Development and assessment of a multi-beam continuous-phantom-motion x-ray scatter projection imaging system

Abstract

X-ray image formation using scattered radiation can yield a superior contrast-to-noise ratio compared to conventional transmission x-ray imaging. A barrier to practical implementation of scatter imaging systems has been slow image acquisition. We have developed a projection imaging system which uses five monoenergetic pencil beams in combination with continuous phantom motion to achieve acquisition times that are practical for medical and security applications. The system was configured at the Canadian Light Source synchrotron and consists of a primary collimator, motorized stages for phantom translation, a flat-panel x-ray detector for measuring scattered x rays, and photodiodes for simultaneously measuring transmitted x rays. Image generation requires several corrections to raw data artifacts arising from the nature of the detector, x-ray source, and acquisition procedure. We developed a novel correction for pixel location inaccuracy arising from continuous phantom motion. A five-beam system had nearly five times faster acquisition than a single-beam system. Continuous motion acquisition was approximately 30 times faster than step-and-shoot acquisition. The total acquisition time for a 9 cm × 5 cm phantom with 8425 pixels was just over 2 min. Image quality was also assessed, in part to determine its relation to acquisition speed. The width of sharp material boundaries was found to be at a minimum equal to the pencil beam width (1.75 mm) and to have an additional width equal to the product of the phantom translation speed and the acquisition time per pixel (up to 1.0 mm in our experiments). Contrast-detail performance was independent of acquisition speed, depending only on phantom entrance x-ray fluence. Pixel signal-to-noise ratio measurements indicate that detector readout noise is important for the scatter data, even for phantom air kerma as high as 30 mGy. Images could be improved with a detector having lower readout noise and higher sensitivity. Its spatial resolution could be moderate. We confirmed that for the same range of λ−1 sin(θ/2), where λ is the x-ray wavelength and θ is the scattering angle, scatter images acquired using different beam energies (33–70 keV) had nearly identical contrast.

Spectrum optimization for x-ray dual-mode imager comprising radiography and coherent scatter

“…Our research group started its imager development at a synchrotron 21,31,32 using multiple monoenergetic 33.2 keV pencil beams and the use of a Maximum-Likelihood Expectation Maximization (MLEM) algorithm to disentangle the overlapping scatter patterns to yield each beam's radial profile. Discrete photodiodes captured the primary, and a flat panel detector captured the scatter patterns.…”

Nonlinear Lag Correction Based on the Autoregressive Model for Dynamic Flat-Panel Detectors

“…We first observe the lag correction performance from the correlation-based LCF measurement from (8). For a steadystate image sequence of Fig.…”

“…A certain amount of the lag signal can reduce the noise due 40 to blurring [7]. In this case, using an FPD with no lag and employing digital image processing methods, such as realtime recursive deconvolution [8], can optimize the tradeoff between the required temporal resolution and low image noise. Therefore, it is necessary to research and develop a dynamic FPD that generates small lag signals in fluoroscopic imaging.…”

Depth resolved pencil beam radiography using AI — a proof of principle study

“…Indeed, in the past two decades, and particularly in recent years, we have seen novel approaches for harnessing enhanced information in photon transmission imaging. Proof of principle papers have been published in the fields of crystalography, coherent scatter tomography, coding and sampling, and scatter projection [4,[9][10][11]. Existing and emerging literature demonstrates multiple approaches for utilizing scatter information and warrants continued investigation.…”