Medical Physics 6, pp. 441-451 (1979)

Detectability in computed tomographic images

Kenneth M. Hanson
Los Alamos National Laboratory


The detection limitations inherent in statistically limited computed tomographic (CT) images are described through the application of signal detection theory. The delectability of large-area, loc-contrast objects is shown to be chiefly dependent upon the low-frequency content of the noise power spectral density. For projection data containing uncorrelated noise, the resulting ramplike, low-frequency behavior of the noise power spectrum of CT reconstructions may be conveniently characterized by the number of noise-equivalent x-ray quanta (NEQ) detected in the projection measurements. The NEQ for a given image may be determined either from a measurement of the noise power spectrum or from the noise granularity computed with an appropriate weighting function. A measure of the efficiency of the scanner does utilization is proposed, which compares the average dose required by an ideal scanner to obtain the same NEQ.

Keywords: detectability in CT images, computed tomography (CT), noise equivalent quanta (NEQ), noise power spectrum (NPS), noise granularity, dose efficiency, signal detection theory

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