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Focal spots: III. Field characteristics.

A E Burgess
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Abstract

Experimental results for focal spot field characteristics are presented. These results do not agree completely with results published by Moores and Roeck but are in agreement with Doi's theory as applied to separable focal spots. A new image plane origin called the principal ray is proposed. The variation of the star test pattern image for separable, symmetric focal spots is described. The equation for the field variation of the RMS equivalent rectangle is presented.

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A E Burgess. Focal spots: III. Field characteristics.. https://doi.org/10.1097/00004424-197701000-00013

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Longitudinal image deblurring in spiral CT.

PURPOSE: To assess the feasibility of digital deconvolution techniques to improve longitudinal resolution of spiral computed tomography (CT) multiplanar reformations and evaluate how technical factors in deconvolution affect longitudinal resolution, noise, and edge ringing. MATERIALS AND METHODS: Longitudinal line spread function (LSF) of the system was estimated from longitudinal reformations of transaxial spiral CT images of a step test phantom. By using the estimated LSF, longitudinal reformations of the phantom and three clinical spiral CT studies were deconvolved by the methods of Wiener filtering and constrained iterative deconvolution. Edge ringing and image noise were quantified for Wiener filtering and constrained iterative deconvolution. RESULTS: Longitudinal reformations were substantially deblurred and resolution improved after deconvolution. Anatomic boundaries in clinical images were more clearly delineated after restoration. The methods of Wiener deconvolution and constrained iterative deconvolution improved the sharpness of the phantom step boundary at the expense of increased edge ringing and image noise. CONCLUSION: In longitudinal spiral CT reformations, blurring along the longitudinal axis can be reduced by Wiener filtering or constrained iterative deconvolution.

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