Angular viewing time optimization for slit-slat SPECT

In current SPECT systems, gamma cameras rotate around the subject sampling for the same fixed amount of time at each viewing angle. We suggest that adapting angular viewing time for specific tasks may help to maximize the instrument performance without increasing imaging time. Using a slit-slat collimator as an example, we tested a variety of angular viewing time settings and examined the contrast of hot lesions with various activity concentration at a few locations and proposed a linear model of the locations and angular viewing time near region of interest (ROI) for off-center lesion. Given a fixed scan time, viewing time t at a viewing angle φ can be adjusted as a function of φ for different phantom sizes and ROI locations. In our current framework, viewing time t at viewing angle φ is parameterized as: t(φ) = k(1 + t_a cos(φ φ_o))ⁿ + Δt, where t_a and n control the proportion of the viewing time at φ_o and the rate of change around it, φ_o is the viewing angle closest to the ROI so that viewing time peaks at this angle, k is a normalizer and Δt is the scout scan time per viewing angle. Scans using various parameters over 20 viewing angles of 200 and 600 second total scan time on 2 phantoms were simulated. Poisson noise was added to projection data to create 500 noisy realizations for every angular viewing time configuration. The performance was evaluated based on the average contrast at a matched noise ratio in reconstructions using a maximum likelihood expectation maximization algorithm. These preliminary results show that optimizing the viewing time in angles near the ROI location can increase detectability in off-center ROIs. Our preliminary investigation shows that the optimized viewing time near the ROI follows a linear trend with the location of the ROI. This simplified model can be easily used in SPECT applications.