Experimental correlation-based identification of X-ray CT point spread function. Part 2: Simulation and design of input signal

MTF of columnar phosphors with a homogenous part: an analytical approach

A method for the theoretical estimation of the MTF of columnar phosphors with a homogeneous part at the end used in X-ray imaging has been developed. This method considers the light transport inside the scintillator through an analytical modelling, the optical photon beams distribution on the scintillator-optical sensor interface, and uses the definition of the PSF and a Gauss fitted LSF to estimate the MTF of an indirect detector. This method was applied to a columnar CsI:Tl scintillator and validated against experimental results found in literature, and a good agreement was observed. It was found that, by increasing the pixel size of the optical detector and the thickness of the scintillator, the MTF decreased as expected. This method may be used in evaluating the performance of the columnar phosphors used in medical imaging, given their physical and geometrical characteristics.Graphical abstract (a) Side view of a part of the scintillator where five crystal columns with homogeneous ends attached to an optical sensor is shown. (b) Propagation of two random optical photon beams emitted from point K with different angles of emission is shown. All the symbols are explained analytically in the text.

Experimental evaluation of computerised tomography point spread function variability within the field of view: parametric models

The objective of the paper was to validate non-linear parametric models of computerised tomography point spread function (PSF), to investigate the role of model parameters and to verify the effect of different imaging conditions on estimated parameters. These models were then to be used experimentally to estimate the variation of PSF shape within the field of view of a scanner. Two parametric models of the PSF are presented. The Gaussian model is appropriate when PSF values are positive, and the damped cosine model can account for negative values. These models are non-linear and fully two-dimensional and do not assume radial symmetry. The models were fitted to images of a point source. The models accounted for over 99% of the variance in the PSF signal. Errors in modulation transfer function were limited to 5% when the appropriate model was selected. The difference in the blurring characteristics of three image reconstruction filters was well quantified by shape parameters, and position parameters located the PSF with subpixel accuracy. With a point source located 50mm directly above the centre of the field of view, the PSF was found to be anisotropic.

Experimental correlation-based identification of X-ray CT point spread function. Part 1: Method and experimental results

Knowledge of the point spread function (PSF) of an imaging system is important when studying the characteristics of the blur present in the images. Published experimental PSF identification techniques adapt classical one-dimensional linear system identification strategies using impulse, step function or periodic input signals. This study proposes and successfully applies a correlation method based on the Wiener-Hopf equation to identify the PSF of a CT scanner. The input consists of a series of pseudorandomly located holes. Results are found to be statistically equivalent to those obtained with the impulse method at a 90% two-sided confidence interval. Like the impulse method, it readily yields two-dimensional estimate, but the larger input circumvents the major objection to the use of a wire input. Furthermore, it is relatively immune to output noise, offering an advantage over edge methods. This resistance to noise may prove helpful for nuclear medicine imaging techniques, for which the signal-to-noise ratio is much lower than that X-ray for CT.