F. Zimmer

Biopsy targeting gliomas: do functional imaging techniques identify similar target areas?

Objective:Because of the heterogeneous nature of glioma, biopsies performed should be targeted at the most anaplastic region. Several functional magnetic resonance imaging (MRI) or positron emission tomography (PET) techniques have been proposed for identifying the most anaplastic tumor area. However, it is unclear whether the recommended biopsy targets based on these various functional imaging modalities correspond with each other. Thus, the purpose was to evaluate whether they identify similar target areas. Materials and Methods:A total of 61 patients with suspected glioma were assessed within 2.3 ± 3.5 days by MRI, 18F-fluorothymidine-, and 18F-fluorodeoxyglucose-PET. Thirty-five patients underwent gross total resection and 26 were stereotactically biopsied. MRI was performed on a 1.5 Tesla broadband transmit/receive system, using a double-resonant birdcage coil. The MRI protocol comprised of sodium (23Na)-MRI (3D-radial projection imaging), proton spectroscopic imaging (1H-MRSI, point-resolved spectroscopy), arterial spin-labeling (ASL) perfusion MRI, dynamic contrast-enhanced (DCE) MRI, and dynamic-susceptibility-weighted (DSC) perfusion MRI after a single dose each of gadobenate dimeglumine. Also, apparent diffusion coefficient (ADC) maps were processed from diffusion tensor images. Image analysis comprised a detailed semiquantitative region of interest analysis of the different parameter values as well as visual identification of the most conspicuous tumor areas on parameter maps, for example, areas with maximum tumor perfusion, highest metabolite ratios of choline-containing compounds/N-acetyl-aspartate, or lowest ADC values within tumor tissue. Colocalization of these areas was then assessed. Results:Regarding tumor vascularity-related parameters and tumor proliferation-related parameters, the higher the glioma grade the higher were the respective parameters in semiquantitative analysis. ADC values decreased with glioma grade. In the whole study population comprising low- (N = 15) and high-grade gliomas (N = 42), except for 23Na-MRI, there was good (>50%) or perfect (100%) agreement of the tumor areas with highest values on parameter images in the majority of cases (>80%), that is, tumor areas with increased thymidine-uptake and highest choline, both suggestive of increased tumor proliferation, and elevated microcirculation as demonstrated by DSC-, arterial spin-labeling-, and DCE-MRI. 23Na-MRI depicted the highest signal within necrotic tumor areas, but non-necrotic gliomas also showed a perfect agreement in more than 61%. 18F-fluorothymidine-PET, DSC-, and DCE-MRI, diffusion-weighted imaging as well as MR spectroscopic imaging correctly detected no glioma heterogeneity in all 15 histologically proven grade II gliomas but identified suspicious areas in all 3 nonenhancing grade III gliomas. Conclusion:Both imaging techniques that depict microcirculation and techniques that visualize proliferation identify similar target areas.

Quantitative Renal Perfusion Measurements in a Rat Model of Acute Kidney Injury at 3T: Testing Inter- and Intramethodical Significance of ASL and DCE-MRI

Objectives To establish arterial spin labelling (ASL) for quantitative renal perfusion measurements in a rat model at 3 Tesla and to test the diagnostic significance of ASL and dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in a model of acute kidney injury (AKI). Material and Methods ASL and DCE-MRI were consecutively employed on six Lewis rats, five of which had a unilateral ischaemic AKI. All measurements in this study were performed on a 3 Tesla MR scanner using a FAIR True-FISP approach and a TWIST sequence for ASL and DCE-MRI, respectively. Perfusion maps were calculated for both methods and the cortical perfusion of healthy and diseased kidneys was inter- and intramethodically compared using a region-of-interest based analysis. Results/Significance Both methods produce significantly different values for the healthy and the diseased kidneys (P<0.01). The mean difference was 147±47 ml/100 g/min and 141±46 ml/100 g/min for ASL and DCE-MRI, respectively. ASL measurements yielded a mean cortical perfusion of 416±124 ml/100 g/min for the healthy and 316±102 ml/100 g/min for the diseased kidneys. The DCE-MRI values were systematically higher and the mean cortical renal blood flow (RBF) was found to be 542±85 ml/100 g/min (healthy) and 407±119 ml/100 g/min (AKI). Conclusion Both methods are equally able to detect abnormal perfusion in diseased (AKI) kidneys. This shows that ASL is a capable alternative to DCE-MRI regarding the detection of abnormal renal blood flow. Regarding absolute perfusion values, nontrivial differences and variations remain when comparing the two methods.

High-precision photometry by telescope defocusing - III. The transiting planetary system WASP-2★: High-precision defocused photometry of WASP-2

We present high-precision photometry of three transits of t he extrasolar planetary system WASP-2, obtained by defocussing the telescope, and achievi ng point-to-point scatters of between 0.42 and 0.73 mmag. These data are modelled using the JKTEBOP code, and taking into account the light from the recently-discovered faint s tar close to the system. The physical properties of the WASP-2 system are derived using tabulated pr ictions from five different sets of stellar evolutionary models, allowing both statist ical and systematic errorbars to be specified. We find the mass and radius of the planet to be M = 0.847± 0.038± 0.024MJup andRb = 1.044± 0.029± 0.015RJup. It has a low equilibrium temperature of 1280± 21K, in agreement with a recent finding that it does not have an atmo spheric temperature inversion. The first of our transit datasets has a scatter of only 0.42 mma g with respect to the best-fitting light curve model, which to our knowledge is a record for grou nd-based observations of a transiting extrasolar planet.

Flux and color variations of the quadruply imaged quasar HE 0435-1223

Aims. We present VRi photometric observations of the quadruply imaged quasar HE0435-1223, carried out with the Danish 1.54 m telescope at the La Silla Observatory. Our aim was to monitor and study the magnitudes and colors of each lensed component as a function of time. Methods. We monitored the object during two seasons (2008 and 2009) in the VRi spectral bands, and reduced the data with two independent techniques: difference imaging and point spread function (PSF) fitting. Results. Between these two seasons, our results show an evident decrease in flux by ≈ 0.2–0.4 magnitudes of the four lensed components in the three filters. We also found a significant increase ( ≈ 0.05–0.015) in their V − R and R − i color indices. Conclusions. These flux and color variations are very likely caused by intrinsic variations of the quasar between the observed epochs. Microlensing effects probably also affect the brightest “A” lensed component.

Functional imaging of acute kidney injury at 3 Tesla: Investigating multiple parameters using DCE-MRI and a two-compartment filtration model

OBJECT To investigate how MR-based parameters reflect functional changes in kidneys with acute kidney injury (AKI) using dynamic contrast enhanced MRI and a two-compartment renal filtration model. MATERIALS AND METHODS MRI data of eight male Lewis rats were analyzed retrospectively. Five animals were subjected to AKI, three native rats served as control. All animals underwent perfusion imaging by dynamic contrast-enhanced MRI. Renal blood volume, glomerular filtration rate (GFR) as well as plasma and tubular mean transit times were estimated from regions-of-interest drawn in the renal cortex. Differences between healthy kidneys and kidneys subjected to AKI were analyzed using a paired t-test. RESULTS Significant differences between ischemic and healthy kidneys could only be detected for the glomerular filtration rate. For all other calculated parameters, differences were present, however not significant. In rats with AKI, average single kidney GFR was 0.66 ± 0.37 ml/min for contralateral and 0.26 ± 0.12 ml/ min for diseased kidneys (P = 0.0254). For the healthy control group, the average GFR was 0.39 ± 0.06 ml/min and 0.41 ± 0.11 ml/min, respectively. Differences between diseased kidneys of AKI rats and ipsilateral kidneys of the healthy control group were significant (P = 0.0381). CONCLUSION Significant differences of functional parameters reflecting damage of the renal tissue of kidneys with AKI compared to the contralateral, healthy kidneys could only be detected by GFR. GFR might be a useful parameter that allows for a spatially resolved detection of abnormal changes of renal tissue by AKI.

Renal perfusion in acute kidney injury with DCE-MRI: Deconvolution analysis versus two-compartment filtration model

PURPOSE To investigate the results of different pharmacokinetic models of a quantitative analysis of renal blood flow (RBF) in acute kidney injury using deconvolution analysis and a two-compartment renal filtration model. MATERIALS AND METHODS MRI data of ten male Lewis rats were analyzed retrospectively. Six animals were subjected to unilateral acute kidney injury and underwent perfusion imaging by dynamic contrast-enhanced MRI (DCE-MRI). Renal blood flow was estimated from regions-of-interest depicting the cortex in the DCE-MRI perfusion maps. The perfusion models were compared by a paired t-test and Bland-Altman plots. RESULTS No significant difference was found between the two compartment model and the deconvolution analysis (P=0.2807). Differences between healthy and diseased kidney in the AKI model were significant for both methods (P<0.05). A Bland-Altman plot showed no systematic errors, and values were equally distributed around the mean difference between the methods lying within the range of 1.96 standard deviations. CONCLUSION Both quantification strategies could detect the kidneys that were impaired by AKI. When just aiming at RBF as a marker, a deconvolution analysis can provide similar values as the 2CFM. If functional parameters beyond RBF like glomerular filtration rate are needed, the 2CFM should be employed.

Magnetic resonance fingerprinting using echo-planar imaging: Joint quantification of T1 and T2∗ relaxation times

To develop an implementation of the magnetic resonance fingerprinting (MRF) paradigm for quantitative imaging using echo‐planar imaging (EPI) for simultaneous assessment of T1 and T2∗ .

Flux and color variations of the doubly imaged quasar UM673

Aims. With the aim of characterizing the flux and color variations o f the multiple components of the gravitationally lensed quasar UM673 as a function of time, we have performed multi-epoch and multi-band photometric observations with the Danish 1.54m telescope at the La Silla Observatory. Methods. The observations were carried out in the VRi spectral bands during four seasons (2008‐2011). We reduced the data using the PSF (Point Spread Function) photometric technique as well as aperture photometry. Results. Our results show for the brightest lensed component some significant decrease in flux between the first two seasons (+0.09/+0.11/+0.05 mag) and a subsequent increase during the following ones (−0.11/−0.11/−0.10 mag) in the V/R/i spectral bands, respectively. Comparing our results with previous studies, we find smaller color variations between these seasons as co mpared with previous ones. We also separate the contribution of the lensing galaxy from that of the fainter and close lensed component.

N-octanoyl dopamine treatment exerts renoprotective properties in acute kidney injury but not in renal allograft recipients.

BACKGROUND N-octanoyl dopamine (NOD) treatment improves renal function when applied to brain dead donors and in the setting of warm ischaemia-induced acute kidney injury (AKI). Because it also activates transient receptor potential vanilloid type 1 (TRPV1) channels, we first assessed if NOD conveys its renoprotective properties in warm ischaemia-induced AKI via TRPV1 and secondly, if renal transplant recipients also benefit from NOD treatment. METHODS We induced warm renal ischaemia in Lewis, wild-type (WT) and TRPV1(-/-) Sprague-Dawley (sd) rats by clamping the left renal artery for 45 min. Transplantations were performed in allogeneic and syngeneic donor-recipient combinations (Fisher to Lewis and Lewis to Lewis) with a cold ischaemia time of 20 h. Treatment was instituted directly after restoration of organ perfusion. Renal function, histology and perfusion were assessed by serum creatinine, microscopy and magnetic resonance imaging (MRI) using arterial spin labelling (ASL). RESULTS NOD treatment significantly improved renal function in Lewis rats after warm ischaemia-induced AKI. It was, however, not effective after prolonged cold ischaemia. The renoprotective properties of NOD were only observed in Lewis or WT, but not in TRPV1(-/-) sd rats. Renal inflammation was significantly abrogated by NOD. MRI-ASL showed a significantly lower cortical perfusion in ischaemic when compared with non-ischaemic kidneys. No overall differences were observed in renal perfusion between NOD- and NaCl-treated rats. CONCLUSIONS NOD treatment reduces renal injury in warm ischaemia, but is not effective in renal transplant in our experimental animal models. The salutary effect of NOD appears to be TPRV1-dependent, not involving large changes in renal perfusion.

X-ray microlensing in the quadruply lensed quasar Q2237+0305

We use archival data of NASAs Chandra X-ray telescope to compile an X-ray light curve of all four images of the quadruply lensed quasar Q2237+0305 (z Q = 1.695) from 2006 January to 2007 January. We fit simulated point spread functions to the four individual quasar images using Cashs C-statistic to account for the Poissonian nature of the X-ray signal. The quasar images display strong flux variations up to a factor of ∼4 within one month. We can disentangle the intrinsic quasar variability from flux variations due to gravitational microlensing by looking at the flux ratios of the individual quasar images. Doing this, we find evidence for microlensing in image A. In particular, the time sequence of the flux ratio A/B in the X-ray regime correlates with the corresponding sequence in the optical monitoring by OGLE in the V band. The amplitudes in the X-ray light curve are larger. For the most prominent peak, the increase of the X-ray ratio A/B is larger by a factor of ∼1.6 compared to the signal in the optical. In agreement with theory and other observations of multiply-imaged quasars, this suggests that the X-ray emission region of this quasar is significantly smaller than the optical emission region.