A Relationship Between Sampling Error And Signal To Noise Ratio In Gated SPECT

摘要

Gated SPECT provides temporal resolution at the expense of a deteriorating SNR. While the level of noise in an image data set is thought to be complex due to the filtering process, this article provides a simple method for determining the trade-off in SNR when altering acquisition parameters. Introduction Gated single photon emission computed tomography (SPECT) provides temporal resolution at the expense of a deteriorating signal to noise ratio (SNR) (1). A potential weakness of gated SPECT is the possibility of insufficient count density per individual frame interval despite the relatively high 99m Tc activity (2). Each projection set will be reduced in counts by a factor equal to the number of collected frames (plus any rejected beats) (3). SPECT image quality is adversely affected by noise which is more problematic in low count gated SPECT. Smaller numbers of counts result in larger statistical uncertainties, or noise (4). Radioactivity counting error (random error) is characterised by Poisson statistics (4) which assumes pixels are independent of one another (e.g. planar images and SPECT raw data) and, thus, does not hold for reconstructed SPECT data where reconstructed pixels are not independent. Discussion The level of noise in an image data set, or SNR, is not as intuitive as it might seem due to the filtering process (5). The reconstructed SNR for data reconstructed using a ramp filter can be determined with the following equation: