3D functional models of monkey brain through elastic registration of histological sections

In this paper we describe a method for the reconstruction and visualization of functional models of monkey brains. Models are built through the registration of high resolution images obtained from the scanning of histological sections with reference photos taken during the brain slicing. From the histological sections it is also possible to acquire specifically activated neuron coordinates introducing functional information in the model. Due to the specific nature of the images (texture information is useless and the sections could be deformed when they were cut and placed on glass) we solved the registration problem by extracting corresponding cerebral cortex borders (extracted with a snake algorithm), and computing from their deformation an image transform modeled as an affine deformation plus a non-linear field evaluated as an elastically constrained deformation minimizing contour distances. Registered images and contours are used then to build 3D models of specific brains by a software tool allowing the interactive visualization of cortical volumes together with the spatially referenced neurons classified and differently colored according to their functionalities

Reproducibility of three different cardiac T2-mapping sequences at 1.5T and impact of cofactors on T2-relaxation times

Background: The high interindividual variability of myocardial T2 relaxation times appears to be one of the main challenges for the clinical application of cardiac T2-mapping. This study therefore aimed to evaluate potential underlying causes for this variability, analyzing the reproducibility of three different cardiac T2-mapping sequences and evaluating the influence of cofactors on T2 relaxation times. Methods: 30 healthy volunteers were examined three times on a clinical 1.5T scanner (scan 1: in the morning; scan 2: in the evening of the same day; scan 3: in the evening 2-3 weeks later). In each examination three different T2-mapping sequences were acquired at three slices in short axis view: Multi Echo Spin Echo (MESE), T2-prepared balanced Steady State Free Precession (T2prep; [1]) and Gradient Spin Echo (GraSE). Repeated measurements were performed for T2prep and GraSE. Segmented T2-maps were generated for each slice according to the AHA 17-segment model. Intra- and inter-observer reproducibility was tested in a subgroup of 10 randomly selected subjects, where manual ROIs were drawn independently to measure T2 values of each segment blinded to the other results. Results: Overall, we observed no systematic difference of T2 times due to diurnal effects and on long-term analysis. Differentiated analysis of variance components for all sequences, however, revealed a greater variance of T2 times over multiple time points than for repeated measurements within the same scan. Our study revealed a low intra-observer and inter-observer variability of manual ROI-definition and the acquired T2 times for each sequence. The coefficients of variation and intraclass correlation coefficients for intra-observer variability were: 1.3% and 0.89 for T2prep, 1.5% and 0.93 for GraSE, 3.1% and 0.83 for MESE; and for inter-observer variability: 3.3% and 0.66 for T2prep, 2.0% and 0.83 for GraSE, 3.6% and 0.77 for MESE. With respect to the influence of potential cofactors on T2 times, we observed a negative effect of the cofactor heart rate on mean T2 values, yet this effect proved to be not significant. Conversely, we found significant and positive relation between mean T2 times and the cofactors age, weight and height (p < 0.005, p < 0.05 and p < 0.05) in single linear regression models. Using multiple regression models, we observed significant relations between mean T2 times and age (p < 0.005), gender (p < 0.01), and either weight or height (p < 0.005), for given values of the remaining cofactors. Conclusions: Intra- and inter-observer reproducibility of all tested T2-mapping sequnces is high, thereby confirming previous studies. According to our study, the high interindividual variability of myocardial T2 relaxation times is most likely due to proband-related effects such as age, gender, weight and height and other cofactors intraindividually varying with time

A new approach to the assessment of lumen visibility of coronary artery stent at various heart rates using 64-slice MDCT

Coronary artery stent lumen visibility was assessed as a function of cardiac movement and temporal resolution with an automated objective method using an anthropomorphic moving heart phantom. Nine different coronary stents filled with contrast fluid and surrounded by fat were scanned using 64-slice multi-detector computed tomography (MDCT) at 50–100 beats/min with the moving heart phantom. Image quality was assessed by measuring in-stent CT attenuation and by a dedicated tool in the longitudinal and axial plane. Images were scored by CT attenuation and lumen visibility and compared with theoretical scoring to analyse the effect of multi-segment reconstruction (MSR). An average increase in CT attenuation of 144 ± 59 HU and average diminished lumen visibility of 29 ± 12% was observed at higher heart rates in both planes. A negative correlation between image quality and heart rate was non-significant for the majority of measurements (P > 0.06). No improvement of image quality was observed in using MSR. In conclusion, in-stent CT attenuation increases and lumen visibility decreases at increasing heart rate. Results obtained with the automated tool show similar behaviour compared with attenuation measurements. Cardiac movement during data acquisition causes approximately twice as much blurring compared with the influence of temporal resolution on image quality

A Spectroscopic Orbit for Regulus

We present a radial velocity study of the rapidly rotating B-star Regulus that indicates the star is a single-lined spectroscopic binary. The orbital period (40.11 d) and probable semimajor axis (0.35 AU) are large enough that the system is not interacting at present. However, the mass function suggests that the secondary has a low mass (M_2 > 0.30 M_sun), and we argue that the companion may be a white dwarf. Such a star would be the remnant of a former mass donor that was the source of the large spin angular momentum of Regulus itself.Comment: 18 pages, 2 figures, ApJL in pres

Automated diffeomorphic registration of anatomical structures with rigid parts: application to dynamic cervical MRI.

International audienceWe propose an iterative two-step method to compute a diffeomorphic non-rigid transformation between images of anatomical structures with rigid parts, without any user intervention or prior knowledge on the image intensities. First we compute spatially sparse, locally optimal rigid transformations between the two images using a new block matching strategy and an efficient numerical optimiser (BOBYQA). Then we derive a dense, regularised velocity field based on these local transformations using matrix logarithms and M-smoothing. These two steps are iterated until convergence and the final diffeomorphic transformation is defined as the exponential of the accumulated velocity field. We show our algorithm to outperform the state-of-the-art log-domain diffeomorphic demons method on dynamic cervical MRI data

Be Stars: Rapidly Rotating Pulsators

I will show that Be stars are, without exception, a class of rapidly rotating stars, which are in the majority of cases pulsating stars as well, while none of them does possess a large scale (i.e. with significant dipolar contribution) magnetic field.Comment: Review talk given at "XX Stellar Pulsation Conference Series: Impact of new instrumentation and new insights in stellar pulsations", Granada, 5-9 September 2011, in press in AIP Conf. Se

Quantification of biventricular myocardial function using cardiac magnetic resonance feature tracking, endocardial border delineation and echocardiographic speckle tracking in patients with repaired tetralogy of fallot and healthy controls

Background: Parameters of myocardial deformation have been suggested to be superior to conventional measures of ventricular function in patients with tetralogy of Fallot (ToF), but have required non-routine, tagged cardiovascular magnetic resonance (CMR) techniques. We assessed biventricular myocardial function using CMR cine-based feature racking (FT) and compared it to speckle tracking echocardiography (STE) and to simple endocardial border delineation (EBD). In addition, the relation between parameters of myocardial deformation and clinical parameters was assessed. Methods: Overall, 28 consecutive adult patients with repaired ToF (age 40.4 ± 13.3 years) underwent standard steadystate- free precession sequence CMR, echocardiography, and cardiopulmonary exercise testing. In addition, 25 healthy subjects served as controls. Myocardial deformation was assessed by CMR based FT (TomTec Diogenes software), CMR based EBD (using custom written software) and STE (TomTec Cardiac Performance Analysis software). Results: Feature tracking was feasible in all subjects. A close agreement was found between measures of global left (LV) and right ventricular (RV) global strain. Interobserver agreement for FT and STE was similar for longitudinal LV global strain, but FT showed better inter-observer reproducibility than STE for circumferential or radial LV and longitudinal RV global strain. Reproducibility of regional strain on FT was, however, poor. The relative systolic length change of the endocardial border measured by EBD yielded similar results to FT global strain. Clinically, biventricular longitudinal strain on FT was reduced compared to controls (P<0.0001) and was related to the number of previous cardiac operations. In addition, FT derived RV strain was related to exercise capacity and VE/VCO2-slope. Conclusions: Although neither the inter-study reproducibility nor accuracy of FT software were investigated, and its interobserver reproducibility for regional strain calculation was poor, its calculations of global systolic strain showed similar or better inter-oberver reproducibility than those by STE, and could be applied across RV image regions inaccessible to echo. ‘Global strain’ calculated by EBD gave similar results to FT. Measurements made using FT related to exercise tolerance in ToF patients suggesting that the approach could have clinical relevance and deserves further study

The Kinematic Properties of BHB and RR Lyrae stars towards the Anticentre and the North Galactic Pole: The Transition between the Inner and the Outer Halo

We identify 51 blue horizontal branch (BHB) stars, 12 possible BHB stars and 58 RR Lyrae stars in Anticentre fields. Their selection does not depend on their kinematics. Light curves and ephemerides are given for 7 previously unknown RR Lyrae stars. All but 4 of the RR Lyrae stars are of Oosterhoff type I. Our selection criteria for BHB stars give results that agree with those used by Smith et al. (2010) and Ruhland et al. (2011). We use 5 methods to determine distances for the BHB stars and 3 methods for the RR Lyrae stars to get distances on a uniform scale. Absolute proper motions (largely derived from the GSCII and SDSS (DR7) databases) are given for these stars; radial velocities are given for 31 of the BHB stars and 37 of the RR Lyrae stars. Combining these data for BHB and RR Lyrae stars with those previously found in fields at the North Galactic Pole, we find that retrograde orbits dominate for galactocentric distances greater than 12.5 kpc. The majority of metal-poor stars in the solar neighbourhood are known to be concentrated in a Lperp vs. Lz angular momentum plot. We show that the ratio of the number of outliers to the number in the main concentration increases with galactocentric distance. The location of these outliers with Lperp and Lz shows that the halo BHB and RR Lyrae stars have more retrograde orbits and a more spherical distribution with increasing galactocentric distance. Six RR Lyrae stars are identified in the H99 group of outliers; the small spread in their [Fe/H] suggests that they could have come from a single globular cluster. Another group of outliers contains two pairs of RR Lyrae stars; the stars in each pair have similar properties.Comment: 40 pages, 19 figures, to be published in MNRA

Accelerating Feature Based Registration Using the Johnson-Lindenstrauss Lemma

Abstract. We introduce an efficient search strategy to substantially accelerate feature based registration. Previous feature based registration algorithms often use truncated search strategies in order to achieve small computation times. Our new accelerated search strategy is based on the realization that the search for corresponding features can be dramat-ically accelerated by utilizing Johnson-Lindenstrauss dimension reduc-tion. Order of magnitude calculations for the search strategy we propose here indicate that the algorithm proposed is more than a million times faster than previously utilized naive search strategies, and this advan-tage in speed is directly translated into an advantage in accuracy as the fast speed enables more comparisons to be made in the same amount of time. We describe the accelerated scheme together with a full complex-ity analysis. The registration algorithm was applied to large transmission electron microscopy (TEM) images of neural ultrastructure. Our experi-ments demonstrate that our algorithm enables alignment of TEM images with increased accuracy and efficiency compared to previous algorithms.