Regional changes in lung microstructure are an important component of several common lung disorders and even in healthy lungs alveolar mechanics are poorly understood. Existing techniques capable of studying the lung microstructure have various limitations including poor temporal resolution. We present a technique, which can measure the distribution of alveolar diameters from a single, phase contrast chest X-ray. We present the results of analysis of synchrotron images of a rabbit pup’s lungs, which we compare with high-resolution computed tomography images. We demonstrate that measurements can be made with an exposure time of 40 ms, highlighting the unique potential for performing dynamic in vivo measurements. Applications include disease detection, assessment of therapeutics and physiological studies.
In many animals, including humans, the lungs encase the majority of the heart thus the motion of each organ affects the
other. The effects of the motion of the heart on the lungs potentially provides information with regards to both lung and
heart health. We present a novel technique that is capable of measuring the effect of the heart on the surrounding lung
tissue through the use of advanced synchrotron imaging techniques and recently developed X-ray velocimetry methods.
This technique generates 2D frequency response maps of the lung tissue motion at multiple projection angles from
projection X-ray images. These frequency response maps are subsequently used to generate 3D reconstructions of the
lung tissue exhibiting motion at the frequency of ventilation and the lung tissue exhibiting motion at the frequency of the
heart. This technique has a combined spatial and temporal resolution sufficient to observe the dynamic and complex 3D
nature of lung-heart interactions.
All lung disease dramatically alters the local motion of the lung during breathing. It stands to reason, therefore, that detailed measurement of lung motion could provide dramatic improvements in assessment of lung function. Using synchrotron-based phase contrast imaging, we have developed and applied tools for lung motion and function measurement. We demonstrate a low-dose alternative to traditional 4D-CT methods, capable of measuring instantaneous 3D tissue motion using only 6 projection images. Additionally, our technique provides estimation of the airflow distribution throughout the bronchial tree during the breathing cycle. The ability to measure lung function at a regional level will provide invaluable information for studies into normal and pathological lung dynamics, and may provide new pathways for diagnosis of regional lung diseases. Although proof-of-concept data were acquired on a synchrotron, the low-dose methodology developed lends itself to clinical scanning and offers translational opportunities.
A novel system to image and reconstruct a 3-dimensional map of the refractive index based on the diffraction of light through a transparent sample is presented. This method is tested and validated on computer-generated data sets. The proposed system is an advanced variation of an imaging technique used in engineering for the study of aerodynamics. This method, which is termed Reference Image Topography, is used to reconstruct the water/air interface of the free surface in fluid dynamics studies. This surface profile is reconstructed by comparing an image of a random pattern viewed through the transparent free surface against a reference image, to determine the change in the refractive index caused by changes in the height. The proposed system is highly sensitive and capable of imaging intricate features in the transparent sample that are of low contrast when imaged with other imaging methods. For each projection, the change in direction of the light passing through the sample when placed in between the light source and the imaging system, can be related to the line integral for the change in refractive index across the sample. Utilizing multiple projections, a 3- dimensional map of the refractive index of the sample is reconstructed with computed tomography.
The ability to accurately measure velocity within the embryonic zebrafish heart, at high spatial and temporal resolution, enables further insight into the effects of hemodynamics on heart development. Unfortunately, currently available techniques are unable to provide the required resolution, both spatial and temporal, for detailed analysis. Advances in imaging hardware are allowing bright field imaging combined with particle image velocimetry to become a viable technique for the broader community at the required spatial and temporal resolutions. While bright field imaging offers the necessary temporal resolution, this approach introduces heart wall artifacts that interfere with accurate velocity measurement. This study presents a technique for cardiac-phase filtering of bright field images to remove the heart wall and improve velocimetry measurements. Velocity measurements were acquired for zebrafish embryos ranging from 3 to 6 days postfertilization. Removal of the heart wall was seen to correct a severe (3-fold) underestimation in velocity measurements obtained without filtering. Additionally, velocimetry measurements were used to quantitatively detect developmental changes in cardiac performance in vivo, investigating both changes in contractile period and maximum velocities present through the ventricular-bulbar valve.
An adaptation of current image shifting techniques has been developed that permits cross-correlation PIV analysis of non- overlapping images recorded on photographic media. The image acquisition technique utilizes pulsed lasers to produce two singly exposed sub-images of particles in one photographic frame. The technique can also provide images suitable for cross-correlation analysis on digitally recorded images without the need for a specialized camera. An adaptive cross- correlation PIV analysis method is employed to extract the in- plane velocity field information with high velocity sampling resolution and large velocity dynamic range. Further capabilities and limitations of the technique are presented as well as an analysis of the associated measurement errors. Some of the more interesting problems that were encountered during the development of the experimental technique are also discussed. The application of this method to the unsteady flow of a vortex ring will be illustrated as an example. High spatial resolution measurements using film recording have yielded the detailed instantaneous 2-D velocity and vorticity fields. Measurements made from digital recordings using this technique provide the evolution of instantaneous in-plane velocity and vorticity fields.
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