Quasi-Exact Helical Cone Beam Reconstruction for Micro CT

A cone beam micro-CT system is set up to collect truncated helical cone beam data. This system includes a micro-focal X-ray source, a precision computer-controlled X-Y-Z-theta stage, and an image-intensifier coupled to a large format CCD detector. The helical scanning mode is implemented by rotating and translating the stage while keeping X-ray source and detector stationary. A chunk of bone and a mouse leg are scanned and quasi-exact reconstruction is performed using the approach proposed in J. Hu et al. (2001). This approach introduced the original idea of accessory paths with upper and lower virtual detectors having infinite axial extent. It has a filtered backprojection structure which is desirable in practice and possesses the advantages of being simple to implement and computationally efficient compared to other quasi-exact helical cone beam algorithms for the long object problem

Measuring the effect of airway pressure on pulmonary arterial diameter in the intact rat lung

To study the relationship between transpulomnary pressure (Ptp), intravascular pressure (Pv), and the pulmonary arterial tree structure, morphometric measurements of pulmonary arterial trees were made in intact lungs from Sprague-Dawley rats. Using cone beam micro-CT and techniques we developed for imaging small animal lungs, volumetric CT data were acquired for Ptp from 0 - 12 mmHg and Pv from 5 - 30 mmHg. The diameter, D (measured range approximately 0.08-2.0 mm), vs. pressure, P, relation can be described by D(P) = D(0)(1+ α P), where α is a distensibility coefficient. Unlike studies performed in larger animals, where changes in either Ptp or Pv had nearly identical effect on vessel distensibility, we found that there is only a small dependence of arterial diameter on Ptp in the rat. For example, using the above relation where P=Ptp and Pv is held constant at 12mmHg, alpha = 0.55±0.42(SE) %/mmHg, compared with when P=Pv and Ptp is held at 12mmHg, alpha = 2.59±0.17(SE) %/mmHg

Estimation of Pulmonary Arterial Volume Changes in the Normal and Hypertensive Fawn-Hooded Rat from 3D Micro-CT data

In the study of pulmonary vascular remodeling, much can be learned from observing the morphological changes undergone in the pulmonary arteries of the rat lung when exposed to chronic hypoxia or other challenges which elicit a remodeling response. Remodeling effects include thickening of vessel walls, and loss of wall compliance. Morphometric data can be used to localize the hemodynamic and functional consequences. We developed a CT imaging method for measuring the pulmonary arterial tree over a range of pressures in rat lungs. X-ray micro-focal isotropic volumetric imaging of the arterial tree in the intact rat lung provides detailed information on the size, shape and mechanical properties of the arterial network. In this study, we investigate the changes in arterial volume with step changes in pressure for both normoxic and hypoxic Fawn-Hooded (FH) rats. We show that FH rats exposed to hypoxia tend to have reduced arterial volume changes for the same preload when compared to FH controls. A secondary objective of this work is to quantify various phenotypes to better understand the genetic contribution of vascular remodeling in the lungs. This volume estimation method shows promise in high throughput phenotyping, distinguishing differences in the pulmonary hypertensive rat model

Changes in Pulmonary Arterial Wall Mechanical Properties and Lumenal Architecture with Induced Vascular Remodeling

To explore and quantify pulmonary arterial remodeling we used various methods including micro-CT, high-resolution 3-dimensional x-ray imaging, to examine the structure and function of intact pulmonary vessels in isolated rat lungs. The rat is commonly used as an animal model for studies of pulmonary hypertension (PH) and the accompanying vascular remodeling, where vascular remodeling has been defined primarily by changes in the vessel wall composition in response to hypertension inducing stimuli such as chronic hypoxic exposure (CHE) or monocrotaline (MCT) injection. Little information has been provided as to how such changes affect the vessel wall mechanical properties or the lumenal architecture of the pulmonary arterial system that actually account for the hemodynamic consequences of the remodeling. In addition, although the link between primary forms of pulmonary hypertension and inherited genetics is well established, the role that genetic coding plays in hemodynamics and vascular remodeling is not. Therefore, we are utilizing Fawn-Hooded (FH), Sprague-Dawley (SD) and Brown Norway (BN)rat strains along with unique imaging methods to parameterize both vessel distensibility and lumenal morphometry using a principal pulmonary arterial pathway analysis based on self-consistency. We have found for the hypoxia model, in addition to decreased body weight, increased hematocrit, increased right ventricular hypertrophy, the distensibility of the pulmonary arteries is shown to decrease significantly in the presence of remodeling

Post-Acquisition Small-Animal Respiratory Gated Imaging Using Micro Cone-Beam CT

On many occasions, it is desirable to image lungs in vivo to perform a pulmonary physiology study. Since the lungs are moving, gating with respect to the ventilatory phase has to be performed in order to minimize motion artifacts. Gating can be done in real time, similar to cardiac imaging in clinical applications, however, there are technical problems that have lead us to investigate different approaches. The problems include breath-to-breath inconsistencies in tidal volume, which makes the precise detection of ventilatory phase difficult, and the relatively high ventilation rates seen in small animals (rats and mice have ventilation rates in the range of a hundred cycles per minute), which challenges the capture rate of many imaging systems (this is particularly true of our system which utilizes cone-beam geometry and a 2 dimensional detector). Instead of pre-capture ventilation gating we implemented a method of post-acquisition gating. We acquire a sequence of projections images at 30 frames per second for each of 360 viewing angles. During each capture sequence the rat undergoes multiple ventilation cycles. Using the sequence of projection images, an automated region of interest algorithm, based on integrated grayscale intensity, tracts the ventilatory phase of the lungs. In the processing of an image sequence, multiple projection images are identified at a particular phase and averaged to improve the signal-to-ratio. The resulting averaged projection images are input to a Feldkamp cone-beam algorithm reconstruction algorithm in order to obtain isotropic image volumes. Minimal motion artifact data sets improve qualitative and quantitative analysis techniques useful in physiologic studies of pulmonary structure and function

Semiautomated Skeletonization of the Pulmonary Arterial Tree in Micro-CT Images

We present a simple and robust approach that utilizes planar images at different angular rotations combined with unfiltered back-projection to locate the central axes of the pulmonary arterial tree. Three-dimensional points are selected interactively by the user. The computer calculates a sub- volume unfiltered back-projection orthogonal to the vector connecting the two points and centered on the first point. Because more x-rays are absorbed at the thickest portion of the vessel, in the unfiltered back-projection, the darkest pixel is assumed to be the center of the vessel. The computer replaces this point with the newly computer-calculated point. A second back-projection is calculated around the original point orthogonal to a vector connecting the newly-calculated first point and user-determined second point. The darkest pixel within the reconstruction is determined. The computer then replaces the second point with the XYZ coordinates of the darkest pixel within this second reconstruction. Following a vector based on a moving average of previously determined 3- dimensional points along the vessel\u27s axis, the computer continues this skeletonization process until stopped by the user. The computer estimates the vessel diameter along the set of previously determined points using a method similar to the full width-half max algorithm. On all subsequent vessels, the process works the same way except that at each point, distances between the current point and all previously determined points along different vessels are determined. If the difference is less than the previously estimated diameter, the vessels are assumed to branch. This user/computer interaction continues until the vascular tree has been skeletonized

It’s how you said it and what I heard: a comparison of motivational and emotional tone of voice

Previous research has viewed motivational and emotional vocal expressions as the same (e.g., Meyer & Turner, 2006; Fontaine & Scherer, 2013), but until now no direct comparison of these types of prosody has been available. Building on the new motivational prosody literature (e.g., Weinstein, Zougkou & Paulmann, 2014; 2018), this series of studies was the first to explore the differences and similarities between these forms of prosody. Initially, contextually valid sentences were intoned in angry, joyful, supportive, and controlling tones of voice by trained speakers, which were then acoustically analysed. Results revealed that each state was intoned with a different acoustic profile. Subsequently, exemplars were validated in a forced choice categorisation study and acoustics were extracted again. Results confirmed that each state was communicated with a different configuration of vocal cues, thus indicating that emotional and motivational states do not share the same prosodic profiles. In a final study, using an event-related potential (ERP) approach the time-course processing of these constructs was investigated. Findings suggest that emotional and motivational prosody share similar processing time-courses and neural resources. Weak evidence indicated possibly deviations in processing but were not strong enough to draw any conclusions. Taken together, the results of this investigation suggest that emotional and motivational prosody are likely distinct constructs. We conclude that these constructs differ on an encoding level and different vocal cues potentially lead to their effective recognition, but they are similar with respect to how they are processed in the brain. Implications, limitations and directions for future research are discussed

Pulmonary arterial remodeling revealed by microfocal x-ray tomography

Animal models and micro-CT imaging are useful for understanding the functional consequences of, and identifying the genes involved in, the remodeling of vascular structures that accompanies pulmonary vascular disease. Using a micro-CT scanner to image contrast-enhanced arteries in excised lungs from fawn hooded rats (a strain genetically susceptible to hypoxia induced pulmonary hypertension), we found that portions of the pulmonary arterial tree downstream from a given diameter were morphometrically indistinguishable. This \u27self-consistency\u27 property provided a means for summarizing the pulmonary arterial tree architecture and mechanical properties using a parameter vector obtained from measurements of the contiguous set of vessel segments comprising the longest (principal) pathway and its branches over a range of vascular pressures. This parameter vector was used to characterize the pulmonary vascular remodeling that occurred in rats exposed to a hypoxic (11.5% oxygen) environment and provided the input to a hemodynamic model relating structure to function. The major effect of the remodeling was a longitudinally (pulmonary artery to arterioles) uniform decrease in vessel distensibility that resulted in a 90% increase in arterial resistance. Despite the almost uniform change in vessel distensibility, over 50% of the resistance increase was attributable to vessels with unstressed diameters less than 125 microns

Micro-CT Image-Derived Metrics Quantify Arterial Wall Distensibility Reduction in a Rat Model of Pulmonary Hypertension

We developed methods to quantify arterial structural and mechanical properties in excised rat lungs and applied them to investigate the distensibility decrease accompanying chronic hypoxia-induced pulmonary hypertension. Lungs of control and hypertensive (three weeks 11% O2) animals were excised and a contrast agent introduced before micro-CT imaging with a special purpose scanner. For each lung, four 3D image data sets were obtained, each at a different intra-arterial contrast agent pressure. Vessel segment diameters and lengths were measured at all levels in the arterial tree hierarchy, and these data used to generate features sensitive to distensibility changes. Results indicate that measurements obtained from 3D micro-CT images can be used to quantify vessel biomechanical properties in this rat model of pulmonary hypertension and that distensibility is reduced by exposure to chronic hypoxia. Mechanical properties can be assessed in a localized fashion and quantified in a spatially-resolved way or as a single parameter describing the tree as a whole. Micro-CT is a nondestructive way to rapidly assess structural and mechanical properties of arteries in small animal organs maintained in a physiological state. Quantitative features measured by this method may provide valuable insights into the mechanisms causing the elevated pressures in pulmonary hypertension of differing etiologies and should become increasingly valuable tools in the study of complex phenotypes in small-animal models of important diseases such as hypertension