List mode for continuous data acquisition in fast SPECT

Objectives In fast SPECT, continuous acquisition significantly increases counts and hence reduces image noise. However, the counts acquired during the rotation of the detector degrade special resolution and produce other artifacts. In this study, list mode was proposed for continuous acquisition to remove these artifacts.

Methods A count acquired with list mode, (x,t), was converted to a point of the sonogram, (x,ϕ), by calculating the projection direction ϕ from the acquisition time t. The sonogram was then input to filtered backprojection to reconstruct the image. Computer simulation was conducted to assess the proposed list-mode acquisition. Step-and-shoot, standard continuous and list-mode continuous acquisition were simulated for fast SPECT. The number of views was 16 over 360° and the stationary time of the detector at a view was 2 seconds plus 3 second rotation time between two adjacent views. The reconstructed images obtained from list-mode continuous acquisition were compared with those obtained from standard continuous acquisition and step-and-shoot acquisition.

Results For noise-free data, standard continuous acquisition resulted in a slight rotation of the whole phantom in the opposite direction to detector rotation and blurred internal structures. These artifacts were eliminated by list mode. For noisy data, list-mode continuous acquisition produced appreciably clearer images than step-and-shoot acquisition. This is because it reduced the noise level by 40% compared to step-and-shoot acquisition and produced few artifacts of detector rotation.

Conclusions It was demonstrated by computer simulation that list mode for continuous acquisition significantly reduced image noise in fast SPECT with few artifacts caused by detector rotation. The encouraging results need to be verified by experiments of physical phantoms and patient studies on gamma cameras.