Artifacts in camera based single photon emission tomography due to time activity variation

Abstract

Image quality in single photon emission computed tomography (SPECT) using a rotating gamma camera is dependent on the time course of the tracer in the field of view. If acquisition times are slow compared to the tracer turnover, artifacts may occur in the reconstructed images. The properties of such artifacts were studied by computer simulation. Experimental projection data of point sources, cylindrical phantoms, and an anatomically realistic brain phantom were altered by sequentially weighting the projections with a function that varied exponentially or linearly with time. The observed distortion in the reconstructed images could be related to the ratio between the object activity variation and the camera rotation time. If the tracer concentration changed less than a factor of two during one camera rotation then little image distortion was visible although quantitatively the resolution was degraded. If the object's activity variation with time is fast enough to produce noticeable distortion, the artifacts can be reduced by performing multiple, rapid, camera rotations, instead of one rotation, for the same total acquisition time. The proposed procedure is computer storage space intensive and takes longer to produce the transaxial images, but improves image quality.

Quantitative analysis in single photon emission tomography (SPET)

“…Distortions of the reconstructed slice due to timeactivity variation during acquisition can be visually assessed if the tracer concentration changes by more than a factor of 2 during one rotation (Bok et al 1987). As a possible solution Bok et al (1987) proposed performing multiple, fast SPET acquisitions and adding these studies together.…”

“…As a possible solution Bok et al (1987) proposed performing multiple, fast SPET acquisitions and adding these studies together. Then each projection image represents a mean distribution during the total acquisition time.…”

A filter model to analyze reconstruction artifacts in perfusion C-arm CT

“…To date there exist some studies on FBP artifacts due to time-varying attenuation values [1], [2], [3] but there is no model to describe the characteristics of these artifacts. Therefore, in this paper we present a novel formalism to model reconstruction artifacts by a spatio-temporal filter in the object domain with terms that depend on the temporal derivatives of the attenuation values and derivative-weighted point spread functions.…”

Time‐varying reconstruction in single photon emission computed tomography

“…The effect of the time-varying activity for the reconstruction of SPECT images was studied by Bok et al (1987) using simulations. They found that the time variation smeared the reconstructed images nonuniformly.…”

“…Both Bok et al (1987) and Nakajima et al (1992) assumed uniform uptake and washout of the tracer. Links et al (1991) assumed that there are cold defects in the myocardial tissue.…”