described them with a Gaussian distribution in each case.Multi-slice quantitative maps were produced for the relaxation parameters T1 (near whole-brain coverage with 41 slices), T2* (whole-brain coverage, 55 slices), and T2 (27 slices). A clear age dependence was identified for grey matter T1 values and correlated with similar behaviour observed in a separate study of the brain water content. The increase with field strength of the bulk white and grey matter T1 values was well reproduced by both Bottomley's [1] and Fischer's [2] formulae, with parameters taken from the literature. The separation between the centroids was, however, either overestimated or underestimated by the two formulae. The width of the T1 distributions was found to increase with increasing field.The study of the field dependence of the NMR relaxation times is expected to allow for better differentiation between regions which are structurally different, provide a better insight into the microscopic structure of the brain and the molecular substrate of its function

Quality-based UnwRap of SUbdivided Large Arrays (URSULA) for high-resolution MRI data

In Magnetic Resonance Imaging, mapping of the static magnetic field and the magnetic susceptibility is based on multidimensional phase measurements. Phase data are ambiguous and have to be unwrapped to their true range in order to exhibit a correct representation of underlying features. High-resolution imaging at ultra-high fields, where susceptibility and phase contrast are natural tools, can generate large datasets, which tend to dramatically increase computing time demands for spatial unwrapping algorithms. This article describes a novel method, URSULA, which introduces an artificial volume compartmentalisation that allows large-scale unwrapping problems to be broken down, making URSULA ideally suited for computational parallelisation. In the presented study, URSULA is illustrated with a quality-guided unwrapping approach. Validation is performed on numerical data and an application on a high-resolution measurement, at the clinical field strength of 3T is demonstrated. In conclusion, URSULA allows for a reduction of the problem size, a substantial speed-up and for handling large data sets without sacrificing the overall accuracy of the resulting phase information