Abstract
Conventional x-ray computed tomography (CT) scanners are limited in their scanning speed by the mechanical constraints of their rotating gantries and as such do not provide the necessary temporal resolution for imaging of fast-moving dynamic processes, such as moving fluid flows. The Real Time Tomography (RTT) system is a family of fast cone beam CT scanners which instead use multiple fixed discrete sources and complete rings of detectors in an offset geometry. We demonstrate the potential of this system for use in the imaging of such high speed dynamic processes and give results using simulated and real experimental data. The unusual scanning geometry results in some challenges in image reconstruction, which are overcome using algebraic iterative reconstruction techniques and explicit regularisation. Through the use of a simple temporal regularisation term and by optimising the source firing pattern, we show that temporal resolution of the system may be increased at the expense of spatial resolution, which may be advantageous in some situations. Results are given showing temporal resolution of approximately 500 µs with simulated data and 3 ms with real experimental data.
Highlights
Medical x-ray tomographic imaging systems have used a single x-ray source and an array of detectors which together rotate around the object of interest to form a set of x-ray projections through the object
Sources are located in the plane z = 0, with the detector offset in the direction of the positive z-axis; note that the z scale in the figure is highly exaggerated in order to show the offset source-detector geometry
We have introduced the concept of the Real Time Tomography (RTT) system, as applied to the problem of imaging fast-moving dynamic processes, such as fluid and granular flows
Summary
Medical x-ray tomographic imaging systems have used a single x-ray source and an array of detectors which together rotate around the object of interest to form a set of x-ray projections through the object. In some applications, such frame rates are too slow to provide the required temporal resolution; for example in the visualisation of the flow of liquids or granular materials To address this problem, it is necessary to eliminate the mechanical scanning motion, replacing this with an electronic equivalent comprising a circular array of xray sources which can be fired individually under computer control. The larger production systems were designed for application in airport security, in order to provide fast three-dimensional imaging of baggage as it passes through on a conveyor belt at up to 0.5ms−1 In this application, the third dimension is used to provide z information rather than time; the resulting reconstruction process is a different problem than that discussed in detail in this work, but owing to the offset geometry, this has necessitated development of new algorithms. The 3D reconstruction problem will not be discussed further in this work
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