3D sensitivity encoded ellipsoidal MR spectroscopic imaging of gliomas at 3T

Purpose

The goal of this study was to implement time efficient data acquisition and reconstruction methods for 3D magnetic resonance spectroscopic imaging (MRSI) of gliomas at a field strength of 3T using parallel imaging techniques.

Methods

The point spread functions, signal to noise ratio (SNR), spatial resolution, metabolite intensity distributions and Cho:NAA ratio of 3D ellipsoidal, 3D sensitivity encoding (SENSE) and 3D combined ellipsoidal and SENSE (e-SENSE) k-space sampling schemes were compared with conventional k-space data acquisition methods.

Results

The 3D SENSE and e-SENSE methods resulted in similar spectral patterns as the conventional MRSI methods. The Cho:NAA ratios were highly correlated (P<.05 for SENSE and P<.001 for e-SENSE) with the ellipsoidal method and all methods exhibited significantly different spectral patterns in tumor regions compared to normal appearing white matter. The geometry factors ranged between 1.2 and 1.3 for both the SENSE and e-SENSE spectra. When corrected for these factors and for differences in data acquisition times, the empirical SNRs were similar to values expected based upon theoretical grounds. The effective spatial resolution of the SENSE spectra was estimated to be same as the corresponding fully sampled k-space data, while the spectra acquired with ellipsoidal and e-SENSE k-space samplings were estimated to have a 2.36–2.47-fold loss in spatial resolution due to the differences in their point spread functions.

Conclusion

The 3D SENSE method retained the same spatial resolution as full k-space sampling but with a 4-fold reduction in scan time and an acquisition time of 9.28 min. The 3D e-SENSE method had a similar spatial resolution as the corresponding ellipsoidal sampling with a scan time of 4:36 min. Both parallel imaging methods provided clinically interpretable spectra with volumetric coverage and adequate SNR for evaluating Cho, Cr and NAA.     

Reliability of Clinician-Based (GRBAS and CAPE-V) and Patient-Based (V-RQOL and IPVI) Documentation of Voice Disorders

This study examined the reliability of two methods for documenting voice quality by clinicians and compared the methods for documenting patients' perceptions of voice quality. It involved a prospective reliability study and a retrospective chart review. Reliability of two clinician-based voice assessment protocols-Grade, Roughness, Breathiness, Asthenia, Strain (GRBAS) and Consensus Auditory Perceptual Evaluation-Voice (CAPE-V)-was evaluated. These two protocols were then compared after use in voice assessments of 42 males and 61 females performed by a certified speech-language pathologist specializing in the assessment of voice disorders. In addition, two patient-based scales (Voice Related Quality of Life, or V-RQOL, and Iowa Patient's Voice Index, or IPVI) obtained from the same patients were compared with each other and with the clinician-based scales. Reliability of clinicians' ratings of overall severity of dysphonia using GRBAS and CAPE-V scales was very good (r>0.80). Agreement between V-RQOL Total scores and IPVI ratings of the patient's perceptions of impact of dysphonia was less strong (Spearman's r=-0.76). There was relatively weak agreement between patient-based and clinician-based scales. Clinician's perceptions of dysphonia appeared to be reliable and unaffected by rating tool, as indicated by the high level of agreement between the two rating systems when they were used together. The CAPE-V system appeared to be more sensitive to small differences within and among patients than the GRBAS system. The V-RQOL and IPVI approaches to documenting patient's perceptions of dysphonia agreed less well possibly due to differences in patient dependence on voice and on interpretation of the rating tool items. The differences between clinician-based and patient-based data support the conclusion that clinicians and patients experience and consider dysphonia very differently.     

Studies of porous media by thermally polarized gas NMR: current status

Three examples of thermally polarized gas NMR performed at New Mexico Resonance are presented to demonstrate its unique advantages in porous media studies. 1) In-vivo animal lung imaging by Kuethe et al., in which useful quality 3D images of rat lungs were obtained in 30 min. It is conjectured that comparable human lung images would take much less time to make, possibly by the ratio of body weights, a factor of several hundred. 2) The success of the lung imaging suggested other porous media as candidates for thermally polarized gas NMR. Caprihan and coworkers obtained excellent images from partially sintered ceramics and Vycor glass. Since then, Beyea has developed the technique of spatially resolved BET curves for ceramics and other nanoporous solids. In this way, surface area, pore size, and porosity, averaged over an image voxel, can be spatially resolved. This greatly aids in the characterization of such materials, especially with regards to spatial heterogeneities. 3) Finally, we describe Codd's propagator experiments on propane gas flowing through a packed bed of 300 microm beads. In order to increase signal-to-noise ratio, the flowing gas was pressurized to 170 kPa. Excellent quality propagators showing the discrete nature of the bead pack were obtained. This type of information is not available in comparable liquid studies because most spins will not diffuse far enough to sample the walls in the time available.     

Direct Synthesis of ZIF-8 on Transmission Electron Microscopy Grids Allows Structure Analysis and 3D Reconstruction

The first example of layer-by-layer growth of a metal–organic framework (MOF) directly on transmission electron microscopy (TEM) grids is described. ZIF-8 is deposited on thin amorphous carbon films and subjected to a structure analysis by (scanning) TEM ((S)TEM). This method serves as a two-in-one synthesis and TEM sample-preparation technique and allows straightforward analysis of ZIF-8 crystallites. Artifacts resulting from sample preparation are completely avoided by this approach. The morphological properties, crystal structure, and the chemical composition of the material are investigated with high spatial resolution by a variety of methods of (analytical) electron microscopy. Furthermore, the incorporation of metallic nanoparticles in ZIF-8 by integrating a corresponding step into the layer-by-layer deposition process is examined. The formation of ZIF-8 crystals on the film proceeds as under the absence of nanoparticle-forming synthesis steps. However, the nanoparticles rather cover the supporting amorphous carbon film than being incorporated in the ZIF-8 material. This information cannot be obtained from standard characterization techniques but requires the application of analytical (S)TEM techniques.     

Radiation-induced cathodoluminescent signatures in calcite

At ambient temperatures, a permanent change due to neutron irradiation has been identified in the luminescent properties of the common mineral calcite. Calcite is one of many ubiquitous minerals that are known to exhibit luminescence under electron bombardment, a process known as cathodoluminescence (CL). The UV–Visible spectra of individual calcite grains were measured with CL spectroscopy before and after neutron irradiation. Exposure to neutrons causes additional crystal lattice defects (beyond those naturally-occurring) that leave a permanent, readily-measurable CL signature in the 515 nm region of the spectrum. Dose response results following irradiation have been measured and a spectroscopic signature is described that increases proportionately to neutron dose. The CL measurements are complicated by a dependence on the orientation relative to direction of excitation. When taken into account, the total dose to the crystal can be estimated, and possibly even the direction of the neutron source can be determined. This signature could potentially be developed into a nuclear forensics tool to help identify locations where special nuclear materials have been stored.     

Investigation and Development of Quantum Dot-Encoded Microsphere Bioconjugates for DNA Detection by Flow Cytometry

The development of screening assays continues to be an active area of research in molecular diagnostics. Fluorescent microspheres conjugated to biomarkers (nucleic acids, proteins, lipids, carbohydrates) and analyzed on flow cytometer instruments offered a new approach for multiplexed detection platform in a suspension format. Quantum dots encoded into synthetic microspheres have the potentials to improve current screening bioassays and specifically suspension array technology. In this paper, commercialized quantum dot-encoded microsphere were evaluated and optimized as fluorescent probes to address some of the limitations of suspension array technologies. A comprehensive study was undertaken to adapt the bioconjugation procedure to the quantum dot-encoded microsphere structural and optical properties. Both the leaching-out of quantum dots and microspheres degradation under bioconjugation experimental conditions were minimized. A rapid, efficient and reproducible conjugation method was developed for the detection of single-stranded DNA with the commercialized quantum dot-encoded microsphere. Approximately ten thousand microspheres were conjugated to short amino-modified DNA sequences in one hour with high efficiency. The bioconjugated microspheres acting as fluorescent probes successfully detected a DNA target in suspension with high specificity. Quantum dot-encoded microsphere commercial products are limited which strongly prevents reproducible and comparative studies between laboratories. The method developed here contributes to the understanding of quantum dot-encoded microsphere reactivity, and to the optimization of adapted experimental procedure. This step is essential in the development of this new fluorescent probe technology for multiplex genotyping assay and molecular diagnostic applications.     

Information Dimension of Stochastic Processes on Networks: Relating Entropy Production to Spectral Properties

We consider discrete stochastic processes, modeled by classical master equations, on networks. The temporal growth of the lack of information about the system is captured by its non-equilibrium entropy, defined via the transition probabilities between different nodes of the network. We derive a relation between the entropy and the spectrum of the master equation’s transfer matrix. Our findings indicate that the temporal growth of the entropy is proportional to the logarithm of time if the spectral density shows scaling. In analogy to chaos theory, the proportionality factor is called (stochastic) information dimension and gives a global characterization of the dynamics on the network. These general results are corroborated by examples of regular and of fractal networks.     

Sequential streaming due to manipulation of interaural time differences

The effect of apparent spatial location on sequential streaming was investigated by manipulating interaural time differences (ITDs). The degree of obligatory stream segregation was inferred indirectly from the threshold for detecting a rhythmic irregularity in an otherwise isochronous sequence of interleaved "A" and "B" tones. Stimuli were bandpass-filtered harmonic complexes with a 100-Hz fundamental. The A and B tones had equal but opposite ITDs of 0, 0.25, 0.5, 1, or 2 ms and had the same or different passbands. The passband ranges were 1250-2500 Hz and 1768-3536 Hz in experiment 1, and 353-707 Hz and 500-1000 Hz in experiment 2. In both experiments, increases in ITD led to increases in threshold, mainly when the passbands of A and B were the same. The effects were largest for ITDs above 0.5 ms, for which rhythmic irregularities in the timing of the A or B tones alone may have disrupted performance. It is concluded that the differences in apparent spatial location produced by ITD have only weak effects on obligatory streaming.     

Colour and lighting in hospital design

Little information or guidance has been available to assist the development of a hospital's visual environment. A report on lighting and colour design schemes, accessible to non professionals with responsibility for refurbishment strategies, was required by NHS Estates. Firstly, 20 hospitals were audited to establish a picture of current practice and to identify key issues where colour design could broadly enhance the environment for patients, staff and visitors. Critical areas were outlined in this report, where colour design can be utilised and applied, for the benefit of all users, from ambience to essential legal requirements such as colour contrast for the visually impaired.Provision of staff relaxation rooms that are different in terms of colour and lux levels from immediate work spaces, or thoughtfully designed areas for patients awaiting intensive treatment, have been shown to have some beneficial effects on a sense of well being. Colour and design have not been established as a definite cure for sickness and ill health, but certainly monotony and poor conditions in premises that have not been refurbished with any care, have had a detrimental affect on recovery rates and staff morale. The realisation that a well balanced and attractive environment is of major importance to patients’ health is, in no way new; Florence Nightingale observed that ‘a variety of form and brilliance of colour in the objects presented to patients are an actual means of recovery’.     

A simple and inexpensive optical technique to help students visualize mode shapes

An imaging technique is introduced that is suitable for visualizing the mode shapes of vibrating structures in an educational setting. The method produces images similar to those obtained using electronic speckle pattern interferometry (ESPI), but it can be implemented for less than 1/10 the cost of a commercial ESPI system, and the apparatus is simple enough that it can be constructed by undergraduate students. This technique allows for real-time visualization of the normal modes and deflection shapes of harmonically vibrating structures, including those with shapes that make generating Chladni patterns with sand or powder impossible. The theory of operation and construction details are discussed.