Multi-resolution multi-sensitivity design for parallel-hole SPECT collimators

Abstract

Multi-resolution multi-sensitivity (MRMS) collimator offering adjustable trade-off between resolution and sensitivity, can make a SPECT system adaptive. We propose in this paper a new idea for MRMS design based on, for the first time, parallel-hole collimators for clinical SPECT. Multiple collimation states with varied resolution/sensitivity trade-offs can be formed by slightly changing the collimator’s inner structure. To validate the idea, the GE LEHR collimator is selected as the design prototype and is modeled using a ray-tracing technique. Point images are generated for several states of the design. Results show that the collimation states of the design can obtain similar point response characteristics to parallel-hole collimators, and can be used just like parallel-hole collimators in clinical SPECT imaging. Ray-tracing modeling also shows that the proposed design can offer varied resolution/sensitivity trade-offs: at 100 mm before the collimator, the highest resolution state provides 6.9 mm full width at a half maximum (FWHM) with a nearly minimum sensitivity of about 96.2 cps MBq−1, while the lowest resolution state obtains 10.6 mm FWHM with the highest sensitivity of about 167.6 cps MBq−1. Further comparisons of the states on image qualities are conducted through Monte Carlo simulation of a hot-spot phantom which contains five hot spots with varied sizes. Contrast-to-noise ratios (CNR) of the spots are calculated and compared, showing that different spots can prefer different collimation states: the larger spots obtain better CNRs by using the larger sensitivity states, and the smaller spots prefer the higher resolution states. In conclusion, the proposed idea can be an effective approach for MRMS design for parallel-hole SPECT collimators.